A method for reducing surface bump defects in silicon carbide epitaxial films

Abstract

The present invention relates to a method for reducing bump defects on the surface of a silicon carbide epitaxial film, comprising the following steps: a first step: growing a buffer layer and an epitaxial layer; a second step: maintaining the pressure in the reaction chamber constant, abruptly changing the hydrogen flow rate to 10-50 slm, and simultaneously introducing 50-100 slm of argon for a first-stage cooling process; a third step: when the temperature in the reaction chamber drops to 1000-1200°C, performing a second-stage cooling process; a fourth step: instantaneously reducing the hydrogen flow rate to 0 slm and the argon flow rate to 10-30 slm, while simultaneously restoring the internal pressure of the reaction chamber; and a fifth step: purging under an argon atmosphere, turning off the argon after the purge is complete, and removing the epitaxial wafer after standing. This method can reduce the bump defect density on the surface of a silicon carbide epitaxial film to 0.03 cm ‑2 and below, thereby improving the quality of silicon carbide epitaxial wafers and enhancing the performance of semiconductor devices.

Description

Technical Field

[0001] The present invention relates to a silicon carbide preparation technology, in particular to a method for reducing bump defects on the surface of a silicon carbide epitaxial film. Background Art

[0002] Silicon carbide (SiC) is a unique semiconductor material that is inherently non-magnetic. However, it possesses the spin and charge properties of electrons (or holes), making it widely applicable in electronic devices. Through specialized processing techniques, it can also achieve specific magnetic properties.

[0003] SiC epitaxial layers are the foundation of semiconductor device growth, so their quality is closely linked to device performance. One of the key evaluation criteria is the number of surface defects, such as bumps, triangles, and drops. The fewer surface defects, the higher the epitaxial layer quality.

[0004] Among them, bump defects, also known as nipple defects, refer to bulges or depressions that appear on the external surface of the product. They are usually caused by local deformation or damage of the material due to external forces. The morphology presents a convex point with linear bulges along the step plane, such as Figure 1 shown.

[0005] Regarding the formation of bump defects, some studies suggest that they are typically caused by tiny particles, silicon carbide particles, carbon inclusions, etc., falling onto the wafer surface during the pre-epitaxial growth phase, subsequently forming a raised bump during the epitaxial growth process. This requires stringent process control during the pre-epitaxial growth phase to prevent the falling of tiny particles, silicon carbide particles, carbon inclusions, etc. However, achieving the desired reduction in bump defects has proven difficult in practice.

[0006] Previously, bumps in SiC devices were not considered fatal defects. Bumps were not strictly controlled during the SiC epitaxial wafer growth process. However, as device development progressed, the impact of bump defects on devices became increasingly significant. During device fabrication, bump defects can cause localized current flow changes in circuits passing through them, leading to short circuits and potentially damaging device performance.

[0007] Chinese patent application CN105448647A discloses a method for reducing bump defects in hydrogenated amorphous carbon films. The method involves first smoothing the surface of the hydrogenated amorphous carbon film with oxygen plasma to remove bump defects. The surface of the hydrogenated amorphous carbon film is then smoothed again with a plasma containing hydrogen and helium to improve the smoothness of the film surface. This smoothing method introduces an oxygen source and is not suitable for films in anaerobic conditions, thus limiting its application scenarios.

[0008] Because bump defects can cause local short circuits in SiC devices during fabrication, thus reducing device performance and yield, finding effective ways to reduce the number of bumps is of practical significance. Summary of the Invention

[0009] The present invention aims to overcome the high number of bump defects found in existing silicon carbide epitaxial wafer preparation and to provide a method for reducing bump defects on the surface of silicon carbide epitaxial films. Through experimental investigation, the inventors discovered that varying the hydrogen flow rate during the cooling phase significantly affects the number of bumps. They further deduced that bumps primarily form during the cooling phase after epitaxial growth, not before epitaxial growth. Before the temperature drops to the standby temperature, hydrogen introduced into the cavity promotes etching of the SiC epitaxial wafer surface. However, small particles and surface protrusions on the surface hinder the hydrogen's etching of the surrounding area, resulting in a raised morphology.

