Treatment method for falling of metal product on back surface of wafer

Abstract

The invention discloses a treatment method for metal product falling on the back of a wafer, which comprises the steps of sheet film pasting, metal deplating, cleaning, drying, grinding, corrosion and re-evaporation, and can be used again after rework treatment of wafers which have metal falling or have metal falling and cannot be used after evaporation. In the treatment process, the cracking rate of thin film pasting can be effectively reduced through secondary film pasting; when the deplating liquid medicine is used for removing nickel and silver, no heat is released, the reaction degree is not violent, the operation is free of risks, the nickel and silver can be removed in a whole batch, the metal layer removing operation efficiency is improved, the product quality is not influenced, and the problems that the metal deplating difficulty is large, the operation risk is large, deplating is not thorough, the back face is floating after deplating, and the deplating efficiency is low are solved; during secondary grinding, only Z2 accurate grinding is used, so that the thickness of the wafer subjected to secondary grinding can be ensured to be within a required range standard, the problem that materials cannot be automatically taken due to warping of the wafer is solved, and meanwhile, a series of problems that the back surface of the wafer is rough due to too small grinding amount and the like are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor power devices, and in particular to a method for processing the shedding of metal products on the back side of a wafer. Background Art

[0002] Wafer backside grinding and backside metallization (BGBM) technology is a process for the back side of power device wafers. The process is to grind a thick wafer (725μm) from the back side to a thin wafer (100-200μm), then use the back side wet etching method to roughen the back side and remove the mechanical stress generated during back side grinding, and finally use high vacuum back side evaporation to evaporate metal. Chips processed by BGBM can effectively reduce the thermal resistance of the device, improve the working heat dissipation and cooling performance, realize the wafer back side welding function, and achieve great improvements in various aspects such as reducing the package size.

[0003] After BGBM, the product is stored for too long, which leads to oxidation of the metal on the back. After dicing, all the metal on the back of the film falls off, which leads to large voids on the core during packaging. During the welding and wire bonding process, the chip is cracked and the product is scrapped. In addition, during the BGBM process, the equipment is abnormal during evaporation, which causes half of the metal evaporation process to stop and cannot be continued. The half-evaporated product cannot be used normally and can only be scrapped, which seriously affects the product yield and brings great economic losses. Therefore, a new technology is needed to rework products with metal shedding to recover the economic losses caused by abnormal metal shedding. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention aims to provide a method for processing the detachment of metal products on the back of a wafer, so that the wafer with metal detachment or half of the wafer being unusable due to vapor deposition can be used normally after rework, thereby reducing product scrap rate and production costs.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: a method for treating the falling off of metal products on the back of a wafer, comprising the following steps:

[0006] S1, Thin film

[0007] Perform secondary film bonding on the wafer that has been ground to the required thickness;

[0008] S2, Metal Stripping

[0009] For the metal layer that has been evaporated on the surface of the wafer, use a stripping solution that does not release reactive heat to remove the metal layer;

[0010] S3. Cleaning

[0011] Cleaning the wafer surface from which the metal layer has been removed;

[0012] S4. Drying

[0013] Drying the cleaned wafer surface to improve the dehydration of the wafer surface;

[0014] S5. Grinding

[0015] The surface of the wafer after drying is ground to improve the brightness of the wafer surface.

[0016] Furthermore, in step S1, the secondary film lamination pressure is 0.3 MPa.

[0017] Furthermore, in step S2, the stripping solution is made of nitric acid and glacial acetic acid, and the ratio of the nitric acid to the glacial acetic acid is 10:4.

[0018] Furthermore, in step S3, the nickel-silver metal layer is washed with deionized water after being removed, and then the titanium layer is removed with hydrofluoric acid, and then washed again and dried after the titanium layer is removed.

[0019] Furthermore, in step S4, during drying, the wafer is first immersed in deionized water added with isopropyl alcohol, and then the wafer is removed from the deionized water and blown dry using heated nitrogen at 80°C.

[0020] Furthermore, in step S5, the wafer is ground to the required grinding depth using Z2 fine grinding.

