Silicon carbide thick film, its epitaxial growth method and application

Abstract

The application belongs to the technical field of semiconductor manufacturing, and discloses a silicon carbide thick film, an epitaxial growth method and application thereof, and the epitaxial growth method comprises the following steps: growing to a first thickness on a first surface of a substrate at a first growth rate; performing a first in-situ annealing; continuing to grow to a target thickness at a second growth rate; and performing a second in-situ annealing. In the epitaxial growth of the target silicon carbide thick film, the step-by-step process sequence of twice epitaxial growth and twice in-situ annealing and the whole-process in-situ process design effectively release the intrinsic stress and thermal stress accumulated in the growth process of the silicon carbide thick film, fundamentally inhibit the warping problem, promote the annihilation and recombination of dislocations and other defects, and significantly improve the crystal quality of the epitaxial layer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor manufacturing, and particularly relates to a silicon carbide thick film, an epitaxial growth method thereof and application. BACKGROUND

[0002] SiC power devices have become the core key devices in the fields of new energy vehicles, high-voltage power transmission, rail transit, etc. due to their excellent characteristics such as high breakdown electric field, high thermal conductivity and fast switching speed. The blocking voltage capability of MOSFET and diode devices directly depends on the thickness and doping concentration of the epitaxial layer. With the upgrading of power electronic equipment to high voltage and high power, the market demand for high-voltage devices of tens of volts is increasingly urgent, which requires the thickness of the SiC epitaxial layer to reach more than 100 microns to meet the insulation and voltage withstand requirements of the devices in the high-voltage scenario. At the same time, in order to improve production efficiency and reduce the cost per device, the semiconductor industry is accelerating the transition to 8-inch large-size wafer processing, and 8-inch SiC thick film epitaxial technology has become one of the core bottlenecks to realize the mass production of high-voltage devices.

[0003] However, growing a SiC thick epitaxial layer of more than 100 microns on an 8-inch large-size wafer faces insurmountable technical challenges. On the one hand, there is inevitably a lattice constant difference between the SiC substrate and the epitaxial layer. This lattice mismatch will generate initial stress at the interface, and as the thickness of the epitaxial layer increases, the stress will continuously accumulate and superimpose, and cannot be completely released by self-lattice relaxation. On the other hand, the epitaxial growth process needs to be carried out in a high-temperature environment above 1500℃, and there is an inherent difference in the thermal expansion coefficients of the SiC substrate and the epitaxial layer. During the subsequent cooling process, the shrinkage of the two is different, which will further generate significant thermal stress. The superposition of the two stresses forms a huge internal stress acting on the inside of the wafer, which is extremely easy to cause serious warping of the 8-inch large-size wafer, and even cause fatal defects such as cracking and peeling of the epitaxial layer.

[0004] Serious warping of the wafer will directly lead to the failure of subsequent precision processing technologies such as photolithography and etching. The photolithography process has very high requirements for the flatness of the wafer. The warped wafer will cause uneven coating of the photoresist and too large pattern transfer precision deviation, ultimately leading to failure of the device structure. The cracking of the epitaxial layer will directly cause the product to be scrapped, which not only greatly reduces the production yield, but also significantly increases the cost of raw materials and manufacturing, and seriously restricts the industrialization process of tens-of-volt 8-inch SiC high-voltage devices. At present, there is no mature and effective solution in the industry to balance the contradiction between thick film growth, large-size compatibility and stress control. How to effectively suppress the stress accumulation in the thick film epitaxial process and avoid wafer warping and epitaxial layer cracking has become a key technical problem that must be overcome for the realization of mass production of 8-inch SiC high-voltage power devices. SUMMARY

[0005] The present application aims to improve at least one technical problem in the background art.

