Method and device for depositing n-doped sic

Abstract

The invention relates to a method for depositing an SiC layer, wherein an NH3-containing first doping gas flow (D1), a second N2-containing doping gas flow (D2), a C2H4-containing first growth gas flow (Q1) and an HCLS3-containing second growth gas flow (Q2) flow in a horizontal direction over a heated substrate. The two doping gas flows (D1, D2) are fed, in a manner controlled separately from one another, into a process chamber (2) through gas inlet zones (4, 5, 6) arranged vertically one above the other. The mass flows of the doping gas flows (D1, D2) or the vertical position of the gas inlet zones (4, 5, 6) through which the two doping gas flows (D1, D2) flow are selected such that they generate first and second doping profiles (a, b) which are oppositely curved in relation to one another and therefore by way of a beneficial selection of the ratio of the doping gas flows (D1, D2) and an additional argon feed, a homogeneous dopant profile can be achieved in the deposited layer.

Description

Description Method and apparatus for depositing n-doped SiC field of technology

[0001] The invention relates to a method for depositing a SiC layer on a substrate in a process chamber of a CVD reactor, wherein walls of the process chamber are heated to a process temperature using a heating device. A process gas flow is fed into the process chamber through a gas inlet element. The process gas flow flows through the process chamber and over the substrates arranged therein in a horizontal direction. The process gas flow contains growth gas flows that contain a silicon-containing and a carbon-containing reactive gas. The process gas flow also contains doping gas flows that contain gaseous dopant carriers. The carbon- and nitrogen-containing reactive gases decompose at the process temperature in the process chamber or on surfaces of the heated walls of the process chamber and on the substrate surface.The decomposition products of the reactive gases deposit as a single-crystalline layer on the substrate. The dopant carriers also decompose in the process chamber, on the walls of the process chamber, or on the substrate surface. The decomposition products of the dopant carriers are incorporated into the SiC layer as dopants. The dopant preferably leads to an n-doped layer. The dopant is preferably nitrogen. State of the art

[0002] In another prior art process described in DE 102011 054566 Al is described, namely when depositing GaN layers, the process emerging from the cold gas inlet element heats up. gas initially accumulates in a pre-flow zone. During this phase, parasitic growth occurs on the surface of the pre-flow zone. As the carrier gas flows over the substrate, the concentration or partial pressure of the reactive gases in the carrier gas flow through the process chamber decreases. This leads to a depletion that progresses in the direction of flow of the process gas. As a result, the growth rate of the layer or the transport of the dopant from the gas phase towards the substrate surface steadily decreases in the direction of flow. If the substrate is rotated about a vertical axis during deposition, this effect can be compensated for. If the depletion curve above the substrate runs on a straight line that decreases in the direction of flow, a layer with a homogeneous layer thickness can still be deposited.

[0003] In reality, however, the depletion curve does not follow an ideal straight line, but rather a curved one. The above-mentioned DE 10 2011 054566 A1 describes a process in which various reactive gases are fed into the process chamber through a gas inlet device located in the center of the process chamber and through gas inlet zones arranged vertically one above the other. Due to the depletion effect described above, the partial pressures of the reactive gases used decrease along non-linear depletion curves. A lateral profile of the layer thickness can be influenced by a suitable mixture of the reactive gases flowing through different gas inlet zones.

[0004] US 2020 / 0043725 Al describes an apparatus and a method for depositing n-doped SiC using NH3 and N2 as dopants.

[0005] JP 2015-143168 A describes a process in which a process gas containing a silicon compound, a carbon compound, and NH3 is fed into a fully heated process chamber. The surfaces of the process chamber walls are coated with SiC. N-doped SiC is deposited on a substrate rotating around a rotating axis using NH3 as the dopant carrier. The partial pressure of the process gas components decreases steadily in the direction of flow.

[0006] From the publication "Experimental Study of the Pyrolysis of NH3 under Flow Reactor Conditions, Mario Benes, et al, 2021 American Chemical Society, p 7193" it is known that at high temperatures on SiC surfaces, intermediates containing nitrogen, for example HCN or Si3N, are formed from ammonia, methane or ethane, trichlorosilane and hydrogen.

[0007] WO 2022 / 053963 Al describes a similar process for depositing n-doped SiC.

[0008] The depletion described above does not occur when using N2 as a dopant carrier. However, N2 reacts catalytically on the surface of the process chamber and in particular in the immediate vicinity of the substrate or on the surface of a pre-flow zone located between the gas inlet element and the substrate. HCN can form here. The amount of HCN that reaches the substrate depends essentially on the geometry of the pre-flow zone and in particular on the cover plate arranged there and its surface. As a result, when depositing nitrogen-doped SiC, an increase in the dopant incorporation can be observed in the region of the edge of the substrate, which rotates during deposition. The dopant distribution in the deposited SiC layer thus depends on the Concentration of N2, HCN and the carbon-containing reactive gas in the gas phase.

[0009] US Pat. No. 7,118,781 B1 and JP 6424384 B2 disclose the deposition of SiC layers using argon as the carrier gas for feeding growth gases into the process chamber. Due to its high molecular weight, argon is said to reduce parasitic deposits on the process chamber ceiling and improve the thickness homogeneity of a layer deposited on a substrate. Summary of inventions

[0010] A first invention is based on the object of improving the dopant homogeneity and the layer thickness homogeneity during the deposition of n-doped SiC, and in particular in a CVD reactor in which a gas inlet element is surrounded by substrates to be coated, which are simultaneously coated with a SiC layer.

[0011] The problem is solved by the method and the claimed device specified in claims 1 to 18 and 33. The subclaims not only represent advantageous developments of the technical teachings specified in the subordinate claims, but also represent independent solutions to the problem. The reference numerals of claims 1 to 18 refer to Figures 1 to 38.

[0012] The invention relates to a method for depositing a SiC layer on a substrate, in which, in addition to the growth gases described above and at least one of the doping gas flows described above, a further gas or a gas mixture is fed into the process chamber, wherein this further gas has a molar mass which is greater than the molar mass of the hydrogen used as carrier gas and is preferably greater than the molar mass of the dopant. Argon or a mixture of argon and hydrogen is particularly suitable for this purpose. This additional gas effects a modification of the flow profile of the process gas in the process chamber. The additional heavier gas also effects a change in the transport mechanism of the decomposition products vertical to the flow direction, i.e. the diffusion of the reaction products to the substrate or to the floor of the process chamber. The diffusion coefficient depends on the molar mass of the gas molecules. If the molar mass is increased, this inhibits diffusion. The injection of a gas, hereinafter referred to as a barrier gas, whose molar mass is at least heavier than hydrogen, thus influences the diffusion of the reaction products or reactants.The barrier gas flow is preferably pure argon or a mixture of hydrogen and argon. This mixture is used instead of the carrier gas in the previously described embodiments.

[0013] The increased-mass carrier gas, which is also referred to as the barrier gas to distinguish it from hydrogen as a carrier gas, is fed through a gas inlet device. This can occur in one or more partial flows, for example, through stacked gas inlet zones. At least one of these partial flows has a molar mass that is increased by the addition of a heavier gas.

[0014] According to a preferred development of the invention, argon, if appropriate, together with hydrogen, is fed into the uppermost gas inlet zone. This reduces the diffusion of the decomposition products to the process chamber ceiling and also influences the doping profile in the deposited layer. The barrier gas can also be fed into the lowermost gas inlet zone. It can be fed into several gas inlet zones simultaneously, including the middle gas inlet zone. In one variant of the invention, a 15% argon / hydrogen mixture is fed into the uppermost gas inlet zone as a carrier gas. Another barrier gas flow can be fed into the lowermost gas inlet zone. In this case, it can be provided that the argon proportion of the barrier gas fed into the lower gas inlet zone is lower than the argon proportion of the barrier gas flow fed into the uppermost gas inlet opening. The mass flow fed through the lower gas inlet zone can, for example, have 50%, 20%, or only 10% of the argon proportion of the barrier gas flow fed in at the top.By additionally feeding in a barrier gas, whose molar mass is preferably greater than the molar mass of the doping gas, the doping profile is influenced in such a way that a relative maximum deviation from the mean value of the dopant concentration in the layer can be minimized. A doping profile that, for example, has a tub shape can be modified by feeding in the argon flow in such a way that the edge enhancement of the doping profile is reduced. Similarly, a doping profile that is bell-shaped can be influenced by additionally feeding in argon in such a way that the center enhancement is reduced. This results in a further possibility, in particular by combining ammonia and molecular nitrogen as dopant carriers, of depositing a layer with a doping profile with improved homogeneity.The introduction of additional argon through one or more of the gas inlet openings thus offers the possibility of "fine-tuning" the doping profile. It is therefore particularly advantageous if at least ammonia or at least N2 is used as a dopant. Particularly preferred are ammonia and molecular nitrogen used simultaneously, whereby these two dopant carriers can be fed into the process chamber at different vertical levels. One of these dopant gas flows generates. a first availability curve representing the availability of the dopant immediately above the substrate surface. This can have a first curvature. The curvature of a second availability curve of the second dopant gas flow is opposite to this curvature. Both curvatures can be influenced by the barrier gas, which in particular contains argon. Ammonia can be fed in through the topmost, but preferably through the bottommost, gas inlet opening. Nitrogen is preferably fed in through a central gas inlet zone.

[0015] It is further proposed to divide the process gas flow into several gas inlet zones arranged vertically one above the other and to select the pairing of the different dopant carriers such that the dopant carrier of the first doping gas flow generates a lateral doping profile in a SiC layer that has a different profile, particularly at the edge of the substrate, than a lateral doping profile generated in the SiC layer by the dopant carrier of the second doping gas flow. Thus, in particular, it can be provided that the lateral doping profile generated by the first doping gas flow has a dopant concentration that decreases toward the edge of the substrate, and the second lateral doping profile has a dopant concentration that increases toward the edge of the substrate.By appropriately selecting the doping gas flows, i.e. the mass flows of the dopant carriers into the process chamber, a superimposed doping profile can be generated, which is generated by both the first dopant carrier and the second dopant carrier. A cumulative profile is formed. The edge enhancement generated by one doping gas flow can be compensated for by an edge reduction of the cumulative profile by the other doping gas flow. For example, one of the doping gas flows can generate a dopant profile measured on a diametrical line through the substrate that is A-, U-, V-, or W-shaped. The other of the doping gas flows can generate a dopant profile that is opposite to this dopant profile. A specific dopant profile can be generated, which, for example, corresponds to the shape of an upside-down A, U, V, or W. The different dopant carriers are fed into the process chamber, in particular, through different gas inlet zones, wherein the gas inlet zones are located at different vertical levels. The dopant carrier of a first doping gas flow can, for example, generate a doping profile that is curved upwards in the middle. The dopant carrier of a second doping gas flow can, for example, generate a doping profile that is curved downwards in the middle. An effective doping profile can be set by suitably mixing the two doping gas flows.

[0016] The dopant carriers are preferably gases containing nitrogen. For example, the first dopant carrier can be NH3 and the second dopant carrier can be N2. It is particularly preferred that the nitrogen atoms in the molecules of the dopant carriers are bonded to the other atoms of the molecules with different bonding strengths. Thus, it can be provided that in one dopant carrier, the nitrogen is bonded to the other molecules with a single bond, and in another dopant carrier, the nitrogen is bonded to the other molecules with a double or triple bond. In particular, it is provided that the dopant carriers used react at different reaction rates on the surface of the substrate, on the surface of the precursor zone, and / or with the growth gases.

[0017] It may further be provided that a doping gas flow containing NH3 does not flow through the same gas inlet zone as a growth gas flow containing chlorine, for example trichlorosilane. Another growth gas flow may contain carbon, for example methane or Ethylene. However, the growth gas flow can also contain dichlorosilane. In this case, HCl can also be fed into the process chamber.

[0018] The following nitrogen compounds are particularly suitable as dopant carriers: N2, NH3 HCN, pyridine (C5H5N), hydrazine (N2H4), dimethylhydrazine (C2H8N2) or asymmetric dimethylhydrazine.

[0019] According to a preferred variant of the method, the process gas flow fed into the process chamber through at least three gas inlet zones arranged vertically one above the other contains two different doping gas flows, which are fed through different gas inlet zones. The doping gas flows can each be fed into the process chamber through the same gas inlet zone together with a growth gas flow, i.e., a carbon-containing or silicon-containing gas. In particular, exactly three gas inlet zones arranged vertically one above the other are provided, namely one gas inlet zone arranged at the top, one gas inlet zone arranged at the bottom, and one gas inlet zone arranged in the middle. However, additional gas inlet zones can also be provided.

[0020] According to one variant of the invention, a first doping gas flow is fed through a topmost gas inlet zone and a second doping gas flow is fed into a lower gas inlet zone. Another variant provides that the first doping gas flow flows together with a first growth gas flow through the same gas inlet zone. In this case, it can be provided that NH3 flows together with C2H4 through the same gas inlet zone. In a further variation, it can be provided that the second doping gas flow, for example N2, is fed into the process chamber together with a second growth gas flow, for example a silicon-containing growth gas flow, for example HChSi. Another variant provides that a third growth gas flow, which in particular contains carbon, flows through a gas inlet zone arranged at the bottom. It can be provided that a growth gas flow containing carbon flows through all gas inlet zones and a growth gas flow containing silicon and in particular containing chlorine flows only through a middle gas inlet zone. It can also be provided that no doping gas flow flows through the lowest gas inlet zone or through the top gas inlet zone. It can also be provided that the dopant carriers of the various doping gas flows do not differ. In this case, the various doping gas flows are fed in through different gas inlet zones. The vertical height of the gas inlet zone influences the shape of the doping profile, so that the doping profile can be influenced solely by the choice of the gas inlet zone.In particular, it is provided that the two doping gas flows are fed into the process chamber through the gas inlet zones that are vertically furthest apart from each other. For example, NH3 can be fed into the process chamber through a topmost gas inlet zone, and NH3 can be fed into the process chamber through a bottommost gas inlet zone. Preferably, no doping gas flow flows through the gas inlet zones located in between.

[0021] The device according to the invention has a CVD reactor and a gas mixing device, as well as a control device. The gas mixing device has storage containers for the reactive gases containing silicon and carbon. It also has storage containers for the at least one dopant carrier, but preferably storage containers for at least two dopant carriers. The gas mixing device also has mass flow controllers and valves for appropriately distributing the reactive gases and the dopant carriers as growth gas flows and doping gas flows to the vertically stacked gas inlet zones of the gas inlet element. The mass flow controllers and the valves are controlled by the control device. controlled by a control program. The reactive gases are fed into the gas inlet zones together with H2, with at least one gas inlet zone preferably also being fed with a gas whose molecular weight is greater than 20 g / mol, 30 g / mol, or 35 g / mol, or argon.

[0022] The CVD reactor has a gas inlet device. The latter is located in the center of a process chamber. The gas inlet device is surrounded by a susceptor, which has substrate supports arranged on a circular arc around the center of the gas inlet device. The substrate supports can be circular disk-shaped bodies, each located in a pocket on an upward-facing surface of the susceptor. A gas supply line opens into the bottom of each pocket, through which a purge gas is fed into the pocket, so that the substrate support is lifted and rotated on a gas cushion. At least one substrate can be arranged on the substrate support, which is rotated about a vertical axis during the deposition of the SiC layer. The susceptor can rotate about a central axis. The susceptor and a process chamber ceiling opposite the susceptor can be made of graphite.The surface of these graphite parts is coated, in particular with SiC or TaC. The gas inlet element can also be made of graphite. However, the gas inlet element is preferably made of quartz, steel (stainless steel), or a ceramic material. The surface of the susceptor can also be covered with cover plates made of graphite, in particular graphite coated with SiC or TaC, or of SiC or TaC. The substrate supports can be made of the same coated or uncoated graphite material. The process chamber ceiling can be supported by a support. This support can be made of a different material.

[0023] The invention is based on findings obtained through experiments and model calculations, according to which a suitable feed-in A gas with a high molecular weight not only influences the homogeneity of the layer thickness profile, but also affects the homogeneity of the doping profile. The deviation of a mean value of a large number of dopant concentrations measured in a layer at various distances from the center of the substrate from a minimum or maximum, and in particular the quotient of the difference between the maximum and minimum and twice the mean value (relative maximum deviation ((Max - Min) / (2*p) from the mean value p) of the measured values, should be as small as possible.

[0024] The invention is based on the experimental results described below: A gas flow is fed into a process chamber with a height of 20 mm at several levels, in particular three levels arranged vertically one above the other. The same mass flow of 94 slm of a gas mixture is fed into a vertically extending process chamber through a gas outlet surface of identical height, which is heated from below by a heating device. A first growth gas, which is trichlorosilane SiHCh, is fed into the process chamber together with hydrogen through a central gas inlet surface arranged at a middle level.A second growth gas, which is a hydrocarbon and in particular ethylene (C2H4), is fed into the process chamber through a lowest gas inlet located at the lowest level and through a top gas inlet located at the top level. Hydrogen is additionally fed into the process chamber at each of the levels formed by a gas inlet zone of a gas inlet device, i.e., through each gas inlet.

[0025] Ammonia or molecular nitrogen is used as the dopant. The dopant is introduced through different gas inlet surfaces, The gases are fed into the process chamber at different levels. The flows through the gas inlet surfaces are stabilized by introducing hydrogen to a total mass flow of 94 slm each.

[0026] A doping gas flow comprising one or more dopants and growth gas flows of the two growth gases, each together with hydrogen as a carrier gas, flow from the associated gas inlet zones of the gas inlet device into a pre-flow zone of the process chamber, where the gases heat up. The doping gas and the growth gas reach temperatures at which they decompose into their components. These decomposition products diffuse in a direction perpendicular to the horizontal flow direction in a vertical direction to the process chamber floor. The process parameters are set so that the deposition rate of the decomposition products of the growth gases reaches a peak immediately upstream of a growth zone adjacent to the pre-flow zone in the flow direction.An availability curve of silicon and carbon at the surface, which is reflected in the growth rate, then decreases in the direction of flow in the growth zone in which the substrate to be coated is located. The decrease should be as linear as possible, i.e. straight, so that a layer with a high layer thickness homogeneity is deposited on a rotating substrate. Just like the growth gases, the doping gases also decompose. However, due to different binding energies and pre-decomposition reactions in the gas phase, the availability curves of the various dopants immediately above the surface have different profiles. For ammonia as a dopant carrier, the availability curve is curved downwards, so that a doping profile with an exaggerated center line develops in a layer deposited on a rotating substrate.For nitrogen as a dopant carrier, the availability curve is curved upwards, resulting in a doping profile that is elevated at the edges. The shape of the availability curve for nitrogen. can also be influenced by depositing a suitable conditioning layer in the pre-treatment zone. By selecting a suitable mixing ratio of ammonia and molecular nitrogen, the edge enhancement of one doping profile can be at least partially compensated by the center enhancement of the other doping profile.

[0027] In the experiments, a barrier gas was fed in addition to the doping gas flow. This barrier gas has a molecular weight greater than the molecular weight of the doping gas or a carrier gas, such as hydrogen, and therefore inhibits the diffusion-based transport of the reactive gases in the process chamber. Argon or a mixture of argon and hydrogen was fed in at different levels. The levels at which at least one doping gas flow was fed into the process chamber were also varied. Feeding argon through a topmost gas inlet zone leads to reduced diffusion of the dopant carriers towards the process chamber ceiling. Feeding argon through a bottommost gas inlet zone leads to flow stabilization, as the heavier gas increases the dynamic pressure in the gas flow.At the same time, the introduction of argon generally inhibits diffusion in the direction perpendicular to the flow, since the diffusion coefficient depends on the molecular mass of the gas. While introducing argon through the lowest gas inlet zone leads to a reduced growth rate, it also simultaneously reduces depletion in the gas phase, so that the growth curve or availability curve is flatter than with the same process parameters without the additional introduction of argon into the region near the process chamber floor.

[0028] From the results of these repeated experiments, the technical teaching was derived that by additionally feeding in a barrier gas whose molecular weight is greater than the molecular weight of the doping gas, the doping profile can be influenced in such a way that a relative maximum deviation from the mean value can be minimized. It is also advantageous if the first doping gas flow generates an availability curve that has a curvature that is opposite to the curvature of an availability curve generated by the second doping gas flow. The curvature can be influenced by the barrier gas. It has also proven advantageous for the carrier gas flowing into the process chamber at the highest level to be a mixture of argon and hydrogen, with the mixing ratio being between 5% and 40% or 10% and 30%.Ammonia should preferably be fed in at the level closest to the process chamber floor.

