A carbon protective film on the surface of a SiC wafer, its preparation method and application

Abstract

The present invention provides a carbon protective film on the surface of a SiC wafer, a preparation method thereof and an application, belonging to the technical field of semiconductor devices. The preparation method comprises the following steps: providing a PECVD device, wherein a SiC wafer is placed in the chamber of the PECVD device; introducing a precursor source into the chamber and maintaining it under 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 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, with the unit of W, and t2 and t3 are the deposition times under the second condition and the third condition respectively, with the unit of s. The present invention improves the uniformity of the carbon protective film and increases the pull-off strength of the carbon protective film. Even when the thickness of the carbon protective film exceeds 800 nm, it still has excellent thickness uniformity and pull-off strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and particularly 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 manufacturing process of SiC devices, there is a high-temperature annealing process after ion implantation. Usually, high-temperature annealing needs to be carried out at a temperature 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, resulting in the volatilization of Si from the SiC surface and redeposition on the wafer surface in the forms of Si, Si2C, SiC2, etc. This process not only makes the device surface rough but also changes the chemical composition of the device surface, thus seriously affecting the performance of SiC devices.

[0003] Research has found that depositing a carbon film on the surface of silicon carbide, due to the high thermal stability of the carbon film itself, is not prone to reaction or decomposition at high temperatures, so it significantly slows down the evaporation of silicon from the SiC surface and protects the underlying SiC material. Nowadays, magnetron sputtering or PECVD (plasma-enhanced chemical vapor deposition) methods are generally used to make carbon films. After the high-temperature annealing process is completed, the carbon film can be removed by using O2 plasma, etc. For example, CN113745118A discloses a preparation method of 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 the method of high-temperature carbonization of photoresist or magnetron sputtering. However, the carbon film made by the magnetron sputtering method belongs to a crystal, with poor adhesion and low mechanical strength. It not only has a loose and porous film quality but also a slow deposition rate. For this reason, the PECVD method is also used to make carbon films in the prior art. For example, CN119694881A discloses a wafer with an amorphous carbon film deposited on the back surface, a preparation method thereof, and an application thereof. The method includes the steps of using acetylene or propylene as a deposition gas to deposit an amorphous carbon film on the back surface 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, when the thickness of the carbon film made by the PECVD method exceeds 800 nm, there are two difficulties. 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 the carbon film in the carbon film preparation process by the PECVD method is a current research hotspot. Summary of the Invention

[0005] Aiming at 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, a preparation method thereof and an application. By introducing a first deposition process and defining a specific parameter relationship between the first deposition and the second deposition, the present invention significantly improves the uniformity of the prepared carbon protective film, increases the pull-off strength of the carbon protective film, reduces the possibility of the carbon protective film falling off, and even when the thickness of the carbon protective film exceeds 800 nm, it still has excellent thickness uniformity and pull-off strength. Therefore, this preparation method has a significant protective effect on the SiC wafer, ensures the stability of semiconductor devices, and thus greatly improves the yield and market competitiveness of semiconductor devices.

[0006] To achieve the purpose of this invention, the following technical solutions are adopted:

[0007] In the first aspect, the present invention provides a preparation method of a carbon protective film on the surface of a SiC wafer, and the preparation method includes the following steps:

[0008] Provide a PECVD device, and place a SiC wafer in the chamber of the PECVD device.

[0009] Introduce a precursor source into the chamber and maintain it under a first condition.

[0010] Perform a first deposition under a second condition to deposit a first carbon film on the surface of the SiC wafer.

[0011] Perform 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, with the unit of W, and t2 and t3 are the deposition times under the second condition and the third condition respectively, with the unit of s.

[0012] By introducing a first deposition process and defining a specific parameter relationship between the first deposition and the second deposition, the present invention significantly improves the uniformity of the prepared carbon protective film, increases the pull-off strength of the carbon protective film, reduces the possibility of the carbon protective film falling off, and even when the thickness of the carbon protective film exceeds 800 nm, it still has excellent thickness uniformity and pull-off strength. Therefore, this preparation method has a significant protective effect on the SiC wafer, ensures the stability of semiconductor devices, and thus greatly improves the yield and market competitiveness of semiconductor devices.