[0006] The first aspect of the present application provides an epitaxial growth method of silicon carbide thick film, comprising the following steps:

[0007] Step S1: under the condition of the first temperature, the first reaction source is introduced to grow to the first thickness on the first surface of the substrate at the first growth rate;

[0008] Step S2: stop introducing the first reaction source, introduce inert gas, and perform first in-situ annealing under the condition of the second temperature;

[0009] Step S3: under the condition of the first temperature, stop introducing the inert gas, introduce the first reaction source again, and continue to grow to the target thickness at the second growth rate;

[0010] Step S4: stop introducing the first reaction source, introduce the inert gas, and perform second in-situ annealing under the condition of the second temperature;

[0011] Wherein, the first temperature is 1580-1650℃, and the second temperature is 1500-1550℃;

[0012] Wherein, the first growth rate is 30μm / h, and the second growth rate is 60μm / h;

[0013] Wherein, the first in-situ annealing time is 15-30min, and the second in-situ annealing time is 5-10min;

[0014] Wherein, the first thickness is 40-50μm, and the target thickness is not less than 100μm.

[0015] The method for epitaxial growth of silicon carbide thick film provided by the application reduces stress accumulation in the thick film growth process from the root by the synergistic design of stage-by-stage growth and in-situ annealing. The first temperature is set to 1580-1650 DEG C, which is the best temperature range for silicon carbide epitaxial growth, which can ensure the crystal quality and growth stability of the epitaxial layer. The first growth rate is controlled to be 30 um / h, and the lower growth rate can ensure that the base epitaxial layer with a first thickness of 40-50 um has a flat surface morphology and a low defect density, laying a good foundation for subsequent growth. After the growth is completed, the first reaction source is stopped and inert gas is introduced, which can not only avoid the interference of residual reaction gas on the subsequent process, but also maintain the stable pressure of the reaction chamber. The second temperature is 1500-1550 DEG C, which is slightly lower than the first temperature and is also in the atomic high-activity range. The first in-situ annealing is performed for 15-30 min under this condition, which can provide enough energy for the rearrangement of lattice atoms, release the intrinsic stress accumulated in the first stage growth, and promote the annihilation and recombination of dislocations and other defects, thereby optimizing the surface state of the base epitaxial layer. Then the first reaction source is introduced again by increasing the temperature to the first temperature, and the second growth is continued at a second growth rate of 60 um / h. The higher growth rate can improve the process efficiency on the premise of ensuring the quality, and finally the total thickness of the thick film reaches the target of not less than 100 um, realizing the balance between low stress and high efficiency. Finally, the second in-situ annealing is performed to perform the final stress relaxation and structure stabilization treatment on the silicon carbide thick film, so as to ensure that the silicon carbide thick film has a low stress state and good structure integrity after the growth is completed. The second in-situ annealing is a short-time high-temperature annealing, which can release the stress of the overall silicon carbide thick film formed by the two epitaxial growths, further repair the possible residual small defects in the growth process, and improve the overall crystal quality of the silicon carbide thick film.

[0016] Preferably, the substrate is made of 4H-SiC, and the thickness of the substrate is 350 um.

[0017] 4H-SiC has excellent crystal structure stability, high thermal conductivity and good electrical properties, and is an ideal substrate material for preparing high-performance silicon carbide thick film, which can match the process requirements of thick film epitaxial growth and guarantee the performance of the final device. The thickness of the substrate is set to 350 um, which can ensure that the substrate itself has sufficient structure strength and stability, reduce the initial warping of the substrate in the high-temperature epitaxial and subsequent process, provide a stable support foundation for the uniform growth of the thick film, and avoid the problem of uneven stress of the epitaxial layer caused by insufficient rigidity of the substrate itself.

[0018] Preferably, the step S1 further comprises a step S0, and the step S0 comprises:

[0019] The second reaction source is introduced at the first temperature to grow to a second thickness on the second surface of the substrate;

[0020] The second surface is opposite to the first surface, and the second thickness is the same as the first thickness.

[0021] The step S0 is provided in the present application to further optimize the flatness and structural stability of the substrate by the symmetry design of the double-sided growth of the substrate. The second surface of the substrate is opposite to the first surface. The second surface is grown to the same second thickness as the first thickness designed later under the first temperature condition by introducing the second reaction source, which can effectively increase the overall thickness of the substrate and reduce the initial warping degree.

[0022] Preferably, the second reaction source is doped with trimethylaluminum, and the doping concentration of the trimethylaluminum is 4x10 14 cm -3 - 8x10 14 cm -3 .

