Process for treating a silicon carbide substrate

Abstract

The invention relates to a method for treating a substrate (10) comprising at least one surface layer of single-crystal silicon carbide, said method comprising: placing said substrate (10) in a furnace, lowering the pressure in the furnace to a pressure (pF) between 0.01 and 0.5 Pa, heating the substrate to a temperature (TF) above the sublimation temperature of silicon at said pressure (pF), so as to form a carbon layer on the single-crystal silicon carbide layer by sublimation of silicon from the surface of said single-crystal silicon carbide layer. Figure for the abstract: Fig 3A

Description

Title of the invention: Process for treating a silicon carbide substrate technical field

[0001] The present invention relates generally to the field of manufacturing silicon carbide substrates for the formation of electronic components. More particularly, it proposes a method for treating the surface of a single-crystal silicon carbide substrate. State of the art

[0002] Monocrystalline silicon carbide (m-SiC) is used for the formation of electronic components, for example for power electronics or radio frequency applications. In some applications, bulk monocrystalline SiC substrates are used, while in other applications, substrates such as polycrystalline silicon carbide, comprising a surface layer of monocrystalline SiC, are used.

[0003] Microelectronic manufacturing processes often involve heat treatments of substrates, for example to activate dopants, to heal defects in the crystal lattice caused by the implantation of ionic species, or to modify the crystalline structure of the substrate. Such treatments are often carried out at high temperatures, up to 2000°C.

[0004] However, the surface of single-crystal SiC is susceptible to destabilization under the effect of high temperature. This destabilization can result in surface degradation, in particular through a modification of its morphology and / or composition.

[0005] In particular, as illustrated in [Fig. 1], smooth SiC surfaces are sensitive to high-temperature treatments, typically from about 1200°C. In the absence of adequate protection of said surface, the morphology reorganizes itself to minimize surface energy, forming terraces 22. This effect is known by the English term "step bunching." The reorganization of the surface 222 is due to diffusion of atoms on the surface when it is exposed to high temperatures. It also depends on the atmosphere and pressure to which the surface is exposed.

[0006] In order to obtain smooth surfaces, the aim is therefore to avoid the formation of terraces or to remove them in a subsequent step. For example, mechanical or chemical-mechanical polishing (CMP) can be carried out after heat treatment. However, if the height of the terraces formed is too great, for example on If the distance between two consecutive platens is greater than 80 nm, the required thickness is too great, resulting in a lengthy and laborious process. Furthermore, the remaining m-SiC layer is often too thin for the intended applications.

[0007] Another method is to use very rapid annealing ramps to limit the formation of terraces. This method requires temperature increases of approximately 400°C per minute and is therefore not compatible with industrial furnaces.

[0008] Alternatively, silane overpressure can be applied, which limits silicon sublimation in SiC, thus preventing terrace formation. This method is described in the article by R. Zhang et al. However, it requires the introduction of SiH4 gas and equipment to create the overpressure. Furthermore, silicon droplets can appear on the SiC surface at temperatures above 1600°C.

[0009] Another possibility for preventing terrace formation is to use a protective layer. The article by J. Bao et al. proposes a carbon protective layer obtained by centrifuging a resin onto a SiC surface. The resin is annealed at 750°C–900°C to form a carbon film approximately 1 µm thick. This technique involves additional steps in the formation process, the use of additional equipment, and carries a risk of substrate contamination by the resin.

[0010] In some cases, the protective layer can also be formed from aluminum nitride (AIN). However, this material is difficult to remove, especially after heat treatment at a high temperature. Description of the invention

[0011] An object of the invention is to provide a method for treating the surface of a single-crystal silicon carbide substrate in order to reduce terrace formation through an easy-to-implement step. Such a treatment must be easy to integrate into the manufacturing process of a substrate having a single-crystal silicon carbide surface and must not present a risk of contamination of such a substrate.

[0012] To this end, the invention proposes a method for treating a substrate comprising at least one surface layer of single-crystal silicon carbide, said method comprising • placing said substrate in an oven, • lowering the pressure in the furnace to a pressure between 0.01 and 0.5 Pa, • heating the substrate to a temperature above the sublimation temperature of silicon at said pressure, so as to form a layer of carbon on the single-crystal silicon carbide layer by sublimation of silicon from the surface of said single-crystal silicon carbide layer.

