Method for growing high-quality single-crystal silicon carbide

Abstract

A method for growing an epitaxial layer on a single-crystal silicon carbide (SiC) substrate (20) is disclosed. This method comprises providing a source material (10) of monolithic polycrystalline silicon carbide (SiC) having a columnar fine grain structure and a substrate (20) of single-crystal SiC at a distance between them in the chamber (5) of the inner container (31, 32) of the crucible (S100), placing a carbon getter (1) in close proximity to the source material (10) and the substrate (20) in the chamber (5) of the crucible (S102) - said carbon getter (1) has a melting point higher than 2200°C and has the ability to form a carbon species and a carbide layer evaporated from SiC - reducing the pressure in the chamber (S106), inserting an inert gas into the chamber (5) (S108), raising the temperature in the chamber (5) to achieve a growth rate between 1 μm / h and 1 mm / h (S110), and maintaining the growth temperature until at least 5 μm of growth is achieved on the substrate (20) (S112).

Description

Technology Field

[0001] The present invention generally 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 a high-quality silicon carbide single crystal with almost no carbon inclusions and basal plane dislocations. Background Technology

[0002] In recent years, there has been an increasing demand for improved electronic devices capable of high energy efficiency, high power levels, and high temperatures. Silicon (Si) is currently the most commonly used material in the semiconductor industry for power devices in high-temperature, high-voltage, and high-power applications. SiC is a highly suitable alternative material because it has higher thermal conductivity, a higher saturation electron drift velocity, and a higher breakdown electric 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 source material, often in powder form, are placed in a reaction crucible and heated to the sublimation temperature of the source material. A thermal gradient exists between the source material and the slightly cooler seed crystal. This thermal gradient promotes vapor phase transfer, causing vapor species from the source material to deposit onto the seed crystal, thereby allowing the single-crystal layer to grow. However, using powder as a source material has several disadvantages. Powders often contain impurities generated during the manufacturing process. Additionally, the thermal distribution of the powder is not sufficiently uniform, making it difficult to control the sublimation and silicon depletion of the powder. Another disadvantage is the risk that solid particles of the powder may fall onto the seed, leading to inclusions and impurities in the final crystal structure. Furthermore, the stability of SiC powder presents another technical challenge for PVT growth. To grow relatively thick and large-diameter SiC single-crystal boules, a correspondingly large amount of SiC powder must be fed into the crucible. During PVT growth, temperatures can vary significantly at different locations within the SiC powder, which can lead to recrystallization and even carbonization of the SiC powder. These problems significantly reduce the crystal quality and yield of single-crystal SiC manufacturing.

[0004] One version of PVT is the sublimation sandwich method (SSM), in which monolithic SiC plates are used as the source material instead of powder. Using plates is advantageous, for example, for controlling the temperature uniformity of the source material. Another advantage of this method is the positive effect that vapor species do not react with the crucible walls because the distance between the source material and the seed crystal / substrate is short.

[0005] U.S. Patent No. 7,918,937 discloses a method for manufacturing an epitaxial layer on a SiC substrate. The source material is a polycrystalline high-purity material. Using a polycrystalline source material allows for a more uniform supply to the growing epitaxial layer, so the layer thickness and doping characteristics are more uniform compared to a single-crystal material.

[0006] The method disclosed in U.S. Patent No. 7,918,937 is an improvement over the previously described method, but there is still room for improvement. With the recent increase in interest regarding the commercialization of SiC power electronic devices, there is a significant demand for high-quality SiC single-crystal wafers with large diameters, primarily referred to herein as 6 inches or larger. In conventional PVT methods, SiC single crystals are grown at high temperatures in semi-closed carbon crucibles. As the growth time increases, the Si vapor species sublimated from the SiC powder gradually decrease, creating an increasingly carbon-rich growth atmosphere. Under carbon-rich conditions, carbon particles can be generated on the sublimated source surface and transferred to the growth surface, which is referred to as a carbon inclusion defect. Carbon inclusion defects can further induce the formation of micropipes, carrot defects, stacking defects, and other types of defects. Therefore, it is crucial to secure a stable and suitable growth atmosphere during the PVT growth process. However, as the SiC diameter increases, the aforementioned growth atmosphere becomes increasingly complex, posing a significant challenge to the PVT method.