[0010] During typical epitaxial growth processes, the temperature inside the reaction chamber is typically above 1000°C, and surface etching occurs when gas is introduced. Hydrogen, in particular, has a strong promoting effect on surface etching. The inventors believe that after the epitaxial growth phase, when the temperature has not yet dropped below 1000°C, the introduction of hydrogen will intensify the etching of the SiC surface, resulting in the formation of a large number of bumps. Furthermore, pressure changes can easily cause small particles in the chamber to fall out, which are then etched into bumps.

[0011] Based on the above-mentioned inventive principle, the present invention optimizes the cooling process, reduces the promoting effect of hydrogen on the surface etching during the cooling stage, slows down the etching effect, and thus reduces bump defects; on this basis, the cavity is maintained at a low pressure during the cooling process, and the pressure is restored after the cooling is completed, thereby further reducing the falling of small particles during the cooling process.

[0012] The specific plan is as follows:

[0013] A method for reducing bump defects on the surface of a silicon carbide epitaxial film comprises the following steps:

[0014] The first step is to place the silicon carbide substrate in a reaction chamber, etch the substrate in a hydrogen atmosphere, and then introduce a carbon source and a silicon source as growth sources to grow a buffer layer and an epitaxial layer.

[0015] Step 2: After the epitaxial layer growth is completed, the growth source is turned off, the pressure in the reaction chamber remains unchanged, the hydrogen flow rate is suddenly changed to 10-50 slm, and 50-100 slm of argon is introduced at the same time to perform the first stage of cooling;

[0016] Step 3: When the temperature in the reaction chamber drops to 1000-1200° C., a second stage of cooling is performed, including maintaining the pressure in the reaction chamber constant, increasing the argon flow rate to 100-300 slm in a sudden manner, and maintaining the argon flow rate until the temperature in the reaction chamber drops to the target temperature;

[0017] Step 4: Instantly reduce the hydrogen flow rate to 0 slm and the argon flow rate to 10-30 slm, while restoring the internal pressure of the reaction chamber to the target pressure;

[0018] Step 5: Purge in an argon atmosphere. After the purge is completed, turn off the argon and take out the epitaxial wafer after standing.

[0019] In a specific embodiment, in the first step, the carbon source is any one of methane, ethane, and ethylene, the silicon source is any one of trichlorosilane and dichlorosilane, and the growth temperature of the epitaxial layer is 1500-1800°C.

[0020] In a specific embodiment, in the first step, a doping source is introduced during the growth of the epitaxial layer, and the doping source is nitrogen or trimethylaluminum.

[0021] In a specific embodiment, in the second step, the hydrogen flow rate is suddenly changed to 15-40 slm, and 55-70 slm of argon is introduced at the same time.

[0022] In a specific embodiment, in the second step, the first stage of cooling is from the epitaxial temperature to 1200-1000° C., and the cooling time is 8-13 minutes.

[0023] In a specific embodiment, in the third step, the hydrogen flow rate of the second stage cooling remains unchanged or is reduced.

[0024] In a specific embodiment, in the third step, the second stage of cooling is from 1200-1000° C. to room temperature, and the cooling time is 10-20 minutes; the target temperature is room temperature.

[0025] In a specific embodiment, in the fourth step, the internal pressure of the reaction chamber is increased at a rate of 130-200 mbar / min in a linear and gradual manner, and the target pressure is normal pressure.

[0026] The present invention also protects the silicon carbide epitaxial wafer prepared by the method for reducing Bump defects on the surface of the silicon carbide epitaxial film.

[0027] In a specific embodiment, the bump defect density of the silicon carbide epitaxial wafer does not exceed 0.03cm -2 .

