A silicon carbide epitaxial growth method for reducing native defects

Abstract

The present invention provides a method for epitaxial growth of silicon carbide to reduce native defects. Under the predetermined temperature of not less than 1500°C and the predetermined pressure of not less than 50 mbar defined in step S1, hydrogen is introduced in step S2 to etch the doped silicon carbide substrate. In this step, a doping source gas of not less than 0.06% of the hydrogen flow rate is introduced to adjust the collision frequency between hydrogen molecules and the substrate, thereby reducing or avoiding the situation where hydrogen etching may lead to excessive removal of the substrate atomic layer. In step S3, in addition to the introduction of hydrogen and doping source gases, a chlorine-containing gas of not more than 0.4% of the hydrogen flow rate is introduced to cooperate with the hydrogen to refine the etching and enhance the mobility of the etched carbon and silicon to avoid the formation of silicon clusters on the substrate. A carbon-containing source gas of not more than 0.04% of the hydrogen flow rate is introduced to fill the carbon vacancies caused by etching by carbon atom migration, thereby reducing deep energy level traps caused by lattice defects.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor device processing, and in particular to a silicon carbide epitaxial growth method for reducing native defects. Background Art

[0002] With the rapid growth in demand for high-frequency, high-power radio frequency and power electronics, such as 5G and new energy, the physical limits of silicon-based semiconductor devices are becoming increasingly apparent. How to increase power while limiting device size, controlling heat generation, and controlling the rapid cost inflation have become key concerns within the semiconductor industry. In this context, third-generation semiconductor materials, led by silicon carbide, are gradually transitioning from scientific research to industrialization, becoming a clear replacement for some silicon-based power devices. To promote the practical application of SiC devices, establishing high-quality epitaxial growth technology is essential.

[0003] Defects from the substrate will gradually diffuse or evolve to the epitaxial layer as the epitaxial growth progresses, resulting in an increase in surface defects on the SiC epitaxial wafer. In addition, based on the high conductivity requirements of some semiconductor devices, it is necessary to grow functional layers such as doped buffer layers and doped epitaxial layers on the doped substrate. However, due to the structure of the epitaxial growth equipment itself or the epitaxial growth process, the doping concentration difference between the substrate and the buffer layer is too large, causing high stress per unit length, thereby reducing the blocking effect on native defects and generating or increasing stacking faults and basal plane dislocations. These defects will restrict the performance of devices made on the SiC epitaxial wafer.

[0004] Therefore, there is an urgent need to provide a new silicon carbide epitaxial growth method that can reduce native defects. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides a method for epitaxial growth of silicon carbide with reduced native defects, which is beneficial to reducing stacking faults and basal plane dislocations and improving epitaxial quality.

[0006] The method for epitaxial growth of silicon carbide with reduced native defects of the present invention comprises the following steps:

[0007] S1: placing a doped silicon carbide substrate in a reaction chamber, introducing hydrogen into the reaction chamber, and controlling the reaction chamber to reach a predetermined temperature of not less than 1500° C. and a predetermined pressure of not less than 50 mbar;

[0008] S2: adjusting the flow rate of the hydrogen gas to a first flow rate, and introducing a doping source gas into the reaction chamber at a second flow rate that is not less than 0.06% of the first flow rate to perform a first surface pretreatment on the silicon carbide substrate;

[0009] S3: maintaining the first flow rate unchanged, adjusting the second flow rate to no less than 0.3% of the first flow rate, introducing a chlorine-containing gas into the reaction chamber at a third flow rate no more than 0.4% of the first flow rate, and introducing a carbon-containing source gas at a fourth flow rate no more than 0.04% of the first flow rate, to perform a second surface pretreatment on the surface of the substrate obtained in step S2;

[0010] S4: introducing the hydrogen gas, the doping source gas, the silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas into the reaction chamber to grow a doping buffer layer on the surface of the substrate obtained in step S3.

[0011] Optionally, in step S1, the predetermined temperature does not exceed 1700° C., and the predetermined pressure does not exceed 500 mbar.

[0012] Optionally, in step S2, the time for the first surface pretreatment is between 3 minutes and 15 minutes.

[0013] Optionally, in step S2, performing a first surface pretreatment on the silicon carbide substrate further includes:

[0014] S21: after stopping the introduction of the hydrogen gas into the reaction chamber, introducing the doping source gas into the reaction chamber at the second flow rate, and controlling the duration of introducing the doping source gas to be the first duration;

[0015] S22: After stopping the introduction of the dopant source gas into the reaction chamber, introducing the hydrogen gas into the reaction chamber at the first flow rate, and controlling the second duration of the introduction of the hydrogen gas to be no less than the first duration;

[0016] S23: alternately perform step S21 and step S22 until the duration of the first surface pretreatment is 3 minutes to 15 minutes.

[0017] Optionally, the first duration does not exceed 5 seconds, and the second duration is 1 to 3 times the first duration.

[0018] Optionally, in step S2, the first flow rate is between 80 slm and 150 slm; and the second flow rate does not exceed 1% of the first flow rate.

[0019] Optionally, in step S3, the duration of the second surface treatment does not exceed 30 seconds, the second flow rate is not less than 0.3% of the first flow rate and does not exceed 1% of the first flow rate, the third flow rate is 0.2%~0.4% of the first flow rate, and the fourth flow rate is 0.003%~0.04% of the first flow rate.

[0020] Optionally, the chlorine-containing gas includes hydrogen chloride, the doping source gas includes trimethylaluminum, borane, nitrogen, ammonia or phosphine, the silicon-containing source gas includes silane, trichlorosilane or dichlorosilane, and the carbon-containing source gas includes propane, ethylene, methane or acetylene.

[0021] Optionally, the doped silicon carbide substrate is an N-type doped beveled substrate or a P-type doped beveled substrate, the beveled angle of the beveled substrate does not exceed 8 degrees, the beveled direction is that the c-axis deviates to the (1-102) crystal plane, the (11-20) crystal plane or the (10-10) crystal plane, and the doping concentration of the doped silicon carbide substrate is not less than 1×10 18 cm -3 .

[0022] Optionally, in step S4, the step of growing a doped buffer layer on the surface of the substrate obtained in step S3 includes:

[0023] S41: while maintaining the first flow rate of the hydrogen gas and the second flow rate of the dopant source gas unchanged, the chlorine-containing gas, the silicon-containing source gas, and the carbon-containing source gas are introduced into the reaction chamber so that the carbon-to-silicon ratio is 1-1.2 and the chlorine-to-silicon ratio is 1-20, thereby forming a first doped buffer layer having the same doping type as the doped silicon carbide substrate.

[0024] S42: maintaining the flow rates of the hydrogen, chlorine-containing gas, silicon-containing source gas and carbon-containing source gas unchanged, and adjusting the flow rate of the doping source gas to be lower than the flow rate of the doping source gas introduced in step S41 to form a second doping buffer layer.

[0025] Optionally, in step S41, the flow rate of the doping source gas is not less than 0.3% of the first flow rate and not more than 1% of the first flow rate. In steps S41 and S42, the flow rate of the silicon-containing source gas is not less than 0.1% of the first flow rate, so that the growth rate of the first doped buffer layer and the second doped buffer layer is not less than 10 microns / hour.

[0026] Optionally, the duration of step S42 is greater than the duration of step S41;

[0027] Repeating step S42, and adjusting the flow rate of the doping source gas introduced in each step to be lower than the flow rate of the doping source gas introduced in the previous step, and the duration of each step being longer than the duration of the previous step, until an Nth doped buffer layer is formed, and the thickness of each doped buffer layer increases sequentially along the growth direction, and the doping concentration decreases sequentially along the growth direction, where N is a positive integer greater than 2;

[0028] Among the N doped buffer layers, the thickness of the xth doped buffer layer is h x Satisfy: h x =0.2h(x-1) -0.1, where h (x-1) is the thickness of the (x-1)th doped buffer layer, and the (x-1)th doped buffer layer is closer to the doped silicon carbide substrate than the xth doped buffer layer.

[0029] Optionally, in step S41 and step S42, the flow rate of the chlorine-containing gas is 2000 sccm to 5000 sccm, the flow rate of the silicon-containing source gas is 200 sccm to 400 sccm, and the flow rate of the carbon-containing source gas is 70 sccm to 155 sccm;

[0030] In step S41, the flow rate of the doping source gas is 500 sccm to 2000 sccm, so that the doping concentration of the first doped buffer layer is 2×10 18 cm -3 ~ 9×10 18 cm -3 ;

[0031] In step S42, the flow rate of the doping source gas is 50 sccm to 400 sccm, so that the doping concentration of the second doped buffer layer is 9×10 17 cm -3 ~ 2×10 18 cm -3 .

