Ultrathin wafer BGBM thinning back metal processing method

Abstract

The invention provides an ultrathin wafer BGBM thinning back metal processing method, which is characterized in that a combined structure of a sheet BG film, a wafer, a cutting film and a metal ring is arranged, and the materials of the cutting film and the metal ring are flexibly switched in acid pickling and film coating links, so that the warping state of the wafer is reduced, the whole wafer can be used for cutting and preparing independent chip particles, special equipment and a production line are not needed, and the production cost is reduced. The production cost is greatly reduced, and the international clamping problem is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wafer back-gold processing, and specifically relates to a method for thinning back-gold of ultra-thin wafers. The method uses a membrane as a support to achieve the purpose of processing ultra-thin wafers below 100um without breaking in the entire process. Background Art

[0002] Currently in the field of power chips, current technology can stably mass-produce ultra-thin BGBM products within 100um, with two main process routes:

[0003] Route 1: Japan DISCO's TAIKO process, this process leaves a 2-5mm edge when thinning the back of the wafer, and thins from the middle. After thinning, a particularly regular pit is formed in the middle area, and the edge is raised, which effectively prevents the ultra-thin wafer from being fragile during transportation or thinning, and can also improve the stress warping problem caused by ultra-thinness. This process uses a method of leaving a 3mm circle on the edge after wafer thinning without thinning, so that the warping of the usable wafer is very small. At the same time, the remaining wafer edge plays a good supporting role, which can ensure that the wafer is not easy to break in the subsequent pickling and back gold process. However, the disadvantage of this process is that it is in a monopoly state, the equipment price is more than 1.5 times higher than the conventional one, and the equipment delivery time is also more than 1 year.

[0004] Route 2: Wafer bonding process. This process starts with the wafer thinning process. A supporting wafer is bonded to the processed wafer. The supporting wafer is combined with the wafer to be processed and the supporting wafer through a bonding adhesive or a bonding film. In the process after thinning, the two bonded wafers are not easy to break, ensuring the stability of the entire process. However, the disadvantage of this process is that it requires bonding equipment and debonding equipment, and the procurement investment and bonding material costs are also relatively expensive. Summary of the invention

[0005] In order to overcome the deficiencies in the prior art, the present invention provides an ultra-thin wafer BGBM (back gold thinning) processing technology, which solves the technical problem that ultra-thin wafers are prone to breakage when they are below 100μm and have a warpage greater than or equal to 5mm, and improves the mechanical bearing performance of ultra-thin wafers during the manufacturing process.

[0006] To achieve the above object, the present invention provides: a method for processing ultra-thin wafer BGBM thinning back gold, which comprises the following steps:

[0007] A first cutting film is attached to the back of the wafer having the BG film attached to the front after thinning, and a first metal ring is further attached to the first cutting film to obtain a thin sheet;

[0008] The thin sheet is placed on a film peeling machine, and fixed on the film peeling machine platform by vacuuming, the first cutting film is cut along the outer contour of the product, and the first metal ring is removed, and then the second circular iron ring (special circular iron ring) and the second cutting film (special material cutting film) are attached to the front of the product in step (1), so that the BG film is sandwiched between the second cutting film and the product, and the second circular iron ring is on the outermost layer on the front, and then the first cutting film on the back is torn off;

[0009] Carry out pickling, and the etching thickness is 2-4um;

[0010] Carry out back coating, and then use UV dissolving machine to dissolve the film;

[0011] The debonded product is pasted with film again in a vacuum machine, and a third cutting film and a third iron ring are pasted on the front side, wherein the third iron ring is on the outer layer;

[0012] Perform film inversion, remove the film on the front side and stick the film on the back side;

[0013] The individual chip particles can be obtained by cutting.

[0014] Preferably, the sheet is a multi-layer structure, which includes BG film, product, cutting film and metal ring in sequence.

[0015] Preferably, the outer layer of the second circular iron ring has an acid-resistant coating.

[0016] Preferably, the cutting film is a high temperature resistant cutting film.

[0017] Preferably, the metal ring is made of iron.

[0018] Preferably, the coating temperature of the coating is 80°C-110°C.

