Separation method for reducing wafer deformation
By adopting a combination of pre-cutting and plasma etching during the semiconductor wafer cutting process, the problems of wafer deformation and edge cracking in the prior art are solved, and the effect of reducing wafer stress deformation and improving yield is achieved.
Patent Information
- Application Number
- CN202311078551.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-08-24
- Publication Date
- 2025-02-25
AI Technical Summary
The existing semiconductor wafer cutting methods can easily lead to an increase in the stress in the wafer, resulting in deformation and edge cracking.
Using a combination of pre-cutting and plasma etching, the wafer is first pre-cut on the machine, with a cutting depth less than the wafer thickness, and then plasma etching is performed in the vacuum chamber to form a mask and a protective layer to control the etching area.
By pre-cutting and then plasma etching, the stress deformation of the wafer during separation is reduced, the yield is improved, and the wafer deformation and edge cracking are avoided.
Smart Images
Figure CN119517847A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of semiconductor processing, and in particular to a separation method for reducing wafer deformation. Background Art
[0002] At present, semiconductor wafer cutting is generally achieved through mechanical processing. The traditional process flow is: grinding and cutting. The process flow requires grinding and thinning the bottom of the wafer, and then cutting the wafer with a rotating tool; or cutting first and then grinding. However, no matter which method is used, the mechanical processing process can easily cause an increase in the internal stress of the wafer, thereby causing deformation of the wafer and cracking of the edge. Summary of the invention
[0003] In view of the deficiencies in the prior art, an embodiment of the present invention provides a separation method for reducing wafer deformation, comprising:
[0004] Pasting the wafer on the machine table for pre-cutting, wherein the cutting depth is less than the thickness of the wafer;
[0005] forming a first protective layer on the front side of the pre-cut wafer;
[0006] Forming a mask on the back side of the wafer, wherein the area of the wafer to be etched is not covered by the mask, and the area to be etched corresponds to the pre-cut area;
[0007] The wafer is placed in a vacuum chamber for plasma etching.
[0008] As a preferred solution, the tool width used in the pre-cutting process is 0.6-1.0 mm, the spindle speed is 15000 rpm, the feed rate is 450-550 rpm, the cutting depth is 0.45-0.5 mm, and the cooling water temperature during cutting is 20-25°C.
[0009] As a preferred solution, CF is used in the plasma etching process. 4 , CHF 3 and O 2 A mixture of.
[0010] As a preferred solution, CF 4 , CHF 3 and O 2 The flow rate is 1200-1350sccm.
[0011] As a preferred solution, during the plasma etching process, the temperature of the vacuum chamber is 20-25° C., the pressure of the vacuum chamber is 80-100 mtorr, the source power is 1000-1500 W, and the bias power is 100-150 W.
[0012] As a preferred solution, the etching time of plasma etching is 10 minutes.
[0013] As a preferred solution, the etching depth of the wafer during the plasma etching process is 1.5-1.55 mm.
[0014] As a preferred solution, the step of pasting the wafer on the machine table for pre-cutting is specifically as follows: pasting the wafer on the machine table and pre-cutting the wafer by a dicing knife;
[0015] The dicing knife includes a plurality of hard abrasive particles and a binder; the plurality of hard abrasive particles are classified according to length into: first hard abrasive particles, second hard abrasive particles and third hard abrasive particles;
[0016] Among them, A2≤L1≤A1, A3≤L2<A2, A4≤L3<A3, and A1>A2>A3>A4, L1 is the first hard abrasive, L2 is the second hard abrasive, L3 is the third hard abrasive, A1 is the first length threshold, A2 is the second length threshold, A3 is the third length threshold, and A4 is the fourth length threshold; the number of the first hard abrasives accounts for 40% of the total number of hard abrasives, the number of the second hard abrasives accounts for 30% of the total number of hard abrasives, and the number of the third hard abrasives accounts for 30% of the total number of hard abrasives.
[0017] As a preferred embodiment, the dicing knife is installed on a rotating shaft, and the number of the first hard abrasive particles gradually decreases from the tip of the dicing knife toward the rotating shaft.
[0018] As a preferred embodiment, the number of the second hard abrasive particles and the third hard abrasive particles gradually increases from the tip of the dicing knife toward the direction of the rotation axis.
