A magnetron crystal pulling method for reducing the porosity of single crystal silicon ingot

Abstract

The present invention discloses a magnetically controlled crystal pulling method for reducing the porosity of a single-crystal silicon rod, and belongs to the technical field of vertically pulled single-crystal silicon. The main processes of the method include: material preparation, material coding process, material processing process, stabilization process, crystal seeding process, shoulder release process, shoulder rotation process, equal diameter process and finishing process; the stabilization process includes two steps: (1) after the material processing is completed, the power of the bottom heater is increased to 35-45kW, the power of the main heater is reduced to 75-85kW, and maintained for 1h-2h, the natural convection at the bottom of the melt is enhanced, and the bubble escape rate is increased; (2) the power of the bottom heater is reduced to the power required for crystal pulling 0-10kW, the power of the main heater is adjusted, and the power of the main heater is adjusted to 90-105kW, and the magnetic field strength is 0.3-0.4T. The method of the present invention reduces the generation of bubbles in the melt on the one hand, and increases the escape rate of bubbles in the melt on the other hand, reduces the ratio of pores in single-crystal silicon, and improves the product qualification rate.

Description

Technical Field

[0001] The invention relates to a magnetron crystal pulling method for reducing the porosity of a single-crystal silicon crystal rod, and belongs to the technical field of direct-pulling single-crystal silicon. Background Art

[0002] As the semiconductor industry continues to increase its requirements for single-crystal silicon wafer technology, magnetron crystal pulling (MCZ) technology has become a core technology in the semiconductor industry. Magnetron CZ single-crystal silicon technology adds an external magnetic field to the traditional CZ silicon single crystal growth, thereby suppressing the heat convection generated during crystal growth, effectively improving the success rate of crystal growth, and reducing the oxygen content in the crystal, thereby improving the crystal quality.

[0003] At present, the process of pulling single crystal silicon ingots by the Czochralski method mainly includes furnace loading, vacuuming, leak detection, material processing, stabilization, seeding, shoulder release, shoulder rotation, equal diameter, and finishing. In the process of material processing, after the silicon material is melted, a large number of bubbles will be mixed in the melt. In the process of pulling crystals, the presence of the magnetic field will inhibit the convection in the melt, and the bubbles in the melt are not easy to escape. The bubbles will then remain in the crystal ingot as the crystal ingot grows during the growth of the crystal ingot. After the single crystal silicon ingot is sliced, the bubbles in the crystal ingot appear on the single crystal in the form of "holes". The presence of pores will lead to an increase in the defective rate of single crystal slices. The defective rate of single crystals caused by pores is the porosity of the single crystal silicon ingot. Therefore, reducing the porosity of single crystal silicon ingots is particularly important for improving crystal quality. Summary of the invention

[0004] The object of the present invention is to provide a magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot, so as to solve the technical problem of pores existing in a single crystal silicon ingot prepared by the magnetron crystal pulling method.

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

[0006] A magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot, the main processes include: material preparation, material stacking process, material processing process, stabilization process, crystal seeding process, shoulder release process, shoulder rotation process, equal diameter process and finishing process; the stabilization process includes two steps:

[0007] (1) After the material is mixed, increase the bottom heater power to 35-45kW and reduce the main heater power to 75-85kW, maintain for 1h-2h, enhance the natural convection at the bottom of the melt, and increase the bubble escape speed;

[0008] (2) Reduce the bottom heater power to the power required for crystal pulling (0-10kW), adjust the main heater power to 90-105kW, and the magnetic field strength to 0.3-0.4T.

[0009] Preferably, during the material preparation stage, 45-100 mm blocks and 5-45 mm crushed materials are used to load the crucible, and the proportion of blocks is adjusted to 80%-90%, thereby reducing the specific surface area of ​​the polysilicon material.

[0010] Preferably, in the stacking process, the polysilicon block material is in full contact with the surface of the quartz crucible to avoid the polysilicon material squeezing the quartz crucible to produce sharp depressions during the material processing.