[0032] Optionally, it also includes: step S5: maintaining the first flow rate of the hydrogen gas, controlling the flow rate of the doping source gas to be lower than the minimum flow rate of the doping source gas introduced in step S4, and the flow rates of the silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas to be higher than the flow rates of the corresponding silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas introduced in step S4, so as to grow an epitaxial layer on the doping buffer layer.

[0033] Optionally, a step of growing a transition layer is further included between step S4 and step S5:

[0034] Keep introducing hydrogen at the first flow rate, linearly reduce the flow rate of the doping source gas until it reaches the doping source gas flow rate introduced in step S5, and linearly increase the flow rates of the silicon-containing source gas, the carbon-containing source gas, and the chlorine-containing gas until they reach the corresponding flow rates of the silicon-containing source gas, the carbon-containing source gas, and the chlorine-containing gas introduced in step S5.

[0035] Optionally, the following steps are further included between step S4 and step S5: stopping the introduction of the doping source gas, the silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas, and maintaining the introduction of the hydrogen gas at the first flow rate for purging and cleaning.

[0036] Optionally, in step S5, the flow rate of the carbon-containing source gas is 90 sccm~200 sccm; the flow rate of the silicon-containing source gas is 250 sccm~500 sccm; the flow rate of the chlorine-containing gas is 2500 sccm~5000 sccm, and the flow rate of the doping source gas is 50 sccm~150 sccm, so that the growth rate of the epitaxial layer is not less than 60 μm / h.

[0037] Optionally, the doped silicon carbide substrate is controlled to rotate at a speed not less than 300 rpm.

[0038] The silicon carbide epitaxial growth method for reducing native defects of the present invention has the following beneficial effects:

[0039] Under the predetermined temperature of not less than 1500°C and the predetermined pressure of not less than 50 mbar defined in step S1, hydrogen is introduced in step S2 to etch the doped silicon carbide substrate, thereby removing irregular areas raised on the substrate surface, such as the subsurface damage layer remaining from mechanical polishing. In addition, in this step, a dopant source gas of not less than 0.06% of the hydrogen flow rate is introduced to regulate the collision frequency between hydrogen molecules and the substrate, reducing or avoiding the situation where hydrogen etching may cause excessive removal of substrate atomic layers. In step S3, on the basis of the introduction of hydrogen and dopant source gases, a chlorine-containing gas of not more than 0.4% of the hydrogen flow rate is introduced to cooperate with hydrogen etching, which is beneficial to enhancing the mobility of the etched carbon and silicon and avoiding the formation of silicon clusters on the substrate. A carbon-containing source gas of not more than 0.04% of the hydrogen flow rate is introduced to fill the carbon vacancies caused by etching by carbon atom migration, thereby reducing deep energy level traps caused by lattice defects and avoiding triangular defects caused by carbon-rich due to excessive carbon-containing source gas concentration. The doping source gas of a certain flow rate introduced in step S2 and step S3 can also form the atmosphere environment required for high doping in advance in the reaction chamber, making the doping concentration of the subsequent buffer layer closer to the substrate doping concentration, and reducing basal plane dislocations and stacking faults caused by sudden changes in doping concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of a reaction chamber for performing the silicon carbide epitaxial growth method of the present invention is shown.

[0041] Figure 2 It is a schematic flow chart of the silicon carbide epitaxial growth method of the present invention.

[0042] Figure 3 Shown by Figure 2 Schematic diagram of a silicon carbide epitaxial wafer produced by the method shown.

[0043] Figure 4 and Figure 5The near-ultraviolet photoluminescence images of the silicon carbide epitaxial wafer prepared in Comparative Example 1 and the silicon carbide epitaxial wafer prepared by the method of Example 3 are shown respectively. DETAILED DESCRIPTION

[0044] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0045] The present invention provides a method for epitaxial growth of silicon carbide with reduced native defects, which is performed using epitaxial growth equipment. The epitaxial growth equipment can be a chemical vapor deposition (CVD) device, and further, can be a plasma-enhanced chemical vapor deposition (PECVD) device, a metal-organic chemical vapor deposition (MOCVD) device, or the like. An embodiment of the present invention provides an MOCVD device to achieve the above-mentioned silicon carbide epitaxial growth. It should be understood that this device is merely exemplary, and the epitaxial growth equipment used to implement the silicon carbide epitaxial growth method of the present invention is not limited to this type.

[0046] like Figure 1 As shown, the epitaxial growth device of the present invention has a reaction chamber 5, in which a carrier 1 for carrying a substrate 200 is provided. In the present invention, the substrate 200 is a doped silicon carbide substrate. The reaction chamber 5 is also provided with a gas injection mechanism 4 for providing process gas into the reaction chamber 5. The gas injection mechanism 4 is arranged opposite to the carrier 1. Specifically, the gas outlet side of the gas injection mechanism 4 is arranged opposite to the top surface 11 of the carrier 1 for carrying the substrate 200. The bottom surface 12 of the carrier 1 is also provided with a heating device 2, which can heat the carrier 1 and heat the substrate 200 carried by the carrier 1 through heat transfer. As shown Figure 1 As shown, the epitaxial growth equipment of the present invention also includes a rotation drive device 3, which is arranged in a dynamic sealing manner in the reaction chamber 5 and is fixedly connected to the middle of the carrier 1 to drive the carrier 1 to drive the substrate 200 to rotate around the rotation axis T2 during the epitaxial reaction.

[0047] The cross section of the reaction chamber 5 of the epitaxial growth equipment is generally circular or quasi-circular, or it can be a rectangular structure or other structures well known to those skilled in the art, which will not be described in detail here. In the present invention, the reaction chamber 5 is a vertical flow chamber with vertical gas intake. The reaction chamber 5 can be a vertical chamber in which the gas injection mechanism 4 and the carrier 1 are arranged opposite to each other, and the gas injection mechanism 4 is located at the upper part and the carrier 1 is located at the lower part. This embodiment is based on Figure 1 The cross section of the reaction chamber 5 shown is circular, and the gas injection mechanism 4 is located at the top and the supporting platform 1 is located at the bottom. The gas injection mechanism 4 provided in this embodiment has a disc-shaped structure as a whole.

[0048] Also refer to Figure 1 As shown, a main axis T1 is defined, which is perpendicular to the outlet surface of the disc-shaped gas injection mechanism 4 and passes through the geometric center of the outlet surface of the gas injection mechanism 4. The main axis T1 may be parallel to or non-parallel to the rotation axis T2 of the supporting platform 1. Preferably, the main axis T1 is parallel to the rotation axis T2 of the supporting platform 1 (that is, the central axis of the top surface of the supporting platform 1). Preferably, the main axis T1 coincides with the rotation axis T2.

[0049] The top surface 11 of the carrier 1 is provided with a plurality of recesses 100, which are recessed from the top surface 11 toward the bottom surface 12. The size, number, and distribution of the recesses 100 on the carrier 1 can be designed based on the size, thickness, and number of substrates 200 to be supported and retained, as well as the size of the carrier 1. For substrates 200, which are typically disc-shaped, the recesses 100 are designed with circular openings, and the opening size is set to correspond to the size of the substrate 200.

[0050] like Figure 2 As shown, the silicon carbide epitaxial growth method for reducing native defects of the present invention includes steps S1 to S4, specifically:

[0051] S1: placing a doped silicon carbide substrate in a reaction chamber, introducing hydrogen into the reaction chamber, and controlling the reaction chamber to reach a predetermined temperature of not less than 1500° C. and a predetermined pressure of not less than 50 mbar;

[0052] S2: adjusting the flow rate of the hydrogen gas to a first flow rate, and introducing a doping source gas into the reaction chamber at a second flow rate that is not less than 0.06% of the first flow rate to perform a first surface pretreatment on the silicon carbide substrate;

[0053] S3: maintaining the first flow rate unchanged, adjusting the second flow rate to no less than 0.3% of the first flow rate, introducing a chlorine-containing gas into the reaction chamber at a third flow rate no more than 0.4% of the first flow rate, and introducing a carbon-containing source gas at a fourth flow rate no more than 0.04% of the first flow rate, to perform a second surface pretreatment on the surface of the substrate obtained in step S2;

[0054] S4: introducing the hydrogen gas, the doping source gas, the silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas into the reaction chamber to grow a doping buffer layer on the surface of the substrate obtained in step S3.

