Method for preventing back corrosion and acid entering of groove Schottky diode wafer

Abstract

The invention discloses a method for preventing back corrosion and acid entering of a groove Schottky diode wafer, which comprises the following steps of: fixing a plurality of trapezoidal clamps in an edge annular area of the wafer at intervals, and enabling the bottoms of the trapezoidal clamps to face a photoetching pattern area of the wafer, an obtuse angle is formed between the contact area of the trapezoidal clamp and the edge annular area and the photoetching pattern area; performing polycrystalline silicon deposition and reverse etching processes; carrying out passivation layer deposition, dry etching and metallization processes; and carrying out a chip thinning process, pasting a blue film on the front surface for protection, and carrying out an acid corrosion liquid to carry out a back surface corrosion process. According to the method, the trapezoidal clamp design and the high-selection-ratio etching gas SF6 are adopted, the groove structure and the thickness of the polycrystalline silicon layer are optimized, the gradient of the inner wall of the groove is smoother, and a good foundation is provided for subsequent uniform coverage of a blue film.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductors, and in particular to a method for preventing acid from entering the back of a trench Schottky diode wafer. Background Art

[0002] Schottky diodes are widely used in communication power supplies, solar cell protection, inverters and other fields due to their low forward voltage drop and fast switching speed. Trench Schottky diodes are diodes that optimize Schottky contacts by forming a deep trench structure on the surface of a silicon wafer. This structure improves the reverse recovery characteristics and low leakage current performance of the device by reducing the contact area between the metal and the silicon surface, while also improving the thermal stability and reliability of the device.

[0003] The backside etching process in wafer manufacturing is used to remove the physical damage layer after wafer thinning on the backside, reduce wafer stress, and prepare for subsequent packaging, electrode contact and other operations. The process flow includes: sticking a protective blue film on the surface of the wafer to prevent the corrosion liquid from affecting the front side of the wafer; then selecting a suitable corrosion liquid (such as hydrofluoric acid, sodium hydroxide or sulfuric acid) for backside etching, and accurately controlling the depth and uniformity of the corrosion by controlling the concentration of the corrosion liquid and the immersion time. In this process, the backside material of the wafer can be removed or thinned to improve the photoelectric efficiency or optimize the thermal performance; finally, the protective blue film is torn off to complete the entire backside etching process, which can prepare for subsequent wafer packaging and connection.

[0004] In the semiconductor manufacturing industry, the photoresist on the edge of the wafer is usually unevenly coated during the manufacturing process, so generally a good pattern cannot be obtained. Sometimes the photoresist will peel off and many particles will remain. These particles will fall on the surface or back of the wafer and affect the yield. In view of this, the relevant technology will use edge photoresist removal technology with a removal distance of 1-3mm to prevent uneven edge coating or photoresist falling.

[0005] When a conventional trench Schottky diode is used for trenching, a ring-shaped trench structure is usually etched in the edge area, such as Figure 1 shown. Figure 1In the figure, 10 is the whole wafer, 1 is the edge ring area, 2 is the photolithography pattern area, and the groove depth of the trench Schottky diode design is generally 1-5um, which will produce a ring groove structure on the wafer surface. The width of this groove is very wide, and the subsequent process steps cannot be completely filled. When it comes to the back-end back etching process, a height difference will be generated. The height of the edge ring area 1 is lower than the height of the photolithography pattern area 2, and the height difference is equivalent to the groove depth. When the blue film is attached to the front side of the wafer for back acid corrosion protection, due to the softness of the blue film and the thickness of the glue, the blue film at the edge of the wafer will cover the edge ring area 1 along the slope of the photolithography pattern area 2, forming a perfect protection of the front wafer structure to avoid acid corrosion.