[0013] In the present invention, it is defined that the power under the second condition is less than the power under the third condition, and at the same time, the deposition time of the first deposition is less than the deposition time of the second deposition. Under the synergistic action of the two, the deposited carbon film can have good uniformity and pull-off strength.

[0014] The purpose of introducing the precursor source into the chamber and maintaining it under the first conditions 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.

[0015] It should be noted that the PECVD equipment used in the present invention is of the single-chamber and single-wafer type, which mainly includes a chamber, in which a carrier stage is provided for carrying the SiC wafer; a radio frequency system for dissociating the precursor source into an ionic state, for example, an AENI radio frequency system; and a heater for providing heat to the SiC wafer. Exemplarily, the material of the heater is aluminum or the like.

[0016] Preferably, the preheating temperature of the SiC wafer is 400 - 500 °C, for example, it can be 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, 480 °C, 490 °C or 500 °C, etc.

[0017] In the present invention, preheating at an appropriate temperature can improve the deposition rate and quality of the subsequent carbon film, enabling the carbon protective film to cover the surface of the SiC wafer more uniformly and densely; at the same time, it can improve the cleanliness of the SiC wafer surface, creating good conditions for the anti-peeling performance of the carbon protective film.

[0018] Preferably, the precursor source is a carbon source gas and an inert gas source gas.

[0019] Preferably, the carbon source gas includes C3H6.

[0020] Preferably, the inert gas source gas includes helium and / or argon.

[0021] Preferably, the first conditions include:

[0022] The chamber pressure is 4 - 6 torr, for example, it can be 4 torr, 4.2 torr, 4.4 torr, 4.6 torr, 4.8 torr, 5 torr, 5.2 torr, 5.4 torr, 5.6 torr, 5.8 torr or 6 torr, etc.; the flow rate of the carbon source gas is 220 - 300 sccm, for example, it can be 220 sccm, 250 sccm, 270 sccm or 300 sccm, etc.; the flow rate of argon is 5000 - 6000 sccm, for example, it can be 5000 sccm, 5200 sccm, 5400 sccm, 5600 sccm, 5800 sccm or 6000 sccm, etc.; the flow rate of helium is 150 - 250 sccm, for example, it can be 150 sccm, 180 sccm, 200 sccm, 220 sccm or 250 sccm, etc.

[0023] Preferably, the maintenance time of the first condition is 8 - 12 s, for example, it can be 8 s, 9 s, 10 s, 11 s or 12 s, etc.

[0024] Preferably, the value range of P2 is 450 - 550 W, for example, it can be 450 W, 460 W, 470 W, 480 W, 490 W, 500 W, 510 W, 520 W, 530 W, 540 W or 550 W, etc.

[0025] In the present invention, performing the first deposition under suitable power conditions helps to fully dissociate the carbon source gas, generate sufficient active particles, so that they can more effectively participate in the deposition process of the carbon film, and the active particles are evenly distributed on the wafer surface, and a uniform and dense carbon film can be formed. In addition, before performing the second deposition of a relatively thick carbon film, first performing the first deposition under the above power conditions to form a relatively thin first carbon film can effectively improve the bonding force between the carbon protective film and the wafer, thereby improving the adhesion of the carbon protective film.

[0026] Preferably, the value range of t2 is 2 - 4 s, for example, it can be 2 s, 3 s or 4 s, etc.

[0027] In the present invention, using the above deposition time can obtain a relatively thin first carbon film, and the carbon film at this thickness has good uniformity and pull-off strength.

[0028] Preferably, the second condition includes:

[0029] The flow rate of the carbon source gas is 220 - 300 sccm, for example, it can be 220 sccm, 250 sccm, 270 sccm or 300 sccm, etc., the flow rate of argon is 5000 - 6000 sccm, for example, it can be 5000 sccm, 5200 sccm, 5400 sccm, 5600 sccm, 5800 sccm or 6000 sccm, etc., the flow rate of helium is 150 - 250 sccm, for example, it can be 150 sccm, 180 sccm, 200 sccm, 220 sccm or 250 sccm, etc., the working pressure is 2 - 8 torr, for example, it can be 2 torr, 3 torr, 4 torr, 5 torr, 6 torr, 7 torr or 8 torr, etc., and the deposition temperature is 300 - 400 °C, for example, it can be 300 °C, 320 °C, 340 °C, 360 °C, 380 °C or 400 °C, etc.