[0029] According to a further preferred development of the invention, argon, optionally together with another gas, for example hydrogen, is fed into the process chamber through a gas inlet opening arranged in the process chamber ceiling. The gas inlet opening can preferably be arranged in the advance zone located between the gas inlet element and the substrate. However, the gas inlet opening can also be arranged above the substrate within the growth zone. The gas inlet opening can be arranged in the region of a step at which the height of the process chamber ceiling increases. The change in the process chamber height can be between 5% and 15%, preferably between 5% and 10% of the reactor height immediately in front of the gas inlet element. The gas inlet opening can preferably be arranged at a distance of at least 10%, if possible greater, in particular at least 20% of the length of the advance zone.

[0030] The gas outlet openings can generate a gas stream that flows parallel to the process chamber ceiling. However, it is also possible for the gas outlet openings to be nozzles that direct the gas stream obliquely to the process chamber ceiling, particularly toward the process chamber floor. The gas outlet openings preferably generate a wide, low-profile, i.e., flat, gas stream that extends across the entire width of the process chamber. A homogeneous, linear flow profile should be formed. If the process chamber extends around a central gas inlet element, it is preferably provided that the gas outlet openings extend along a circular arc around the gas inlet element, so that the gas flow generated thereby leaves the gas outlet openings virtually continuously along a circular arc. A laminar flow preferably develops within the process chamber.

[0031] The results of extensive model calculations underlying this patent application, which have also been verified by experiments, show that both the dopant incorporation and the homogeneity of the layer thickness can be specifically improved by arranging the gas inlet openings in the process chamber ceiling and thereby feeding in an inert gas with an increased molecular mass.

[0032] The positions of the gas inlet openings or the gas flows through the gas inlet openings and their composition are selected such that the curvature of a growth curve or the dopant concentration curve is minimal.

[0033] Model calculations show that the diffusion of the decomposition products vertically to the flow direction is locally influenced by a barrier gas fed through a gas inlet opening arranged in the process chamber ceiling By feeding the barrier gas through gas inlet openings arranged in the process chamber ceiling, the diffusion of the growth gas flow fed through the gas inlet device towards the substrate is increased in the area below the gas inlet opening. The gases fed in via the gas inlet device are thus pushed towards the process chamber floor. This leads to an increase in the concentration of the growth gas above the process chamber floor in this area. The model calculations show that if the gas inlet opening is arranged before the maximum of the decomposition rate of the decomposition products within the pre-flow zone, the maximum is reduced. This leads to an increased linearity of the decrease in the growth rate in the flow direction.Thus, by means of a barrier gas fed in via a gas inlet opening arranged in the process chamber ceiling within the pre-run zone, the growth rate profile can be locally influenced in such a way that the layer thickness homogeneity of a layer deposited on a substrate in the deposition zone adjoining the pre-run zone is increased.

[0034] The extent of the reduction in the maximum depends on the mass flow of the barrier gas injected through the gas inlet. Model calculations show that the higher the mass flow, the more the maximum growth rate is reduced. However, a high mass flow through the first gas outlet can also lead to an unstable overall flow.

[0035] In a variant of the invention, in addition to a first gas inlet opening arranged in the pre-flow zone, a further gas inlet opening arranged downstream of the first gas inlet opening within the pre-flow zone can be provided. A barrier gas can also be fed into the process chamber through this second gas inlet opening. By using a second gas inlet opening, the mass flow through the first gas inlet opening can be reduced, which leads to a stabilization of the overall flow. Preferably, the mass flow of the barrier gas flowing through the second gas outlet opening can be higher than the mass flow of the barrier gas flowing through the first gas outlet opening. The further gas inlet opening can preferably be arranged within the advance zone downstream of the first gas outlet opening. Model calculations show that the growth rate is more strongly influenced by using two gas outlet openings in the advance zone than by using only one gas inlet opening in the advance zone. Model calculations show that the maximum of the growth curve is significantly reduced when both gas inlet openings are arranged within the advance zone.If, on the other hand, the first gas inlet opening is arranged within the flow zone and the second gas inlet opening downstream of the upstream edge of the storage area, this only leads to a shift in the position of the maximum in or against the flow direction, but to no reduction in the growth rate in the area of ​​the maximum.

[0036] In a further variant of the invention, in addition to at least one gas inlet opening arranged in the advance zone, one or more steps or one or more slopes can be arranged downstream of the upstream edge of the storage location and upstream of the center of the storage location. The additional steps or slopes result in a further reduction in the growth rate in the region of the layer deposited below the steps / slopes. This leads to the layer thickness profile of a layer deposited on a rotating substrate having neither an edge elevation nor a center elevation. The vertical height of the steps / slopes can be between 3 mm and 10 mm. In model calculations, values ​​of 3 mm, 5 mm, and 6 mm were assumed. A preferred height is 6 mm, but can also be 5 mm. Downstream of the steps / bevels arranged in the deposition zone, a further bevel can be arranged in the process chamber ceiling, at which the height of the process chamber decreases. This bevel can be arranged, at least in some regions, downstream of the downstream edge of the storage location. Instead of discrete steps or bevels arranged in the process chamber ceiling between the upstream and downstream edges of the storage location, a bevel extending continuously across the diameter of the storage location can also be provided, at which the height of the process chamber increases.In a preferred embodiment of the invention, this continuous slope can be followed by a slope at which the process chamber decreases in size and which extends at least partially downstream of the downstream edge and / or upstream of the downstream edge of the storage area. Model calculations show that a slope extending continuously across the diameter of the storage area produces a higher homogeneity of the growth rate than one or more discrete steps / slopes. To achieve a higher homogeneity of the growth rate with a continuous slope, it may be necessary to reduce the mass flow of the hydrogen fed through the gas inlet element. The model calculations show that a reduction of 15% compared to the mass flow fed in when using discrete steps / slopes is optimal.

[0037] A further aspect of the invention relates to influencing the doping profile by feeding the barrier gas through gas inlet openings arranged in the process chamber ceiling. A doping profile of a layer deposited on a rotating substrate, which has a bell shape for ammonia as a dopant carrier, for example, can be influenced by feeding the barrier flux from a gas inlet opening arranged in the process chamber ceiling. The gas inlet opening can be modified to reduce the center elevation. This creates the possibility of depositing a layer with a doping profile with improved homogeneity. Feeding the barrier gas through one or more of the gas inlet openings thus offers the possibility of fine-tuning the doping profile.

[0038] The invention relates to a method for depositing a SiC layer or N-doped SiC on a substrate, the optimization of such a method, or a device for carrying out the method, in which, in addition to the growth gases and doping gas flows described above, fed in via the gas inlet surfaces of the gas inlet element arranged vertically one above the other, a further gas or gas mixture is fed into the process chamber, this further gas having a molar mass that is greater than the molar mass of the hydrogen used as carrier gas and preferably greater than the molar mass of the dopant. Argon or a mixture of argon and hydrogen is particularly suitable for this purpose. This additional gas effects a modification of the flow profile of the process gas in the process chamber.The barrier gas is fed into the process chamber through at least one gas inlet opening located in the process chamber ceiling at a distance of at least 25% of the length of the supply zone extending between the gas inlet element and the upstream edge of the storage area. The gas inlet opening can preferably be located in the region of a step and / or slope where the height of the process chamber increases.

[0039] The invention is essentially based on model calculations, but also on experiments which show that by feeding a gas with a high molecular mass, in particular argon, downstream of the gas inlet The doping profile in a deposited SiC layer can be influenced by gas inlet openings arranged in the process chamber ceiling. Ammonia is preferably used as the dopant. The dopant is fed into the process chamber through different gas inlet surfaces of the gas inlet device, i.e. at different levels. Preferably, 85% of the total ammonia flow is fed through the uppermost gas inlet surface and 15% of the total ammonia flow is fed through the lowest gas inlet surface. However, it is also possible, for example, to feed in 50% of the total ammonia flow through the uppermost or lowermost gas inlet surface, or 100% of the total dopant flow through the uppermost gas inlet surface. The flows flowing through the gas inlet surfaces are stabilized to a total mass flow by feeding in hydrogen.

[0040] The results obtained from the model calculations also apply, at least in principle, to devices and processes for depositing other, in particular semiconductor layers, such as III-V layers or II-VI layers, but also other IV-IV layers.

[0041] In the model calculation results described below, a first growth gas is fed into the process chamber through a middle gas inlet surface, which is trichlorosilane SiHCh, located at a middle level. A second growth gas, which is a hydrocarbon and in particular ethene (C2H4), is fed into the process chamber through a lowest gas inlet surface located at the lowest level, through an uppermost gas inlet surface located at the highest level, and through the middle gas inlet surface. The mass flow of the second growth gas through the lowest gas inlet surface was 10 slm, through the middle gas inlet surface 75 slm, and through the uppermost gas inlet surface 15 slm. In addition, hydrogen is fed into the process chamber through each of the gas inlet surfaces. chamber. Ammonia is also used as a dopant, with 85% of the total ammonia flow being fed through the top gas inlet surface and 15% of the total ammonia flow being fed through the bottom gas inlet surface.

[0042] To feed the barrier gas into the process chamber, a first gas inlet opening is provided, arranged at a distance of at least 10%, preferably greater, in particular at least 20%, of the length of the supply zone extending between the gas inlet element and the upstream edge of the storage area. At least one further gas inlet opening can be provided downstream of the first gas inlet opening and upstream of the upstream edge of the storage area. Feeding the barrier gas through a further gas inlet opening arranged downstream of the first gas inlet opening can reduce recirculation, thereby achieving greater flow stability.

[0043] The gas inlet openings can preferably be arranged in the region of a step. The step height is preferably between 2 and 6 mm, with the results of model calculations and experiments showing an optimal step height of 3 mm. The horizontal distance between the two steps for the deposition of SiC layers can be between 2% and 15%, preferably between 10% and 13% of the distance between the gas inlet element and the gas outlet. The mass flow of the barrier gas fed through the first gas inlet opening can preferably be smaller than the mass flow of the barrier gas fed through the second gas inlet opening. The highest homogeneity of the doping profile of an N-doped SiC layer was achieved by feeding a mass flow of 20 slm through the first gas inlet opening and 30 slm through the second gas inlet opening.

[0044] The second gas inlet opening can also be arranged between the upstream edge of the storage area and the center of the storage area. Preferably, the gas inlet openings are arranged within the flow zone.

[0045] In a further variant of the invention, in addition to at least one gas inlet opening arranged in the advance zone, one or more steps or one or more slopes can be arranged downstream of the upstream edge of the storage location and upstream of the center point of the storage location. The additional steps or the slope cause a further reduction in the dopant concentration, in particular a reduction in the center elevation of the dopant concentration, thus increasing the homogeneity of the doping profile.

[0046] From the results of these model calculations and experiments, the technical lesson was derived that by feeding a barrier gas with a molar mass greater than the molar mass of the doping gas through at least one gas inlet opening located between the gas inlet device and the upstream edge of the storage location in the process chamber ceiling, the doping profile can be influenced in such a way that a relative maximum deviation from the mean dopant concentration can be minimized. The curvature of an availability curve generated by at least one doping gas flow fed through the gas inlet device can be influenced by the barrier gas.

[0047] A second invention relates to a CVD reactor with a process chamber having a process chamber floor and a process chamber ceiling. One or more substrates are located on the process chamber floor. A process gas can be fed into the process chamber through a gas inlet device. The process gas contains a carrier gas, in particular hydrogen, and reactive gases, which chemically decompose in the process chamber, with decomposition products being deposited on the walls of the process chamber and on the substrate. In particular, a SiC layer, and in particular a nitrogen-doped SiC layer or a III-V layer, is deposited on the substrate. By introducing one or more doping gases, the dopant concentration of the layer deposited on the substrate can be influenced. The following state of the art exists

[0048] TW 1721514 B describes the effect of a changing cross-section of a process chamber on the growth rate of a layer and the layer thickness homogeneity of a layer deposited on a rotating substrate.

[0049] JP 2020-64978 A describes the effect of an inert gas flow fed through a gas inlet opening in the process chamber ceiling on the growth rate of a layer and the layer thickness homogeneity of a layer deposited on a rotating substrate.

[0050] From US 8,927,302 B2 and EP 2253 734 B1 it is known to feed inert gas flows into the process chamber, in particular at different positions, through gas inlet openings of the process chamber ceiling in order to suppress parasitic growth on the process chamber ceiling.

[0005] DE 10 2021 103 245 A1 describes a CVD reactor with a gas inlet device arranged in the center of a process chamber for feeding in a process gas. A similar device is described in DE 10 2018 124 957 A1. There, two different gas flows can be The gas outlet openings are fed into the process chamber. DE 10 2023 107111 A1 describes a method and a device in which different doping gas flows are fed into a process chamber at different locations in order to compensate for inhomogeneities in a doping profile generated by feeding only one of the doping gas flows by using a second doping gas flow.

[0051] The second invention is based on the object of providing measures by which the homogeneity of the dopant concentration in a layer deposited in a CVD reactor can be increased. The invention is further based on the object of developing a method for depositing SiC layers or GaN layers to increase the quality of the deposited layers and to provide a suitable device for this purpose.

[0052] The problem is solved in particular by the invention specified in claims 19 to 33. The subclaims represent not only advantageous developments of the invention specified in the subordinate claims, but also independent solutions to the problem. The reference numerals of the claims relate to Figures 39 to 53.

[0053] First and foremost, it is provided that, in addition to a process gas flow fed into a process chamber of a CVD reactor by means of a gas inlet element together with a carrier gas and a first doping gas flow, a second doping gas flow is fed into the process chamber via one or more gas outlet openings arranged in the process chamber ceiling that delimits the process chamber at the top. The process chamber extends in a horizontal direction and can have a constant width. The process gas flow flows together with the carrier gas flow in one flow direction over a substrate-supporting Storage location of a susceptor arranged in the process chamber. Additionally, the first doping gas flow can be fed in via the gas inlet element or through first gas outlet openings arranged downstream of the gas inlet element and upstream of a downstream edge of the substrate storage location in the process chamber ceiling. The second doping gas flow can be fed into the process chamber through second gas outlet openings arranged downstream of the first gas outlet openings and upstream of a downstream edge of the storage location.

[0054] In the following, the term storage location refers to the area that is intended to receive a substrate during the deposition of layers, in particular the area occupied by the substrate. Edges of a storage location therefore also correspond to edges of a substrate. The region of the storage location or of the substrate that extends in the direction of flow is also referred to below as the growth zone. The growth zone can be directly adjacent to a pre-flow zone that is arranged between the gas inlet element and the storage location. The first and second gas outlet openings can be arranged in the pre-flow zone in the process chamber ceiling, wherein the second gas outlet openings can also be arranged in the growth zone, i.e. above the storage location in the process chamber ceiling.According to a preferred embodiment, the CVD reactor has a gas inlet element arranged at its center with a gas outlet surface extending along a cylindrical surface, which has several gas outlet zones arranged vertically one above the other. The first doping gas flow can be fed into the process chamber either through an upper gas outlet zone of the gas inlet element, for example, or through the first gas outlet openings arranged in the process chamber ceiling. Various reactive gases, each together with a carrier gas, for example, can be fed through the gas outlet zones of the gas inlet element. Hydrogen or another inert gas can be fed into the process chamber. Different doping gases can be fed into the process chamber through the first and second gas outlet openings. Nitrogen compounds, such as N2 or NH3, are particularly suitable as dopant carriers. For example, the first doping gas can be NH3 and the second doping gas N2, or an inert gas mixture, such as N2 and Ar. Other doping carriers can also be used. However, only one doping gas, such as NH3 or N2, can also be used.

[0055] In a first embodiment of the invention, the gas outlet openings can be openings arranged in the surface of the process chamber ceiling facing the susceptor. The gas outlet openings can, for example, be individual openings. The gas outlet openings can be regularly spaced from one another. However, the gas outlet openings can also be slit-shaped. A single slit-shaped gas outlet opening can, for example, extend along a circular line around the center of the susceptor. The gas outlet openings can preferably be arranged such that the first and second doping gas flows flow across the entire width of the substrate. The gas outlet openings can also be arranged on a step formed by the process chamber ceiling, at which the process chamber height changes.It can be provided that the first doping gas flow is fed into the process chamber in the advance zone, and the second doping gas flow is fed into the process chamber downstream of the advance zone. It can further be provided that a first elevation of the process chamber ceiling is provided in the advance zone, and a second elevation of the process chamber ceiling is provided downstream of the advance zone. The second elevation of the process chamber ceiling can be provided in the region of the growth zone, which extends between the upstream and downstream edges of a storage location. It can also be provided that each of the two gas outlet openings is assigned to a stage.

[0056] According to a preferred embodiment, the CVD reactor has a gas inlet element arranged at its center with a gas outlet surface extending along a cylindrical surface, which has several gas outlet zones arranged vertically one above the other. Various reactive gases, each together with a carrier gas, for example, hydrogen or another inert gas, can be fed into the process chamber through the gas outlet zones. A circular process chamber extends around the gas inlet element, with a susceptor as the process chamber floor. The susceptor can be heated by a heater. Storage spaces are arranged on the susceptor in a ring around the center of the susceptor, each for holding a substrate. The storage spaces can be formed by circular disk-shaped substrate holders that are driven by a gas cushion, so that the substrates rotate during the deposition of the layer.

[0057] The inventive concept is based on model calculations and their results, which show that the incorporation of dopant materials, both with molecular nitrogen as the dopant carrier and with another nitrogen-containing dopant carrier, leads to a non-flat doping profile in a layer deposited on the substrate. This is independent of whether the dopant gas flow is fed into the process chamber through a first gas outlet opening arranged near the gas inlet element or in the gas inlet element, or through a second gas outlet opening arranged further downstream. However, the shape of the doping profile depends not only on the type of dopant, but also on the position of the gas outlet opening within the process chamber. A dopant carrier can be N2. Other dopant carriers can be ammonia or another molecule of a nitrogen compound in which the nitrogen is not triple-bonded. Model calculations and experiments show that when ammonia is used as a dopant carrier, a doping profile is established for a SiC layer deposited on a substrate rotating around its center point that has a flat central profile and decreases towards the edge of the substrate. The doping profile can be described as essentially bell-shaped. In contrast, feeding N2 as a doping gas flow into the process chamber leads to an edge-high doping profile of the layer deposited on the rotating substrate.To compensate for this reduced dopant incorporation observed at the edge when using NH3 as a dopant, the invention therefore proposes simultaneously feeding a second dopant gas flow containing N2 into the process chamber via the second gas outlet openings arranged in the process chamber ceiling, in addition to the first dopant gas flow. The two different dopant gas flows each individually generate characteristic doping profiles. The two characteristic doping profiles are each inhomogeneous but are capable of simultaneously compensating for the respective inhomogeneity in a manner of superposition. This creates a cumulative profile. The edge reduction generated by the first dopant gas flow can be compensated by the edge increase generated by the second dopant gas flow.The different dopant carriers are fed into the process chamber in particular through gas outlet openings arranged at different positions relative to the center of the susceptor.

[0058] Furthermore, it is intended to control the shape of the doping profile generated by the second doping gas flow by changing the distance between the second gas outlet openings and the gas inlet element. For example, by feeding N2 through the central gas inlet element, a doping profile can be created that has a W shape, i.e., in addition to the edge elevation, it also has a center elevation. Such a doping profile would not compensate, for example, for a strong center elevation of the doping profile generated by the first doping gas flow. The method according to the invention therefore proposes that the second doping gas flow be fed not through one of the gas inlet zones of the gas inlet element, but through the second gas outlet openings arranged downstream of the first gas outlet openings and thus of the gas inlet element and upstream of the downstream edge of the storage area.The distance between the second gas outlet openings and the gas inlet element can be selected such that the doping profile generated by the first doping gas flow is compensated by the doping profile generated by the second doping gas flow toward a homogeneous total profile. It is provided that the position of the second gas outlet openings is selected such that a total profile is generated that exhibits a homogeneous dopant concentration in the layer deposited on the substrate over the entire surface of the substrate.

[0059] The invention proposes a method for depositing layers on substrates, wherein the layers are preferably SiC layers or III-V layers, such as GaN layers. The invention further proposes a device having gas outlet openings arranged in the process chamber ceiling through which a second doping gas flow and optionally also a first doping gas flow can be fed. The device has a control device in which the process parameters are programmed and with which mass flow controllers and valves are controlled to feed carrier gases, inert gases, and reactive gases into the process chamber.