[0013] The carbon layer has the function of protecting the silicon carbide during heat treatment at a higher temperature, and thus minimizing the formation of steps on the surface of the silicon carbide.

[0014] Pumping at a pressure below 0.01 to 0.5 Pa (0.1 to 5 pbar) allows for the rapid removal of silicon atoms evaporating from the substrate surface. Furthermore, when multiple substrates are in the same furnace, silicon atoms are removed from the spaces between the silicon carbide substrates. This removal results in a relatively homogeneous atmosphere on the substrate surface, which allows for the formation of a protective layer with minimal thickness variation between the edge and the center of each substrate.

[0015] Advantageously, the formation temperature of the carbon layer is between 1200°C and 1500°C.

[0016] Preferably, the carbon layer is a graphene layer.

[0017] Advantageously, the carbon layer has a thickness between 0.2 nm and 1.2 nm.

[0018] Advantageously, a plurality of substrates is treated simultaneously in the same furnace.

[0019] The substrates can be vertically stacked in the oven so that a vertical space is provided between two adjacent substrates.

[0020] Preferably, said vertical space between two adjacent substrates has a height of between 4 and 10 mm.

[0021] In some embodiments the process includes, after the formation of the carbon layer, a heat treatment of the substrate at a temperature higher than the formation temperature of the carbon layer and under a pressure higher than the formation pressure of the carbon layer.

[0022] Advantageously, the heat treatment temperature is greater than or equal to 1700°C.

[0023] The heat treatment pressure is preferably greater than or equal to 2 Pa.

[0024] Advantageously, the formation of the carbon layer and the treatment thermal processes are implemented in the same furnace.

[0025] Preferably, the process further includes a step of removing the carbon layer after heat treatment.

[0026] Advantageously, the process further includes a mechano-chemical polishing step after heat treatment to remove steps formed on the surface of the silicon carbide layer during said heat treatment.

[0027] Said mechano-chemical polishing can lead to the removal of a silicon carbide thickness of less than 200 nm.

[0028] The invention also relates to a method for manufacturing a structure comprising a layer of single-crystal silicon carbide on a support substrate, comprising successively:

[0029] - the formation of a weakening zone in a carbide donor substrate single-crystal silicon by implantation of ionic species, so as to delimit a layer of single-crystal silicon carbide to be transferred,

[0030] - the bonding of the donor substrate to the support substrate,

[0031] - the detachment of the donor substrate along the weakening zone so as to transfer the single-crystal silicon carbide layer onto the substrate support,

[0032] - the implementation of the treatment as described above on the carbide layer of single-crystalline silicon transferred.

[0033] Preferably, the single-crystal silicon carbide layer comprises dopants and the heat treatment is carried out at a suitable temperature to activate said dopants.

[0034] Advantageously, the silicon carbide layer includes defects due to the implantation of ionic species and in that the heat treatment is carried out at a suitable temperature to cure at least part of said defects.

[0035] Advantageously, the process further comprises, after mechano-chemical polishing, a step of resuming epitaxy of single-crystal silicon carbide on the surface of the single-crystal silicon carbide layer. Brief description of the figures

[0036] Other features and advantages of the invention will become apparent from the detailed description that follows, with reference to the accompanying drawings, in which:

[0037] Fig. 1 illustrates the formation of terraces on a front face in a single-crystal semiconductor material.

[0038] Figure [Fig.2] illustrates a substrate comprising a portion of single-crystal SiC on its front face.

[0039] Fig. 3A illustrates the substrate of Fig. 2 after the formation of a carbon layer.

[0040] Fig. 3B illustrates the substrate of Fig. 2 during the formation of a carbon layer.

[0041] Fig. 3C illustrates the substrate of Fig. 2 after the formation of a particular embodiment of the carbon layer.

[0042] Fig. 3D illustrates the distribution of the different thicknesses of a carbon layer on the surface of a substrate.

[0043] Figure 4 shows the thermal profile used for a process according to the invention.

[0044] Figures 5A to 5C illustrate the manufacture of a substrate comprising a portion su m-SiC surface on its front face.

[0045] Figure 6 illustrates an annealing furnace adapted for the formation of a carbon layer according to a preferred embodiment of the invention.

[0046] Fig. 7 shows the roughness of a single-crystal SiC surface as a function of the radial position on the substrate.

[0047] Fig. 8 shows the height of the steps between the terraces formed on a monocrystalline SiC surface as a function of the radial position on the substrate.