[0007] Another issue with bipolar devices fabricated on SiC substrates and grown via the PVT process is performance degradation, particularly in devices used in high-power applications. The most frequent underlying cause of this degradation is Basal Plane Dislocations (BPDs). Stacking defects in the epitaxial layer mostly originate from BPDs propagating from the substrate. Under high current stress, these stacking defects expand, increasing the forward voltage of bipolar SiC devices and, in the case of nominal unipolar SiC devices with a positive contribution from embedded pn-junctions, causing an increase in reverse leakage current and a decrease in forward current. Currently, many device manufacturers accommodate BPDs in the substrate, assuming that BPDs can transition into Threading Edge Dislocations (TEDs) during the growth of the epitaxial buffer layer. However, according to the research results of Kazuya Konishi et al. in the paper “Stacking fault expansion from basal plane dislocations converted into threading edge dislocations in 4H-SiC epilayers under high current stress”, Journal of Applied Physics 114, 014504 (2013), it was found that BPDs can continue to expand as stacking faults even after being converted into TEDs. Therefore, to prevent bipolar degradation, a substrate free of BPDs is highly desirable. This is especially true for safety-critical applications such as automobiles or aircraft. Using the method according to the present invention, approximately 500 cm², which can generally be obtained from a 4-inch PVT-grown high-quality substrate -2 Compared to BPD density of 5cm -2 It can be reduced to below this level. By reducing BPD density, stacking defect expansion can be largely avoided, and reliable high-power SiC devices can be produced.

[0008] Therefore, as the demand for BPD-free SiC single crystals increases, the need to improve production capacity, efficiency, and quality, particularly in high-power applications, is also growing.

[0009] The object of the present invention is to implement a method for growing an epitaxial layer on a single-crystal SiC substrate that is essentially free of carbon inclusions and basal plane dislocations. This is achieved by a method for growing an epitaxial layer on a single-crystal SiC substrate comprising: providing a source material of monolithic polycrystalline SiC having a columnar micrograin structure and a substrate of single-crystal SiC at a distance between them within a chamber of an inner container of a crucible; placing a carbon getter within the chamber of the crucible to achieve a stable and suitable Si / C stoichiometry in the inner container—the carbon getter having a high melting point of 2200°C or higher and having the ability to form a carbon species and a carbide layer evaporated from SiC—reducing the pressure within the chamber; inserting an inert gas into the chamber and maintaining the pressure at least 0.01 mbar after insertion; raising the temperature within the chamber to a growth temperature to achieve a growth rate between 1 μm / h and 1 mm / h; and maintaining the growth temperature until at least 5 μm of growth is achieved on the substrate.

[0010] According to an exemplary embodiment of the present method, the temperature is increased by an increase of 10 ℃ / min to 50 ℃ / min, preferably about 20 ℃ / min to 30 ℃ / min.

[0011] According to another exemplary embodiment of the present method, the temperature is raised to 1550 ℃ to 2300 ℃, preferably about 1950 ℃.

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

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

[0014] In another embodiment of the present method, the pressure during the rising step and the holding step is about 0.01 mbar to 25 mbar, preferably 0.1 mbar to 10 mbar, most preferably 1 mbar to 3 mbar.

[0015] In an exemplary embodiment of the present method, the fine grain size of the source material is less than 250 μm, preferably less than 100 μm, and most preferably within the range of 1 μm to 50 μm.

[0016] According to another exemplary embodiment of the method, the fine grains of the source material have a cubic structure substantially oriented toward the (111) or (110) crystal planes.

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

[0018] In another embodiment of the method, the carbon getter is selected from the group consisting of tantalum, niobium, and tungsten, and preferably consists of several pieces distributed throughout the inner container.

[0019] According to another exemplary embodiment of the present invention, the surface of the substrate has a root-mean-square roughness smaller than 5 nm, preferably smaller than 0.4 nm.