[0060] The gas outlet openings arranged in the process chamber ceiling can generate a gas stream that flows parallel to the process chamber ceiling. However, it is also possible for the gas outlet openings to be nozzles that direct the gas stream obliquely to the process chamber ceiling, particularly toward the process chamber floor. The gas outlet openings preferably generate a wide, low-profile, i.e., flat, gas stream that extends across the entire width of the process chamber. A homogeneous, laminar flow profile should be formed. If the process chamber extends around a central gas inlet element, it is preferably provided that the gas outlet openings extend along a circular arc around the gas inlet element, so that the gas flow generated thereby leaves the gas outlet openings virtually continuously along a circular arc. A laminar flow preferably develops within the process chamber.

[0061] The method according to the invention can have the following features: A first doping gas flow, which is fed into the advance zone either via a gas inlet element or first gas outlet openings arranged in the process chamber ceiling. Downstream of the first position at which the first doping gas flow is fed, several further positions can be provided, at each of which a further doping gas flow is fed into the process chamber via further gas outlet openings arranged in the process chamber ceiling. At least some of the further gas outlet openings can be located in the growth zone. However, it is preferred that the positions of the further gas outlet openings lie in the upstream half of the growth zone, namely in a region between an upstream edge of the storage location and a center of the storage location.Thus, a first second doping gas flow can be provided which is fed into the downstream half of the advance zone, a third doping gas flow which is fed into the growth zone, and a fourth doping gas flow which is also. if fed into the growth zone. The first, second, third, and fourth gas outlet openings can each be formed by the steps described above, so that the process chamber height also changes at the positions where the doping gas flows are fed into the process chamber.

[0062] It is possible to feed only the second doping gas flow into the process chamber through the gas outlet openings arranged in the process chamber ceiling. The first doping gas flow is preferably fed into the process chamber via an upper gas inlet zone of the gas inlet device or a downstream opening in the process chamber ceiling.

[0063] The positions of the first and second gas outlet openings through which the first and second doping gas flows are fed into the process chamber, respectively, and their composition are selected such that the curvature of the total doping profile of the layer deposited on the substrate is minimal. The total pressure in the process chamber can be in the range between 80 mbar and 1000 mbar.

[0064] The invention further relates to a method for depositing a SiC layer on a substrate, in which, according to a further variant of the invention, different doping gas flows are fed through different gas inlet zones of the gas inlet element. The vertical height of the gas inlet zone influences the shape of the doping profile, so that the doping profile of the layer deposited on the substrate can be influenced solely by the choice of the gas inlet zone. In this case, it is particularly provided that the two doping gas flows are fed into the process chamber through the gas inlet zones that are furthest vertically from one another, for example, through a gas inlet zone arranged at the top A first doping gas flow and a second doping gas flow are fed into the process chamber through a gas inlet zone arranged at the bottom. It can be provided that the dopant carriers of the various doping gas flows do not differ; for example, the dopant carrier can be NH3 or a mixture of NH3 and N2. Preferably, no doping gas flow flows through the gas inlet zones located between them. It can be provided that a carbon-containing growth gas flow flows through all gas inlet zones, and a silicon-containing, and in particular chlorine-containing, growth gas flow flows only through a central gas inlet zone.

[0065] In addition to the growth gases and doping gas flows described above, it is envisaged that another gas or gas mixture is fed into the process chamber, whereby this additional gas has a molar mass that is greater than the molar mass of the hydrogen used as the carrier gas and preferably greater than the molar mass of the dopant. Argon or a mixture of argon and hydrogen is particularly suitable for this purpose. This additional gas modifies the flow profile of the process gas in the process chamber. The additional heavier gas also changes the transport mechanism of the decomposition products vertical to the flow direction, i.e., the diffusion of the reaction products to the substrate or to the floor of the process chamber. The diffusion coefficient depends on the molar mass of the gas molecules. If the molar mass is increased, this inhibits diffusion.The introduction of a gas, referred to below as a barrier gas, whose molecular mass is at least heavier than hydrogen, thus influences the diffusion of the reaction products or reactants. The barrier gas flow is preferably pure argon or a mixture of hydrogen and argon.

[0066] By additionally feeding in a barrier gas, whose molar mass is preferably greater than the molar mass of the doping gas, the doping profile is further influenced in such a way that a relative maximum deviation from the mean value of the dopant concentration in the layer can be minimized. A doping profile that, for example, has a tub shape can be modified by feeding in the argon flow in such a way that the edge enhancement of the doping profile is reduced. Similarly, a doping profile that is bell-shaped can be influenced by additionally feeding in argon in such a way that the center enhancement is reduced. This results in a further possibility, in particular by combining ammonia and molecular nitrogen as dopant carriers, of depositing a layer with a doping profile with improved homogeneity.The introduction of additional argon through one or more of the gas inlet openings thus offers the possibility of "fine-tuning" the doping profile.

[0067] The first doping gas flow generates a first availability curve that reflects the availability of the dopant immediately above the substrate surface. This first availability curve can have a first curvature. The curvature of a second availability curve of the second doping gas flow is opposite to this curvature. By selecting selected parameters, the surface curvature profiles of the availability curves can be adjusted such that a cumulative profile formed by the availability curves exhibits greater homogeneity than the individual curves. A selected parameter can, for example, be the ratio of the mass flow of the first doping gas flow to the mass flow of the second doping gas flow. Ammonia can, for example, be fed in through the topmost and bottommost gas inlet openings. Furthermore, the two curvature profiles can be influenced by the barrier gas, which in particular contains argon.

[0068] The barrier gas can be fed into the process chamber in one or more partial flows via one or more gas outlet openings. For example, the barrier gas can be fed via the uppermost gas inlet zone. However, the barrier gas can also be fed into the process chamber via one or more gas outlet openings arranged downstream of the gas inlet element in the process chamber ceiling. In one variant of the invention, a first gas outlet opening can be arranged between the gas inlet element and an upstream edge of the storage space, and a second gas outlet opening can be arranged between the upstream and downstream edges of the storage space. Another selected parameter is the position of the gas outlet openings in the process chamber ceiling relative to the substrate.In addition, the mass flow of the partial flows of the second process gas flowing through the gas outlet openings is another selected parameter with which the curvature of the doping profiles can be adjusted. For example, a higher mass flow can flow through the first gas outlet opening than through the second gas outlet opening, which can be located above the substrate.

[0069] One or more of the gas outlet openings can be arranged in the region of a step in the process chamber ceiling. The height offset of the process chamber ceiling created by the step can preferably be 3 mm or 5 mm. The height offset can be another selected parameter that can be used to influence the curvature of the doping profile.

[0070] In a further development of the invention, argon can also be fed into the process chamber as a barrier gas together with another gas, for example hydrogen or nitrogen. Brief description of the drawings of the first invention

[0071] The first invention is explained in more detail below using exemplary embodiments. They show: Fig. 1 schematically shows in the manner of a half-section according to the line II in Figure 2 a CVD reactor 1, Fig. 2 shows the section along line II in Figure 1, Fig. 3 shows schematically a device for depositing SiC layers with a gas mixing system and a CVD reactor, Fig. 4 is a diagram showing two dopant profiles through a SiC layer at the top and two dopant profiles each produced by different dopant carriers at the bottom, Fig. 5 is a schematic representation of a second embodiment with regard to the composition and distribution of the process gas flow, Fig. 6 is a representation according to Figure 5 of a third embodiment, Fig. 7 is a representation according to Figure 5 of a fourth embodiment, Fig. 8 is a representation according to Figure 5 of a fifth embodiment, Fig. 9 is a representation according to Figure 5 of a sixth embodiment, Fig. 10 shows an embodiment in which argon is additionally fed into the top and bottom gas inlet zones 4, 6, Fig. 11 the embodiment according to Figure 6, wherein additional argon is also fed through the lowest gas inlet zone 4, Fig. 12 the embodiment according to Figure 11, wherein argon is fed through all gas inlet zones, Fig. 13 is a representation of the embodiment according to Figure 6, wherein argon is additionally fed through all gas inlet zones, Fig. 14 schematically shows a section of a process chamber 2 of the CVD reactor, where VI and V2 represent availability curves of various dopants, namely NH3 and N2, at the process chamber floor 4, Fig. 15 schematically shows the course of the dopant concentration C over the diameter of a SiC layer of a first doping profile PD1, which is created in a SiC layer when only ammonia is fed into the process chamber 2 as a dopant and a- a second doping profile PD2 that is created in a SiC layer when only molecular nitrogen is fed into the process chamber 2 as a dopant, wherein the substrate 12 is rotated during deposition so that the two doping profiles are rotationally symmetrical, Fig. 16 schematically shows the profile of the dopant concentration C of a sum of the two doping profiles PD1 and PD2 in Figure 15 as doping profile PD, when both ammonia and thick matter are fed into the process chamber 2 as dopant, wherein the substrate 12 is rotated during deposition so that the doping profile is rotationally symmetrical, Fig. 17 schematically shows a layer thickness profile PG of a SiC layer, wherein the substrate 12 is rotated during deposition so that the layer thickness profile is rotationally symmetrical, Fig. 18 is a representation according to Figure 1, wherein in addition to a first barrier gas flow Bl through a topmost gas inlet zone 6, a second barrier gas flow B2 is fed into the process chamber 2 through a bottommost gas inlet zone 4, Fig. 19 schematically shows the flow F of carbon (c) determined by model calculation based on diffusion towards the substrate surface in the area of ​​growth zone 8 (a without argon feed, b with argon feed at the top and c with argon feed at the bottom), Fig. 20 shows the diffusion-based flow F of silicon (Si) towards the substrate surface in the area of ​​growth zone 8, determined by model calculation (a without argon injection, b with argon injection at the top, c with argon injection at the bottom, but a', b' and c' each show the growth rates calculated from this). Fig. 21 the diffusion-based flow F of decomposition products NHx of ammonia towards the substrate surface in the area of ​​growth zone 8, determined by model calculation (a without argon feed, b with argon feed at the top, c with argon feed at the bottom), Fig. 22 the calculated ratio of Si to C availability in growth zone 8, Fig. 23 the calculated ratio of the availability of Si to the availability of C perpendicular to the flow direction above the substrate approximately in the substrate center, Fig. 24 the calculated ratio of the availability of Si to C averaged over a rotating substrate, Fig. 25 schematically shows, in the form of a half-section, an illustration of an embodiment of the CVD reactor 1 according to the invention, with gas inlet openings 35, 36 arranged in the process chamber ceiling 34, through which a barrier gas flow B1, B2 can be fed into the process chamber 2, Fig. 26 schematically shows the layer thickness curves of a SiC layer in the flow direction S, wherein curve a is a reference curve when no argon is fed into the process chamber 2 according to Figure 25 through the first and second gas outlet openings 35, 36 arranged in the region of a step 37, 38 within the advance zone 7, wherein curve b shows the layer thickness curve when only argon is fed in with a mass flow of 20 slm through the first gas outlet opening 35, and curve c shows the layer thickness curve when argon is additionally fed in with a mass flow of 30 slm through the second gas outlet opening 36, Fig. 27 is a representation of a further embodiment according to Figure 25, wherein in the flow zone 7 only one gas inlet opening 35 is arranged in the region of a step 37, which is located approximately 30 mm downstream of the gas inlet element 3, Fig. 28 schematically shows the layer thickness curves of a SiC layer in the flow direction S, wherein curve a indicates the layer thickness curve when no argon is fed through the gas inlet opening 35 into the process chamber 2 according to Figure 27, curve b indicates the layer thickness curve when argon is fed with a mass flow of 20 slm through the gas inlet opening 35 according to Figure 27 and curve c indicates the layer thickness curve when argon is fed with a mass flow of 30 slm through the gas inlet opening 35 according to Figure 27, Fig. 29 is a representation of a further embodiment according to Figure 25, wherein the second gas inlet opening 36 is arranged in the region of a step 3650 mm downstream of the position shown in Figure 25 within the deposition zone 8, Fig. 30 schematically shows the layer thickness curves of a SiC layer in the flow direction S, wherein curve a indicates the layer thickness curve when no argon is fed through the two gas inlet openings 35, 36 into the process chamber 2 according to Figure 29, curve b the layer thickness curve when argon is fed with a mass flow of 20 slm through the first gas inlet opening 35 according to Figure 29 and curve c the layer thickness curve when argon is additionally fed with a mass flow of 30 slm through the second gas inlet opening 36 according to Figure 29, Fig. 31 is a representation of a further embodiment according to Figure 25, wherein the second gas inlet opening 36 is arranged in the region of a step 38 75 mm downstream of the position shown in Figure 25 within the deposition zone 8, Fig. 32 schematically shows the layer thickness curves of a SiC layer in the flow direction S, wherein curve a indicates the layer thickness curve when no argon is fed through the two gas inlet openings 35, 36 into the process chamber 2 according to Figure 31, curve b the layer thickness curve when argon is fed with a mass flow of 20 slm through the first gas inlet opening 35 according to Figure 31 and curve c the layer thickness curve when argon is additionally fed with a mass- flow of 30 slm is fed through the second gas inlet opening 36 according to Figure 31, Fig. 33 is a representation of a further embodiment according to Figure 25, wherein the second gas inlet opening 36 is arranged in the region of a step 38 100 mm downstream of the position shown in Figure 25 within the deposition zone 8, Fig. 34 schematically shows the layer thickness curves of a SiC layer in the flow direction S, wherein curve a indicates the layer thickness curve when no argon is fed through the two gas inlet openings 35, 36 into the process chamber 2 according to Figure 33, curve b the layer thickness curve when argon is fed with a mass flow of 20 slm through the first gas inlet opening 35 according to Figure 33 and curve c the layer thickness curve when argon is additionally fed with a mass flow of 30 slm through the second gas inlet opening 36 according to Figure 33, Fig. 35 is a representation of a further embodiment according to Figure 25, wherein two additional steps 39, 40 are arranged within the deposition zone 8 in the process chamber ceiling 34, Fig. 36 schematically shows the layer thickness curves of a SiC layer in the flow direction S, which was deposited on a rotating substrate 12, wherein the curve a is a reference curve when no argon is fed through the two gas inlet openings 35, 36 arranged in the pre-flow zone 7 according to Figure 35. and no steps are arranged within the deposition zone 8 in the process chamber ceiling 34, the curve b shows the layer thickness profile when fed through the two gas inlet openings 35, 36 arranged in the advance zone 7 according to Figure 35 and no steps are arranged within the deposition zone 8 in the process chamber ceiling 34 and curve c shows the layer thickness profile when, in addition, as shown in Figure 35, two steps 39, 40 are arranged within the deposition zone 8 in the process chamber ceiling 34, Fig. 37 schematically shows the course of the dopant concentration C in the flow direction S of a SiC layer deposited on a rotating substrate 12, wherein curve a shows a doping profile when, according to Figure 25, 20 slm of argon are fed into the process chamber 2 via a first gas inlet opening 35 and 30 slm of argon via a second gas inlet opening 36, curve b shows a doping profile when the second gas inlet opening 36 is arranged 100 mm downstream of the position shown in Figure 25, curve c shows a doping profile when the second gas inlet opening 36 is arranged 75 mm downstream of the position shown in Figure 25, curve d shows a doping profile when the second gas inlet opening 36 is arranged 50 mm downstream of the position shown in Figure 25, and curve e shows a doping profile when the second gas inlet opening 36 mm is arranged in the position shown in Figure 25, Fig. 38 schematically shows the course of the dopant concentration C over the diameter of a SiC layer deposited on a rotating substrate 12, of a first doping profile a, which arises in a SiC layer when no argon is fed into the process chamber 2, and a second doping profile b, which arises in a SiC layer when, as shown in Figure 25, argon is fed in through two gas inlet openings 35, 36 arranged in the advance zone 7, wherein the mass flow through the first gas inlet opening 35 is 20 slm and through the second gas inlet opening is 3630 slm, and a third doping profile c, which arises in a SiC layer when, in addition to the gas inlet openings 35, 36 through which argon is fed in, as shown in Figure 39, two steps 39, 40 are arranged in the deposition zone 8, Description of the embodiments of the first invention

[0072] Figures 1 and 2 schematically show the structure of a CVD reactor 1. A housing of the CVD reactor 1, which may be made of stainless steel, contains a susceptor 10, which may be made of graphite and whose surface may be coated with SiC. The susceptor can be driven to rotate around a central axis. The susceptor has the circular disk shape shown in Figure 2.

[0073] Above the susceptor 10 is a process chamber 2, which is bounded at the top by a process chamber ceiling. The process chamber ceiling is formed by a ceiling plate 19, which can be supported on a holding element 18. The ceiling plate 19 can also be supported on a gas outlet element 9 arranged around the susceptor 10. The ceiling plate 19 can be made of SiC-coated graphite. The gas outlet The valve 9 can also be made of this material. However, it can also be made of a ceramic material.

[0074] The susceptor 10 is covered with cover plates 15, 16, which can also be made of SiC-coated graphite. However, they can also be made of SiC. Pockets 17 are formed, each having a pocket bottom into which a gas supply line 13 opens. The purge gas, for example, hydrogen, flowing from the gas supply line 13 can create a rotating gas cushion that suspends a substrate holder 11, which can also be made of SiC-coated or uncoated graphite, and drives the substrate holder 11 around a rotational axis.

[0075] A heating device 14 is provided below the susceptor 10. This heating device can be an RF heater, which is used to heat the susceptor 10. Furthermore, a further heating device (not shown) can be provided to heat the process chamber ceiling, i.e., the ceiling plate 19, so that the process chamber 2 is heated from all sides. Preferably, however, the ceiling plate 19 is not actively heated. The ceiling plate 19 is passively heated via thermal radiation from the susceptor 10 or from the cover plates 15, 16, so that the surface temperature of the ceiling plate 19 is significantly lower than the surface temperature of the cover plates 15, 16. This results in different surface reactions taking place on the ceiling plate 19 than on the cover plates 15, 16 or on the susceptor 10.The intermediate products mentioned above, which arise during the decomposition of NH3 or N2, can thus be formed to a reduced extent in the upper area of ​​process chamber 2. This can also influence the doping profile.

[0076] Located in the center of the process chamber 2 is a gas inlet element 3, which can be made of a ceramic material, stainless steel, quartz, or SiC-coated graphite. The gas inlet element 3 forms three (see Figure 3) superimposed gas inlet zones 4, 5, 6, each connected to a supply line 24, 25, 26 through which portions of a process gas flow can be fed into the respective gas inlet zone 4, 5, 6. The process gas flow is provided in a gas mixing system comprising a gas source 27 for nitrogen, a gas source 28 for ammonia, a gas source 29 for trichlorosilane, a gas source 31 for argon, a gas source 32 for hydrogen, and a gas source 30 for ethene (C2H4). A gas source for HCl can also be provided.

[0077] In an embodiment not shown, the gas inlet element 3 has, for example, four or five or more gas inlet zones arranged one above the other. Both a growth gas flow and a doping gas flow can flow through each of these gas inlet zones 4, 5, 6. In addition, a carrier gas can be fed into the process chamber 2 through one or more, through each or through all of the gas inlet zones, wherein the carrier gas can be hydrogen. Preferably, however, the carrier gas is a mixture of a gas with a high molecular weight, for example argon, and hydrogen, wherein the proportion of argon in this gas mixture can be in the range between 0% and 100%. Preferably, however, the proportion of argon in the carrier gas flow is in a range between 10% and 90%.

[0078] Argon, as well as the dopant carriers, are provided in the gas mixing system.

[0079] Each of the gas sources 27 to 31 is connected to at least one of the supply lines 24, 25, 26 by means of valves 22 and mass flow controllers 21. The Mass flow controller 21 and the valves 20 are controlled according to a program of the control device 20.

[0080] The gas mixing system provides at least two doping gas flows D1, D2, each containing a dopant carrier, for example N2 or NH3 or one of the above-mentioned nitrogen compounds that can still be used. Furthermore, the gas mixing system provides at least two growth gas flows Q1, Q2, but preferably several growth gas flows Q1, Q2, Q3, Q4, Q5. The growth gas flows contain carbon and silicon. One of these gases can also contain chlorine, for example trichlorosilicon, dichlorosilicon, or HCl. The gas sources 31, 32 provide a carrier gas containing argon and / or hydrogen. The mass flow controllers 21 can be used to feed any desired mixture of argon and hydrogen into each of the supply lines 24, 25, 26.