[0048] Figures 9A and 9B are electron beam scanning microscopy images of a substrate after heat treatment according to a known process.

[0049] Figures 10A and 10B are electron beam scanning microscopy images of a substrate after heat treatment according to a process according to the invention. Detailed description of embodiments

[0050] Generally, a protective carbon layer is formed on a substrate containing a surface portion of single-crystal silicon carbide. The carbon layer temporarily protects the substrate surface against terrace formation during heat treatment. The protective layer is formed by transforming the surface into m-SiC under temperature and pressure conditions adapted to induce sublimation of the silicon atoms present on said surface while minimizing terrace formation. After heat treatment, the protective layer is removed from the substrate surface.

[0051] Figure 2 illustrates a substrate having a surface layer 20 made of monocrystalline silicon carbide. This layer 20 is arranged on a support 11 formed of one or more materials other than monocrystalline silicon carbide. The support may comprise a monocrystalline or polycrystalline semiconductor material, for example, polycrystalline silicon carbide. Alternatively, the substrate may be a bulk substrate of monocrystalline silicon carbide, with the layer 20 forming a surface portion of said substrate. Formation of the carbon layer

[0052] With reference to [Fig. 3A], a layer of carbon 30 is formed on the surface 200 of the m-SiC layer 20. The carbon 30 layer protects the surface of layer 20 against terrace formation upon heating to a high temperature. It thus stabilizes the crystalline structure of the surface.

[0053] The carbon layer 30 is formed by sublimation of silicon on the surface of the m-SiC layer. Advantageously, the formation of the carbon layer is carried out in a furnace which will be described later. In order to obtain such sublimation, the pressure in the furnace is lowered to a pressure of pF. The pressure pF is preferably between 0.01 and 0.5 Pa (0.1 and 5 pbar).

[0054] No additional gas is injected into the furnace, which helps to maintain a low pressure and avoid any risk of contamination by impurities that may be present in such a gas.

[0055] During the pressure reduction to the pF pressure, the substrate is started to be heated to a temperature TF. The pressure reduction and heating processes are adjusted so that the pF pressure is reached before or simultaneously with the reaching of the TF temperature.

[0056] Alternatively, the temperature is raised after the pressure has been lowered to pF. The temperature TF is higher than the sublimation temperature of silicon at said pF in the furnace. Typically, the temperature TF is between 1200°C and 1500°C.

[0057] A temperature below 1200°C does not allow the sublimation of silicon within the pF pressure range that can be obtained in a substrate processing furnace. A temperature above 1500°C induces a terrace formation phenomenon that competes with silicon sublimation, leading to the formation of excessively high steps between the terraces.

[0058] The aim is indeed to limit the formation of steps between terraces to a height of less than 25 nm in order to minimize the polishing required to remove said steps. The formation of higher terraces would require lengthy and laborious polishing. Moreover, such polishing often leads to the creation of defects such as scratches in the m-SiC, which increases the number of defective substrates.

[0059] Lowering the pressure in the furnace allows the silicon to sublimate at a temperature TF lower than the temperature at which terrace formation becomes significant. The pressure pF is thus adjusted to avoid or reduce terrace formation during the formation of the carbon layer.

[0060] The pressure pF and temperature TF are maintained until a carbon layer 30 is obtained covering the entire surface of the single-crystal silicon carbide. In order to maintain the pressure pF, vacuum pumping of the furnace is maintained throughout the carbon layer formation step. This continuous pumping causes silicon atoms to be evacuated from the furnace. Such evacuation is necessary to lower the partial pressure of silicon and thus allow the sublimation of other silicon atoms from the substrate surface.

[0061] When the carbon layer is finalized, it prevents the sublimation of silicon. At this stage, the terraces and the height of the steps are fixed. As a result, it is possible to continue the heat treatment at a higher temperature. temperature without degrading the surface condition. Typically, the pressure is increased by injecting an inert gas into the furnace, for example argon. Carbon layer structure

[0062] The free face 200 of the m-SiC layer 20 is a single-crystal silicon carbide surface of the 4H or 6H polytype of one face (0001). This crystal orientation favors the growth of carbon in the form of two distinct layers on the surface.

[0063] Optionally, the free face 200 forms an angle between 0 and 8 degrees, for example between 3 and 5 degrees, with the (0001) face of the SiC single crystal. The free face 200 is, in particular, formed by a set of (0001) facets separated from each other by atomic steps. Such a misorientation limits, during epitaxy on this free face, the risk of generating 3C polytype regions.