[0023] The trimethylaluminum in the present application adjusts the warping trend of the substrate by reverse doping, provides warping correction support for the growth of the subsequent first surface epitaxial layer, further reduces the thick film warping caused by single-sided growth, and guarantees the flatness and electrical performance consistency of the entire epitaxial structure.

[0024] Preferably, before the step S1, the first surface is further subjected to surface treatment, and the surface treatment comprises the following steps:

[0025] hydrogen etching is performed at 1350-1450℃ for 5-10min;

[0026] The pressure of the hydrogen etching is 80-120mbar.

[0027] The hydrogen etching of the first surface of the substrate in the present application can effectively remove the oxide layer, organic impurities and small defects on the surface of the first surface, and realize the atomic-level clean surface state. This surface treatment can significantly improve the interfacial bonding force between the epitaxial layer and the substrate, reduce the interfacial defects, provide a flat and clean growth interface for the subsequent first-stage epitaxial growth, and guarantee the crystal quality and growth uniformity of the epitaxial layer.

[0028] Preferably, the C / Si stoichiometric ratio in the first reaction source is 1.05-1.1.

[0029] The C / Si stoichiometric ratio of the first reaction source is controlled in the range of 1.05-1.1 in the application, which is slightly higher than the stoichiometric ratio, and is a key parameter design for inhibiting the generation of 3C-SiC polytype defects. In the process of silicon carbide epitaxial growth, the accurate control of the C / Si ratio directly affects the integrity of the crystal structure. A slightly higher C / Si ratio can avoid the precipitation of 3C-SiC polytype phase caused by excessive silicon content, ensure that the epitaxial layer always grows with the target crystal structure, improve the crystal consistency and overall quality of the silicon carbide thick film, and avoid the adverse effects of polytype defects on the electrical properties and structural stability of the silicon carbide thick film.

[0030] Preferably, the carbon source in the first reaction source is ethylene, and the silicon source is trichlorosilane.

[0031] Preferably, the first reaction source is doped with a first doping source, the first doping source is ammonia or nitrogen, and the doping concentration of the first doping source is 4×10 14 cm -3 - 8×10 14 cm -3 .

[0032] Ammonia or nitrogen as the first doping source can both introduce nitrogen element impurities into the epitaxial layer to achieve the required conductivity type control and meet the electrical performance requirements of subsequent device applications.

[0033] Preferably, after the second in-situ annealing is completed in the step S4, the temperature is lowered to a third temperature at a first cooling rate, and then the temperature is continuously lowered to a fourth temperature at the first cooling rate, and the temperature is naturally cooled to room temperature;

[0034] wherein the third temperature is 1000℃, and the fourth temperature is not more than 600℃;

[0035] wherein the time for the heat preservation is 10min-15min;

[0036] wherein the first cooling rate is 30℃ / min.

[0037] The slow cooling design at a first cooling rate of 30℃ / min in the application can reduce the thermal stress of the silicon carbide thick film caused by temperature gradient during the cooling process, and further reduce the warping or cracking caused by thermal stress during the cooling process. The heat preservation at the third temperature of 1000℃ for 10min-15min can relax the thermal stress in the medium temperature range, so that the temperature distribution inside the silicon carbide thick film is more uniform. After the temperature is continuously lowered to a fifth temperature of not more than 600℃ and then naturally cooled to room temperature, the influence of sudden temperature change on the structure of the silicon carbide thick film in the subsequent cooling process can be avoided, and the low stress, high integrity and structural stability of the silicon carbide thick film are further guaranteed.

[0038] Further, after the epitaxial growth is completed, the silicon carbide film grown on the second surface is subjected to chemical mechanical polishing treatment, and the removal amount is 40 μm to 50 μm.

[0039] The second aspect of the present application provides a silicon carbide thick film obtained by the epitaxial growth method described above.

[0040] The third aspect of the present application provides the use of the silicon carbide thick film described above in the production of a megavolt high-voltage device.