[0081] The doping gas flows D1, D2, and optionally D3 or D4 are fed into the process chamber 2 through the different and vertically stacked gas inlet zones 4, 5, 6, together with the multiple growth gas flows Q1 to Q5. The resulting process gas flow first flows through a pre-flow zone 7 of the process chamber 2, which is heated by the heating device 14 or another heating device arranged above and not shown. In this pre-flow zone 7, the process gas, which may in particular contain hydrogen as a carrier gas, is heated to a process temperature.

[0082] At the end of the pre-flow zone 7, the doping gas flows D1, D2, D3, D4 and the growth gas flows Q1 to Q5 reach a temperature at which the components of the doping gas flows and the growth gas flows can decompose or react with each other. The components of the doping gas flows and the growth gas flows can also react catalytically on the surfaces of the cover plates 15 or the ceiling plate 19. Intermediate products and, in particular, decomposition products are formed in the process. The intermediate or decomposition products and, if present, undecomposed dopant carriers (e.g., N2) migrate from the gas phase above the substrate holder 11 in a deposition zone 8 toward the surface of a rotating substrate 12 resting on the substrate holder 11. This occurs essentially by diffusion due to a depletion of the gas phase caused by the condensation or consumption of the intermediate or decomposition products on the substrate surface 12.

[0083] Due to this consumption of Si, C, and N at the surface of the substrate 12 or the n-doped SiC layer deposited there, the partial pressure of the growth gas and the dopant carrier in the gas phase above the substrate 12 decreases. Figure 1 schematically shows two doping profiles a and b measured across a diameter of the substrate 2. The linear doping profiles a and b, shown as curved lines, are rotationally symmetric and represent a section through the lateral doping profile in the layer deposited on the substrate 12.

[0084] The doping profile a is generated in a SiC layer deposited on the substrate 11 when the substrate 11 is rotated during deposition and only the first doping gas flow D1 is fed into the process chamber 2 through the gas inlet zone 6. The dopant profile b is generated in a SiC layer deposited on the substrate 11 when the substrate 11 is rotated during deposition and only the second doping gas flow D2 is fed into the process chamber 2 through the gas inlet zone 5.

[0085] In the exemplary embodiment, the dopant carrier of the first doping gas flow D1 is NH3 and the dopant carrier of the second doping gas flow D2 is N2. It can be seen that the two doping profiles are not straight, but curved. The selection of the dopant carriers or the selection of the gas inlet zones 4, 5, 6 through which the respective doping gas flow D1, D2 flows is carried out in such a way that two doping profiles a, b are formed that are curved in opposite directions. For example, in the exemplary embodiment, doping profile a is curved upwards and doping profile b is curved downwards. By varying the mass flows of the two doping gas flows D1, D2, a doping profile that is almost straight can be set.A rectilinear doping profile in a rotationally driven substrate 12 results in a nearly homogeneous dopant distribution being formed in the SiC layer deposited on the substrate 12.

[0086] The choice of dopant carriers and the choice of gas inlet zones 4, 5, 6 through which the dopant carriers are fed into the process chamber can be made such that the inhomogeneous, rotationally symmetric doping profile generated by one dopant carrier is compensated by the equally inhomogeneous, rotationally symmetric doping profile generated by another dopant carrier, toward a homogeneous, rotationally symmetric total profile. For example, one doping profile can be U-shaped. The other doping profile can be in the shape of an inverted U.

[0087] In the first embodiment shown in Figure 1, hydrogen and a fourth growth gas flow Q4, which is C2H4, are fed into the lowest gas inlet zone 4. The mass flow of the fourth growth gas flow Q4 corresponds to approximately 10% of the sum of all carbon containing growth gas flows Ql + Q3 + Q4. In the middle gas inlet zone 5, in addition to hydrogen, a third growth gas flow Q3 is fed in, which contains C2H4, and a second growth gas flow Q2 contains HCl3Si. The third growth gas flow Q3 contains approximately 80% of the sum of all carbon-containing growth gas flows. In addition, a second doping gas flow D2, which is nitrogen, is fed in through the middle gas inlet zone 5. Nitrogen and a first growth gas flow Ql, which contains C2H4, are fed in through the uppermost gas inlet zone 6. The mass flow of this growth gas flow Ql corresponds to approximately 10% of the sum of all carbon-containing growth gas flows. In addition, a first doping gas flow Dl, which contains NH3, is fed in through the uppermost gas inlet zone 6. Argon can also be fed in through a gas inlet zone 6, preferably the uppermost.

[0088] Figure 4 describes the effect that the introduction of different doping gas flows D1, D2 through gas inlet zones 5, 6 arranged at different levels has on the dopant distribution within the deposited layer. The upper curve, represented as open and closed triangles, shows a section through the center of a layer deposited on the substrate 12 and the dopant distribution within the layer, which is almost uniform. Only in the region near the edge of the layer of the circular disk-shaped substrate 12 is a slight reduction in the dopant concentration observed.

[0089] The two lower curves show the dopant incorporation that would be generated by only one of the two different dopant carriers. The open and closed squares represent the dopant incorporation that would be generated by only N2. Using only N2 as the dopant carrier results in a strong edge enhancement of the dopant incorporation. The open and closed circles represent the dopant incorporation that would be achieved using only NH3. When using only NH3 as the dopant carrier, a strong center enhancement of the dopant incorporation is observed. By appropriately selecting the ratio of the mass flows of N2 and NH3 or by appropriately selecting the vertical height of the gas inlet zones through which the different dopant carriers are fed into the process chamber, a doping profile can be generated that compensates for the center enhancement or edge enhancement.

[0090] In the embodiment shown in Figure 5, unlike the embodiment shown in Figure 1, a third doping gas flow D3, which is NH3, is additionally fed through the bottommost gas inlet zone 4. Argon can also be fed into the topmost gas inlet zone 6.

[0091] In the embodiment illustrated in Figure 6, no doping gas flow is fed into the process chamber 2 through the uppermost gas inlet zone 6. Here, only a first doping gas flow D1 (NH3) is fed through the lowest gas inlet zone 4, and a second doping gas flow D2 (N2) is fed through the middle or immediately above gas inlet zone. Argon can also be fed into the uppermost gas inlet zone 6.

[0092] In the embodiment shown in Figure 7, two doping gas flows D1 and D2 are fed into the process chamber 2, each containing NH3 as the dopant carrier. The two doping gas flows D1 and D2 are fed into the process chamber 2 through the lowest gas inlet zone 4 and the uppermost gas inlet zone 6, respectively. By selecting vertically different or spaced gas inlet zones 4 and 6, the shape of the depletion curves a and b can be adjusted. Argon can also be fed into the uppermost gas inlet zone 6.

[0093] In the embodiment shown in Figure 8, two doping gas flows D1, D2 are fed simultaneously through the uppermost gas inlet zone 6 into the process chamber 2. In this embodiment, N2 and NH3 are fed into the process chamber 2 through the same gas inlet zone 6. It can be provided that the doping gas flows D1, D2 are fed into the process chamber exclusively through the uppermost gas inlet zone 6, and that no doping gas flows are fed through the remaining gas inlet zones 5, 4, but rather at most a carrier gas or growth gas flows. In particular, it is provided that a gas mixture comprising two different dopant carriers flows through a gas inlet zone 6, wherein the gas mixture consists of NH3 and N2. Argon can also be fed into the uppermost gas inlet zone 6.

[0094] In the embodiment shown in Figure 9, two different doping gas flows D1, D2, D3, D4 are fed into the process chamber 2 through two different gas inlet zones 5, 6, which are preferably upper gas inlet zones. The mass flows of the doping gas flows D1, D2, D3, D4 fed through the different gas inlet zones 5, 6 then differ. As in the embodiment shown in Figure 8, it can be provided that a gas mixture comprising two different dopant carriers flows through a gas inlet zone 5, 6. The gas mixture can consist of NH3 and N2. The NEE flow through the gas inlet zone 5 can be different from the NEE flow through the gas inlet zone 6. Likewise, the two N flows. Argon can also be fed into the uppermost gas inlet zone 6.

[0095] Distributing the doping gases across different feed levels makes it possible to specifically adjust the doping profile. The following procedure can be used for this purpose: First, a doped layer is deposited using only an NH3 flux. The dopant profile is determined for this layer. A second layer is deposited on a second substrate, using only an N2 flux as the dopant. Alternatively, the second layer can also be deposited by simultaneously feeding an NH3 flux and an N2 flux into the process chamber. The dopant profile is then measured for these layers. The NH3 flux or N2 flux is then adjusted / varied, i.e., increased or decreased, for example, in model calculations or in further experiments, until an acceptable "flat" doping profile is achieved.

[0096] When using NH3, it is considered essential that a gas inlet zone 4 or 6 is used through which no chlorine-containing gas mixture flows. Thus, it is specifically intended that a chlorine-containing growth gas flow be fed into the process chamber exclusively through a central gas inlet zone 5.

[0097] It can be provided that a gas flow of a carbon-containing growth gas flows through all gas inlet zones 4, 5, 6.

[0098] When selecting the pairing of the dopant carriers, it can be advantageous if the dopant carriers have different nitrogen bonds (single, double or triple bonds), or if the dopant The dopant carriers are bound with chemical bonds of varying strength within the dopant carrier molecule. It can be assumed that these dopant carriers decompose differently and thus exhibit different depletion curves, allowing the dopant profile to be adjusted within the layer to be cut off.

[0099] It may be advantageous if NH3 is fed in through the top and bottom gas inlet zones 4 and 6, respectively, and N2 is fed in through the middle gas inlet zone 5.

[0100] The carbon-containing reaction gas, for example C2H4, is preferably fed into the process chamber 2 in the following mass distribution: 10% each through the lowest and the uppermost gas inlet zones 4, 6 and 80% through the middle gas inlet zone 5. The silicon-containing reactive gas, in particular trichlorosilane or dichlorosilane, is preferably fed into the process chamber 2 exclusively through the middle gas inlet zone 5.

[0101] Figure 10 shows a further embodiment of the invention, in which hydrogen is not fed as the carrier gas through the uppermost gas inlet zone 6, but rather a mixture of argon and hydrogen. The argon content can vary between 0% and 100%. An argon content of this carrier gas flow between 10% and 40% is preferred; the argon content is preferably between 15% and 30%. Here, argon can also be fed into the lowermost gas inlet zone 4.

[0102] Figure 11 shows a further embodiment of a modification of the embodiment shown in Figure 6, where here too, instead of hydrogen, a mixture of argon and hydrogen is passed through the uppermost Gas inlet zone 6 is fed into the process chamber. Argon can also be fed in through the lowest gas inlet zone 4.

[0103] Figures 12 and 13 show further embodiments as modifications of the embodiments illustrated in Figures 1 and 6, wherein, instead of a carrier gas flow consisting of hydrogen, a carrier gas flow consisting of argon and hydrogen is fed through the lowest gas inlet zone 4. The argon content of the barrier gas fed through the lowest gas inlet zone 4 is preferably lower than the argon content of the barrier gas flow fed through the uppermost gas inlet zone 6. Argon can also be fed through the middle gas inlet zone 5.

[0104] The doping gas flow D1, D2, D3, D4 from the one or more dopants and growth gas flows Q1, Q2, Q3, Q4, Q5 of the growth gases each flow together with hydrogen as carrier gas or admixed argon from the associated gas inlet zones 4, 5, 6 of the gas inlet device 3 into a pre-flow zone of the process chamber 2, where the gases heat up. The doping gas and the growth gases reach temperatures at which they decompose into their components. The decomposition products diffuse in a direction perpendicular to the horizontal flow in a vertical direction to the process chamber floor. The process parameters are set such that the deposition rate of the decomposition products of the growth gases reaches a peak immediately upstream of a growth zone adjoining the pre-flow zone in the flow direction.A silicon and carbon availability curve at the surface, which is reflected in the growth rate, then decreases in the direction of flow in the growth zone where the substrate to be coated is located. The decrease should be as linear as possible, i.e., straight, so that a layer with with a high layer thickness homogeneity. This layer homogeneity can also be influenced by the introduction of argon.

[0105] Just like the growth gases, the doping gases also decompose. However, due to different binding energies and pre-decomposition reactions in the gas phase, the availability curves of the various dopants immediately above the surface have different profiles. For ammonia, the availability curve is downwardly curved, resulting in a doping profile with a centrally elevated doping level on a layer deposited on a rotating substrate. This central elevation can be reduced by introducing argon, particularly by introducing argon into the uppermost gas inlet zone 6.

[0106] For nitrogen as a dopant carrier, the availability curve curves downwards, resulting in a dopant profile with increased edge height. The edge height is reduced by the introduction of argon. The introduction of argon into the uppermost gas inlet zone 6 leads to reduced diffusion of the dopant carriers toward the process chamber ceiling. The introduction of argon through a lowermost gas inlet zone 4 stabilizes the flow, as the heavier gas increases the dynamic pressure in the gas flow. At the same time, the introduction of argon fundamentally inhibits the diffusion of the reactive gases or their decomposition products in the direction perpendicular to the flow, as the diffusion coefficient depends on the molar mass of the gas.Feeding argon through the lowest gas inlet zone 4 can lead to a reduced growth rate, but at the same time also leads to a reduction in the depletion in the gas phase, so that the growth curve or the availability curve of the. Growth gases are flatter than with the same process parameters without the additional injection of argon into the process chamber.

[0107] By a suitable choice of the carrier gas composition, i.e. the molar mass of the carrier gas and the vertical level at which heavier carrier gas is fed into the process chamber, the result shown in Figure 4 of increasing the homogeneity of the dopant concentration in the layer can be further improved towards a doping profile that is as smooth as possible, in which a relative deviation of a maximum value of the dopant concentration or a minimum value of the dopant concentration from an average value measured over the entire layer is kept below, for example, 10%.

[0108] Experiments were conducted in a CVD reactor 1 having a stainless steel housing. The housing contains a process chamber 2, which is bounded at the top by a process chamber ceiling 34. The process chamber ceiling 34 is formed by a ceiling plate made of graphite, the graphite being coated with SiC. In the center of the process chamber 2 is a gas inlet element 3, through which process gases are fed into the process chamber 2. The process chamber 2 has a height H of 20 mm. In the exemplary embodiment, the distance between a process chamber floor 33, which is formed by a susceptor, and the process chamber ceiling 32 is constant over the entire length of the process chamber 2 extending in the direction of flow.

[0109] The gas inlet element 3 has three gas inlet zones 4, 5, 6 arranged vertically one above the other. The gas inlet zones 4, 5, 6 each form a vertical level at which the process gases can be fed into the process chamber. The gas inlet element 3 has a gas supply line through which the Process gases are fed separately into the gas inlet zones 4, 5, 6. The process gases are provided by a gas mixing system shown in Figure 3. The gas mixing system has valves and mass flow controllers controlled by the control device 20. The control device 20 can be operated by a control program that executes a recipe during the deposition of layers on substrates 12 arranged within the process chamber.

[0110] The process chamber 2 surrounds the gas inlet element 3 located in the center of the process chamber 2. Several substrates 12 are arranged in a circle around a center of the process chamber 2 located in the gas inlet element 3. Figure 1 shows the cross-section through two opposing substrates 6.

[0111] Each of the, for example, five, six, eight, or more substrates 12 arranged in the process chamber 2 is supported by a substrate holder 11. The substrate holder 11 lies in a pocket 17 of the susceptor 15. A gas supply line opens into the bottom of the pocket 17, through which a carrier gas is fed into the pocket 17. The carrier gas creates a gas cushion on which the substrate holder 11 floats. The carrier gas transfers angular momentum to the substrate holder 5, causing the substrate holder 11 and, along with the substrate holder 11, the substrate 12 it supports to rotate about a vertical axis of rotation.

[0112] The process chamber 2 can essentially be divided into two sections: a pre-flow zone 7, which extends in the flow direction of the process gas exiting the gas inlet element 3 from the gas inlet element 9 to the upstream edge of the substrate holder 11. This pre-flow zone 7 is followed in the flow direction by a growth zone 8, which The ejector is surrounded by a constant distance. The substrate holders 11 and the substrates 12 are arranged in the growth zone 8.

[0113] The susceptor 15 forming the process chamber floor 33 can be made of graphite, in particular SiC-coated graphite. The substrate holder 11 can also be made of this material and coated accordingly. A heater arranged below the susceptor is an RF heating device 14, which generates eddy currents in the susceptor or substrate holder 11, which heat the process chamber floor 33. The gas flowing through the process chamber 2 is also heated by thermal conduction.

[0114] The heating device 8 heats the process chamber floor 4 to a temperature between 1590°C and 1620°C.

[0115] Figure 14 schematically shows that a growth gas flow Q3, together with a first doping gas flow D1, can flow into the process chamber 2 through a gas inlet zone 4 located closest to the process chamber floor 33, which represents a lowest level. A growth gas flow Q2, together with a second doping gas flow D2, can flow into the process chamber 2 through an overlying, middle gas inlet zone 5, which represents a middle level. A growth gas flow Q1, another doping gas flow D3, and a barrier gas flow B1 can be fed into the process chamber 2 through an overlying, uppermost gas inlet zone 6, which is closest to the process chamber ceiling 34.

[0116] In the exemplary embodiment, the gas inlet zones 4, 5, and 6 each have the same height, which corresponds to the process chamber 2. In the experiments and model calculations, the total pressure in the process chamber was 80 mbar.

[0117] In the experiments underlying the invention, the first growth gas flow Q1, which flows through the uppermost gas inlet zone 6, contains 0.038 slm of C2H4. The second growth gas flow Q2, which is fed through the middle gas inlet zone 5, contains 0.28 slm of C2H4 and 0.78 slm of HChSi. The third growth gas flow Q3, which is fed through the lowest gas inlet zone 3, contains 0.056 slm of C2H4. Hydrogen is additionally fed into each of the gas inlet zones 4, 5, and 6, with the hydrogen flow being dimensioned such that a total flow of 94 slm flows through each of the gas inlet zones 4, 5, and 6.

[0118] Several reference experiments were conducted using these process parameters. In these reference experiments, doping gas flows D1, D2, and D3 were fed into process chamber 2 through gas inlet zones 4, 5, and 6. The total flow was kept constant by the hydrogen flows. In further experiments, the hydrogen flow flowing through gas inlet zone 4 was replaced by a barrier gas flow B1. The barrier gas flow B1 was 14.1 slm of argon, so the hydrogen flow fed through gas inlet zone 4 was reduced to 79.9 slm.

[0119] A first reference experiment, conducted without the introduction of argon, shows that the relative maximum deviation from the mean value of the doping profile is approximately 26% when depositing a SiC layer on a rotary-driven substrate with a diameter of 120 mm using only ammonia as the dopant, which flows through the lowest gas inlet zone. The doping profile is bell-shaped, with a center elevation. The relative maximum deviation from the mean value of the doping profile is approximately 26%. The maximum deviation from the mean is approximately 3%. However, the layer thickness profiles of different layers differ considerably. The maximum relative deviation from the mean is approximately 34%.

[0120] A second reference experiment, conducted without the introduction of argon, shows that the relative maximum deviation from the mean of the dopant profile is approximately 17% when depositing a SiC layer on a rotating substrate with a diameter of 120 mm using only molecular nitrogen as the dopant, which flows through the central gas inlet zone. The dopant profile is elevated at the edges, i.e., trough-shaped. The relative maximum deviation from the mean of the layer thickness profile is also approximately 3%. Here, too, the layer thickness profiles of different layers differ from one another.

[0121] In a third reference experiment, conducted without argon injection, using only ammonia as the dopant, which, however, flows into the process chamber through the topmost gas inlet zone, the relative maximum deviation from the mean of the doping profile is approximately 30%. Here, too, the doping profile is mid-high. The relative maximum deviation from the mean of the layer thickness profile is approximately 3%.

[0122] The following tables show the results of several reference experiments: Table 1 shows the process parameters of three reference experiments

[0123] Table 2 shows the process parameters of four experiments in which additional argon was fed into the process chamber in a top-located gas inlet zone 6

[0124] Table 3 shows the process parameters of another experiment in which twice the amount of argon was fed into the process chamber in the topmost gas inlet zone 6

[0125] Table 4 shows the process parameters of another experiment in which Argon is fed into the topmost gas inlet zone 6 but the total flow in the process chamber has been reduced

[0126] Table 1 shows the three key process parameters of the reference experiments RI, R2, and R3. These reference experiments were conducted without additional argon injection. In all reference experiments, the total flow through the three gas inlet zones 4, 5, and 6 was maintained at a constant value of 94 slm by additionally injecting hydrogen. In the reference experiments, a growth gas flow Q1 of C2H4 was fed into the lowest gas inlet zone 4, a growth gas flow Q2 of HChSi and C2H4 was fed into the middle gas inlet zone 5, and a growth gas flow Q3 of C2H4 was fed into the top gas inlet zone 6. Several reference experiments were conducted with the same parameters. The averaged results are shown below:

[0127] In the first reference experiment RI, a doping gas flow Dl consisting of 0.0004 slm of NH? was fed into the lowest gas inlet zone 4. A relative maximum deviation of layer thickness measurements at various locations on the deposited layer from a mean value of the measured layer thicknesses HG was 3%. A relative maximum deviation of dopant concentrations at various locations on the deposited layer from a mean value of the measured dopant concentrations HD was 26%.

