Cutting method for an ultra-fine diamond wire saw

Abstract

The present invention relates to a cutting method for an ultra-fine diamond wire saw. The method includes: taking the position where the silicon ingot just contacts the wire mesh as the zero point, and starting to cut the silicon ingot from the position with a coordinate of -1 mm along the direction from the take-up wheel to the pay-off wheel; during cutting, the silicon ingot on the crystal bonding plastic plate is cut in a segmented manner by an ultra-fine diamond wire, including a low-position cutting stage, a middle-position cutting stage, and a high-position cutting stage that are continuously carried out in sequence. Moreover, during the cutting process, the silicon ingot moves in a one-way uniformly variable speed manner towards the ultra-fine diamond wire mesh, and at the same time, the ultra-fine diamond wire mesh makes a reciprocating cyclic motion. The cutting of the silicon ingot by the ultra-fine diamond wire saw is realized, which can effectively reduce wire breakage, improve the yield and quality of silicon wafer production. At the same time, the wafer yield can be increased by the ultra-fine diamond wire saw, thereby improving the production efficiency of silicon wafers.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon wafer production, and particularly relates to a cutting method for an ultra-fine diamond wire saw. Background Art

[0002] Solar energy is a high-quality and renewable green energy. It mainly converts solar energy into electrical energy through the photovoltaic effect of silicon, providing continuous power for various regions and industries. The most important raw material for battery wafers is silicon wafers. The silicon wafers are obtained through a slicing process: the silicon ingot is clamped and placed on the corresponding cutting platform. Under the support of the main roller, the wire mesh of the diamond wire saw makes a reciprocating circular motion in the form of an equally spaced diagonal wire mesh. The silicon ingot makes a one-way uniform variable motion towards the wire mesh at a certain rate. The diamond wire saw contacts the silicon ingot, and the diamond wire saw cuts the silicon ingot. After the cutting is completed, the purpose of cutting out silicon wafers is achieved.

[0003] However, the applicant has found that: during the process of cutting silicon wafers, as the silicon ingot moves unidirectionally, new wire saws need to continuously participate in the cutting of the wire mesh so that the wire saw will not break due to excessive wear. The wire break will greatly affect the production efficiency, yield, and quality of the silicon wafers.

[0004] Moreover, currently the photovoltaic industry is developing rapidly, and the requirements for the production efficiency, yield, and quality of silicon wafers are also getting higher and higher. The existing diamond wire saws also tend to be thinner. The diamond wire saws with conventional bus bar material of carbon steel generally consider the limit of the bus bar wire diameter to be between 34μm and 32μm. The diamond wire saws with a bus bar wire diameter less than 32μm are called ultra-fine diamond wire saws; when tungsten or tungsten alloy is used as the bus bar material, the limit of carbon steel can be broken through to reach a smaller wire diameter, reaching 30μm and 28μm. The smaller the wire diameter, the higher the wafer yield. Currently, the advantages of using ultra-fine diamond wire saws to cut silicon wafers are far greater than those of the mainstream carbon steel wire cutting. However, the existing carbon steel wire cutting process cannot be applied to the cutting of ultra-fine diamond wire saws. As the bus bar wire diameter of the diamond wire saw decreases, in the traditional carbon steel wire cutting process, problems such as too large wire bow and increased abnormal wire breaks are likely to occur during the cutting process, and the cutting time and wire consumption also increase, seriously affecting the cutting efficiency and cutting quality. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a cutting method for an ultra-fine diamond wire saw.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The cutting method for an ultra-fine diamond wire saw according to the present invention includes:

[0008] Take the position where the silicon ingot just touches the wire mesh as the zero point, and start cutting the silicon ingot from the position with a coordinate of -1 mm along the direction from the take-up reel to the pay-off reel.

[0009] During cutting, use an ultra-fine diamond wire to perform segmented cutting on the silicon ingot on the crystal bonding plastic plate, including a low-position cutting stage, a middle-position cutting stage, and a high-position cutting stage that are continuously carried out in sequence. Moreover, during the cutting process, the silicon ingot moves in a one-way uniformly variable speed motion towards the ultra-fine diamond wire mesh, while the ultra-fine diamond wire mesh performs a reciprocating cyclic motion.