[0030] In the first deposition process of the present invention, in addition to limiting the power and deposition time, the flow rate of a suitable precursor source, the working pressure, and the deposition temperature are also limited. With the coordinated cooperation of the above-mentioned multiple parameters, not only can a high-quality first carbon film be obtained, but also this first carbon film can serve as a good bridge, laying a foundation for improving the bonding strength between the subsequent second carbon film and the wafer, and at the same time laying a good foundation for the deposition thickness uniformity of the carbon protective film.

[0031] Preferably, the thickness of the first carbon film is 150 - 250 Å, and for example, it can be 150 Å, 175 Å, 200 Å, 225 Å, 250 Å, etc.

[0032] It should be noted that the thickness of the first carbon film is determined by t2.

[0033] Preferably, the value range of P3 is 750 - 850 W, and for example, it can be 750 W, 760 W, 770 W, 780 W, 790 W, 800 W, 810 W, 820 W, 830 W, 840 W, 850 W, etc.

[0034] In the present invention, using a power condition greater than P2 for the second deposition can provide more energy for the carbon source gas, so that the carbon source gas can be more fully ionized and excited, obtaining a higher deposition rate, which helps to shorten the process time and improve production efficiency; at the same time, the higher-energy particles can also promote the atomic arrangement in the carbon film to be more orderly, reducing the content of defects and impurities, thereby improving the quality and performance of the carbon protective film.

[0035] Preferably, the value range of t3 is 55 - 65 s, and for example, it can be 55 s, 56 s, 57 s, 58 s, 59 s, 60 s, 61 s, 62 s, 63 s, 64 s, 65 s, etc.

[0036] Preferably, the third condition includes:

[0037] 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.

[0038] 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.

[0039] 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.

[0040] Preferably, the preparation method comprises the following steps:

[0041] (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).

[0042] (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.

[0043] (3) Perform the first deposition under the 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 is 450 - 550 W, t2 is 2 - 4 s, the flow rate of the carbon source gas is 220 - 300 sccm, the flow rate of argon is 5000 - 6000 sccm, the flow rate of helium is 150 - 250 sccm, the working pressure is 2 - 8 torr, and the deposition temperature is 300 - 400 °C.

[0044] (4) Perform the second deposition under the 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 - 850 W, t3 is 55 - 65 s, the flow rate of the carbon source gas is 220 - 300 sccm, the flow rate of argon is 5000 - 6000 sccm, the flow rate of helium is 150 - 250 sccm, the working pressure is 2 - 8 torr, and the deposition temperature is 300 - 400 °C.

[0045] (5) Perform purging and pumping to restore the chamber to a vacuum state, and take out the SiC wafer with the carbon protective film.

[0046] In a second aspect, the present invention provides a carbon protective film on the surface of a SiC wafer, and the carbon protective film on the surface of the SiC wafer is prepared by using the preparation method described in the first aspect.

[0047] The thickness of the carbon protective film is 500 - 1200 nm, for example, it can be 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm or 1200 nm, etc. The surface roughness Ra of the carbon protective film is less than 2 nm, for example, it can be 1.5 nm, 1.2 nm, 1 nm or 0.5 nm, etc.

[0048] The carbon protective film prepared by the present invention can still have excellent thickness uniformity and peel strength while the thickness exceeds 800 nm.

[0049] It should be noted that the measurement of the surface roughness Ra can be carried out by using the atomic force microscopy method (AFM), or the scanning electron microscopy method (SEM), etc.

[0050] In a third aspect, the present invention provides a preparation method of a SiC device, and the preparation method includes:

[0051] 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 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.

[0052] Preferably, the temperature of the annealing treatment is ≥1600 °C, and for example, it can be 1600 °C, 1700 °C, 1800 °C, 1900 °C, 2000 °C, etc.