[0128] In the second reference experiment R2, a doping gas flow D2 consisting of 100 slm N2 was fed into the middle gas inlet zone 5. HG was 3% and HD 17%.

[0129] In the third reference experiment R3, a doping gas flow D3 consisting of 40 slm NH3 was fed into the uppermost gas inlet zone 13. HG was 3% and HD 30%.

[0130] In the experiments described below, the hydrogen flow in the gas stream fed into the process chamber at the top level was replaced by a barrier gas. Instead of hydrogen, a mixture of argon and hydrogen was fed into the top level along with other reactive gases in such a way that the total gas flows through the three levels were equal.

[0131] In a first experiment, in which a 15% argon / hydrogen mixture flows into the process chamber through the topmost gas inlet zone in addition to the growth gas and otherwise ammonia flows into the process chamber through the bottommost gas inlet zone, the relative maximum deviation from the mean value of the dopant profile compared to the The first reference experiment was reduced to approximately 9%. The relative maximum deviation from the mean value for the layer thickness profile is approximately 3%.

[0132] In a second experiment, in which a 15% argon / hydrogen mixture flows into the process chamber through the topmost gas inlet zone in addition to the growth gas, and ammonia flows into the process chamber through the topmost gas inlet zone, the relative maximum deviation from the mean of the dopant profile was reduced to approximately 11% compared to the second reference experiment. For the layer thickness profile, the relative maximum deviation from the mean is approximately 3%.

[0133] In a third experiment, in which a 15% argon / hydrogen mixture flows into the process chamber through the topmost gas inlet zone in addition to the growth gas, and nitrogen otherwise flows into the process chamber through the middle gas inlet zone, the relative maximum deviation from the mean of the dopant profile could not be reduced compared to the third reference experiment. Surprisingly, a trend in the opposite direction was observed here. The value of the relative maximum deviation from the mean increased to approximately 36%. For the layer thickness profile, the relative maximum deviation from the mean is approximately 3%.

[0134]

[0135] From these experiments, it was found that the injection of argon into the topmost gas inlet zone leads to an increase in the homogeneity of the doping profile, if Assuming that only the first doping gas flow, i.e., ammonia, is fed into the process chamber, the most significant increase in homogeneity, i.e., reduction in the relative maximum deviation from the mean value, is observed when ammonia is fed into the lowest zone of the process chamber. The homogeneity of the layer thickness profile, however, was barely affected, but the deviation of the layer thickness profiles from each other in multiple experiments conducted with the same process parameters was.

[0136] In a fourth experiment, in which a 15% argon / hydrogen mixture flows into the process chamber through the topmost gas inlet zone in addition to the growth gas, and nitrogen flows through the middle gas inlet zone and ammonia flows through the bottommost gas inlet zone, the relative maximum deviation from the mean value of the dopant profile was reduced to approximately 4% compared to the third reference experiment. The homogeneity of the layer thickness profile was barely affected.

[0137] In the experiments, the barrier gas flow B1 and various doping gas flows D1 and D2 were fed through gas inlet zones 4, 5, and 6. The first doping gas flow contained ammonia, the second doping gas flow molecular nitrogen, and the third doping gas flow ammonia. The ammonia gas flow was 0.4 * 10 3slm. The flows were adjusted so that the same mass flow flowed through each of the three gas inlet zones 4, 5, and 6. In experiments R1 to R3 and E1 to E5, 694 slm flowed through each gas outlet area of ​​gas inlet zones 4, 5, into process chamber 2. This was achieved by appropriately diluting the reactive gas flows with hydrogen.

[0138] The substrates had a diameter of 120 mm.

[0139] Curve VI in Figure 14 schematically shows the availability of nitrogen-containing decomposition products from the first dopant, which in the exemplary embodiment is NH3, immediately above the surface of the pre-run zone 7 or the growth zone 8. The course of this curve essentially corresponds to the incorporation of the dopant, here nitrogen, into the SiC layer. The doping profile generated solely by this doping gas flow during the deposition of a layer on a substrate rotating during the process is shown schematically in Figure 15 with PD1. It can be seen that this doping profile PD1 is elevated in the center and decreases towards the edge. This availability curve is attributed to the delayed decomposition of NH3 into decomposition products in the gas phase. The cause of this decomposition are hydrogen radicals forming on the process chamber floor 33, which arise during the deposition of a conditioning layer of SiC in the pre-run zone VZ.The conditioning layer forms simultaneously with the layer deposited on the substrate.

[0140] Curve V2 in Figure 14 schematically shows the availability of nitrogen-containing decomposition products, which in the exemplary embodiment is N2, directly above the surface of the pre-run zone 7 or the growth zone 8. The course of this curve essentially corresponds to the incorporation of the dopant, here nitrogen, into the SiC layer. The doping profile generated solely by this doping gas flow during the deposition of the layer on a substrate rotating during the process is shown schematically in Figure 15 with PD2. This doping profile PD2 is slightly exaggerated in the middle. However, an edge elevation of this doping profile PD2 is significant. This edge elevation is due to edge effects during the thermal decomposition of N2 in the pre-run zone 7. The above-mentioned conditioning layer is of significant importance in this thermal decomposition. The distance a nitrogen molecule travels across the conditioning layer to the azimuthal edge is greater than the path across the conditioning layer towards the center of the substrate, so that there is a higher availability of nitrogen as a dopant at the edge.

[0141] By feeding both N2 and NH3, a sum profile PD of the two doping profiles PD1, PD2 can be generated, as shown, for example, in Figure 16. By appropriately selecting the partial pressures of the dopants in the gas phase or the doping gas flows D1, D2, D3, the homogeneity of the sum profile PD can be maximized.

[0142] The experiments described above have shown that both the course of the availability curve VI and the availability curve V2 can be influenced by injecting argon into one of the gas inlet zones 4, 5, and 6. Thus, by injecting argon, a "fine-tuning" of the doping profile PD can be achieved.

[0143] Table 2 shows four experiments in which, in addition to the doping gas flows, a barrier gas flow B1 was fed into the uppermost gas inlet zone 13. Here, too, the flows through the individual gas inlet zones 4, 5, and 6 were maintained at the above-mentioned constant value by introducing hydrogen. A 15% argon / hydrogen gas mixture was fed through the uppermost gas inlet zone 6 in addition to the respective growth gas flow Q1 or doping gas flow D3.

[0144] In experiment El, whose process parameters essentially correspond to those of the reference experiment RI, the relative maximum deviation of the dopant concentration from its mean value could be reduced to 9%.

[0145] In experiment E2, whose process parameters essentially correspond to those of the reference experiment R3, the relative maximum deviation of the dopant concentration from its mean value could be reduced to 11%.

[0146] Experiment E3 shows that the additional injection of argon at process parameters essentially corresponding to those of the reference experiment R2 results in an increase in the relative maximum deviation of the dopant concentration from its mean value.

[0147] Experiment E4 shows that a suitable choice of the dopant gas flows Dl (0.0004 slm ammonia through the lowest gas inlet zone 4) and D2100 slm nitrogen through the middle gas inlet zone 5) leads to a further reduction of the maximum deviation of the dopant concentration from its mean value, to 4%.

[0148] In a fifth experiment, in which a 30% argon / hydrogen mixture flows into the process chamber through the topmost gas inlet zone in addition to the growth gas, and otherwise, as in the first experiment, ammonia flows into the process chamber through the bottommost gas inlet zone, the relative maximum deviation from the mean of the doping profile was reduced to approximately 7% compared to the second reference calculation. However, with these process parameters, the relative maximum deviation from the mean of the layer thickness profile deteriorated from approximately 3% to approximately 4%.

[0149] Table 3 shows that experiment E5, in which the argon concentration was increased by introducing a 30% argon / hydrogen gas mixture into the uppermost gas inlet zone 6 in addition to the gas flow Ql, leads to only a slight improvement in the homogeneity of the doping profile. However, the layer thickness homogeneity deteriorates with these process parameters. The value for the relative maximum deviation from the mean value is 4%.

[0150] In a sixth experiment, in which, as in the fourth experiment, molecular nitrogen flows into the process chamber through the middle gas inlet zone and ammonia flows into the process chamber through the lowest gas inlet zone, and a 15% argon / hydrogen mixture flows into the process chamber through the topmost gas inlet zone in addition to the growth gas, the total flow was reduced to 89 slm instead of 94 slm flowing through each of the gas inlet zones. Surprisingly, it was found that both the relative maximum deviation from the mean value of the doping profile and the relative maximum deviation from the mean value of the layer thickness profile could be further improved, namely to a value of 1.5% for the doping profile and 2.2% for the layer thickness profile.

[0151] Table 4 shows that Experiment E6 produces optimal results. The barrier gas flow B1 consists of a 15% argon in hydrogen mixture. The total flow through each of the gas inlet zones 4, 5, and 6 was reduced to 89 slm each.

[0152] Figure 18 schematically shows the influence on the course of the availability curves VI, V2 when, in addition to a barrier gas flow B1 through the uppermost gas inlet zone 6, a second barrier gas flow B2 is fed into the process chamber through the lowermost gas inlet zone 4, whereby the second barrier gas flow B2 is lower than the first barrier gas flow B1. The gradient of the curves changes. The curves become flatter overall.

[0153] This curve shape is due to the fact that the two barrier gas flows B1 and B2 change the dynamic pressure in process chamber 2. Without argon being introduced, the maximum dynamic pressure is approximately in the vertical center of the process chamber height. The argon fed into process chamber 2 through the uppermost gas inlet zone 6 shifts the maximum dynamic pressure toward the process chamber ceiling 34. The introduction of the second barrier gas flow B2 through the lowest gas inlet zone 4 shifts the maximum toward the process chamber floor 33.

[0154] Figure 19 shows how the diffusion of carbon from the gas phase to the substrate changes when, starting from a reference curve (curve a) in which no argon is fed into the process chamber, argon is fed into the process chamber through the uppermost gas inlet zone 6 (curve b) and when argon is fed into the process chamber through the lowermost gas inlet zone 4 (curve c).

[0155] Figure 20 shows how the diffusion of silicon from the gas phase to the substrate, which determines the growth rate, changes when, starting from a reference calculation (curve a) in which no argon is fed into the process chamber, argon is fed into the process chamber through the uppermost gas inlet zone 6 (curve b) and when argon is fed into the process chamber through the lowermost gas inlet zone 4 (curve c).

[0156] Figure 21 shows the influence of argon injection on the diffusion of decomposition products of NH3 from the gas phase to the substrate (a no argon injection, b argon injection through the uppermost gas inlet zone 6 and c argon injection through the lowermost gas inlet zone 4).

[0157] Figures 22 to 24 show that the introduction of a barrier gas, namely a 15% argon / hydrogen mixture, also influences the Si / C ratio.

[0158] Figure 22 shows that the increase in this ratio decreases in the flow direction when argon is fed into the uppermost gas inlet zone 6. Curve a shows the Si / C ratio when only hydrogen is fed into the uppermost gas inlet zone 6. Curve b shows the Si / C ratio when a 15% argon / hydrogen mixture is fed in instead of hydrogen.

[0159] Figure 23 shows the Si / C ratio curve in the direction perpendicular to the flow direction, with the curve passing through the center of the substrate. Curve b, which indicates the Si / C ratio when argon is fed through the uppermost gas inlet zone 6, is clearly at a lower level.

[0160] Figure 24 shows the averaged Si / C ratio immediately above the substrate surface, averaging over one rotation of the substrate. Curve b, which represents the Si / C ratio when argon is additionally fed in, is significantly flatter than curve a, which represents the Si / C ratio when only hydrogen is fed in through the uppermost gas inlet zone 6.

[0161] Figure 17 shows the layer thickness profile PG of a silicon carbide layer when barrier gas is also fed through the gas inlet device located at the bottom.

[0162] Figure 25 shows a further embodiment of the invention. In the region of two stages 37, 38 arranged in the pre-run zone 7, a gas outlet opening 35, 36 is arranged, through which a barrier gas flow B1, B2 with increased molecular weight can be fed into the process chamber 2.

[0163] Figure 26 shows calculated layer thickness profiles of a SiC layer deposited on a stationary substrate in the region of the pre-run zone 7 and the growth zone 8. Curve a shows the profile of the growth rate r in the flow direction S of a reference in which only two stages 37, 38 are arranged in the pre-run zone 7, through which no barrier gas flow Bl, B2 is fed into the process chamber 2. Curve b shows the profile of the growth rate r in the flow direction S when a first barrier gas flow Bl containing argon is fed into the process chamber 2 through the first gas outlet opening 35 with a mass flow of 20 slm. Curve c shows the profile of the growth rate r in the flow direction S when, in addition, a second barrier gas flow B2 also containing argon is fed into the process chamber 2 through the second gas inlet opening 36 with a mass flow of 30 slm.In the model calculation, the distances of the two steps 37, 38 from the origin were 63 mm and 100 mm respectively, with a step height of 3 mm each.

[0164] It is evident that an argon flow fed through the first gas inlet opening 35 reduces the height of the maximum of the growth curve. The second gas inlet opening 36, arranged downstream of the first gas inlet opening 35, reduces the height of the maximum to such an extent that the decrease in the growth rate r over the growth zone 30 is almost linear. The second gas inlet opening 36 thus has a significant influence on the homogeneity of the layer thickness within the growth zone 8. It is also important here that at least one of the two gas inlet openings 35, 36 has a Minimum distance from the gas outlet surface of the gas inlet element 3, the 10% or 32% of the length of the lead zone 7.

[0165] Figure 27 shows a further embodiment of the invention in which a gas inlet opening 35 is arranged in the region of a step 37 arranged in the advance zone 7, through which a barrier gas flow Bl can be fed into the process chamber 2.

[0166] Figure 28 shows calculated growth curves of a SiC layer deposited on a stationary substrate 12, wherein curve a is a reference curve indicating the course of the growth rate r in the flow direction S when no argon is fed through the gas inlet opening 35. Curve b shows the course of the growth rate r in the flow direction S when 20 slm of argon are fed through this gas inlet opening 35. Curve c shows the course of the growth rate r in the flow direction S when 30 slm of argon are fed through this gas inlet opening 35. It can be seen that the height of the maximum of the growth curve is influenced by the height of the mass flow through an individual gas inlet opening 35 arranged in the advance zone 7, and thus an optimization of the growth rate course is achieved.Here, too, the position of the gas inlet opening 35, which may also coincide with a step, should have a minimum distance from the gas outlet surface of the gas inlet element 3, whereby the minimum distance should be at least 10%, preferably at least 25% of the length of the pre-flow zone 31. In the model calculations, the position of the gas outlet surface is approximately 30 mm from the origin, the position of the gas inlet opening 35 is 63 mm from the origin, and the position of the edge 42' is 147 mm from the origin.

[0167] Figure 29 shows a further embodiment of the invention, wherein a first gas inlet opening 35 is arranged in the region of a step 37 in the pre-flow zone 7, and a second gas inlet opening 36 is arranged in the region of a step 38 in the deposition zone 8, through which a barrier gas flow B1, B2 can be introduced into the process chamber 2. At each of the two steps 37, 38, the height H0, H1, H2 of the process chamber ceiling 34 increases.

[0168] Figure 30 shows calculated growth curves of a SiC layer deposited on a stationary substrate 12 in the region of the pre-deposition zone 7 and growth zone 8. The position of the two gas inlet openings 35 and 36 was 63 mm and 150 mm apart, respectively. Figure 29 shows a change in the process chamber height at these locations, but this is optional. The effects achieved by introducing a barrier gas are crucial here.

[0169] Curve a shows the course of the growth rate r in the flow direction S of a reference when no barrier gas flow B1, B2 is fed into the process chamber 2 through the first and second gas inlet openings 35, 36, the gas inlet openings 35, 36 being arranged at the position shown in Figure 29. Curve b shows the course of the growth rate r in the flow direction S when argon with a mass flow of 20 slm is fed in only through the first gas inlet opening 35. Curve c shows the growth curve for the case where argon with a mass flow of 30 slm is additionally fed in through the second gas inlet opening 36. It can be seen that the maximum of the growth curve due to the feeding of argon through the second gas inlet opening 36 influences the shape of the growth curve, particularly in the region of its maximum.

[0170] Figure 31 shows a further embodiment, wherein, unlike the embodiment shown in Figure 29, the second gas inlet opening 36 is arranged 25 mm further downstream within the deposition zone 8. The position of the second gas inlet opening 36 was 175 mm from the origin in the model calculation.

[0171] Figure 32 shows growth curves calculated analogously to Figure 30. Curve a shows the course of the growth rate r in the flow direction S of a reference when no barrier gas flow B1, B2 is fed into the process chamber 2 through the first and second gas inlet openings 35, 36, wherein the gas inlet openings 35, 36 are arranged at the position shown in Figure 31. Curve b shows the course of the growth rate r in the flow direction S when argon with a mass flow of 20 slm is fed only through the first gas inlet opening 35. Curve c shows the growth curve for the case where argon with a mass flow of 30 slm is additionally fed through the second gas inlet opening 36.

[0172] Figure 33 shows a further embodiment, wherein the second gas inlet opening 36 is arranged at a position that is 50 mm further in the flow direction S than the position of the second gas inlet opening 36 in Figure 29 and 25 mm further downstream in the deposition zone 8 than the position of the second gas inlet opening 36 in Figure 31. The position of the second gas inlet opening 36 relative to the origin was 200 mm here.

[0173] Figure 34 shows growth curves calculated analogously to Figures 30 and 32. Curve a shows the course of the growth rate r in the flow direction S of a reference when no barrier gas flow Bl, B2 is fed into the process chamber 2 through the first and second gas inlet openings 35, 36, where- with the gas inlet openings 35, 36 arranged at the position shown in Figure 31. Curve b shows the course of the growth rate r in the flow direction S when argon is fed in only through the first gas inlet opening 35 at a mass flow of 20 slm. Curve c shows the growth curve for the case where argon is additionally fed in through the second gas inlet opening 36 at a mass flow of 30 slm.

[0174] Comparing the growth curve c in Figures 30, 32, and 34 with the growth curve c in Figure 26, it can be seen that the position of the second gas inlet openings 36 influences the height of the maximum of the growth curve. If the second gas inlet opening 36 is arranged within the advance zone 7 in the process chamber ceiling 34 (see Figure 25), this leads to a local reduction in the height of the maximum of the growth rate r (see curve c in Figure 26). However, if the second gas inlet opening 36 is arranged within the growth zone 8 in the process chamber ceiling 34, as shown in Figures 29, 31, and 33, this leads to a shift of the maximum of the growth rate r either in the flow direction S (see Figures 32 and 34) or in the upstream direction (see Figure 30). Here, too, it is evident that an optimization of the layer thickness profile can be achieved by a suitable optimization with regard to the position of the second gas inlet opening 36.The calculations show that positioning the second gas inlet opening 36 within the flow zone 7 is optimal.

[0175] In the further embodiment of the invention shown in Figure 35, in addition to two gas inlet openings 35, 36 arranged in the region of a step 37, 38 within the advance zone 7, through which a barrier gas flow Bl, B2 can be fed into the process chamber 2, two steps 39, 40 without gas inlet openings are provided in the growth zone 8 between the upstream edge 42' of the storage location 42 and the center of the storage location 42 arranged in the process chamber ceiling 34. At the steps 37, 38, the height H0, H1, H2, H3, H4 of the process chamber 2 increases. Alternatively, the process chamber height can also change continuously there in the form of a slope 41.

[0176] In the model calculations, the first gas inlet opening 35 was located 63 mm from the origin, and the second gas inlet opening 36 was located 100 mm from the origin. At both inlets 35 and 36, the process chamber height increased by 3 mm each. The two steps 39 and 40 were located 175 mm and 200 mm from the origin, respectively, and each had a step height of 3 mm. A relative slope 41 can have a length of 25 mm and a height of 6 mm.