[0041] The present application has the following beneficial effects: In the epitaxial growth of the target silicon carbide thick film, the step-by-step process sequence of two epitaxial growths and two in-situ annealings and the full-process in-situ process design effectively release the intrinsic stress and thermal stress accumulated during the growth of the silicon carbide thick film, fundamentally inhibit the warping problem, and promote the annihilation and recombination of dislocations and other defects, thereby significantly improving the crystal quality of the epitaxial layer. The first in-situ annealing optimizes the surface state of the first epitaxial growth, provides a stable and flat growth foundation for the second epitaxial growth, and ensures a high-quality interlayer interface. The full-process does not require the wafer to be removed, and the key in-situ annealing step uses an inert gas atmosphere, which completely avoids the risk of interface contamination and oxidation, while ensuring the stability of the surface morphology and the process repeatability, and ultimately realizes the preparation of a silicon carbide thick film with low stress, high purity, and high consistency, thereby providing reliable support for the mass production of high-voltage power devices. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 An optical photograph of the surface of a silicon carbide thick film obtained by the epitaxial growth method of Example 1;

[0043] Figure 2 An optical photograph of the surface of a silicon carbide film obtained by the epitaxial growth method of Comparative Example 6. DETAILED DESCRIPTION

[0044] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the present application after reading the content described in the present application, and these equivalent forms also fall within the scope defined by the claims attached hereto.

[0045] Example 1

[0046] An epitaxial growth method of a silicon carbide thick film, wherein the substrate used in the epitaxial growth method is a 4H-SiC substrate with a thickness of 350 μm, the substrate includes a first surface and a second surface (the first surface and the second surface are opposite to each other), and the substrate is subjected to standard RCA (semiconductor industry standard wet cleaning process) cleaning, ultrapure water rinsing, and nitrogen drying; the epitaxial growth method includes the following steps:

[0047] The substrate was placed in a CVD reaction chamber with the second surface (back surface) as the epitaxial surface, and trichlorosilane and ethylene were introduced (while doping with trimethylaluminum, the doping concentration of trimethylaluminum was 5x10 14 cm -3 ), and epitaxial growth was performed on the second surface of the substrate to a thickness of 50 μm. After cooling to 900°C, the substrate was removed and cooled;

[0048] The substrate was placed in a CVD reaction chamber with the first surface (front surface) as the epitaxial surface, and hydrogen gas (purity 99.99999%) was introduced. Hydrogen etching was performed at 1450°C for 5 min, and the pressure of the hydrogen etching was 120 mbar.

[0049] The temperature was raised to 1620°C, and trichlorosilane and ethylene were introduced (the C / Si stoichiometric ratio was 1.05; while doping with nitrogen, the doping concentration of nitrogen was 4x10 14 cm -3 ). Epitaxial growth was performed on the first surface of the substrate to a thickness of 50 μm at a growth rate of 30 μm / h.

[0050] The introduction of trichlorosilane, ethylene, nitrogen, and hydrogen was stopped, and argon was introduced. The temperature was lowered to 1520°C, and a first in-situ annealing was performed for 15 min.

[0051] The temperature was raised to 1620°C, and the introduction of argon was stopped. Hydrogen, trichlorosilane, and ethylene were introduced again (the C / Si stoichiometric ratio was 1.05; while doping with nitrogen, the doping concentration of nitrogen was 4x10 14 cm -3 ). Epitaxial growth was continued to a thickness of 100 μm at a growth rate of 60 μm / h.

[0052] The introduction of trichlorosilane, ethylene, nitrogen, and hydrogen was stopped, and argon was introduced. The temperature was lowered to 1520°C, and a second in-situ annealing was performed for 5 min. The temperature was then lowered to 1000°C at a rate of 30°C / min, and the substrate was held at 1000°C for 10 min. The temperature was then lowered to 600°C at a rate of 30°C / min, and the substrate was naturally cooled to room temperature. Epitaxial growth of the silicon carbide thick film was completed.

[0053] An optical photograph of the surface of the silicon carbide thick film obtained by the epitaxial growth method of Example 1 is shown in Figure 1 .