[0028] Beneficial effect: The method provided by the present invention for reducing bump defects on the surface of silicon carbide epitaxial films includes: in the cooling stage after the epitaxy is completed, the hydrogen used for purging the cavity is switched to a mixed gas of 10-50slm hydrogen and 50-300slm argon, so as to reduce the etching-promoting effect of hydrogen on the surface, slow down the etching effect, and thus reduce bump defects.

[0029] Furthermore, the method provided by the present invention for reducing bump defects on the surface of silicon carbide epitaxial films maintains the pressure in the reaction chamber unchanged during the cooling stage, delays the pressure recovery time, and performs pressure recovery after the cooling is completed, thereby reducing the occurrence of small particles falling during the cooling process, and can reduce bump defects caused by the falling of small particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings. Obviously, the drawings described below only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0031] Figure 1 This is a schematic diagram of a Bump defect provided by the background technology of the present invention;

[0032] Figure 2 This is a schematic diagram of process conditions provided in Example 1 of the present invention;

[0033] Figure 3 This is a bump defect distribution diagram provided by Example 1 of the present invention (obtained by an AOI optical inspection instrument);

[0034] Figure 4 This is a schematic diagram of the process conditions provided in Comparative Example 1 of the present invention;

[0035] Figure 5 This is a Bump defect distribution diagram provided in Comparative Example 1 of the present invention (obtained by an AOI optical detector). DETAILED DESCRIPTION

[0036] In order to clearly describe the inventive concept of the present invention, the key process control conditions in the method of the present invention are described below in a tabular form, see Table 1.

[0037]

[0038] As can be seen from Table 1, the method of the present invention includes an epitaxial growth stage, a first cooling stage, a second cooling stage, a pressure recovery stage, and an argon purge stage. The temperature, hydrogen flow rate, argon flow rate, and pressure in the reaction chamber are controlled differently in different stages. In a specific embodiment, the following conditions can be adopted:

[0039] Temperature ①: 1500~1800℃ Temperature ②: 1800~1000℃ (cooling) Temperature ③: 1200~25℃ (cooling to room temperature) Temperature ④: 25℃ (room temperature)

[0040] Hydrogen flow rate ①: 80~200slm Hydrogen flow rate ②: 10~50slm Hydrogen flow rate ③: 0slm

[0041] Argon flow rate ①: 0 slm Argon flow rate ②: 50~100 slm Argon flow rate ③: 100~300 slm Argon flow rate ④: 10~30 slm

[0042] Pressure ①: 50~300mbar Pressure ②: 50~1000mbar (return to normal pressure) Pressure ③: 1000mbar (normal pressure)

[0043] It should be noted that the above specific conditions are merely examples to illustrate the concept of the present invention and do not constitute a limitation to the present invention.

[0044] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be realized in various forms and should not be limited by the embodiments set forth herein. In the examples, if specific techniques or conditions are not indicated, the techniques or conditions described in the literature in this area or the product specifications are carried out. Reagents used or instruments that are not indicated by manufacturers are conventional products that can be obtained commercially. In the following examples, if not clearly stated, "%" refers to percentage by weight.

[0045] Example 1

[0046] A method for reducing Bump defects on the surface of silicon carbide epitaxial films, mainly controlling process conditions such as Figure 2 As shown, the following steps are included:

[0047] Step 1: Select an 8-inch silicon carbide substrate with a 4° tilt toward the <11-20> direction for etching and growth of a buffer layer and epitaxial layer.

