Preparation method of N-type or P-type ultrathin silicon wafer

Abstract

The invention belongs to the technical field of diamond wire cutting of silicon wafers, and particularly relates to a preparation method of an N-type or P-type ultrathin silicon wafer, which comprises the following steps: switching a cutting head of a cutting machine from a carbon steel diamond wire to a tungsten wire diamond wire when a wire saw method is used for cutting a silicon ingot, designing new guide wheel parameters for a guide wheel suitable for the ultrathin silicon wafer, and toughening the guide wheel, according to the characteristics of a tungsten wire diamond wire cutting head, a new cutter outlet mode is designed, the concentration of cutting liquid is adjusted, and a quick cutting process is adopted during cutting. In actual application, due to the fact that the tungsten wire diamond wire is adopted, cutting capacity is enhanced, new wires are saved, machine efficiency is improved, the problem that a traditional cutting wire is high in wire breakage rate is solved, meanwhile, by controlling the concentration of cutting liquid, the cutting yield of silicon wafers is improved, the problem that the ultra-thin silicon wafers are poor in nanoscale cooling effect due to small saw kerfs and silicon powder particles is poor in nanoscale cooling effect is solved, and the service life of the ultra-thin silicon wafers is prolonged. The problem of poor cutting and cost loss caused by wire breakage is solved, and the cutting yield of the ultrathin silicon wafer is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of tungsten diamond wire cutting, and in particular relates to a method for preparing an N-type or P-type ultra-thin silicon slice. Background Art

[0002] The existing ultra-thin slice cutting process optimizes the cutting process matching and the performance of the cutting equipment parts to achieve the thin slice cutting of high-hardness and brittle materials, thereby reducing the amount of materials required for the finished slice and improving the flexibility of the finished slice. Carbon steel diamond wire cutting technology is the mainstream silicon wafer cutting technology for a long time in the future. How to continuously improve the technical performance of diamond wire cutting equipment and carbon steel diamond wire, optimize the cutting production process, and meet the high efficiency, high quality and low cost requirements of photovoltaic silicon wafer production will be the core technology of future silicon wafer competitiveness. In general, "thin wire, high speed, automation and intelligence" are the main development trends of photovoltaic silicon wafer cutting production. However, with the thinning of the traditional carbon steel wire diameter, the cutting process window is getting narrower and narrower, the breaking tension is reduced, the wire breakage ratio is increased, the yield rate fluctuates greatly, the guide wheel slot is getting smaller and smaller, and the new guide wheel slotting and running-in wire breakage ratio is significantly increased, which has a great impact on the yield rate of cutting silicon wafers. The existing large wire diameter cutting method uses a high-concentration cutting fluid, which is easy to cause batch line marks and abnormal total thickness variation.

[0003] Patent No. CN116587440A discloses a silicon nitride wire cutting method, which uses silicon nitride wire to cut silicon wafers. The method cannot solve the problem of insufficient diamond wire carrying liquid caused by ultra-thin wafer cutting, and cannot solve the problem of poor silicon powder capacity of sawing seams and high wire breakage. The silicon nitride wire is used for high-speed cutting. Although the cutting speed is improved, the tensile strength and wear resistance of the silicon nitride wire are not high, and the cutting wire is easily damaged due to the high cutting speed. Therefore, it is urgent for technicians to solve this problem. Summary of the invention

[0004] In view of the above existing problems and defects, the present invention designs a cutting method for cutting ultra-thin silicon wafers using a tungsten diamond wire.

[0005] The present invention provides a method for preparing an N-type or P-type ultra-thin silicon wafer, and the process of preparing the ultra-thin silicon wafer comprises the following steps: S1: Put the polysilicon raw material into the quartz crucible of the single crystal furnace; S2: Silicon ingots are made by Czochralski method; S3: grinding and cutting the silicon ingot; S4: Ultra-thin silicon wafers were made using the wire saw method; In step S4, when cutting ultra-thin silicon wafers, the cutting head of the cutting machine is first replaced from carbon steel diamond wire to tungsten diamond wire; before using tungsten diamond wire to perform wire sawing operation on silicon ingots, the grooving parameters of the guide wheel of the cutting machine are designed according to the characteristics of the tungsten diamond wire, and the guide wheel parameters are updated and toughened.

