Back metal reworking process of silicon carbide power device

Abstract

The invention relates to the field of silicon carbide power devices, and discloses a back metal reworking process of a silicon carbide power device, which comprises the following steps: preparing a PI glue passivation layer on the front side of a silicon carbide wafer, only exposing a complete chip area, not exposing a chip area with incomplete edges, and forming a continuous PI glue ring on the edge of the wafer; pasting a UV film on the front surface of the wafer on which the PI adhesive passivation layer is completed, carrying out thinning treatment on the back surface, then cutting off the UV film exceeding the wafer along the edge of the wafer, and evaporating a Ni / Ti metal layer on the back surface of the wafer after cleaning; wet etching liquid is adopted to remove an abnormal metal layer on the back surface of the wafer, and the UV film is tightly attached to the PI rubber ring, so that the etching liquid can be prevented from permeating into the front surface of the wafer, and the front surface structure of the wafer is protected; cleaning the back surface of the wafer; and the back metal layer is evaporated again, and the UV film is removed. According to the back metal reworking process provided by the invention, the problem that the back metal layer cannot be reworked in the prior art is effectively solved, and the whole wafer is prevented from being scrapped.

Description

Technical Field

[0001] The present invention relates to the field of silicon carbide power devices, and discloses a back metal rework process for silicon carbide power devices. Background Art

[0002] In the field of power electronics technology, silicon carbide (SiC) power devices are gradually becoming an important alternative to traditional silicon-based power devices due to their excellent high-temperature stability, high breakdown electric field strength, and low-loss characteristics. In the manufacturing process of silicon carbide power devices, the back metal process of the chip is a key process link, and its quality directly affects the core performance indicators such as the on-resistance, thermal resistance, and long-term reliability of the device.

[0003] The current mainstream back metal process in the industry generally includes the following two steps: First, deposit a Ni / Ti metal layer by evaporation, and then use laser annealing to achieve ohmic contact between the metal and the semiconductor. It should be noted that this process needs to be implemented after the completion of the front electrode, passivation layer and other structures, and in order to reduce the on-resistance of the device, the wafer needs to be pre-thinned. However, this process has significant technical bottlenecks: when there is uneven film thickness or incomplete pretreatment cleaning during the metal deposition process, it will directly lead to an abnormal increase in the ohmic contact resistance. More seriously, due to the significant warping and decreased mechanical strength of the wafer after thinning, traditional front protection methods such as coating photoresist can no longer be effectively implemented. Once a process anomaly occurs, the existing technology cannot remove and rework the back metal layer while ensuring the integrity of the front structure, ultimately resulting in the scrapping of the entire wafer and causing a loss in yield.

[0004] The existing patent CN118712045A proposes a method of laminating the front of the wafer with process anomalies and then removing the abnormal layer on the back of the wafer. However, it does not consider the problem that the etching solution easily penetrates into the front of the wafer from the scribe lane at the edge of the wafer, causing damage to the front structure and metal contamination. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a back metal rework process for silicon carbide power devices to solve the problems pointed out in the above background art.

[0006] In order to achieve the above invention purpose, the following technical solutions are further adopted:

[0007] A back metal rework process for silicon carbide power devices includes the following steps:

[0008] S1. PI glue passivation layer structure optimization: Prepare a PI glue passivation layer on the front of the silicon carbide wafer. Among them, only the complete chip area is exposed, and the incomplete chip area at the edge is not exposed, forming a continuous PI glue ring at the edge of the wafer;

[0009] S2, Front protection process: Stick a UV film on the front of the wafer with a PI glue passivation layer, thin the back of the wafer, then cut off the UV film exceeding the wafer along the wafer edge, and after cleaning, evaporate a Ni / Ti metal layer on the back of the wafer;

[0010] S3, Back metal layer rework: Use a wet etching solution to remove the abnormal metal layer on the back of the wafer. Among them, the UV film is closely attached to the PI glue ring, which can block the etching solution from penetrating into the front of the wafer, thereby protecting the front structure of the wafer;

[0011] S4, Clean the back of the wafer;

[0012] S5, Re-evaporate the back metal layer and remove the UV film.