[0054] Comparative Example 1

[0055] A method for epitaxial growth of a silicon carbide film, wherein a substrate used in the method is a 4H-SiC substrate having a thickness of 350 μm, the substrate includes a first surface and a second surface (the first surface and the second surface are opposite to each other), and the substrate is subjected to standard RCA (standard wet cleaning process in the semiconductor industry) cleaning, ultrapure water rinsing, and nitrogen drying; the method includes the following steps:

[0056] The substrate is placed in a CVD reaction chamber with the second surface (back surface) as an epitaxial surface, and trichlorosilane and ethylene are introduced at 1620°C (while doping with trimethylaluminum at a doping concentration of 5×10 14 cm -3 Epitaxial growth is performed on the second surface of the substrate to a thickness of 50 μm, and the substrate is removed after being cooled to 900°C;

[0057] The substrate is placed in a CVD reaction chamber with the first surface (front surface) as an epitaxial surface, and hydrogen gas (purity 99.99999%) is introduced, and hydrogen etching is performed at 1450°C for 5 min, the pressure of the hydrogen etching being 120 mbar;

[0058] The temperature is raised to 1620°C, trichlorosilane and ethylene are introduced (the C / Si stoichiometric ratio being 1.05; while doping with nitrogen gas at a doping concentration of 4×10 14 cm -3 Epitaxial growth is performed on the first surface of the substrate to a thickness of 100 μm at a growth rate of 60 μm / h, and the substrate is naturally cooled to room temperature, thereby completing the epitaxial growth of the silicon carbide film.

[0059] Comparative Example 2

[0060] A method for epitaxial growth of a silicon carbide film, wherein a substrate used in the method is a 4H-SiC substrate having a thickness of 350 μm, the substrate includes a first surface and a second surface (the first surface and the second surface are opposite to each other), and the substrate is subjected to standard RCA (standard wet cleaning process in the semiconductor industry) cleaning, ultrapure water rinsing, and nitrogen drying; the method includes the following steps:

[0061] The substrate is placed in a CVD reaction chamber with the second surface (back surface) as an epitaxial surface, and trichlorosilane and ethylene are introduced at 1620°C (while doping with trimethylaluminum at a doping concentration of 5×10 14 cm -3 Epitaxial growth is performed on the second surface of the substrate to a thickness of 50 μm, and the substrate is removed after being cooled to 900°C;

[0062] The substrate is placed in a CVD reaction chamber with the first surface (front surface) as an epitaxial surface, and hydrogen gas (purity 99.99999%) is introduced, and hydrogen etching is performed at 1450°C for 5 min, the pressure of the hydrogen etching being 120 mbar;

[0063] The temperature was raised to 1620°C, and trichlorosilane and ethylene were introduced (C / Si stoichiometric ratio of 1.05; nitrogen was simultaneously doped at a doping concentration of 4 x 10 14 cm -3 ) at a growth rate of 30 pm / h to a thickness of 50 pm on the first side of the substrate;

[0064] The temperature was raised to 1620°C, and trichlorosilane and ethylene were introduced (C / Si stoichiometric ratio of 1.05; nitrogen was simultaneously doped at a doping concentration of 4 x 10 14 cm -3 ) at a growth rate of 30 pm / h to a thickness of 50 pm on the first side of the substrate;

[0065] The introduction of trichlorosilane, ethylene, nitrogen and hydrogen was stopped, argon was introduced, and the temperature was lowered to 1520°C for in-situ annealing for 5 min, then lowered to 1000°C at a rate of 30°C / min for 10 min, then lowered to 600°C at a rate of 30°C / min, and finally naturally cooled to room temperature, thereby completing the epitaxial growth of the silicon carbide film.

[0066] Comparative Example 3

[0067] An epitaxial growth method of a silicon carbide film, wherein the substrate used in the epitaxial growth method is a 4H-SiC substrate with a thickness of 350 pm, the substrate includes a first side and a second side (the first side and the second side are opposite to each other), the substrate is subjected to standard RCA (semiconductor industry standard wet cleaning process) cleaning, ultrapure water rinsing and nitrogen drying; the epitaxial growth method includes the following steps:

[0068] The second side (back side) was used as the epitaxial surface, the substrate was placed in a CVD reaction chamber, trichlorosilane and ethylene were introduced at 1620°C (simultaneously doped with trimethylaluminum at a doping concentration of 5 x 10 14 cm -3 ), and epitaxial growth was performed on the second side of the substrate to a thickness of 50 pm, and then the temperature was lowered to 900°C and the substrate was removed for cooling;

