SiC wafer surface carbon protection film and preparation method and application thereof

Abstract

The invention provides a SiC wafer surface carbon protection film and a preparation method and application thereof, and belongs to the technical field of semiconductor devices. The preparation method comprises the following steps: providing PECVD equipment, wherein a SiC wafer is placed in a cavity of the PECVD equipment; introducing a precursor source into the chamber, and maintaining under a first condition; performing first deposition under a second condition to deposit a first carbon film on the surface of the SiC wafer; performing second deposition under a third condition to deposit a second carbon film on the first carbon film to form a carbon protection film; wherein P3 is larger than P2, t3 is larger than t2, P2 and P3 are power under the second condition and the third condition respectively, the unit is W, t2 and t3 are deposition time under the second condition and the third condition respectively, and the unit is s. The uniformity of the carbon protective film is improved, the pull-off strength of the carbon protective film is improved, and even if the thickness of the carbon protective film exceeds 800 nm, the carbon protective film has excellent thickness uniformity and pull-off strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and in particular relates to a carbon protective film on the surface of a SiC wafer, a preparation method thereof and an application thereof. Background Art

[0002] In the SiC device manufacturing process, there is a high-temperature annealing step after ion implantation, which usually requires high-temperature annealing at above 1600°C. The extremely high annealing temperature brings a problem: the Si-C bonds on the surface of the SiC wafer are prone to breakage, causing Si to volatilize from the SiC surface and re-deposit on the wafer surface in the form of Si, Si2C, SiC2, etc. This process not only causes the device surface to become rough, but also changes the chemical composition of the device surface, which seriously affects the performance of the SiC device.

[0003] The study found that a carbon film was coated on the surface of silicon carbide. Since the carbon film itself has high thermal stability, it is not easy to react or decompose at high temperature, so it significantly slows down the evaporation of silicon from the SiC surface and protects the SiC material underneath. Nowadays, magnetron sputtering or PECVD (plasma enhanced chemical vapor deposition) is generally used to make carbon films. After the high-temperature annealing process is completed, O2 plasma (plasma) can be used to remove the carbon film. For example, CN113745118A discloses a method for preparing a silicon carbide power device, including: forming a carbon film on the surface of a gate structure and a silicon carbide epitaxial layer, which is achieved by high-temperature carbonization of photoresist or magnetron sputtering. However, the carbon film produced by magnetron sputtering is crystalline, has poor adhesion, low mechanical strength, and is not only loose and porous, but also has a slow deposition rate. For this reason, the prior art also uses the PECVD method to make carbon films. For example, CN119694881A discloses a wafer with an amorphous carbon film deposited on the back, and a preparation method and application thereof, wherein the method comprises the steps of: using acetylene or propylene as a deposition gas to deposit an amorphous carbon film on the back of the wafer. The amorphous carbon film prepared by this method is not only dense, but also has a faster deposition rate than the magnetron sputtering method. However, the carbon film prepared by the PECVD method has two difficulties when the thickness exceeds 800nm. First, the uniformity tends to deteriorate; second, the film will peel off.

[0004] Therefore, how to improve the problems of poor uniformity and easy peeling of carbon films in the PECVD carbon film process is a hot topic in current research. Summary of the invention

[0005] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a carbon protective film on the surface of a SiC wafer and a preparation method and application thereof. The present invention introduces a first deposition process and simultaneously defines a specific parameter relationship between the first deposition and the second deposition, thereby significantly improving the uniformity of the prepared carbon protective film, increasing the pull-off strength of the carbon protective film, and reducing the possibility of the carbon protective film falling off. Even if the thickness of the carbon protective film exceeds 800nm, it still has excellent thickness uniformity and pull-off strength. Therefore, the preparation method has a significant protective effect on SiC wafers, ensures the stability of semiconductor devices, and thus greatly improves the yield and market competitiveness of semiconductor devices.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for preparing a carbon protective film on a SiC wafer surface, the preparation method comprising the following steps: A PECVD device is provided, wherein a SiC wafer is placed in a chamber of the PECVD device.

[0007] A precursor source is introduced into the chamber and maintained at a first condition.

