CN113524471A - Diamond wire slicing process for silicon wafer - Google Patents
Diamond wire slicing process for silicon wafer Download PDFInfo
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- CN113524471A CN113524471A CN202010323224.1A CN202010323224A CN113524471A CN 113524471 A CN113524471 A CN 113524471A CN 202010323224 A CN202010323224 A CN 202010323224A CN 113524471 A CN113524471 A CN 113524471A
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- 229910003460 diamond Inorganic materials 0.000 title claims abstract description 124
- 239000010432 diamond Substances 0.000 title claims abstract description 124
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 119
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 87
- 239000010703 silicon Substances 0.000 title claims abstract description 87
- 238000000034 method Methods 0.000 title claims abstract description 33
- 239000000110 cooling liquid Substances 0.000 claims abstract description 88
- 238000005520 cutting process Methods 0.000 claims abstract description 80
- 238000005406 washing Methods 0.000 claims abstract description 56
- 235000012431 wafers Nutrition 0.000 claims abstract description 54
- 239000003513 alkali Substances 0.000 claims abstract description 45
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 32
- 238000004140 cleaning Methods 0.000 claims abstract description 27
- 239000007788 liquid Substances 0.000 claims abstract description 23
- 238000001816 cooling Methods 0.000 claims abstract description 14
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 15
- 238000007599 discharging Methods 0.000 claims description 9
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 5
- HUCVOHYBFXVBRW-UHFFFAOYSA-M caesium hydroxide Chemical compound [OH-].[Cs+] HUCVOHYBFXVBRW-UHFFFAOYSA-M 0.000 claims description 4
- 230000001186 cumulative effect Effects 0.000 claims description 4
- CPRMKOQKXYSDML-UHFFFAOYSA-M rubidium hydroxide Chemical compound [OH-].[Rb+] CPRMKOQKXYSDML-UHFFFAOYSA-M 0.000 claims description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 3
- 229910052760 oxygen Inorganic materials 0.000 claims description 3
- 239000001301 oxygen Substances 0.000 claims description 3
- 239000011863 silicon-based powder Substances 0.000 abstract description 30
- 239000002826 coolant Substances 0.000 description 10
- 239000011550 stock solution Substances 0.000 description 9
- 235000015073 liquid stocks Nutrition 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 229910000831 Steel Inorganic materials 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
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- 239000002699 waste material Substances 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
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- 238000005299 abrasion Methods 0.000 description 2
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- 239000004570 mortar (masonry) Substances 0.000 description 2
- KMUONIBRACKNSN-UHFFFAOYSA-N potassium dichromate Chemical compound [K+].[K+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O KMUONIBRACKNSN-UHFFFAOYSA-N 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28D—WORKING STONE OR STONE-LIKE MATERIALS
- B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
- B28D5/04—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor by tools other than rotary type, e.g. reciprocating tools
- B28D5/045—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor by tools other than rotary type, e.g. reciprocating tools by cutting with wires or closed-loop blades
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28D—WORKING STONE OR STONE-LIKE MATERIALS
- B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
- B28D5/0058—Accessories specially adapted for use with machines for fine working of gems, jewels, crystals, e.g. of semiconductor material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28D—WORKING STONE OR STONE-LIKE MATERIALS
- B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
- B28D5/0058—Accessories specially adapted for use with machines for fine working of gems, jewels, crystals, e.g. of semiconductor material
- B28D5/0076—Accessories specially adapted for use with machines for fine working of gems, jewels, crystals, e.g. of semiconductor material for removing dust, e.g. by spraying liquids; for lubricating, cooling or cleaning tool or work
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Mechanical Treatment Of Semiconductor (AREA)
- Processing Of Stones Or Stones Resemblance Materials (AREA)
Abstract
The invention provides a silicon wafer diamond wire slicing process. The diamond wire slicing process comprises the following steps: adding cooling liquid into a cutting liquid cylinder of a diamond wire slicing machine, starting the diamond wire slicing machine to cut a silicon rod into silicon wafers, circulating the cooling liquid to wash diamond wires while cutting, and cleaning a cutting chamber, a cooling pipeline and a heat exchanger of the diamond wire slicing machine by using alkali liquor after accumulated cutting for a period of time, wherein the cleaning comprises alkali washing, water washing and cooling liquid washing. According to the invention, after the diamond wire slicing machine is operated for a period of time in an accumulated mode, the cutting chamber, the cooling pipeline and the heat exchanger are cleaned, and the attached silicon powder is removed, so that the wire breakage rate of the diamond wire is effectively reduced, the yield of silicon wafers is improved, and the productivity is improved.