[0019] Compared with the prior art, the beneficial effects of the embodiments of the present invention are as follows: the embodiments of the present invention provide a separation method for reducing wafer deformation, by pasting the wafer on a machine table for pre-cutting, the cutting depth is less than the thickness of the wafer, at this time the wafer is not completely separated, and the stress deformation of the wafer is small; then, a first protective layer is formed on the front side of the pre-cut wafer, and a mask is formed on the back side of the wafer, the area to be etched of the wafer is not covered by the mask, the area to be etched corresponds to the pre-cut area, and then, the wafer is placed in a vacuum chamber for plasma etching, so that the wafer is completely separated. In this way, the wafer is pre-cut first, and then the wafer is completely separated by plasma etching. The whole process will not produce huge stress deformation, which is beneficial to improving the yield. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 It is a schematic flow chart of a separation method for reducing wafer deformation in an embodiment of the present invention. DETAILED DESCRIPTION
[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0022] See also Figure 1 As shown, it is a schematic flow chart of a separation method for reducing wafer deformation in an embodiment of the present invention.
[0023] The separation method for reducing wafer deformation according to an embodiment of the present invention includes:
[0024] Step S101, pasting the wafer on the machine table for pre-cutting, and the cutting depth is less than the thickness of the wafer;
[0025] Step S102, forming a first protective layer on the front side of the pre-cut wafer;
[0026] Step S103, forming a mask on the back side of the wafer, wherein the area of the wafer to be etched is not covered by the mask, and the area to be etched corresponds to the pre-cut area;
[0027] Step S104, placing the wafer in a vacuum chamber for plasma etching.
[0028] In an embodiment of the present invention, a wafer is pasted on a machine table for pre-cutting, and the cutting depth is less than the thickness of the wafer. At this time, the wafer is not completely separated, and the stress deformation of the wafer is small; then, a first protective layer is formed on the front side of the pre-cut wafer, and a mask is formed on the back side of the wafer, and the area to be etched of the wafer is not covered by the mask, and the area to be etched corresponds to the pre-cut area. Then, the wafer is placed in a vacuum chamber for plasma etching to completely separate the wafer. In this way, the wafer is pre-cut first, and then the wafer is completely separated by plasma etching. The whole process will not produce huge stress deformation, which is beneficial to improving the yield rate.
[0029] In an optional embodiment, the blade width of the tool used in the pre-cutting process is 0.6-1.0mm, for example, it can be 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, etc. Of course, the blade width can also be set to other values according to actual use requirements, which will not be described in detail here; the spindle speed of the tool is 15000rpm, and the feed rate is 450-550rpm, for example, it can be 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, etc. Of course, the feed rate of the tool can also be set to other values according to actual use requirements. The actual use requirements are set to other values, which will not be described in detail here; the cutting depth is 0.45-0.5mm, for example, it can be 0.45mm, 0.46mm, 0.47mm, 0.48mm, 0.49mm, 0.5mm, etc. Of course, the cutting depth can also be set to other values according to the actual use requirements, which will not be described in detail here; the cooling water temperature during cutting is 20-25℃, for example, it can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, etc. Of course, the cooling water temperature during cutting can also be set to other values according to the actual use requirements, which will not be described in detail here.
[0030] In this embodiment, the cutter goes deep into the position where cutting is required (i.e., the separation position of each chip in the wafer) to pre-divide the wafer, so that the chips in the wafer are not completely fallen off, and there is still a thickness of about 1600um at the cutting position still connected to the bottom of the wafer. After measurement, the stress deformation range of the semiconductor is still in the range of 0.13-0.18um, which meets the requirements.
[0031] In an optional embodiment, in the step S102 of "forming a first protective layer on the front side of the pre-cut wafer", the first protective layer may be, for example, UV glue, and the front side of the wafer is adhered by the first protective layer, thereby playing a protective role and also avoiding confusion of the chips after the chips in the wafer are separated after the ion etching is completed.
[0032] In an optional embodiment, in the step S103 "forming a mask on the back side of the wafer, the area to be etched of the wafer is not covered by the mask, and the area to be etched corresponds to the pre-cut area", the wafer is flipped to expose the back side, and the chip area is protected by setting a mask, and the area to be etched is exposed to facilitate subsequent plasma etching, and the area to be etched is opposite to the area that has been cut in the pre-cutting. The mask can be made of photoresist, for example, and is made by exposure and development, which will not be described in detail here. In addition, after the ion etching is completed, the mask can be removed.
