Method for improving edge breakage in silicon wafer cutting process

Abstract

The invention provides a method for improving edge breakage in a silicon wafer cutting process, the method is suitable for cutting a silicon wafer by using a cutting line, and in a cutter retracting stage, the linear speed of the cutting line is reduced and then constant speed is kept. According to the method, under the condition that the original cutting process is not changed, the cutting edge breakage proportion can be greatly reduced by controlling the cutting conditions.

Description

Technical Field

[0001] The invention belongs to the field of single crystal silicon slice processing and relates to a method for improving edge collapse in a silicon slice cutting process. Background Art

[0002] The hardness of monocrystalline silicon is very high, and its material removal is mainly brittle and broken. Therefore, edge collapse is one of the major abnormalities in the process of cutting silicon rods by cutting wire. Common edge collapses include adhesive surface edge collapse, chamfer edge collapse, cleaning and sorting edge collapse, etc. Chamfer edge collapse and collision edge collapse are caused by compression and collision, while adhesive surface edge collapse is caused by the mismatch of the cutting process. It is the most common, most complex and most difficult to improve type of edge collapse. The morphology of adhesive surface edge collapse is as follows: Figure 1 As shown in the figure, the edge chipping of the adhesive surface is concentrated in the middle of the silicon wafer. Figure 2 As shown in the morphology, the cause of edge collapse in the middle of the adhesive surface of the silicon wafer and its improvement are the focus of the present invention.

[0003] In view of the urgent need to reduce costs in the current photovoltaic industry chain, the thinning of the slice end is developing rapidly. Therefore, the problem of increased edge collapse on the adhesive surface caused by thinning needs to be solved urgently. According to the latest cutting data statistics, the edge collapse rate of 182-size monocrystalline silicon wafers changes as the thickness decreases. Figure 3 As shown in the figure, when the thickness of silicon wafer decreases from 160μm to 150μm, the edge collapse ratio increases by 0.14%; when the thickness of silicon wafer decreases from 150μm to 140μm, the edge collapse ratio increases by 0.36%; when the thickness of silicon wafer decreases from 140μm to 130μm, the edge collapse ratio increases by 0.09%. Therefore, the existing cutting process is no longer suitable for cutting single crystal thin slices, and it is urgent to match the thin slice cutting process to reduce the edge collapse rate, improve the yield rate, and achieve the purpose of cost reduction. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for improving chipping in the silicon wafer cutting process. The method can significantly reduce the chipping ratio by controlling the cutting conditions without changing the original cutting process.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for improving edge chipping during silicon wafer cutting. The method is applicable to silicon wafer cutting using a cutting wire. In the knife closing stage, the linear speed of the cutting wire is reduced and then maintained at a constant speed.

[0007] As a preferred technical solution of the present invention, in the knife retracting stage, before reducing the linear speed of the cutting line and maintaining a uniform speed, the wire bow of the cutting line is reduced.

[0008] As a preferred technical solution of the present invention, in the knife retracting stage, the table speed of the cutting line is reduced to a set value and then maintained at a constant speed and / or the circulation amount of the cutting line is increased.

[0009] As a preferred technical solution of the present invention, in the knife retracting stage, the wire feed amount of the cutting wire is less than the wire return amount.

[0010] As a preferred technical solution of the present invention, the cutting wire includes diamond wire with a comprehensive wire diameter of 47 to 53 μm, such as 47 μm, 48 μm, 49 μm, 50 μm, 51 μm, 52 μm or 53, but is not limited to the listed values. Other unlisted values ​​within the above numerical ranges are also used.

[0011] As a preferred technical solution of the present invention, cutting fluid is added before cutting, the temperature and flow rate of the cutting fluid are adjusted, and the falling point of the cutting fluid is made at the intersection of the silicon rod and the cutting line.

[0012] As a preferred technical solution of the present invention, the temperature of the cutting fluid is 20-22°C, such as 20°C, 20.2°C, 20.5°C, 20.8°C, 21°C, 21.2°C, 21.5°C, 21.8°C or 22°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also used.

[0013] As a preferred technical solution of the present invention, the flow rate of the cutting fluid is 200-220L / min, such as 200L / min, 202L / min, 205L / min, 208L / min, 210L / min, 212L / min, 215L / min, 218L / min or 220L / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also used.

[0014] As a preferred technical solution of the present invention, the cutting fluid is a mixture of coolant and pure water, and the volume ratio of the coolant to pure water is 3.5-4:450-500, such as 3.5:450, 3.6:460, 3.7:470, 3.8:480, 3.9:490 or 4:500, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also used.

