CN201058893Y - Device for growing gallium-doped silicon single crystal by Czochralski method - Google Patents

Abstract

The utility model relates to a device for growing gallium-doped silicon single crystal by Czochralski method. It includes single crystal furnace, heater, guide cylinder, quartz crucible, graphite crucible, insulation cover, insulation cylinder, tray, solidified thermal insulation carbon felt, solidified furnace bottom guard plate and exhaust hole. A graphite insulation cylinder is installed on the periphery of the heater, and a solidified thermal insulation carbon felt is installed outside the insulation cylinder; the upper edge of the graphite insulation cylinder is also positioned by the lower opening of the graphite upper tray, and the upper edge of the guide tube is positioned by the upper opening of the graphite upper tray. The insulation cover is positioned by the upper outer slit of the graphite upper tray. The graphite crucible rod supports the graphite crucible, the quartz crucible is seated in the graphite crucible, and the upper edge of the quartz crucible is higher than the upper edge of the graphite crucible. The utility model fills the thermal field system with argon gas, has a simple and reasonable structure, can improve the quality of silicon single crystals, and can obtain gallium-doped silicon single crystals with a large diameter and low dislocation density whose longitudinal resistivity fully meets the requirements. It meets the requirements of high-efficiency solar cell substrate materials and has wide application value.

Description

Device for growing gallium-doped silicon single crystal by Czochralski method

technical field

The utility model relates to the preparation technology of gallium-doped Czochralski silicon single crystal, in particular to a method and device for growing gallium-doped silicon single crystal by Czochralski method. In the crystal growth process, the vertical resistivity distribution range of the crystal ingot is compressed so that it is completely distributed within the resistivity range of the current crystalline silicon solar cell preparation.

technical background

There are a lot of literature reports on the resistivity distribution process and characteristics research of Ga-doped silicon single crystal at home and abroad. Pei Suhua et al. reported (Ga diffusion model and distribution law in SiO ₂ /Si system, Rare Metal Materials and Engineering, 2005, 6, 920-923.) Using secondary ion mass spectrometry and sheet resistance measurement methods, Ga The diffusion characteristics, silicon surface and body distribution in SiO ₂ /Si system were studied and conclusions were drawn. Japan also has a production method for gallium-doped silicon single crystals. In order to improve the resistivity distribution of gallium-doped silicon single crystals in the pulling axis direction and produce silicon single crystals with uniform resistivity, a production method based on the Czochralski method is proposed. A method for silicon single crystals, which includes lowering the atmospheric pressure when pulling silicon single crystals (ABE TAKAO. METHOD FOR PRODUCTING Ga-DOPED SILICON SINGLE CRYSTAL.: JP 2002154896, 2002-05-28).

The biggest difficulty in growing gallium-doped silicon single crystal by the Czochralski method (CZ method) is that the segregation coefficient of gallium in silicon is very small k ₀ =0.08 (while the segregation coefficient of boron in silicon is 0.8), so the ordinary direct The resistivity of the head and tail of the gallium-doped silicon single crystal ingot grown by lafa is very different, and the ratio of the head resistivity to the tail resistivity is as high as 50 to 60 times, and only a small part can be used in the production of solar cells. Although the U.S. Patent (US 6,815,605) has reported the production method of the relevant gallium-doped silicon single crystal, it is combined with a kind of original crystal and molten silicon and drawn into a kind of silicon single crystal ingot by circulation, and its resistivity The range is from 5Ω·cm to 0.1Ω·cm (50 times). The disadvantage is that the original crystal needs to be prepared in advance and drawn cyclically, the process is complex and costly, and the longitudinal resistivity range of the drawn ingot is large, which cannot be industrialized.

Contents of the invention

The purpose of the utility model is to provide a device for growing gallium-doped silicon single crystal by the Czochralski method, which can overcome the shortcomings of the prior art. It is an improvement to the existing Czochralski growth single crystal device. The utility model provides a thermal field device specially used for growing gallium-doped silicon single crystal, the combination of crystal turning crucible and pulling speed, multi-layer highly heat-insulated funnel-shaped heat shield, forming an optimized rapid crystallization latent heat carrying argon flow field . Fill the thermal field system with argon to protect the growth of gallium-doped silicon single crystals and improve the quality of silicon single crystals. The structure is simple and reasonable, and the longitudinal resistivity of gallium-doped silicon single crystals fully meets the requirements of large diameter and low dislocation density. crystal, which can meet the requirements of high-efficiency solar cell substrate materials, and has a wide range of application values.