[0033] In this embodiment, the chip separation position is pre-cut by mechanical cutting, and then the remaining part of the chip separation position is etched by ion etching, so as to achieve chip separation in the wafer. Compared with the traditional grinding and cutting separation method, the internal stress deformation range of the semiconductor chip in the embodiment of the present invention is in the range of 0.13-0.18um, which meets the requirements of semiconductor processing and will not affect the subsequent use of semiconductors.
[0034] In an optional embodiment, CF is used in the plasma etching process. 4 , CHF 3 and O 2 A mixture of CF 4 , CHF 3 and O 2 The flow rate is 1200-1350 sccm. During the plasma etching process, the temperature of the vacuum chamber is 20-25° C., the pressure of the vacuum chamber is 80-100 mtorr, the source power is 1000-1500 W, and the bias power is 100-150 W. The etching time of plasma etching is 10 minutes.
[0035] In an optional embodiment, the etching depth of the wafer during plasma etching is 1.5-1.55mm, for example, it can be 1.5mm, 1.51mm, 1.52mm, 1.53mm, 1.54mm, 1.55mm, etc. Of course, the etching depth of the wafer during plasma etching can also be set to other values according to actual use requirements, which will not be elaborated here.
[0036] In an optional embodiment, the step of pasting the wafer on the machine table for pre-cutting is specifically: pasting the wafer on the machine table and pre-cutting the wafer with a dicing knife;
[0037] The dicing knife includes a plurality of hard abrasive particles and a binder; the plurality of hard abrasive particles are classified according to length into: first hard abrasive particles, second hard abrasive particles and third hard abrasive particles;
[0038] Among them, A2≤L1≤A1, A3≤L2<A2, A4≤L3<A3, and A1>A2>A3>A4, L1 is the first hard abrasive, L2 is the second hard abrasive, L3 is the third hard abrasive, A1 is the first length threshold, A2 is the second length threshold, A3 is the third length threshold, and A4 is the fourth length threshold; the number of the first hard abrasives accounts for 40% of the total number of hard abrasives, the number of the second hard abrasives accounts for 30% of the total number of hard abrasives, and the number of the third hard abrasives accounts for 30% of the total number of hard abrasives.
[0039] Exemplarily, the hard abrasive grains are diamond abrasive grains. Of course, the hard abrasive grains may also be made of other materials according to actual use requirements, which will not be further elaborated herein. The embodiment of the present invention is described by taking the hard abrasive grains as diamond abrasive grains as an example.
[0040] In practical applications, the larger the size of the hard abrasive, the stronger the cutting ability of the dicing knife, the slower the wear of the hard abrasive, and the longer the life of the dicing knife. However, the impact force on the wafer cutting surface during cutting is greater, which can easily introduce greater mechanical stress and cause serious defects such as cracks and edge collapse. Smaller hard abrasives can reduce the impact force on the wafer cutting surface during the cutting process, thereby reducing the risk of larger cutting defects. However, smaller hard abrasives are not easy to fall off. If they cannot be shed and updated in time, the knife wrapping phenomenon is likely to occur, causing a sharp drop in the cutting ability of the hard abrasives and serious defects. This embodiment designs three types of hard abrasive particles, which are the first hard abrasive particles, the second hard abrasive particles and the third hard abrasive particles in order of length from large to small. This embodiment ensures that the dicing tool has sufficient cutting ability and does not generate a large impact force on the cutting surface of the wafer during cutting, so as to avoid defects such as wafer cracks and edge collapse. At the same time, the first hard abrasive particles can ensure that there are enough hard abrasive particles to fall off and be updated in time.
[0041] In an optional embodiment, the dicing knife is mounted on a rotating shaft, and the number of the first hard abrasive particles gradually decreases from the tip of the dicing knife toward the direction of the rotating shaft. In a specific implementation, the dicing knife is usually roughly circular in shape, and the dicing knife is driven by the rotating shaft to perform cutting. For details, please refer to the prior art, and no further details are given here. In this embodiment, the number of the first hard abrasive particles gradually decreases from the tip of the dicing knife toward the direction of the rotating shaft, so that after a small amount of the first hard abrasive particles near the tip of the knife fall off, some first hard abrasive particles are added to the adjacent parts of the fallen hard abrasive particles to ensure that there is still sufficient cutting ability after the hard abrasive particles fall off.