[0064] By convention, the (0001) face of m-SiC is generally referred to as the "Si face", and the (000-1) face is referred to as the "carbon face".

[0065] During the initial sublimation of silicon from the surface of layer 20, as shown in [Fig. 3B], a first carbon layer 31 forms on the surface. Layer 31 extends over the entire surface 200 of the m-SiC layer 20 and acts as a buffer layer between the substrate surface 200 and any subsequent carbon layers. The first layer 31 consists of hexagonal carbon with a low proportion of sp3 hybridizations linked to the silicon atoms of layer 20. The proportion of sp3 bonds decreases from the face in contact with layer 20 to the free face of layer 31.

[0066] During the continued sublimation of silicon, further carbon layers form on the buffer layer 31. The carbon layers on the buffer layer 31 are graphene monolayers, meaning that these layers consist solely of sp2 bonds between the carbon atoms. The stacked graphene monolayers together form a surface layer 32.

[0067] The formation and characterization of such a carbon layer on an m-SiC surface are described for example by Strupinski et al. and by Razado-Colambo et al.

[0068] Thus, with reference to [Fig. 3C], the carbon layer 30 is typically composed of a buffer layer 31 in contact with the m-SiC surface of the substrate, and a surface layer 32 arranged on the surface of the buffer layer 31. Preferably, the surface layer 32 comprises between one and three graphene monolayers. The presence of a carbon layer composed of a buffer layer 31 and a surface layer 32 strongly limits terrace formation during high-temperature heat treatment.

[0069] The m-SiC surfaces of the 4H and 6H polytypes promote graphene growth in a plane parallel to the surface of the buffer layer 31. Such parallel growth limits silicon evaporation from the surface during heat treatment This process subsequently prevents thermal decomposition of the silicon carbide layer. Growth in the form of graphene also limits the mobility of silicon and carbon atoms on the substrate surface. Furthermore, m-SiC surfaces with such a crystalline structure are particularly susceptible to terrace formation.

[0070] In the case of a substrate with a large surface area, the thickness of the carbon layer may exhibit inhomogeneities. Forming a buffer layer and a surface layer ensures that the entire surface of the substrate is protected by a carbon layer and prevents the risk of forming areas lacking a carbon layer on the substrate surface.

[0071] In some embodiments, only a buffer layer 31 is formed. In this case, the carbon layer formation process is stopped when the buffer layer is complete, and no surface layer 32 is formed. Such a buffer layer alone can also limit the formation of terraces on the surface of the m-SiC layer 20.

[0072] Generally, the buffer layer 31 extends over the entire surface of the substrate. In contrast, the surface layer of graphene 32 can be arranged over the entire surface or only over certain areas of the buffer layer 31, and / or have different thicknesses depending on its position on the substrate.

[0073] Typically, with increasing distance from the center of the substrate, the thickness of the carbon layer increases due to the presence of graphene monolayers. Such a distribution of graphene monolayers typically occurs during the simultaneous processing of several superimposed substrates, due to the more efficient evacuation of silicon atoms in areas near the B edge of the substrate.

[0074] By way of illustration and without limitation, with reference to [Fig. 3D], the carbon layer may consist of a bare buffer layer 31 in a first zone near the center C of the substrate. The carbon layer may include a second zone 321 in which the carbon layer comprises a single graphene monolayer arranged on the buffer layer 31, and a third zone 322 in which the carbon layer comprises two graphene monolayers arranged on the buffer layer 31. In a fourth zone extending from the edge B, the carbon layer comprises three graphene monolayers arranged on the buffer layer 31.

[0075] The buffer layer 31 typically has a thickness of approximately 0.2 nm. The surface layer 32 typically has a thickness between 0 and 1 nm. Thus, the thickness of the carbon layer 30 is between 0.2 and 1.2 nm.

[0076] A carbon layer thickness between 0.2 and 1.2 nm is sufficient to limit terrace formation during heat treatment to a height of less than 25 nm. At the pressure pF and temperature TF in the furnace, it is possible to covering the entire surface of the substrate with a carbon layer of such thickness is impossible. A greater thickness is difficult to achieve because the sublimation of silicon atoms on the substrate's top surface is blocked by the presence of the already formed carbon layer. Therefore, the formation of additional graphene monolayers takes longer than the initial formation and would unnecessarily prolong the process.