[0055] In some embodiments, the doped silicon carbide in step S1 may be an N-type doped substrate or a P-type doped substrate. The N-type doping may be, for example, nitrogen doping, and the P-type doping may be, for example, aluminum doping or boron doping.

[0056] In some embodiments, when the substrate is a P-type doped substrate, the doping source gas is a P-type doping source gas, such as trimethylaluminum or borane.

[0057] In some embodiments, the doped silicon carbide substrate is an N-type doped or P-type doped beveled substrate, and the bevel angle does not exceed 8 degrees.

[0058] In SiC homoepitaxial growth, to further ensure that the epitaxial material effectively inherits the stacking sequence of the substrate and guarantee the quality of the epitaxial crystal, a beveled substrate, cut along the c-axis, can be used to introduce atomic-level steps on the substrate surface. During the epitaxial growth process, adsorbed atoms tend to nucleate and grow at the steps, ensuring that the epitaxial process proceeds in a step-flow pattern.

[0059] In some specific embodiments, the beveled substrate is a silicon carbide substrate with a c-axis tilted 4° or 8° toward the <11-20> direction. The silicon carbide substrate is an N-type doped substrate, such as a nitrogen-doped substrate with a doping concentration of 1×10 18 cm -3 ~9×10 19 cm -3 .

[0060] In some specific embodiments, the doping concentration of the doped silicon carbide substrate is not less than 1×10 19 cm -3 .

[0061] In some embodiments, the c-axis of the c-cut substrate is tilted toward a (1-102) crystal plane, a (11-20) crystal plane, or a (10-10) crystal plane.

[0062] In some embodiments, the doping source gas for forming the N-type doped substrate is an N-type doping source gas, which may be nitrogen, ammonia, or phosphine.

[0063] In some specific embodiments, hydrogen gas is introduced into the reaction chamber, and the pressure in the reaction chamber containing the silicon carbide substrate is controlled to reach a predetermined temperature of no less than 1500°C and a predetermined pressure of no less than 50 mbar. Furthermore, the predetermined temperature is no more than 1700°C, and the predetermined pressure is no more than 500 mbar.

[0064] The temperature and pressure control of steps S2 to S4 are the growth conditions for homoepitaxial growth of silicon carbide. Each step is performed under the epitaxial growth conditions, especially after the in-situ surface treatment of the doped silicon carbide substrate is achieved in conjunction with the various flow conditions defined in the above steps S2 and S3. There is no need to adjust the process parameters of the subsequent doped buffer layer and epitaxial layer, which can improve production efficiency.

[0065] In some embodiments, after the doped silicon carbide substrate is placed in the reaction chamber, the rotation drive device 3 is turned on to drive the carrier 1 to rotate the silicon carbide substrate at a predetermined speed. Optionally, the doped silicon carbide substrate is controlled to rotate at a speed of not less than 300 rpm.

[0066] In the existing technology, due to the limitations of the structure of the epitaxial growth equipment itself or the epitaxial growth process, the doping concentration difference between the doped substrate and the doped buffer layer is too large. The sudden change in doping concentration will cause high stress per unit length of the substrate, thereby reducing the blocking effect of native defects and causing the generation of stacking faults and basal plane dislocations.

[0067] In the process of epitaxial growth of silicon carbide using epitaxial growth equipment, it was found that in an atmosphere with a temperature of not less than 1500°C and a pressure of not less than 50 mbar, a certain amount of doping source gas was introduced during the surface pretreatment of the doped silicon carbide substrate using hydrogen and hydrogen chloride in steps S2 and S3, and the doping concentration of the subsequently grown doped buffer layer was not less than 10 18 cm -3 , which is beneficial to narrowing the gap in doping concentration between the doped silicon carbide substrate and the doped buffer layer, and reducing stacking faults and basal plane dislocations.

[0068] Within the growth process space of the epitaxial growth equipment, the surfaces of the susceptor or chamber inner wall (e.g., graphite or silicon carbide coating) exhibit certain adsorption properties. The parasitic growth layer of polycrystalline silicon carbide formed on the chamber wall or susceptor during the epitaxial growth process also exhibits certain adsorption properties. Under an atmosphere of a temperature of not less than 1500°C and a pressure of not less than 50 mbar, an appropriate amount of dopant source gas can establish a dynamic adsorption-desorption equilibrium between the exposed surfaces of the chamber walls and susceptor and the process space. This creates a certain dopant source gas atmosphere within the chamber prior to the dopant buffer layer growth process, which helps the buffer layer's doping concentration more closely approximate the substrate's doping concentration and reduces basal plane dislocations and stacking faults.

[0069] Furthermore, hydrogen has an isotropic tendency to preferentially etch away raised irregularities on the substrate surface, such as the subsurface damage layer left over from mechanical polishing. This reduces surface roughness and creates a suitable interface for epitaxial growth. The introduction of a small amount of dopant source gas (such as nitrogen) can regulate the collision frequency of hydrogen molecules, avoiding the potential for excessive atomic layer removal when etching doped silicon carbide substrates with pure hydrogen, thereby mitigating or preventing lattice damage caused by excessive atomic loss from the substrate.

[0070] In some embodiments, the first surface pretreatment lasts for 3 minutes to 15 minutes, wherein the first flow rate of the hydrogen gas is 80 slm to 200 slm, and the second flow rate of the dopant source gas does not exceed 1% of the first flow rate.

[0071] In some embodiments, in step S2 , hydrogen gas and dopant source gas are introduced simultaneously at the aforementioned respective flow rates until the introduction time is 3 min to 15 min to complete the first surface pretreatment of the doped silicon carbide substrate.

[0072] In some embodiments, hydrogen gas and dopant source gas are introduced alternately, specifically including:

[0073] S21: After stopping the introduction of hydrogen into the reaction chamber, introducing a doping source gas into the reaction chamber at a second flow rate, and controlling the duration of introducing the doping source gas to be the first duration;

[0074] S22: After stopping the introduction of the dopant source gas into the reaction chamber, introducing hydrogen gas into the reaction chamber at a first flow rate, and controlling the second duration of the introduction of hydrogen gas to be not less than the first duration;

[0075] S23: Alternately perform step S21 and step S22 until the duration of the first surface pretreatment is 3 minutes to 15 minutes.

[0076] During the process of alternately introducing nitrogen and hydrogen, by controlling the duration and flow rate of the doping source gas and hydrogen respectively, an appropriate amount of doping source gas can form a dynamic adsorption-desorption equilibrium between the exposed surfaces of the chamber wall and the base and the process space, thereby creating a certain doping source gas atmosphere in the chamber before the doping buffer layer growth process.

[0077] In a further embodiment, in step S21, the first duration of introducing the dopant source gas is no longer than 5 seconds, and the second duration of introducing the hydrogen gas is 1 to 3 times the first duration. Controlling the first and second durations ensures that the hydrogen gas fully and rapidly etches and optimizes the substrate surface, while also mitigating or avoiding lattice damage caused by excessive atomic loss from the substrate during pure hydrogen etching.

[0078] If the dopant source gas is introduced for too long in step S21, a large number of atoms in the dopant source gas, such as a large number of nitrogen atoms, may enter the parasitic growth layer. During the subsequent growth of the doped buffer layer or doped epitaxial layer, the presence of the hydrogen atmosphere may etch these parasitic growth layers, leading to the precipitation of a large number of nitrogen atoms. This may cause dopant tailing in the epitaxial layer, affect the normal doping concentration, and thus affect device performance.

[0079] In some embodiments, the first duration in step S21 is 2 to 5 seconds. If the duration of introducing the dopant source gas in step S21 is too short, it is not conducive to forming the aforementioned highly doped atmosphere and cannot achieve the aforementioned function of regulating the collision frequency of hydrogen gas molecules.

[0080] After the first surface treatment process is completed, the gas and gas flow rate introduced into the reaction chamber are adjusted to perform a second surface pretreatment on the doped silicon carbide substrate. Specifically, in step S3, the first flow rate is maintained constant, the second flow rate is adjusted to be no less than 0.3% of the first flow rate, a chlorine-containing gas is introduced into the reaction chamber at a third flow rate not exceeding 0.4% of the first flow rate, and a carbon-containing source gas is introduced at a fourth flow rate not exceeding 0.04% of the first flow rate, thereby performing the second surface pretreatment on the substrate surface obtained in step S2.