Description
Technical Field
The invention belongs to the technical field of silicon wafer production, and particularly relates to a diamond wire slicing process for a silicon wafer.
Background
With the gradual depletion of petroleum and other stone resources, the gradual attention of people to environmental protection and the progress of photovoltaic power generation technology, the proportion of photovoltaic power generation in the world energy collection is also getting larger and larger. The solar photovoltaic cell is a device capable of directly converting light energy into electric energy, and most of the existing photovoltaic cells are silicon solar cells with silicon as a substrate, including monocrystalline silicon, polycrystalline silicon, amorphous silicon solar cells and the like. These silicon solar cells exhibit good energy conversion efficiency and service life.
The silicon material used to fabricate the substrate of a silicon solar cell is a square piece of silicon, typically cut from a silicon rod. At present, two cutting methods for processing silicon wafers mainly comprise mortar cutting and diamond wire cutting. Compared with mortar cutting, diamond wire cutting has the advantages of high cutting speed, small environmental pollution, narrow saw kerf, less silicon material loss, uniform silicon wafer thickness and high yield. However, since diamond wire cutting is to cut a silicon wafer by using a diamond wire moving at a high speed, high temperature and a large amount of silicon powder are not easily brought out during cutting, and factors such as cutting abrasion and wire tension affect the silicon wafer, wire breakage easily occurs, and the diamond wire needs to be stopped and replaced, resulting in reduction of production efficiency.
With the advance of large-size silicon wafers, the size of the silicon wafer required by a cell in the photovoltaic industry is increased from 156-157mm of the traditional side length to 166mm of the side length or even larger, so that the cost per watt is greatly reduced, and the progress of photovoltaic power generation on line at a flat price is accelerated. However, negative effects are also brought in the field of silicon wafer processing: with the increase of the size of a processed silicon rod, the abrasion loss of diamond wires in the cutting process is increased, so that the wire breakage rate in the cutting process is increased rapidly, the capacity of a slicing machine is reduced seriously, the single wire consumption of a cut silicon wafer is increased, the yield of the silicon wafer is reduced, and the processing cost of the silicon wafer is increased. And with the popularization of thinning in the industry, the diameter of the diamond wire bus is reduced to 60 micrometers and 57 micrometers, and is even thinner, so that the wire breakage problem of the diamond wire is further aggravated, and the problem is urgently needed to be solved.
Therefore, the wire breakage rate in the diamond wire slicing process of the silicon wafer is reduced, and the method has important significance for the development of the photovoltaic industry.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a silicon wafer diamond wire slicing process. The process can obviously reduce the wire breakage rate of the diamond wire in the production of the silicon wafer, improve the yield of the silicon wafer and improve the productivity.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a diamond wire slicing process for a silicon wafer, the diamond wire slicing process comprising:
adding cooling liquid into a cutting liquid cylinder of a diamond wire slicing machine, and starting the diamond wire slicing machine to cut the silicon rod into silicon wafers;
circulating the cooling liquid to flush the diamond wire while cutting;
after accumulated cutting is carried out for a period of time, cleaning a cutting chamber, a cooling pipeline and a heat exchanger of the diamond wire slicing machine by using alkali liquor;
the cleaning method comprises the following steps:
alkali washing: adding alkali liquor into a cutting hydraulic cylinder of the diamond wire slicing machine for circular cleaning, wherein the concentration of the alkali liquor is 0.08-0.5mol/L, and discharging the alkali liquor after the circulation cleaning is finished;
washing with water: after the alkali washing is finished, adding water into a cutting liquid cylinder of the diamond wire slicing machine for circular cleaning, and discharging water after the circular cleaning is finished;
cooling liquid washing: and after the water washing is finished, adding cooling liquid into a cutting liquid cylinder of the diamond wire slicing machine for circular washing, and discharging the cooling liquid after the circular washing is finished.