[0020] In another exemplary embodiment, the present method further comprises providing a spacer between the source material and the substrate to fix the distance between the substrate and the source material 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 of the advantages of this method according to the present invention is that by providing monolithic polycrystalline SiC having a columnar fine-grain structure as a source material, sublimation from the source material can be performed very uniformly and stably, and high-quality single-crystal SiC with almost no carbon inclusion defects can be grown.

[0022] The present invention will now be described with reference to the attached drawings as an example. Brief explanation of the drawing

[0023] FIG. 1a is a schematic diagram showing a cross-section of a type of source material provided in the prior art. Figure 1b is an external photograph of polycrystalline SiC showing the macro-grain structure of a conventional source material. Figure 2a shows a schematic cross-section of monolithic polycrystalline SiC having a columnar fine grain structure as a source material. Figure 2b is a photograph of the appearance of polycrystalline SiC having a columnar fine grain structure. FIG. 3 is a schematic diagram illustrating a system used to perform the method according to the present invention. FIG. 4 is a schematic diagram showing a preferred arrangement of components within an internal container of the system of FIG. 3. Figure 5 schematically illustrates the temperature change of the substrate during epitaxial sublimation. Figures 6a and 6b show optical microscope images of samples grown using a source material according to the present invention and a source material of the type provided in the prior art. FIG. 7 is a diagram showing a flowchart of a method according to the present invention. Figure 8 shows a region-specific BPD density map (Si-Face) of a 4-inch substrate manufactured according to the method of the present invention. Specific details for implementing the invention

[0024] In the following, a detailed description of a method for growing an epitaxial layer on a single-crystal silicon carbide (SiC) substrate will be provided by way of example. However, it should be understood that these embodiments are merely illustrative and that many other embodiments may exist within the scope of the invention that a person skilled in the art can implement through the teachings of this disclosure. Identical reference numerals in the drawings refer to identical or corresponding elements throughout the drawings. It should be understood that these drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention.

[0025] The method of growing an epitaxial layer on a substrate will be carried out in a system for facilitating sublimation epitaxy with high growth rate, high reproducibility, and high quality, and this will be explained in detail below with reference to FIGS. 3 and FIGS. 4.

[0026] As mentioned in the background section above, the most commonly used technique for growing single-crystal SiC layers via sublimation is PVT, which uses powder as the source material. However, as mentioned above, U.S. Patent No. 7,918,937 discloses a method of providing a polycrystalline source material instead of powder. Now, returning to Figures 1a and 1b, we will describe the source material provided in U.S. Patent No. 7,918,937 in more detail 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-sectional view of the source material provided in U.S. Patent No. 7,918,937. As can be seen, the SiC grains have randomly distributed crystal orientations without any dominant orientation. This source material is also shown in Figure 1b as an external photograph of polycrystalline SiC exhibiting a macro-grain structure. The grain size of this source material is greater than 100 μm.

[0027] Compared to the method described above, the method according to the present invention provides a source material of monolithic polycrystalline SiC having a columnar fine grain structure as shown in the schematic cross-sectional view of the source material in FIG. 2a. Unlike the randomly distributed crystal orientations seen in the prior art, the columnar fine grain structure provides grains grown in the same crystallographic direction. This can be explained as the crystal planes in each grain being arranged substantially parallel to the crystal planes of other grains. The columnar fine grain structure can be described as a columnar structure or a microstructure having parallel grains. The grains in the columnar fine grain structure are elongated so that the length direction of the grain is longer than the width of the grain. The size of the fine grains in this columnar structure is in the range of 1 μm to 100 μm when measured in the width direction of the grain. The fine grains preferably have a cubic structure oriented to the (111) crystal plane. In another embodiment, the cubic structure may be oriented to the (110) crystal plane. According to another embodiment, the size of the fine grains may be in the range of 1 μm to 250 μm in the grain width direction. The size in the grain length direction is not limited here, but it is not uncommon to provide grains with a length direction size of 1 mm or more. FIG. 2b shows a photograph of the appearance of polycrystalline SiC having a columnar fine grain structure. By providing a source material having such a columnar structure, a substrate can be grown that is essentially free of carbon inclusions and basal plane dislocation defects. By providing a SiC source material having a columnar fine grain structure, highly uniform and stable sublimation from the source material can be realized, and high-quality single-crystal SiC free of carbon inclusion defects can be obtained. During the manufacture of the source material, it is preferable to grow the source material from the bottom for growth with controlled crystallographic orientation. The polycrystalline SiC source material can be produced by chemical vapor deposition.In addition, the source material can be processed into a standard shape and size using a wafering tool such as a surface grinder, and formed to be suitable for use as a source material for the growth of single-crystal SiC.

