Method for reducing Bump defect on surface of silicon carbide epitaxial film

Abstract

The invention relates to a method for reducing Bump defects on the surface of a silicon carbide epitaxial film. The method comprises the following steps of: 1, growing a buffer layer and an epitaxial layer; 2, keeping the pressure in the reaction cavity unchanged, suddenly changing the hydrogen flow to 10-50 slm, and simultaneously introducing 50-100 slm of argon to carry out first-stage cooling; 3, when the temperature in the reaction cavity is reduced to 1000-1200 DEG C, carrying out second-stage cooling; 4, instantly reducing the hydrogen flow to 0 slm, reducing the argon flow to 10-30 slm, and recovering the internal pressure of the reaction cavity; and 5, purging in an argon atmosphere, closing argon after purging is completed, and taking out the epitaxial wafer after standing. According to the method, the Bump defect density on the surface of the silicon carbide epitaxial film can be reduced to 0.03 cm <-2 > or below, so that the quality of a silicon carbide epitaxial wafer is improved, and the performance of a semiconductor device is improved.

Description

Technical Field

[0001] The 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 special semiconductor material that has no magnetism itself, but has the spin and charge properties of electrons (or holes) and can be widely used in the field of electronic devices. Through specific processing technology, it can also obtain a certain magnetic property.

[0003] SiC epitaxial layer is the basis for the growth of semiconductor devices, so the quality of epitaxial layer is closely related to the performance of semiconductor devices. One of the core evaluation criteria is the number of surface defects, such as bumps, triangles, drops, etc. The fewer surface defects, the higher the quality of the corresponding epitaxial layer.

[0004] Among them, the bump defect, also known as the nipple defect, refers to the bulge or depression on the external surface of the product. It is usually caused by the local deformation or damage of the material due to the action of external forces. It presents a convex point in the morphology. The convex point has a linear bulge along the step plane direction, such as Figure 1 shown.

[0005] Regarding the formation of Bump defects, some studies believe that it is usually caused by tiny particles, silicon carbide particles, carbon inclusions, etc. falling on the wafer surface before epitaxial growth, and then forming a convex shape during the epitaxial growth process. This means that strict process control is required before epitaxial growth to avoid the falling of tiny particles, silicon carbide particles, carbon inclusions, etc. In practice, it has been proven difficult to achieve the ideal effect of reducing Bump defects.

[0006] Previously, bumps were not classified as fatal defects in SiC devices. Bumps were not strictly controlled during the growth of SiC epitaxial wafers. However, as the device development process progressed, the impact of bump defects on devices became more and more significant. The existence of bump defects caused local current changes when the circuit passed through it during the device manufacturing process, resulting in short circuits and damaging device performance.

[0007] Chinese patent application CN105448647A discloses a method for reducing Bump defects in hydrogenated amorphous carbon film layers, by first passing oxygen plasma through the surface of the hydrogenated amorphous carbon film for surface smoothing to remove the Bump defects on the surface of the hydrogenated amorphous carbon film, and then using hydrogen and helium plasma to smooth the surface of the hydrogenated amorphous carbon film again to improve the smoothness of the film surface. The smoothing method of this method introduces an oxygen source, which is not applicable to films under anaerobic conditions, so the use scenarios are limited.

[0008] Since Bump defects can cause short circuits in local circuits during SiC device manufacturing, thus reducing device performance and yield, finding ways to effectively reduce the number of Bumps has positive practical significance. Summary of the invention

[0009] The purpose of the present invention is to overcome the problem of a high number of Bump defects in the existing preparation of silicon carbide epitaxial wafers, and to provide a method for reducing Bump defects on the surface of silicon carbide epitaxial films. After experimental exploration, the inventor found that changing the size of the hydrogen flow rate in the cooling stage will significantly affect the number of Bumps, and then inferred that the main time of Bump formation is not in the pre-epitaxial growth stage, but in the cooling stage after the epitaxy is completed. When the temperature has not yet dropped to the standby temperature, the hydrogen introduced into the cavity promotes the etching effect on the surface of the SiC epitaxial wafer, and some small particles and surface protrusions on the surface will hinder the etching effect of hydrogen on its surroundings, so that it presents a protruding morphology.

[0010] Usually, during the epitaxial growth process, the temperature in the reaction chamber is higher than 1000°C, and surface etching will occur when gas is passed through, among which hydrogen has a strong promoting effect on surface etching. The inventor believes that when the temperature has not dropped below 1000°C after the epitaxial stage, the hydrogen introduced will intensify the etching of the SiC surface, thereby forming a large number of bumps. At the same time, the change in pressure can easily cause small particles in the cavity to fall off and be etched into bumps.