[0006] Furthermore, the wire diameter of the tungsten diamond wire is 25-26 μm, and the tungsten diamond wire is evenly placed into the groove opened by the guide wheel of the cutting machine through a winding device.

[0007] Tungsten diamond wire has high strength and rigidity, can maintain shape stability and provide stable cutting force during cutting, which helps to ensure the stability and reliability of the cutting wire. Tungsten diamond wire has excellent wear resistance and can withstand greater friction and wear during cutting, thereby extending the service life of the cutting wire and reducing the frequency of cutting wire replacement.

[0008] The parameters of the cutting machine guide wheel are updated by designing the slotting parameters on the cutting machine guide wheel of the cutting machine according to the wire diameter of the tungsten diamond wire, and a tough rail is used to guide the cutting wire. A slotted steel wire with a wire diameter of 3μm is first selected on the silicon ingot and slotted using breaking tension for pre-cutting processing. The slotting angle of the cutting machine guide wheel is 30-32°, the groove depth of the cutting machine guide wheel is 0.220-0.224mm, the groove bottom radius of the cutting machine guide wheel is 0.070-0.072mm, the distance from the steel wire to the groove edge of the cutting machine guide wheel is 0.011-0.0114mm, the groove spacing of the cutting machine guide wheel is 0.19-0.197mm, and the outer diameter of the slotted steel wire is 0.04-0.043mm.

[0009] By creating a tough track on the guide wheel of the cutting machine, the path and direction of the cutting line can be guided during the cutting process to ensure the accuracy and consistency of the cutting. The tough track can be used as a positioning reference for the cutting line to ensure the precise positioning of the cutting position to obtain silicon wafers of the required size and shape, and can reduce errors and offsets during the cutting process, improve the quality and consistency of the cutting. The use of steel wire for tough track design can reduce damage to the edge of the silicon wafer and reduce the fragments and cracks that may be generated during the cutting process. Accurate tough track design and cutting parameters can improve cutting efficiency and reduce time and energy consumption during the cutting process. The slotting parameters are designed according to the efficiency of tungsten diamond wire cutting ultra-thin slices, which is more compatible with the tungsten diamond wire and has higher cutting efficiency.

[0010] Furthermore, the cutting height of the tungsten diamond wire was adjusted to 3.6-3.8 μm, and the cutting tension was set to 3.5-3.7N.

[0011] The tungsten diamond wire has high breaking force, strong tensile strength and fatigue resistance. The cutting tension is set to 3.5-3.7N, which solves the problem of large-size ultra-thin sheet cutting without coolant due to small saw seam, and enhances the ability of saw seam to discharge silicon powder and the problem of high wire breakage during the cutting process.

[0012] Furthermore, when the single crystal silicon ingot is cut using the wire saw method, the concentration of the cutting fluid in the circulation system is also adjusted. The tungsten diamond wire adopts a low-concentration cutting circulation system, and the cutting fluid concentration is set to a chemical oxygen demand of 24,000 mg / L.

[0013] By adopting the low-concentration cutting process, the chemical oxygen demand concentration was reduced from 41,000 mg / L to 24,000 mg / L, solving the problems of line marks and abnormal total thickness of silicon wafers caused by high concentration of cutting fluid in wire cutting of large-size ultra-thin tungsten wire and diamond wire.