[0028] FIG. 3 illustrates a schematic diagram of a system (100) used to perform a method according to the present invention. In short, the system (100) includes a crucible comprising various parts to be described below and a heating means (70) surrounding the crucible. When referring to the upper or lower part in this disclosure, it refers to a crucible in an operating state standing on a floor, platform, etc. The system (100) is designed to facilitate sublimation epitaxy that enables the growth of a single-crystal SiC layer by providing the monolithic polycrystalline SiC described above as a source material (10). The source material (10) and the substrate (20) are placed in a chamber (5) (see FIG. 4) of an inner container comprising an upper part (31) and a lower part (32). The inner container (31, 32) is also placed within an insulating container (50) comprising an upper part and a lower part. The insulating container (50) is then placed in an outer container (60). A heating means (70) that can be used to heat the cavity of the inner container (31, 32) is provided on the outside of the outer container (60). According to this embodiment, the heating means (70) includes an induction coil for high-frequency heating. In this embodiment, the outer container (60) is a quartz tube, and the insulating container (50) and the inner container (31, 32) are cylindrical about axis T and are made of insulating graphite foam and high-density graphite, respectively. The insulating container (50) and the inner container (31, 32) may also be made of other suitable materials that can withstand high temperatures and facilitate coupling with the high-frequency induction coil when the high-frequency induction coil is used as the heating means (8). The heating means (70) is used to heat the crucible to sublimate the source material (10). The heating means (70) can move vertically to control the temperature and heat drop of the inner container (31, 32).As is known to those skilled in the art, the temperature drop between the source material (10) and the substrate (20) may be changed by changing the characteristics of the inner container (31, 32), such as the thickness of the upper (31) and lower (32). In addition, to exhaust the inner container, i.e., about 10. -4 to 10 -6 There is a pump (not shown) to provide a pressure of mbar.

[0029] Now, referring to FIG. 4, which illustrates an exemplary arrangement of various components within the inner containers (31, 32) of the crucible, the following description is made. The components are a carbon getter (1), a spacer (3), a source material (10), and a substrate (20). The source material (10) and the substrate (20) have diameters adjusted to the size of the inner containers (31, 32), said diameters vary depending on the desired size of the substrate (20). When the diameter of the inner containers (31, 32) is 100 mm, 150 mm, 200 mm, or 250 mm, the inner containers (31, 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 to be within the ability of a person skilled in the art to adjust the components and the inner containers (31, 32) to a given size of the substrate (20).

[0030] In the illustrated embodiment, the carbon getter (1) is placed in the inner container (31, 32) close to the source material (10) and the substrate (20), in this case, close to the source material (10). However, in the context of this disclosure, when the word carbon getter is used, it should be understood that the carbon getter does not necessarily mean a single unit, but may be divided into a number of small pieces placed throughout the inner container (31, 32), which will be explained in more detail in other exemplary embodiments below. The carbon getter (1) is provided to maintain a stable and suitable Si / C stoichiometry during growth inside the carbon crucible, facilitates thickness uniformity, and also controls the vapor stoichiometry inside the container (31, 32). The characteristics of the carbon getter (1) are characterized by a high melting point, preferably higher than 2200°C, high carbon absorption, and high chemical stability, that is, the ability of the carbon getter (1) 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 materials having such properties. The carbon getter (1) has a thickness of about 0.05 mm to 2 mm, preferably 0.1 mm to 1 mm, and the thickness may vary depending on how the carbon getter (1) is provided and whether it is a single unit or composed of multiple pieces, and may have various shapes such as a foil in the form of a small piece, sheet, or plate, or may have a shape such as a mesh. If the carbon getter (1) is in the form of a small piece, 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 in the inner container (31, 32). If made too thin, the carbon getter (1) may deform and adversely affect the temperature distribution and surface quality of the grown crystal.If the carbon getter (1) is made too thick, impurities such as aluminum contained therein may be released. A low-concentration epitaxial layer is achieved by using high-purity graphite material and a suitable carbon getter. Some of the characteristics of the carbon getter (1) are determined when the carbon getter (10) is prepared prior to growth. Another exemplary embodiment includes small pieces provided in various places on the inner container (31, 32). Some of these pieces are provided under the source material to increase the silicon / carbon ratio of the inner container, and some pieces are provided on the sides of the inner container (31, 32) to promote uniform growth at the edges of the substrate (20).