[0081] In step S3, hydrogen gas is continuously introduced into the reaction chamber at the first flow rate from step S2, while the second flow rate of the dopant source gas is adjusted to be no less than 0.3% of the first flow rate. Simultaneously, chlorine-containing gas is introduced at a third flow rate not exceeding 0.4% of the first flow rate, and carbon-containing source gas is introduced at a fourth flow rate not exceeding 0.04% of the first flow rate.

[0082] In some embodiments, the second surface pretreatment lasts no longer than 30 seconds.

[0083] In some other embodiments, the third flow rate of the chlorine-containing gas is 0.2%-0.4% of the first flow rate; and the fourth flow rate of the carbon source gas is 0.003%-0.04% of the first flow rate.

[0084] In some embodiments, the chlorine-containing gas is hydrogen chloride gas, and the carbon-containing source gas includes any one of propane, ethylene, methane, and acetylene.

[0085] In the second surface pretreatment process of step S3, a chlorine-containing gas of no more than 0.4% of the first flow rate is introduced in combination with hydrogen etching, which can enhance the mobility of C and Si atoms, so that the etched C and Si atoms leave the reaction interface of the substrate, provide a clean substrate surface for subsequent epitaxial growth, and reduce or prevent the appearance of polycrystalline in the subsequent epitaxial growth process; in addition, the chlorine-containing gas plays a role in reducing or preventing Si-Si bonding, avoiding the formation of silicon clusters on the substrate due to Si-Si bonding, which affects the quality of subsequent epitaxial layer growth. A carbon-containing source gas of no more than 0.04% of the first flow rate is introduced, and carbon atoms are used to migrate to fill carbon vacancies caused by etching, thereby reducing deep energy level traps caused by lattice defects. If the flow rate of the carbon-containing source gas is too high, it is easy to affect the subsequent epitaxial layer growth due to carbon enrichment, resulting in triangular defects.

[0086] After the doped silicon carbide substrate undergoes the first and second surface pretreatment processes, a doped buffer layer is grown on the surface of the doped silicon carbide substrate. Specifically, in step S4, the hydrogen gas, the dopant source gas, the silicon-containing source gas, the carbon-containing source gas, and the chlorine-containing gas are introduced into the reaction chamber to grow the doped buffer layer on the surface of the substrate obtained in step S3.

[0087] As described above, under the process conditions of step S1, through the first surface pretreatment of step S2 and the second surface pretreatment of step S3, a doping nitrogen source is introduced into the reaction chamber and its flow rate is controlled to form a doping atmosphere in advance. The hydrogen control of step S2 combined with the control of step S3 also pre-treats the surface of the substrate, which is beneficial to reducing defects such as dislocations. On this basis, a doped buffer layer is formed on the doped silicon carbide substrate, and the doped buffer layer has the same doping type as the doped silicon carbide. In some embodiments, the above-mentioned doped buffer layer is a single-layer structure with a single doping concentration; in other embodiments, the above-mentioned doped buffer layer is a multi-layer structure with different doping concentrations.

[0088] The thickness of the doped buffer layer can be controlled according to the thickness of the epitaxial layer to be formed subsequently and the performance requirements of the semiconductor device. For example, in some embodiments, the thickness of the doped buffer layer is 5% to 15% of the thickness of the epitaxial layer.

[0089] In some embodiments, when growing the doped buffer layer, hydrogen is continuously introduced as the atmosphere gas, and the flow rate is maintained at the same rate as the first flow rate in step S3. Simultaneously, a dopant source gas is continuously introduced to act as a buffer, and the flow rate of the dopant source gas is adjusted to be no less than 0.3% of the first flow rate of hydrogen. Simultaneously, the silicon-containing source gas, carbon-containing source gas, and chlorine-containing gas required for growing the doped buffer layer are introduced into the reaction chamber. The chlorine-containing gas, acting as an auxiliary gas, can suppress Si-Si bonding caused by decomposition of the carbon source during the reaction to form silicon carbide, which can affect growth.

[0090] In some embodiments, in step S4, the flow rate of the chlorine-containing gas is 2000 sccm to 5000 sccm, the flow rate of the silicon-containing source gas is 200 sccm to 400 sccm, and the flow rate of the carbon-containing source gas is 70 sccm to 155 sccm.

[0091] In some embodiments, the above step S4 forms a doped buffer layer having a two-layer structure, and the specific formation steps are as follows:

[0092] S41: maintaining the first flow rate of the hydrogen gas and the second flow rate of the doping source gas unchanged, introducing a chlorine-containing gas, a silicon-containing source gas, and a carbon-containing source gas into the reaction chamber to form a first doped buffer layer having the same doping type as the doped silicon carbide substrate;

[0093] S42: maintaining the flow rates of the hydrogen, chlorine-containing gas, silicon-containing source gas and carbon-containing source gas unchanged, and adjusting the flow rate of the doping source gas to be lower than the flow rate of the doping source gas introduced in step S41 to form a second doping buffer layer.

[0094] Specifically, growing a second doped buffer layer can alleviate the doping mutation between the first doped buffer layer and the epitaxial layer, reduce the dislocation between crystal layers caused by drastic changes in doping - stacking faults (SF), and at the same time reduce or even eliminate basal plane dislocations (BPD) that affect device yield.

[0095] In some embodiments, in the above step S41, the flow rate of the doping source gas is adjusted to be not less than 0.3% of the first flow rate of the hydrogen gas, the chlorine-silicon ratio (Cl / Si) between the chlorine-containing gas and the silicon-containing source gas is 1~20, the carbon-silicon ratio (C / Si) between the carbon-containing source gas and the silicon-containing source gas is 1.0~1.2, and the flow rate of the silicon-containing source gas is not less than 0.1% of the first flow rate, so that the growth rate of the first doped buffer layer and the second doped buffer layer is not less than 10 microns / hour.

[0096] In some specific embodiments, in step S41 and step S42, the flow rate of the silicon-containing source gas is 0.1% to 0.4% of the first flow rate of the introduced hydrogen gas.

[0097] In a more specific embodiment, in step S41, the flow rate of the doping source gas is adjusted to 500 sccm to 2000 sccm, the flow rate of the chlorine-containing gas is adjusted to 2000 sccm to 5000 sccm, the flow rate of the silicon-containing source gas is adjusted to 200 sccm to 400 sccm, and the flow rate of the carbon-containing source gas is adjusted to 70 sccm to 155 sccm, so that the doping concentration of the first doped buffer layer is 2×10 18 cm -3 ~ 9×10 18 cm -3 .

[0098] In step S42 of a more specific embodiment, after step S41 is completed, the flow rates of the chlorine-containing gas, the silicon-containing source gas, and the carbon-containing source gas are maintained unchanged, and the flow rate of the doping source gas is adjusted to 50 sccm to 400 sccm, so that the doping concentration of the second doped buffer layer is 9×10 17 cm -3 ~ 2×10 18 cm -3 .

[0099] In some embodiments, the duration of step S42 is greater than the duration of step S41 , so that the thickness of the second doped buffer layer is greater than the thickness of the first doped buffer layer.

[0100] In some embodiments, the thickness of the first doped buffer layer is 0.1 micrometer to 0.9 micrometer.

[0101] In some embodiments, the thickness of the second doped buffer layer is 0.1 micrometer to 1 micrometer.

[0102] In other embodiments, a doped buffer layer comprising a structure greater than two layers is formed in step S4. Specifically, the duration of step S42 is greater than the duration of step S41. Step S42 is repeated, and the flow rate of the introduced doping source gas is adjusted to be lower than the flow rate of the introduced doping source gas in the previous step when step S42 is repeated in each step. The duration of each step is greater than the duration of the previous step until the Nth doped buffer layer is formed, and the thickness of each doped buffer layer increases sequentially along the growth direction, and the doping concentration decreases sequentially along the growth direction, so as to help reduce the basal plane dislocation and stacking fault of the epitaxial layer, and N is a positive integer greater than 2.

[0103] In some specific embodiments, in the multi-layer doped buffer layer, the thickness h of the xth doped buffer layer is x Satisfy: h x =0.2h x-1 -0.1, where h x-1 is the thickness of the (x-1)th doped buffer layer, and the (x-1)th doped buffer layer is closer to the doped silicon carbide substrate than the xth doped buffer layer.

[0104] In some embodiments, after the doped buffer layer is grown, an epitaxial layer is grown. Specifically, as in step S5: hydrogen is introduced at the first flow rate, the flow rate of the doping source gas is controlled to be lower than the minimum flow rate of the doping source gas introduced in step S4, and the flow rates of the silicon-containing source gas, carbon-containing source gas, and chlorine-containing gas are respectively higher than the flow rates of the corresponding silicon-containing source gas, carbon-containing source gas, and chlorine-containing gas introduced in step S4, so as to grow the epitaxial layer on the doped buffer layer.