[0006] At present, when performing the trench etching process, a fixture is generally used to fix the wafer, such as Figure 2 As shown, 20 is a fixture for fixing the wafer, which is a rectangular structure. Figure 2 There are 5 such fixtures in the process. During the dry etching process of the groove, due to the blocking effect of the fixture, the area below the edge ring area 1 fixture is not etched. Figure 3 The unetched area 3 shown in the figure is equivalent to the height of the photolithography pattern area 2 and lower than the edge ring area 1. The height difference is equivalent to the depth of the groove. When the back-end back-etching process is carried out, due to the existence of the unetched area 3, when the blue film is laminated, the unetched area 3 and the photolithography pattern area 2 form a 90-degree clamp. During the process of covering the blue film, due to the relatively small angle, the blue film at this clamping position cannot be spread to the edge ring area 1, which is easy to form pores, causing acid to enter during the back acid etching process, causing the metal and oxide layer on the surface of the device to be corroded by acid, affecting the electrical performance and reliability of the device. Summary of the invention

[0007] In view of the problem in the prior art that acid enters the wafer during the back acid etching process, causing the metal and oxide layer on the surface of the device to be corroded by the acid, thereby affecting the electrical performance and reliability of the device, the present invention provides a method for preventing acid from entering the back of a trench Schottky diode wafer. This method can effectively prevent acid from corroding the front wafer without adding obvious process steps, thereby improving the yield of the wafers on the production line.

[0008] The technical solution provided by the present invention is as follows:

[0009] A method for preventing acid corrosion from entering the back of a trench Schottky diode wafer comprises the following steps:

[0010] A plurality of trapezoidal clamps are fixed at intervals on the edge annular region of the wafer, with the bottom of the trapezoidal clamps facing the photolithography pattern region of the wafer, so that an obtuse angle is formed between the area where the trapezoidal clamps contact the edge annular region and the photolithography pattern region;

[0011] Perform polysilicon deposition and reverse etching processes;

[0012] Perform passivation layer deposition, dry etching and metallization processes;

[0013] The chip is thinned, a blue film is applied to the front for protection, and then an acid etching solution is used to etch the back side.

[0014] Furthermore, two inner angles at the bottom of the trapezoidal clamp are both less than 45°, and two inner angles at the top of the trapezoidal clamp are greater than 135°.

[0015] Furthermore, the polysilicon deposition adopts a furnace tube LPCVD method, and the reverse etching process adopts a dry etching method.

[0016] Furthermore, the etching gas used in the reverse etching process is SF6.

[0017] Furthermore, the passivation layer is deposited by LPCVD deposition.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides a method for preventing acid from back-corroding a trench Schottky diode wafer. The method adopts a trapezoidal fixture design and a high-selectivity etching gas SF6, optimizes the trench structure and the thickness of the polysilicon layer, and makes the slope of the inner wall of the trench more gentle, providing a good foundation for the subsequent uniform coverage of the blue film. This improvement effectively prevents the acid from penetrating into the trench during the corrosion process, thereby avoiding damage to the front of the wafer. The comprehensive use of passivation layer deposition, metallization process and blue film protection enables the wafer to be multiplexly protected during the entire manufacturing process, reducing defects and losses caused by corrosion. Through these optimization measures, the present invention not only improves the yield of the wafer, but also improves production efficiency and reduces production costs without adding additional process steps, and has significant technical advantages and commercial value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the structure diagram of the edge removal during wafer lithography;

[0021] Figure 2 This is a diagram showing the fixture fixing effect during wafer dry etching;

[0022] Figure 3 This is the unetched image of the edge area of ​​the wafer due to the fixture after etching;

[0023] Figure 4 This is a rendering of the trapezoidal clamp used in the present invention;

[0024] Figure 5 This is a schematic diagram of the trapezoidal clamp structure used in the present invention.

[0025] The reference numerals are as follows:

[0026] 1-edge ring area, 2-lithography pattern area, 21-trapezoidal fixture, 10-whole wafer. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the embodiments described below are part of the embodiments of the present application, not all of the embodiments.

[0028] The present invention provides a method for preventing acid from entering the back of a trench Schottky diode wafer, comprising the following steps:

[0029] Step S1, using a plurality of trapezoidal clamps 21 to be fixed at intervals on the edge annular region 1 of the wafer, such as Figure 4 As shown, the bottom of the trapezoidal fixture 21 faces the photolithography pattern area 2 of the wafer, so that an obtuse angle is formed between the area where the trapezoidal fixture 21 contacts the edge annular area 1 and the photolithography pattern area 2 .

