Method for growing high-quality single-crystal silicon carbide

Abstract

A method for growing an epitaxial layer on a substrate (20) of single crystal silicon carbide (SiC). The method includes providing a monolithic polycrystalline SiC source material (10) having a columnar fine grain structure and a single crystal SiC substrate (20) with a distance therebetween in a crucible chamber (5) (S100); disposing a carbon getter (1) (having a melting point greater than 2200°C and the ability to form a carbide layer with carbon species evaporated from the SiC) in the crucible chamber (5) adjacent the source material (10) and the substrate (20) (S102); reducing the pressure in the chamber (5) (S106); introducing an inert gas into the chamber (5) (S108); increasing the temperature in the chamber (5) to a growth temperature such that a growth rate of between 1 μm / hr and 1 mm / hr is achieved (S110); and maintaining the growth temperature until at least 5 μm of growth is achieved on the substrate (20) (S112).

Description

[Technical Field]

[0001] The present invention relates to a method for growing an epitaxial layer on a single-crystal silicon carbide (SiC) substrate. Specifically, it relates to a method for growing high-quality silicon carbide single crystals that contain almost no carbon-containing material and basal plane dislocations. [Background technology]

[0002] In recent years, there has been a growing demand for improved electronic devices that are energy-efficient and capable of operating at high power levels and high temperatures. Silicon (Si) is currently the most commonly used material in the semiconductor industry for power elements in high-temperature, high-voltage, and high-power applications. SiC is a very suitable alternative material due to its high thermal conductivity, high saturation electron drift rate, and higher breakdown field strength compared to Si.

[0003] The most common technique used to grow single-crystal SiC layers by sublimation is physical vapor transport (PVT). In this technique, both the seed crystal on which the single-crystal layer will grow and the raw material, often in powder form, are placed in a reaction crucible heated to the sublimation temperature of the raw material. There is a thermal gradient between the raw material and the slightly cooler seed crystal. This thermal gradient facilitates vapor phase transfer, allowing the single-crystal layer to grow as vapor chemical species from the raw material are deposited onto the seed crystal. However, using powder as the raw material has several drawbacks. Powder often contains impurities resulting from the manufacturing process. Furthermore, the thermal distribution within the powder is not sufficiently uniform, resulting in reduced control over powder sublimation and silicon depletion. An additional drawback is the risk of solid particles from the powder falling onto the seed, introducing inclusions and impurities into the final crystal structure. Moreover, the stability of SiC powder is another technical challenge for PVT growth. To grow relatively thick, large-diameter SiC single-crystal boules, a correspondingly large amount of SiC powder must be loaded into the crucible. During PVT growth, the temperature at different locations in the SiC powder can vary considerably, potentially leading to recrystallization and even carbonization of the SiC powder. Such problems significantly reduce crystal quality and yield when manufacturing single-crystal SiC.

[0004] One version of PVT is the Sublimation Sandwich Method (SSM), in which a monolithic SiC plate is used as the raw material instead of powder. The use of a plate is beneficial, for example, to control the temperature uniformity of the raw material. Another advantage of this method is the short distance between the raw material and the seed crystal / substrate, which has the positive effect of preventing vapor species from reacting with the crucible walls.

[0005] Patent Document 1 discloses a method for producing (manufacturing) an epitaxial layer on a SiC substrate. The raw material is a high-purity material that is polycrystalline. The use of a polycrystalline raw material results in a more uniform supply to the growing epitaxial layer, and therefore, more uniform layer thickness and doping properties compared to single-crystal materials. The method disclosed in Patent Document 1 is an improvement over the above method, but there is still room for improvement. In recent years, there has been growing interest in the commercialization of SiC power electronic devices, and there is a strong demand for large-diameter, high-quality SiC single-crystal wafers, mainly referring to those of 6 inches or larger. In the conventional PVT method, SiC single crystals are grown in a high-temperature, semi-sealed carbon crucible. As the growth time increases, the Si vapor chemical species sublimated from the SiC powder gradually decrease, and the growth atmosphere becomes increasingly carbon-rich. Under carbon-rich conditions, carbon particles are produced on the sublimated source surface and can migrate to the growth surface, which are called carbon-containing defects. Carbon-containing defects can further lead to the formation of micropipes, carrot defects, stacking faults, and other types of defects. Therefore, obtaining a stable and suitable growth atmosphere during PVT growth is extremely important. However, this poses a significant challenge to the PVT method as the aforementioned growth atmosphere becomes increasingly complex as the SiC diameter increases.