[0177] Figure 36 shows calculated growth curves for a SiC layer deposited on a rotating substrate 12. Curve a shows the course of the growth rate r in the flow direction S of a reference in which no argon is fed into the process chamber 2 through the gas inlet openings 35, 36 arranged in the advance zone 7, as shown in Figure 35, and no steps are arranged in the process chamber ceiling 34 within the deposition zone 8. Curve b shows the course of the growth rate r in the flow direction S when argon is fed into the process chamber 2 with a mass flow of 20 slm through the first gas inlet opening 35 and argon with a mass flow of 30 slm through the second gas inlet opening 36, and no steps are arranged in the process chamber ceiling 34 within the deposition zone 8.Curve c shows the course of the growth rate r in the flow direction S when argon with a mass flow of 20 slm is fed through the first gas inlet opening 35 and argon with a mass flow of 30 slm through the second gas inlet opening 36 into the process chamber 2 and two stages 39, 40, as shown in Figure 35, in the process chamber ceiling 34. are arranged within the deposition zone 8. It can be seen that if, in addition to the gas inlet openings 35, 36 arranged in the advance zone 7, through which argon is fed into the process chamber 2, steps 39, 40 are arranged in the deposition zone 8, the course of the growth curve is further optimized. The steps 39, 40 lead to a significant reduction in the center elevation of the bell-shaped growth curve. Instead of the two steps 39, 40, in a further exemplary embodiment not shown, the above-mentioned slope 41 can be arranged in the process chamber ceiling 34 within the growth zone 8, in particular between the upstream edge 42' of the storage location 42 and the center M of the storage location 42. The horizontal length of the slope 41 is preferably 6 mm. The vertical height of the steps shown in Figures 25, 27, 29, 31, 33 and 35 is preferably 3 mm.

[0178] The previously described embodiments show that with the addition of the parameters selected according to the invention, such as steps and slopes, a finer adjustment of the course of the growth rate r in the growth zone 8 is possible.

[0179] Figure 37 shows the effect of the argon flow on the dopant distribution within a SiC layer deposited on a substrate 6 in a process chamber 2 according to Figure 25, when argon is fed in not via the uppermost gas inlet zone 6, but through gas inlet openings 35, 36 arranged in the process chamber ceiling 34. Shown is the profile of the dopant concentration C over the diameter of the substrate 12, which has rotated during deposition. Curve a is a reference curve that shows the influence of the argon flow on the profile of the doping profile when argon is fed into the process chamber 2 only via a first gas outlet opening 35 arranged at a position of 63 mm with a mass flow of 20 slm.

[0180] Curves b, c, d and e show the effect when argon is fed in at a mass flow of 30 slm, i.e. a higher mass flow than through the first gas outlet opening 35, via an additional gas outlet opening 36 arranged downstream of the first gas outlet opening 35. By feeding argon through an additional second gas outlet opening 36 arranged downstream of the first gas outlet opening 35, the center peak of the doping profile is further reduced (see curves b, c, d and e). Curve b shows the doping profile when the second gas outlet opening 36 is arranged at a position 200 mm, i.e. within the deposition zone 8 at a distance of approximately D / 2 from the upstream edge 42' of the storage location 42, where D is the diameter of the storage location 42. Curve c shows the doping profile when the second gas outlet opening 36 is arranged at the position 175 mm, ie also within the deposition zone 8.Curve d is significantly flatter than curve b. Curve d represents the dopant concentration C when the second gas outlet opening 36 is arranged in the edge region of the upstream edge 42' of the storage location 42 within the deposition zone 8. Curve d is in turn flatter than curve c. The flattest curve is curve e, which indicates the dopant concentration C when the second gas outlet opening 36 is arranged within the advance zone 7 at a position of 100 mm. The greatest reduction in the center elevation of the doping profile and thus the most homogeneous doping profile is achieved when argon is fed in not only through a first gas outlet opening 35 arranged in the advance zone 7, but also through a second gas outlet opening 36 arranged downstream of the first gas outlet opening 35 within the advance zone 7.The argon flow fed through the second gas outlet opening 36 reduces the risk of recirculation caused by the argon flow fed through the first gas outlet opening 35 and thus increases the flow stability.

[0181] Figure 38 shows the influence of the steps 39, 40 shown in Figure 35, arranged in the deposition zone 8, on the dopant distribution within a SiC layer deposited on a rotating substrate 12. The curve shown is the profile of the dopant concentration C over the diameter D of the substrate 12. Curve a shows, as a reference, the doping profile of a SiC layer deposited without the introduction of argon. Curve b corresponds to curve e in Figure 37 and shows the influence of argon fed in through the gas inlet openings 35, 36 arranged in the advance zone 7. Curve c shows the profile of the dopant concentration C when, in addition, two steps 39, 40 are arranged within the process chamber ceiling 34 within the upstream half of the storage space 42, at which steps the process chamber height H0, H1, H2, H3, H4 increases, as shown in Figure 35.Curve b shows that the introduction of argon has the greatest influence on the dopant distribution profile. If, in addition to the introduction of argon, the two steps 39, 40 are provided within the deposition zone 8 (see curve c), a "fine-tuning" of the dopant distribution profile is possible, whereby the center elevation is slightly reduced compared to curve b. Instead of the two steps 39, 40, a slope 41 can also be arranged in the deposition zone 8 (shown in dashed lines in Figure 35). The slope 41 can also be used to influence the dopant concentration profile. The curve representing the dopant concentration C is flattened.

[0182] From the previously discussed findings, it is clear that the course of the dopant concentration in the deposition zone 8 is influenced by the feed of gas inlet openings 35, 36 arranged in particular in the pre-run zone 7. Furthermore, it is also possible to influence the course of the dopant concentration in the deposition zone 8 via a slope 41 arranged within the pre-run zone 7 in the process chamber ceiling 34. Furthermore, a fine adjustment of the course of the dopant concentration is possible. This is possible by adding steps 1 or slopes to the gas inlet openings, steps, or slopes located in the pre-flow zone 7, as well as by adding steps 1 or slopes located in the deposition zone 8. The curves were plotted on linear axes. Brief description of the drawings of the second invention

[0183] Embodiments of the second invention are explained below with reference to the following drawings. They show: Fig. 39 is a schematic representation of a cross section through a CVD reactor 1 with a process chamber 6 which is bounded at the top by a process chamber ceiling 5, in which first gas outlet openings 9 and second gas outlet openings 10 are arranged, through which a first doping gas flow Q1 and a second doping gas flow Q2 can be fed into the process chamber 6; Fig. 40 is a schematic plan view of a susceptor 4 of the CVD reactor 1 according to Fig. 1, wherein a plurality of gas outlet openings 9, 10 arranged in the process chamber ceiling 5 are arranged on circular arc lines around a gas inlet element 7 arranged in the center C of the process chamber 6; Fig. 41 is a view according to Fig. 2, wherein the second gas outlet opening is shown at different distances d1, d2, d3, d4 from the center C of the process chamber; Fig. 42 the course of calculated dopant concentrations in a layer, where the gas outlet openings are different distances from the center C of the process chamber 6, wherein the substrate 2 does not rotate during coating but remains stationary; Fig. 43 shows the course of the dopant concentration in the layer deposited in the process chamber 6 on the substrate 2 in the flow direction S according to Figure 3, wherein the substrate 2 rotates about its central axis during the deposition process; Fig. 44 schematic comparison of the first doping profile (Ql;dO) of the layer deposited on the rotating substrate 2, generated only by the first doping gas flow Ql, wherein the first doping gas flow Ql was fed through the gas inlet element 7, and the second doping profile (Q2;d4) generated only by the second doping gas flow Q2, wherein the second doping gas flow Q2 was fed into the process chamber 6 through the second gas outlet opening 10 arranged at a distance d4 from the gas inlet element; Fig. 45 is a schematic representation of a cross section through the process chamber 6 of the CVD reactor 1, wherein the first doping gas flow Q1 is fed into the process chamber 6 through the uppermost gas inlet zone of the gas inlet element 7 and the second doping gas flow Q2 is fed into the process chamber 6 through the second gas outlet opening 10; Fig. 46 is a representation according to Figure 6, wherein the first doping gas flow Q1 passes through the first gas outlet opening 9 arranged in the process chamber ceiling 5 and the second doping gas flow Q2 passes through the second gas outlet opening 10 arranged downstream of the first gas outlet opening 9 is fed into the process chamber 6; Fig. 47 is a representation according to Figure 7, wherein further gas outlet openings 10', 10" are provided in the process chamber ceiling 5, through which further doping gas flows Q3, Q4 respectively; Fig. 48 is a plan view of a section of the susceptor 4, wherein the gas outlet openings 9, 10, 10', 10" are designed as slots arranged on circular lines around the center of the susceptor 4 in the process chamber ceiling 5; Fig. 49 is a plan view of a section of the susceptor 4, wherein the gas outlet openings 9, 10 are arranged as individual openings in the process chamber ceiling 5 arranged on a circular line around the center of the susceptor 4; Fig. 50 schematically shows a cross section through a susceptor 4 of a CVD reactor 1 of a further embodiment; Fig. 51 schematically shows a cross section through a susceptor 4 of a CVD reactor 1 of a further embodiment, wherein the first doping gas flow Q1 is fed through a topmost gas inlet zone 15, the second doping gas flow Q2 is fed through a bottommost gas inlet zone 15'', and a second process gas flow Q0' is fed into the process chamber 6 through gas outlet openings 9, 10 arranged in the process chamber ceiling 5; Fig. 52 schematically shows a cross section through a susceptor 4 of a CVD reactor 1 of a further embodiment, wherein the gas outlet openings 9, 10, 10', 10" are arranged in the region of steps in the process chamber ceiling 5; Fig. 53 shows the course of calculated dopant concentrations in a layer deposited on a rotating substrate 2, wherein the first doping gas flow Q1 and / or the second doping gas flow Q2 were fed into the process chamber 6 together with the second process gas flow Q0'. Description of the embodiments of the second invention

[0184] Figure 39 shows a schematic representation of the CVD reactor 1. The CVD reactor 1 comprises a housing 12, which is made in particular of stainless steel and is gas-tight and can be evacuated. Located in the housing 12 is a gas inlet element 7, which is supplied with reactive gases through at least one supply line 13. These gases are fed into the process chamber 6 together with a carrier gas. The gas inlet element 7 is essentially cylindrical in shape and has several gas inlet zones arranged vertically one above the other. One of the supply lines opens into each gas inlet zone to feed in the carrier gas and one of the reactive gases. The cylindrical surface of the gas inlet element 7 forms a gas outlet surface for each of the gas inlet zones. Each gas outlet surface has a plurality of evenly distributed gas outlet openings for the passage of the process gas.The gas inlet element 7 is surrounded by a circular disk-shaped susceptor 4, which forms the floor of the process chamber 6. The process chamber 6 is limited at the top by a process chamber ceiling 5. The process chamber 6 is surrounded by a gas outlet element 11, through which the carrier gas fed into the process chamber 6 through the gas inlet element 7, as well as decomposition products of the reaction, are removed. active gases can be removed. Below the susceptor 4 there is a heating device 3, with which the susceptor 4 or the process chamber 6 can be heated. The process chamber ceiling 5 can also be heated. In the present case, however, the process chamber ceiling 5 is not heated. It can be provided that a temperature control device (not shown) is provided above the process chamber ceiling 5, with which the process chamber ceiling 5 can be either cooled or heated. Storage locations 8 are arranged on an annular surface around the center C of the gas inlet element 7. The storage locations 8 are formed by circular disk-shaped substrate carriers 14 (see Figure 40), on each of which a substrate 2 lies. The substrate carriers 14 can float on a gas cushion and be set into rotation by this.

[0185] In the process chamber ceiling 5, downstream of the gas inlet element 7 and upstream of the upstream edge of the storage locations 8, the first gas outlet openings 9 are arranged, through which the first doping gas flow Q1 is fed into the process chamber 6. Downstream of the first gas outlet openings 9 and upstream of the downstream edge of the storage locations 8, the second gas outlet openings 10 are arranged, through which the second doping gas flow Q2 is fed into the process chamber 6.

[0186] Figure 40 shows a plan view of the susceptor 4 of the CVD reactor 1. In the embodiment shown in Figure 40, the susceptor 4 has a circular disk shape and forms the floor of the process chamber 6. In the center of the process chamber 6 is the gas inlet element 7, through which the process gas flow Q0 containing, for example, silane, disilane, methane, ethane or organometallic compounds of an element of a III main group or hydrides of an element of a V main group together with an inert gas, in particular hydrogen or helium, into the process chamber 6 is fed in. The gas inlet element 7 can form a plurality of gas inlet zones arranged vertically one above the other, through which different reactive gases and the dopant carrier of the first doping gas flow Ql, for example NH3, can be fed separately from one another, each together with a carrier gas, into the process chamber 6. The first doping gas flow Ql is preferably fed into the process chamber 6 through the uppermost gas inlet zone of the gas inlet element 7. In the exemplary embodiment shown in Figure 40, the first gas outlet opening 9, through which the first doping gas flow Ql is fed in, is not arranged in the gas inlet element 7 itself, but on a circular line arranged around the center of the gas inlet element 7 at a distance d1 from the center of the gas inlet element 7.

[0187] Figure 41 illustrates model calculations used to calculate dopant profiles in deposited layers. The doping gas flows were fed into the process chamber 6 through gas outlet openings 10, which were spaced at different distances d1, d2, d3, d4 from the center C of the process chamber 6. The gas outlet openings 10, spaced at a distance d1 from the center C, are located directly downstream of the gas inlet element 7. The gas outlet openings 10, spaced at a distance d2 from the center C, are located approximately centrally in the advance zone. The gas outlet openings 10, spaced at a distance d3 from the center C, are located directly behind the upstream edge of the storage location 8. The gas outlet openings 10, spaced at a distance d4 from the center, are located approximately in the center of the storage location 8.

[0188] To achieve homogeneous doping in a layer deposited on a rotating substrate, it is necessary that the availability of the doping gas in the growth zone decreases as linearly as possible in the flow direction. The course of this availability in the flow direction S corresponds to a A dopant concentration of a layer deposited on a stationary, i.e., non-rotating, substrate. Only if this availability is sufficiently straight across the substrate does the averaging achieved by the rotation of the substrate lead to a homogeneous dopant concentration extending over the entire surface of the substrate.

[0189] Figure 42 shows several calculated doping profiles generated solely by the second doping gas flow Q2 in a layer deposited on a stationary substrate 2, wherein the second doping gas flow is fed into the process chamber 6 either through the gas inlet element 7 or one of the gas outlet openings 9, 10 arranged in the process chamber ceiling 5 at different distances d1, d2, d3, d4 from the center of the gas inlet element 7. The doping profiles each correspond to the dopant concentration in the layer in the flow direction S in the region of the growth zone between the upstream edge (-100) and the downstream edge (+100) of the storage location 8, determined for a different position of the second gas outlet opening through which the second doping gas flow Q2 generating the doping profile is fed.

[0190] Curve a shows the doping profile generated in the layer by a second doping gas flow Q2 fed through the gas inlet element 7. Curves b, c, d and e correspond to the feeding of the second doping gas flow through a gas outlet opening 9, 10, 10', 10" arranged at a distance d1, d2, d3 and d4, respectively, from the center of the gas inlet element 7. In this exemplary illustration, the distances correspond to the positions of the gas outlet openings 9, 10' shown in Figure 40. Curves d and e result from the feeding of the second doping gas flow through the second gas outlet openings 10 arranged above the storage location 8, which have a distance d3 or d4 from the center of the gas inlet element 7.

[0191] It is evident that the linearity of the doping profile can be controlled by changing the distance between the gas outlet openings 9, 10 through which the second doping gas flow Q2 is fed into the process chamber 6. Thus, the calculations show that with increasing distance from the gas inlet element 7, the doping profile changes toward a linear doping profile.

[0192] Figure 43 shows, analogously to Figure 42, the doping profiles generated solely by the second doping gas flow, but for a layer deposited on a rotating substrate 2. Curve a shows a doping profile characterized by an increased dopant concentration in the edge region and in the center region. With increasing distance between the second gas outlet openings and the gas inlet element 7 (curves b to e), this center elevation changes to a center reduction. This means that by feeding only the second doping gas flow Q3 through gas outlet openings 10 arranged above the substrate, a doping profile can be generated that has both an edge elevation and a center reduction. Of course, the doping profile can also have a different profile than that shown here as an example.What is essential to the invention is that the course of the doping profile of the layer deposited on the substrate 2 can be controlled by changing the position in the process chamber ceiling 5 at which the second doping gas flow Q2 is fed into the process chamber 6.

[0193] Figure 44 shows a comparison of the first doping profile (Ql;d0) of the layer deposited on the rotating substrate 2, which is generated only by the first doping gas flow Ql, wherein the first doping gas flow Ql is generated by the Gas inlet element 7 was fed in, and the second doping profile (Q2;d4) generated only by the second doping gas flow Q2, wherein the second doping gas flow Q2 was fed into the process chamber 6 through the second gas outlet opening 10 arranged at a distance d4 from the gas inlet element (see Figure 40). The first doping gas flow Q1 can contain, for example, ammonia, and the second doping gas flow Q2 can contain a gas mixture containing, for example, nitrogen and argon.

[0194] The first doping profile (Ql, dO), generated solely by the first doping gas flow Ql, is characterized by a flat mean profile and decreases toward the edge of the substrate. In contrast, the second doping profile (Q2, d4), generated solely by the second doping gas flow Q2 at position d4, is characterized by an edge elevation and a center reduction. By feeding the first and second doping gas flows into the process chamber 6, a superimposed doping profile can be generated, which is generated by both the first doping gas flow Ql and the second doping gas flow Q2. A cumulative profile is formed. By appropriately selecting the distance d2 - d4 of the second gas outlet openings 10', through which the second doping gas flow Q2 is fed, from the center of the gas inlet element 7, the cumulative profile can exhibit greater homogeneity than the individual doping profiles.

[0195] As shown by way of example in Figure 44, by a suitable choice of the distance, for example by feeding the second doping gas flow Q2 through the second gas outlet opening 10" at a distance d4 from the center of the gas inlet element, a second doping profile (Q2, d4) directed opposite to the first doping profile (Q1, d0) can be generated. A sum profile formed from these two doping profiles would produce a dopant concentration that is homogeneous over the entire surface of the substrate. The two However, doping profiles can also have different patterns than those shown here as examples.

[0196] Figures 45, 46, and 47 each schematically show a section of a cross-section of the process chamber 6 according to the exemplary embodiment of the CVD reactor 1 shown in Figure 39. On the left, at a distance dO from the center C of the gas inlet element 7, the gas outlet surface of the gas inlet element 7 is shown. There, the process chamber 6 has a process chamber height HO, which corresponds to the distance between the surface of the susceptor 4 facing the process chamber ceiling 5 and the process chamber ceiling 5. The height HO can be between 20 and 30 mm. In Figure 45, the first doping gas flow Q1 is fed into the process chamber 6 via the uppermost gas inlet zone of the gas inlet element 7. The first gas outlet opening 9 is thus located within the gas inlet element 7, so that its distance dl to the center of the gas inlet element corresponds to the distance dO of the gas outlet surface of the gas inlet element 7 to the center of the gas inlet element 7.Downstream of the gas inlet element 7, at a distance d2 from the center of the gas inlet element 7, in the process chamber ceiling 5, is the second gas outlet opening 10 through which the second doping gas flow Q2 is fed into the process chamber 6. This position influences the flow profile of the gas flow through the process chamber 6. For example, an inert gas can be fed as a doping gas through the second gas outlet opening 10. The inert gas is preferably nitrogen or a mixture of nitrogen and argon.

[0197] The doping gas can be a mixture of ammonia and molecular nitrogen, for example, 80% ammonia and 20% molecular nitrogen. However, the doping gas can also be pure ammonia, for example 100% ammonia and 0% molecular nitrogen. However, the doping gas can also be pure nitrogen, i.e., 0% ammonia and 100% nitrogen.

[0198] A doping gas that would otherwise act as an inert gas, such as nitrogen, can be fed through the second gas outlet opening 10 in Figures 39 to 53. Nitrogen can be mixed with argon here. These are two gases that would otherwise act as inert gases, but molecular nitrogen (N2) acts as the dopant here. Nitrogen is fed in together with argon, with argon also acting as an inert gas here. Instead of nitrogen, 100% NH3 can also be fed through the second gas outlet 10. However, it is also possible to feed in a mixture of, for example, 80% NH3 and 20% N2.