In the invention, the concentration of the alkali liquor is 0.08-0.5 mol/L; for example, it may be 0.08mol/L, 0.1mol/L, 0.12mol/L, 0.15mol/L, 0.17mol/L, 0.2mol/L, 0.22mol/L, 0.25mol/L, 0.28mol/L, 0.3mol/L, 0.32mol/L, 0.35mol/L, 0.38mol/L, 0.4mol/L, 0.42mol/L, 0.45mol/L, 0.48mol/L, or 0.5 mol/L.
The inventor found through research that when the diamond wire slicer cuts the silicon rod, the generated silicon powder enters along with the cooling liquid and adheres to a cutting chamber, a cooling pipeline and a heat exchanger of the diamond wire slicer, the cooling liquid is replaced after each cutting for a certain number of cutters, but the silicon powder cannot be completely discharged along with the cooling liquid, the silicon powder in the components gradually gathers and agglomerates along with the increase of cutting time, and the formed silicon block (millimeter level) impacts on the diamond wire moving at high speed along with the cooling liquid, so that the diamond wire is easily broken and the cutting is poor. According to the invention, after the diamond wire slicing machine is operated for a period of time in an accumulated mode, the cutting chamber, the cooling pipeline and the heat exchanger are cleaned, and the attached silicon powder is removed, so that the wire breakage rate of the diamond wire is effectively reduced, and the yield of silicon wafers is improved.
In the present invention, the process of cutting one or more bonded silicon rods (the total length of the silicon rods is 685mm) into silicon wafers is referred to as one knife. In actual industrial production, the cooling liquid circulating in the slicing machine is obtained by diluting the high-concentration cooling liquid, and for the convenience of distinguishing, the cooling liquid refers to the solution after dilution; the high-concentration coolant before dilution is referred to as "stock coolant".
As a preferable technical scheme of the invention, the alkali in the alkali liquor is selected from one or the combination of at least two of NaOH, KOH, RbOH and CsOH.
In one embodiment of the invention, the side length of the silicon wafer is 156-157mm, and the concentration of the alkali liquor is 0.08-0.17 mol/L; for example, it may be 0.08mol/L, 0.09mol/L, 0.1mol/L, 0.11mol/L, 0.12mol/L, 0.13mol/L, 0.14mol/L, 0.15mol/L, 0.16mol/L or 0.17 mol/L.
In one embodiment of the invention, the side length of the silicon wafer is more than or equal to 166mm, and the concentration of the alkali liquor is 0.25-0.5 mol/L; for example, it may be 0.25mol/L, 0.28mol/L, 0.3mol/L, 0.32mol/L, 0.35mol/L, 0.38mol/L, 0.4mol/L, 0.42mol/L, 0.45mol/L, 0.48mol/L, or 0.5 mol/L.
In the diamond wire slicing process, as the size of a silicon wafer is increased, the silicon powder generated by each knife is increased, and the accumulation of the silicon powder in a cutting chamber, a cooling pipeline and a heat exchanger is accelerated. Therefore, for the silicon wafers with larger sizes, alkali liquor with higher concentration is needed for cleaning. If the concentration of the alkali liquor is too low, the removal effect on the silicon powder is poor; if the concentration of the alkali liquor is too high, the alkali liquor is excessive, which causes waste, and the number of times of water washing in the next step is increased in order to adjust the pH value in the machine. After alkaline cleaning, the accumulated silicon powder becomes fluffy and easily falls off from the inner walls of the cutting chamber, the cooling pipeline and the heat exchanger, and is more easily dispersed in the cooling liquid, so that the silicon powder is removed after the cooling liquid is cleaned.
As a preferable technical scheme of the invention, in the alkali washing step, the volume of the added alkali liquor accounts for 50-70% of the volume of a cutting hydraulic cylinder of the diamond wire slicing machine; for example, it may be 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, etc.