[0021] The beneficial effects of the present invention are as follows: the processing method disclosed in the present application can make the wafers with metal falling off or the wafers with metal falling off and unused due to incomplete evaporation be reused after reprocessing. The secondary filming during the processing can effectively reduce the cracking rate of the thin film;

[0022] The stripping solution of the present application does not release heat when stripping nickel-silver, and the nickel-silver layer can be completely stripped in 8-10 minutes, and the reaction degree is not violent, the operation is risk-free, and the whole batch can be stripped, which improves the efficiency of the metal layer stripping operation and does not affect the product quality;

[0023] The deplating process of the present invention solves the problems of great difficulty in metal deplating, great operation risk, unclean deplating, flowery back surface after deplating, and low deplating efficiency;

[0024] This application only uses Z2 fine grinding during the secondary grinding, which can ensure that the thickness of the secondary ground wafer is within the required range and solve the problem of being unable to automatically pick up materials due to wafer warping, while also changing a series of problems such as the rough back side of the wafer due to insufficient grinding. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1It is a diagram of the film of the sheet of the present invention.

[0026] Figure 2 This is a diagram of the secondary grinding of the present invention.

[0027] Figure 3 This is a diagram of the wafer after stripping using the current conventional process.

[0028] Figure 4 This is a diagram showing the wafer after stripping according to the present invention.

[0029] In the figure: 1- positioning pin; 2- rolling rod; 3- wafer. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0031] See attached Figures 1 to 4 A method for treating the fall-off of a metal product on the back of a wafer is shown, comprising the following steps:

[0032] S1, Thin film

[0033] The wafer 3 that has been ground to the required thickness is subjected to secondary film bonding. The specific operation process is as follows: Figure 1 As shown: Since the current secondary film pressure resistance is too low, according to the thick film standard, the wafer 3 is close to the positioning pin 1, and the film is pasted with a pressure of 0.5 MPa, which is very easy to cause the wafer 3 to crack. The secondary film pasting method of this application is: put the wafer 3 on the table, 1mm away from the two positioners (not shown in the figure) (to prevent the positioners from popping out and causing the wafer 3 to hit the edge of the wafer 3), and then use 0.3 MPa pressure to paste the film, let the rolling rod 2 slowly press from the front of the wafer 3, and then cut off the excess film along the edge of the wafer 3 less than 1mm to remove the wafer 3, which can effectively reduce the crack rate of thin film pasting.

[0034] S2, Metal Stripping

[0035] For the metal that has been evaporated on the surface of wafer 3, a stripping solution with no reaction heat release is used to remove the metal layer. The existing stripping method uses aqua regia (hydrochloric acid: nitric acid 6:1) to strip the Ag layer and nickel layer on the back of wafer 3, and then uses hydrofluoric acid to strip the titanium layer. The existing method is accompanied by a large amount of heat release when stripping the nickel-silver layer. The reaction is very violent, the operation risk is relatively large, and the metal stripping speed is too slow. It usually takes more than 20 minutes to strip the nickel-silver layer, and it cannot be completely stripped clean, resulting in severe floweriness on the back of wafer 3 after the titanium layer is stripped. If the whole batch is processed, the heat released will cause carbonization on the front of wafer 3. Therefore, currently only single-wafer operation can be performed each time, and there are still defects such as floweriness after stripping and low stripping efficiency.

[0036] The present application uses a new stripping solution (nitric acid: glacial acetic acid 10:4) to first strip the nickel-silver layer, and then uses hydrofluoric acid to strip the titanium layer. The stripping solution of the present application does not release heat when stripping nickel-silver, and the nickel-silver layer can be completely stripped in 8-10 minutes. The reaction is not violent, the operation is risk-free, and the whole batch can be stripped, which improves the efficiency of the metal layer stripping operation and does not affect product quality.

[0037] S3. Cleaning

[0038] The surface of the wafer 3 from which the metal layer has been removed is cleaned. The specific cleaning process is as follows: after the nickel-silver layer is removed, it is cleaned with deionized water to prevent cross contamination of the chemical solution when removing the titanium layer, which may cause the deplating flower phenomenon. After cleaning, the titanium layer is removed with hydrofluoric acid, and the titanium layer is cleaned again after it is removed.

[0039] S4. Drying

[0040] The cleaned surface of wafer 3 is dried to improve the dehydration property of the surface of wafer 3. The specific operation process is as follows: when drying, first fill the drying tank with deionized water, then inject a small amount of isopropyl alcohol to make the back side of wafer 3 more dehydrating, and then use 80°C heated nitrogen to blow dry.