[0015] As a preferred technical solution of the present invention, after reducing the linear speed of the cutting line, the linear speed maintained at a uniform speed is 25 to 30 m / s, such as 25 m / s, 25.5 m / s, 26 m / s, 26.5 m / s, 27 m / s, 27.5 m / s, 28 m / s, 28.5 m / s, 29 m / s, 29.5 m / s or 30 m / s, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also used.

[0016] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0017] The present invention provides a method for improving edge collapse during silicon wafer cutting, which can significantly reduce the edge collapse ratio by controlling cutting conditions without changing the original cutting process. Compared with the common cutting process, the edge collapse ratio can be reduced by 0.5% to 0.81%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a real picture of the edge collapse of the adhesive surface during the process of cutting single crystal silicon wafers;

[0019] Figure 2 This is a schematic diagram of the edge collapse of the adhesive surface during the process of cutting single crystal silicon wafers;

[0020] Figure 3 This is a comparison chart of the edge collapse ratio of 182 single crystals with different slice thicknesses during the process of single crystal silicon wafer cutting;

[0021] Figure 4 This is a theoretical model diagram of the suspension bridge in the process of cutting silicon wafers of single crystal silicon;

[0022] Figure 5 This is a theoretical model diagram of coolant carrying liquid during the process of cutting single crystal silicon wafers.

[0023] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0025] A specific embodiment of the present invention provides a method for improving edge chipping during silicon wafer cutting. The method is applicable to using a cutting wire to cut silicon wafers. The wire bow of the cutting wire is reduced during the knife retracting stage, and then the wire speed of the cutting wire is reduced and maintained at a constant speed.

[0026] like Figure 4 As shown in the figure, when the steel wire is cut to the end, both ends of the steel wire have cut into the plastic plate, while the middle of the steel wire is still in the silicon rod, forming a suspension bridge. Therefore, the present invention advances the wire bow to reduce the arc of the suspension bridge, and reduces the wire speed in advance, ensuring that the steel wire is cut at a uniform speed during the knife closing stage, eliminating the steel wire swing caused by acceleration and deceleration of the steel wire, and thus reducing the occurrence of edge collapse.

[0027] In a specific embodiment of the present invention, Figure 5As shown in the figure, as the cutting progresses, the saw kerf becomes narrower and narrower, and it becomes increasingly difficult for the coolant to enter the middle of the silicon wafer, resulting in a coolant island in the middle of the silicon wafer. Therefore, in the knife closing stage, the table speed is reduced, the unit forward distance is increased, the cutting time is increased, the steel wire circulation volume is increased, and the steel wire's ability to carry liquid is increased.

[0028] In a specific embodiment of the present invention, the cutting depth when entering the knife collection stage can be 160-180 mm, such as 160 mm, 162 mm, 165 mm, 168 mm, 170 mm, 172 mm, 175 mm, 178 mm or 180 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also used.

[0029] In a specific embodiment of the present invention, in the knife retracting stage, the table speed can be 80-150 μm / min, such as 80 μm / min, 90 μm / min, 100 μm / min, 110 μm / min, 120 μm / min, 130 μm / min, 140 μm / min or 150 μm / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also used.

[0030] In a specific embodiment of the present invention, in the knife-closing stage, the steel wire circulation amount can be 200 to 1000 m, such as 200 m, 300 m, 400 m, 500 m, 600 m, 700 m, 800 m, 900 m or 1000 m, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also used.

[0031] In a specific embodiment of the present invention, the incoming wire amount of the steel wire can be 1100-1290m, such as 1100m, 1120m, 1150m, 1180m, 1200m, 1220m, 1250m or 1290m, and the return wire amount can be 1050-1320m, such as 1050m, 1100m, 1150m, 1200m, 1250m, 1300m or 1320m, but is not limited to the listed values, and other unlisted values ​​within the above numerical ranges are also used.

[0032] In a specific embodiment of the present invention, the height and width of the nozzle are adjusted before cutting so that the cutting liquid falls at the intersection of the silicon rod and the wire mesh; its function is to fully carry the cutting liquid through the steel wire to the saw seam, thereby exerting the effects of wetting, dispersing and cooling of the coolant.

[0033] In a specific embodiment of the present invention, when cutting thin silicon wafers (such as 130 μm), the slot pitch is greatly reduced, and the number of saw seams per unit area of ​​the silicon rod increases, thereby increasing the heat generated. In this regard, increasing the amount of liquid used in a single blade and increasing the temperature of the cutting fluid will effectively reduce the problem of dark cracks in the silicon rod caused by excessive heat. Therefore, the volume ratio of coolant to pure water in the cutting fluid is 3.5-4:450-500, and the temperature is 20-22°C.