[0011] Preferably, in the material chemical process, the power of the bottom heater is 15-30 kW, the power of the main heater is 100-115 kW, the argon flow rate in the furnace is controlled to be 100-130 slpm (L / min), and the atmosphere pressure inside the furnace is 1.5-2.5 kPa.

[0012] Preferably, in the seeding process, shoulder release process, shoulder rotation process, equal diameter process and finishing process, the bottom heater power is 0-10kW.

[0013] Preferably, in the seeding process, shoulder release process, shoulder rotation process, equal diameter process and finishing process, the magnetic field strength is 0.3-0.4T.

[0014] Preferably, the quartz crucible selected in the material preparation stage is 32 inches, and the diameter of the equal-diameter process single crystal is 12 inches.

[0015] Beneficial effects of the present invention:

[0016] According to the improved magnetron crystal pulling method of the present invention, after the material processing step is completed, the melt convection is enhanced by increasing the bottom heater to 35-45kW and reducing the main heater power to 75-85kW, so that bubbles in the melt can escape quickly; if the bottom heater power is reduced to below 35kW, the upward convection from the bottom of the melt becomes weak, the escape rate of bubbles in the melt is reduced, and the porosity of the single crystal silicon rod is increased; in the material preparation and furnace loading stage, large blocks of materials are used for loading in the crucible and the material stacking method is adjusted to reduce the generation of bubbles; in the stabilization, crystal induction, shoulder release, shoulder rotation, equal diameter and finishing processes, the bottom heater power is reduced to reduce the convection at the bottom of the melt and inhibit the upward flow of bubbles.

[0017] The ratio of pores in the single crystal silicon ingot slices drawn by the method of the present invention is significantly reduced, and the product qualification rate is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The following is a curve showing the change of the bottom heater power during the process from the completion of the material fusion to the seeding of the crystal in Example 1 and Comparative Example 1.

[0019] Figure 2 The curves of the change of magnetic field intensity from the completion of the material chemistry to the seeding process of Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but this does not limit the protection scope of the present invention.

[0021] In the following embodiments and comparative examples, a Czochralski single crystal furnace is used, a 32-inch thermal field is installed, a horizontal superconducting magnetic field is used, and 360 kg of polysilicon material is loaded. After material preparation, material stacking process, material processing process, stabilization process, seeding process, shoulder release process, shoulder rotation process, equal diameter process and finishing process, a single crystal silicon ingot with a diameter of 12 inches is pulled. The following is a comparative analysis of only the improvements involved in the technical solution of the present invention through the embodiments and comparative examples, and the description of other operating processes and related parameter controls is omitted.

[0022] Comparative Example 1

[0023] The main parameters controlled during the single crystal silicon ingot pulling process are as follows, among which the change curves of the bottom heater power and magnetic field intensity during the process from the completion of the material fusion to the seeding process are as follows: Figure 1 , 2 shown.

[0024] (1) A 32-inch synthetic quartz crucible is used, and 360 kg of polysilicon material is used. The crucible is loaded with 180 kg of 45-100 mm block material and 60 kg of 5-45 mm crushed material. The block material accounts for 75%. The feeder is fed with 120 kg of material. The process of material preparation, material stacking, material processing, stabilization, seeding, shoulder release, shoulder rotation, equal diameter and finishing is carried out in sequence.

[0025] (2) In the chemical process, the power of the bottom heater of the chemical process is controlled to be 20 kW, the power of the main heater is controlled to be 100 kW, the argon flow rate is controlled to be 120 slpm, and the furnace pressure is controlled to be 2.7 kPa;

[0026] (3) During the processes of stabilization, seeding, shoulder release, shoulder rotation, equal diameter, and finishing, the bottom heater power is 20 kW and the magnetic field strength is 0.4 T.