[0013] As a further improvement of the present invention, in step S3, using a wet etching solution to remove the abnormal metal layer on the back of the wafer specifically includes the following steps:

[0014] S3-1, Use a Ti etching solution to etch the Ti metal layer, where the composition of the Ti etching solution includes ammonia water, hydrogen peroxide and water, and the volume ratio of ammonia water, hydrogen peroxide and water is 15:13:11;

[0015] S3-2, Use deionized water to wash away the residual Ti etching solution;

[0016] S3-3, Use a Ni etching solution to etch the Ni metal layer;

[0017] S3-4, Use deionized water to wash away the residual Ni etching solution;

[0018] S3-5, Use a diluted BOE solution to clean the back of the wafer.

[0019] As a further improvement of the present invention, in step S4, cleaning the back of the wafer specifically means: using deionized water to clean the wafer and spin it dry.

[0020] As a further improvement of the present invention, in step S5, re-evaporating the back metal layer and removing the UV film specifically means: re-evaporating the Ni / Ti metal layer on the back of the wafer and removing the UV film.

[0021] As a further improvement of the present invention, in step S1, the formation range of the PI glue ring is a continuous closed structure within 5 mm of the wafer edge, completely covering the scribing lanes of the incomplete chip area.

[0022] As a further improvement of the present invention, in step S3-3, the Ni etching solution is a mixed solution of nitric acid and phosphoric acid, and the volume ratio of nitric acid to phosphoric acid is 1:3.

[0023] The beneficial effects of the present invention are as follows: When preparing the PI glue passivation layer on the front side of the wafer, the present invention only exposes the complete chip area, and does not expose the incomplete chip area at the edge. A continuous PI glue ring is formed within a range of 5 mm from the wafer edge. A UV film is pasted on the front side of the wafer. Through the fitting of the UV film and the edge PI glue ring, it can effectively prevent the wet etching solution from penetrating into the front side of the wafer, thereby protecting structures such as the front electrode and the passivation layer from damage and metal contamination.

[0024] When an abnormality occurs during the backside metal deposition process, the rework process provided by the present invention can remove and re-evaporate the backside metal layer on the premise of ensuring the integrity of the front side structure, effectively solving the problem in the prior art that the backside metal layer cannot be reworked, avoiding the scrapping of the entire wafer, significantly improving the device yield, avoiding material waste and manufacturing cost losses caused by wafer scrapping, thereby reducing the production cost and improving the economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0026] Figure 1 is a front view of a silicon carbide wafer before forming the PI glue passivation layer;

[0027] Figure 2 is a front view of a silicon carbide wafer after forming the PI glue passivation layer;

[0028] Figure 3 is a cross-sectional view of the wafer before backside metal rework. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0030] In order to enable those skilled in the art of the present technology to better understand the solutions of this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

[0031] A backside metal rework process for a silicon carbide power device includes the following steps:

[0032] The last step of the front process of silicon carbide power devices is to prepare the PI glue passivation layer. Before the PI glue passivation layer process, the front of the wafer is as Figure 1 shown, where region 1 is the complete chip region and region 2 is the incomplete chip region at the edge. At this time, the etching solution can penetrate into the complete chip region from the scribe lane of the incomplete chip region.

[0033] S1. Optimization of the PI glue passivation layer structure: Prepare the PI glue passivation layer on the front of the silicon carbide wafer. When the PI glue passivation layer is exposed, only the complete chip region is exposed, and the incomplete chip region at the edge is not exposed. Therefore, a continuous PI glue ring will be formed within a range of 5 mm from the wafer edge, as Figure 2 shown in the front schematic diagram of the silicon carbide wafer after the PI glue passivation layer is formed on the wafer. Region 1 is the PI glue ring at the wafer edge, and the PI glue ring will cover the scribe lane of the incomplete chip region at the edge.

[0034] The formation range of the PI glue ring is a continuous closed structure within 5 mm from the wafer edge, completely covering the scribe lane of the incomplete chip region.