[0006] Another problem with bipolar devices produced on SiC substrates and grown by the PVT process is the degradation of bipolar devices, especially those used in high-power applications. The most frequent root cause of such degradation is basal plane dislocations (BPDs). Stacking faults in the epitaxial layer are largely due to BPDs propagating from the substrate. Under high current stress, these stacking faults expand, causing an increase in the forward voltage of bipolar SiC devices, as well as an increase in the reverse leakage current and decrease in the forward current of nominal unipolar SiC devices with bipolar contributions from embedded pn junctions. Currently, many device manufacturers accept BPDs in the substrate, assuming they can be converted into threading edge dislocations (TEDs) during the growth of the epitaxial buffer layer. However, findings in Non-Patent Literature 1 indicate that BPDs can continue to expand into stacking faults even after conversion to TEDs. Therefore, substrates that do not contain BPDs are highly desirable to avoid bipolar degradation, especially in safety-critical applications such as automobiles and airplanes. By using the method according to the present invention, approximately 500 cm² can be typically obtained in 4-inch size PVT-grown high-quality substrates. -2 In comparison, BPD density is 5cm -2 It can be reduced to less than [amount missing]. By reducing the BPD density, the expansion of stacking faults can be largely avoided, and reliable high-power SiC devices can be produced (manufactured). Therefore, as the demand for BPD-free SiC single crystals increases, there is a need to improve production capacity, efficiency, and quality, especially for high-power applications. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent No. 7,918,937 [Non-patent literature]

[0008] [Non-Patent Document 1] "Stacking fault expansion from basal plane dislocations converted into threading edge dislocations in 4H-SiC epilayers under high current stress," by Kazuya Konishi et al., Journal of Applied Physics, Vol. 114, No. 014504 (2013). [Overview of the Initiative]

[0009] The object of the present invention is to achieve a method for growing an epitaxial layer on a single-crystal SiC substrate that is essentially free of carbon-containing material and basal plane dislocations. This is achieved by the following method for growing an epitaxial layer on a single-crystal SiC substrate. That is, this method is In the chamber of the inner container of the crucible, a monolithic (single-piece) polycrystalline SiC raw material having a columnar fine particle structure and a single-crystal SiC substrate are placed at a distance from each other. The arrangement of carbon getters in the chamber of the crucible to achieve a stable and suitable Si / C stoichiometry within the inner vessel, wherein the carbon getters have a melting point higher than 2200°C and the ability to form a carbide layer with carbon species evaporated from SiC. To reduce the pressure inside the chamber, The process involves introducing an inert gas into the chamber and maintaining a pressure higher than 0.01 mbar after introduction. To achieve a growth rate between 1 μm / hour and 1 mm / hour, the temperature inside the chamber is raised to the growth temperature. Maintain the growth temperature until at least 5 μm of growth is achieved on the substrate, Includes.

[0010] In an exemplary embodiment of the method, the temperature rises at a rate of 10 °C / min to 50 °C / min, preferably at a rate of about 20 °C / min to 30 °C / min.

[0011] In another exemplary embodiment of the method, the temperature rises to 1550 °C to 2300 °C, preferably up to about 1950 °C.

[0012] In yet another exemplary embodiment of the method, the pressure during the rising stage is 150 mbar to 950 mbar, and the pressure during the holding stage is reduced to approximately 0.1 mbar to 10 mbar, preferably approximately 1 mbar to 3 mbar.

[0013] In another exemplary embodiment of the method, after the growth temperature reaches a pumping rate of 1 mbar / min to 100 mbar / min, preferably a pumping rate of 5 mbar / min, the pressure in the holding stage is reduced until it reaches a pressure of 0.1 mbar to 10 mbar, preferably 1 mbar to 3 mbar.

[0014] In an alternative embodiment of the method, the pressure during the rising and holding stages is approximately 0.01 mbar to 25 mbar, preferably 0.1 mbar to 10 mbar, and most preferably 1 mbar to 3 mbar.

[0015] In an exemplary embodiment of the method, the raw material has a fine particle size in the range of less than 250 μm, preferably less than 100 μm, and most preferably 1 μm to 50 μm.

[0016] In yet another exemplary embodiment of the method, the fine particles of the raw material have a cubic structure substantially oriented on the crystal plane of

[0111] or

[0110] .

[0017] In another exemplary embodiment of the method, the carbon getter is selected from the group consisting of tantalum, niobium, and tungsten, and preferably has the shape of a foil.

[0018] In an alternative embodiment of the method, the carbon getter is selected from the group consisting of tantalum, niobium, and tungsten, and preferably includes several parts (pieces, small pieces) distributed throughout the inner container.