[0031] The carbon getter (1) acts as a carbon absorber by reacting with carbon species sublimated from the SiC source during growth. As mentioned above, the placement of the carbon getter (1) can be done in various ways, provided that it improves stable and suitable Si / C stoichiometry in the inner container (31, 32). In one exemplary embodiment, as shown in FIG. 4, the carbon getter (1) is placed below the source material (10). This placement can help improve the temperature distribution horizontally across the source material (10), that is, in a direction orthogonal to the growth direction of the epitaxial layer. That is, as the carbon getter (1) engages with the induced RF field generated by the heating means (70), the heating of the source material (10) is increased. Additionally, the carbon getter (1) promotes a more uniform heat distribution on the surface (10b) of the source material (10) toward the carbon getter (1). Consequently, heat is also diffused more uniformly axially across the substrate (20), that is, toward the opposite surface (10a) of the source material (10), providing more uniform characteristics of the epitaxial layer. It should be understood that, even though the carbon getter (1) is placed below the source material (10) in the exemplary embodiment described above, the carbon getter (1) can be placed between the source material (10) and the substrate (20) or at other locations as described above, as long as it facilitates thickness uniformity and also controls the vapor stoichiometry inside the container (31, 32), and can be divided into many small pieces and distributed along the walls of the inner container (31, 32) or on the bottom, and should be understood as mentioned above.

[0032] As described above, the source material (10) is placed on the carbon getter (1) in an exemplary embodiment, but may be placed below the carbon getter (1) or surrounded by the carbon getter (1). The thickness of the source material (10) is approximately 0.5 mm to 5 mm. By providing a polycrystalline source material (10) having a columnar fine-grain structure, a more uniform supply can be provided to the growing epitaxial layer (20b) of the substrate (20), thereby inducing more uniform characteristics of layer thickness and doping.

[0033] A substrate (20) is placed over a source material (10) but separated from it by a spacer (3) having a height in the range of 0.5 mm to 2.5 mm, the height of which is adjusted to the desired distance between the substrate (20) and the source material (10). The spacer (3) is arranged and formed so that the distance between the substrate (20) and the source material (10) is within the range of 0.5 mm to 2.5 mm, preferably within the range of 0.7 mm to 1.2 mm. The spacer (3) may be ring-shaped or may include three individual spacers to stably support the substrate (20). Preferably, the substrate (20) comprises a SiC carbide crystal having a mirror-like surface and minimal surface defects. In an exemplary embodiment, the surface of the substrate (20) has a root mean square (RMS) roughness smaller than 5 nm, preferably smaller than 0.4 nm. To maintain stable growth of the polytype of the SiC crystal inherited from the substrate (20), the off-cut angle of the substrate (20) is in the range of 0 to 8 degrees, preferably 4 degrees. In an exemplary embodiment, the polytype of the grown single crystal is determined by the seed polytype. To maintain good surface morphology and low-density surface defects of the grown SiC crystal, in one exemplary embodiment, the polarity of the substrate (20) is (000-1), also referred to as the carbon face. There are other options, and in another exemplary embodiment, the polarity of the substrate is (0001), also referred to as the silicon face polarity.