[0014] When using the wire saw method for cutting, the fast cutting process is used for cutting. The specific parameters of the fast cutting process are: the main table speed is 2.3mm / min, the process time is 85min, the wire consumption is 13KM / knife, and the cutting process uses a large cycle method for cutting in and out. The fast-cut process uses a high-speed rotating cutting tool, such as a cutting disc or guide wheel, to cut silicon wafers at a faster speed. Compared with the traditional slow-cutting process, the fast-cutting process can significantly increase the cutting speed, thereby improving production efficiency, and uses high-speed cutting to cut silicon wafers, which results in less heat accumulation in the cutting area. Lower thermal impact can reduce thermal stress and deformation of silicon wafers, help maintain the structure and performance of silicon wafers stable, and can complete cutting in a shorter time, reducing the mechanical force and heat action time on silicon wafers. This helps to reduce damage to the surface and edges of silicon wafers during the cutting process, improve cutting quality and consistency, have higher cutting accuracy and precision, and can achieve smaller cutting errors and dimensional changes. This is very important for manufacturing applications that require high-precision silicon wafers, such as microelectronic devices and optical components.

[0015] Furthermore, dopants are added into the quartz crucible to obtain P-type or N-type ultra-thin silicon wafers.

[0016] Different ultra-thin silicon wafers can be produced according to the added dopants to meet more usage requirements.

[0017] Furthermore, the temperature gradient is set to 1420-1500° C. during the growth of the single crystal silicon crystal.

[0018] By controlling the growth environment of single crystal silicon crystals in a gradient manner, the manufacturing quality of single crystal silicon can be improved, thereby improving the finished product yield of semiconductors.

[0019] Furthermore, the uneven parts at both ends of the N-type or P-type silicon ingot are cut off, and the surface of the N-type or P-type semiconductor silicon ingot is ground.

[0020] The uneven parts at both ends of the silicon ingot are cut off to facilitate obtaining thin slices of uniform thickness after wire sawing. The N-type or P-type silicon ingot is ground to make the surface flat, which is convenient for the subsequent wire cutting steps.

[0021] The beneficial effects of the present invention are: (1) The trend of thinning traditional silicon wafer cutting wires has led to higher and higher cutting process requirements. Thin wire cutting is easily affected by vibration, external force interference and cutting tool wear, which may lead to reduced cutting quality. The cutting wire is easy to break due to the fragility of the material, thus affecting the smoothness and shape of the cutting surface. Tungsten diamond wire is used as the cutting wire because it has a high tensile strength and is not easily affected by external force during cutting. It is easier to cut out intact silicon wafers during silicon wafer cutting, and the silicon wafer yield is higher. The thinning of the cutting wire will increase the cutting resistance during cutting, thus leading to a decrease in cutting speed. The degree of cutting is reduced, and the thin wire needs to be cut more carefully and slowly, and the cutting process may be more time-consuming. The use of tungsten diamond wire can increase the breaking force due to its high strength, and because the wire diameter of tungsten diamond wire has been increased, the fast cutting process can be used during cutting, which not only increases the cutting speed, but also allows for greater cutting force and reduces cutting resistance. By adjusting the cutting tension and knife height of the tungsten diamond wire installed on the cutting head of the cutting machine, the ability of the diamond wire to carry silicon powder is increased, thereby improving the cutting ability. The fast cutting process designed according to the cutting characteristics of tungsten diamond wire has a short time, low wire consumption, and improved machine efficiency. (2) High-concentration cutting fluid usually contains more corrosive chemicals, which may aggravate the corrosion of the cutting steel wire, causing the cutting steel wire to break abnormally, affecting the silicon wafer cutting work. Tungsten wire diamond wire cutting wire is resistant to acid, alkali and corrosion, and can withstand higher concentration cutting fluid; in order to ensure the yield rate of cutting silicon wafers, the concentration of the cutting fluid can be reduced. The reduction in cutting ability caused by the reduction in cutting fluid concentration can be compensated by the cutting ability of the tungsten wire diamond wire itself. According to the cutting characteristics of the diamond wire, the cutting fluid formula is adjusted to use low-concentration cutting fluid; high-concentration cutting fluid is more difficult to handle and dispose of. High-concentration chemical substances will pollute the environment and may cause safety hazards. Therefore, this method uses low-concentration cutting fluid to reduce the impact of the cutting fluid on the environment while ensuring the cutting ability. Low-concentration cutting fluid reduces the emission of chemical oxygen demand and reduces the difficulty of wastewater treatment. The waste wire after cutting can be collected and the waste tungsten wire diamond wire can be reused, saving production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1It is an optimized schematic diagram of an embodiment of the present invention.