[0008] A first deposition is performed under a second condition to deposit a first carbon film on the surface of the SiC wafer.

[0009] A second deposition is performed under a third condition to deposit a second carbon film on the first carbon film to form the carbon protective film; wherein, P3 is greater than P2, t3>t2, P2 and P3 are the powers under the second condition and the third condition, respectively, in W, and t2 and t3 are the deposition times under the second condition and the third condition, respectively, in s.

[0010] The present invention introduces a first deposition process and defines a specific parameter relationship between the first deposition and the second deposition, thereby significantly improving the uniformity of the prepared carbon protective film, increasing the pull-off strength of the carbon protective film, and reducing the possibility of the carbon protective film falling off. Even if the thickness of the carbon protective film exceeds 800nm, it still has excellent thickness uniformity and pull-off strength. Therefore, the preparation method has a significant protective effect on SiC wafers, ensures the stability of semiconductor devices, and thus greatly improves the yield and market competitiveness of semiconductor devices.

[0011] In the present invention, the power under the second condition is limited to be less than the power under the third condition, and the deposition time of the first deposition is limited to be less than the deposition time of the second deposition. The synergistic effect of the two can make the deposited carbon film have good uniformity and pull-off strength.

[0012] The purpose of introducing the precursor source into the chamber and maintaining the first condition in the present invention is to stabilize the environment of the chamber and the flow rate of the precursor source, which is beneficial to the subsequent deposition of the carbon film.

[0013] It should be noted that the PECVD equipment used in the present invention is a single-chamber single-wafer type, which mainly includes a chamber, in which a carrier is provided for carrying a SiC wafer; a radio frequency system for dissociating a precursor source into an ion state, illustratively, such as an AENI radio frequency system; a heater for providing heat to the SiC wafer, illustratively, the material of the heater is aluminum or the like.

[0014] Preferably, the preheating temperature of the SiC wafer is 400-500°C, for example, it may be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C or 500°C.

[0015] In the present invention, preheating at an appropriate temperature can improve the deposition rate and quality of the subsequent carbon film, allowing the carbon protective film to cover the surface of the SiC wafer more evenly and densely; at the same time, it can improve the cleanliness of the SiC wafer surface, creating good conditions for the anti-falling performance of the carbon protective film.

[0016] Preferably, the precursor sources are carbon source gas and inert source gas.

[0017] Preferably, the carbon source gas comprises C3H6.

[0018] Preferably, the inert source gas includes helium and / or argon.

[0019] Preferably, the first condition includes: The chamber pressure is 4-6torr, for example, it can be 4torr, 4.2torr, 4.4torr, 4.6torr, 4.8torr, 5torr, 5.2torr, 5.4torr, 5.6torr, 5.8torr or 6torr, etc., the flow rate of carbon source gas is 220-300sccm, for example, it can be 220sccm, 250sccm, 270sccm or 300sccm, etc., the flow rate of argon gas is 5000-6000sccm, for example, it can be 5000sccm, 5200sccm, 5400sccm, 5600sccm, 5800sccm or 6000sccm, etc., the flow rate of helium gas is 150-250sccm, for example, it can be 150sccm, 180sccm, 200sccm, 220sccm or 250sccm, etc.

[0020] Preferably, the first condition is maintained for 8-12 seconds, for example, 8 seconds, 9 seconds, 10 seconds, 11 seconds or 12 seconds.

[0021] Preferably, the value range of P2 is 450-550W, for example, it can be 450W, 460W, 470W, 480W, 490W, 500W, 510W, 520W, 530W, 540W or 550W.

[0022] In the present invention, the first deposition is performed under appropriate power conditions, which helps to fully dissociate the carbon source gas and generate sufficient active particles, so that the carbon source gas can more effectively participate in the deposition process of the carbon film, and the active particles are evenly distributed on the surface of the wafer, so that a uniform and dense carbon film can be formed. In addition, before the second deposition of a thicker carbon film is performed, the first deposition is performed under the above power conditions to form a thinner first carbon film, which can effectively improve the bonding force between the carbon protective film and the wafer, thereby improving the adhesion of the carbon protective film.