[0019] In another exemplary embodiment of the method, the surface of the substrate has a root mean square roughness of less than 5 nm, preferably less than 0.4 nm.

[0020] In yet another exemplary embodiment of the method, the method further includes providing a spacer between the source material and the substrate to keep the distance between the source material and the substrate fixed within a range of 0.5 mm to 2.5 mm, preferably within a range of 0.7 mm to 1.2 mm.

[0021] One advantage of this method according to the present invention is that it provides a monolithic polycrystalline SiC having a columnar fine particle structure as a source material, and a very uniform and stable sublimation can be obtained from the source material, and a high-quality single crystal SiC with few carbon-containing defects can be grown. The present invention will be described by way of example with reference to the accompanying drawings.

Brief Description of the Drawings

[0022] [Figure 1a] A schematic cross-sectional view of a certain type of source material provided in the prior art is shown. [Figure 1b] An exterior photograph of polycrystalline SiC showing the macro particle structure of the prior art source material. [Figure 2a] A schematic cross-sectional view of a monolithic polycrystalline SiC having a columnar fine particle structure as a source material is shown. [Figure 2b] An exterior photograph of polycrystalline SiC having a columnar fine particle structure. [Figure 3] A schematic diagram of a system used to perform the method according to the present invention. [Figure 4] A schematic diagram of a preferred arrangement of components inside the inner container of the system of FIG. 3. [Figure 5]The temperature change in the substrate during epitaxial sublimation is schematically shown. [Figure 6a] The image shows an optical microscope image of a sample grown using the raw material provided according to the present invention. [Figure 6b] This shows an optical microscope image of a sample grown using the type of raw material provided in the prior art. [Figure 7] A flowchart of the method according to the present invention is shown. [Figure 8] This shows a BPD density map of a region (Si surface) of a 4-inch substrate produced according to the method of the present invention. [Modes for carrying out the invention]

[0023] The following describes in detail, with reference to exemplary embodiments, a method for growing an epitaxial layer on a single-crystal silicon carbide (SiC) substrate. However, it should be understood that these embodiments are illustrative only, and there are many other embodiments that can be implemented within the scope of the invention by those skilled in the art with the help of the teachings of this disclosure. In the drawings, the same reference numerals indicate the same or corresponding elements throughout several drawings. It should be understood that these figures are for illustrative purposes only and in no way limit the scope of the invention.

[0024] The method for growing an epitaxial layer on a substrate is carried out using a system that facilitates high growth rate, high reproducibility, and high quality sublimation epitaxy, as will be described in more detail below in relation to Figures 3 and 4.

[0025] As mentioned above in the background information section, the most common technique used to grow single-crystal SiC layers by sublimation is PVT, which uses powder as the raw material. However, as also mentioned above, there is a method disclosed in U.S. Patent No. 7,918,937 that provides a polycrystalline raw material instead of powder. Now, referring to Figures 1a and 1b, the raw material provided in U.S. Patent No. 7,918,937 will be described in more detail in order to fully understand the difference between the present invention and the method described in U.S. Patent No. 7,918,937. Figure 1a shows a schematic cross-section of the raw material provided in U.S. Patent No. 7,918,937. As can be seen, the SiC grains have randomly distributed crystal orientations with no dominant orientation. This raw material is also shown in Figure 1b as an external photograph of polycrystalline SiC showing a macroparticle structure. The particle size of such a raw material is greater than 100 μm.

[0026] In comparison to the methods described above, the method according to the present invention provides a monolithic polycrystalline SiC raw material having a columnar microparticle structure as shown in the schematic cross-sectional view of the raw material in Figure 2a. In contrast to the randomly distributed crystal orientations found in the prior art, the columnar microstructure provides grains grown in the same crystal orientation. This can be explained as the crystal planes of each grain being substantially parallel to the crystal planes of other grains. The columnar microparticle structure may also be referred to as a pillar structure or a microstructure having parallel grains. The grains in the columnar microparticle structure are elongated such that the longitudinal extension of the grain is longer than the width of the grain. The size of the microparticles in this columnar structure is in the range of 1 μm to 100 μm when measured in the width direction of the grain. Preferably, the microparticles have a cubic structure oriented in the

[0111] crystal plane. In another embodiment, the cubic structure may also be oriented in the

[0110] crystal plane. According to yet another exemplary embodiment, the microparticle diameter may also be in the range of 1 μm to 250 μm in the width direction of the grain. The longitudinal size of the grains is not limited herein, however, it is not uncommon to provide grains having longitudinal sizes in the range of 1 mm or more. Figure 2b shows a photograph of the appearance of polycrystalline SiC having a columnar fine-grained structure. This provides a raw material having this columnar structure that enables the growth of a substrate that is essentially free of carbon content and basal plane dislocations. By providing a SiC raw material having a columnar fine-grained structure, highly uniform and stable sublimation from the raw material can be achieved, thereby achieving high-quality single-crystal SiC without carbon-containing defects. During the production of the raw material, it is preferable that the raw material be grown from bottom to top to provide controlled growth of crystal orientation. The polycrystalline SiC raw material may be produced by chemical vapor deposition. The raw material may further be processed by wafering tools such as a surface grinder to form standard shapes and sizes suitable for subsequent use as a raw material for the growth of single-crystal SiC.