[0023] Figure 2 Schematic diagram of guide wheel slotting parameters in an embodiment of the present invention.

[0024] Figure 3 It is a cutting effect statistical diagram in an embodiment of the present invention.

[0025] In the figure, ①- slot angle; ②- slot distance; ③- slot bottom radius; ④- slot depth; ⑤- distance from steel wire to slot edge; ⑥- outer diameter of steel wire. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings.

[0027] When polysilicon raw materials are placed in a quartz crucible of a single crystal furnace, adding trivalent elements such as boron (B) or aluminum (Al) into the quartz crucible can produce N-type ultra-thin silicon wafers. If pentavalent elements such as phosphorus (P) or arsenic (As) are added into the quartz crucible, P-type ultra-thin silicon wafers can be produced. The following steps are mainly involved in making ultra-thin silicon wafers using the Czochralski method: (1) Melt: Melt all the polycrystalline material; (2) Seeding: Put the seed crystal down and bake it, make it contact with the melt, pull the seed crystal upward, and control the temperature so that the melt crystallizes on the seed crystal; (3) Necking: The purpose is to reduce or eliminate dislocations and obtain dislocation-free single crystals; (4) Shoulder release: Allow the single crystal to grow to the required diameter; (5) Equal diameter: the single crystal grows in a cylindrical shape; (6) Finishing: Gradually reduce the diameter of the single crystal and finally make it conical to avoid dislocation back extension. The temperature of the polysilicon raw material in the quartz crucible is adjusted in different time periods according to the preparation time. In step (1), polysilicon will soften at 1420°C. Before heating begins, the temperature is controlled at 1500°C until the polysilicon softens. Accurate temperature control can improve the quality of the silicon ingot. The single crystal furnace is heated by a resistor, and the temperature of the single crystal furnace can be changed by adjusting the size of the resistor.

[0028] The manufactured silicon ingot needs to be cut at both ends first, and the surface of the silicon ingot needs to be ground to make the silicon ingot into a cylinder to facilitate the subsequent wire cutting steps.

[0029] Reference Figure 1 and Figure 2It can be seen that before cutting the ultra-thin silicon wafer, the tungsten diamond wire is first wound on the cutting head of the cutting machine by winding. The tungsten diamond wire is driven by the cutting machine to run in the track of the guide wheel and cut the ultra-thin wafer. The tungsten diamond wire has strong wear resistance and can be used for a longer time, but it will still wear out if used for a long time. If the tungsten diamond wire is worn out after long-term cutting, the staff can remove the tungsten diamond wire on the cutting head for recycling.