[0048] Specifically, the etching adopts a constant temperature hydrogen etching method with a pressure of 50 mbar, a temperature of 1500°C, a hydrogen flow rate of 80 slm, and a time of 5 minutes;

[0049] After etching, the buffer layer was grown under the following conditions: pressure of 50 mbar, temperature of 1600°C, hydrogen flow rate of 80 slm, a mixture of TCS (SiHCl3) and ethylene (C2H4) gas was introduced into the reaction chamber, the TCS flow rate was set to 40 sccm, the C / Si ratio was 1.0, high-purity nitrogen was used as the doping source, the growth thickness was 1 μm, and the doping concentration was ~1E18 cm -3 n-type buffer layer;

[0050] An epitaxial layer is then grown on top of the buffer layer. The specific conditions involve linearly ramping the TCS and ethylene flow rates over 60 seconds, ultimately controlling the TCS flow rate to 240 sccm and the C / Si ratio to 1.20. High-purity nitrogen is then introduced to grow an n-type epitaxial layer to the target thickness and doping concentration.

[0051] Step 2: After the epitaxial layer growth is completed, the growth source and doping source are turned off, the pressure remains unchanged, the hydrogen flow rate is suddenly increased to 10 slm, and 90 slm of argon is introduced at the same time to cool down;

[0052] Step 3: When the temperature in the chamber drops to 1000°C, the pressure remains unchanged, the hydrogen flow rate remains unchanged, and the argon flow rate is suddenly increased to 220slm and maintained until the temperature in the chamber drops to room temperature;

[0053] Step 4: Instantly reduce the hydrogen flow rate to 0 slm and the argon flow rate to 25 slm. At the same time, the pressure in the chamber is increased linearly (ramping) at a rate of 130 mbar / min until it reaches normal pressure.

[0054] Step 5: Keep the argon flow constant and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before removing the epitaxial wafer with the robot.

[0055] The surface morphology of the epitaxial wafer is inspected using an AOI optical detector, such as Figure 3 As shown, the number of bump defects on the surface of the epitaxial wafer is 8, and the defect density is 0.03cm -2 .

[0056] Example 2

[0057] A method for reducing bump defects on the surface of a silicon carbide epitaxial film comprises the following steps:

[0058] Step 1: Select an 8-inch silicon carbide substrate with a silicon surface tilted 4° in the <11-20> direction, perform etching, and grow a buffer layer and an epitaxial layer. The specific operations are the same as those in Example 1.

[0059] Step 2: After the epitaxial layer growth is completed, the growth source and doping source are turned off, the pressure remains unchanged, the hydrogen flow rate is suddenly increased to 20 slm, and 70 slm of argon is introduced at the same time to cool down;

[0060] Step 3: When the temperature in the chamber drops to 1100°C, the pressure remains unchanged, the hydrogen flow rate remains unchanged, and the argon flow rate is suddenly increased to 200 slm and maintained until the temperature in the chamber drops to room temperature;

[0061] Step 4: Instantly reduce the hydrogen flow rate to 0 slm and the argon flow rate to 15 slm. At the same time, the pressure in the chamber is increased linearly (ramping) at a rate of 150 mbar / min until it reaches normal pressure.

[0062] Step 5: Keep the argon flow constant and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before removing the epitaxial wafer with the robot.

[0063] The surface morphology of the epitaxial wafer was inspected using an AOI optical detector. The number of bump defects on the surface of the epitaxial wafer was 5, and the defect density was 0.02cm -2 .

[0064] Example 3

[0065] A method for reducing bump defects on the surface of a silicon carbide epitaxial film comprises the following steps:

[0066] Step 1: Select an 8-inch silicon carbide substrate with a silicon surface tilted 4° in the <11-20> direction, perform etching, and grow a buffer layer and an epitaxial layer. The specific operations are the same as those in Example 1.

[0067] Step 2: After the epitaxial layer growth is completed, the growth source and doping source are turned off, the pressure remains unchanged, the hydrogen flow rate is suddenly increased to 30 slm, and 60 slm of argon is introduced at the same time to cool down;

[0068] Step 3: When the temperature in the chamber drops to 1000°C, the pressure remains unchanged, the hydrogen flow rate remains unchanged, and the argon flow rate is suddenly increased to 300 slm and maintained until the temperature in the chamber drops to room temperature;

[0069] Step 4: Instantly reduce the hydrogen flow rate to 0 slm and the argon flow rate to 30 slm. At the same time, the pressure in the chamber is increased linearly (ramping) at a rate of 180 mbar / min until it reaches normal pressure.