[0027] Figure 3 shows a schematic diagram of a system 100 used to carry out the method according to the present invention. In short, the system 100 includes a crucible having different components (parts) described below, and a heating means 70 surrounding the crucible. When the top or bottom is referred to in this disclosure, the reference refers to the crucible in an operating state standing on a floor, platform, etc. The system 100 is designed to facilitate sublimation epitaxy that provides the above-mentioned monolithic polycrystalline SiC as a raw material 10, enabling the growth of a single-crystal SiC layer. The raw material 10 and substrate 20 are placed in an inner container chamber 5 (see Figure 4), which has an upper part 31 and a bottom part 32. The inner containers 31, 32 are placed in an insulating container 50, which also has an upper part and a bottom part. The insulating container 50 is then placed in an outer container 60. Outside the outer container 60 is a heating means 70 that can be used to heat the cavities of the inner containers 31, 32. According to this embodiment, the heating means 70 includes an induction coil for high-frequency heating. The outer container 60 is a quartz tube in this example, and the insulating container 50 and the inner containers 31, 32 are cylindrical with an axis T and are made of insulating graphite foam and high-density graphite, respectively. The insulating container 50 and the inner containers 31, 32 may also be made of other suitable materials that have the ability to withstand high temperatures and also facilitate coupling to a high-frequency induction coil when a high-frequency induction coil is used as a heating means 8. The crucible is heated using the heating means 70 to sublimate the raw material 10. The heating means 70 is vertically movable to adjust the temperature and heat drop inside the inner containers 31, 32. The temperature drop between the raw material 10 and the substrate 20 can also be changed by changing the properties of the inner containers 31, 32, such as the thickness of the top 31 and bottom 32, as is known in the art. In addition, for evacuating the inner container, i.e., about 10 -4 ~10 -6 There is a pump (not shown) to provide a pressure of mbar.

[0028] Referring here to Figure 4, a schematic diagram of exemplary arrangements of different components within the inner crucible vessels 31 and 32 is shown and will be described. The components are a carbon getter 1, a spacer 3, a raw material 10, and a substrate 20. The raw material 10 and the substrate 20 have diameters that are sized to fit the inner vessels 31 and 32 and depend on the desired size of the substrate 20. When the diameters of the inner vessels 31 and 32 are 100 mm, 150 mm, 200 mm, or 250 mm, the inner vessels 31 and 32 are particularly suitable for growth on substrates having diameters of approximately 50 mm, 100 mm, 150 mm, or 200 mm, respectively. It is considered that fitting the components and the inner vessels 31 and 32 to a given size of the substrate 20 is within the capabilities of those skilled in the art.

[0029] In the illustrated embodiment, the carbon getter 1 is positioned in the inner vessels 31, 32, close to the raw material 10 and the substrate 20, and in this case, below and close to the raw material 10. However, when the term carbon getter is used in the context of this disclosure, it should be understood that this term does not necessarily mean that the carbon getter is a single unit, but can also be divided into many smaller parts arranged throughout the inner vessels 31, 32, as will be explained in another exemplary embodiment below. The carbon getter 1 is provided to maintain a stable and suitable Si / C stoichiometry during growth in the carbon crucible, promote thickness uniformity, and also control the vapor stoichiometry within the vessels 31, 32. The properties of the carbon getter 1 are characterized by a high melting point, preferably above 2200°C, high carbon absorption, and high chemical stability, i.e., the carbon getter 1 has the ability to form a carbide layer with carbon species evaporated from SiC. The carbon getter 1 is preferably made of tantalum, but may also be made of niobium, tungsten, or other material having such properties. The carbon getter 1 is about 0.05 mm to 2 mm thick, preferably 0.1 mm to 1 mm thick, depending on how the carbon getter 1 is provided and whether it is a single unit or comprises many pieces and may have many different shapes such as foil in the form of small pieces, sheets, plates, or mesh-like shapes. If the carbon getter 1 is in the form of small pieces, the small pieces may be slightly curved or L-shaped. The thickness and shape of the carbon getter 1 are carefully selected so that a stable and suitable Si / C stoichiometry is achieved within the inner vessels 31, 32. If it is too thin, the carbon getter 1 will deform, which can adversely affect the temperature distribution and surface quality of the grown crystal. If the carbon getter 1 is too thick, it may release impurities such as aluminum compounds contained therein. A low-doped epitaxial layer is achieved by using a high-purity graphite material and a suitable carbon getter 1. Some of the properties of the carbon getter 1 are determined when the carbon getter 1 is prepared before growth. In exemplary embodiments, the carbon getter 1 may include small pieces located at different locations within the inner containers 31 and 32.Some of the pieces are placed beneath the raw material to enhance the silicon / carbon relationship within the inner container, and some of the pieces are placed on the sides of the inner containers 31 and 32 to enhance uniform growth at the edges of the substrate 20.