[0199] The process chamber 6 forms a pre-flow zone extending from the first position dO, i.e., the gas outlet surface of the gas inlet element 7, to an upstream edge of the storage location 8. Adjoining this in the flow direction S is a growth zone extending over the substrate 2 or the storage location 8 supporting the substrate 2.

[0200] Furthermore, a gas mixing system (not shown) is provided, which comprises gas lines, valves, and mass flow controllers, with which the reactive gases can be provided. The gas mixing system is also capable of providing inert gas flows, which in particular consist of a mixture, using gas lines, valves, and mass flow controllers arranged therein. The mixing ratio of the inert gas flows and their total flow can be individually adjusted by a control device. The control device can execute a recipe for depositing a layer on the substrate 2 and, for this purpose, control valves and mass flow controllers.

[0201] In a further exemplary embodiment of the invention, which is illustrated in Figure 46, the first gas outlet opening 9 is located in the process chamber ceiling 5 at a distance d1 from the center of the gas inlet element 7. The first gas outlet opening 9 is arranged on a step of the process chamber ceiling 5 at which the process chamber ceiling 5 rises. The first doping gas flow Q1 is fed through the first gas outlet opening and flows horizontally into the process chamber 6 directly beneath the process chamber ceiling 5. Downstream of the first gas outlet opening 9, the second gas outlet opening 10 is also arranged on a step of the process chamber ceiling 5. The first gas outlet opening 9 and the second gas outlet opening 10 can be slit-shaped. The second doping gas flow Q2 is fed into the process chamber 6 through the second gas outlet opening 10.The second gas outlet opening 10 is located in the growth zone, just like the first position dl in the advance zone.

[0202] Figure 47 shows a further exemplary embodiment, wherein two further second gas outlet openings 10', 10" are optionally provided, through which the respective doping gas flows Q3 and Q4 flow into the process chamber. The gas outlet openings 10', 10" are also slot-shaped and are each arranged on a step of the process chamber ceiling 5. The doping gas flow Q3 is fed in between the doping gas flows Q2 and Q1. The doping gas flow Q4 is fed in between the doping gas flows Q3 and Q2. At the positions d1, d2, d3 and d4, the process chamber height H increases from a height H1 to the process chamber heights H1, H2, H3 and H4. The step height can be, for example, 3 to 5 mm. The step length extending in the flow direction S of a step having, for example, an oblique step flank can be, for example, 3 to 10 mm. The second gas outlet opening 10 can also be located downstream of the center of the eager place 8.

[0203] Between the second gas outlet openings 10 and the first gas outlet openings 9, third gas outlet openings 10' and fourth gas outlet openings 10" are provided. These gas outlet openings, from which a third doping gas flow Q3 and a fourth doping gas flow Q4 respectively flows, can be arranged in the flow zone, i.e. between the gas inlet element 7 and the storage location 8. However, they can also be arranged vertically above the storage location 8, i.e. within the growth zone.

[0204] Here and in the other exemplary embodiments in Figures 45 and 47, the step is depicted with a vertically extending step flank. Other exemplary embodiments of the invention have a step that runs diagonally, i.e., rises diagonally in the flow direction S. The step can extend over a length that approximately corresponds to the step height. Between the individual steps, the process chamber ceiling 5 runs on planes that run parallel to the susceptor 4, which runs in one plane.

[0205] As shown in Figures 48 and 49, the gas outlet openings 9, 10, 10', 10" can each be arranged on circular lines around the center of the gas inlet element 7. As schematically shown in Figure 48, the gas outlet openings 9, 10, 10', 10" can be slots extending along the circular lines. A gas outlet opening 9, 10, 10', 10" can be designed as a single, uninterrupted slot. However, the gas outlet openings 9, 10, 10', 10" can also each be divided into several slot sections, wherein the storage locations 8 arranged around the center of the gas inlet element 7 at a fixed pitch angle can each be assigned a slot section along each of the circular lines. However, the gas outlet openings 9, 10, 10', 10" may also each comprise a plurality of evenly spaced openings through which a doping gas flow flows into the process chamber 6. The gas outlet openings 9, 10, 10', 10" are arranged so that a homogeneous gas flow flows over the entire width of the substrate 2.

[0206] The embodiment shown in Figure 50 differs from the embodiment shown in Figure 39 essentially in that the process gas flows through the process chamber 6 in a linear manner. The gas outlet surface of the gas inlet element 7 can be a flat surface here. The first gas outlet openings 9 and the second gas outlet openings 10 are each arranged on a line running perpendicular to the flow direction S. The length of the line corresponds at least to the diameter of the storage location 8 in order to ensure a gas flow over the entire surface of the substrate 2. The gas outlet openings 9, 10 can also be slit-shaped here, wherein the length of the slit-shaped opening corresponds at least to the diameter of the storage location 8. In the embodiment shown in Figure 50, the second gas outlet opening 10 is arranged in the advance zone.However, the second gas outlet opening 10 can also be arranged at any position in the process chamber ceiling 5 above the storage location 8.

[0207] The inventive design development of a CVD reactor creates the possibility of achieving a homogeneous dopant profile in a layer under various process conditions, and in particular both during the deposition of SiC layers, in which nitrogen is used as a dopant, and during the deposition of III-V layers, in which other dopants are used, by appropriately selecting the mass flows of the dopants through the gas outlet openings arranged at different distances from the gas inlet element. The invention thus also relates to an optimization method with which the most homogeneous dopant profile possible is created. In this optimization method, for example, in model Calculations vary the positions of the gas outlets. In addition, the mass flows or the ratios of the mass flows through the various gas outlets can be varied until the dopant profile has an optimal shape.

[0208] Further optimization parameters available in these model calculations are the different process chamber heights HO Hl H2 H3 and H4, which can be varied to optimize the dopant profile.

[0209] The previously described embodiments show that the course of the dopant concentration in the growth zone is possible by feeding a second doping gas flow through gas outlet openings arranged in the process chamber ceiling and by varying the feed position.

[0210] Figure 51 shows a further embodiment in which a first process gas flow Q0 is fed into the process chamber 6 through three gas inlet zones 15, 15', 15" arranged vertically one above the other. In addition, the first doping gas flow Q1 is fed into the process chamber 6 through the uppermost gas inlet zone 15 of the gas inlet element 7, and the second doping gas flow Q2 is fed into the process chamber 6 through the lowermost gas inlet zone 15". The first doping gas flow Q1 and the second doping gas flow Q2 preferably both contain the same dopant carrier. The mass flows of the doping gas flows Q1, Q2 are preferably different; in particular, the mass flow of the first doping gas flow Q1 is greater than the mass flow of the second doping gas flow. For example, the first doping gas flow Q1 contains 85% of the dopant fraction and the second doping gas flow Q2 contains 15% of the dopant fraction.For example, 85% of the total ammonia flow can be fed through the top gas inlet zone 15 and 15% of the total ammonia flow can be fed through the bottom gas inlet zone 15".

[0211] In addition to the doping gas flows Q1, Q2, a second process gas flow Q0'1, Q0'2, Q0'3, Q0'4 is fed into the process chamber 6 in several partial flows. The second process gas flow Q0'1, Q0'2, Q0'3, Q0'4 preferably contains a gas whose molar mass is greater than the molar mass of a dopant carrier fed into the process chamber 6. The second process gas flow can consist exclusively of one or more inert gases. In the embodiment shown in Figure 51, the feed takes place via two gas outlet openings 9, 10 arranged in the process chamber ceiling 5. The first gas outlet opening 9 is arranged downstream of the gas inlet element 7 and upstream of an upstream edge of the storage location 8. The first partial flow Q0'1 of the second process gas flows into the process chamber 6 through the first gas outlet opening 9.The second partial flow Q0'2 flows into the process chamber 6 through the second gas outlet opening 10, which is located downstream of the upstream edge of the storage location 8 and upstream of the downstream edge of the storage location 8. The second gas outlet opening is located in the region of a step in the process chamber ceiling 5. The first gas outlet opening 9 can also be located in the region of a step. The second process gas flow Q0'1, Q0'2, Q0'3, Q0'4 essentially inhibits the diffusion of the reactive gases flowing from the gas inlet element 7 toward the process chamber ceiling 5.

[0212] Figure 52 shows a further embodiment which differs from that in Figure 51 in that two gas outlet openings 9, 10 are provided between the gas inlet element 7 and the upstream edge of the storage location 8 and two further gas outlet openings 10', 10" are provided between the upstream edge of the storage location 8 and the center C of the storage location 8. All gas outlet openings 9, 10, 10', 10" are each arranged in the region of a step in the process chamber ceiling 5. By the gas outlet- A partial flow Q0'l, Q0'2, Q0'3, Q0'4 of the second process gas flow flows through the outlet openings 9, 10, 10', 10".

[0213] Figure 53 shows exemplary results of model calculations for the deposition of a SiC layer on a rotating substrate 2 in a CVD reactor 1, as schematically illustrated in Figure 52. The course of various lateral doping profiles is shown. During the deposition process, a carbon-containing growth gas flow flows through all gas inlet zones 15, 15', 15", and a silicon-containing, and in particular chlorine-containing, growth gas flow flows only through the central gas inlet zone 15'. The first and second doping gas flows Q1, Q1 each contain ammonia as a dopant carrier.A partial flow Q0'1, Q0'2, Q0'3, Q0'4 of the second process gas flow containing argon flows through the gas outlet openings 9, 10, 10', 10" arranged in the process chamber ceiling 5, wherein, for example, an argon flow of 60 slm flows through the first gas outlet opening 9 and an argon flow of 3 slm flows through the second, third and fourth gas outlet openings 10, 10', 10" into the process chamber 6. The height offset k generated by the steps in the process chamber ceiling 5 is, for example, 5 mm for all steps.

[0054] Each of the two doping gas flows Q1, Q2 generates a lateral profile of its dopant with a characteristic surface curvature in the layer deposited on the substrate. If only one doping gas flow is fed in, the profiles f and g result, which have opposite curvatures. If only the first doping gas flow Q1 is fed into the process chamber 6 through the uppermost gas inlet zone 15, the lateral profile g results, which has a U-shaped curvature. If only the second doping gas flow Q2 is fed in through the lowermost gas inlet zone 15", a curved profile opposite to the profile g results. Profile f. By feeding in both the first doping gas flow Q1 and the second doping gas flow Q2, a cumulative profile h or i can be generated. Profile h has a U-shaped curvature, with the curvature being less than that of profile f. In this case, the dopant content of both doping gas flows Q1 and Q2 was 50% each. By increasing the ammonia content of the first doping gas flow Q1 to 85% and reducing the ammonia content of the second doping gas flow Q2 to 15%, the curvature can be further reduced, as can be seen in profile i. The course of profile i essentially corresponds to a straight line.This shows that by appropriately selecting the mass flows of the doping flows Ql, Q2, the mass flows of the partial flows QO'l, Q0'2, Q0'3, Q0'4 of the second process gas flow through the gas outlet openings 9, 10, 10', 10" and the relative position of the gas outlet openings 9, 10, 10', 10" and the downstream end of the storage location 8, the homogeneity of the total profile can be maximized.

[0214] The above statements serve to explain the inventions covered by the application as a whole, which each independently develop the state of the art by at least the following combinations of features, whereby two, several or all of these combinations of features can also be combined, namely:

[0215] A method which is characterized in that the carrier gas of at least one of the partial flows has a molecular mass which is greater than the molecular mass of the dopant carrier and is in particular argon or a mixture of argon and hydrogen.

[0216] A method which is characterized in that the process gas flow contains a second doping gas flow D2 containing a second gaseous dopant carrier, wherein the two doping gas flows D1, D2 are separated controlled by one another, are fed into the process chamber 2 as a partial flow through gas inlet zones 4, 5, 6 arranged vertically one above the other, and each of the two doping gas flows Dl, D2 generates a lateral profile a, b of its dopant with a characteristic surface curvature in a SiC layer.

[0217] A method which is characterized in that the mass flows of the first and second doping gas flows Dl, D2 and / or the molar mass of the carrier gas, the vertical position of the gas inlet zones 4, 5, 6 through which the two doping gas flows Dl, D2 and / or the carrier gas flows having the increased molar mass flow, are selected such that the lateral profiles a, b have different surface curvature profiles.

[0218] A method characterized in that the first dopant carrier is a nitrogen-containing gas, in particular NH3, and the second dopant carrier is a nitrogen-containing gas, in particular N2.

[0219] A method characterized in that the binding forces of a nitrogen atom to other atoms of the second dopant carrier are greater than the binding forces of a nitrogen atom to other atoms of the first dopant carrier.

[0220] A method characterized in that the second growth gas flow Q2 contains chlorine and the first growth gas flow Ql does not flow through the same gas inlet zone 4, 5, 6 together with the first doping gas flow Dl containing NH3.

[0221] A method characterized in that the first and second dopant carriers and the mass flows of the dopant gases carrying them flows Dl, D2 or the mass flows or molar masses of the carrier gas are chosen such that a sum of the two profiles a, b weighted by the ratio of the mass flows approaches a plane.

[0222] A process characterized in that the dopant carriers are selected from the following nitrogen compounds: N2, NH3, HCN, pyridine (C5H5N), hydrazine (N2H4), dimethylhydrazine (C2H8N2) or unsymmetrical dimethylhydrazine.

[0223] A method characterized in that the process gas flow is fed into a central gas inlet element 3 which is surrounded by substrate holders 11 arranged in a circle around the gas inlet element 3 and lying in pockets 17 of a susceptor 10, wherein the substrate holders 11 are carried by a gas cushion and driven in rotation.

[0224] A method characterized in that the first doping gas flow D1 flows through a topmost gas inlet zone 6 and the second doping gas flow D2 flows through a lower-lying gas inlet zone 5 and / or that the first doping gas flow D1 flows together with the first growth gas flow Q1 through the same gas inlet zone 6 and / or that the second doping gas flow D2 flows together with the second growth gas flow Q2 through the same gas inlet zone 5 and / or that a third growth gas flow Q3 flows through a bottommost gas inlet zone 4 and no doping gas flow flows through the bottommost gas inlet zone 4 and / or that a third doping gas flow D3 flows through a bottommost gas inlet zone 4 and / or that the first doping gas flow D1 flows through a bottommost gas inlet zone 4 and the second doping gas flow D2 flows through an overlying gas inlet zone 5 and / or that the first doping gas flow D1 and the secondDoping gas flow D2 contain the same dopant carrier, whereby the first doping gas flow Dl flows through a topmost gas inlet zone 6 and the second doping gas flow D2 flows through a bottommost gas inlet zone 4 and / or that two mutually different doping gas flows Dl, D2; D3, D4 are fed into the process chamber 2 through a gas inlet zone 6, in particular the topmost gas inlet zone, or through two gas inlet zones 5, 6, in particular through toply arranged gas inlet zones 5, 6, wherein the doping gas flows Dl, D2;D3, D4 have different dopant carriers, and / or that a gas with a high molecular weight, in particular argon, is fed in through at least one, preferably the upper or the lower gas inlet zone 4, 5, 6, wherein preferably a mixture of argon and hydrogen is used, wherein the argon proportion of the gas mixture can be between 15 and 30%, and / or, simultaneously and in particular through different gas inlet zones 4, 5, 6, ammonia and nitrogen are fed into the process chamber 2 as dopant carriers and additionally through at least one gas inlet zone 4, 5, 6, preferably through the uppermost gas inlet zone 6, argon or another gas with a molecular weight that is greater than the molecular weight of one of the dopant carriers is fed into the process chamber 2.

[0225] A method characterized in that by additionally feeding in a gas whose molar mass is greater than the molar mass of the doping gas, a relative maximum deviation ((Max - Min) / (2*p)) from a mean value of a dopant concentration C in a doping profile PD of the layer is reduced.

[0226] A method which is characterized in that a gas whose molecular mass is greater than the molecular mass of the doping gas is passed through the uppermost gas inlet zone 6 of the gas inlet element 3 and / or through one or more the process chamber ceiling 34 arranged gas inlet openings 35, 36 are fed into the process chamber 2.

[0227] A method characterized in that the first doping gas flow D1 is fed into the process chamber 2 at a level closest to the process chamber floor 4 and the partial flow with a larger molecular mass is fed into the process chamber 2 at a level closest to the process chamber ceiling 7.

[0228] A method characterized in that the second doping gas flow D2 is fed into the process chamber 2 through a middle level located between the uppermost level and the lowermost level or at the lowermost level or at the uppermost level.

[0229] A method characterized in that a further partial flow with a larger molecular mass is additionally fed into the process chamber 2 at the lowest level, wherein the partial flow with a larger molecular mass flowing through the uppermost level is larger than the partial flow with a larger molecular mass flowing through the lowest level.

[0230] A device characterized in that the control device 20 is configured to carry out a method according to one of the preceding claims.

[0231] A device characterized by gas inlet openings 35, 36 arranged in the process chamber ceiling 34.

[0232] A device characterized in that the gas inlet openings are arranged in the region of a step 37, 38 at which the height H0, H1, H2, H3, H4 of the process chamber ceiling 34 increases.

[0233] A device characterized in that the gas inlet openings 35, 36 are arranged between the gas inlet member 3 and an upstream edge 42' of a storage location 42 carrying the substrate 12.

[0234] A CVD reactor characterized in that the second gas outlet opening 10 is assigned to the process chamber ceiling 5.

[0235] A CVD reactor characterized in that the second gas outlet opening 10 is arranged downstream of an upstream edge of the storage location 8.

[0236] A CVD reactor, characterized in that the first gas outlet opening (9), the second gas outlet opening (10), the third gas outlet opening (10 1 ) and / or the fourth gas outlet opening (10") is arranged in the region of a step of the process chamber ceiling (5).

[0237] A method for depositing a layer, in particular a SiC layer, on a substrate 2 in a process chamber 6 of a CVD reactor 1 heated to a process temperature by a heating device 3, wherein the process chamber 6 is delimited at the top by a process chamber ceiling 5 and at the bottom by a susceptor 4 extending in a horizontal plane, with a storage location 8 assigned to the susceptor 4 for receiving the substrate 2, wherein a gas inlet element 7 having gas inlet zones 15, 15', 15" arranged vertically one above the other in one or more partial flows together with a carrier gas, a first process gas flow Q0 is introduced into the Process chamber 6 is fed and flows horizontally in a flow direction S over the rotationally driven substrate 2, wherein a first doping gas flow Q1 is fed into the process chamber 6 through a topmost gas inlet zone 15 and a second doping gas flow Q2 is fed into the process chamber 6 through a bottommost gas inlet zone 15", wherein the first doping gas flow Q1 and the second doping gas flow Q2 contain the same dopant carrier, in particular ammonia, wherein each of the two doping gas flows Q1, Q2 generates a lateral profile f, g of its dopant with a characteristic surface curvature in the layer, wherein a second process gas flow Q0'1, Q0'2, Q0'3, Q0'4 is fed into the process chamber 6 through one or more gas outlet openings 9, 10 into one or more separately regulated partial flows,which contains a gas whose molar mass is greater than the molar mass of the carrier gas and preferably greater than the molar mass of the dopant carrier, wherein at least one second gas outlet opening 10 is arranged in the process chamber ceiling 5 downstream of at least one first gas outlet opening 9 and upstream of a downstream edge of the storage location 8, wherein by selecting selected parameters the characteristic surface curvature profiles of the lateral profiles f, g are adjusted such that a sum profile h, i formed by the lateral profiles f, g has a higher homogeneity than the individual profiles f, g, wherein the selected parameters at least the mass flows of the first and second doping gas flows Ql, Q2, the mass flows of the partial flows of the second process gas Q0'l, Q0'2, Q0'3, Q0'4 flowing through the gas outlet openings 9, 10 and / or the relative position of the gas outlet openings 9, 10 and the downstream end of storage area 8.

[0238] A method according to, which is characterized in that a selected parameter is a parameter determined by a step in the process chamber ceiling 5, on which the first and / or second gas outlet opening 9, 10 is arranged, caused height offset k is.

[0239] A method which is characterized in that the mass flow of the first partial flow of the second process gas QO'l, Q0'2, Q0'3, Q0'4 flowing through the first gas outlet opening 9 is higher than the mass flow of the second partial flow of the second process gas QO'l, Q0'2, Q0'3, Q0'4 flowing through the second gas outlet opening 10.