[0010] Further, the low-position cutting stage has a total of four steps, and the table speed in the low-position cutting stage is increased from 1500 μm / min in four steps to the table speed A1 μm / min in the high-speed cutting stage, and the wire speed is increased from 750 m / min in four steps to the wire speed B1 m / min in the high-speed cutting stage. And control the incoming wire amount in the first step to be 50 m - 60 m greater than the outgoing wire amount; where A1 is 80% of the limit table speed of this ultra-fine diamond wire, and B1 is 80% of the limit wire speed of this ultra-fine diamond wire.

[0011] Further, the middle-position cutting stage has a total of thirteen steps, and the table speed in the first six steps of the middle-position cutting stage remains A1 μm / min, and the table speed in the last seven steps gradually decreases from A1 μm / min to A2 μm / min. The wire speed in this stage remains B1 m / min throughout, and control the incoming wire amount in the first step to be 80 m - 150 m greater than the outgoing wire amount.

[0012] Further, the high-position cutting stage has a total of four steps, and the table speed in the high-position cutting stage is gradually decreased from A2 μm / min in four steps to A3 μm / min, and the wire speed is gradually decreased from B1 m / min in four steps to B2 m / min, and control the outgoing wire amount in the first step to be 400 m - 700 m greater than the incoming wire amount.

[0013] Further, the temperatures in both the low-position cutting stage and the middle-position cutting stage are 20 °C, and the temperature in the high-position cutting stage is 19 °C.

[0014] Further, the cutting tension in the low-position cutting stage, the middle-position cutting stage, and the high-position cutting stage is the breaking tension × 0.6 N.

[0015] Further, the wire diameter of the ultra-fine diamond wire is 28μm to 30μm, and the silicon square bar is a G10 specification silicon square bar or a G12 specification silicon square bar; when the silicon square bar is a G10 specification silicon square bar, the cutting range in the low-position cutting stage is at the position of 0mm to 20mm of the cross-sectional height of the silicon square bar, excluding 20mm, the cutting range in the middle-position cutting stage is at the position of 20mm to 180mm of the cross-sectional height of the silicon square bar, excluding 180mm, and the cutting range in the high-position cutting stage is at the position of 180mm to 191mm of the cross-sectional height of the silicon square bar and the crystal-bonding plastic plate;

[0016] When the silicon square bar is a G12 specification silicon square bar, the cutting range in the low-position cutting stage is at the position of 0mm to 20mm of the cross-sectional height of the silicon square bar, excluding 20mm, the cutting range in the middle-position cutting stage is at the position of 20mm to 215mm of the cross-sectional height of the silicon square bar and the crystal-bonding plastic plate, excluding 215mm, and the cutting range in the high-position cutting stage is at the position of 215mm to 221mm of the cross-sectional height of the crystal-bonding plastic plate.

[0017] Further, when the silicon square bar is a G12 specification silicon square bar, the starting coordinate positions of each step of the cutting in the low-position cutting stage are -1mm, 5mm, 9mm, and 12mm respectively, the starting coordinate positions of each step of the cutting in the middle-position cutting stage are 20mm, 50mm, 80mm, 110mm, 130mm, 150mm, 165mm, 180mm, 190mm, 200mm, 205mm, 210mm, and 214mm respectively, and the starting coordinate positions of each step of the cutting in the high-position cutting stage are 215mm, 218mm, 219mm, and 221mm respectively.

[0018] Advantages of the present invention:

[0019] Through the above technical solutions, the present invention can achieve the cutting of the silicon square bar by the ultra-fine diamond wire saw, effectively reduce wire breakage, improve the yield and quality of silicon wafer production, and at the same time improve the wafer yield through the ultra-fine diamond wire saw, thereby improving the production efficiency of silicon wafers. Description of the drawings

[0020] Figure 1 is a schematic flow chart of the cutting method of the ultra-fine diamond wire saw of the present invention;

[0021] Figure 2 is a schematic cutting principle diagram of the cutting method of the ultra-fine diamond wire saw of the present invention. Detailed implementation manners

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] As Figure 1 shown, a cutting method of an ultra-fine diamond wire saw according to the present invention includes the following steps:

[0024] Step S1. Take the position where the silicon square bar just touches the wire mesh as the zero point, and start cutting the silicon square bar from the position with a coordinate of -1 mm along the direction from the take-up reel to the pay-off reel. By setting the cutting direction to be from the take-up reel to the pay-off reel, it is beneficial to reduce the abnormal breakage due to diagonal pulling during the cutting process.