[0023] Preferably, the value range of t2 is 2-4s, for example, 2s, 3s or 4s.

[0024] In the present invention, a thinner first carbon film can be obtained by using the above deposition time. The carbon film at this thickness has good uniformity and pull-off strength.

[0025] Preferably, the second condition includes: The flow rate of the carbon source gas is 220-300sccm, for example, it can be 220sccm, 250sccm, 270sccm or 300sccm, the flow rate of the argon gas is 5000-6000sccm, for example, it can be 5000sccm, 5200sccm, 5400sccm, 5600sccm, 5800sccm or 6000sccm, the flow rate of the helium gas is 150-250sccm, for example, it can be 150sccm, 180sccm, 200sccm, 220sccm or 250sccm, the working pressure is 2-8torr, for example, it can be 2torr, 3torr, 4torr, 5torr, 6torr, 7torr or 8torr, and the deposition temperature is 300-400℃, for example, it can be 300℃, 320℃, 340℃, 360℃, 380℃ or 400℃, etc.

[0026] In the first deposition process, the present invention not only limits the power and deposition time, but also limits the flow rate, working pressure and deposition temperature of the appropriate precursor source. With the coordinated cooperation of the above multiple parameters, not only can a high-quality first carbon film be obtained, but the first carbon film can also serve as a good bridge, laying a foundation for the subsequent improvement of the bonding strength between the second carbon film and the wafer, and also laying a good foundation for the uniformity of the deposition thickness of the carbon protective film.

[0027] Preferably, the thickness of the first carbon film is 150-250Å, for example, 150Å, 175Å, 200Å, 225Å or 250Å.

[0028] It should be noted that the thickness of the first carbon film is determined by t2.

[0029] Preferably, the value range of P3 is 750-850W, for example, it can be 750W, 760W, 770W, 780W, 790W, 800W, 810W, 820W, 830W, 840W or 850W.

[0030] In the present invention, a power condition greater than that of P2 is used for the second deposition, which can provide more energy for the carbon source gas, thereby making the carbon source gas more fully ionized and excited, obtaining a higher deposition rate, and helping to shorten the process time and improve production efficiency; at the same time, higher energy particles can also make the atomic arrangement in the carbon film more orderly, reduce the content of defects and impurities, and thus improve the quality and performance of the carbon protective film.

[0031] Preferably, the value range of t3 is 55-65s, for example, it can be 55s, 56s, 57s, 58s, 59s, 60s, 61s, 62s, 63s, 64s or 65s.

[0032] Preferably, the third condition includes: The flow rate of the carbon source gas is 220-300sccm, for example, it can be 220sccm, 250sccm, 270sccm or 300sccm, the flow rate of the argon gas is 5000-6000sccm, for example, it can be 5000sccm, 5200sccm, 5400sccm, 5600sccm, 5800sccm or 6000sccm, the flow rate of the helium gas is 150-250sccm, for example, it can be 150sccm, 180sccm, 200sccm, 220sccm or 250sccm, the working pressure is 2-8torr, for example, it can be 2torr, 3torr, 4torr, 5torr, 6torr, 7torr or 8torr, and the deposition temperature is 300-400℃, for example, it can be 300℃, 320℃, 340℃, 360℃, 380℃ or 400℃, etc.

[0033] Preferably, the third condition further includes: Q3>Q2, wherein Q3 is the flow rate of the carbon source gas under the third condition, and Q2 is the flow rate of the carbon source gas under the second condition, in units of sccm.

[0034] The present invention limits the flow rate of the carbon source during the second deposition to be greater than the flow rate of the carbon source during the first deposition, so that the carbon film can obtain a suitable carbon source gas supply at different growth stages, thereby forming a carbon protective film with more uniform thickness and composition on the entire wafer surface; at the same time, it helps to accurately control the growth structure of the carbon film, so that the grain growth of the carbon film is more uniform, defects and pores are reduced, and the density and pull-off strength of the carbon protective film are improved.