Preferably, the temperature of the alkali liquor is kept between 40 and 60 ℃ during the alkali washing; for example, the temperature may be 40 ℃, 42 ℃, 43 ℃, 45 ℃, 46 ℃, 48 ℃, 50 ℃, 52 ℃, 53 ℃, 55 ℃, 56 ℃, 58 ℃ or 60 ℃.
In general, when the diamond wire slicer cuts normally, the cooling liquid is kept at about 20 ℃ under the action of the heat exchanger. When the heat exchanger normally works during alkaline cleaning, the temperature of the alkaline liquor is too low, and the alkaline cleaning effect is influenced, so that the temperature of the system needs to be set to be 40-60 ℃, and the temperature of the system is set to be the temperature of a cutting process after cleaning is finished.
Preferably, in the alkali washing step, the time for circulating washing is 1-2 h; for example, it may be 1h, 1.2h, 1.3h, 1.5h, 1.6h, 1.8h, 2h, etc.
In the present invention, the alkali washing temperature and time are within the above ranges, and the silicon powder can be substantially fully reacted. If the temperature of the alkali liquor is too low or the alkali washing time is too short, the alkali liquor and the silicon powder can not fully react, and the cleaning effect is poor; if the temperature of the alkali liquor and the alkali washing time are continuously increased, the cost and the potential safety hazard are increased.
As a preferable technical scheme of the invention, in the water washing step, the time of each circulation cleaning is 15-30 min; for example, it may be 15min, 16min, 18min, 20min, 22min, 23min, 25min, 26min, 28min or 30 min.
Preferably, in the water washing step, the water washing is stopped until the pH of the discharged water is 6.5 to 7.5.
In the water washing step, water needs to be added for multiple times and the water needs to be circularly washed, and the water adding and washing times are based on the condition that the pH value of discharged water meets the requirement.
Preferably, the concentration of the cooling liquid in the cooling liquid washing step is 40-60% (for example, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, etc.) of the concentration of the cooling liquid at the time of cutting.
Preferably, in the cooling liquid washing step, the time of circulating washing is 5-15 min; for example, it may be 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min or 15 min.
The cooling liquid used for cutting the diamond wire contains components such as surfactant, and the silicon powder after alkali washing is easy to disperse and remove in the cooling liquid. The cooling liquid used during the cooling liquid washing can be less than that added during normal slicing, so that the cost is saved.
In an embodiment of the present invention, the side length of the silicon wafer is 156-157mm, and the diamond wire slicer cleans every 900-1000 cumulative cuts (for example, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, or 1000 cuts, etc.).
In one embodiment of the invention, the side length of the silicon wafer is equal to or greater than 166mm, and the diamond wire slicer cleans every 300-350 cumulative cuts (for example, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345 or 350 cuts, etc.).
In the diamond wire slicing process, as the size of a silicon wafer is increased, the silicon powder generated by each knife is increased, and the accumulation of the silicon powder in a cutting chamber, a cooling pipeline and a heat exchanger is accelerated. Therefore, for the silicon wafer with larger size, the cleaning frequency needs to be increased.
As a preferred technical scheme of the invention, the cooling liquid is replaced every 1-2 times of cutting.
When the silicon rod is cut by the diamond wire, the silicon powder is brought into the cooling liquid, the content of the silicon powder is gradually increased along with the cutting, and if the content of the silicon powder is too high, the slicing efficiency is seriously reduced, so that after a certain number of cutting tools are cut, mixed waste liquid of the silicon powder and the cooling liquid needs to be discharged, and new cooling liquid needs to be added. Generally, it is more preferred to replace the cooling fluid every 1 knife cut.
Preferably, the Chemical Oxygen Demand (COD) of the cooling liquid is 400-; for example, it may be 400. mu.g/L, 410. mu.g/L, 420. mu.g/L, 430. mu.g/L, 440. mu.g/L, 450. mu.g/L, 460. mu.g/L, 470. mu.g/L, 480. mu.g/L, 490. mu.g/L or 500. mu.g/L, etc.
In the invention, the chemical oxygen demand is measured by a potassium dichromate method by adopting a COD tester.