[0077] High-temperature stages requiring a protective layer

[0078] After the carbon layer has formed, further steps can be carried out on the substrate at a heat treatment temperature Tt higher than the carbon layer formation temperature TF. Such steps include, for example, annealing for dopant activation or annealing to repair defects in the crystal lattice caused during ion implantation. Such implantation can be used for transferring the m-SiC layer onto a base substrate as described below. Ion implantation can also be performed to dope m-SiC.

[0079] During the annealing step(s), the surface of the single-crystal semiconductor material is protected by the carbon layer, thus preventing the formation of terraces on said surface. An annealing step is typically carried out at a heat treatment temperature Tt between 1300°C and 2000°C, typically above 1700°C. Typically, the heat treatment is carried out under a protective gas atmosphere, for example, argon. During this step, the heat treatment pressure pT in the furnace is between the pressure PF and atmospheric pressure, for example, greater than or equal to 2 Pa.

[0080] Advantageously, such heat treatments are carried out directly after the formation of the carbon layer in the same furnace. The temperature ramp up to the heat treatment temperature can be achieved from the TF temperature without intermediate cooling. The pressure ramp-up can be achieved from the pF pressure under a protective gas atmosphere, without exposing the substrate to ambient air. The subsequent treatment in the same furnace avoids intermediate cooling steps, exposure to ambient air, and the removal and loading of the substrate into separate chambers. This reduces the required labor, the cooling and heating time, and the risk of substrate contamination. Temperature profile

[0081] By way of illustration and without limitation, [Fig. 4] shows a temperature profile of such a process. The substrate is placed in the furnace at time t0. The pressure is lowered to reach the pressure pF. Subsequently, the temperature is increased to the temperature TF at time tb. This temperature is, for example, approximately 1450°C for a The pressure is set to 2.10⁻¹ Pa (pF). The carbon layer is formed by sublimation until time t2. The carbon layer formation time is typically between 10 and 120 minutes. The pressure in the furnace is then increased to stop the silicon sublimation and carbon formation on the substrate surface. Typically, the pressure is raised to approximately 2 Pa under an argon atmosphere. The substrate is heated until time t3, when the temperature Tt required for heat treatment is reached, for example, 1700°C. The heat treatment temperature Tt is maintained according to the substrate type and the objective of the heat treatment. After heat treatment, at time t4, the furnace temperature is lowered. After the substrate has cooled, at time t5, it can be removed from the furnace for further processing such as polishing. Removal of the terraces and the carbon layer

[0082] At the end of the carbon layer formation and heat treatment steps, the temperature is lowered in order to remove the substrate from the oven.

[0083] The terraces formed during the heat treatment can then be removed, for example by mechanical or chemical polishing. The carbon layer is removed in the same step. The thinness of the carbon layer makes it possible to avoid additional steps for removing the carbon layer.

[0084] The small step height that can appear during heat treatment and the thinness of the carbon layer make it possible to limit the shrinkage of the silicon carbide to a thickness of 200 nm or less. This significantly reduces polishing time and material consumption compared to polishing steps on a substrate treated using a process without a protective layer.

[0085] At the end of this step, the substrate is finalized. The free surface of m-SiC can then be used for the epitaxial growth of a layer of a single-crystal semiconductor material, for example another layer of m-SiC or a layer of GaN, and / or for the fabrication of a power electronic or radio frequency component.

[0086] Method for manufacturing a semiconductor structure

[0087] We will now describe a manufacturing process for a semiconductor structure for electronic applications, having a surface layer 20 of single-crystal silicon carbide.

[0088] A donor substrate 220 of single-crystal silicon carbide is provided from which the surface layer of single-crystal silicon carbide will be formed. Typically, the donor substrate also includes dopants incorporated into the crystalline matrix. With reference to [Fig. 5A], as schematically indicated by the arrows, an implantation of ionic species, such as hydrogen and / or helium, is implemented so as to form a weakening zone 21 in the donor substrate 220. Said weakening zone 21 defines a layer 20 of single-crystal silicon carbide. crystalline lens to be transferred.

[0089] With reference to [Fig.5B], the donor substrate 220 thus implanted is glued onto a base substrate 11. The donor substrate can be glued directly onto the base substrate as illustrated in [Fig.5B], or via one or more intermediate layers which can be arranged on the donor substrate and / or on the base substrate before gluing (not shown).