[0240] A method which is characterized in that the choice of the selected parameters is limited to the ratio of the mass flow of the first doping gas flow Q1 to the mass flow of the second doping gas flow Q2 being greater than one, in particular greater than five, the second gas outlet opening 10 being arranged between an upstream edge of the storage location 8 and a center C of the storage location 8 and the height offset k being between 2.5 mm and 5.5 mm, preferably between 3 mm and 5 mm.

[0241] A CVD reactor or a process characterized in that a third gas outlet opening 10' and / or a fourth gas outlet opening 10" is arranged downstream of the first gas outlet opening 9 and upstream of the second gas outlet opening 10 in the process chamber ceiling 5.

[0242] A CVD reactor or a process characterized in that the first gas outlet opening 9 is assigned to the gas inlet element 7 or is arranged between the gas inlet element 7 and the upstream edge of the storage location 8 on the process chamber ceiling 5.

[0243] A CVD reactor or a method, characterized in that a plurality of first gas outlet openings 9, a plurality of second gas outlet openings 10, a plurality of third gas outlet openings 10' and / or a plurality of fourth gas outlet openings 10" are arranged on a line which runs at a constant distance from a gas outlet surface 7' of the gas inlet element 7, wherein the line is a straight line or a circular arc line around a center of the gas inlet element 7 arranged in a center of the susceptor 4.

[0244] A method for depositing a layer on a substrate 2 in a CVD reactor according to one of claims 1 to 3 or 8 to 10, wherein the susceptor 4 is heated to a process temperature by means of the heating device 3, wherein a first process gas flow Q0 is fed into the process chamber 6 through the gas inlet element 7, wherein a first doping gas flow Q1 is fed into the process chamber 6 through the first gas outlet opening 9, which first doping gas flow Q1 has the effect of generating a first inhomogeneous doping profile in the layer, wherein a second doping gas flow Q2 is fed into the process chamber 6 through the second gas outlet opening 10, which second doping gas flow Q2 has the effect of generating a second inhomogeneous doping profile in the layer, wherein the ratio of the first doping gas flow Q1 to the second doping gas flow Q2 is selected such thatthat a sum profile formed by the two doping profiles has a higher homogeneity than the individual doping profiles.

[0245] A method characterized in that the first doping gas flow Q1, the second doping gas flow Q2, a third doping gas flow Q3, which is fed into the process chamber 6 through the third gas outlet opening 10', and / or a fourth doping gas flow Q4, which is fed into the process chamber 6 through the fourth gas outlet opening 10', extend uniformly over the entire width of the storage location 8.

[0246] A method characterized in that the layer is a SiC layer and the doping gas flows Q1, Q2, Q3, Q4 comprise a nitrogen-containing dopant.

[0247] A method characterized in that the dopant is nitrogen and / or that the dopant flows together with an inert gas and / or argon through the gas outlet openings 9, 10, 10', 10".

[0248] All disclosed features are essential to the invention (individually, but also in combination with one another). The disclosure of the application hereby fully incorporates the disclosure content of the associated / attached priority documents (copy of the prior application), also for the purpose of incorporating features of these documents into claims of the present application. The subclaims, even without the features of a referenced claim, characterize independent inventive developments of the prior art with their features, in particular for filing divisional applications based on these claims. The invention specified in each claim may additionally comprise one or more of the features provided in the above description, in particular with reference numerals, and / or specified in the list of reference numerals.The invention also relates to designs in which individual features mentioned in the above description are not implemented, in particular insofar as they are clearly unnecessary for the respective intended use or can be replaced by other technically equivalent means. List of reference numerals used in Figures 1 to 38 1 CVD reactor 30 gas source, ethylene 2 process chamber 31 gas source, argon 3 Gas inlet device 32 Gas source, hydrogen 4 Gas inlet zone 33 Process chamber floor 5 Gas inlet zone 34 Process chamber ceiling 6 Gas inlet zone 35 first gas inlet opening 7 Pre-flow zone 36 second gas inlet opening 8 Deposition zone 37 level 9 Gas outlet 38 stage 10 Susceptor 39 Level 11 Substrate holder 40 level 12 Substrate 41 Slope 13 Gas supply line 42 Storage area 14 Heating device 42' upstream edge 15 Cover plate 42" downstream edge 16 Cover plate 17 Pocket Bl Barrier gas flow (argon flow) 18 Holding element B2 Barrier gas flow (argon flow) 19 Ceiling plate C Dopant concentration 20 Control device D diameter 21 Mass flow controller Dl doping gas flow (NH?) 22 Valve D2 doping gas flow (N2) 24 Supply line D3 doping gas flow (NH3) 25 Supply line D4 doping gas flow 26 Supply line HO process chamber height 27 Gas source, nitrogen Hl Process chamber height 28 Gas source, ammonia H2 Process chamber height 29 Gas source, Trichlorosilane H3 Process chamber height H4 Process chamber height VI Availability curve first PD Doping profile (sum pro dopant fil) V2 Availability curve second PD1 first doping profile dopant PD2 second doping profile PG layer thickness profile a curve Ql growth gas flow b curve Q2 growth gas flow c curve Q3 Growth gas flow d curve Q4 Growth gas flow curve Q5 Growth gas flow S Flow direction p Mean value List of delay figures used in Figures 39 to 53 1 CVD reactor h curve 2 Substrate i Curve 3 Heating device 4 Susceptor 5 Process chamber ceiling dl Position of the first gas outlet 6 Process chamber opening 7 Gas inlet element d2 Position of the second gas outlet 7' gas outlet area outlet opening 8 Storage location d3 Position of the third gas outlet 9 first gas outlet opening 10 second gas outlet opening d4 position of the fourth gas outlet 10' third gas outlet opening 10" fourth gas outlet 11 Gas outlet HO process chamber height 12 Housing Hl Process chamber height 13 Supply line H2 Process chamber height 14 substrate carrier H3 process chamber height 15, 15', 15" Gas inlet zone Q0 first process gas flow QO'l, Q0'2, Q0'3, Q0'4 second process gas flow a Curve Q1 first doping gas flow c Curve Q2 second doping gas flow d Curve Q3 third doping gas flow e Curve Q4 fourth doping gas flow f Curve g Curve S flow direction C Center k Height offset

Claims

Claims 1. A method for depositing a SiC layer on a substrate (12) in a process chamber (2) of a CVD reactor (1) heated to a process temperature by a heating device (14), wherein a process gas flow is fed into the process chamber (2) through a gas inlet element (3) in one or more partial flows together with a carrier gas and flows in a flow direction (S) over the substrate (12) which is driven in rotation in a horizontal plane, wherein the process gas flow is composed of at least one first dopant gas flow (D1) containing a first gaseous dopant carrier, a carbon-containing first growth gas flow (Q1), and a silicon-containing second growth gas flow (Q2), wherein the one or more dopant carriers decompose as they flow through the process chamber (2), Decomposition products of the one or more dopant carriers are incorporated as dopant into the SiC layer on the surface of the SiC layer growing on the substrate, wherein the carrier gas of at least one of the partial flows has a molar mass which is greater than the molar mass of the dopant carrier and is in particular argon or a mixture of argon and hydrogen, characterized in that partial flows emerge from several gas inlet zones (4, 5, 6) of the gas inlet element (3) arranged vertically one above the other and the flow direction is a horizontal direction, wherein the first dopant carrier, without the use of the molar mass-increased carrier gas, produces a dopant profile in the layer which is elevated at the edges or in the center, wherein by feeding the molar mass-increased carrier gas through a topmost gas inlet zone (6) or a bottommost gas inlet zone (4) the edge elevation or center elevation is lowered.

2. A method for depositing a SiC layer on a substrate (12) in a process chamber (2) of a CVD reactor (1) heated to a process temperature by a heating device (14), wherein a process gas flow is fed into the process chamber (2) through a gas inlet element (3) in one or more partial flows together with a carrier gas and flows in a horizontal direction in a flow direction (S) over the rotationally driven substrate (12), wherein the process gas flow is composed of at least one first dopant gas flow (D1) containing a first gaseous dopant carrier, a carbon-containing first growth gas flow (Q1), and a silicon-containing second growth gas flow (Q2), wherein the one or more dopant carriers decompose as they flow through the process chamber (2), Decomposition products of the one or more dopant carriers are incorporated as dopant into the SiC layer on the surface of the SiC layer growing on the substrate, characterized in that the process gas flow contains a second doping gas flow (D2) containing a second gaseous dopant carrier, wherein the two doping gas flows (Dl, D2) are fed into the process chamber (2) in a separately regulated manner as a partial flow through different gas inlet zones (4, 5, 6) arranged vertically one above the other, and each of the two doping gas flows (Dl, D2) produces a lateral profile (a, b) of its dopant with a characteristic surface curvature in a SiC layer.

3. Method according to claim 1 or 2, characterized in that the mass flows of the first and second doping gas flows (Dl, D2) and / or the molar mass of the carrier gas, the vertical position of the gas inlet zones (4, 5, 6) through which the two doping gas flows (Dl, D2) and / or the carrier gas flows having the increased molar mass flow, are selected such that the lateral profiles (a, b) have surface curvature profiles that differ from one another.

4. Method according to one of claims 2 or 3, characterized in that the first dopant carrier is a nitrogen-containing gas and in particular NH3 and the second dopant carrier is a nitrogen-containing gas and in particular N2 and / or that the binding forces of a nitrogen atom to other atoms of the second dopant carrier are greater than the binding forces of a nitrogen atom to other atoms of the first dopant carrier.

5. Method according to one of the preceding claims, characterized in that the second growth gas flow (Q2) contains chlorine and the first growth gas flow (Ql) does not flow through the same gas inlet zone (4, 5, 6) together with the first doping gas flow (Dl) containing NH3.

6. Method according to one of the preceding claims, characterized in that the first and second dopant carriers and the mass flows of the dopant gas flows (Dl, D2) carrying them or the mass flows or molar masses of the carrier gas are selected such that a sum of the two profiles (a, b) weighted by the ratio of the mass flows approximates a plane.

7. Method according to one of the preceding claims, characterized in that the dopant carriers are selected from the following nitrogen compounds: N2, NH3, HCN, pyridine (C5H5N), hydrazine (N2H4), dimethylhydrazine (C2H8N2) or asymmetrical dimethylhydrazine and / or that the process gas flow is fed into a central gas inlet element (3) which is surrounded by substrate holders (11) arranged in a circle around the gas inlet element (3), which lie in pockets (17) of a susceptor (10), wherein the substrate holders (11) are carried by a gas cushion and driven in rotation.

8. Method according to one of claims 1 to 7, characterized in that the first doping gas flow (Dl) flows through a topmost gas inlet zone (6) and the second doping gas flow (D2) flows through a lower gas inlet zone (5).

9. Method according to one of claims 1 to 7, characterized in that the first doping gas flow (Dl) flows together with the first growth gas flow (Ql) through the same gas inlet zone (6).

10. The method according to any one of claims 1 to 7, characterized in that the second doping gas flow (D2) flows together with the second growth gas flow (Q2) through the same gas inlet zone (5).

11. Method according to one of claims 1 to 7, characterized in that a third growth gas flow (Q3) flows through a gas inlet zone (4) arranged at the bottom and no doping gas flow flows through the gas inlet zone (4) arranged at the bottom.

12. Method according to one of claims 1 to 7, characterized in that a third doping gas flow (D3) flows through a gas inlet zone (4) arranged at the bottom.

13. Method according to one of claims 1 to 7, characterized in that the first doping gas flow (Dl) flows through a gas inlet zone (4) arranged at the bottom and the second doping gas flow (D2) flows through a gas inlet zone (5) arranged above it.

14. Method according to one of claims 1 to 7, characterized in that the first doping gas flow (Dl) and the second doping gas flow (D2) contain the same dopant carrier, wherein the first doping gas flow (Dl) flows through a topmost gas inlet zone (6) and the second doping gas flow (D2) flows through a bottommost gas inlet zone (4).

15. The method according to any one of claims 1 to 7, characterized in that two mutually different doping gas flows (Dl, D2; D3, D4) are fed into the process chamber (2) through a gas inlet zone (6), in particular the uppermost gas inlet zone, or through two gas inlet zones (5, 6), in particular through gas inlet zones (5, 6) arranged at the top, wherein the doping gas flows (Dl, D2; D3, D4) flowing through a common gas inlet zone (5, 6) have mutually different dopant carriers.

16. Method according to one of claims 1 to 7, characterized in that in particular only through at least one, preferably the upper or the lower gas inlet zone (4, 5, 6) a gas with a high molecular mass, in particular argon, is fed, wherein preferably a mixture of Argon and hydrogen are used, whereby the argon content of the gas mixture can be between 15 and 30%.

17. The method according to any one of claims 1 to 7, characterized in that ammonia and nitrogen are fed into the process chamber (2) as dopant carriers simultaneously and in particular through different gas inlet zones (4, 5, 6) and additionally argon or another gas with a molecular mass that is greater than the molecular mass of one of the dopant carriers is fed into the process chamber (2) through at least one or only one gas inlet zone (4, 5, 6), preferably through the uppermost gas inlet zone (6) or simultaneously through the uppermost and lowermost gas inlet zones (4, 6).

18. Device with a CVD reactor (1) which has a susceptor (10) extending in a horizontal plane for receiving substrates (12) and a gas inlet element (3) having a plurality of gas inlet zones (4, 5, 6) arranged vertically one above the other, wherein the gas inlet zones (4, 5, 6) are connected by means of supply lines (24, 25, 26) and mass flow controllers (21) and valves (22) arranged in the supply lines to gas sources (27, 28, 29, 30), in which first and second dopant carriers as well as a carbon-containing reactive gas and a silicon-containing reactive gas are stored separately from one another, and with a control device (20) for controlling the mass flow controllers (21) and valves (22), characterized in that the control device (20) is designed to carry out a method according to one of the preceding claims.

19. CVD reactor (1) for depositing a layer on a substrate (2), wherein a process chamber (6) is arranged in a housing (12), which is delimited at the bottom by a susceptor (4) extending in a horizontal plane and at the top by a process chamber ceiling (5), with a storage space (8) assigned to the susceptor (4) for receiving the substrate (2), with a heating device (3) for heating the susceptor (4), with a gas inlet element (7) for feeding a first process gas flow (QO) into the process chamber (6), with a first gas outlet opening (9) for feeding a first doping gas flow (Ql) into the process chamber (6) and with a second gas outlet opening (10) arranged downstream of the first gas outlet opening (9) and upstream of a downstream edge of the storage space (8), characterized in that the second gas outlet opening (10) is assigned to the process chamber ceiling (5).

20. CVD reactor according to claim 19, characterized in that the second gas outlet opening (10) is arranged downstream of an upstream edge of the storage area (8).

21. CVD reactor according to one of claims 19-20, characterized in that the first gas outlet opening (9), the second gas outlet opening (10), the third gas outlet opening (10') and / or the fourth gas outlet opening (10") is arranged in the region of a step of the process chamber ceiling (5).

22. Method for depositing a layer, in particular a SiC layer, on a substrate (2) in a process chamber (6) of a CVD reactor (1) heated to a process temperature by a heating device (3), wherein the process chamber (6) is delimited at the top by a process chamber ceiling (5) and at the bottom by a susceptor (4) extending in a horizontal plane, with a storage space (8) assigned to the susceptor (4) for receiving the substrate (2), wherein a first process gas flow (QO) is fed into the process chamber (6) in one or more partial flows together with a carrier gas through a gas inlet element (7) having gas inlet zones (15, 15', 15") arranged vertically one above the other and flows horizontally in a flow direction (S) over the rotationally driven substrate (2), wherein a first doping gas flow (Q1) is fed into the process chamber (6) through a gas inlet zone (15) arranged at the top and a second doping gas flow (Q2) is fed into the process chamber (6) through a gas inlet zone (15) arranged at the bottom, wherein the first doping gas flow (Q1) and the second doping gas flow (Q2) have the same Dopant carriers, especially ammonia,wherein each of the two doping gas flows (Ql, Q2) generates a lateral profile (f, g) of its dopant with a characteristic surface curvature in the layer, wherein a second process gas flow (Q0'l, Q0'2, Q0'3, Q0'4) is fed into the process chamber (6) through one or more gas outlet openings (9, 10) into one or more separately controlled partial flows, said second process gas flow containing a gas whose molar mass is greater than the molar mass of the carrier gas and preferably greater than the molar mass of the dopant carrier, wherein at least one second gas outlet opening (10) is arranged in the process chamber ceiling (5) downstream of at least one first gas outlet opening (9) and upstream of a downstream edge of the storage space (8), wherein by selecting selected parameters the characteristic surface curvatures of the lateral profiles (f, g) are adjusted such that a profiles (f, g) formed sum profile (h,i) has a higher homogeneity than the individual profiles (f, g), wherein the selected parameters comprise at least the mass flows of the first and second doping gas flows (Ql, Q2), the mass flows of the partial flows of the second process gas (QO'l, Q0'2, Q0'3, Q0'4) flowing through the gas outlet openings (9, 10) and / or the relative position of the gas outlet openings (9, 10) and the downstream end of the storage location (8).

23. The method according to claim 22, characterized in that a selected parameter is a height offset (k) caused by a step in the process chamber ceiling (5) on which the first and / or second gas outlet opening (9, 10) is arranged.

24. Method according to claim 22 or 23, characterized in that the mass flow of the first partial flow of the second process gas (QO'l, Q0'2, Q0'3, Q0'4) flowing through the first gas outlet opening (9) is higher than the mass flow of the second partial flow of the second process gas (QO'l, Q0'2, Q0'3, Q0'4) flowing through the second gas outlet opening (10).

25. Method according to one of claims 22 to 24, characterized in that the choice of the selected parameters is limited to the ratio of the mass flow of the first doping gas flow (Q1) to the mass flow of the second doping gas flow (Q2) being greater than one, in particular greater than five, the second gas outlet opening (10) being arranged between an upstream edge of the storage location (8) and a center (C) of the storage location (8) and the height offset (k) being between 2.5 mm and 5.5 mm, preferably between 3 mm and 5 mm.

26. CVD reactor according to claim 19 or method according to any one of claims 22-25, characterized in that a third gas outlet opening (10') and / or a fourth gas outlet opening (10") is arranged downstream of the first gas outlet opening (9) and upstream of the second gas outlet opening (10) in the process chamber ceiling (5).

27. CVD reactor according to claim 19 or method according to one of claims 22-26, characterized in that the first gas outlet opening (9) is assigned to the gas inlet element (7) or is arranged between the gas inlet element (7) and the upstream edge of the storage location (8) on the process chamber ceiling (5).

28. CVD reactor according to claim 19 or method according to one of claims 22-27, characterized in that a plurality of first gas outlet openings (9), a plurality of second gas outlet openings (10), a plurality of third gas outlet openings (10') and / or a plurality of fourth gas outlet openings (10") are arranged on a line which runs at a constant distance from a gas outlet surface (7') of the gas inlet element (7), wherein the line is a straight line or a circular arc line around a center of the gas inlet element (7) arranged in a center of the susceptor (4).

29. Method for depositing a layer on a substrate (2) in a CVD reactor according to one of claims 19 to 21 or 26 to 28, wherein the susceptor (4) is heated to a process temperature by means of the heating device (3), wherein a first process gas flow (Q0) is fed into the process chamber (6) through the gas inlet element (7), wherein a first doping gas flow (Q1) is fed into the process chamber (6) through the first gas outlet opening (9), which first doping gas flow has the effect of to generate a first inhomogeneous doping profile in the layer, wherein a second doping gas flow (Q2) is fed into the process chamber (6) through the second gas outlet opening (10), which second doping gas flow has the effect of generating a second inhomogeneous doping profile in the layer, wherein the ratio of the first doping gas flow (Q1) to the second doping gas flow (Q2) is selected such that a sum profile formed by the two doping profiles has a higher homogeneity than the individual doping profiles.

30. The method according to claim 29, characterized in that the first doping gas flow (Q1), the second doping gas flow (Q2), a third doping gas flow (Q3) which is fed into the process chamber (6) through the third gas outlet opening (10'), and / or a fourth doping gas flow (Q4) which is fed into the process chamber (6) through the fourth gas outlet opening (10"), extend uniformly over the entire width of the storage location (8).

31. Method according to claim 29 or 30, characterized in that the layer is a SiC layer and the doping gas flows (Q1, Q2, Q3, Q4) comprise a nitrogen-containing dopant.

32. Method according to claim 31, characterized in that the dopant is nitrogen and / or that the dopant flows together with an inert gas and / or argon through the gas outlet openings (9, 10, 10', 10").

33. Method or device characterized by one or more of the characterizing features of one of the preceding claims.

Images