[0030] The carbon getter 1 reacts with the C species sublimated from the SiC source during growth to act as a carbon absorber. The placement of the carbon getter 1 can be done in many different ways, as long as it improves the stable and favorable Si / C stoichiometry within the inner vessels 31, 32, as described above. In one exemplary embodiment, as shown in Figure 4, the carbon getter 1 is placed beneath the raw material 10. Such placement can help improve the temperature distribution of the raw material 10 in the horizontal direction, i.e., in the direction perpendicular to the growth direction of the epitaxial layer. In other words, when the carbon getter 1 is coupled to the induced RF field produced by the heating means 70, the heating of the raw material 10 increases. The carbon getter 1 also promotes a more uniform heat distribution across the surface 10b of the raw material 10 facing the carbon getter 1. As a result, the heating also spreads more uniformly axially across the substrate 20, i.e., toward the opposite surface 10a of the raw material 10, thereby resulting in more uniform properties of the epitaxial layer. Even in the exemplary embodiments described above, where the carbon getter 1 is placed beneath the raw material 10, it is understood and stated above that, insofar as it promotes uniformity of thickness and controls the vapor stoichiometry inside the containers 31, 32, the carbon getter 1 can also be placed in other locations, such as between the raw material 10 and the substrate 20 or above the raw material 10 and the substrate 20, and divided into many small pieces distributed along the walls and at the bottom of the inner containers 31, 32.

[0031] As described above, in exemplary embodiments, the raw material 10 is placed on top of the carbon getter 1, but it may also be placed below the carbon getter 1 or surrounded by the carbon getter 1. The thickness of the raw material 10 is approximately 0.5 mm to 5 mm. By providing a polycrystalline raw material 10 having a columnar fine particle structure, a more uniform supply to the growing epitaxial layer 20b of the substrate 20 is obtained, which results in more uniform layer thickness and doping characteristics.

[0032] The substrate 20 is placed on top of the raw material 10, but is separated from the raw material 10 via spacers 3 having a height in the range of 0.5 mm to 2.5 mm, the height of which is adapted to a desired distance between the substrate 20 and the raw material. The spacers 3 are positioned and shaped such that the distance between the substrate 20 and the raw material 10 is in the range of 0.5 mm to 2.5 mm, preferably in the range of 0, 7 mm and 1, 2 mm. The spacers 3 may be ring-shaped, or may consist of three separate spacers to provide stable support to the substrate 20. Preferably, the substrate 20 contains a SiC carbide crystal having a mirror-like surface and minimal surface defects. In exemplary embodiments, the surface of the substrate 20 has a root-mean-square (RMS) roughness of less than 5 nm, preferably less than 0.4 nm. To maintain stable growth of the polytype SiC crystal inherited from the substrate 20, the offcut angle of the substrate 20 is in the range of 0 to 8 degrees, preferably 4 degrees. In exemplary embodiments, the polytype of the grown single crystal is determined by the seed polytype. To maintain good surface morphology and low density of surface defects in the grown SiC crystal, the polarity of the substrate 20 is also (000-1) in one exemplary embodiment, also referred to as the carbon plane. Other options are also available, and in another exemplary embodiment, the polarity of the substrate is also (0001) and also referred to as the silicon plane polarity.

[0033] A method for growing an epitaxial layer on a single-crystal SiC substrate 20 is described here with reference to Figures 5 and 7. Figure 7 shows a flowchart of the method, and Figure 5 schematically shows an exemplary temperature change in the substrate 20 during epitaxial sublimation. Any step of the method is indicated by a dotted (dashed) line. It should be understood that the method according to the present invention is not limited to whether or not the substrate 20 is doped. The substrate 20 may be doped with, for example, nitrogen, boron, or aluminum. Nitrogen doping is typically induced by nitrogen gas pumped into the chamber 5. P-type substrates may be grown by aluminum doping. In such cases, aluminum may be introduced into the chamber 5 by aluminum carbide powder or gas.