[0090] With reference to [Fig. 5C], the donor substrate 220 is then detached along the embrittlement zone 21, resulting in the transfer of the single-crystal silicon carbide layer onto the base substrate 11, thus forming the substrate 10 as shown in [Fig. 2]. The detached portion 221 of the donor substrate can be reused for transferring other single-crystal silicon carbide layers onto other base substrates.

[0091] A treatment process is then carried out, comprising successively a surface stabilization step by the formation of a protective carbon layer 30, a high-temperature annealing intended to activate the dopants and / or cure the defects created in the single-crystal silicon carbide layer during the implantation of the ionic species, and the subsequent removal of the protective carbon layer. Introducing the oven

[0092] In order to make a process for treating a plurality of substrates efficient and rapid, it is preferable to use an annealing furnace capable of simultaneously treating a batch of substrates under identical conditions. Such a furnace is classically called a "batch anneau" furnace in the field of microelectronics.

[0093] Figure 6 illustrates a 70 oven adapted to receive a quantity between 120 and 150 substrates are placed in an annealing chamber. The substrates are positioned horizontally in the furnace and stacked vertically to maximize the number of substrates processed. A gap is maintained between each substrate and adjacent substrates to optimize gas flow and achieve consistent pressure during de-icing. Consistent pressure facilitates carbon layer formation and results in a more uniform carbon layer thickness across each substrate. The optimal vertical distance depends on the substrate diameter. Typically, the vertical distance between two stacked substrates is between 4 and 10 mm for substrates with a diameter between 150 and 200 mm.The distance between substrates can be increased for large substrate diameters, and decreased for smaller diameters to allow gas circulation between two adjacent substrates, while optimizing the space in the furnace to allow the simultaneous processing of a large number of substrates.

[0094] Such a furnace uses a "top flow" type configuration, that is to say that a flow of Gas can be supplied to the furnace via the top 71 and / or discharged through an outlet 79 at the bottom of the furnace. During carbon layer formation, no gas is injected into the furnace. Pressure reduction is achieved by pumping at the furnace outlet 79. During pressure buildup, a flow of gas can be supplied to the furnace via the top 71.

[0095] All the elements of the annealing chamber inside the furnace, i.e., the inner walls 75, the substrate holders for maintaining the substrates in a horizontal and vertically overlapping position, and the gas contained within the annealing chamber, are at the same temperature during furnace operation, with the exception of external elements such as the outer wall 76 and the ends of the gas supply pipes. By "same temperature," it is understood that the temperature difference between the upper end 74 of the furnace and the lower end 78 of the furnace is minimal, typically a few degrees °C, for example, less than 3 degrees for a furnace temperature between 800 and 1200 °C.

[0096] The substrates are heated mainly by conduction from the walls of the furnace. The gases are injected at the same temperature as the temperature inside the furnace.

[0097] An annealing furnace is not intended for layer formation but for applying heat treatment to the substrates placed in the furnace. These furnaces are therefore optimized for high temperature homogeneity of the substrates received within them, but not for ensuring homogeneity of gas evacuation in the space between the substrates. The overlapping positioning of the substrates particularly impairs this homogeneity since, when reducing the pressure, it is more difficult to lower the pressure in the space between the substrates near the center of the substrates than at their edges. It is also more difficult to remove the silicon atoms following sublimation during the formation of the carbon layer.

[0098] In order to obtain a homogeneous carbon layer, it is necessary to control the thickness so as to obtain a sufficient thickness over the surface area of ​​all the substrates contained in the furnace, in particular in the central area of ​​the substrates.

[0099] The pF pressure between 0.01 and 0.5 Pa is particularly suitable for processing a batch of substrates in such a furnace.

[0100] On the one hand, a pressure exceeding 0.5 Pa results in insufficient evacuation of silicon atoms between two adjacent substrates, particularly near the center of the substrate. This insufficient evacuation leads to the presence of a significant number of silicon atoms near the substrate surface, thus preventing the sublimation of other silicon atoms from the m-SiC on the surface of the lower substrate. Such a blockage of silicon sublimation therefore prevents the formation of the carbon layer.

[0101] On the other hand, a pressure below 0.01 Pa is difficult to achieve in an industrial furnace and requires significant pumping effort and time. Such pumping necessitates additional equipment and considerably slows down the process. Furthermore, it is difficult to ensure sufficient furnace sealing to reliably achieve lower pressures.