[0035] Preferably, the preparation method comprises the following steps: (1) In a single-chamber single-wafer PECVD device, a SiC wafer is placed on a carrier and preheated from room temperature (the present invention is not limited to this, and illustratively, it can be 25°C, etc.) to 400-500°C, and the time is set to 50-70s (i.e., the time required for preheating from room temperature to 350-400°C, which can be, for example, 50s, 55s, 60s, 65s or 70s).

[0036] (2) Introducing a carbon source gas and an inert source gas into the chamber and maintaining the chamber under a first condition; wherein the first condition includes: a chamber pressure of 4-6 torr, a flow rate of the carbon source gas of 220-300 sccm, a flow rate of the argon gas of 5000-6000 sccm, and a flow rate of the helium gas of 150-250 sccm; and the first condition is maintained for 8-12 seconds.

[0037] (3) performing a first deposition under a second condition to deposit a first carbon film with a thickness of 150-250Å on the surface of the SiC wafer; wherein the second condition includes: P2 of 450-550W, t2 of 2-4s, a flow rate of the carbon source gas of 220-300sccm, a flow rate of the argon gas of 5000-6000sccm, a flow rate of the helium gas of 150-250sccm, a working pressure of 2-8torr, and a deposition temperature of 300-400°C.

[0038] (4) performing a second deposition under a third condition to deposit a second carbon film on the first carbon film to form a carbon protective film; wherein the third condition includes: P3 is 750-850W, t3 is 55-65s, the flow rate of the carbon source gas is 220-300sccm, the flow rate of the argon gas is 5000-6000sccm, the flow rate of the helium gas is 150-250sccm, the working pressure is 2-8torr, and the deposition temperature is 300-400°C.

[0039] (5) Purging and evacuating are performed to restore the chamber to a vacuum state, and the SiC wafer with the carbon protective film is taken out.

[0040] In a second aspect, the present invention provides a carbon protective film on the surface of a SiC wafer, wherein the carbon protective film on the surface of the SiC wafer is prepared by the preparation method described in the first aspect.

[0041] The thickness of the carbon protective film is 500-1200nm, for example, it can be 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm or 1200nm, etc. The surface roughness Ra of the carbon protective film is less than 2nm, for example, it can be 1.5nm, 1.2nm, 1nm or 0.5nm, etc.

[0042] The carbon protective film prepared by the present invention can have a thickness exceeding 800 nm while still having excellent thickness uniformity and pull-off strength.

[0043] It should be noted that the surface roughness Ra can be tested by atomic force microscopy (AFM) or scanning electron microscopy (SEM).

[0044] In a third aspect, the present invention provides a method for preparing a SiC device, the method comprising: After the SiC wafer is ion implanted, the carbon protective film on the surface of the SiC wafer is prepared on the ion implanted surface of the SiC wafer using the preparation method described in the first aspect, and then the carbon protective film on the surface of the SiC wafer is annealed to obtain the SiC device.

[0045] Preferably, the temperature of the annealing treatment is ≥ 1600°C, for example, it may be 1600°C, 1700°C, 1800°C, 1900°C or 2000°C.

[0046] In a fourth aspect, the present invention provides a SiC device, wherein the SiC device is prepared by the preparation method described in the third aspect.

[0047] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0048] Compared with the prior art, the present invention has the following beneficial effects: The present invention introduces a first deposition process and defines a specific parameter relationship between the first deposition and the second deposition, thereby significantly improving the uniformity of the prepared carbon protective film, increasing the pull-off strength of the carbon protective film, and reducing the possibility of the carbon protective film falling off. Even if the thickness of the carbon protective film exceeds 800nm, it still has excellent thickness uniformity and pull-off strength. Therefore, the preparation method has a significant protective effect on SiC wafers, ensures the stability of semiconductor devices, and thus greatly improves the yield and market competitiveness of semiconductor devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a process flow chart provided for Example 1 of the present invention. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0051] In one embodiment, the present invention provides a single-chamber single-wafer PECVD device, comprising: The cavity is used for carbon film deposition, and a carrier is arranged in the cavity, and the carrier is used for carrying a SiC wafer.

[0052] AENI radio frequency system, used to dissociate the precursor source into ion state, with a frequency of 13.56MHZ.

[0053] Aluminum heater used to provide heat to the SiC wafer.