[0042] In an optional embodiment, the number of the second hard abrasive and the third hard abrasive gradually increases from the tip of the dicing knife toward the direction of the rotation axis. When the first hard abrasive falls off, in order to further ensure that the dicing knife has sufficient cutting ability and does not form a large impact force on the cutting surface of the wafer during cutting, the number of the second hard abrasive and the third hard abrasive is gradually increased from the tip of the knife toward the direction of the rotation axis to cooperate with the first hard abrasive to provide cutting force, while avoiding defects such as easy cracks and edge collapse of the wafer.
[0043] Compared with the prior art, the beneficial effects of the embodiments of the present invention are as follows: the embodiments of the present invention provide a separation method for reducing wafer deformation, by pasting the wafer on a machine table for pre-cutting, the cutting depth is less than the thickness of the wafer, at this time the wafer is not completely separated, and the stress deformation of the wafer is small; then, a first protective layer is formed on the front side of the pre-cut wafer, and a mask is formed on the back side of the wafer, the area to be etched of the wafer is not covered by the mask, the area to be etched corresponds to the pre-cut area, and then, the wafer is placed in a vacuum chamber for plasma etching, so that the wafer is completely separated. In this way, the wafer is pre-cut first, and then the wafer is completely separated by plasma etching. The whole process will not produce huge stress deformation, which is beneficial to improving the yield.
[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.
Claims
1. A separation method for reducing wafer deformation, characterized in that: include: Pasting the wafer on the machine table for pre-cutting, wherein the cutting depth is less than the thickness of the wafer; forming a first protective layer on the front side of the pre-cut wafer; Forming a mask on the back side of the wafer, wherein the area of the wafer to be etched is not covered by the mask, and the area to be etched corresponds to the pre-cut area; The wafer is placed in a vacuum chamber for plasma etching.
2. The separation method for reducing wafer deformation according to claim 1, characterized in that: The tool used in the pre-cutting process has a blade width of 0.6-1.0 mm, a spindle speed of 15000 rpm, a feed rate of 450-550 rpm, a cutting depth of 0.45-0.5 mm, and a cooling water temperature of 20-25° C. during cutting.
3. The separation method for reducing wafer deformation according to claim 1, characterized in that: A mixture of CF4, CHF3 and O2 is used in the plasma etching process.
4. The separation method for reducing wafer deformation according to claim 3, characterized in that: The flow rates of CF4, CHF3 and O2 are 1200-1350 sccm.
5. The separation method for reducing wafer deformation according to claim 4, characterized in that: During the plasma etching process, the temperature of the vacuum chamber is 20-25° C., the pressure of the vacuum chamber is 80-100 mtorr, the source power is 1000-1500 W, and the bias power is 100-150 W.
6. The separation method for reducing wafer deformation according to claim 5, characterized in that: The etching time of the plasma etching is 10 minutes.
7. The separation method for reducing wafer deformation according to claim 1, characterized in that: The etching depth of the wafer during plasma etching is 1.5-1.55mm.
8. The separation method for reducing wafer deformation according to any one of claims 1 to 7, characterized in that: The step of pasting the wafer on the machine table for pre-cutting is specifically: pasting the wafer on the machine table and pre-cutting the wafer by a dicing knife; The dicing knife includes a plurality of hard abrasive particles and a binder; the plurality of hard abrasive particles are classified according to length into: first hard abrasive particles, second hard abrasive particles and third hard abrasive particles; Among them, A2≤L1≤A1, A3≤L2<A2, A4≤L3<A3, and A1>A2>A3>A4, L1 is the first hard abrasive, L2 is the second hard abrasive, L3 is the third hard abrasive, A1 is the first length threshold, A2 is the second length threshold, A3 is the third length threshold, and A4 is the fourth length threshold; the number of the first hard abrasives accounts for 40% of the total number of hard abrasives, the number of the second hard abrasives accounts for 30% of the total number of hard abrasives, and the number of the third hard abrasives accounts for 30% of the total number of hard abrasives.
9. The separation method for reducing wafer deformation according to claim 8, characterized in that: The dicing knife is installed on a rotating shaft, and the number of the first hard abrasive particles gradually decreases from the tip of the dicing knife toward the rotating shaft.
10. The separation method for reducing wafer deformation according to claim 9, characterized in that: The number of the second hard abrasive particles and the third hard abrasive particles gradually increases from the tip of the dicing knife toward the direction of the rotation axis.