[0019] Preferably, the second cutting film has a temperature resistance range of 70°C-120°C.

[0020] The beneficial effects of the present invention are as follows:

[0021] The present invention application uses the currently available conventional equipment, adds a film transfer process after thinning, and uses a high-temperature resistant BG film (back grinding protective film) so that the film can follow the product throughout the process, and is further supported by an iron ring. The warping after support is less than 1mm, achieving the purpose of preventing ultra-thin wafers within 100um from breaking in the process. The present invention solution does not require additional equipment or additional bonding materials, and uses current ordinary equipment + special auxiliary materials to replace DISCO's exclusive TAIKO equipment, which can save about 5 million US dollars in investment for a TAIKO line. At the same time, in response to the problem of the 3mm invalid area at the edge of the current TAIKO process, this process can ensure that all wafers are available, improve the use efficiency of wafers, and reduce losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a process flow chart of the present invention;

[0023] Figure 2 The diagram of the film layer structure change in the process flow of the present invention; wherein, a is BG film + cutting film, b is tearing off the original cutting film and adding a special material cutting film on the side of the BG film, c is metal back coating, d is tearing off the BG film and the special material cutting film, e is pasting the cutting film on the front side (cutting side), and f is inverted film (front cutting) and pasting the cutting film on the back side;

[0024] Figure 3 This is a comparison of the effects of products that are not supported by metal rings. Products without rings and membranes have severe warping, with a warping of >20mm. Products without rings cannot be used in subsequent operations.

[0025] Figure 4 The product with the ring and the film produced by the method of the present invention has a warping of less than 1 mm and almost no warping.

[0026] Figure 5 It is a schematic diagram of the structure of the circular ring in the present invention, which plays a positioning role to prevent the problem of wafer reversal in the subsequent process. DETAILED DESCRIPTION

[0027] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present application will be further described below in conjunction with specific embodiments.

[0028] In order to solve the problems of wafers with thickness below 100um, severe wafer warpage (warpage > 10mm), and easy wafer cracking, there is no way to transfer and produce wafers during wafer thinning, pickling, and back-gold processing.

[0029] Example 1

[0030] After thinning, the wafer with the BG film on the front side is attached with the first cutting film on the back side. The film layer alone cannot play the function of stretching support, so a first metal ring is further attached to the first cutting film to achieve support and obtain a thin sheet;

[0031] The thin sheet is placed on a film peeling machine, and fixed on the film peeling machine platform by vacuuming, the first cutting film is cut along the outer contour of the product, and the first metal ring is removed, and then the second circular iron ring (special circular iron ring) and the second cutting film (special material cutting film) are attached to the front of the product in step (1), so that the BG film is sandwiched between the second cutting film and the product, and the second circular iron ring is on the outermost layer on the front, and then the first cutting film on the back is torn off;

[0032] Perform pickling and etching to a thickness of 2-4um;

[0033] Carry out back coating, and then use UV dissolving machine to dissolve the film;

[0034] The debonded product is filmed again in a vacuum machine, and a second cut film and a second iron ring are pasted on the front, and the second iron ring is on the outer layer;

[0035] Perform film inversion, remove the second cutting film on the front side and stick the first cutting film or the second cutting film on the back side;

[0036] The individual chip particles can be obtained by cutting.

[0037] Specifically,

[0038] 1. Thin the wafer by rotating the grinding wheel counterclockwise and the wafer clockwise. After thinning, you will get a wafer with a BG film on the front (the BG film plays a protective role in the pickling process, protecting the front of the wafer, preventing corrosion and scratches, and ensuring that there is no residual glue in the high-temperature coating temperature range of 80-130℃), a cutting film on the back, and a thin sheet attached to the iron ring. The thin sheet is a BG film + wafer + cutting film + iron ring structure. The BG film is on the front of the product, and the cutting film is on the back. The cutting film is attached to the iron ring. The size of the BG film is the same as the product, and the cutting film is larger than the product to ensure full coverage;

