A method for pulling a six-inch zone melting silicon single crystal and a heat shield used therein

Abstract

The present invention relates to a method for drawing a six-inch zone melting silicon single crystal and a heat shield used therein. A heat shield is arranged 40 mm below a heating coil in a middle furnace chamber of a zone melting single crystal furnace, the upper diameter of the heat shield cover is 90 mm, the lower diameter is 215 mm, the height is 40 mm, and the pressure of cooling water in the condensation pipeline is 3.2 bar; when performing shoulder expansion, shoulder rotation, equal diameter, and finishing processes, the silicon single crystal moves downward along the lower axis and enters the heat shield area, and the heat reflected by the heat shield cover acts on the lower part of the single crystal, avoiding the single crystal from bursting or remelting due to excessive or insufficient temperature gradient, resulting in crystallization failure.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor silicon single crystal growth, in particular to a method for pulling a six-inch zone melting silicon single crystal and a heat shield used therein. Background Art

[0002] Zone-melting silicon single crystals have irreplaceable advantages over direct-grown silicon single crystals, such as high purity, high resistivity, and low oxygen and carbon content. They are gaining more and more attention in the semiconductor market and are gradually becoming an indispensable material for high-power devices such as power electronic devices, detectors, and high-voltage rectifiers.

[0003] Foreign melt zone manufacturers such as Wacker in Germany, Shin-Etsu in Japan, and Sumco have already grown large-sized dislocation-free melt zone silicon single crystals, imposed a technical blockade on my country, and have a monopoly position in the melt zone silicon single crystal market. In recent years, as the diameter of the single crystal silicon market has gradually moved towards larger sizes, the trend of larger melt zone silicon single crystals has become inevitable. However, with the larger diameter of melt zone silicon single crystals, the difficulty of dislocation-free growth of silicon single crystals has increased exponentially, and single crystal crystallization has become increasingly difficult. For the growth of melt zone silicon single crystals, as the diameter gradually increases, the cooling and heat dissipation of silicon single crystals is particularly important. When the cooling rate is too high, the temperature gradient inside and outside the single crystal is too large, causing the single crystal to burst and crystallization to fail; when the cooling rate is too low, the melt cannot solidify in time, resulting in a remelting phenomenon, which causes the single crystal to change crystals and crystallization to fail. When large-sized zone melting silicon single crystals grow, the heat dissipation is faster at the edges and slower at the center. The edges solidify before the center and the center solidifies later. The volume expands and internal stress is generated. When the expansion reaches a certain extent and the stress reaches the limit, the single crystal will explode or undergo crystal transformation, resulting in a large number of dislocations, which will lead to crystallization failure. Summary of the invention

[0004] In view of the above analysis of the problems existing in the prior art, the purpose of the present invention is to provide a method for pulling a six-inch melt-zone silicon single crystal and a heat shield used therefor, which effectively solves the internal and external cooling and heat dissipation problems of the six-inch melt-zone silicon single crystal during the growth process by controlling the size of the heat shield and adjusting the cooling water pressure in the heat shield, thereby achieving the pulling of a six-inch dislocation-free melt-zone silicon single crystal, improving the cooling and heat preservation technical problems of the single crystal during the growth process, and thereby improving the crystallization rate of the melt-zone silicon single crystal.

[0005] The technical solution of the present invention is: a method for pulling a six-inch zone melting silicon single crystal, including evacuation, preheating, material melting, neck pulling, shoulder expansion, shoulder rotation, equal diameter, finishing, furnace shutdown and furnace disassembly and assembly processes; a heat shield is arranged below the heating coil in the middle furnace chamber of the zone melting single crystal furnace, and when the shoulder expansion, shoulder rotation, equal diameter and finishing processes are performed, the silicon single crystal moves downward along the lower axis and enters the heat shield cover area, and the heat reflected by the heat shield cover acts on the lower part of the single crystal.

[0006] In the above technical solution, the cooling water pressure in the condensation pipeline of the heat screen is controlled at 3.2 bar.

[0007] In the above technical solution, the heat shield is arranged 40 mm below the heating coil in the middle furnace chamber of the zone melting single crystal furnace.

[0008] A heat shield for drawing six-inch zone melt silicon single crystals, comprising a heat shield cover and a condensation pipeline. The heat shield cover is a cone cover that is transparent from top to bottom, and the condensation pipeline is arranged along the upper edge of the entire heat shield cover.

[0009] In the above technical solution, the heat shield cover and the condensation pipeline are both made of copper.

[0010] In the above technical solution, the upper edge diameter of the heat shield cover is 190 mm, the lower edge diameter is 215 mm, and the height is 40 mm.

[0011] The beneficial effect of the present invention is that: in the process of pulling silicon single crystal, since the lower part of the single crystal is far away from the heating coil,

[0012] Heat dissipates quickly. The heat shield of the present invention is designed with an upper diameter smaller than a lower diameter, and cooling water flows through the upper part, which can ensure that there is a certain temperature gradient inside and outside the upper part of the single crystal, avoiding excessive melt, melting back and causing crystallization failure; for pulling six-inch silicon single crystals, the best parameters of the heat shield are found through repeated experiments (Table 1 is a comparison table of the influence of heat shield parameters on crystallization effect), that is, the upper diameter of the heat shield cover is 190mm, the lower diameter is 215mm, the height is 40mm, the pressure of cooling water in the condensation pipeline is 3.2bar, and the heat shield is arranged 40mm below the heating coil in the middle furnace chamber of the zone melting single crystal furnace. The position of the heat reflected by the heat shield acting on the lower part of the single crystal during the pulling process can be accurately controlled, so as to better control the temperature gradient inside and outside the single crystal and ensure the single crystal crystallization rate. Compared with the growth of zone melting silicon single crystals without heating screen, it solves the problem of single crystal cracking or crystal change caused by excessive or small temperature gradient inside and outside the single crystal, improves the single crystal formation rate, reduces the production cost of the enterprise, and more importantly, ensures the mass production of six-inch zone melting silicon single crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the position of the heat shield of the present invention during the growth process of the zone melting silicon single crystal;