[0030] According to the tungsten diamond wire pair, a new guide wheel parameter is designed for the guide wheel suitable for ultra-thin silicon wafers, wherein the slotting angle ① of the guide wheel of the cutting machine is 32°, the slot depth ④ of the guide wheel of the cutting machine is 0.224mm, the slot bottom radius ③ is 0.072mm, the distance from the slotted steel wire to the slot edge ⑤ is 0.0114mm, the slot distance ② is 0.197mm, and the slotted steel wire diameter ⑥ is 0.043mm. Since the guide wheel is coated with polyurethane, the coated guide wheel is slotted according to the relevant parameters by a precision lathe after coating. The slotting parameters include slot distance ②, slot depth ④, slotting angle ①, and slot bottom radius ③. Because the slotting process is relatively delicate, at the micron level, each slot is opened due to particles and polymers. Urethane residue, etc., as well as the groove bottom fillet ③, grooving angle ①. Because the guide wheel is tough, in order to maintain the stability of the groove type, it is also necessary to perform toughening. The groove steel wire used for toughening is gold-toughened. The diameter of the groove steel wire is smaller than the groove pitch ②. By increasing the tension for wiring and heat-up, the groove pitch ② will not be deformed during the formal cutting process to avoid wire breakage and poor cutting. The steel wire uses a groove steel wire with a wire diameter of 3μm and uses breaking tension for groove toughening. The guide wheel grooving method is designed according to the wire diameter of the tungsten diamond wire and the size requirements of the ultra-thin silicon wafer to ensure that the tungsten diamond wire is not easily broken when cutting in the guide wheel and to give full play to the advantages of the tungsten diamond wire cutting line.

[0031] After the guide wheel is slotted and the tough rail is completed, the tungsten diamond wire cutting height can also be adjusted from 2.2-2.4μm to 2.6-2.8μm. The traditional carbon steel wire diameter is 33μm and the cutting tension is set to 3.3N, but the tungsten diamond wire has a high breaking force and strong tensile strength, so the cutting tension can be set to 3.7N. Since the cutting tension is larger than the traditional cutting tension setting, it is more convenient to bring out silicon powder when cutting ultra-thin silicon wafers, which will not affect the cutting efficiency. After the silicon powder is discharged, the coolant can enter the cutting gap to cool down the temperature generated during the cutting of the tungsten diamond wire and the silicon wafer, ensuring that the yield of ultra-thin silicon wafers will not be affected by temperature and reducing the problem of high wire breakage rate.

[0032] The cutting fluid concentration is adjusted according to the cutting characteristics of diamond wire. During the experiment, although the corrosion resistance of tungsten diamond wire is relatively high, the high concentration of cutting fluid will cause abnormal line marks and excessive cutting fluid concentration when cutting large-size ultra-thin silicon wafers, which will also cause a high proportion of total thickness changes in ultra-thin silicon wafers. Experiments have shown that when the concentration of 26μm tungsten diamond wire cutting fluid is reduced from 41,000 mg / L of chemical oxygen demand to 24,000 mg / L of chemical oxygen demand, it can greatly reduce the proportion of abnormal line marks and total thickness changes caused by high cutting fluid concentration in the cutting of large-size ultra-thin wafers with tungsten diamond wire. Combined with the corrosion resistance of tungsten diamond wire, the cutting wire can have a longer service life without frequent replacement of the cutting wire.

[0033] While maintaining the tungsten diamond wire cutting height at 3.8μm, the cutting tension at 3.7N, and using a cutting fluid with a chemical oxygen demand concentration of 24,000 mg / L, the tungsten diamond wire cutting adopts a fast cutting process, the main table speed of the cutting machine is set to 2.3mm / min, the process time is set to 85min, the wire consumption is 13KM / knife, and the cutting process adopts a large cycle method for cutting in and out.

[0034] Reference Figure 3 It can be seen that the ultra-thin silicon wafers cut through the above steps can effectively solve the wire breaking problem of the new guide wheel and thus improve the cutting yield. The wire breaking rate of the new guide wheel used in the experiment has dropped from the previous 27% to the current 5.8%. The A-grade yield has been improved to be basically the same as the yield of the old guide wheel, contributing 3% to the overall yield. If the tungsten diamond wire is broken after cutting, it can be manually recycled, which greatly reduces the cost compared to the traditional carbon steel diamond wire.

[0035] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined in the present invention may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed in the invention.