[0070] Step 5: Keep the argon flow constant and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before removing the epitaxial wafer with the robot.

[0071] The surface morphology of the epitaxial wafer was inspected using an AOI optical detector. The number of bump defects on the surface of the epitaxial wafer was 9, and the defect density was 0.03cm -2 .

[0072] Example 4

[0073] A method for reducing bump defects on the surface of a silicon carbide epitaxial film comprises the following steps:

[0074] Step 1: Select an 8-inch silicon carbide substrate with a silicon surface tilted 4° in the <11-20> direction, perform etching, and grow a buffer layer and an epitaxial layer. The specific operations are the same as those in Example 1.

[0075] Step 2: After the epitaxial layer growth is completed, the growth source and doping source are turned off, the pressure remains unchanged, the hydrogen flow rate is suddenly increased to 40 slm, and 50 slm of argon is introduced at the same time to cool down;

[0076] Step 3: When the temperature in the chamber drops to 1100°C, the pressure remains unchanged, the hydrogen flow rate remains unchanged, and the argon flow rate is suddenly increased to 150slm and maintained until the temperature in the chamber drops to room temperature;

[0077] Step 4: Instantly reduce the hydrogen flow rate to 0 slm and the argon flow rate to 20 slm. At the same time, the pressure in the chamber is increased linearly (ramping) at a rate of 200 mbar / min until it reaches normal pressure.

[0078] Step 5: Keep the argon flow constant and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before removing the epitaxial wafer with the robot.

[0079] The surface morphology of the epitaxial wafer was inspected using an AOI optical detector. The number of bump defects on the surface of the epitaxial wafer was 1, and the defect density was 0.003cm -2 .

[0080] Example 5

[0081] A method for reducing bump defects on the surface of a silicon carbide epitaxial film comprises the following steps:

[0082] Step 1: Select an 8-inch silicon carbide substrate with a silicon surface tilted 4° in the <11-20> direction, perform etching, and grow a buffer layer and an epitaxial layer. The specific operations are the same as those in Example 1.

[0083] Step 2: After the epitaxial layer growth is completed, the growth source and doping source are turned off, the pressure remains unchanged, the hydrogen flow rate is suddenly changed to 50 slm, and 100 slm of argon is introduced at the same time to cool down;

[0084] Step 3: When the temperature in the chamber drops to 1200°C, the pressure remains unchanged, the hydrogen flow rate remains unchanged, and the argon flow rate is suddenly increased to 250slm and maintained until the temperature in the chamber drops to room temperature;

[0085] Step 4: Instantly reduce the hydrogen flow rate to 0 slm and the argon flow rate to 10 slm. At the same time, the pressure in the chamber is increased linearly (ramping) at a rate of 140 mbar / min until it reaches normal pressure.

[0086] Step 5: Keep the argon flow constant and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before removing the epitaxial wafer with the robot.

[0087] The surface morphology of the epitaxial wafer was inspected using an AOI optical detector. The number of bump defects on the surface of the epitaxial wafer was 7, and the defect density was 0.03cm -2 .

[0088] Comparative Example 1

[0089] A method for preparing a silicon carbide epitaxial film, referring to Example 1, except that the cooling process after the epitaxial layer growth is different, the specific process conditions are as follows: Figure 4 As shown, the following steps are included:

[0090] Step 1: Select an 8-inch silicon carbide substrate with a silicon surface tilted 4° in the <11-20> direction, perform etching, and grow a buffer layer and an epitaxial layer. The specific operations are the same as those in Example 1.

[0091] Step 2: After the epitaxial layer growth is completed, the growth source and doping source are turned off, and hydrogen is continuously introduced into the chamber to maintain a hydrogen atmosphere for cooling. The hydrogen flow rate is 100 slm, and the pressure in the chamber is increased at a rate of 130 mbar / min using a linear ramping method until it reaches normal pressure.