[0053] Fourthly, the present invention provides a SiC device, and the SiC device is prepared by using the preparation method described in the third aspect.

[0054] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] By introducing the first deposition process and simultaneously defining the specific parameter relationship between the first deposition and the second deposition, the present invention significantly improves the uniformity of the prepared carbon protective film, increases the pull-off strength of the carbon protective film, reduces the possibility of the carbon protective film falling off, and even when the thickness of the carbon protective film exceeds 800 nm, it still has excellent thickness uniformity and pull-off strength. Therefore, this preparation method has a significant protective effect on the SiC wafer, ensures the stability of the semiconductor device, and thus greatly improves the yield and market competitiveness of the semiconductor device. Description of the Drawings

[0057] Figure 1 It is the process flow chart provided in Embodiment 1 of the present invention. Detailed Embodiments

[0058] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0059] In a specific embodiment, the present invention provides a single-chamber single-wafer PECVD device, including:

[0060] A chamber for carbon film deposition, and a susceptor is arranged in the chamber, and the susceptor is used for carrying the SiC wafer.

[0061] An AENI radio frequency system for dissociating the precursor source into an ionic state, with a frequency of 13.56 MHz.

[0062] An aluminum heater for providing heat to the SiC wafer.

[0063] In another specific embodiment, the present invention provides a method for preparing a carbon protective film on the surface of a SiC wafer, and the process flow chart of the preparation method is as Figure 1 shown, including the following steps:

[0064] Provide a PECVD device, and a SiC wafer is placed in the chamber of the PECVD device.

[0065] Introduce a precursor source into the chamber and maintain it under the first condition.

[0066] Perform a first deposition under the second condition to deposit a first carbon film on the surface of the SiC wafer.

[0067] Perform a second deposition under the third condition to deposit a second carbon film on the first carbon film to form a carbon protection 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.

[0068] The following room temperature refers to 25°C.

[0069] Example 1

[0070] This example provides a method for preparing a carbon protection film on the surface of a SiC wafer, and the preparation method includes the following steps:

[0071] (1) In a single-chamber single-wafer PECVD device, place the SiC wafer on the stage and preheat the SiC wafer from room temperature to 450°C for 60 s.

[0072] (2) Introduce C3H6 and helium into the chamber and maintain it under the first condition; wherein, the first condition includes: chamber pressure 5 torr, flow rate of C3H6 260 sccm, flow rate of argon 5500 sccm, flow rate of helium 200 sccm; the maintenance time of the first condition is 10 s.

[0073] (3) Perform a first deposition under the second condition to deposit a first carbon film with a thickness of 200 Å on the surface of the SiC wafer; wherein, the second condition includes: P2 is 500 W, t2 is 3 s, flow rate of C3H6 (Q2) 260 sccm, flow rate of argon 5500 sccm, flow rate of helium 200 sccm, working pressure 5 torr, deposition temperature 350°C.

[0074] (4) Perform a second deposition under the third condition to deposit a second carbon film on the first carbon film to form a carbon protection film with a total thickness of 800 nm; wherein, the third condition includes: P3 is 800 W, t3 is 60 s, flow rate of C3H6 (Q3) 260 sccm, flow rate of argon 5500 sccm, flow rate of helium 200 sccm, working pressure 5 torr, deposition temperature 350°C.

[0075] (5)Fully open the butterfly valve, perform purging and pumping to restore the vacuum state of the cavity, and take out the SiC wafer with a carbon protective film.

[0076] This embodiment also provides a method for fabricating a SiC device, and the fabrication method includes:

[0077] After ion implantation of the SiC wafer, the carbon protective film on the surface of the SiC wafer is fabricated on the ion implantation surface of the SiC wafer by using the fabrication 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 of the carbon protective film on the surface of the SiC wafer, thereby obtaining the SiC device.

[0078] Example 2

[0079] This embodiment provides a method for fabricating a carbon protective film on the surface of a SiC wafer, and the fabrication method includes the following steps:

[0080] (1)In a single-chamber single-wafer PECVD device, place the SiC wafer on the stage and preheat the SiC wafer from room temperature to 400 °C for 50 s.