[0041] The present application has been compared with the experiment. At present, the original process of stripping a batch of wafers 3 (25 pieces) takes at least 10 hours, while the present application can be completed in 35 minutes. The stripping process of the present application solves the problems of great difficulty in metal stripping, great operation risk, unclean stripping, back surface rust after stripping, and low stripping efficiency.

[0042] S5. Grinding

[0043] The surface of the wafer 3 after drying is ground to improve the brightness of the surface of the wafer 3. Since the back of the wafer 3 after stripping is darker than that after normal grinding, the back of the wafer 3 after secondary evaporation is not bright, which cannot meet customer needs. In response to this problem, the present application solves it through a secondary grinding method. Since the wafer 3 after metal shedding and stripping is thinner, it usually has warping, and the grinding equipment cannot take the material, resulting in an alarm in the grinding program. The grinding amount of the reworked product is limited, and the conventional Z1 (rough grinding) grinding reserves too little Z2 (fine grinding) grinding, which will cause the back of the wafer 3 to be rough. To address this problem, the present application places a test piece in the grinding and loading process, waits for the robot arm to automatically turn to the wafer 3 positioning table and presses the pause button, then removes the test piece on the wafer 3 positioning table and replaces it with the wafer 3 to be ground. Before grinding, measure the thickness of wafer 3 with a micrometer, and then adjust the z1 parameter to make the final thickness of z1 grinding consistent with the actual measured thickness of wafer 3. When the grinding wafer 3 turns to Z1, it is skipped directly, and Z2 is fine-grinded by 5-8μm. The core of the secondary grinding is to only use Z2 fine grinding, which can ensure that the thickness of the secondary ground wafer 3 is within the required range and solve the problem of automatic material removal caused by the warping of wafer 3. At the same time, it changes a series of problems such as the rough back side of wafer 3 due to insufficient grinding. The structure of the grinding equipment is a conventional structure.

[0044] After grinding, etching and evaporation processes are also included, which are the same as normal processing processes, that is, the rapid rework operation of metal shedding of wafer 3 is completed through the above steps.

[0045] The principle of the present invention is: through the steps of thin film lamination, metal stripping, cleaning, drying and grinding, the present application can make the wafer 3 with metal falling off or half of the vapor deposition unusable be used normally after rework, thereby reducing the product scrap rate and reducing production costs.

[0046] The above shows and describes the basic principle, main features and advantages of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention claimed.

Claims

1. A method for treating the falling off of metal products on the back of a wafer, characterized in that: The following steps are involved: S1, Thin film Perform secondary film bonding on the wafer that has been ground to the required thickness; S2, Metal Stripping For the metal layer that has been evaporated on the surface of the wafer, use a stripping solution that does not release reactive heat to remove the metal layer; S3. Cleaning Cleaning the wafer surface from which the metal layer has been removed; S4, Drying Drying the cleaned wafer surface to improve the dehydration of the wafer surface; S5. Grinding The surface of the wafer after drying is ground to improve the brightness of the wafer surface.

2. The method for treating the falling off of metal products on the back of a wafer according to claim 1, characterized in that: In step S1, the secondary film lamination pressure is 0.3 MPa.

3. The method for treating the falling off of metal products on the back of a wafer according to claim 2, characterized in that: In step S2, the stripping solution is made of nitric acid and glacial acetic acid, and the ratio of the nitric acid to the glacial acetic acid is 10:

4.

4. The method for treating the falling off of metal products on the back of a wafer according to claim 3, characterized in that: In step S3, after the nickel-silver metal layer is removed, it is washed with deionized water, and then the titanium layer is removed with hydrofluoric acid. After the titanium layer is removed, it is washed again and dried.

5. The method for treating the falling off of metal products on the back of a wafer according to claim 4, characterized in that: In step S4, during drying, the wafer is first immersed in deionized water added with isopropyl alcohol, and then the wafer is removed from the deionized water and blown dry using heated nitrogen at 80°C.

6. The method for treating the falling off of metal products on the back of a wafer according to claim 5, characterized in that: In step S5, the wafer is ground to the required grinding depth using Z2 fine grinding.

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