The inventor finds that in the actual silicon wafer production process, the discharged mixed waste liquid of silicon powder and cooling liquid needs to be filtered by a filter press, solid substances such as silicon powder and the like are filtered, and the filtrate (namely the cooling liquid) is recycled. Since a part of water is lost during the filter pressing process, and in order to keep the amount of cooling liquid added to the slicer equal to the amount of cooling liquid obtained by recovery in continuous production, the cooling liquid stock solution needs to be supplemented after recovery, which leads to a significant increase in the COD value of the recovered cooling liquid after a certain period of production. The COD value of the cooling liquid cannot be concerned in the existing diamond wire slicing process, and the inventor finds that when the COD value of the cooling liquid is too large, the diamond wire is easy to slip when cutting a silicon rod, the cutting capability is reduced, the movement of the silicon rod along the direction vertical to the diamond wire is kept unchanged, the tension borne by the diamond wire is increased, and the wire breakage rate is increased; when the COD value of the cooling liquid is too small, the heat absorption capacity of the cooling liquid and the dispersibility of the cooling liquid on the silicon powder are reduced, and the heat and the silicon powder generated by cutting cannot be taken away in time, so that the wire breakage rate is increased. Therefore, in the present invention, it is necessary to control the COD value of the cooling liquid added during slicing to 400-500. mu.g/L.
The invention has no special limit on how to control the COD value of the cooling liquid, exemplarily, the COD value of the cooling liquid can be detected after the cooling liquid is recovered, and if the COD value is higher than the upper limit value, water is supplemented for dilution; if the COD value is lower than the lower limit value, the cooling liquid is supplemented.
As a preferred technical scheme of the invention, the tension of the diamond wire on the diamond wire slicing machine is 60-70% of the breaking tension value of the diamond wire; for example, it may be 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, or the like.
The tension of the diamond wire on the main roller of the diamond wire slicing machine needs to be controlled within the range, and if the tension is too small, the cutting capability is insufficient; if the tension is too large, the diamond wire is easily broken, and the wire breakage rate is increased.
Before wiring, a section of diamond wire sample wire to be used can be intercepted, the sample wire is broken by using a tensile testing machine, and a corresponding tensile value (namely the breaking tensile value of the diamond wire) during wire breaking is recorded. Testing sample lines of the same manufacturer and specification for more than 5 times to obtain the average value of breaking tension; the controlled steel wire tension value set by the slicer is 60-70% of the breaking tension value tested above.
As a preferred technical scheme, in the cutting process, the distance between the falling point of the cooling liquid on the diamond wire and the junction of the diamond wire and the silicon rod is not more than 5 mm; for example, it may be 0, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, or the like.
In the existing diamond wire slicing process, the falling point of the cooling liquid is usually far away from the junction of the diamond wire and the silicon rod, the cooling liquid is brought into a cutting interface by the diamond wire, but the cooling liquid is less, heat and silicon powder generated by cutting cannot be taken away in time, and the wire breakage rate is high. According to the invention, the distance between the falling point of the cooling liquid on the diamond wire and the junction of the diamond wire and the silicon rod is adjusted to be not more than 5mm by adjusting the height of the flow guide groove, so that the cooling liquid can fully take away heat and silicon powder, and the wire breakage rate is reduced.
As a preferred technical scheme of the invention, the average cutting rate of the diamond wire to the silicon rod in the cutting process is 1-3 mm/min; for example, it may be 1mm/min, 1.2mm/min, 1.3mm/min, 1.5mm/min, 1.6mm/min, 1.8mm/min, 2mm/min, 2.1mm/min, 2.2mm/min, 2.3mm/min, 2.4mm/min, 2.5mm/min, 2.6mm/min, 2.7mm/min, 2.8mm/min, 2.9mm/min, or 3 mm/min.
Preferably, the linear speed of the diamond wire during cutting is 10-40 m/s; for example, it may be 10m/s, 12m/s, 15m/s, 18m/s, 20m/s, 22m/s, 25m/s, 28m/s, 30m/s, 32m/s, 35m/s, 38m/s, 40m/s, or the like.