[0034] Now, with reference to FIGS. 5 and FIGS. 7, a method for growing an epitaxial layer on a substrate (20) of single-crystal SiC is described. FIGS. 7 shows a flowchart of the method, and FIGS. 5 schematically shows an exemplary temperature change in the substrate (20) during epitaxial sublimation. Optional steps of the method are indicated by dashed lines. It should be understood that the method according to the present invention is not limited to whether 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). A P-type substrate may be grown by aluminum doping. In this case, aluminum may be introduced into the chamber (5) via aluminum carbide powder or gas.

[0035] Step S100 of the present method provides a source material (10) of monolithic polycrystalline SiC having a columnar fine-grain structure and a substrate (20) of single-crystal SiC within the chamber (5) of the inner container (31, 32) of the crucible. The source material (10) and the substrate (20) are arranged at 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 to 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 container (31, 32). The carbon getter (1) has a melting point of 2200 °C or higher and has the ability to form a carbide layer with carbon species evaporated from SiC, i.e., high carbon absorption and high chemical stability.

[0036] When the source material (10), carbon getter (1), and substrate (20) are all provided within the chamber (5), the pressure within the chamber (5) is reduced in step S106. In an exemplary embodiment, the pressure during the reduction step S106 is 10 -3It is reduced to a basic vacuum level lower than mbar. The chamber (5) is exhausted using conventional pumping means.

[0037] In step S108, an inert gas is introduced into the chamber (5). Any inert gas may 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 will be reduced after reaching the growth temperature (see step S110 below). The pressure is then reduced at a pumping rate, for example, 1 mbar / min to 10 mbar / min, preferably 5 mbar / min, until the pressure reaches a range of 1 mbar to 10 mbar.

[0038] In step S110, the temperature of the chamber (5) is raised to a growth temperature by a heating means (70) as shown in the temperature diagram of FIG. 5. The growth process includes a preheating step (401). During the preheating step S110, the temperature may be increased within an interval between 1°C / min and 245°C / min, depending on the situation 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 source material (10). The pressure during the rise step S110 is generally maintained at 0.01 mbar or higher, preferably 950 mbar or lower, as previously described. Also, as mentioned above, the pressure during the rise phase may be constant in, for example, the range of 1 mbar to 10 mbar, or may be reduced by 5 mbar / min from an initial pressure in, for example, the range of 150 mbar to 950 mbar, preferably 700 mbar, to a pressure in the range of 1 mbar to 10 mbar during the rise phase S110. The rise phase S110 continues until the temperature rises to an appropriate growth temperature (413), generally about 1550°C to 2300°C, preferably about 1950°C. Once the appropriate growth temperature (413), that is, the growth temperature that promotes the desired growth rate, is reached, the temperature rise is rapidly reduced. The desired growth rate may be in intervals of 1 µm / h to 1 mm / h, which again depends on the balance between productivity and quality. Preferably, the growth rate is maintained between 10 µm / h and 300 µm / h to maintain balance. In a preferred embodiment, the growth temperature is maintained at 1950°C, providing a growth rate of about 90 μm / h in the aforementioned setting. Those skilled in the art know at what temperature the desired growth rate can be obtained. The temperature is maintained at that level (413) until an epitaxial layer of the desired thickness is achieved.The period following the heating step is called the growth step (403), during which the temperature is preferably maintained substantially constant, and the pressure during the holding step S112 is in the range of approximately 1 mbar to 10 mbar, preferably in the range of 3 mbar to 6 mbar. The growth step S112 is maintained until a preferably thick SiC single-crystal layer is formed, i.e., at point (414) in FIG. 5. The preferred growth thickness on the substrate (20) is at least 5 μm, but generally less than 5000 μm. For low-doping epitaxial drift layers used in high-voltage devices, a layer thickness of 10 μm / kV is preferred. In such applications, the growth thickness of the substrate (20) is generally thicker, in the range of 10 μm to 200 μm depending on the voltage class. The doping concentration of this layer is generally 1 x 10⁻⁶. 16 cm -3 It is less than. For example, the doping concentration is 1 x 10 18 cm -3 For N-type substrates exceeding [value], a thickness in the range of 1 mm to 7 mm can be grown. The thickness of the grown crystal is determined by the thickness of the source material (10), which can have a maximum thickness of 7 mm.