[0102] The formation of a buffer layer and one or more graphene layers on the surface of each substrate makes it possible to obtain a sufficient and homogeneous thickness to limit terrace formation on each substrate. When the substrates are stacked in a furnace, the carbon layer is typically thicker near the edge of each substrate and thinner near the center. Using a carbon layer formation pressure (pF) between 0.01 and 0.5 Pa, the carbon layer typically has a thickness between 0.2 and 1.2 nm over the entire surface of the substrate.

[0103] Unlike a deposition chamber, such a furnace allows a large number of substrates to be treated simultaneously thanks to the vertically stacked arrangement.

[0104] Homogeneity of the protective layer and its effect on terrace formation

[0105] Figure 7 shows the root mean square (RMS) value of the surface roughness generated by terrace formation on a single-crystal SiC surface, measured by AFM. The roughness is measured as a function of the radial position on the substrate.

[0106] The curve ri corresponds to the roughness measured on substrates that have undergone heat treatment at 1700°C for 30 minutes without the formation of a protective carbon layer. Due to the limited gas flow between the substrates, significant inhomogeneity is observed between measurement points near the center C of the substrate and measurement points near the edge B of the substrate. The average roughness is greater than 15 nm near the center C and between approximately 7 and 9 nm near the edge B.

[0107] Curve r2 corresponds to the roughness of substrates after a treatment comprising the formation of a carbon layer and heat treatment at 1700°C for 30 minutes. The temperature and duration of the heat treatment are therefore identical to the temperature and duration of the substrate treatment in curve rL. During the heat treatment, each substrate was thus protected by its respective carbon layer. The roughness is approximately 5 nm near the center C and between 3 and 4 nm near the edge B of each substrate. The roughness of a substrate with a carbon layer formed by a process as described above (curve r2) is therefore clearly lower than the roughness of a substrate treated without a carbon layer (curve ri).

[0108] In both processes (curves ri and r2), the substrates were arranged within a batch of substrates in a furnace as shown above. The vertical distance between two adjacent substrates was 4 mm. The difference in roughness at the center and near the edge is due to the limited gas flow and the difference in the partial pressures of the different gases in the central zone between two superimposed substrates in the furnace.

[0109] Figure 8 shows the step height between two terraces formed on the single-crystal SiC surfaces of the same substrates as in Figure 7. The step height is evaluated as the average height in a 30x30 pm² area. The x-axis corresponds to the radial position on the substrate.

[0110] The step height of substrates that have undergone heat treatment without carbon layer formation is illustrated by curve Hh. The average step height Hi is approximately 80 nm near the center C and approximately 40 nm near the edge B of the substrate. Curve H2 shows the average step height for substrates after a process comprising the formation of a carbon layer as described above, followed by heat treatment identical to that of the substrates in curve H. The step height H2 on the substrate protected by a carbon layer is between 30 and 40 nm near the center C of the substrate, and between 25 nm and 30 nm near the edge B of the substrate. The step height formed during heat treatment is therefore considerably reduced by the presence of a carbon layer at both radial positions.

[0111] Figures 9A and 9B are electron beam scanning microscopy images of the m-SiC surface of a substrate after heat treatment according to a known process without carbon layer formation. Each image represents a 5x5 pm² area. [Fig. 9A] is the image of an area near the center of the substrate. [Fig. 9B] is the image of an area near the edge of the same substrate. The terraces exhibit a greater extent and height in the area near the center of the substrate.

[0112] Figures 10A and 10B are electron beam scanning microscopy images of the m-SiC surface of a substrate after heat treatment according to a process as described above, comprising the formation of a carbon layer by silicon sublimation. Each image represents a 5x5 pm² area. [Fig. 1OA] is the image of an area near the center of a substrate. [Fig. 1OB] is the image of an area near the edge of the same substrate. As with the substrate in Figures 9A and 9B, the terraces exhibit greater width and height in the area near the center of the substrate. However, the terraces are considerably smaller in extent and size than all the terraces obtained on the substrate after heat treatment without carbon layer formation.

