Method for preventing warping of wafer after invisible cutting

Abstract

The invention relates to the technical field of wafers, in particular to a method for preventing warping of a wafer after invisible cutting. Comprising the following steps that S1, a wafer is provided, and the surface of the wafer is provided with a plurality of longitudinal cutting channels and transverse cutting channels; s2, the wafer is arranged on a table top of an invisible laser cutting machine with the back face upward and the front face downward; s3, the longitudinal cutting channel and the transverse cutting channel are cut through an invisible laser cutting machine, and a modified layer is formed; s4, a blocking layer is machined in the position, close to the last modified layer, above the longitudinal cutting channel and the transverse cutting channel in a laser invisible cutting mode; and S5, carrying out thinning grinding on the back surface of the wafer, and grinding off the blocking layer in the step S4. Compared with the prior art, the problems that after the small chip wafer is subjected to laser invisible cutting, invisible cutting cracks continue to grow, wafer warping is too large, and a machine arm cannot carry the wafer are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of wafers, and specifically to a method for preventing warping of wafers after invisible cutting. Background Art

[0002] As shown in Figure 1 , during the chip packaging process, a grinding adhesive film layer is first attached to the front surface of the wafer, the wafer is pre-ground, cut along the cutting channels between the chips by invisible laser cutting, and then the wafer is ground to the target final thickness to separate the chips on the wafer.

[0003] However, in the current cutting method, especially when processing wafers with small-sized chips, during the wafer handling operation after invisible cutting, the cracks 3 formed by invisible cutting will continue to extend, as shown in Figure 2 , resulting in a larger warping of the wafer, and the handling components of the machine tool cannot grasp the wafer, affecting the operation. Summary of the Invention

[0004] The present invention aims to overcome the deficiencies of the prior art and provides a method for preventing warping of wafers after invisible cutting.

[0005] To achieve the above object, a method for preventing warping of wafers after invisible cutting is designed, including the following steps: S1. Provide a wafer, on the surface of which there are several longitudinal cutting channels and transverse cutting channels; S2. Place the wafer with the back surface facing up and the front surface facing down on the table of the invisible laser cutting machine; S3. Cut the longitudinal cutting channels and transverse cutting channels through the invisible laser cutting machine to form a modified layer; S4. Above the longitudinal cutting channels and transverse cutting channels, near the position of the last modified layer, process a blocking layer by invisible laser cutting; S5. Thinly grind the back surface of the wafer to grind off the blocking layer in step S4.

[0006] In the above step S4, the cutting speed for processing the blocking layer is 100 - 300 mm / s, and the laser energy is 1 - 2 W.

[0007] In the above step S4, the position of the blocking layer is above the current laser processing point position, and the distance from the current laser processing point position is 50 - 100 um.

[0008] When performing steps S3 - 4 by invisible laser cutting, the laser enters from the back surface of the wafer, and when grinding in step S5, the back surface of the wafer faces up and grinding is performed from the back surface.

[0009] Between the aforesaid step S1 and step S2, the following steps are further included: attaching a layer of grinding adhesive film on the front side of the wafer, and performing pre-grinding on the wafer.

[0010] After the aforesaid step S5, the following steps are further included: S6, attaching a back adhesive film on the back side of the ground wafer and fixing it on an iron ring; S7, removing the grinding adhesive film on the front side of the wafer.

[0011] Compared with the prior art, the present invention prevents the problem that after the small-chip wafer is subjected to laser stealth dicing, the cracks formed by the stealth dicing continue to grow, resulting in excessive warping of the wafer and the inability of the machine arm to carry it. Description of the Drawings

[0012] Figure 1 It is a schematic side view of a wafer after laser stealth dicing in the prior art.

[0013] Figure 2 It is a schematic view showing that the internal cracks of the wafer become longer and the wafer warps in the prior art.

[0014] Figure 3 It is a schematic view showing that the barrier layer in the embodiment of the present invention prevents the existing cracks from growing upward continuously.

[0015] Figure 4 It is a wafer processing flow chart in the embodiment of the present invention. Detailed Embodiments

[0016] The present invention will be further described below with reference to the drawings.

[0017] As Figures 3 to 4 shown, in this embodiment, the method for preventing warping of the wafer after laser stealth dicing includes the following steps: S1, providing a wafer 1, on the surface of which there are a plurality of longitudinal dicing channels and transverse dicing channels; S2, placing the wafer 1 with the back side facing up and the front side facing down on the table of the stealth laser dicing machine; S3, cutting the longitudinal dicing channels and transverse dicing channels through the stealth laser dicing machine to form a modified layer; S4, above the longitudinal dicing channels and transverse dicing channels, near the position of the last modified layer, processing a barrier layer 2 by means of laser stealth dicing; S5, thinning and grinding the back side of the wafer 1 to grind off the barrier layer 2 in step S4.