[0035] S2. Front protection process: Paste the UV film on the front of the wafer with the PI glue passivation layer completed, and perform thinning treatment on the back of the wafer. Subsequently, cut off the UV film exceeding the wafer along the wafer edge. After cleaning, evaporate the Ni / Ti metal layer on the back of the wafer. The formed wafer structure is as Figure 3 shown. At this time, the UV film pasted on the front is closely attached to the PI glue ring at the wafer edge, which can block the penetration of the solution during wet etching. Therefore, it can protect the front of the wafer.

[0036] S3. Rework of the back metal layer: Use the wet etching solution to remove the abnormal metal layer on the back of the wafer. The UV film and the PI glue ring are closely attached, which can block the penetration of the etching solution into the front of the wafer, thus protecting the front structure of the wafer.

[0037] S3-1. Use the Ti etching solution to etch the Ti metal layer. The composition of the Ti etching solution includes ammonia water, hydrogen peroxide and water, and the volume ratio of ammonia water, hydrogen peroxide and water is 15:13:11.

[0038] S3-2. Use deionized water to wash away the residual Ti etching solution.

[0039] S3-3. Use the Ni etching solution to etch the Ni metal layer.

[0040] S3-4. Use deionized water to wash away the residual Ni etching solution.

[0041] S3-5. Use the diluted BOE solution to clean the back of the wafer.

[0042] S4. Use deionized water to wash the wafer and spin it dry.

[0043] S5. Re - evaporate the Ni / Ti metal layer on the back of the wafer and remove the UV film.

[0044] In step S3 - 3, the Ni etching solution is a mixed solution of nitric acid and phosphoric acid, and the volume ratio of nitric acid to phosphoric acid is 1:3.

[0045] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, component disassembly or combination, etc., made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A backside metal rework process for a silicon carbide power device, characterized in that, It includes the following steps: S1. PI glue passivation layer structure optimization: Prepare a PI glue passivation layer on the front side of the silicon carbide wafer. Among them, only the complete chip area is exposed, and the incomplete chip area at the edge is not exposed, forming a continuous PI glue ring at the wafer edge; S2. Front protection process: Paste a UV film on the front side of the wafer with the PI glue passivation layer completed, and perform thinning treatment on the back side of the wafer. Subsequently, cut off the UV film exceeding the wafer along the wafer edge. After cleaning, evaporate and deposit a Ni / Ti metal layer on the back side of the wafer; S3. Back metal layer rework: Use a wet etching solution to remove the abnormal metal layer on the back side of the wafer. Among them, the UV film is closely attached to the PI glue ring, which can block the etching solution from penetrating into the front side of the wafer, thereby protecting the front side structure of the wafer; S4. Clean the back side of the wafer; S5. Redeposit the back metal layer and remove the UV film.

2. The back metal rework process of a silicon carbide power device according to claim 1, characterized in that: In step S3, using a wet etching solution to remove the abnormal metal layer on the back side of the wafer specifically includes the following steps: S3-1. Use a Ti etching solution to etch the Ti metal layer. The composition of the Ti etching solution includes ammonia water, hydrogen peroxide and water, and the volume ratio of ammonia water, hydrogen peroxide and water is 15:13:11; S3-2. Use deionized water to wash away the residual Ti etching solution; S3-3. Use a Ni etching solution to etch the Ni metal layer; S3-4. Use deionized water to wash away the residual Ni etching solution; S3-5. Clean the back side of the wafer with a diluted BOE solution.

3. The backside metal rework process of a silicon carbide power device according to claim 1, wherein: In step S4, cleaning the back side of the wafer specifically means: using deionized water to clean the wafer and spin-drying it.

4. The backside metal rework process of a silicon carbide power device according to claim 1, characterized in that: In step S5, redepositing the back metal layer and removing the UV film specifically means: redepositing the Ni / Ti metal layer on the back side of the wafer and removing the UV film.

5. The backside metal rework process of a silicon carbide power device according to claim 1, characterized in that: In step S1, the formation range of the PI glue ring is a continuous closed structure within 5 mm of the wafer edge, completely covering the scribe lane of the incomplete chip area.

6. The back metal rework process of a silicon carbide power device according to claim 1, characterized in that: In step S3-3, the Ni etching solution is a mixed solution of nitric acid and phosphoric acid, and the volume ratio of nitric acid to phosphoric acid is 1:3.

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