[0034] In a specific embodiment of the present invention, the flow rate of the cutting fluid is 200-220 L / min. The reason for limiting the above flow rate is that due to the small groove pitch of the guide wheel, the silicon powder generated in the cutting process is more difficult to be brought out from the saw seam. In order to increase the amount of silicon powder brought out of the saw seam, the cutting fluid flow rate during cutting is increased.

[0035] In a specific embodiment of the present invention, in addition to the knife closing stage, it also includes a knife entry stage and a mid-cutting stage which are sequentially performed before the knife closing stage according to the running speed of the steel wire.

[0036] In a specific embodiment of the present invention, the conditions of the knife entry stage may be: the knife entry area is between 0 and 25 mm from the zero point, the table speed is set to 1800 to 2500 μm / min, the incoming wire amount is set to be greater than the return wire amount, the incoming wire amount is set to 730 to 1000 m, the return wire amount is set to 710 to 980 m, and the circulation amount is 20 to 60 m.

[0037] In a specific embodiment of the present invention, the conditions in the middle of cutting can be: the main cutting area is between 25 and 160 mm from the zero point, the table speed is set to 2300 to 2500 μm / min, the incoming wire amount is set to be greater than the return wire amount, the incoming wire amount is set to 8500 to 1200 m, the return wire amount is set to 790 to 880 m, and the circulation amount is 120 to 350 m.

[0038] In a specific embodiment of the present invention, the acceleration of the cutting line during the cutting stage, the middle cutting stage and the closing stage is 5 to 8 m / s. 2 .

[0039] In one specific embodiment of the present invention, the single crystal silicon wafer cutting process includes:

[0040] S1. Picking the ingot: Select qualified ingots, conduct routine inspection on the ingots, clean the surface of the ingots and set them aside;

[0041] S2, loading the ingot: loading the cleaned ingot into the clamping guide rail of the cutting machine workbench;

[0042] S3, wiring net: use a cutting wire with a comprehensive wire diameter of 50μm (tolerance ±3μm) as the cutting wire, and lay the cutting wire net on the cutting main roller;

[0043] S4, adding cutting fluid: the cutting fluid is a mixture of coolant and pure water;

[0044] S5, running line before cutting: the cutting line used for cutting is run from the pay-off wheel to the take-up wheel through the rotation of the main roller;

[0045] S6, process program setting: set the cutting program in the machine;

[0046] S7. Turn on the machine, click the cutting confirmation button, and the device will enter the automatic cutting state.

[0047] In a specific implementation manner of the present invention, the tension of the cutting line is set to 3.7-3.8N when laying the wiring network in step S3.

[0048] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0049] Example 1

[0050] This embodiment provides a method for improving edge collapse during silicon wafer cutting. The method involves a single crystal silicon wafer cutting process including:

[0051] S1. Picking the ingot: Select qualified ingots, conduct routine inspection on the ingots, clean the surface of the ingots and set them aside;

[0052] S2, loading the ingot: loading the cleaned ingot into the clamping guide rail of the cutting machine workbench;

[0053] S3, wiring net: use a cutting wire with a comprehensive wire diameter of 50μm (tolerance ±3μm) as the cutting wire, and lay the cutting wire net on the cutting main roller;

[0054] S4, adding cutting fluid: the cutting fluid is a mixture of coolant and pure water;

[0055] S5, running line before cutting: the cutting line used for cutting is run from the pay-off wheel to the take-up wheel through the rotation of the main roller;

[0056] S6, process program setting: set the cutting program in the machine;

[0057] S7. Turn on the machine, click the cutting confirmation button, and the device will enter the automatic cutting state.

[0058] Among them, the cutting fluid in S4 is a mixture of coolant and pure water, the volume ratio of coolant to pure water is 3.5:450, the temperature is 20°C, the flow rate of the cutting fluid is 220L / min, and the coolant is 3.5L.

[0059] In S6, the knife-entry stage, mid-cutting stage and knife-closing stage are set according to the running speed of the steel wire;

[0060] The conditions of the knife entry stage are: the knife entry area is between 0 and 25 mm from the zero point, the knife is fed at 25 mm, the table speed is set to 2500 μm / min, the steel wire speed is set to 38 m / s, the wire feed amount is set to be greater than the return wire amount, the wire feed amount is set to 850 m, the return wire amount is set to 790 m, and the circulation amount is 60 m;

[0061] The conditions in the middle of cutting are: the main cutting area is between 25 and 160 mm from the zero point, the feed position is 160 mm, the table speed is set to 2300 μm / min, the steel wire speed is set to 38 m / s, the feed amount is set to be greater than the return amount, the feed amount is set to 1200 m, the return amount is set to 850 m, and the circulation amount is 350 m;