[0025] Step S2. During cutting, use an ultra-fine diamond wire (a diamond wire with a bus wire diameter less than 32 μm) to perform segmented cutting on the silicon square bar on the crystal bonding plastic plate, including a low-position cutting stage, a middle-position cutting stage, and a high-position cutting stage that are continuously carried out in sequence. Moreover, during the cutting process, the silicon square bar makes a one-way uniformly variable motion towards the ultra-fine diamond wire mesh, and at the same time, the ultra-fine diamond wire mesh makes a reciprocating cyclic motion; wherein the silicon square bar makes a one-way uniformly variable motion towards the ultra-fine diamond wire mesh, specifically: make a uniformly variable motion according to the position and the table speed. Taking the 1st and 2nd steps of the low-position cutting stage as an example, during this period, the uniformly variable motion increases from 1500 μm / min to 1800 μm / min, and the total distance is 5 - (-1), that is, 6 mm. Then the uniformly variable motion satisfies the formula V2 2 - V1 2 = 2×a1×S, where V2 is the final velocity, V1 is the initial velocity, a1 is the acceleration, and S is the total distance.

[0026] The cutting working principle of the cutting method of the ultra-fine diamond wire saw according to the present invention is as Figure 2 shown, where 1 is the pay-off reel, 2 is the take-up reel, 3 is the guide pulley, 4 is the tension arm, 5 is the main roller, 6 is the silicon square bar, and 7 is the wire mesh.

[0027] In order to be more beneficial to reducing problems such as large wire bows and abnormal breakage-free, the cutting method of the ultra-fine diamond wire saw according to the present invention adopts a form of segmented different-period transformation. Specifically,

[0028] The low - level cutting stage consists of four steps. The table speed in the low - level cutting stage is increased from 1500μm / min to the table speed A1μm / min in the high - speed cutting stage in four steps, and the wire speed is increased from 750m / min to the wire speed B1m / min in the high - speed cutting stage in four steps. A1 is 80% of the limit table speed of the ultra - fine diamond wire, and B1 is 80% of the limit wire speed of the ultra - fine diamond wire. Also, the wire feeding amount in the first step is controlled to be 50m - 60m greater than the wire returning amount. By controlling the difference between the wire feeding amount and the wire returning amount within this small range, it is possible to reduce the production of defective products such as chamfer chipping and scratches during the low - speed cutting stage of the new wire.

[0029] The middle - level cutting stage consists of thirteen steps. The table speed in the first seven steps of the middle - level cutting stage remains at A1μm / min, and the table speed in the last seven steps gradually decreases from A1μm / min to A2μm / min. The wire speed in this stage remains at B1m / min throughout the process, and the wire feeding amount in the first step is controlled to be 80m - 150m greater than the wire returning amount.

[0030] The high - level cutting stage consists of four steps. The table speed in the high - level cutting stage is gradually decreased from A2μm / min to A3μm / min in four steps, and the wire speed is gradually decreased from B1m / min to B2m / min in four steps. By reducing the wire speed to B2m / min, it can not only avoid the production of defective products such as scratches and bright edges due to excessive wire speed in the high - level stage, but also avoid the problem of additional cutting when the cutting in the high - level stage is about to be completed due to too low wire speed. Also, the wire returning amount in the first step is controlled to be 400m - 700m greater than the wire feeding amount.

[0031] In the low - level cutting stage, the table speed is increased from 1500μm / min to the table speed A1μm / min in the high - speed cutting stage and the wire speed is increased from 750m / min to the wire speed B1m / min in the high - speed cutting stage in four steps. The method of increasing in each step is to make a fine - tuning increment based on the actual cutting line mark problem on the basis of equal increment. The fine - tuning standard is that no severe wide - stripe line marks appear during normal cutting. In the last seven steps of the middle - level cutting stage, the table speed is gradually decreased from A1μm / min to A2μm / min. The method of decreasing in each step is to make a fine - tuning decrement based on the actual cutting line mark problem on the basis of equal decrement. The fine - tuning standard is that no severe wide - stripe line marks appear during normal cutting. Similarly, in the high - level cutting stage, the table speed is gradually decreased from A2μm / min to A3μm / min and the wire speed is gradually decreased from B1m / min to B2m / min in four steps. The method of decreasing in each step is to make a fine - tuning decrement based on the actual cutting line mark problem on the basis of equal decrement. Among them, A2 is about 700μm / min and B2 is about 1350μm / min. For ultra - fine diamond wires with different wire diameters, the values of A2 and B2 are slightly different.