[0069] The first side (front side) was used as the epitaxial surface, the substrate was placed in a CVD reaction chamber, and hydrogen gas (purity of 99.99999%) was introduced, and hydrogen etching was performed at 1450°C for 5 min, and the pressure of the hydrogen etching was 120 mbar;

[0070] The temperature was raised to 1620°C, and trichlorosilane and ethylene were introduced (C / Si stoichiometric ratio of 1.05; nitrogen was simultaneously doped at a doping concentration of 4 x 10 14 cm -3 ) at a growth rate of 30 pm / h to a thickness of 50 pm on the first side of the substrate;

[0071] The introduction of trichlorosilane, ethylene, nitrogen and hydrogen was stopped, argon was introduced, and the temperature was lowered to 1520°C for first in-situ annealing for 15 min;

[0072] The temperature is raised to 1620°C, the argon gas is stopped, and the hydrogen gas, trichlorosilane and ethylene (C / Si stoichiometric ratio of 1.05; nitrogen gas is doped at a doping concentration of 4 x 10 14 cm -3 ) are introduced again. The growth is continued at a growth rate of 60 μm / h to 100 μm, and the silicon carbide thick film is grown by epitaxy.

[0073] Comparative Example 4

[0074] An epitaxial growth method of a silicon carbide film, wherein a substrate is a 4H-SiC substrate having a thickness of 350 μm, and the substrate includes a first surface and a second surface (the first surface and the second surface are opposite to each other), and the substrate is cleaned by a standard RCA (standard wet cleaning process in the semiconductor industry), rinsed with ultrapure water, and dried with nitrogen gas; the epitaxial growth method includes the following steps:

[0075] The second surface (back surface) is used as an epitaxial surface, the substrate is placed in a CVD reaction chamber, trichlorosilane and ethylene (trimethylaluminum is doped at a doping concentration of 5 x 10 14 cm -3 ) are introduced at a temperature of 1620°C, and the second surface of the substrate is epitaxially grown to 50 μm. After being cooled to 900°C, the substrate is taken out and cooled;

[0076] The first surface (front surface) is used as an epitaxial surface, the substrate is placed in a CVD reaction chamber, and hydrogen gas (purity of 99.99999%) is introduced. Hydrogen etching is performed at a temperature of 1450°C for 5 min, and the pressure of the hydrogen etching is 120 mbar;

[0077] The temperature is raised to 1620°C, the argon gas is stopped, and the hydrogen gas, trichlorosilane and ethylene (C / Si stoichiometric ratio of 1.05; nitrogen gas is doped at a doping concentration of 4 x 10 14 cm -3 ) are introduced again. The growth is continued at a growth rate of 60 μm / h to 100 μm, and the silicon carbide thick film is grown by epitaxy.

[0078] The introduction of the trichlorosilane, ethylene, nitrogen gas and hydrogen gas is stopped, argon gas is introduced, and the first in-situ annealing is performed at a temperature of 1300°C for 15 min;

[0079] The temperature is raised to 1620°C, the argon gas is stopped, and the hydrogen gas, trichlorosilane and ethylene (C / Si stoichiometric ratio of 1.05; nitrogen gas is doped at a doping concentration of 4 x 10 14 cm -3 ) are introduced again. The growth is continued at a growth rate of 60 μm / h to 100 μm, and the silicon carbide thick film is grown by epitaxy.

[0080] The silicon carbide film is epitaxially grown by stopping the introduction of trichlorosilane, ethylene, nitrogen and hydrogen, introducing argon, and performing a second in-situ annealing at 1520°C for 5 minutes, then cooling to 1000°C at a cooling rate of 30°C / min and maintaining the temperature for 10 minutes, then continuing to cool to 600°C at a cooling rate of 30°C / min, and finally naturally cooling to room temperature.