[0054] In another specific embodiment, the present invention provides a method for preparing a carbon protective film on a SiC wafer surface. The process flow chart of the preparation method is as follows: Figure 1 As shown, the following steps are included: A PECVD device is provided, wherein a SiC wafer is placed in a chamber of the PECVD device.

[0055] A precursor source is introduced into the chamber and maintained at a first condition.

[0056] The first deposition is performed under the second condition to deposit a first carbon film on the surface of the SiC wafer.

[0057] A second deposition is performed under the third condition to deposit a second carbon film on the first carbon film to form a carbon protective film; wherein, P3 is greater than P2, t3>t2, P2 and P3 are the powers under the second condition and the third condition respectively, and t2 and t3 are the deposition times under the second condition and the third condition respectively.

[0058] The room temperature below refers to 25°C.

[0059] Example 1 This embodiment provides a method for preparing a carbon protective film on a SiC wafer surface, the preparation method comprising the following steps: (1) In a single-chamber single-wafer PECVD device, a SiC wafer is placed on a carrier and preheated from room temperature to 450° C. for 60 seconds.

[0060] (2) C3H6 and helium are introduced into the chamber and maintained at a first condition; wherein the first condition includes: a chamber pressure of 5 torr, a C3H6 flow rate of 260 sccm, an argon flow rate of 5500 sccm, and a helium flow rate of 200 sccm; and the first condition is maintained for 10 s.

[0061] (3) performing a first deposition under a second condition to deposit a first carbon film with a thickness of 200Å on the surface of the SiC wafer; wherein the second condition includes: P2 of 500W, t2 of 3s, a flow rate of C3H6 (Q2) of 260sccm, a flow rate of argon of 5500sccm, a flow rate of helium of 200sccm, an operating pressure of 5torr, and a deposition temperature of 350°C.

[0062] (4) performing a second deposition under a third condition to deposit a second carbon film on the first carbon film to form a carbon protective film with a total thickness of 800 nm; wherein the third condition includes: P3 is 800 W, t3 is 60 s, the flow rate of C3H6 (Q3) is 260 sccm, the flow rate of argon is 5500 sccm, the flow rate of helium is 200 sccm, the working pressure is 5 torr, and the deposition temperature is 350°C.

[0063] (5) The butterfly valve is fully opened to perform purge and exhaust to restore the chamber to a vacuum state, and the SiC wafer with a carbon protective film is taken out.

[0064] This embodiment also provides a method for preparing a SiC device, the method comprising: After the SiC wafer is ion implanted, the carbon protective film on the surface of the SiC wafer is prepared on the ion implanted surface of the SiC wafer using the preparation method described above, and then the carbon protective film on the surface of the SiC wafer is annealed at 1600° C. to remove the carbon film on the surface of the SiC wafer to obtain the SiC device.

[0065] Example 2 This embodiment provides a method for preparing a carbon protective film on a SiC wafer surface, the preparation method comprising the following steps: (1) In a single-chamber single-wafer PECVD device, a SiC wafer is placed on a carrier and preheated from room temperature to 400° C. for 50 seconds.

[0066] (2) C3H6 and helium are introduced into the chamber and maintained at a first condition; wherein the first condition includes: a chamber pressure of 4 torr, a C3H6 flow rate of 240 sccm, an argon flow rate of 5000 sccm, and a helium flow rate of 150 sccm; and the first condition is maintained for 8 s.

[0067] (3) performing a first deposition under a second condition to deposit a first carbon film with a thickness of 250Å on the surface of the SiC wafer; wherein the second condition includes: P2 is 450W, t2 is 4s, a flow rate of C3H6 (Q2) is 220sccm, a flow rate of argon is 5000sccm, a flow rate of helium is 150sccm, an operating pressure of 4torr, and a deposition temperature of 300°C.

[0068] (4) performing a second deposition under a third condition to deposit a second carbon film on the first carbon film to form a carbon protective film with a total thickness of 1200 nm; wherein the third condition includes: P3 is 750 W, t3 is 65 s, the flow rate of C3H6 (Q3) is 240 sccm, the flow rate of argon is 5000 sccm, the flow rate of helium is 150 sccm, the working pressure is 4 torr, and the deposition temperature is 300 °C.