[0014] Figure 2 It is a schematic structural diagram of the heat shield of the present invention. DETAILED DESCRIPTION

[0015] like Figure 2As shown, a heat shield for pulling six-inch zone melting silicon single crystals includes a heat shield cover 11 and a condensation pipeline 12. The heat shield cover 11 is a copper plate conical cover that is transparent from top to bottom. The condensation pipeline 12 uses a copper tube and is spirally arranged along the upper edge 111 of the entire heat shield cover 11. The copper tubes 5 at both ends of the condensation pipeline 12 are led out to form the outlet and inlet ends of the cooling water.

[0016] like Figure 1 , Figure 2 As shown, a method for pulling a six-inch zone melting silicon single crystal includes evacuation, preheating, chemical treatment, neck thinning, shoulder expansion, shoulder rotation, equal diameter, finishing, furnace shutdown and furnace disassembly and assembly processes; before evacuation, firstly, the copper tube of the condensation pipeline 12 is surrounded into a ring with a diameter of 190 mm, the upper edge 111 of the heat shield is fixed to the ring of the condensation pipeline 12 by welding, and two through holes are drilled 40 mm below the heating coil 4 of the middle furnace chamber 21 of the zone melting single crystal furnace 2 according to the diameter of the copper tube 5, the copper tube 5 passes through the two through holes and is welded and fixed to the furnace wall of the zone melting single crystal furnace 2, the inlet end is connected to the cooling water inlet, and the outlet end is connected to the cooling water outlet, the diameter of the upper edge 111 of the heat shield is 190 mm, the diameter of the lower edge 112 is 215 mm, the height is 40 mm, and the pressure of the cooling water in the condensation pipeline 12 is 3.2 bar;

[0017] When pulling six-inch silicon single crystals, a German PVA FZ 35 zone melting single crystal furnace is used with a furnace pressure of 4 bar and polycrystalline material produced by German Wacker with a diameter of 127 mm, a carbon content of ≤80 ppba, a boron content of ≤50 ppta, a phosphorus content of ≤130ppta, and an arsenic content of ≤8 ppta.

[0018] The vacuum degree is 0.006 mbar, and the polycrystalline material rod 3 is preheated and melted by using the heating coil 4, so that the seed crystal 7 contacts the droplet-shaped silicon. The rotation speed of the upper shaft of the polycrystalline material rod 3 is 4 rpm, and the rotation speed of the lower shaft is 20 rpm. The upper and lower shafts simultaneously pull the neck downward. During the shoulder expansion, the rotation speed of the upper shaft slowly decreases to 0.6 rpm, and the rotation speed of the lower shaft slowly decreases to 10 rpm.

[0019] like Figure 1 As shown, when the shoulder expansion, shoulder rotation, equal diameter and finishing processes are performed, the silicon single crystal 6 moves downward along the lower axis and enters the heat shield 1 area. The heat reflected by the heat shield cover 11 acts on the lower part of the single crystal to avoid the single crystal from bursting or melting back due to excessive or insufficient temperature gradient, resulting in crystallization failure, thereby pulling and growing a six-inch single crystal with a crystal direction of <100> of melt-zone silicon single crystal.

[0020] Table 1 Comparison of the effects of heat shield parameters on crystallization effects

[0021] Upper edge diameter (mm) 170 190 215 220 Bottom edge diameter (mm) 195 215 190 245 Height (mm) 30 40 40 50 Cooling water pressure (bar) 2.8 3.2 3.2 3.6 Crystallization Crystal Transformation Single Crystal burst burst

[0022] It can be seen from Table 1 that the upper diameter of the heat shield is 190mm, the lower diameter is 215mm, the height is 40mm, and the condensed water pressure is 3.2bar, which can prevent the six-inch silicon single crystal from being deformed or exploded when being pulled in the zone melting single crystal furnace, and obtain a complete six-inch zone melting silicon single crystal.

Claims

1. A method for pulling a six-inch melt zone silicon single crystal, comprising the processes of evacuation, preheating, material processing, neck thinning, shoulder expansion, shoulder rotation, equal diameter, finishing, furnace shutdown and furnace disassembly; characterized in that: A heat shield (1) is arranged 40 mm below the heating coil (4) in the middle furnace chamber (21) of the zone melting single crystal furnace (2); the heat shield (1) comprises a heat shield cover (11) and a condensation pipeline (12); the heat shield cover (11) is a conical cover that is transparent from top to bottom, the upper edge (111) of the heat shield cover (11) has a diameter of 190 mm, the lower edge (112) has a diameter of 215 mm, and the height is 40 mm; the condensation pipeline (12) is arranged along the upper edge (111) of the entire heat shield cover (11); when the shoulder expansion, shoulder rotation, equal diameter, and finishing processes are performed, the silicon single crystal (6) moves downward along the lower axis and enters the heat shield (1) area, and the heat reflected by the heat shield cover (11) acts on the lower part of the silicon single crystal (6); the cooling water pressure in the condensation pipeline (12) of the heat shield (1) is controlled at 3.2 bar.

2. A method for pulling a six-inch melt-zone silicon single crystal according to claim 1, characterized in that: The heat shield (11) and the condensation pipeline (12) are both made of copper.

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