[0034] Step S100 of this method provides a monolithic polycrystalline SiC raw material 10 having a columnar fine particle structure and a single-crystal SiC substrate 20 in the chambers 5 of the inner containers 31 and 32 of the crucible. The raw material 10 and the substrate 20 are arranged with a fixed distance between them, preferably in the range of 0.5 mm to 2.5 mm, more preferably in the range of 0.7 mm and 1.2 mm. In step S102, a carbon getter 1 is placed in the chamber 5 of the crucible so that a stable and suitable Si / C stoichiometry is achieved in the inner containers 31 and 32. The carbon getter 1 has a melting point exceeding 2200°C and the ability to form a carbide layer with carbon species evaporated from SiC, i.e., it has high carbon absorption and high chemical stability.

[0035] When the raw material 10, carbon getter 1, and substrate 20 are all placed inside the chamber 5, the pressure inside the chamber 5 is reduced in step S106. In an exemplary embodiment, the pressure S106 during the reduction (depressurization) step is 10 -3 The base vacuum level is reduced to below mbar. Chamber 5 is evacuated using conventional pumping means.

[0036] In step S108, an inert gas is introduced into the chamber 5. Any inert gas can be used, but argon is preferred. The pressure is then maintained at a pressure higher than 0.01 mbar. In one exemplary embodiment, the inert gas is introduced into the chamber 5 until the pressure reaches a range of 1 mbar to 10 mbar. In another exemplary embodiment, the inert gas is introduced until the pressure reaches a range of 150 mbar to 950 mbar, preferably 700 mbar. In this second exemplary embodiment, the pressure is reduced after reaching the growth temperature (see step S110 below). The pressure is then reduced to a range of 1 mbar to 10 mbar at a pumping rate of, for example, 1 mbar / min to 10 mbar / min, preferably 5 mbar / min.

[0037] In step S110, the temperature inside the chamber 5 is raised to the growth temperature by the heating means 70, as shown in the temperature diagram of Figure 5. The growth process includes a preheating stage 401. During the preheating stage, step S110, the temperature may be increased within an interval of 1°C / min to 245°C / min, depending on the circumstances and the balance between productivity and quality. However, the inventors have found that a temperature increase of 10°C / min to 50°C / min, preferably about 30°C / min to 20°C / min, provides good initial sublimation and nucleation of the raw material 10. The pressure during the rising stage, step S110, is usually kept above 0.01 mbar, preferably below 950 mbar, as described above. As mentioned above, the pressure during the rising stage may be constant, for example, within the range of 1 mbar to 10 mbar, or it may be reduced at a rate of 5 mbar / min from an initial pressure, for example, within the range of 150 mbar to 950 mbar, preferably within the range of 700 mbar, to a pressure within the range of 1 mbar to 10 mbar during the rising stage, process S110. Process S110 continues until the temperature rises to a suitable growth temperature 413, typically about 1550°C to 2300°C, preferably about 1950°C. When the suitable growth temperature 413 reaches the growth temperature, i.e., the growth temperature that promotes the desired growth rate, the temperature rise decreases rapidly. The desired growth rate may be in the range of 1 μm / hour to 1 mm / hour, and again depends on the balance between productivity and quality. Preferably, to achieve a good balance, the growth rate is maintained between 10 μm / hour and 300 μm / hour. In a preferred embodiment, the growth temperature is maintained at 1950°C, and a growth rate of approximately 90 μm / hour is obtained with the above settings. Those skilled in the art know at what temperature the desired growth rate can be obtained. The temperature is maintained at this level 413 until an epitaxial layer of the desired thickness is achieved. The period following the heating stage is referred to as the growth stage 403, during which the temperature is preferably kept substantially constant, and the pressure during the holding stage, step S112, is in the range of approximately 1 mbar to 10 mbar, preferably 3 mbar to 6 mbar. The growth stage, step S112, is maintained at point 414 in Figure 5 until a SiC single crystal layer of the desired thickness is produced.The desired growth thickness on the substrate 20 is at least 5 μm, but typically less than 5000 μm. For the low-doped epitaxial drift layer used in high-voltage devices, a layer thickness of 10 μm / kV is desirable. In such applications, the growth thickness on the substrate 20 is typically thicker within the range of 10 μm to 200 μm depending on the voltage class. The doping concentration in such a layer is typically 1×10. 16 cm -3 less than. As an example, on an N-type substrate having a doping concentration exceeding 1×10 18 cm -3 it can be grown to a thickness within the range of 1 mm to 7 mm. The thickness of the grown crystal is determined by the thickness of the raw material 10, which can have a maximum thickness of 7 mm.