[0032] The cutting ranges of the low - level cutting stage, the middle - level cutting stage, and the high - level cutting stage in the present invention are determined according to the production specifications of silicon ingots. Specifically, the wire diameter of the ultra - fine diamond wire is 28μm - 30μm, and the silicon ingot is a silicon ingot of G10 specification (cross - section: 182mm×182mm) or a silicon ingot of G12 specification (cross - section: 210mm×210mm); when the silicon ingot is a silicon ingot of G10 specification, the cutting range of the low - level cutting stage is the position of 0mm - 20mm (in order to protect the initial cutting position, the starting position of the low - level cutting stage is set to - 1mm) of the height of the cross - section of the silicon ingot, not including 20mm, the cutting range of the middle - level cutting stage is the position of 20mm - 180mm of the height of the cross - section of the silicon ingot, not including 180mm, and the cutting range of the high - level cutting stage is the position of 180mm - 191mm of the height of the cross - section of the silicon ingot and the adhesive crystal plastic plate;

[0033] When the silicon ingot is a silicon ingot of G12 specification, the cutting range of the low - level cutting stage is the position of 0mm - 20mm (in order to protect the initial cutting position, the starting position of the low - level cutting stage is set to - 1mm) of the height of the cross - section of the silicon ingot, not including 20mm, the cutting range of the middle - level cutting stage is the position of 20mm - 215mm of the height of the cross - section of the silicon ingot and the adhesive crystal plastic plate, not including 215mm, and the cutting range of the high - level cutting stage is the position of 215mm - 221mm of the height of the cross - section of the adhesive crystal plastic plate.

[0034] Example:

[0035] In the cutting method of the ultra - fine diamond wire saw according to the embodiment of the present invention, a tungsten wire with a wire diameter of 30μm is used to cut a silicon ingot of G12 specification, and the cutting ranges (the starting position of each step corresponds to the height of the cross - section of the silicon ingot), table speed, wire speed, wire supply amount, wire return amount, and temperature in the low - level cutting stage, the middle - level cutting stage, and the high - level cutting stage are as shown in Table 1 below.

[0036] Table 1

[0037]

[0038] As can be seen from the above table, in the first stage (low - level cutting stage), it cuts to the position of 20mm of the height of the cross - section of the silicon ingot. The table speed in the first stage is increased from 1500μm / min to the table speed of 2300μm / min (A1) in the high - speed cutting stage in four steps (Steps 1 - 4), and the wire speed is increased from 750m / min to the wire speed of 2300m / min (B1) in the high - speed cutting stage in four steps (Steps 1 - 4);

[0039] In the second stage (medium-position cutting stage), it cuts to the position of 215 mm in the cross-sectional height of the silicon ingot plus the bonding crystal plastic plate. The table speed in the first six steps (steps 5 - 10) of the second stage remains at 2300 μm / min (A1), and the table speed in the subsequent seven steps (steps 11 - 17) gradually decreases from 2300 μm / min to 1000 μm / min (A2), and the wire speed remains at 2300 m / min throughout the process (B1);

[0040] In the third stage (high-position cutting stage), it cuts to the position of 221 mm in the cross-sectional height of the silicon ingot plus the bonding crystal plastic plate. The table speed in the third stage decreases gradually from 700 μm / min (A2) to 100 μm / min (A3) in four steps (steps 18 - 21), and the wire speed decreases gradually from 2300 m / min (B1) to 1350 m / min (B2) in four steps (steps 18 - 21).

[0041] Moreover, the temperature in the first stage and the second stage (referring to the temperature of the mixture of mortar and cutting fluid in the cutting chamber) is 20 °C, and the temperature in the third stage is 19 °C.

[0042] By adopting the above-mentioned segmented cutting method, the present invention can achieve the cutting of the silicon ingot with an ultra-fine diamond wire saw. At the same time, it is easier to analyze problem points during the segmented process (by adopting segmented cutting, it is possible to compare the cut silicon wafers and measure the depth, i.e., the position, of the abnormal part to confirm which stage the abnormal position corresponds to, so as to analyze and solve problems by only adjusting some processes in some stages). It can effectively reduce wire breakage (since the cutting force of the thin wire becomes weaker, the present invention rationally distributes the cutting force with a changing cycle, and the cutting is more evenly distributed, so it is not easy to break the wire). It improves the yield and quality of silicon wafer production. At the same time, the ultra-fine diamond wire saw increases the wafer output rate (wafer output rate = length of silicon ingot / groove pitch. Among them, the length of the silicon ingot is a fixed value. The smaller the wire diameter, the smaller the groove pitch, and the higher the wafer output rate), thereby improving the production efficiency of silicon wafers.