[0030] In step S1, after the trapezoidal clamp 21 is fixed to the edge ring region 1 of the wafer, during the dry etching process of the groove, due to the blocking effect of the clamp, the area below the clamp in the edge ring region 1 forms an unetched area (i.e., the area where the trapezoidal clamp 21 contacts the edge ring region 1). The structural schematic diagram of the trapezoidal clamp is shown in FIG. Figure 5 As shown, the two inner angles at the bottom of the trapezoidal fixture 21 are both less than 45°, and the two inner angles at the top of the trapezoidal fixture are greater than 135°. The inner angle at the bottom of the trapezoidal fixture 21 is designed to be less than 45 degrees, ensuring that the obtuse angle is greater than 135°. The area where the trapezoidal fixture 21 contacts the edge annular area 1 forms a slope, which is conducive to the subsequent blue film covering the groove area and preventing acid from entering the groove to corrode the front wafer.

[0031] Step S2, performing polysilicon deposition and reverse etching processes.

[0032] Step S3, performing passivation layer deposition, dry etching and metallization processes.

[0033] Step S4, perform chip thinning process, attach blue film to the front side for protection, and then use acid etching solution to perform back side etching process.

[0034] It should be noted that the present invention improves the clamp and adopts a trapezoidal clamp to make the slope of the inner wall of the groove more gentle, providing a good foundation for the subsequent uniform coverage of the blue film. The remaining steps of the method are currently commonly used technologies and will not be elaborated here.

[0035] Optionally, the polysilicon deposition adopts a furnace tube LPCVD method, and the reverse etching process adopts a dry etching method.

[0036] Optionally, the etching gas used in the reverse etching process is SF6. In the present invention, an etching gas with a high selectivity, such as SF6, is used to form a gentler slope of the groove height difference. Compared with the traditional Cl2 gas, SF6 gas has a higher selectivity, which can increase the thickness of the polysilicon layer on the inner wall of the wide groove, thereby making the slope between the groove areas more gentle, which is beneficial to the overall coverage of the blue film and further prevents acid corrosion.

[0037] Optionally, the passivation layer is deposited by LPCVD deposition.

[0038] In summary, the method for preventing the back corrosion of trench Schottky diode wafers provided by the present invention successfully solves the problem that the front wafer of the trench Schottky diode wafer is corroded by acid during the back acid corrosion process, thereby effectively improving the yield of the wafer. The present invention adopts a trapezoidal fixture design and a high selectivity etching gas SF6 to optimize the groove structure and the thickness of the polysilicon layer, so that the slope of the inner wall of the groove is more gentle, which provides a good foundation for the subsequent uniform coverage of the blue film. This improvement effectively prevents the acid from penetrating into the groove during the corrosion process, thereby avoiding damage to the front of the wafer. The comprehensive use of passivation layer deposition, metallization process and blue film protection enables the wafer to be multiple protected throughout the manufacturing process, reducing defects and losses caused by corrosion. Through these optimization measures, the present invention not only improves the yield of the wafer, but also improves production efficiency and reduces production costs without adding additional process steps, and has significant technical advantages and commercial value.

[0039] The above is only the best specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present application shall be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for preventing acid from entering the back of a trench Schottky diode wafer, characterized in that: The following steps are involved: A plurality of trapezoidal clamps are fixed at intervals on the edge annular region of the wafer, with the bottom of the trapezoidal clamps facing the photolithography pattern region of the wafer, so that an obtuse angle is formed between the area where the trapezoidal clamps contact the edge annular region and the photolithography pattern region; Perform polysilicon deposition and reverse etching processes; Perform passivation layer deposition, dry etching and metallization processes; The chip is thinned, a blue film is applied to the front for protection, and then an acid etching solution is used to etch the back side.

2. The method for preventing acid from entering the back of a trench Schottky diode wafer according to claim 1, characterized in that: The two inner angles at the bottom of the trapezoidal clamp are both less than 45°, and the two inner angles at the top of the trapezoidal clamp are greater than 135°.

3. The method for preventing acid from back-corrosion of a trench Schottky diode wafer according to claim 1, characterized in that: The polysilicon deposition adopts a furnace tube LPCVD method, and the reverse etching process adopts a dry etching method.

4. The method for preventing acid from entering the back of a trench Schottky diode wafer according to any one of claims 1 to 3, characterized in that: The etching gas used in the reverse etching process is SF6.

5. The method for preventing acid from back-corrosion of a trench Schottky diode wafer according to claim 4, characterized in that: The passivation layer is deposited by LPCVD deposition.

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