[0038] After a preferably thick SiC crystal layer is formed, the heating is stopped and the substrate 20 is cooled, which is referred to as the cooling phase 404. To shorten the production time, the preheating phase and the cooling phase can be optimized. When the system is cooled to room temperature, the chamber 5 is refilled with argon or any other safe gas to reach atmospheric pressure, and the sample is taken out by opening the chamber 5, which is a cooling process well-known to those skilled in the art. After growth and cooling, the sample can be processed by grinding or continuously separating it into wafers using any wafer separation technique so that the grown single crystal can be separated from the substrate 20.

[0039] In yet another exemplary embodiment, the spacer 3 is provided between the raw material 10 and the substrate 20 to keep the distance between the substrate 20 and the raw material within the range of 0.5 mm to 2.5 mm, preferably within the range of 0.7 mm to 1.2 mm, and fixed during any process S104. The spacer 3 has a height within the range of approximately 0.5 mm to 2.5 mm as described above, and is arranged and shaped such that the distance between the substrate 20 and the raw material 10 is kept constant as described above. Also as described above, the spacer 3 may be in a ring shape, or may include at least three separate spacers for providing stable support to the substrate 20.

[0040] To illustrate the importance of providing polycrystalline SiC having a columnar fine particle structure as the raw material 10 according to the present invention, two experiments were conducted under the same conditions but providing different raw materials. In the first experiment, as shown in Figures 2a and 2b, polycrystalline SiC having a columnar fine particle structure according to the present invention was provided as the raw material. In the second experiment, a prior art raw material for polycrystalline SiC grains was provided, having randomly distributed crystal orientations with no significant orientation, as shown in Figures 1a and 1b.

[0041] The experiment was performed in a system having a face-down configuration, i.e., growth on the substrate 20 was on the side 20b (Figure 4) facing downward toward the raw material 10. However, the method according to the present invention is not limited to a system having a face-down configuration, but can be performed in a system having a face-up configuration or any other configuration. The experiment was performed under the following conditions: Once the raw material 10, substrate 20, spacer 3, and carbon absorber 1 were loaded into the chamber 5 as described above, the chamber 5 was 10 -3 The chamber was pumped to a pressure of less than mbar. Then, argon was introduced into chamber 5 until a pressure of 1 mbar was reached. Next, the heating means 70 was activated and the system was heated to the desired temperature of 1950°C at a ramp-up rate of approximately 20°C / min. At a growth temperature of 1950°C, the growth rate was approximately 90 μm / hour, and this temperature was maintained for 4.5 hours until the thickness of the grown single-crystal SiC reached approximately 500 μm. Then, power to the heating means 70 was cut off, and the temperature was allowed to decrease naturally until the system cooled to room temperature. Next, the chamber was refilled with argon until atmospheric pressure was reached. Finally, the sample was removed by opening chamber 5.

[0042] The experimental results are shown in Figures 6a and 6b. Figures 6a and 6b are optical microscope images of samples grown using different raw material materials. Figure 6a shows the results using the raw material material according to the present invention, and Figure 6b shows the results using the raw material material of the prior art. The thickness of the grown single crystal SiC in both samples is similar, approximately 500 μm. After growth, the sample using the raw material material 10 according to the present invention has a very smooth surface with no carbon inclusions whatsoever, while the sample using the raw material material of the prior art has a surface thickness of 100 / cm². 2 It exhibits high-density carbon-containing defects with a density exceeding [a certain value]. Carbon-containing defects are highly detrimental to the quality of grown crystals because they can lead to new structural defects such as stacking faults, SFs, and BPDs.

[0043] Stacking faults and bipolar discharge plates (BPDs) lead to bipolar degradation of SiC devices applied in high-power classes exceeding 1.7kV. BPDs, or BPDs that narrow to TEDs during initial epitaxial growth and are reconverted to BPDs during device operation, cause stacking fault formation under high current stress, which sooner or later leads to device failure. SF in the epitaxial layer is largely due to BPDs propagating from the substrate. Under high current stress, these SFs expand, causing an increase in the forward voltage of bipolar SiC devices, as well as an increase in the reverse leakage current and decrease in the forward current of nominal unipolar SiC devices with bipolar contributions from the embedded pn junction.