[0043] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A cutting method for an ultra-fine diamond wire saw, characterized in that, Including: Taking the position where the silicon ingot just touches the wire mesh as the zero point, and starting to cut the silicon ingot from the position with a coordinate of -1 mm along the direction from the take-up reel to the pay-off reel; During cutting, an ultra-fine diamond wire is used to cut the silicon ingot on the crystal bonding plastic plate in a segmented manner, including a low-position cutting stage, a middle-position cutting stage, and a high-position cutting stage that are continuously carried out in sequence. Moreover, during the cutting process, the silicon ingot moves in a one-way uniformly variable speed motion towards the ultra-fine diamond wire mesh, and at the same time, the ultra-fine diamond wire mesh makes a reciprocating circular motion; The low-position cutting stage has four steps, and the table speed in the low-position cutting stage is increased from 1500 μm / min to the table speed A1 μm / min in the high-speed cutting stage in four steps, and the wire speed is increased from 750 m / min to the wire speed B1 m / min in the high-speed cutting stage in four steps. And it is controlled that the wire feeding amount in the first step is greater than the wire returning amount by 50 m to 60 m; where A1 is 80% of the limit table speed of this ultra-fine diamond wire, and B1 is 80% of the limit wire speed of this ultra-fine diamond wire; The middle-position cutting stage has thirteen steps, and the table speed in the first six steps of the middle-position cutting stage remains A1 μm / min, and the table speed in the last seven steps is gradually reduced from A1 μm / min to A2 μm / min. The wire speed in this stage remains B1 m / min throughout the process, and it is controlled that the wire feeding amount in the first step is greater than the wire returning amount by 80 m to 150 m; The high-position cutting stage has four steps, and the table speed in the high-position cutting stage is gradually reduced from A2 μm / min to A3 μm / min in four steps, and the wire speed is gradually reduced from B1 m / min to B2 m / min in four steps. And it is controlled that the wire returning amount in the first step is greater than the wire feeding amount by 400 m to 700 m; The wire diameter of the ultra-fine diamond wire is 28 μm to 30 μm, and the silicon ingot is a silicon ingot of G10 specification or G12 specification; when the silicon ingot is a silicon ingot of G10 specification, the cutting range in the low-position cutting stage is the position of 0 mm to 20 mm of the cross-sectional height of the silicon ingot, not including 20 mm, the cutting range in the middle-position cutting stage is the position of 20 mm to 180 mm of the cross-sectional height of the silicon ingot, not including 180 mm, and the cutting range in the high-position cutting stage is the position of 180 mm to 191 mm of the cross-sectional height of the silicon ingot and the crystal bonding plastic plate; When the silicon ingot is a silicon ingot of G12 specification, the cutting range in the low-position cutting stage is the position of 0 mm to 20 mm of the cross-sectional height of the silicon ingot, not including 20 mm, the cutting range in the middle-position cutting stage is the position of 20 mm to 215 mm of the cross-sectional height of the silicon ingot and the crystal bonding plastic plate, not including 215 mm, and the cutting range in the high-position cutting stage is the position of 215 mm to 221 mm of the cross-sectional height of the crystal bonding plastic plate.

2. The method according to claim 1, wherein The temperature in the low-position cutting stage and the middle-position cutting stage is 20 °C, and the temperature in the high-position cutting stage is 19 °C.

3. The method according to claim 1, characterized in that The cutting tension in the low-position cutting stage, the middle-position cutting stage, and the high-position cutting stage is 0.6 N of the breaking tension.

4. The method according to claim 1, wherein When the silicon square bar is a G12 - sized silicon square bar, the cutting start coordinate positions at each step of the low - level cutting stage are - 1mm, 5mm, 9mm, and 12mm respectively; the cutting start coordinate positions at each step of the middle - level cutting stage are 20mm, 50mm, 80mm, 110mm, 130mm, 150mm, 165mm, 180mm, 190mm, 200mm, 205mm, 210mm, and 214mm respectively; the cutting start coordinate positions at each step of the high - level cutting stage are 215mm, 218mm, 219mm, and 221mm respectively.

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