[0011] Based on the above-mentioned inventive principle, the present invention optimizes the cooling process, reduces the etching promotion effect of hydrogen on the surface during the cooling stage, slows down the etching effect, and thus reduces the Bump defect; 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: A method for reducing Bump defects on the surface of a silicon carbide epitaxial film comprises the following steps: 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 changed to 10-50 slm, and 50-100 slm of argon is introduced at the same time to perform the first stage of cooling; Step 3: When the temperature in the reaction chamber drops to 1000-1200° C., the second stage of cooling is performed, including keeping the pressure in the reaction chamber constant, increasing the argon flow rate to 100-300 slm by a sudden change, and maintaining the argon flow rate until the temperature in the reaction chamber drops to the target 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 reach 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] In a specific embodiment, in the third step, the hydrogen flow rate of the second stage of cooling remains unchanged, or the hydrogen flow rate is reduced.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] In a specific embodiment, the bump defect density of the silicon carbide epitaxial wafer is no more than 0.03 cm -2 .

[0022] Beneficial effect: The method for reducing bump defects on the surface of silicon carbide epitaxial films provided by the present invention comprises the following steps: during 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.

[0023] Furthermore, the method for reducing Bump defects on the surface of silicon carbide epitaxial films provided by the present invention 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

[0024] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings will be briefly introduced below. Obviously, the accompanying drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0025] Figure 1 It is a schematic diagram of a Bump defect provided by the background technology of the present invention; Figure 2 This is a schematic diagram of process conditions provided in Example 1 of the present invention; Figure 3 This is a Bump defect distribution diagram provided by Example 1 of the present invention (obtained by an AOI optical detector); Figure 4 This is a schematic diagram of process conditions provided in Comparative Example 1 of the present invention; Figure 5 This is a Bump defect distribution diagram provided in Comparative Example 1 of the present invention (obtained by AOI optical inspection instrument). DETAILED DESCRIPTION

[0026] 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 manner, see Table 1.

[0027]

[0028] 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 used: Temperature ①: 1500~1800℃ Temperature ②: 1800~1000℃ (cooling down) Temperature ③: 1200~25℃ (cooling down to room temperature) Temperature ④: 25℃ (room temperature) Hydrogen flow ①: 80~200slm Hydrogen flow ②: 10~50slm Hydrogen flow ③: 0slm Argon flow rate ①: 0slm Argon flow rate ②: 50~100slm Argon flow rate ③: 100~300slm Argon flow rate ④: 10~30slm Pressure ①: 50~300mbar Pressure ②: 50~1000mbar (restored to normal pressure) Pressure ③: 1000mbar (normal pressure) It should be noted that the above specific conditions are merely examples for illustrating the concept of the present invention and do not constitute a limitation to the present invention.

[0029] 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, those without specifying specific techniques or conditions are carried out according to the techniques or conditions described in the documents in this area or according to the product specification. Those without specifying the manufacturer of reagents used or instruments are conventional products that can be obtained commercially. In the following examples, if not clearly stated, "%" refers to weight percentage.

[0030] Example 1 A method for reducing Bump defects on the surface of silicon carbide epitaxial film, mainly controlling process conditions such as Figure 2 As shown, the following steps are included: Step 1: Select an 8-inch silicon-surface silicon carbide substrate with a 4° tilt toward the <11-20> direction for etching and growth of a buffer layer and an epitaxial layer.

[0031] 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 mins; After etching, the buffer layer is grown. The specific conditions are as follows: pressure of 50 mbar, temperature of 1600 °C, hydrogen flow rate of 80 slm, TCS (SiHCl3) + ethylene (C2H4) mixed gas is introduced into the reaction chamber, TCS flow rate is set to 40 sccm, C / Si is 1.0, high-purity nitrogen is used as the doping source, the growth thickness is 1 μm, and the doping concentration is ~1E18 cm -3 An n-type buffer layer; Then, an epitaxial layer is grown on the buffer layer. The specific conditions are to change the TCS and ethylene flow rates within 60 seconds by linear ramping, and finally control the TCS flow rate to 240sccm, the C / Si to 1.20, and continue to introduce high-purity nitrogen to grow to the target thickness and an n-type epitaxial layer with the target doping concentration.

[0032] 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 10slm, and 90slm of argon is introduced to cool down; 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 increased to 220slm by a sudden change, and maintained until the temperature in the chamber drops to room temperature; 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 at a rate of 130 mbar / min in a linear ramping manner until it reaches normal pressure. Step 5: Keep the argon flow rate unchanged and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before taking out the epitaxial wafer with the robot.

[0033] The surface morphology of the epitaxial wafer is inspected using an AOI optical detector, such as Figure 3 As shown in the figure, the number of bump defects on the surface of the epitaxial wafer is 8, and the defect density is 0.03cm -2 .

[0034] Example 2 A method for reducing Bump defects on the surface of a silicon carbide epitaxial film comprises the following steps: Step 1: Select an 8-inch silicon-surface silicon carbide substrate with a 4° inclination toward 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.