[0105] In some embodiments, in the above step S5, the flow rate of the carbon-containing source gas is 90 sccm~200 sccm; the flow rate of the silicon-containing source gas is 250 sccm~500 sccm; the flow rate of the chlorine-containing gas is 2500 sccm~5000 sccm, and the flow rate of the doping source gas is 50 sccm~150 sccm, so that the growth rate of the epitaxial layer is not less than 60 μm / h.

[0106] In some embodiments, a step of growing a transition layer is further included between the above-mentioned step S4 and step S5, specifically: maintaining the introduction of hydrogen at the first flow rate, linearly reducing the flow rate of the doping source gas until the doping source gas flow rate introduced in step S5 is reached, and linearly increasing the flow rates of the silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas until the corresponding flow rates of the silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas introduced in step S5 are reached.

[0107] Alternatively, in some other embodiments, instead of growing the buffer layer, after step S4, the dopant source gas, silicon-containing source gas, carbon-containing source gas, and chlorine-containing gas are stopped, and hydrogen is continued at the first flow rate for purge cleaning. Then, step S5 is performed to grow the epitaxial layer.

[0108] Whether the transition layer is grown first or hydrogen is introduced for purging and cleaning, a clean growth surface can be provided for growing the epitaxial layer, which is beneficial to improving the growth quality of the epitaxial layer.

[0109] In some embodiments, after the epitaxial layer growth is completed in step S5, the process further includes step S6: maintaining the flow rates of hydrogen, silicon-containing source gas, carbon-containing source gas, and chlorine-containing gas into the reaction chamber, stopping or reducing the flow of dopant source gas, and forming a cap layer above the epitaxial layer to protect the epitaxial layer. The duration of the flow of each gas is controlled to ensure that the thickness of the cap layer does not exceed 0.2% of the thickness of the epitaxial layer.

[0110] After the cap layer is grown, a cooling step is performed to cool the reaction chamber and the silicon carbide substrate to approximately 900°C.

[0111] The silicon carbide epitaxial wafer prepared by the above method is as follows Figure 3As shown, the silicon carbide epitaxial wafer at least includes a silicon carbide substrate 300 processed by the above steps, and structures such as a buffer layer 301, an epitaxial layer 302, and an epitaxial cap layer 303 grown on the silicon carbide substrate.

[0112] The silicon carbide epitaxial growth method of the present invention is compared and illustrated in detail through the following examples and comparative examples.

[0113] Example 1

[0114] This embodiment provides the use of Figure 1 The silicon carbide epitaxial growth method for reducing native defects is performed by the MOCVD equipment shown. In this embodiment, the doped silicon carbide is an N-type doped 4H-SiC substrate (size is 6 inches), more specifically a nitrogen-doped silicon carbide substrate with a doping concentration of 1×10 19 cm -3 , and the substrate is beveled, the bevel angle is 4 degrees, and the bevel direction is the c-axis biased to the (11-20) crystal plane. The doping source gas is nitrogen N2, the chlorine-containing gas is hydrogen chloride HCl gas, the silicon-containing source gas is monosilane SiH4, and the carbon-containing source gas is propane C3H8. In this embodiment, the growth rate is measured by dividing the thickness by the growth time using an FTIR film thickness meter. The specific operation method is a well-known conventional technical means. The doping concentration is tested using a Semilab doping concentration tester. The test method is a well-known conventional technical means.

[0115] Specifically, the method of this embodiment includes the following steps:

[0116] S1: Place a doped silicon carbide substrate in a reaction chamber. Hydrogen gas is introduced into the reaction chamber. The temperature in the reaction chamber is controlled at 1610°C and the pressure is controlled at 267 mbar. The doped silicon carbide substrate rotates at 600 rpm on a support platform.

[0117] S2: hydrogen and nitrogen are introduced simultaneously, with the flow rate of hydrogen adjusted to 150 slm and the flow rate of nitrogen adjusted to 100 sccm for 3 minutes, to perform a first surface pretreatment on the doped silicon carbide substrate.

[0118] S3: Maintaining the hydrogen flow rate at 150 slm, adjust the nitrogen flow rate to 1050 sccm, and simultaneously introduce hydrogen chloride gas at a flow rate of 500 sccm and propane at a flow rate of 10 sccm to perform a second surface pretreatment on the substrate surface obtained in step S2. The introduction time of these gases is controlled to be 7.0 s.

[0119] S4: Two doped buffer layers are grown on the surface of the doped silicon carbide substrate obtained in step S3.

[0120] First, a first doped buffer layer was grown on the surface of the silicon carbide substrate: hydrogen was introduced at a flow rate of 150 slm, nitrogen was introduced at a flow rate of 1050 sccm, silane was introduced at a flow rate of 350 sccm, propane was introduced at a flow rate of 128.3 sccm, and hydrogen chloride gas was introduced at a flow rate of 3850 sccm. The above-mentioned flow rates were maintained for each gas for 60.0 s, that is, the growth time of the first doped buffer layer was 60 s. During the growth of the first doped buffer layer, the chlorine-silicon ratio (Cl / Si) in hydrogen chloride gas and silane was controlled to be 11.0; the carbon-silicon ratio (C / Si) in propane and silane was controlled to be 1.1, thereby controlling the growth rate of the first doped buffer layer to be 36.0 μm / h. The thickness of the grown first doped buffer layer was 0.6 μm, and its doping concentration was 5.90×10 18 cm -3 .

[0121] Next, a second doped buffer layer was grown on top of the first doped buffer layer. The flow rates of hydrogen, silane, propane, and hydrogen chloride were maintained constant, maintaining a chlorine-to-silicon ratio of 11.0 and a carbon-to-silicon ratio of 1.1. The growth rate of the second doped buffer layer was also maintained at 36.0 μm / h. The flow rate of nitrogen was adjusted to 235 sccm, and the growth time was 90.0 s. The thickness of the grown second doped buffer layer was 0.9 μm, and its doping concentration was 1.01×10 18 cm -3 That is, the thickness of the second doped buffer layer is greater than that of the first doped buffer layer, and the doping concentration of the second doped buffer layer is less than that of the first doped buffer layer.

[0122] S5: Epitaxial layer growth: Hydrogen is introduced at a flow rate of 150 slm, nitrogen at a flow rate of 120 sccm, silane (a Si-containing source gas) at a flow rate of 360 sccm, propane at a flow rate of 154.8 sccm, and hydrogen chloride at a flow rate of 4500 sccm. The above-mentioned flow rates are maintained for each gas for 605.0 s, i.e., the epitaxial layer growth duration is 605.0 s. During the epitaxial layer growth process, the chlorine-silicon ratio in the hydrogen chloride gas and silane is controlled to be 12.5; the carbon-silicon ratio in the propane and silane is controlled to be 1.3, thereby controlling the epitaxial layer growth rate to 65.5 μm / h.

[0123] After the growth of the doped buffer layer in step S4 is completed and before the epitaxial layer is grown in step S5, this embodiment also includes: maintaining the flow rate of hydrogen gas at 150.0 slm, adjusting the flow rate of nitrogen gas to linearly decrease from 235 sccm when growing the second doped buffer layer to 120.0 sccm when growing the epitaxial layer, and adjusting the flow rate of silane gas to linearly increase from 350 sccm when growing the second doped buffer layer to 360 sccm when growing the epitaxial layer, adjusting the flow rate of propane gas to linearly increase from 128 sccm when growing the second doped buffer layer to 154.8 sccm when growing the epitaxial layer, and adjusting the flow rate of hydrogen chloride gas to linearly increase from 3850 sccm when growing the second doped buffer layer to 4500 sccm when growing the epitaxial layer. The above process takes 5.0 s to grow a transition layer on the second doped buffer layer.

[0124] S6: Maintaining the flow rates of hydrogen, silicon-containing source gas, carbon-containing source gas, and chlorine-containing gas into the reaction chamber, stop introducing the dopant source gas to form a cap layer above the epitaxial layer to protect it. The above gases are introduced for 10 seconds, and the thickness of the grown cap layer does not exceed 0.2% of the thickness of the epitaxial layer.

[0125] After the cap layer growth is completed, a cooling step is performed, that is, the gas injection mechanism 4 stops the introduction of silicon-containing source gas, carbon-containing source gas and chlorine-containing source gas into the reaction chamber 5, the introduction of hydrogen is maintained, and the heating device 2 is turned off to cool down until the temperature in the reaction chamber is below 900 degrees Celsius.