A device for growing gallium-doped silicon single crystal by the Czochralski method provided by the utility model includes a single crystal furnace, a heater, a guide tube, a quartz crucible, a graphite crucible, a heat preservation cover, a heat preservation cylinder, a tray, a curing heat preservation carbon felt, a curing Bottom guard and vent.

The utility model adopts a general-purpose single-crystal furnace (the inner diameter of the furnace is φ=620-700mm) to install a heater in the furnace. Graphite insulation cylinder is installed on the periphery of the heater, and solidified thermal insulation carbon felt is installed outside the insulation cylinder; the graphite insulation cylinder is located in the mouth of the graphite lower tray on the bottom protection plate of the curing furnace, and the upper edge of the graphite insulation cylinder is also covered by the bottom of the graphite upper tray. The mouth is positioned, the upper edge of the guide tube is positioned by the upper mouth of the graphite upper tray, and the upper insulation cover is positioned by the upper outer mouth of the graphite upper tray. The graphite crucible rod supports the graphite crucible, the quartz crucible is seated in the graphite crucible, and the upper edge of the quartz crucible is higher than the upper edge of the graphite crucible.

A graphite insulation cylinder is installed at 15 mm outside the heater, and the upper edge of the quartz crucible is 20-25 mm higher than the upper edge of the graphite crucible.

The heater is divided into 32 equal petals, and the electrode position is not slitted, which is actually 30 petals. The seam width is 10mm, and the seam height is 285mm. The outer diameter of the heater is 495mm, the inner diameter is 458mm, and the electrode opening spacing is 320mm.

The effective height of the heater is in the range of 330-375mm, and the total height of the heater is 480mm.

Using the method and device of the present utility model, the resistivity of the head and the tail can be obtained by using gallium with a purity of 69 and solar-grade bulk polysilicon (B≤0.1ppba, D≤0.9ppba, C≤0.5ppma) High-quality monocrystalline silicon with a ratio of 5 to 6 times. That is, 0.5Ω·cm～3Ω·cm.

Since the segregation coefficient of gallium is very small k ₀ =0.08, and it is volatile, the resistivity is extremely difficult to control. The use of the special guide tube of the utility model not only greatly blocks the radiant heat from the heater to the ingot, but also increases the longitudinal temperature gradient of the crystal, and the direction of the argon gas diversion blows directly to the front of the crystal, so that the crystallization latent heat can be dissipated rapidly. Improve crystallization. The lower edge of the guide tube is placed 5-25cm away from the liquid surface, which overcomes the turbulence phenomenon of the argon flow field in the furnace. In addition, the ratio of crystal rotation, crucible rotation and pulling speed of the utility model also ensures that gallium in silicon enters the crystal under abnormal segregation.

The physical parameters of the gallium-doped silicon single crystal grown by the utility model are conductivity type P type, crystal orientation <100>, Φ154mm, resistivity ρ is 0.5Ω·cm～3Ω·cm, interstitial oxygen content is [O _i ]≤ 17.5ppma, replacement carbon content [Cs]≤0.5ppma, non-equilibrium minority carrier lifetime τ≥150μs, dislocation density EPD≤500/cm ² .

The gallium-doped P-type <100> crystal-oriented silicon single crystal Czochralski growth device provided by the utility model makes the resistivity of the whole gallium-doped silicon single crystal completely distributed in the resistivity range required for battery production from the head to the tail. within. Produced with a specific thermal device and a specific process, the resistivity of a Φ150mm, P-type <100> oriented silicon single crystal grown under a Φ16″ thermal field device with a feeding capacity of 42-45 kg can be controlled at 0.5Ω·cm～3Ω Within the cm range, it creates an industrialized basis for improving the efficiency of high-efficiency solar cells and suppressing efficiency decay.

The crystal growth method of the utility model is practical, high in efficiency and low in cost, and can obtain a gallium-doped silicon single crystal with a large diameter and low dislocation density whose longitudinal resistivity range fully meets the requirements, and can meet the requirements of high-efficiency solar cell substrate materials.

The device for growing gallium-doped silicon single crystal by the Czochralski method provided by the utility model is an obvious improvement on the existing single crystal growth device by the Czochralski method. Using the heat device of the present invention, the combination of the rotating and pulling speed of the crystal turning crucible, the guide cylinder fully guides the directional flow of argon, and the multi-layer highly insulated funnel-shaped heat shield forms an optimized rapid crystallization latent heat carrying argon flow field. The thermal system is always filled with the freshest low-temperature argon, and the application of solidified thermal insulation materials as thermal insulation materials, etc. The use of the heater is to reduce the thermal convection of the high-temperature melt, which is beneficial to the stability of the molten silicon at the crystallization front. Guarantee the normal growth of gallium-doped silicon single crystal. Improve the quality of silicon single crystal, the structure is simple and reasonable, and has a wide range of application value.