[0069] (5) The butterfly valve is fully opened to perform purge and exhaust to restore the chamber to a vacuum state, and the SiC wafer with a carbon protective film is taken out.

[0070] This embodiment also provides a method for preparing a SiC device, the method comprising: After the SiC wafer is ion implanted, the carbon protective film on the surface of the SiC wafer is prepared on the ion implanted surface of the SiC wafer using the preparation method described above, and then the carbon protective film on the surface of the SiC wafer is annealed at 1600° C. to remove the carbon film on the surface of the SiC wafer to obtain the SiC device.

[0071] Example 3 This embodiment provides a method for preparing a carbon protective film on a SiC wafer surface, the preparation method comprising the following steps: (1) In a single-chamber single-wafer PECVD device, a SiC wafer is placed on a carrier and preheated from room temperature to 500° C. for 70 seconds.

[0072] (2) C3H6 and helium are introduced into the chamber and maintained at a first condition; wherein the first condition includes: a chamber pressure of 6 torr, a C3H6 flow rate of 300 sccm, an argon flow rate of 6000 sccm, and a helium flow rate of 250 sccm; and the first condition is maintained for 12 s.

[0073] (3) performing a first deposition under a second condition to deposit a first carbon film with a thickness of 150Å on the surface of the SiC wafer; wherein the second condition includes: P2 is 550W, t2 is 2s, a flow rate of C3H6 (Q2) is 250sccm, a flow rate of argon is 6000sccm, a flow rate of helium is 250sccm, an operating pressure of 6torr, and a deposition temperature of 400°C.

[0074] (4) performing a second deposition under a third condition to deposit a second carbon film on the first carbon film to form a carbon protective film with a total thickness of 500 nm; wherein the third condition includes: P3 is 850 W, t3 is 55 s, the flow rate of C3H6 (Q3) is 300 sccm, the flow rate of argon is 6000 sccm, the flow rate of helium is 250 sccm, the working pressure is 6 torr, and the deposition temperature is 400 °C.

[0075] (5) The butterfly valve is fully opened to perform purge and exhaust to restore the chamber to a vacuum state, and the SiC wafer with a carbon protective film is taken out.

[0076] This embodiment also provides a method for preparing a SiC device, the method comprising: After the SiC wafer is ion implanted, the carbon protective film on the surface of the SiC wafer is prepared on the ion implanted surface of the SiC wafer using the preparation method described above, and then the carbon protective film on the surface of the SiC wafer is annealed at 1600° C. to remove the carbon film on the surface of the SiC wafer to obtain the SiC device.

[0077] Example 4 The difference between this embodiment and embodiment 1 is that the flow rate of C3H6 in step (3) is adjusted to 220 sccm, so that the flow rate of C3H6 in step (3) is smaller than the flow rate of C3H6 in step (4), that is, Q3>Q2.

[0078] The rest of the preparation methods and parameters were the same as those in Example 1.

[0079] Example 5 The difference between this embodiment and embodiment 1 is that the P2 in step (3) is 400W.

[0080] The rest of the preparation methods and parameters were the same as those in Example 1.

[0081] Example 6 The difference between this embodiment and embodiment 1 is that the P2 in step (3) is 600W.

[0082] The rest of the preparation methods and parameters were the same as those in Example 1.

[0083] Example 7 The difference between this embodiment and embodiment 1 is that the time t2 in step (3) is 1 s.

[0084] The rest of the preparation methods and parameters were the same as those in Example 1.

[0085] Example 8 The difference between this embodiment and embodiment 1 is that the t2 in step (3) is 5s.

[0086] The rest of the preparation methods and parameters were the same as those in Example 1.

[0087] Comparative Example 1 The difference between this comparative example and Example 1 is that step (3) is not performed.

[0088] The rest of the preparation methods and parameters were the same as those in Example 1.

[0089] Comparative Example 2 The difference between this comparative example and Example 1 is that the P2 in step (3) is 800W, while the P3 in step (4) is 500W.

[0090] The rest of the preparation methods and parameters were the same as those in Example 1.