Compared with the prior art, the invention has the following beneficial effects:
according to the diamond wire slicing process provided by the invention, after the diamond wire slicing machine is operated for a period of time in an accumulated mode, the cutting chamber, the cooling pipeline and the heat exchanger are cleaned, and the attached silicon powder is removed, so that the wire breakage rate of the diamond wire is effectively reduced, the yield of a silicon wafer is improved, and the productivity is improved. By controlling the COD value of the coolant, the tension of the diamond wire, and the drop point of the coolant within appropriate ranges, the wire breakage rate of the diamond wire can be further reduced.
Drawings
FIG. 1 is a schematic view of a diamond wire slicing according to an embodiment of the present invention;
wherein, 1 is the silicon rod, 2 is the bonding board, 3 is the work piece board, 4 is the guiding gutter, 5 is the home roll, 6 is the diamond wire, 7 is the joint piece groove.
FIG. 2 is a schematic view of a coolant recovery system according to an embodiment of the present invention.
FIG. 3 is a schematic diagram of automated cleaning according to an embodiment of the present invention.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings. It should be understood by those skilled in the art that the specific embodiments are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
In the embodiment of the invention, the adopted material sources are as follows:
a diamond wire: the diameter of a bus of an electroplating diamond wire of Luoyang Giwa science and technology Limited company is 57 mu m;
stock solution of cooling liquid: one-component cooling fluid XD-100 from Changzhou ancient technologies, Inc.
Example 1
The embodiment provides a diamond wire slicing process of a silicon wafer (with side length of 166mm), which comprises the following steps:
adding a stock solution of cooling liquid into a cutting liquid cylinder (the volume is 300L) of a diamond wire slicing machine, diluting to 300L, wherein the stock solution of the cooling liquid is used for each slicing machine by 1000mL, and the temperature of a cooling system is set to be 20 ℃;
a schematic diagram of diamond wire slicing is shown in fig. 1, a breaking tension value is tested on a sampling wire on each diamond wire coil used by each diamond wire slicing machine, each sampling wire is tested for 5 times, and the cutting tension value set by each slicing machine is 60% of the average breaking tension value of the diamond wires used by each slicing machine; starting a diamond wire slicing machine, driving a diamond wire 6 to move at a linear speed of 28m/s by a main roller 5, and simultaneously driving a silicon rod 1 (with the length of 685mm) to move downwards at a speed of 2.6mm/min under the driving of a workpiece plate 3 and an adhesive plate 2 for cutting, wherein a silicon wafer falls into a wafer collecting groove 7; circulating cooling liquid to flush the diamond wire 6 during cutting, wherein the flow rate of the cooling liquid is 8500kg/h, and adjusting the height of the diversion trench 4 to enable the falling point of the cooling liquid on the diamond wire 6 to be at the junction of the diamond wire 6 and the silicon rod 1;
cutting for 100min, stopping slicing after each cut, discharging mixed waste liquid of silicon powder and cooling liquid, and adding the cooling liquid into a cutting liquid cylinder of the diamond wire slicing machine again, wherein the operation time between the two cuts is 40 min; the discharged waste liquid is recycled, a cooling liquid recycling system is shown in fig. 2, the waste liquid enters a waste liquid collecting tank and then is sent to a filter press, solid substances such as silicon powder and the like are filtered, the filtered liquid enters a filtered liquid storage tank and is subjected to COD value detection, and if the COD value of the filtered liquid is 450 +/-50 mug/L, the filtered liquid is taken as cooling liquid and flows back to a slicer for reuse; if the COD value of the filtrate exceeds the range of 450 +/-50 mug/L, the filtrate is unqualified, water or a stock solution of cooling liquid needs to be supplemented, and the COD value is adjusted to 450 +/-50 mug/L.