[0039] After a SiC crystal layer of a desired thickness is formed, heating is turned off and the substrate (20) is allowed to cool, which is called a cooling step (404). The preheating and cooling steps can be optimized to reduce production time. When the system cools to room temperature, the chamber (5) is refilled with argon or other safety gas to reach atmospheric pressure, and the chamber (5) is opened to remove the sample, which is a cooling process well known to those skilled in the art. After growth and cooling, the grown single crystal can be separated from the substrate (20) by processing the sample by polishing or by continuously dividing it into wafers using any wafer separation technique.

[0040] In another exemplary embodiment, a spacer (3) is provided between the source material (10) and the substrate (20) in an optional step S104 to fix the distance between the substrate (20) and the source material to a range of 0.5 mm to 2.5 mm, preferably 0.7 mm to 1.2 mm. The spacer (3) has a height in the range of about 0.5 mm to 2.5 mm as described above and is arranged and shaped so that the distance between the substrate (20) and the source material (10) is fixed as described above. Also, as mentioned above, the spacer (3) may be ring-shaped or may include at least three individual spacers to stably support the substrate (20).

[0041] To explain the importance of providing polycrystalline SiC having a columnar fine grain structure according to the present invention as a source material (10), two experiments were conducted in which different source materials were provided under the same conditions. In the first experiment, polycrystalline SiC having a columnar fine grain structure according to the present invention was provided as a source material, as shown in FIGS. 2a and 2b. In the second experiment, a source material of the prior art of polycrystalline SiC grains having a randomly distributed crystal orientation without a specific direction was provided, as shown in FIGS. 1a and 1b.

[0042] The experiment was performed in a system having a face-down configuration. That is, the growth of the substrate (20) is on a side (20b) (Fig. 4) facing downward toward the source material (10). However, the method according to the present invention is not limited to a system having a face-down configuration and can be performed in a system having a face-up configuration or any other configuration. The experiment was performed under the following conditions. As described above, after loading the source material (10), substrate (20), spacer (3), and carbon absorber (1) into the chamber (5), the chamber (5) is 10 -3The pressure was pumped down to less than mbar. Then, argon was introduced into the chamber (5) until the pressure reached 1 mbar. Then, the heating means (70) was turned on and the system was heated to the desired temperature of 1950°C at a ramp-up rate of about 20°C / min. At the growth temperature of 1950°C, the growth rate was about 90 μm / h, and this temperature was maintained for 4 hours and 30 minutes until the thickness of the grown single-crystal SiC reached about 500 μm. After that, the power to the heating means (70) was turned off and the temperature was allowed to cool naturally until the system cooled to room temperature. Then, the chamber was refilled with argon until atmospheric pressure was reached. Then, the chamber (5) was opened and the sample was removed.

[0043] The experimental results are illustrated in FIGS. 6a and 6b. FIGS. 6a and 6b are optical microscope images of samples grown using different source materials. FIG. 6a shows the results of using the source material according to the present invention, and FIG. 6b shows the results of using the source material of the prior art. The thickness of the grown single-crystal SiC of both samples is similar, approximately 500 μm. After growth, the sample using the source material (10) according to the present invention has a very smooth surface without carbon inclusions, whereas the sample using the source material of the prior art has a carbon inclusion defect density of 100 / cm³ 2 It exhibits high-density carbon inclusion defects. Carbon inclusion defects are highly detrimental to the quality of the grown crystal because they can induce novel structural defects such as stacking defects (SF) and BPD.

[0044] Stacking defects and BPDs cause bipolar degradation in SiC devices applied in high-power classes above 1.7 kV. BPDs, which shrink into TEDs during initial epitaxial growth and revert to BPDs during device operation, form stacking defects under high current stress, leading to device failure sooner or later. SFs in the epitaxial layer originate mostly from BPDs propagating from the substrate. Under high current stress, these SFs expand, increasing the forward voltage of bipolar SiC devices and causing an increase in reverse leakage current and a decrease in forward current in the case of nominal unipolar SiC devices with a bipolar contribution at the embedded pn junction.

[0045] By eliminating stacking defect formation, 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 will be significantly improved. This will enable their integration into mass applications over the next decade.