[0091] Comparative Example 3 The difference between this comparative example and Example 1 is that the t2 in step (3) is 60 s, and the t3 in step (4) is 3 s.

[0092] The rest of the preparation methods and parameters were the same as those in Example 1.

[0093] Performance Testing The surface roughness Ra and tensile strength of the carbon protective film were tested for the SiC wafers having the carbon protective film on the surface prepared in the above-mentioned embodiments and comparative examples.

[0094] The test method for surface roughness Ra is atomic force microscopy, and the test steps for tensile strength include: 1) Mount the SiC wafer with a carbon protective film on the surface on a fixture and fix it by mechanical clamping, while ensuring that the surface of the carbon protective film is perpendicular to the tensile direction of the tensile testing machine.

[0095] 2) Start the tensile testing machine, apply tension at a constant speed of 1mm / min, and record the curve of tension versus displacement. When the carbon protective film is pulled off the surface of the SiC wafer, the maximum tension recorded by the testing machine is the pull-off force of the carbon protective film. Then, the pull-off strength is calculated based on the area of ​​the carbon protective film.

[0096] The test results are shown in Table 1.

[0097] Table 1

[0098] analyze: As can be seen from Table 1, the present invention significantly improves the uniformity of the prepared carbon protective film by introducing the first deposition process and defining the specific parameter relationship between the first deposition and the second deposition, thereby increasing the pull-off strength of the carbon protective film and reducing the possibility of the carbon protective film falling off, and even if the thickness of the carbon protective film exceeds 800nm, it still has excellent thickness uniformity and pull-off strength. Therefore, the preparation method has a significant protective effect on SiC wafers, ensures the stability of semiconductor devices, and thus greatly improves the yield and market competitiveness of semiconductor devices.

[0099] By comparing Example 1 with Examples 5-6, it can be seen that if P2 in step (3) is too small, the deposition rate is too slow, which is not only not conducive to improving production efficiency, but also the energy obtained by carbon atoms at low power is insufficient, making it difficult to form a tight and orderly first carbon film, resulting in insufficient bonding between the carbon protective film and the surface of the SiC wafer; if P2 in step (3) is too large, the film thickness uniformity is poor, resulting in a large surface roughness Ra, and excessive power may cause the Si-C bonds on the surface of the SiC wafer to break, destroying the integrity of the crystal and affecting the electrical properties of the wafer.

[0100] By comparing Example 1 with Examples 7-8, it can be seen that if t2 in step (3) is too small, it is difficult to improve the surface roughness Ra and pull-off strength of the carbon protective film; if t2 in step (3) is too large, the thickness of the first carbon film is too large, which will affect the overall etching rate and may cause stratification.

[0101] By comparing Example 1 with Comparative Example 1, it can be seen that if step (3) is not performed, the surface roughness Ra is too large, and the pull-off strength of the carbon protective film is reduced, and peeling is likely to occur.

[0102] By comparing Example 1 with Comparative Example 2, it can be seen that if P2>P3, the film thickness uniformity is poor, resulting in excessive surface roughness Ra, and excessive power may cause the Si-C bonds on the surface of the SiC wafer to break, destroying the integrity of the crystal and affecting the electrical properties of the wafer.

[0103] From the comparison between Example 1 and Comparative Example 3, it can be seen that if t2>t3, the film thickness uniformity is poor, resulting in excessive surface roughness Ra, and the bonding between the carbon protective film and the SiC wafer surface is not strong enough, resulting in a sharp drop in pull-off strength.

[0104] It should be noted that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a carbon protective film on a SiC wafer surface, characterized in that: The preparation method comprises the following steps: Providing a PECVD device, wherein a SiC wafer is placed in a chamber of the PECVD device; introducing a precursor source into the chamber and maintaining it at a first condition; Performing a first deposition under a second condition to deposit a first carbon film on the surface of the SiC wafer; performing a second deposition under a third condition to deposit a second carbon film on the first carbon film to form the carbon protective film; Wherein, P3 is greater than P2, t3>t2, P2 and P3 are the powers under the second condition and the third condition respectively, in W, and t2 and t3 are the deposition times under the second condition and the third condition respectively, in s.