The 36 slicing machines were operated continuously for 30 days as described above, and then the cutting chamber, cooling circuit and heat exchanger were automatically cleaned as follows, the schematic diagram of which is shown in fig. 3:
alkali washing: adding 0.5mol/L NaOH solution into a cutting liquid cylinder of a diamond wire slicing machine, adding 200L NaOH solution into each slicing machine, setting the temperature of a cooling system at 50 ℃, circularly cleaning for 1h, and discharging alkali liquor after finishing cleaning;
washing with water: after the alkali washing is finished, adding water into a cutting hydraulic cylinder of a diamond wire slicing machine, adding 200L of water into each slicing machine, circularly washing for 20min for 2 times, and detecting the pH value of discharged water to be 7.0 to meet the conditions;
cooling liquid washing: and after the water washing is finished, adding a cooling liquid stock solution into a cutting liquid cylinder of the diamond wire slicing machine, adding 500mL of the cooling liquid stock solution into each slicing machine, diluting the cooling liquid stock solution to 300L with water, circularly cleaning the cutting liquid stock solution for 10min, and discharging the cooling liquid after the washing is finished.
The microtome cooling system temperature was reset to 20 ℃ and the operation was continued for 7 days as described above, and the results of slicing for 7 days were counted, and the results are shown in Table 1.
Example 2
The difference from example 1 is that during the last 7 consecutive days of operation, the COD value of the recovered coolant was not controlled, but the coolant stock was supplemented after each filter press, in an amount equal to the volume of liquid lost by the filter press. The results of slicing within 7 days were counted and shown in Table 1.
Example 3
The difference from example 1 is that the cooling liquid dropping point of the diamond wire slicer is far away from the silicon rod during slicing, the cooling liquid dropping point is 15mm away from the boundary point of the silicon rod and the steel wire, and slicing results within 7 days are counted, and the results are shown in table 1.
Comparative example 1
The difference from example 1 is that after the microtome was continuously operated for 30 days, it was continuously operated for 7 days without washing, and the results of slicing in 7 days were counted, and the results are shown in Table 1.
Example 4
The difference from example 1 is that the cut silicon rod has a side length of 157mm (diamond wire cutting rate is kept constant, and the time for cutting is 90min), the concentration of NaOH solution used for alkali washing is 0.15mol/L, and the slicing results in 7 days are shown in Table 1.
Example 5
The difference from example 4 is that during the last 7 consecutive days of operation, the COD value of the recovered coolant was not controlled, but the coolant stock was supplemented after each filter press, in an amount equal to the volume of liquid lost by the filter press. The results of slicing within 7 days were counted and shown in Table 1.
Example 6
The difference from example 4 is that the cooling liquid dropping point of the diamond wire slicer is far away from the silicon rod during slicing, the cooling liquid dropping point is 15mm away from the boundary point of the silicon rod and the steel wire, and the slicing results in 7 days are counted, and the results are shown in table 1.
Comparative example 2
The difference from example 4 is that after the microtome was continuously operated for 30 days, it was continuously operated for 7 days without washing, and the results of slicing in 7 days were counted, and the results are shown in Table 1.
TABLE 1
In table 1, the meaning/calculation method of each test item is as follows:
the single-chip wire consumption: the usage amount of the single-tool diamond wire/the qualified silicon wafer produced by the single tool.
Straight pass ratio (a + B): the proportion of qualified silicon wafers comprises A-grade silicon wafers and B-grade silicon wafers. Namely: the number of the qualified silicon wafers (A grade + B grade)/the number of the silicon wafers to be produced by a single cutter are detected, wherein the A grade silicon wafer refers to a silicon wafer with the height value of the line mark being less than or equal to 15 mu m, and the B grade silicon wafer refers to a silicon wafer with the height value of the line mark being 15-30 mu m.
Grade A rate: the proportion of the A-level silicon wafer is as follows: the number of silicon chips tested by a single blade is A grade/the number of silicon chips which should be produced by a single blade.
Wire breakage rate: the number of knives with broken line is the ratio of all the knives in the cutting.
Capacity of a single machine: the number of knives actually cut in 24h a day for 1 wire slicer.
Comparing example 1 with comparative example 1, and example 4 with comparative example 2, it can be seen that after the cleaning of the invention, the wire breakage rate of the diamond wire slice is reduced by more than half, the silicon wafer yield is also obviously improved, and the productivity is obviously improved.
The COD values of the recovered cooling liquid in examples 2 and 5 were not controlled, and the COD values reached more than 1000. mu.g/L after continuous operation for 3 days. Since the COD value of the coolant was too high and the cutting ability of the diamond wire was lowered, the wire breakage rate and the good chip yield in examples 2 and 5 were lowered compared to examples 1 and 4.