[0081] (2)Introduce C3H6 and helium into the chamber and maintain it under the first condition; wherein, the first condition includes: chamber pressure 4 torr, flow rate of C3H6 240 sccm, flow rate of argon 5000 sccm, flow rate of helium 150 sccm; the maintenance time of the first condition is 8 s.

[0082] (3)Perform the first deposition under the second condition to deposit a first carbon film with a thickness of 250 Å on the surface of the SiC wafer; wherein, the second condition includes: P2 is 450 W, t2 is 4 s, flow rate of C3H6 (Q2) 220 sccm, flow rate of argon 5000 sccm, flow rate of helium 150 sccm, working pressure 4 torr, deposition temperature 300 °C.

[0083] (4)Perform the second deposition under the 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, flow rate of C3H6 (Q3) 240 sccm, flow rate of argon 5000 sccm, flow rate of helium 150 sccm, working pressure 4 torr, deposition temperature 300 °C.

[0084] (5)Fully open the butterfly valve, perform purging and pumping to restore the vacuum state of the cavity, and take out the SiC wafer with a carbon protective film.

[0085] This embodiment also provides a method for manufacturing a SiC device, and the manufacturing method includes:

[0086] After ion implantation of the SiC wafer, the carbon protection film on the surface of the SiC wafer is prepared on the ion implantation surface of the SiC wafer by using the manufacturing method described above. Then, at 1600 °C, the carbon protection film on the surface of the SiC wafer is annealed to remove the carbon film of the carbon protection film on the surface of the SiC wafer, and the SiC device is obtained.

[0087] Embodiment 3

[0088] This embodiment provides a method for manufacturing a carbon protection film on the surface of a SiC wafer, and the manufacturing method includes the following steps:

[0089] (1) In a single-chamber single-wafer PECVD device, place the SiC wafer on the stage, and preheat the SiC wafer from room temperature to 500 °C, with the set time being 70 s.

[0090] (2) Introduce C3H6 and helium into the chamber and maintain it under the first condition; wherein, the first condition includes: chamber pressure 6 torr, flow rate of C3H6 300 sccm, flow rate of argon 6000 sccm, flow rate of helium 250 sccm; the maintenance time of the first condition is 12 s.

[0091] (3) Perform the first deposition under the second condition to deposit a first carbon film with a thickness of 150 Å on the surface of the SiC wafer; wherein, the second condition includes: P2 is 550 W, t2 is 2 s, flow rate of C3H6 (Q2) 250 sccm, flow rate of argon 6000 sccm, flow rate of helium 250 sccm, working pressure 6 torr, deposition temperature 400 °C.

[0092] (4) Perform the second deposition under the third condition to deposit a second carbon film on the first carbon film to form a carbon protection film with a total thickness of 500 nm; wherein, the third condition includes: P3 is 850 W, t3 is 55 s, flow rate of C3H6 (Q3) 300 sccm, flow rate of argon 6000 sccm, flow rate of helium 250 sccm, working pressure 6 torr, deposition temperature 400 °C.

[0093] (5) Fully open the butterfly valve angle, perform purging and pumping to make the chamber return to the vacuum state, and take out the SiC wafer with the carbon protection film.

[0094] This embodiment also provides a method for manufacturing a SiC device, and the manufacturing method includes:

[0095] 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 described above. Then, at 1600 °C, the carbon protective film on the surface of the SiC wafer is annealed to remove the carbon film of the carbon protective film on the surface of the SiC wafer, and the SiC device is obtained.

[0096] Example 4

[0097] The difference between this example and Example 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 less than the flow rate of C3H6 in step (4), that is, Q3 > Q2.

[0098] The remaining preparation methods and parameters are the same as those in Example 1.

[0099] Example 5

[0100] The difference between this example and Example 1 is that P2 in step (3) is 400 W.

[0101] The remaining preparation methods and parameters are the same as those in Example 1.

[0102] Example 6

[0103] The difference between this example and Example 1 is that P2 in step (3) is 600 W.

[0104] The remaining preparation methods and parameters are the same as those in Example 1.

[0105] Example 7

[0106] The difference between this example and Example 1 is that t2 in step (3) is 1 s.