[0113] The extent of the terraces near the center of the substrate, which is protected by a carbon layer ([Fig. 1OA]), is less than the size of the terraces at the edge and center of the treated substrate without the formation of such a protective layer ([Fig. 9A]). Furthermore, in the area near the edge of the substrate (Figures 9B and 10B), terrace formation was virtually suppressed by the presence of the carbon layer. References

[0114] R. Zhang et al. “Growth of large Domains of Epitaxial Graphene on the C-face of SiC”, J. of App. Phys. 2012, 112 (10); doi: 10.1063 / 1.4765666

[0115] J. Bao et al. “Sequential Control of Step-Bunching During Graphene Growth on SiC (0001)”, App. Phys. Lett. 2016, 109(8); doi:10.1063 / 1.4961630

[0116] W. Strupinski et al. “Formation mechanism of graphene buffer layer on SiC(1000), Carbon 81 (2015) page 63-72.

[0117] I. Razado-Colambo et al. « Structural détermination of bilayer graphene on SiC(0001) using synchrotron radiation photoelectron diffraction”, Scientific Reports 2018,8:10190

Claims

Claims

1. A method of treating a substrate (10) comprising at least one surface layer of monocrystalline silicon carbide, said method comprising: • placing said substrate (10) in a furnace, • lowering the pressure in the furnace to a pressure (pF) of between 0.01 and 0.5 Pa, • heating the substrate to a temperature (TF) above a sublimation temperature of silicon at said pressure (p F), so as to form a carbon layer on the monocrystalline silicon carbide layer by sublimation of silicon from the surface of said monocrystalline silicon carbide layer.

2. Method according to claim 1, wherein the temperature (TF) of formation of the carbon layer (30) is between 1200°C and 1500°C.

3. A method according to any preceding claim, wherein the carbon layer (30) is a graphene layer.

4. A method according to any preceding claim, wherein the carbon layer (30) has a thickness of between 0.2 nm and 1.2 nm.

5. A method according to any preceding claim, wherein a plurality of substrates (10) are processed simultaneously in the same oven (70).

6. The method of claim 5, wherein the substrates (10) are vertically superimposed in the oven (70) such that a vertical space is provided between two adjacent substrates.

7. A method according to claim 6, wherein said vertical space between two adjacent substrates (10) has a height of between 4 and 10 mm.

8. Method according to one of claims 1 to 7, comprising, after the formation of the carbon layer (30), a heat treatment of the substrate at a temperature (Tt) higher than the temperature (TF) of formation of the carbon layer and under a pressure (pT) higher than the pressure (pF) of formation of the carbon layer.

9. A method according to claim 8, wherein the temperature (Tt) of the heat treatment is greater than or equal to 1700°C.

10. A method according to claim 8 or claim 9, wherein the pressure (pT) of the heat treatment is greater than or equal to 2 Pa.

11. Method according to one of claims 8 to 10, in which the formation of the carbon layer and the heat treatment are carried out in the same furnace.

12. Method according to one of claims 8 to 11, further comprising a step of removing the carbon layer (30) after the heat treatment.

13. Method according to one of claims 8 to 12, further comprising a step of chemical-mechanical polishing after the heat treatment to remove steps formed on the surface of the silicon carbide layer during said heat treatment.

14. The method of claim 13, wherein said chemical-mechanical polishing results in the removal of a silicon carbide thickness of less than 200 nm.

15. Method for manufacturing a structure comprising a layer of monocrystalline silicon carbide on a support substrate, successively comprising: - the formation of a weakening zone in a donor substrate of monocrystalline silicon carbide by implantation of ionic species, so as to delimit a layer of monocrystalline silicon carbide to be transferred, - the bonding of the donor substrate to the support substrate, - the detachment of the donor substrate along the weakening zone so as to transfer the layer of monocrystalline silicon carbide to the support substrate, - the implementation of the treatment according to one of claims 8 to 14 on the transferred layer of monocrystalline silicon carbide.

16. A method according to claim 15, wherein the layer of monocrystalline silicon carbide comprises dopants and in that the heat treatment is carried out at a temperature suitable for activating said dopants.

17. Method according to one of claims 15 or 16, in which the silicon carbide layer comprises defects due to the implantation of ionic species and in that the heat treatment is carried out at a temperature suitable for curing at least part of said defects.

18. Method according to one of claims 15 to 17 in their dependent relationship with claims 13 or 14, further comprising, after the chemical-mechanical polishing, a step of resuming epitaxy of monocrystalline silicon carbide on the surface of the monocrystalline silicon carbide layer.

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