[0027] Example 1

[0028] While keeping the experimental process of Comparative Example 1 unchanged, the specific control parameters during the pulling process of the single crystal silicon ingot are as follows, wherein the variation curves of the bottom heater power and the magnetic field intensity during the process from the completion of the fusion to the seeding are as follows: Figure 1 , 2 shown.

[0029] (1) Material preparation process: 360 kg of polysilicon material, of which 210 kg of 45-100 mm block material and 30 kg of 5-45 mm crushed material are loaded into the crucible, with block material accounting for 90%, and 120 kg of material is added to the feeder;

[0030] (2) In the stacking process, the polysilicon blocks below the liquid level line are in contact with the quartz crucible surface, while the polysilicon blocks above the liquid level line are not in contact with the quartz crucible;

[0031] (3) In the process of material processing, the power of the bottom heater in the material processing is controlled to be 20kW, the power of the main heater is 100kW, the argon flow rate is 120slpm, and the furnace pressure is maintained at 2.0kPa; after the material processing is completed, the power of the bottom heater is increased to 45kW, and the power of the main heater is reduced to 75kW, and maintained for 2h. During this period, the magnetic field is not turned on;

[0032] (4) Reduce the bottom heater power to 10 kW required for crystal pulling, adjust the main heater power to 95 kW, and continuously adjust the main heater power to find the main heater power suitable for crystal seeding. The magnetic field strength is 0.4 T.

[0033] (5) In the processes of seeding, shoulder release, shoulder rotation, equal diameter, and finishing, the bottom heater power is 10kW and the magnetic field strength is 0.4T.

[0034] Seven sets of experiments were repeated, and seven single crystals were pulled respectively with the parameters of Example 1 and Comparative Example 1. The single crystal silicon ingots were sliced, and porous slices (defective products) with one or more pores on the single crystal slices were excluded by visual inspection. The ratio of porous slices (defective products) was counted, and the results are shown in Table 1.

[0035] Table 1

[0036]

[0037] From the above data, it can be seen that the defective rate of comparative example 1 is 0.38%, and the defective rate of embodiment 1 is 0.08%. The ratio of the porous sheet is reduced by 0.3%, which reduces the generation of defective products.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot, the main steps comprising: Material preparation, material stacking process, material processing process, stabilization process, seeding process, shoulder release process, shoulder transfer process, equal diameter process and finishing process; characterized in that in the material processing process, the power of the bottom heater is 15-30kW, and the power of the main heater is 100-115kW; the stabilization process includes two steps: (1) After the material is quenched, increase the power of the bottom heater to 35-45kW and reduce the power of the main heater to 75-85kW and maintain for 1h-2h; (2) Reduce the bottom heater power to the power required for crystal pulling (0-10kW), adjust the main heater power to 90-105kW, and the magnetic field strength to 0.3-0.4T.

2. The magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot according to claim 1, characterized in that: During the material preparation stage, the crucible is loaded with 45-100mm blocks and 5-45mm crushed materials, and the proportion of block materials is adjusted to 80%-90%.

3. The magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot according to claim 2, characterized in that: During the stacking process, the polysilicon block is in contact with the quartz crucible surface.

4. The magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot according to claim 1, characterized in that: In the chemical process, the argon flow rate in the furnace is 100-130slpm, and the atmosphere pressure inside the furnace is 1.5-2.5kPa.

5. The magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot according to claim 1, characterized in that: In the seeding process, shoulder release process, shoulder rotation process, equal diameter process and finishing process, the bottom heater power is 0-10kW.

6. The magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot according to claim 1, characterized in that: In the seeding process, shoulder release process, shoulder rotation process, equal diameter process and finishing process, the magnetic field intensity is 0.3-0.4T.

7. The magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot according to claim 1, characterized in that: The quartz crucible selected in the material preparation stage is 32 inches.

8. The magnetron crystal pulling method for reducing the porosity of a single crystal silicon ingot according to claim 7, characterized in that: The diameter of the single crystal in the equal diameter process is 12 inches.

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