[0062] The conditions for the knife closing stage are: from the knife closing area 160mm away from the zero point to the end of cutting, the table speed gradually drops to 80μm / min. The setting parameters of the last 4 steps of the program are as follows: the knife feed position is 186mm, the table speed is set to 300μm / min, the steel wire speed is set to 28m / s, the wire feed amount is set to be greater than the return wire amount, the wire feed amount is set to 1300m, the return wire amount is set to 1100m, and the circulation amount is 200m; the knife feed position is 188.5mm, the table speed is set to 240μm / min, the steel wire speed is set to 28m / s, the wire feed amount is set to be less than the return wire amount, the wire feed amount is set to 1100m, the return wire amount is set to 1800m, and the circulation amount is 7 00m; feed at 189.7mm position, table speed set to 150μm / min, steel wire speed set to 28m / s, set the feed amount to be less than the return amount, the feed amount is set to 1100m, the return amount is set to 1800m, and the circulation amount is 700m; feed at 190.2mm position, table speed set to 80μm / min, steel wire speed set to 28m / s, set the feed amount to be less than the return amount, the feed amount is set to 1100m, the return amount is set to 2100m, and the circulation amount is 1000m; cutting is completed.

[0063] The acceleration of the cutting line during the cutting, mid-cutting and closing stages is 5.5m / s 2 .

[0064] Except for the different knife-retracting linear speeds, the other conditions of Examples 2 and 3 are the same as those of Example 1, as shown in Table 1. Except for the different knife-retracting positions and / or knife-retracting linear speeds, the other conditions of Comparative Examples 1-6 are the same as those of Example 1.

[0065] The single crystal silicon wafer cutting process provided in Examples 1-3 and Comparative Examples 1-6 was adopted. Under the same cutting environment, the same type of wire saw was used to cut 182 size single crystal 130 micron thick silicon wafers, and the edge collapse ratio was statistically analyzed. The specific results are shown in Table 1.

[0066] Table 1

[0067]

[0068]

[0069] From the comparison of the edge collapse ratio in Table 1, it can be seen that: (1) Under the same cutting mode, reducing the table speed in advance and taking up the wire bow have a significant improvement effect on the edge collapse ratio. (2) Under the premise of taking up the wire bow in advance, the wire speed of the knife is kept constant and the steel wire has no acceleration or deceleration, which is the key to improving the edge collapse. From the experimental data, it can be seen that the larger the wire bow of the knife, the greater the change in the wire speed of the last four steps, and the higher the edge collapse ratio. (3) Under the premise of taking up the wire bow in advance, the knife is cut at a uniform speed in the last four steps without acceleration or deceleration. The higher the knife speed, the lower the edge collapse rate. This is because under the same small wire bow, if the wire speed of the diamond wire is increased, the maximum stress and lateral impact force on the silicon wafer during the sawing process will be reduced accordingly, thereby reducing the edge collapse ratio.

[0070] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0071] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0072] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0073] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for improving edge collapse during silicon wafer cutting, the method being applicable to silicon wafer cutting using a cutting wire, characterized in that: During the knife closing stage, the linear speed of the cutting line is reduced and then maintained at a constant speed.

2. The method according to claim 1, characterized in that In the knife retracting stage, before reducing the linear speed of the cutting line and maintaining a constant speed step, the wire bow of the cutting line is reduced.

3. The method according to claim 1, characterized in that In the knife retracting stage, the table speed of the cutting line is reduced to a set value and then maintained at a constant speed and / or the circulation amount of the cutting line is increased.

4. The method according to claim 1, characterized in that: In the knife closing stage, the wire feeding amount of the cutting wire is less than the wire returning amount.

5. The method according to claim 1, characterized in that: The cutting wire comprises a diamond wire with a comprehensive wire diameter of 47 to 53 μm.

6. The method according to claim 1, characterized in that Add cutting fluid before cutting, adjust the temperature and flow of the cutting fluid, and make the cutting fluid fall at the intersection of the silicon rod and the cutting line.

7. The method according to claim 6, characterized in that The temperature of the cutting fluid is 20-22°C.

8. The method according to claim 6, characterized in that The flow rate of the cutting fluid is 200-220 L / min.

9. The method according to claim 8, characterized in that The cutting fluid is a mixture of coolant and pure water, and the volume ratio of the coolant to the pure water is 3.5-4:450-500.

10. The method according to claim 1, characterized in that In the knife retracting stage, the linear speed of the cutting line is reduced and then maintained at a uniform linear speed of 25 to 30 m / s.

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