[0044] Eliminating stacking fault formation will significantly improve the reliability of products such as high-power junction barrier Schottky diodes, PiN diodes, insulated-gate bipolar transistors, and metal-oxide-semiconductor field-effect transistors, enabling their integration into numerous applications over the next decade.

[0045] By using the method according to the present invention, approximately 500 cm² can be typically obtained on a 100 mm size PVT-grown high-quality substrate. -2 In comparison, BPD density is 5cm -2It can be reduced to less than [amount missing]. By reducing the BPD density, the expansion of SF can be largely avoided, and reliable high-power SiC devices can be manufactured. Examples of such high-power SiC devices include inverters and converters for hybrid and all electric vehicles, inverters for solar and wind power, power factor correctors for maximum power applications, and devices for power transmission and distribution.

[0046] Referring now to Figure 8, another example of the quality of a substrate produced (manufactured) according to the method of the present invention is shown. Figure 8 shows a BPD density map by region (Si plane) of a 100 mm (4 inch) substrate produced (manufactured) according to the method of the present invention. As can be seen, the average BPD density is very low, significantly lower than that of prior art substrates.

[0047] Although the present invention is described in detail in relation to the embodiments discussed, various modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. Furthermore, the present method can be used to produce (manufacture) multiple layers within the same cavity that can be easily realized by those skilled in the art. [Explanation of Symbols]

[0048] 1 Carbon Getter 3 Spacers 5 Chambers 10 Raw materials 20 circuit boards 31,32 Inner container

Claims

1. A method for growing an epitaxial layer on a single-crystal silicon carbide (SiC) substrate (20), Step (S100) of placing a monolithic polycrystalline silicon carbide (SiC) raw material (10) having a columnar fine particle structure and a single crystal SiC substrate (20) in the chamber (5) of the inner container (31, 32) of the crucible, with a distance between them, The step involves arranging the carbon getter (1) in the chamber (5) of the crucible such that a stable and suitable Si / C stoichiometry is achieved in the inner containers (31, 32). The carbon getter (1) has a melting point higher than 2200°C and has the ability to form a carbide layer with carbon species evaporated from SiC, and the placement step (S102) The process of reducing the pressure in the chamber (5) (S106), The steps include inserting an inert gas into the chamber (5) and maintaining the pressure above 0.01 mbar (1 Pa) after insertion (S108), The steps include raising the temperature inside the chamber (5) to a growth temperature such that a growth rate of 1 μm / hour to 1 mm / hour is achieved (S110), The steps include maintaining the growth temperature (S112) until growth of at least 5 μm is achieved on the substrate (20), A method that includes [something].

2. The method according to claim 1, wherein the temperature increase is performed by increasing it by 10°C / min to 50°C / min.

3. The method according to claim 1 or 2, wherein the temperature rises to 1550°C to 2300°C.

4. The pressure during the aforementioned rising process (S110) is between 150 mbar (15,000 Pa) and 950 mbar (95,000 Pa). The method according to any one of claims 1 to 3, wherein the pressure during the holding step (S112) is reduced to 0.1 mbar (10 Pa) to 10 mbar (1000 Pa).

5. The method according to claim 4, wherein the pressure in the holding step (S112) is reduced after reaching the growth temperature to a pressure of 0.1 mbar (10 Pa) to 10 mbar (1000 Pa) at a pumping rate of 1 mbar (100 Pa) / min to 10 mbar (1000 Pa) / min.

6. The method according to any one of claims 1 to 3, wherein the pressure during the raising step (S110) and the holding step (S112) is 0.01 mbar (1 Pa) to 25 mbar (2500 Pa).

7. The method according to any one of claims 1 to 6, wherein the raw material (10) has a fine particle size of less than 250 μm.

8. The manufacturing method according to claim 7, wherein the fine particles of the raw material (10) have a cubic structure substantially oriented on the crystal plane of [111] or [110].

9. The method according to any one of claims 1 to 8, wherein the carbon getter (1) is selected from the group consisting of tantalum, niobium, and tungsten, and has the shape of a foil.

10. The method according to any one of claims 1 to 8, wherein the carbon getter (1) is selected from the group consisting of tantalum, niobium, and tungsten and includes a plurality of small pieces distributed throughout the inner container (31, 32).

11. The method according to any one of claims 1 to 10, wherein the surface of the substrate (20) has a root mean square roughness of less than 5 nm.

12. The method according to any one of claims 1 to 11, further comprising the step of providing a spacer (3) between the raw material (10) and the substrate (20) in order to keep the distance between the substrate (20) and the raw material (10) fixed at a distance within the range of 0.5 mm to 2.5 mm.

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