[0107] The remaining preparation methods and parameters are the same as those in Example 1.

[0108] Example 8

[0109] The difference between this example and Example 1 is that t2 in step (3) is 5 s.

[0110] The remaining preparation methods and parameters are the same as those in Example 1.

[0111] Comparative Example 1

[0112] The difference between this comparative example and Example 1 is that step (3) is not performed.

[0113] The remaining preparation methods and parameters are the same as those in Example 1.

[0114] Comparative Example 2

[0115] The difference between this comparative example and Example 1 is that P2 in step (3) is 800 W, while P3 in step (4) is 500 W.

[0116] The remaining preparation methods and parameters are the same as those in Example 1.

[0117] Comparative Example 3

[0118] The difference between this comparative example and Example 1 is that t2 in step (3) is 60 s and t3 in step (4) is 3 s.

[0119] The remaining preparation methods and parameters are the same as those in Example 1.

[0120] Performance Test

[0121] The surface roughness Ra and tensile strength of the carbon protective film on the SiC wafers prepared in the above examples and comparative examples were tested.

[0122] Among them, the test method for the surface roughness Ra was atomic force microscopy, and the test steps for the tensile strength included:

[0123] 1) Mount the SiC wafer with a carbon protective film on the 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.

[0124] 2) Start the tensile testing machine, apply a tensile force at a constant speed of 1 mm / min, and record the curve of the tensile force varying with displacement at the same time. When the carbon protective film is pulled off the surface of the SiC wafer, the maximum tensile force recorded by the testing machine is the pull-off force of the carbon protective film, and then the pull-off strength is calculated according to the area of the carbon protective film.

[0125] The test results are shown in Table 1.

[0126] Table 1

[0127]

[0128] Analysis:

[0129] As can be seen from Table 1, the present invention significantly improves the uniformity of the prepared carbon protective film, increases the pull-off strength of the carbon protective film, reduces the possibility of the carbon protective film falling off, and still has excellent thickness uniformity and pull-off strength even when the thickness of the carbon protective film exceeds 800 nm by introducing the first deposition process and defining the specific parameter relationship between the first deposition and the second deposition. Therefore, this preparation method has a significant protective effect on the SiC wafers, ensures the stability of semiconductor devices, and thus greatly improves the yield and market competitiveness of semiconductor devices.

[0130] It can be seen from the comparison between Example 1 and Examples 5-6 that if P2 in step (3) is too small, the deposition rate is too slow, which is not only unfavorable for improving production efficiency, but also the energy obtained by carbon atoms at low power is insufficient to form a tight and ordered first carbon film, resulting in insufficient bonding force between the carbon protection film and the SiC wafer surface; if P2 in step (3) is too large, the film thickness uniformity is poor, resulting in a large surface roughness Ra, and the excessive power may cause the Si-C bonds on the SiC wafer surface to break, damaging the crystal integrity and affecting the electrical properties of the wafer.

[0131] It can be seen from the comparison between Example 1 and Examples 7-8 that if t2 in step (3) is too small, it is difficult to achieve the effect of improving the surface roughness Ra and peel strength of the carbon protection 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 delamination.

[0132] It can be seen from the comparison between Example 1 and Comparative Example 1 that if step (3) is not carried out, the surface roughness Ra is too large, and the peel strength of the carbon protection film decreases, and peeling is likely to occur.

[0133] It can be seen from the comparison between Example 1 and Comparative Example 2 that if P2 > P3, the film thickness uniformity is poor, resulting in a large surface roughness Ra, and the excessive power may cause the Si-C bonds on the SiC wafer surface to break, damaging the crystal integrity and affecting the electrical properties of the wafer.

[0134] It can be seen from the comparison between Example 1 and Comparative Example 3 that if t2 > t3, the film thickness uniformity is poor, resulting in a large surface roughness Ra, and the bonding between the carbon protection film and the SiC wafer surface is not firm enough, and the peel strength drops sharply.