[0081] Comparative Example 5

[0082] An epitaxial growth method of a silicon carbide film, wherein a substrate used in the epitaxial growth method is a 4H-SiC substrate having a thickness of 350 μm, the substrate includes a first surface and a second surface (the first surface and the second surface are opposite to each other), and the substrate is subjected to standard RCA cleaning, ultrapure water rinsing, and nitrogen drying; the epitaxial growth method includes the following steps:

[0083] The substrate is placed in a CVD reaction chamber with the second surface (back surface) as an epitaxial surface, trichlorosilane and ethylene are introduced at 1620°C (while doping with trimethylaluminum, the doping concentration of the trimethylaluminum is 5×10 14 cm -3 ), and epitaxial growth is performed on the second surface of the substrate to a thickness of 50 μm, and then the substrate is removed after cooling to 900°C;

[0084] The substrate is placed in a CVD reaction chamber with the first surface (front surface) as an epitaxial surface, hydrogen gas (purity 99.99999%) is introduced, and hydrogen etching is performed at 1450°C for 5 minutes, the pressure of the hydrogen etching is 120 mbar;

[0085] The temperature is raised to 1620°C, trichlorosilane and ethylene are introduced (the C / Si stoichiometric ratio is 1.05; while doping with nitrogen, the doping concentration of the nitrogen is 4×10 14 cm -3 ), and epitaxial growth is performed on the first surface of the substrate to a thickness of 50 μm at a growth rate of 30 μm / h;

[0086] The temperature is maintained at 1620°C, the introduction of trichlorosilane, ethylene, nitrogen and hydrogen is stopped, and argon is introduced, and the temperature is maintained for 15 minutes;

[0087] The temperature is maintained at 1620°C, the introduction of argon is stopped, and hydrogen, trichlorosilane and ethylene are introduced again (the C / Si stoichiometric ratio is 1.05; while doping with nitrogen, the doping concentration of the nitrogen is 4×10 14 cm -3 ), and epitaxial growth is continued to a thickness of 100 μm at a growth rate of 60 μm / h;

[0088] After the silicon carbide film is epitaxially grown, the silicon trichloride, ethylene, nitrogen and hydrogen are stopped, and the argon is introduced to perform in-situ annealing for 5 minutes at 1520℃, and then the temperature is decreased to 1000℃ at a rate of 30℃ / min, and the temperature is kept for 10 minutes, and then the temperature is continuously decreased to 600℃ at a rate of 30℃ / min, and finally the temperature is naturally cooled to room temperature, and the epitaxial growth of the silicon carbide film is completed.

[0089] Comparative Example 6

[0090] An epitaxial growth method of a silicon carbide film, which is different from that of Example 1 in that the sample is taken out in the middle of the epitaxial growth on the first surface of the substrate. The other is the same as that of Example 1.

[0091] The optical photograph of the surface of the silicon carbide film obtained by the epitaxial growth method of Comparative Example 6 is shown in FIG. 6. Figure 2

[0092] Reference Figure 1 and Figure 2 It can be seen that the surface of the silicon carbide film obtained by Comparative Example 6 is seriously contaminated due to the sample being taken out in the epitaxial growth.

[0093] Performance test

[0094] The local maximum flatness, bending degree and warping degree of the products obtained by the epitaxial growth methods of Example 1 and Comparative Examples 1-5 are tested, and the test method is referred to GB / T 12964-2018. The test results are shown in Table 1.

[0095] Table 1

[0096]

[0097] It can be seen from Table 1 that, by comparing the test data of Example 1 and each comparative example, it can be seen that the silicon carbide thick film epitaxial growth method of the present application has significant advantages in improving the surface state and stress control of the thick film:

[0098] The local maximum flatness, bending degree and warping degree of Example 1 are significantly better than those of Comparative Example 1, which uses a one-time high-speed growth and natural cooling epitaxial growth method, and does not perform step-by-step epitaxy and in-situ annealing. The bending degree and warping degree are much higher than those of Example 1, which shows that the step-by-step strategy of twice epitaxy and twice in-situ annealing can effectively inhibit the stress accumulation in the growth of the thick film, and greatly improve the bending and warping degree of the wafer.