[0126] Example 2

[0127] The method for silicon carbide epitaxial growth with reduced native defects provided in this embodiment differs from that in the first embodiment in that, in step S2, the flow rate of nitrogen is 500 sccm during the simultaneous introduction of hydrogen and nitrogen. The remaining steps are the same as those in the first embodiment. The concentration of the first doped buffer layer is 6.02×10 18 cm -3 , the concentration of the second doped buffer layer is 1.03×10 18 cm -3 .

[0128] Example 3

[0129] The silicon carbide epitaxial growth method for reducing native defects provided in this embodiment is different from that in the first embodiment in that:

[0130] S1: placing a doped silicon carbide substrate in a reaction chamber, introducing hydrogen into the reaction chamber, and controlling the temperature in the reaction chamber to be 1550° C. and the pressure to be 80 mbar.

[0131] S2: hydrogen and nitrogen are introduced simultaneously, with the flow rate of hydrogen adjusted to 120 slm and the flow rate of nitrogen adjusted to 700 sccm for 3 minutes, to perform a first surface pretreatment on the doped silicon carbide substrate.

[0132] S3: Maintaining the hydrogen flow rate at 120 slm, the nitrogen flow rate was adjusted to 1200 sccm. Hydrogen chloride gas was introduced at a flow rate of 480 sccm, and propane was introduced at a flow rate of 11.5 sccm to perform a second surface pretreatment on the substrate surface obtained in step S2. The introduction time of these gases was controlled to be 15.0 s.

[0133] S4: Two doped buffer layers are grown on the surface of the doped silicon carbide substrate obtained in step S3.

[0134] First, the first doped buffer layer was grown on the surface of the silicon carbide substrate: hydrogen was introduced at a flow rate of 120 slm, nitrogen was introduced at a flow rate of 1200 sccm, monosilane was introduced at a flow rate of 400 sccm, propane was introduced at a flow rate of 146.7 sccm, and hydrogen chloride gas was introduced at a flow rate of 4400 sccm. The above-mentioned flow rates were maintained for each gas for 80.0 s, that is, the growth time of the first doped buffer layer was 80 s. During the growth of the first doped buffer layer, the chlorine-silicon ratio in hydrogen chloride gas and silane was controlled to be 11.0; the carbon-silicon ratio in propane and silane was controlled to be 1.1, thereby controlling the growth rate of the first doped buffer layer to 27.0 μm / h. The thickness of the grown first doped buffer layer was 0.6 μm, and its doping concentration was 4.20×10 18 cm -3 .

[0135] Then, a second doped buffer layer is grown on the first doped buffer layer. At this time, the flow rates of hydrogen, silane, propane and hydrogen chloride are kept constant, thereby maintaining the chlorine-silicon ratio at 11.0 and the carbon-silicon ratio at 1.1. miscellaneous The growth rate of the buffer layer was also 27.0 μm / h. The nitrogen flow rate was adjusted to 350 sccm and the growth time was 120.0 s. The thickness of the second doped buffer layer grown at this time was 0.9 μm and its doping concentration was 9.27×10 17 cm -3 That is, the thickness of the second doped buffer layer is greater than that of the first doped buffer layer, and the doping concentration of the second doped buffer layer is less than that of the first doped buffer layer.

[0136] S5: Epitaxial layer growth: Hydrogen is introduced at a flow rate of 120 slm, nitrogen at a flow rate of 150 sccm, silane at a flow rate of 450 sccm, propane at a flow rate of 165.0 sccm, and hydrogen chloride at a flow rate of 4950 sccm. The above flow rates are maintained for each gas for 605.0 s, i.e., the epitaxial layer growth duration is 605.0 s. During the epitaxial layer growth process, the chlorine-silicon ratio in the hydrogen chloride gas and silane is controlled to be 11.0; the carbon-silicon ratio in the propane and silane is controlled to be 1.1, thereby controlling the epitaxial layer growth rate to 65.5 μm / h.

[0137] After the growth of the doped buffer layer in step S4 is completed and before the growth of the epitaxial layer in step S5, the process also includes: maintaining the flow rate of hydrogen gas at 120.0 slm, adjusting the flow rate of nitrogen gas to linearly decrease from 350 sccm when growing the second doped buffer layer to 150.0 sccm when growing the epitaxial layer, and at the same time adjusting the flow rate of silane gas to linearly increase from 400 sccm when growing the second doped buffer layer to 450 sccm when growing the epitaxial layer, adjusting the flow rate of propane gas to linearly increase from 146.7 sccm when growing the second doped buffer layer to 165.0 sccm when growing the epitaxial layer, and adjusting the flow rate of hydrogen chloride gas to linearly increase from 4400 sccm when growing the second doped buffer layer to 4950 sccm when growing the epitaxial layer. The above process takes 5.0 s to grow a transition layer above the second doped buffer layer.

[0138] After step S5 is completed, step S6 and cooling step similar to those in embodiment 1 are performed.

[0139] Example 4

[0140] The difference between the silicon carbide epitaxial growth method for reducing native defects provided in this embodiment and that in the first embodiment is that in step S2, when hydrogen and nitrogen are introduced simultaneously, the nitrogen flow rate is adjusted to 950 sccm. The remaining steps are the same as those in the first embodiment. The doping concentration of the first doped buffer layer is 6.20×10 18 cm -3 The doping concentration of the second doped buffer layer is 1.03×10 18 cm -3 .

[0141] Example 5

[0142] The difference between the silicon carbide epitaxial growth method for reducing native defects provided in this embodiment and that in the first embodiment is that in step S2, when hydrogen and nitrogen are introduced simultaneously, the nitrogen flow rate is adjusted to 1000 sccm. The remaining steps are the same as those in the first embodiment. The doping concentration of the first doped buffer layer is 6.23×1018 cm -3 The doping concentration of the second doped buffer layer is 1.03×10 18 cm -3 .

[0143] Example 6

[0144] The method for silicon carbide epitaxial growth with reduced native defects provided in this embodiment differs from that in the first embodiment in that in step S2, when hydrogen and nitrogen are introduced simultaneously, the nitrogen flow rate is adjusted to 1100 sccm. The remaining steps are the same as those in the first embodiment. The doping concentration of the first doped buffer layer is 6.20×10 18 cm -3 The doping concentration of the second doped buffer layer is 1.03×10 18 cm -3 .

[0145] Example 7

[0146] The silicon carbide epitaxial growth method for reducing native defects provided in this embodiment differs from that in the first embodiment in that:

[0147] In step S2, hydrogen and nitrogen are not introduced simultaneously but alternately. Specifically, S21: Stop the introduction of hydrogen into the reaction chamber, then introduce nitrogen at a flow rate of 700 sccm, and control the duration of the nitrogen introduction to 3.0 seconds. S22: Stop the introduction of nitrogen into the reaction chamber, then introduce hydrogen at a flow rate of 150 slm, and control the second duration of the hydrogen introduction to 9.0 seconds. This alternating cycle of steps S21 and S22 is repeated until the first surface pretreatment lasts for 10 minutes.

[0148] The remaining steps are the same as those in Example 1. The doping concentration of the first doped buffer layer is 6.02×10 18 cm -3 The doping concentration of the second doped buffer layer is 1.02×10 18 cm -3 .

[0149] Example 8

[0150] The silicon carbide epitaxial growth method for reducing native defects provided in this embodiment differs from that in the seventh embodiment in that:

[0151] In step S1, a doped silicon carbide substrate is placed in a reaction chamber, hydrogen is introduced into the reaction chamber, and the temperature in the reaction chamber is controlled to be 1650° C. and the pressure to be 450 mbar.

[0152] In step S2, S21: stop the flow of hydrogen into the reaction chamber, then introduce nitrogen at a flow rate of 1000 sccm, and control the nitrogen flow duration to 3.0 seconds; S22: stop the flow of nitrogen into the reaction chamber, then introduce hydrogen at a flow rate of 200 slm, and control the second hydrogen flow duration to 3.0 seconds. Steps S21 and S22 are alternately performed until the first surface pretreatment duration reaches 3 minutes.

[0153] S3: Maintaining the hydrogen flow rate at 200 slm, the nitrogen flow rate was adjusted to 800 sccm. Hydrogen chloride gas was introduced at a flow rate of 500 sccm, and propane was introduced at a flow rate of 6.4 sccm to perform a second surface pretreatment on the substrate surface obtained in step S2. The introduction time of these gases was controlled to be 5.0 s.