Claims

1. A method for preparing an N-type or P-type ultra-thin silicon wafer, comprising the following steps in the process of preparing the ultra-thin silicon wafer: S1: Put the polysilicon raw material into the quartz crucible of the single crystal furnace; S2: Silicon ingots are made using the Czochralski method; S3: grinding and cutting the silicon ingot; S4: Ultra-thin silicon wafers were made using the wire saw method; It is characterized in that: in step S4, when cutting ultra-thin silicon wafers, the cutting wire of the cutter guide wheel is first replaced from carbon steel diamond wire to tungsten diamond wire; before using the tungsten diamond wire to perform wire sawing operation on the silicon ingot, it is also necessary to design the grooving parameters of the cutter guide wheel according to the characteristics of the tungsten diamond wire, and update and toughen the parameters of the cutter guide wheel.

2. The method for preparing an N-type or P-type ultra-thin silicon wafer according to claim 1, characterized in that: The wire diameter of the tungsten diamond wire is 25-26 μm, and the tungsten diamond wire is evenly placed in the groove opened by the guide wheel of the cutting machine through a winding device.

3. The method for preparing an N-type or P-type ultra-thin silicon wafer according to claim 1, characterized in that: The cutting machine guide wheel parameter update is to design the slotting parameters on the cutting machine guide wheel according to the wire diameter of the tungsten diamond wire, and a tough rail is used to guide the tungsten diamond wire. A slotted steel wire with a wire diameter of 3μm is first selected on the silicon ingot and slotted using breaking tension for pre-cutting processing. The slotting angle of the cutting machine guide wheel is 30-32°, the groove depth of the cutting machine guide wheel is 0.220-0.224mm, the groove bottom radius of the cutting machine guide wheel is 0.070-0.072mm, the distance from the slotted steel wire to the groove edge of the cutting machine guide wheel is 0.011-0.0114mm, the groove pitch of the cutting machine guide wheel is 0.19-0.197mm, and the groove wire diameter of the slotted steel wire is 0.04-0.043mm.

4. The method for preparing an N-type or P-type ultra-thin silicon wafer according to claim 1, further comprising adjusting the cutting mode of the tungsten wire and diamond wire, characterized in that: The cutting height of the tungsten diamond wire is adjusted to 3.6-3.8 μm, and the cutting tension is set to 3.5-3.7N.

5. The method for preparing an N-type or P-type ultra-thin silicon wafer according to any one of claims 1 to 4, characterized in that: When the silicon ingot is cut by the wire saw method, the concentration of the cutting fluid in the circulation system is also adjusted. The tungsten diamond wire adopts a low-concentration cutting circulation system, and the concentration of the cutting fluid is 24,000 mg / L of chemical oxygen demand.

6. A method for preparing an N-type or P-type ultra-thin silicon wafer according to any one of claims 1 to 4, characterized in that: When the wire saw method is used for cutting, a fast cutting process is used for cutting. The specific parameters of the fast cutting process are: the main table speed is 2.3 mm / min, the process time is 85 min, the wire consumption is 13 KM / knife, and the cutting process adopts a large cycle method for cutting in and out.

7. The method for preparing an N-type or P-type ultra-thin silicon wafer according to claim 1, characterized in that: In step S1, dopants are added into the quartz crucible to produce a P-type or N-type ultra-thin silicon wafer.

8. The method for preparing an N-type or P-type ultra-thin silicon wafer according to claim 7, characterized in that: A trivalent element is added into the quartz crucible to obtain an N-type ultra-thin silicon wafer; a pentavalent element is added into the quartz crucible to obtain a P-type ultra-thin silicon wafer.

9. The method for preparing an N-type or P-type ultra-thin silicon wafer according to claim 1, characterized in that: In step S2, the temperature is set to 1420-1500° C. during the growth of the single crystal silicon crystal.

10. The method for preparing an N-type or P-type ultra-thin silicon wafer according to claim 1, characterized in that: In step S3, the uneven portions at both ends of the N-type or P-type silicon ingot are cut off, and the surface of the N-type or P-type silicon ingot is ground.

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