[0018] In step S4, the cutting speed for processing the barrier layer 2 is 100-300 mm / s, and the laser energy is 1-2 W.

[0019] In step S4, the position of the blocking layer 2 is above the current laser processing point, and the distance from the current laser processing point is 50 - 100 um.

[0020] When performing laser stealth cutting in step S3 - 4, the laser is incident from the back side of the wafer 1. When grinding in step S5, the back side of the wafer 1 faces upward and grinding is performed from the back side.

[0021] Between step S1 and step S2, the following steps are further included: attaching a grinding adhesive film to the front side of the wafer 1 and performing pre - grinding on the wafer 1.

[0022] After step S5, the following steps are further included: S6, attaching a back - side adhesive film to the back side of the ground wafer 1 and fixing it on an iron ring; S7, removing the grinding adhesive film on the front side of the wafer 1.

[0023] In step S4, during the processing of the blocking layer, when performing laser stealth cutting, the laser emits laser beams, and the overlapping degree of the modified regions formed by adjacent laser processing points is relatively high. These modified regions with a relatively high overlapping degree will not have cracks growing upward themselves, and can prevent the underlying stealth cutting cracks from continuing to grow upward. In order to prevent cracks from occurring in the blocking layer itself, the cutting speed of the laser stealth cutting for processing the blocking layer is between 100 - 300 mm / s, which is much lower than the normal laser stealth cutting speed; the laser energy for processing is also smaller than the normal laser energy.

[0024] In the existing wafer cutting process, after completing the laser stealth cutting process, there will be a handling operation. If no blocking layer is added, the large warping of the wafer will affect the handling. In step S4 of the present invention, a blocking layer 2 is processed to prevent crack growth, and there will be no large warping, so the handling operation can be carried out normally. And in step S5, after the back - side grinding of the wafer is completed, the grains have been completely separated and the cracks will not continue to grow. In the subsequent step S6, an adhesive film is attached to the back side of the wafer 1 and fixed on an iron ring. When there is another handling operation, only the iron ring needs to be handled, and the situation where the wafer warping affects the handling will not occur.

[0025] In step S5, generally, the position of the blocking layer 2 is set outside the final thickness required for the chip. Therefore, in this embodiment, the blocking layer 2 processed in the previous step can be ground off during the grinding process, and the blocking layer will not be left in the final product, which will also greatly improve the mechanical strength of the chip.

Claims

1. A method for preventing warping of a wafer after invisible cutting, characterized in that: It includes the following steps: S1. Provide a wafer (1) with a plurality of longitudinal cutting channels and transverse cutting channels on its surface; S2. Place the wafer (1) with its back facing up and its front facing down on the table of a stealth laser cutting machine; S3. Cut the longitudinal cutting channels and transverse cutting channels through the stealth laser cutting machine to form a modified layer; S4. Above the longitudinal cutting channels and transverse cutting channels, at a position close to the last modified layer, process a barrier layer (2) by means of laser stealth cutting; S5. Thinning and grinding the back of the wafer (1) to grind off the barrier layer (2) in step S4.

2. A method for preventing warping of a wafer after invisible cutting according to claim 1, characterized in that: In the said step S4, the cutting speed for processing the barrier layer (2) is 100 - 300 mm / s, and the laser energy is 1 - 2 W.

3. A method for preventing warping of a wafer after invisible cutting according to claim 1, characterized in that: In the said step S4, the position of the barrier layer (2) is above the current laser processing point position, and the distance from the current laser processing point position is 50 - 100 um.

4. A method for preventing warping after invisible cutting of a wafer according to claim 1, characterized in that: When performing laser stealth cutting in the said steps S3 - 4, the laser is incident from the back of the wafer (1), and when grinding in step S5, the back of the wafer (1) faces up and grinding is performed from the back.

5. A method for preventing warping of a wafer after invisible cutting according to claim 1, characterized in that: Between the said step S1 and step S2, the following steps are further included: Attach a grinding adhesive film to the front of the wafer (1) and perform pre - grinding on the wafer (1).

6. A method for preventing warping of a wafer after invisible cutting according to claim 5, characterized in that: After the said step S5, the following steps are further included: S6. Attach a back adhesive film to the back of the ground wafer (1) and fix it on an iron ring; S7. Remove the grinding adhesive film on the front of the wafer (1).

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