[0035] 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 20slm, and 70slm of argon is introduced to cool down; 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 increased to 200slm by a sudden change, and maintained until the temperature in the chamber drops to room temperature; 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 at a rate of 150 mbar / min until it reaches normal pressure. Step 5: Keep the argon flow rate unchanged and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before taking out the epitaxial wafer with the robot.

[0036] 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 .

[0037] Example 3 A method for reducing Bump defects on the surface of a silicon carbide epitaxial film comprises the following steps: Step 1: Select an 8-inch silicon-surface silicon carbide substrate with a 4° inclination toward 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.

[0038] 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 30slm, and 60slm of argon is introduced to cool down; 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 increased to 300slm by a sudden change, and maintained until the temperature in the chamber drops to room temperature; 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 at a rate of 180 mbar / min until it reaches normal pressure. Step 5: Keep the argon flow rate unchanged and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before taking out the epitaxial wafer with the robot.

[0039] 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 .

[0040] Example 4 A method for reducing Bump defects on the surface of a silicon carbide epitaxial film comprises the following steps: Step 1: Select an 8-inch silicon-surface silicon carbide substrate with a 4° inclination toward 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.

[0041] 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 40slm, and 50slm of argon is introduced to cool down; 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 increased to 150slm by a sudden change, and maintained until the temperature in the chamber drops to room temperature; 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 at a rate of 200 mbar / min until it reaches normal pressure. Step 5: Keep the argon flow rate unchanged and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before taking out the epitaxial wafer with the robot.

[0042] 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 .

[0043] Example 5 A method for reducing Bump defects on the surface of a silicon carbide epitaxial film comprises the following steps: Step 1: Select an 8-inch silicon-surface silicon carbide substrate with a 4° inclination toward 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.

[0044] Step 2: After the epitaxial layer growth is completed, the growth source and the doping source are turned off, the pressure remains unchanged, the hydrogen flow rate is suddenly changed to 50slm, and 100slm of argon is introduced at the same time to cool down; 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 increased to 250slm by a sudden change, and maintained until the temperature in the chamber drops to room temperature; 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 at a rate of 140 mbar / min until it reaches normal pressure. Step 5: Keep the argon flow rate unchanged and purge for 5 minutes. After completion, turn off the argon gas and let it stand for 3 minutes before taking out the epitaxial wafer with the robot.

[0045] 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 .

[0046] Comparative Example 1 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: Step 1: Select an 8-inch silicon-surface silicon carbide substrate with a 4° inclination toward 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.

[0047] Step 2: After the epitaxial layer growth is completed, the growth source and the doping source are turned off, and hydrogen is continuously introduced into the chamber to maintain the hydrogen atmosphere for cooling. The flow rate of the introduced hydrogen is 100 slm, and at the same time, the pressure in the chamber is increased at a rate of 130 mbar / min in a linear ramping manner until it reaches normal pressure; Step 3: When the temperature in the cavity drops to 1000°C, the hydrogen flow rate is increased to 250slm by a sudden change and maintained until the temperature in the cavity drops to room temperature; 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 taking out the epitaxial wafer with the robot.

[0048] The surface morphology of the epitaxial wafer is inspected using an AOI optical detector, such as Figure 5 As shown in the figure, the number of bump defects on the surface of the epitaxial wafer is 397, and the defect density is 1.33cm -2 .

[0049] 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, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0050] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0051] In addition, 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 in that: 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 changed to 10-50 slm, and 50-100 slm of argon is introduced at the same time to perform the first stage of cooling; Step 3: When the temperature in the reaction chamber drops to 1000-1200° C., the second stage of cooling is performed, including keeping the pressure in the reaction chamber constant, increasing the argon flow rate to 100-300 slm by a sudden change, and maintaining the argon flow rate until the temperature in the reaction chamber drops to the target 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 reach 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 bump defects on the surface of silicon carbide epitaxial film 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 bump defects on the surface of silicon carbide epitaxial film according to claim 2, characterized in that: In the first step, a doping source is introduced during the growth of the epitaxial layer, and the doping source is nitrogen or trimethylaluminum.

4. The method for reducing bump defects on the surface of silicon carbide epitaxial film 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 bump defects on the surface of silicon carbide epitaxial film according to claim 4, characterized in that: 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.

6. The method for reducing bump defects on the surface of silicon carbide epitaxial film according to claim 4 or 5, characterized in that: In the third step, the hydrogen flow rate of the second stage cooling remains unchanged, or the hydrogen flow rate is reduced.

7. The method for reducing surface bump defects of silicon carbide epitaxial thin films according to claim 6, characterized in that: In the third step, the second stage of cooling is from 1200~1000℃ to room temperature, and the cooling time is 10~20mins; the target temperature is room temperature.

8. The method for reducing surface bump defects of silicon carbide epitaxial thin 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.

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

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

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