[0092] Step 3: When the temperature in the chamber drops to 1000°C, the hydrogen flow rate is increased to 250slm by a sudden change and maintained until the temperature in the chamber drops to room temperature;

[0093] Step 4: Instantly reduce the hydrogen flow rate to 0 and then use 30slm argon to purge for 5 minutes to replace the hydrogen in the chamber. After completion, turn off the argon and let it stand for 3 minutes before removing the epitaxial wafer with a robot.

[0094] The surface morphology of the epitaxial wafer is inspected using an AOI optical detector, such as Figure 5 As shown, the number of bump defects on the surface of the epitaxial wafer is 397, and the defect density is 1.33cm -2 .

[0095] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0096] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0097] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for reducing bump defects on the surface of a silicon carbide epitaxial film, characterized by: The following steps are involved: The first step is to place the silicon carbide substrate in a reaction chamber, etch the substrate in a hydrogen atmosphere, and then introduce a carbon source and a silicon source as growth sources to grow a buffer layer and an epitaxial layer. Step 2: After the epitaxial layer growth is completed, the growth source is turned off, the pressure in the reaction chamber remains unchanged, the hydrogen flow rate is suddenly reduced to 10-50 slm, and 50-100 slm of argon is introduced to perform the first stage of cooling; Step 3: When the temperature in the reaction chamber drops to 1000-1200° C., a second stage of cooling is performed, including maintaining the pressure in the reaction chamber constant, maintaining the hydrogen flow rate during the second stage of cooling constant, or reducing the hydrogen flow rate, and increasing the argon flow rate to 100-300 slm in a sudden manner, and maintaining the argon flow rate until the temperature in the reaction chamber drops to a target temperature, which is room temperature; Step 4: Instantly reduce the hydrogen flow rate to 0 slm and the argon flow rate to 10-30 slm, while restoring the internal pressure of the reaction chamber to the target pressure; Step 5: Purge in an argon atmosphere. After the purge is completed, turn off the argon and take out the epitaxial wafer after standing.

2. The method for reducing surface bump defects in silicon carbide epitaxial films according to claim 1, characterized in that: In the first step, the carbon source is any one of methane, ethane, and ethylene, the silicon source is any one of trichlorosilane and dichlorosilane, and the growth temperature of the epitaxial layer is 1500-1800°C.

3. The method for reducing surface bump defects in silicon carbide epitaxial films according to claim 2, characterized in that: In the first step, a doping source is introduced during the growth of the epitaxial layer, wherein the doping source is nitrogen or trimethylaluminum.

4. The method for reducing surface bump defects in silicon carbide epitaxial films according to claim 1, characterized in that: In the second step, the hydrogen flow rate is suddenly changed to 15-40 slm, and 55-70 slm of argon is introduced at the same time.

5. The method for reducing surface bump defects in silicon carbide epitaxial films according to claim 4, characterized in that: In the second step, the first stage of cooling is from the epitaxial temperature to 1000-1200°C, and the cooling time is 8-13 minutes.

6. The method for reducing surface bump defects in silicon carbide epitaxial films according to claim 1, characterized in that: In the third step, the cooling time is 10~20 minutes.

7. The method for reducing surface bump defects in silicon carbide epitaxial films according to claim 1, characterized in that: In the fourth step, the internal pressure of the reaction chamber is increased in a linear and gradual manner at a rate of 130-200 mbar / min, and the target pressure is normal pressure.

8. A silicon carbide epitaxial wafer prepared by the method for reducing surface bump defects in a silicon carbide epitaxial film according to any one of claims 1 to 7.

9. The silicon carbide epitaxial wafer according to claim 8, characterized in that: The bump defect density of the silicon carbide epitaxial wafer is no more than 0.03cm -2 .

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