[0039] 2. Place the sheet with the iron ring on the film peeling machine, fix the sheet on the film peeling machine platform by vacuuming, scratch the cutting film along the outer contour of the product, remove the original iron ring, and then stick the second circular iron ring (one or more of nickel, copper, silver, platinum plated on the surface) and the second cutting film on the front, so that the BG film is sandwiched between the second cutting film and the product, and the second circular iron ring is on the outermost layer on the front, and then tear off the first cutting film on the back;

[0040] 3. Pickling, etching the product to a thickness of about 3μm;

[0041] 4. Carry out back coating with the second circular iron ring and the second cutting film;

[0042] 5. UV debonding: Use the UV debonding machine to debond the film on the thin sheet with the ring, so that the film can be torn off during subsequent wafer testing;

[0043] 6. Wafer test to detect the electrical properties of the chip: Place the sheet with the iron ring on the platform, turn on the vacuum, suck the sheet, and then peel off the cutting film, and then you can do the wafer test. Because the product is very thin, without the film and the iron ring, the warping is very serious, and the height of the warped edge can reach 1cm. The warped sheet cannot be normally transmitted through the transmission box for testing, and can only be put on manually, and press the warped area by pressing, then turn on the vacuum, suck the product, and press by hand, it is likely to cause scratches, resulting in product scrapping.

[0044] 7. After the wafer is tested, stick the third cutting film and the third iron ring on the front, turn off the vacuum machine, and remove the product;

[0045] 8. Turn the film over, remove the film on the front side, and stick the film on the back side;

[0046] 9. Cutting: Cut the chip on the front into individual particles.

[0047] The present invention supports the thin slice after the thinning process through a film + iron ring. In the subsequent process, the wafer is always produced with the film and iron ring. In the subsequent process, there will be pickling and coating processes. In the pickling process, strong acid such as sulfuric acid will be used. We need special films and iron rings to resist strong acid. In the coating process, there will be a high temperature of 80°C. We need the film to be able to withstand high temperatures and no residual glue will be left on the wafer surface. The present invention tried to use the films QH6130B, BT-150E, and BT130E. After use, they were not resistant to high temperatures and left residual glue. Only the E8180 model cutting film was available.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for processing ultra-thin wafer BGBM thinning back gold, characterized by: The following steps are included: A first cutting film is attached to the back of the wafer having the BG film attached to the front after thinning, and a first metal ring is further attached to the first cutting film to obtain a thin sheet; The thin sheet is placed on a film peeling machine, and fixed on the film peeling machine platform by vacuuming, the first cutting film is cut along the outer contour of the product, and the first metal ring is removed, and then the second circular iron ring and the second cutting film are attached to the front of the product in step (1), so that the BG film is sandwiched between the second cutting film and the product, and the second circular iron ring is on the outermost layer on the front, and then the first cutting film on the back is torn off; Carry out pickling and etching with a thickness of 2-4um; Carry out back coating, and then use UV dissolving machine to dissolve the film; The debonded product is pasted with film again in a vacuum machine, and a second cut film and a second iron ring are pasted on the front side, and the second iron ring is on the outer layer; Perform film inversion, remove the second cutting film on the front side and stick the first cutting film or the second cutting film on the back side; The individual chip particles can be obtained by cutting.

2. The ultra-thin wafer BGBM thinning back gold processing method according to claim 1, characterized in that: The thin sheet is a multi-layer structure, which includes a BG film, a product, a cutting film, and a metal ring in sequence, and the cutting film and the metal ring are arranged in multiple groups.

3. The ultra-thin wafer BGBM thinning back gold processing method according to claim 1, characterized in that: The outer layer of the second circular iron ring has an acid-resistant coating.

4. The ultra-thin wafer BGBM thinning back gold processing method according to claim 1, characterized in that: The second cutting film is a high temperature resistant cutting film.

5. The ultra-thin wafer BGBM thinning back gold processing method according to claim 2, characterized in that: The material of the metal ring is iron.

6. The ultra-thin wafer BGBM thinning back metal processing method according to claim 1, characterized in that: The coating temperature of the coating is 80°C-110°C.

7. The ultra-thin wafer BGBM thinning back gold processing method according to claim 4, characterized in that: The thickness of the ultra-thin wafer is less than 100 um.

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