[0099] ​Comparative Example 1 and Comparative Example 2, although using step growth, no intermediate in-situ annealing is set between the two growths, and only one annealing is performed after continuous growth, and the bending degree and warping degree are still higher than that of Example 1, which proves that the intermediate in-situ annealing plays a key role in releasing the stress of the first stage growth and optimizing the surface state, and the lack of this step will lead to the stress not being relaxed in time, and then affect the final morphology index;

[0100] Comparative Example 3 is not subjected to controlled cooling after step and intermediate annealing, but is naturally cooled to room temperature, and the warping degree is obviously higher than that of Example 1, which shows that the controlled cooling design of the final slow cooling and medium temperature holding can further relieve the thermal stress in the cooling process, and is an important link to reduce the warping degree;

[0101] Comparative Example 4 reduces the intermediate in-situ annealing temperature to 1300℃ (deviating from the atomic high activity interval), and Comparative Example 5 does not reduce the temperature (maintaining the growth temperature) during intermediate annealing, and the warping degrees of both are higher than that of Example 1, which shows that the intermediate annealing needs to be controlled in the temperature range of “slightly lower than the growth temperature but in the atomic high activity interval”, so as to effectively promote the lattice relaxation and defect repair, and the temperature that is too high or too low will weaken the stress release effect of annealing.

[0102] In the description of the present specification, the terms “first”, “second” are only used for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with “first”, “second” can explicitly or implicitly include at least one of the features.

[0103] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the method of the present application, a number of improvements and supplements can also be made, and these improvements and supplements should also be considered as the protection scope of the present application.

Claims

1. A method for epitaxial growth of silicon carbide thick films, characterized in that, Includes the following steps: Step S1: Introduce a first reaction source at a first temperature and grow to a first thickness on the first surface of the substrate at a first growth rate; Step S2: Stop the flow of the first reaction source, introduce inert gas, and perform the first in-situ annealing under the condition of cooling to the second temperature; Step S3: Under the condition of heating to the first temperature, stop the inert gas supply, and introduce the first reaction source again to continue growing to the target thickness at the second growth rate; Step S4: Stop the flow of the first reaction source, introduce the inert gas, and perform the second in-situ annealing under the condition of cooling to the second temperature; The C / Si stoichiometric ratio in the first reaction source is 1.05-1.1; the carbon source in the first reaction source is ethylene, and the silicon source is trichlorosilane. The first temperature is 1580℃-1650℃, and the second temperature is 1500℃-1550℃; The first growth rate is 30 μm / h, and the second growth rate is 60 μm / h; The first in-situ annealing time is 15 min-30 min, and the second in-situ annealing time is 5 min-10 min; The first thickness is 40μm-50μm, and the target thickness is not less than 100μm.

2. The epitaxial growth method for silicon carbide thick films according to claim 1, characterized in that, The substrate is made of 4H-SiC and has a thickness of 350 μm.

3. The epitaxial growth method for silicon carbide thick films according to claim 2, characterized in that, Step S0 is included before step S1, and step S0 includes: A second reaction source is introduced under the first temperature condition, and the substrate is grown to a second thickness on the second surface. The second side is the side opposite to the first side; the second thickness is the same as the first thickness.

4. The epitaxial growth method for silicon carbide thick films according to claim 3, characterized in that, The second reaction source is doped with trimethylaluminum, and the doping concentration of trimethylaluminum is 4 × 10⁻⁶. 14 cm -3 - 8×10 14 cm -3 .

5. The epitaxial growth method for silicon carbide thick films according to claim 1, characterized in that, Before step S1, the first surface undergoes a surface treatment, which includes the following steps: Hydrogen etching was performed at 1350℃-1450℃ for 5-10 minutes. The hydrogen etching pressure is 80 mbar-120 mbar.

6. The epitaxial growth method for silicon carbide thick films according to claim 1, characterized in that, The first reaction source is doped with a first dopant source, which is either ammonia or nitrogen, and the doping concentration of the first dopant source is 4 × 10⁻⁶. 14 cm -3 - 8×10 14 cm -3 .

7. The epitaxial growth method for silicon carbide thick films according to claim 1, characterized in that, In step S4, after the second in-situ annealing is completed, the temperature is lowered to the third temperature at the first cooling rate and held at that temperature. Then, the temperature is lowered to the fourth temperature at the first cooling rate and allowed to cool naturally to room temperature. The third temperature is 1000℃, and the fourth temperature does not exceed 600℃; The heat preservation time is 10-15 minutes; The first cooling rate is 30℃ / min.

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