[0154] S4: Two doped buffer layers are grown on the surface of the doped silicon carbide substrate obtained in step S3.

[0155] First, the first doped buffer layer was grown on the surface of the silicon carbide substrate: hydrogen was introduced at a flow rate of 200 slm, nitrogen was introduced at a flow rate of 800 sccm, monosilane was introduced at a flow rate of 200 sccm, propane was introduced at a flow rate of 73.3 sccm, and hydrogen chloride gas was introduced at a flow rate of 2200 sccm. The above-mentioned flow rates were maintained for each gas for 36.0 s, that is, the growth time of the first doped buffer layer was 36 s. During the growth of the first doped buffer layer, the chlorine-silicon ratio in hydrogen chloride gas and silane was controlled to be 11.0; the carbon-silicon ratio in propane and silane was controlled to be 1.1, thereby controlling the growth rate of the buffer layer to 60.0 μm / h. The thickness of the grown first doped buffer layer was 0.6 μm, and its doping concentration was 7.15×10 18 cm -3 .

[0156] Next, a second doped buffer layer was grown on top of the first doped buffer layer. The flow rates of hydrogen, silane, propane, and hydrogen chloride were maintained constant, maintaining a chlorine-to-silicon ratio of 11.0 and a carbon-to-silicon ratio of 1.1. The growth rate of the second doped buffer layer was also maintained at 60.0 μm / h. The nitrogen flow rate was adjusted to 100 sccm, and the growth time was 54.0 s. The thickness of the grown second doped buffer layer was 0.9 μm, and its doping concentration was 1.56×10 18 cm -3 That is, the thickness of the second doped buffer layer is greater than that of the first doped buffer layer, and the doping concentration of the second doped buffer layer is less than that of the first doped buffer layer.

[0157] S5: Epitaxial layer growth: Hydrogen is introduced at a flow rate of 200 slm, nitrogen at a flow rate of 80 sccm, silane at a flow rate of 250 sccm, propane at a flow rate of 91.7 sccm, and hydrogen chloride at a flow rate of 2750 sccm. The above-mentioned flow rates are maintained for each gas for 605.0 s, that is, the epitaxial layer growth time is 605.0 s. During the epitaxial layer growth process, the chlorine-silicon ratio in the hydrogen chloride gas and silane is controlled to 11.0; the carbon-silicon ratio in the propane and silane is controlled to 1.1, thereby controlling the growth rate of the buffer layer to 65.5 μm / h.

[0158] After the growth of the doped buffer layer in step S4 is completed, before the growth of the epitaxial layer in step S5, the process also includes: maintaining the flow rate of hydrogen gas at 200.0 slm, adjusting the flow rate of nitrogen gas to linearly decrease from 100 sccm when growing the second doped buffer layer to 80.0 sccm when growing the epitaxial layer, and at the same time adjusting the flow rate of silane gas to linearly increase from 200 sccm when growing the second doped buffer layer to 250 sccm when growing the epitaxial layer, adjusting the flow rate of propane gas to linearly increase from 73.3 sccm when growing the second doped buffer layer to 91.7 sccm when growing the epitaxial layer, and adjusting the flow rate of hydrogen chloride gas to linearly increase from 2200 sccm when growing the second doped buffer layer to 2750 sccm when growing the epitaxial layer. The above process takes 5.0 s to grow a transition layer on the second doped buffer layer.

[0159] S6: Maintain the flow rates of hydrogen, silicon-containing source gas, carbon-containing source gas, and chlorine-containing gas into the reaction chamber. Stop or reduce the flow of dopant source gas to form a cap layer above the epitaxial layer to protect it. The gases are introduced for 10 seconds. The thickness of the grown cap layer does not exceed 0.2% of the thickness of the epitaxial layer.

[0160] Then, the cooling step of Example 1 is performed in the same manner.

[0161] Embodiment 9

[0162] The silicon carbide epitaxial growth method for reducing native defects provided in this embodiment is different from that in the first embodiment in that the steps for forming the doped buffer layer are different. This embodiment forms three doped buffer layers of the same thickness.

[0163] Specifically, when growing the first doped buffer layer in step S41, the flow rates of hydrogen, nitrogen, silane, propane, and hydrogen chloride were controlled to be the same as the flow rates of the corresponding gases in step S41 in Example 1, and the introduction time of each gas was adjusted to 53.0 s. The thickness of the grown first doped buffer layer was 0.53 μm, and the doping concentration was 5.91×10 18 cm-3 .

[0164] In step S42, when growing the second doped buffer layer, the flow rates of hydrogen, nitrogen, silane, propane, and hydrogen chloride were kept the same as those of the corresponding gases in step S42 of Example 1. The growth time was adjusted to 53.0 s, and the thickness of the grown second doped buffer layer was controlled to be 0.53 μm. The doping concentration was 9.95×10 17 cm -3 .

[0165] In step S43, a third doped buffer layer is grown on top of the second doped buffer layer. The flow rates of hydrogen, silane, propane, and hydrogen chloride gases are maintained at the same flow rates as in step S42 of this embodiment. The flow rate of nitrogen is adjusted to 117.5 sccm. The growth time is also 53.0 s. The thickness of the third doped buffer layer is 0.53 μm. At this time, the doping concentration of the third doped buffer layer is 4.98×10 17 cm -3 .

[0166] Example 10

[0167] The silicon carbide epitaxial growth method for reducing native defects provided in this embodiment is different from that in the fourth embodiment in that the steps for forming the doped buffer layer are different. This embodiment forms three doped buffer layers with gradually increasing thickness.

[0168] Specifically, in step S41, when growing the first doped buffer layer, the flow rates of hydrogen, nitrogen, silane, propane, and hydrogen chloride are controlled to be the same as those of the gases in Example 4, and the duration of each gas introduction is adjusted to 10.0 s. The thickness of the grown first doped buffer layer is 0.1 μm. The doping concentration of the first doped buffer layer is 5.98×10 18 cm -3 .

[0169] When growing the second doped buffer layer in step S42, the flow rates of hydrogen, monosilane, and propane are kept the same as the corresponding gas flow rates in step S41 in Example 4, and the growth time is adjusted to 30.0 s, and the thickness of the second doped buffer layer is controlled to be 0.3 μm. The doping concentration of the second doped buffer layer is 1.1×10 18 cm -3 .

[0170] In step S43, a third doped buffer layer is grown on the second doped buffer layer. The flow rates of hydrogen, silane, propane, and hydrogen chloride are maintained at the same rate as in step S42 of this embodiment. The flow rate of nitrogen is adjusted to 117.5 sccm. The growth time is 50.0 s. The thickness of the third doped buffer layer is 0.5 μm. The doping concentration of the third doped buffer layer is 5.00×1017 cm -3 .

[0171] Example 11

[0172] The method for silicon carbide epitaxial growth with reduced native defects provided in this embodiment differs from that in the fourth embodiment in that after step S43 is completed, step S44 is further performed to form a fourth doped buffer layer:

[0173] Step S44: A fourth doped buffer layer is grown on the third doped buffer layer. The flow rates of hydrogen, silane, propane, and hydrogen chloride gases are maintained at the same flow rates as in step S43 of Example 10. The flow rate of nitrogen is adjusted to 23.5 sccm. The growth time is 70.0 s. The thickness of the third doped buffer layer is 0.7 μm. The doping concentration of the fourth doped buffer layer is 1.04×10 17 cm -3 .

[0174] Comparative Example 1

[0175] This comparative example also provides a method for silicon carbide epitaxial growth with reduced native defects. This comparative example differs from Example 1 in that, in step S2, the nitrogen flow rate is 0 sccm, meaning that no nitrogen is introduced, and only hydrogen is introduced to etch the substrate surface. The remaining steps have the same parameters as those in Example 1.

[0176] Comparative Example 2

[0177] This comparative example also provides a method for silicon carbide epitaxial growth with reduced native defects. This comparative example differs from Example 1 in that, in step S2, the nitrogen gas flow rate is 50 sccm, and hydrogen and nitrogen are also introduced simultaneously in step S2. The remaining steps have the same parameters as those of Example 1.

[0178] The present invention selects the epitaxial wafer obtained in comparative example 1 and the epitaxial wafer obtained in embodiment 3, and uses the Candela8520 surface defect detection system to perform surface defect detection on the silicon carbide epitaxial wafer. The obtained image is as follows: Figure 4 and 5 As shown, Figure 4 is the PL image of the epitaxial wafer obtained in Comparative Example 1, Figure 5 PL image of the epitaxial wafer obtained in Example 3. Figure 4 and Figure 5 As shown, the surface of the epitaxial wafer obtained in Comparative Example 1 is relatively rough and has obvious defects, while the surface of the epitaxial wafer obtained in Example 3 of the present invention is mirror-finished, significantly smoother, and has no obvious defects.

