A method for processing IGBT wafer by using a gentle slope-shaped back surface

Abstract

The application discloses a method for processing IGBT wafer by using a gentle slope-shaped back surface, which comprises the following steps: S1, completing the process before the wafer front metal process; S2, etching the wafer back surface to form a gentle slope; S3, completing the wafer back surface process; S4, coating polyimide on the back surface; S5, manufacturing the front metal process; S6, coating polyimide on the front surface, and exposing the cutting path after developing, curing and etching; S7, completing the cutting by etching and laser, and removing the polyimide on the front surface; and S8, attaching on the cutting mold frame, removing the polyimide on the back surface, and separating the wafer grains. The gentle slope-shaped treatment on the wafer back surface can provide stress support on the edge, and overcomes the limitation of the back surface tempering temperature; meanwhile, the wafer back surface coating polyimide can buffer the stress of the thick metal film, and ensures that the thin wafer will not be warped and damaged after being plated with the thick metal film.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor processing, in particular to a method for processing IGBT wafer by using gentle slope back surface. BACKGROUND

[0002] IGBT is a composite full-control voltage-driven power semiconductor device composed of BJT (bipolar transistor) and MOS (insulated gate field effect transistor), which has the advantages of high input impedance of MOSFET (metal-oxide semiconductor field effect transistor) and low on-state voltage drop of GTR (power transistor). GTR has low saturation voltage drop and large current density, but has large driving current; MOSFET has small driving power and fast switching speed, but has large on-state voltage drop and small current density. IGBT combines the advantages of the above two devices, with small driving power and low saturation voltage drop. It is very suitable for application in variable current system such as AC motor, frequency converter, switching power supply, lighting circuit, traction drive and other fields with DC voltage of 600V and above.

[0003] The current IGBT wafer production process is to first complete the front side process of the wafer, then bond the front side with a glass carrier plate, then thin the back surface and complete the subsequent wafer back surface process. However, due to the high temperature step in the back surface process, the adhesive is a high molecular material that can only withstand 350℃ heating process, and the front side has completed the metal process, AI or Cu can at most withstand 560℃ heating process, so it is impossible to implement on the wafer bonded with the glass carrier plate, but the wafer after debonding is prone to breakage and damage. SUMMARY

[0004] To solve the problems mentioned in the background art, the purpose of the present application is to provide a method for processing IGBT wafer by using gentle slope back surface. The present application processes the wafer back surface in a gentle slope shape to provide stress support after wafer thinning, so as to prevent breakage or edge local cracks, and overcome the limitation of back surface tempering temperature. At the same time, the wafer back surface is coated with polyimide, which can buffer the stress generated during the front side metal thick film and electroplating process. After cutting, the back surface polyimide is removed to ensure that the thin wafer does not warp and break after thick metal plating.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] A method for processing IGBT wafer by using gentle slope back surface, comprising the following steps:

[0007] S1, complete the wafer front side metal process before the process;

[0008] S2, adhere the wafer front side to a grinding tape, then etch the wafer back surface to form a gentle slope wafer structure at the edge;

[0009] S3, removing the polishing tape, completing the backside process of the wafer;

[0010] S4, coating polyimide on the ramp of the backside of the wafer to flatten the backside;

[0011] S5, turning over to the front side of the wafer to make the front side metal process;

[0012] S6, coating polyimide on the front side of the wafer, and exposing the cutting path after photoetching and developing;

[0013] S7, attaching the backside of the wafer to the first cutting mold frame, cutting the cutting path to the backside metal layer through plasma etching, then cutting the backside metal through laser, and then removing the polyimide on the front side;

[0014] S8, attaching the front side of the wafer after cutting to the second cutting mold frame, then turning over the first cutting mold frame, the wafer and the second cutting mold frame as a whole, removing the adhesion of the first cutting film frame through ultraviolet light irradiation, taking off the first cutting mold frame, and then removing the polyimide on the ramp of the backside through oxygen plasma etching;

[0015] S9, removing the adhesion of the second cutting mold frame corresponding to the ramp-shaped area through ultraviolet light irradiation of the ramp-shaped area of the edge of the wafer, removing the annular ramp-shaped edge, then attaching the backside of the wafer to the third cutting mold frame, turning over the second cutting mold frame, the wafer and the third cutting mold frame as a whole, removing the adhesion of the second cutting film frame through ultraviolet light irradiation, and taking off the second cutting mold frame.

[0016] Further preferably, the process before the front side metal process includes trench, ILD and contact hole processes.

[0017] Further preferably, the ramp or step-shaped wafer structure is formed on the edge of the backside of the wafer in step S2 by polishing and edge gas ring or protective liquid etching, and the thickness of the thinned wafer is 40-150um.

[0018] Further preferably, the backside metal process includes photoetching, ion implantation, tempering and backside metal process.