2. The preparation method according to claim 1, characterized in that: The preheating temperature of the SiC wafer is 400-500° C.; and / or, the precursor source comprises a carbon source gas and an inert source gas; And / or, the carbon source gas includes C3H6; and / or, the inert source gas comprises helium and / or argon; And / or, the first condition includes: The chamber pressure is 4-6 torr, the flow rate of the carbon source gas is 220-300 sccm, the flow rate of the argon gas is 5000-6000 sccm, and the flow rate of the helium gas is 150-250 sccm; And / or, the first condition is maintained for 8-12 seconds.

3. The preparation method according to claim 1, characterized in that: The value range of P2 is 450-550W; And / or, the value range of t2 is 2-4s.

4. The preparation method according to claim 2, characterized in that: The second condition includes: The flow rate of carbon source gas is 220-300sccm, the flow rate of argon gas is 5000-6000sccm, the flow rate of helium gas is 150-250sccm, the working pressure is 2-8torr, and the deposition temperature is 300-400°C; And / or, the thickness of the first carbon film is 150-250Å.

5. The preparation method according to claim 1, characterized in that: The value range of P3 is 750-850W; And / or, the value range of t3 is 55-65s.

6. The preparation method according to claim 2, characterized in that: The third condition includes: The flow rate of carbon source gas is 220-300sccm, the flow rate of argon gas is 5000-6000sccm, the flow rate of helium gas is 150-250sccm, the working pressure is 2-8torr, and the deposition temperature is 300-400°C; And / or, the third condition further includes: Q3>Q2, wherein Q3 is the flow rate of the carbon source gas under the third condition, and Q2 is the flow rate of the carbon source gas under the second condition, in units of sccm.

7. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: (1) In a single-chamber single-wafer PECVD device, a SiC wafer is placed on a stage and preheated from room temperature to 400-500°C for a set time of 50-70 seconds; (2) introducing a carbon source gas and an inert source gas into the chamber and maintaining the chamber under a first condition; wherein the first condition includes: a chamber pressure of 4-6 torr, a flow rate of the carbon source gas of 220-300 sccm, a flow rate of the argon gas of 5000-6000 sccm, and a flow rate of the helium gas of 150-250 sccm; and the first condition is maintained for 8-12 seconds; (3) performing a first deposition under a second condition to deposit a first carbon film with a thickness of 150-250 Å on the surface of the SiC wafer; wherein the second condition includes: P2 of 450-550 W, t2 of 2-4 s, a flow rate of the carbon source gas of 220-300 sccm, a flow rate of the argon gas of 5000-6000 sccm, a flow rate of the helium gas of 150-250 sccm, a working pressure of 2-8 torr, and a deposition temperature of 300-400°C; (4) performing a second deposition under a third condition to deposit a second carbon film on the first carbon film to form a carbon protective film; wherein the third condition includes: P3 is 750-850W, t3 is 55-65s, the flow rate of the carbon source gas is 220-300sccm, the flow rate of the argon gas is 5000-6000sccm, the flow rate of the helium gas is 150-250sccm, the working pressure is 2-8torr, and the deposition temperature is 300-400°C; (5) Purging and evacuating are performed to restore the chamber to a vacuum state, and the SiC wafer with the carbon protective film is taken out.

8. A carbon protective film on the surface of a SiC wafer, characterized in that: The SiC wafer surface carbon protective film is prepared by the preparation method according to any one of claims 1 to 7; The thickness of the carbon protective film is 500-1200 nm, and the surface roughness Ra of the carbon protective film is less than 2 nm.

9. A method for preparing a SiC device, characterized in that: The preparation method comprises: After the SiC wafer is ion implanted, the carbon protective film on the surface of the SiC wafer is prepared on the ion implanted surface of the SiC wafer by the preparation method as described in any one of claims 1 to 7, and then the carbon protective film on the surface of the SiC wafer is annealed to remove the carbon protective film on the surface of the SiC wafer to obtain the SiC device.

10. A SiC device, characterized in that: The SiC device is prepared by the preparation method according to claim 9.

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