[0135] It should be noted that the present invention uses the above examples to illustrate the process method of the present invention, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected by the present invention, the addition of auxiliary components, and the 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 the surface of a SiC wafer, characterized in that, The preparation method includes the following steps: Provide a PECVD device, and place a SiC wafer in the chamber of the PECVD device; Introduce a precursor source into the chamber and maintain it under a first condition; Perform a first deposition under a second condition to deposit a first carbon film on the surface of the SiC wafer; the second condition includes: the flow rate of the carbon source gas is 220 - 300 sccm, the flow rate of argon is 5000 - 6000 sccm, the flow rate of helium is 150 - 250 sccm, the working pressure is 2 - 8 torr, and the deposition temperature is 300 - 400 °C; Perform a second deposition under a third condition to deposit a second carbon film on the first carbon film to form the carbon protection film; Wherein, P3 is greater than P2, t3 > t2, P2 and P3 are the powers under the second condition and the third condition respectively, with the unit of W, and t2 and t3 are the deposition times under the second condition and the third condition respectively, with the unit of s; The value range of P2 is 450 - 550 W; the value range of t2 is 2 - 4 s; The thickness of the first carbon film is 150 - 250 Å; The third condition further includes that Q3 > Q2, where 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, with the unit of sccm; The surface roughness Ra of the carbon protection film is less than 2 nm.

2. The preparation method according to claim 1, wherein The preheating temperature of the SiC wafer is 400 - 500 °C; And / or, the precursor source includes a carbon source gas and an inert gas source gas; The carbon source gas includes C3H6; The inert gas source gas includes 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 argon is 5000 - 6000 sccm, and the flow rate of helium is 150 - 250 sccm; And / or, the maintaining time of the first condition is 8 - 12 s.

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

4. The preparation method according to claim 1, characterized in that, The third condition includes: The flow rate of the carbon source gas is 220 - 300 sccm, the flow rate of argon is 5000 - 6000 sccm, the flow rate of helium is 150 - 250 sccm, the working pressure is 2 - 8 torr, and the deposition temperature is 300 - 400 °C.

5. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) In a single - chamber single - wafer PECVD device, place the SiC wafer on the stage and preheat the SiC wafer from room temperature to 400 - 500 °C, with the set time being 50 - 70 s; (2) Introduce a carbon source gas and an inert gas source gas into the chamber and maintain it under a first condition; wherein, 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 argon is 5000 - 6000 sccm, the flow rate of helium is 150 - 250 sccm; the maintaining time of the first condition is 8 - 12 s; (3) Perform the first deposition under the 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 is 450 - 550 W, t2 is 2 - 4 s, the flow rate of the carbon source gas is 220 - 300 sccm, the flow rate of argon is 5000 - 6000 sccm, the flow rate of helium is 150 - 250 sccm, the working pressure is 2 - 8 torr, and the deposition temperature is 300 - 400 °C; (4) Perform the second deposition under the third condition to deposit a second carbon film on the first carbon film to form a carbon protection film; wherein, the third condition includes: P3 is 750 - 850 W, t3 is 55 - 65 s, the flow rate of the carbon source gas is 220 - 300 sccm, the flow rate of argon is 5000 - 6000 sccm, the flow rate of helium is 150 - 250 sccm, the working pressure is 2 - 8 torr, and the deposition temperature is 300 - 400 °C; (5) Perform purging and pumping to restore the chamber to a vacuum state, and take out the SiC wafer with the carbon protection film.

6. A carbon protective film on the surface of a SiC wafer, characterized in that, The carbon protection film on the surface of the SiC wafer is prepared by the preparation method according to any one of claims 1 - 5; The thickness of the carbon protection film is 500 - 1200 nm, and the surface roughness Ra of the carbon protection film is less than 2 nm.

7. A method for preparing a SiC device, characterized in that, The preparation method includes: After the SiC wafer is ion - implanted, the carbon protection film on the surface of the SiC wafer is prepared by the preparation method according to any one of claims 1 - 5 on the ion - implanted surface of the SiC wafer, and then the carbon protection film on the surface of the SiC wafer is annealed to remove the carbon protection film on the surface of the SiC wafer, obtaining the SiC device.

8. A SiC device, characterized in that, The SiC device is prepared by the preparation method according to claim 7.

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