[0179] The detection results of basal plane dislocations and stacking faults of various examples are shown in Table 1 below.

[0180] Table 1 Surface defect detection results of different silicon carbide epitaxial wafers

[0181] Defect Examples Basal plane dislocations (number) Stacking faults (number) Example 1 23 35 Example 2 0 3 Example 3 0 3 Example 4 0 4 Example 5 1 6 Example 6 12 17 Example 7 0 1 Example 8 0 1 Embodiment 9 23 27 Example 10 0 5 Example 11 0 3 Comparative Example 1 50 73 Comparative Example 2 47 65

[0182] From the data of Comparative Examples 1 and 2 and Examples 1 to 11 in the above table, it can be seen that the flow rate of the doping source gas nitrogen in step S2 of each embodiment varies between 100 and 1100 sccm. Compared with Comparative Examples 1 and 2 in which the flow rate of the doping source gas nitrogen in step S2 is controlled at 0 and 50 sccm, the basal plane dislocations and stacking faults of the epitaxial wafer are significantly reduced, and it can be seen that the quality of the silicon carbide epitaxial layer is significantly improved.

[0183] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for epitaxial growth of silicon carbide with reduced native defects, characterized in that: The following steps are involved: S1: placing a doped silicon carbide substrate in a reaction chamber, introducing hydrogen into the reaction chamber, and controlling the reaction chamber to reach a predetermined temperature of not less than 1500° C. and a predetermined pressure of not less than 50 mbar; S2: adjusting the flow rate of the hydrogen gas to a first flow rate, and introducing a doping source gas into the reaction chamber at a second flow rate that is not less than 0.06% of the first flow rate to perform a first surface pretreatment on the silicon carbide substrate; S3: maintaining the first flow rate unchanged, adjusting the second flow rate to no less than 0.3% of the first flow rate, introducing a chlorine-containing gas into the reaction chamber at a third flow rate no more than 0.4% of the first flow rate, and introducing a carbon-containing source gas at a fourth flow rate no more than 0.04% of the first flow rate, to perform a second surface pretreatment on the surface of the substrate obtained in step S2; S4: introducing the hydrogen gas, the doping source gas, the silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas into the reaction chamber to grow a doping buffer layer on the surface of the substrate obtained in step S3.

2. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: In step S1, the predetermined temperature does not exceed 1700° C., and the predetermined pressure does not exceed 500 mbar.

3. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: In step S2, the duration of the first surface pretreatment is 3 minutes to 15 minutes.

4. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: In step S2, performing a first surface pretreatment on the silicon carbide substrate further includes: S21: after stopping the introduction of the hydrogen gas into the reaction chamber, introducing the doping source gas into the reaction chamber at the second flow rate, and controlling the duration of introducing the doping source gas to be the first duration; S22: After stopping the introduction of the dopant source gas into the reaction chamber, introducing the hydrogen gas into the reaction chamber at the first flow rate, and controlling the second duration of the introduction of the hydrogen gas to be no less than the first duration; S23: alternately perform step S21 and step S22 until the duration of the first surface pretreatment is 3 minutes to 15 minutes.

5. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 4, characterized in that: The first duration does not exceed 5 seconds, and the second duration is 1 to 3 times the first duration.

6. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: In step S2, the first flow rate is 80 slm to 200 slm, and the second flow rate does not exceed 1% of the first flow rate.

7. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: In step S3, the duration of the second surface pretreatment does not exceed 30 seconds, the second flow rate is not less than 0.3% of the first flow rate and not more than 1% of the first flow rate, the third flow rate is 0.2%~0.4% of the first flow rate, and the fourth flow rate is 0.003%~0.04% of the first flow rate.

8. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: The chlorine-containing gas includes hydrogen chloride, the doping source gas includes trimethylaluminum, borane, nitrogen, ammonia or phosphine, the silicon-containing source gas includes silane, trichlorosilane or dichlorosilane, and the carbon-containing source gas includes propane, ethylene, methane or acetylene.

9. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: The doped silicon carbide substrate is an N-type doped beveled substrate or a P-type doped beveled substrate, the beveled angle of the beveled substrate does not exceed 8 degrees, the beveled direction is that the c-axis deviates to the (1-102) crystal plane, the (11-20) crystal plane or the (10-10) crystal plane, and the doping concentration of the doped silicon carbide substrate is not less than 1×10 18 cm -3 .

10. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: In step S4, the step of growing a doped buffer layer on the surface of the substrate obtained in step S3 includes: S41: while maintaining the first flow rate of the hydrogen gas and the second flow rate of the dopant source gas unchanged, the chlorine-containing gas, the silicon-containing source gas, and the carbon-containing source gas are introduced into the reaction chamber so that the carbon-silicon ratio is 1-1.2 and the chlorine-silicon ratio is 1-20, thereby forming a first doped buffer layer having the same doping type as that of the doped silicon carbide substrate; S42: maintaining the flow rates of the hydrogen, chlorine-containing gas, silicon-containing source gas and carbon-containing source gas unchanged, and adjusting the flow rate of the doping source gas to be lower than the flow rate of the doping source gas introduced in step S41 to form a second doping buffer layer.

11. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 10, wherein: In step S41, the flow rate of the doping source gas is not less than 0.3% of the first flow rate and not more than 1% of the first flow rate. In steps S41 and S42, the flow rate of the silicon-containing source gas is not less than 0.1% of the first flow rate, so that the growth rate of the first doped buffer layer and the second doped buffer layer is not less than 10 microns / hour.

12. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 10, wherein: The duration of step S42 is longer than the duration of step S41; Repeat step S42, and in each step adjust the flow rate of the doping source gas to be lower than the flow rate of the doping source gas introduced in the previous step, and the duration of each step is longer than the duration of the previous step, until the Nth doped buffer layer is formed, and the thickness of each doped buffer layer increases sequentially along the growth direction, and the doping concentration decreases sequentially along the growth direction, and N is a positive integer greater than 2.

13. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 10, wherein: In step S41 and step S42, the flow rate of the chlorine-containing gas is 2000 sccm to 5000 sccm, the flow rate of the silicon-containing source gas is 200 sccm to 400 sccm, and the flow rate of the carbon-containing source gas is 70 sccm to 155 sccm; In step S41, the flow rate of the doping source gas is 500 sccm to 2000 sccm, so that the doping concentration of the first doped buffer layer is 2×10 18 cm -3 ~ 9×10 18 cm -3 ; In step S42, the flow rate of the doping source gas is 50 sccm to 400 sccm, so that the doping concentration of the second doped buffer layer is 9×10 17 cm -3 ~ 2×10 18 cm -3 .

14. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: Also includes: Step S5: Maintaining the first flow rate of the hydrogen gas, controlling the flow rate of the doping source gas to be lower than the minimum flow rate of the doping source gas introduced in step S4, and the flow rates of the silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas to be higher than the flow rates of the corresponding silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas introduced in step S4, so as to grow an epitaxial layer on the doping buffer layer.

15. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 14, wherein: Between step S4 and step S5, a step of growing a transition layer is also included: Keep introducing hydrogen at the first flow rate, linearly reduce the flow rate of the doping source gas until it reaches the doping source gas flow rate introduced in step S5, and linearly increase the flow rates of the silicon-containing source gas, the carbon-containing source gas, and the chlorine-containing gas until they reach the corresponding flow rates of the silicon-containing source gas, the carbon-containing source gas, and the chlorine-containing gas introduced in step S5.

16. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 14, wherein: The following steps are also included between step S4 and step S5: stopping the introduction of the doping source gas, the silicon-containing source gas, the carbon-containing source gas and the chlorine-containing gas, and maintaining the introduction of the hydrogen gas at the first flow rate for purging and cleaning.

17. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 14, wherein: In step S5, the flow rate of the carbon-containing source gas is 90 sccm~200 sccm; the flow rate of the silicon-containing source gas is 250 sccm~500 sccm; the flow rate of the chlorine-containing gas is 2500 sccm~5000 sccm, and the flow rate of the doping source gas is 50 sccm~150 sccm, so that the growth rate of the epitaxial layer is not less than 60 μm / h.

18. The method for epitaxial growth of silicon carbide with reduced native defects according to claim 1, wherein: The doped silicon carbide substrate is controlled to rotate at a speed not lower than 300 rpm.

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