The cooling liquid dropping point in examples 3 and 6 is far from the boundary point between the silicon rod and the steel wire, the amount of cooling liquid taken into the cutting interface by the diamond wire is small, and the heat and the silicon powder cannot be taken out in time, so the wire breakage rate and the good product rate in examples 3 and 6 are lower than those in examples 1 and 4.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (10)
1. A diamond wire slicing process of a silicon wafer is characterized by comprising the following steps of:
adding cooling liquid into a cutting liquid cylinder of a diamond wire slicing machine, and starting the diamond wire slicing machine to cut the silicon rod into silicon wafers;
circulating the cooling liquid to flush the diamond wire while cutting;
after accumulated cutting is carried out for a period of time, cleaning a cutting chamber, a cooling pipeline and a heat exchanger of the diamond wire slicing machine by using alkali liquor;
the cleaning method comprises the following steps:
alkali washing: adding alkali liquor into a cutting hydraulic cylinder of the diamond wire slicing machine for circular cleaning, wherein the concentration of the alkali liquor is 0.08-0.5mol/L, and discharging the alkali liquor after the circulation cleaning is finished;
washing with water: after the alkali washing is finished, adding water into a cutting liquid cylinder of the diamond wire slicing machine for circular cleaning, and discharging water after the circular cleaning is finished;
cooling liquid washing: and after the water washing is finished, adding cooling liquid into a cutting liquid cylinder of the diamond wire slicing machine for circular washing, and discharging the cooling liquid after the circular washing is finished.
2. The diamond wire slicing process according to claim 1, wherein the alkali in the alkali solution is selected from one or a combination of at least two of NaOH, KOH, RbOH and CsOH;
preferably, the side length of the silicon chip is 156-157mm, and the concentration of the alkali liquor is 0.08-0.17 mol/L;
preferably, the side length of the silicon wafer is more than or equal to 166mm, and the concentration of the alkali liquor is 0.25-0.5 mol/L.
3. The diamond wire slicing process according to claim 1 or 2, wherein in the alkaline washing step, the volume of alkaline liquor added accounts for 50-70% of the volume of a cutting hydraulic cylinder of the diamond wire slicing machine;
preferably, the temperature of the alkali liquor is kept between 40 and 60 ℃ during the alkali washing;
preferably, in the alkaline washing step, the time for circulating washing is 1-2 h.
4. The diamond wire slicing process according to any one of claims 1 to 3, wherein in the water washing step, the time of each cycle of washing is 15-30 min;
preferably, in the water washing step, the water washing is stopped until the pH of the discharged water is 6.5 to 7.5.
5. The diamond wire slicing process according to any one of claims 1 to 4, wherein the concentration of the cooling liquid in the cooling liquid washing step is 40 to 60% of the concentration of the cooling liquid at the time of slicing;
preferably, in the cooling liquid washing step, the time of the circulating washing is 5-15 min.
6. The diamond wire slicing process according to any one of claims 1 to 5, wherein the side length of the silicon wafer is 156-157mm, and the diamond wire slicing machine is cleaned once per cumulative cutting of 900-1000;
preferably, the side length of the silicon wafer is more than or equal to 166mm, and the diamond wire slicer cleans every 300-350 cumulative cutting.
7. Diamond wire slicing process according to any of claims 1-6, wherein the cooling liquid is changed every 1-2 cuts;
preferably, the chemical oxygen demand of the cooling liquid is 400-500 mu g/L.
8. The diamond wire slicing process according to any one of claims 1 to 7, wherein the tension of the diamond wire on the diamond wire slicer is 60-70% of the breaking tension value of the diamond wire.
9. The diamond wire slicing process according to any one of claims 1 to 8, wherein the distance between the falling point of the cooling liquid on the diamond wire and the intersection of the diamond wire and the silicon rod during the cutting process is not more than 5 mm.
10. The diamond wire slicing process according to any one of claims 1 to 9, wherein the average cutting rate of the diamond wire to the silicon rod during cutting is 1 to 3 mm/min;
preferably, the linear speed of the diamond wire during cutting is 10-40 m/s.
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