[0019] The beneficial effects of the present application are:

[0020] The present application makes a gentle slope treatment on the back of the wafer, although the wafer is super-thin, the edge can still contact the heating and metal-related process equipment mechanical transfer arm contact point or edge, so as not to cause broken pieces or edge local cracks, and the limitation of back tempering temperature is overcome; the wafer back of the present application is coated with polyimide, which can buffer the stress generated in the process of front metal thick film and electroplating, and after cutting, the back polyimide can be removed to ensure that the thin wafer does not warp and break after thick metal plating; the present application exposes the cutting path after front coating, developing, curing and etching, and can be automatically aligned on the front, and then etches the cutting path and cuts the back metal by laser, which overcomes the problem that the traditional wafer back cutting is not easy to align. BRIEF DESCRIPTION OF DRAWINGS

[0021] The present application will be further described below in conjunction with the drawings.

[0022] Figure 1 is a forming schematic diagram of process step S1 of the present application;

[0023] Figure 2 is a forming schematic diagram of process step S2 of the present application;

[0024] Figure 3 is a forming schematic diagram of process step S3 of the present application;

[0025] Figure 4 is a forming schematic diagram of process step S4 of the present application;

[0026] Figure 5 is a forming schematic diagram of process step S5 of the present application;

[0027] Figure 6 is a forming schematic diagram of process step S6 of the present application;

[0028] Figure 7 is a forming schematic diagram of process step S7 of the present application;

[0029] Figure 8 is a forming schematic diagram of process step S8 of the present application;

[0030] Figure 9 is a forming schematic diagram of process step S9 of the present application. DETAILED DESCRIPTION

[0031] The technical solutions 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 described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0032] AsFigures 1-8 As shown in the drawings, a method for processing an IGBT wafer using a gentle slope-shaped back surface includes the following steps:

[0033] S1, complete the process before the wafer front metal process, including trench, ILD and contact hole process;

[0034] S2, adhere the wafer front to the grinding tape, and then use grinding and edge gas ring or protective liquid etching method to form a gentle slope-shaped wafer structure on the wafer back edge, and the thickness of the thinned wafer is 40-150um;

[0035] S3, remove the grinding tape, complete the wafer back surface photolithography, ion implantation, tempering and back surface metal process;

[0036] S4, coat polyimide on the gentle slope of the wafer back surface to flatten the back surface;

[0037] S5, flip to the wafer front surface to make the front metal process;

[0038] S6, coat polyimide on the wafer front surface, and expose the cutting path after developing, curing and etching;

[0039] S7, attach the wafer back surface to the first cutting mold frame, cut the cutting path to the back metal layer by plasma etching, then cut off the back metal by laser, and then remove the polyimide on the front surface;

[0040] S8, after cutting, the wafer front surface is attached to the second cutting mold frame, then the first cutting mold frame, wafer and second cutting mold frame are flipped as a whole, the adhesion of the first cutting film frame is removed by ultraviolet light irradiation, the first cutting mold frame is removed, and then the polyimide on the gentle slope of the back surface is removed by oxygen plasma etching;

[0041] S9, irradiate the wafer edge gentle slope-shaped area with ultraviolet light, remove the adhesion of the second cutting mold frame corresponding to the gentle slope-shaped area, remove the annular gentle slope-shaped edge, then attach the wafer back surface to the third cutting mold frame, flip the second cutting mold frame, wafer and third cutting mold frame as a whole, remove the adhesion of the second cutting film frame by ultraviolet light irradiation, and then remove the second cutting mold frame.

[0042] In the description of the present specification, the description of the terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0043] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A method for processing IGBT wafers using a gentle backside, characterized by, The method comprises the following steps: S1, completing the process before the front metal process of the wafer; S2, adhering the grinding tape to the front of the wafer, and then etching the back of the wafer to form a bevel-shaped wafer structure at the edge; S3, removing the grinding tape and completing the back process of the wafer; S4, coating polyimide on the bevel of the back of the wafer to flatten the back; S5, turning over to the front of the wafer to make the front metal process; S6, coating polyimide on the front of the wafer, and then exposing the cutting path after photoetching and developing; S7, adhering the back of the wafer to the first cutting mold, cutting the cutting path to the back metal layer by plasma etching, then cutting the back metal by laser, and then removing the polyimide on the front; S8, adhering the wafer after cutting to the second cutting mold, then turning over the first cutting mold, the wafer and the second cutting mold as a whole, removing the adhesion of the first cutting film frame by ultraviolet irradiation, taking off the first cutting mold, and then removing the polyimide on the bevel of the back by oxygen plasma etching; S9, removing the adhesion of the second cutting film frame corresponding to the bevel-shaped area by ultraviolet irradiation of the bevel-shaped area of the wafer edge, removing the annular bevel-shaped edge, then adhering the back of the wafer to the third cutting mold, turning over the second cutting mold, the wafer and the third cutting mold as a whole, removing the adhesion of the second cutting film frame by ultraviolet irradiation, and then taking off the second cutting mold. In the step S2, the grinding and edge gas ring or protective liquid etching method is used to form a bevel-shaped wafer structure at the edge of the back of the wafer, and the thickness of the thinned wafer is 40-150 μm.

2. The method for processing IGBT wafer with gentle slope back surface according to claim 1, characterized in that, The process before the front metal process of the wafer comprises the processes of groove, ILD and contact hole.

3. The method for processing IGBT wafer with gentle slope back surface according to claim 1, characterized in that, The back process comprises photoetching, ion implantation, tempering and back metal process.

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