[0046] By using the method according to the present invention, the BPD density is generally about 500 cm² obtained from PVT growth on a high-quality substrate with a size of 100 mm. -2 5 cm compared to -2 It can be reduced to less than. By reducing BPD density, SF expansion can be largely avoided, and reliable high-power SiC devices can be produced. Examples of such high-power SiC devices include inverters and converters for hybrid and all-electric vehicles, inverters for solar and wind power generation, power factor correctors for advanced power applications, and devices for power transmission and distribution.

[0047] Now, referring to FIG. 8, another example of the quality of a substrate produced according to the method of the present invention is illustrated. FIG. 8 illustrates a region-specific BPD density map (Si-Face) of a 100 mm (4-inch) substrate produced according to the method of the present invention. As shown in FIG. 8, the average BPD density is very low and significantly lower than that of a prior art substrate.

[0048] Although the present invention has been 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. Additionally, the present method may be used to create one or more layers in the same cavity as can be easily implemented by those skilled in the art.

Claims

Claim 1 A method for growing an epitaxial layer on a single-crystal silicon carbide (SiC) substrate (20), comprising: - providing a source material (10) of monolithic polycrystalline silicon carbide (SiC) having a columnar fine-grain structure and a single-crystal SiC substrate (20) with a distance between them in the chamber (5) of the inner container (31, 32) of the crucible (S100); - placing a carbon getter (1) in the chamber (5) of the crucible to achieve a stable and suitable Si / C stoichiometry in the inner container (31, 32) (S102); - 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; - reducing the pressure in the chamber (S106); - inserting an inert gas into the chamber (5) (S108) and maintaining the pressure higher than 0.01 mbar after insertion; - 1 μm / h to 1 A method comprising raising the temperature inside the chamber (5) to achieve a growth rate of mm / h (S110), and maintaining the growth temperature until at least 5 μm of growth is achieved on the substrate (20) (S112). Claim 2 A method according to claim 1, wherein the temperature increase is carried out by an increase of 10℃ / min to 50℃ / min, or 20℃ / min to 30℃ / min. Claim 3 A method according to claim 1, wherein the temperature is raised to 1550℃ to 2300℃ or 1950℃. Claim 4 A method according to any one of claims 1 to 3, wherein the pressure during the rising step (S110) is 150 mbar to 950 mbar, and the pressure during the holding step (S112) is reduced to 0.1 mbar to 10 mbar, or 1 mbar to 3 mbar. Claim 5 A method according to claim 4, wherein the pressure in the holding step (S112) is reduced until it reaches a pressure of 0.1 mbar to 10 mbar, or 1 mbar to 3 mbar, at a pumping rate of 1 mbar / min to 10 mbar / min, or 5 mbar / min, after reaching the growth temperature. Claim 6 A method according to any one of claims 1 to 3, wherein the pressure in the rising (S110) step and the holding (S112) step is 0.01 mbar to 25 mbar, or 1 mbar to 10 mbar, or 1 mbar to 3 mbar. Claim 7 A method according to any one of claims 1 to 3, wherein the source material (10) has a fine grain size smaller than 250 μm, or a fine grain size smaller than 100 μm, or a fine grain size in the range of 1 μm to 50 μm. Claim 8 In claim 7, the fine crystal grains of the source material (10) have a cubic structure oriented toward the crystal planes (111) or (110). Claim 9 A method according to any one of claims 1 to 3, wherein the carbon getter (1) is selected from the group consisting of tantalum, niobium and tungsten and has a foil form. Claim 10 A method according to any one of claims 1 to 3, wherein the carbon getter (1) is selected from the group consisting of tantalum, niobium and tungsten and comprises several pieces distributed throughout the inner container (31, 32). Claim 11 A method according to any one of claims 1 to 3, wherein the surface of the substrate (20) has a root mean square (RMS) roughness of less than 5 nm or less than 0.4 nm. Claim 12 A method according to any one of claims 1 to 3, further comprising providing a spacer (3) between the source material (10) and the substrate (20) to fix the distance between the substrate (20) and the source material (10) to a distance in the range of 0.5 mm to 2.5 mm or 0.7 mm to 1.2 mm.

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