Description of drawings

Fig. 1 is a schematic cross-sectional view of a thermal field device for growing gallium-doped silicon single crystal by the Czochralski method of the present invention.

Fig. 2 is a schematic diagram of the components of the guide cylinder of the present invention.

Fig. 3 is a schematic diagram of installation of the guide tube components of the utility model.

Fig. 4 is a schematic diagram of the heater of the present invention.

Fig. 5 is a schematic diagram of the graphite crucible of the present invention.

Figure 6 is a schematic diagram of the installation of the thermal insulation material of the present invention.

Fig. 7 is a schematic diagram of the furnace bottom protection plate of the present invention.

Fig. 8 is a schematic diagram of the installation of the heater of the present invention.

Detailed ways

The utility model is described in detail as follows with reference to accompanying drawing:

As shown in the figure, 1 is the crystal rotation direction, 2 is the seed crystal, 3 is the monocrystalline silicon rod, 4 is the furnace body, 5 is the quartz crucible, 6 is the graphite crucible (a is polysilicon and b is gallium), and 7 is the conduction Tube, 8 is molten silicon, 9 is heater, 10 is graphite crucible rod, 11 is air vent, 12 is carbon felt for upper insulation cover, 13 is upper insulation cover, 14 is graphite upper tray, 15 is solidified insulation carbon felt 16 is a graphite insulation tube, 17 is a graphite lower tray, 18 is a curing furnace bottom guard plate, and 19 is a crucible turning direction.

The utility model is to install a composite thermal device with a heater 9 as the core in a single crystal furnace with an inner diameter of φ=620mm, install a graphite heat preservation cylinder 16 at 15mm outside the heater, and install a solidified heat preservation carbon felt 15 outside the graphite heat preservation cylinder 16 . Graphite insulation tube 16 is located in the slit of graphite lower tray 17 on the solidification furnace bottom guard plate 18, and the upper edge of graphite insulation tube 16 is also positioned by the lower slit of graphite upper tray 14, and the upper edge of guide tube 7 is positioned on the graphite. The upper sub-mouth location of tray 14, last insulation cover 13 is also positioned by the upper outer sub-mouth location of tray 14 on graphite. The graphite crucible rod 10 supports the graphite crucible 6, the quartz crucible 5 is seated in the graphite crucible 6, and the upper edge of the quartz crucible 5 needs to be higher than the upper edge of the graphite crucible 6 by 20mm (20-25mm is acceptable).

The heater is divided into 32 equal petals, and the electrode position is not slitted, which is actually 30 petals. The seam width is 10mm, and the seam height is 285mm. The outer diameter of the heater is 495mm, the inner diameter is 458mm, and the electrode opening spacing is 320mm.

The effective height of the heater is in the range of 350mm, and the total height of the heater is 480mm.

The utility model uses solar-grade bulk polysilicon (B≤0.1ppba, D≤0.9ppba, C≤0.5ppma), and gallium (purity 99.9999%) is produced by China Nonferrous Metals Research Institute.

Application example: The method for growing a gallium-doped silicon single crystal using the Czochralski method of the present invention includes steps such as charging, heating, and crystal pulling:

Step 1: Clean the single crystal furnace according to the conventional method, vacuumize it, and when the vacuum leakage rate reaches 1Pa/3min, and confirm that there is no fault, start the furnace, charge the material, and put gallium into the center of the polysilicon raw material in the quartz crucible . Argon is filled to a furnace pressure of 2000Pa.

Step 2: Low crucible level chemical material, the crucible turns to zero, after confirming that the material is slumped, adjust the crucible rotation direction to 1 revolution/min, the chemical material is completed, and the melting temperature of silicon is 1500°C.

Step 3: After the chemical material is finished, the heating power electric control circuit is automatically switched on, and the temperature is lowered until the liquid surface is supercooled. After the temperature of the molten silicon is stable for 30 minutes, the seed crystal is lowered to a place 90mm away from the liquid surface of the molten silicon and preheated for 30 minutes. Minutes, start to drop the thin diameter, at this time the crystal switch is adjusted to 7, pull after immersion and melting for 30 minutes, the pulling speed is 5.5mm/min, the length of the thin diameter is not less than 160mm, and the diameter is ≤3mm.

Step 4: Turn the shoulders at a pulling speed of 2.4mm/min, and adjust the pulling speed to 1.2mm/min after turning the shoulders 1/2.

Step 5: Isometric growth, the furnace pressure is adjusted to 2500Pa, the casting speed is 0.9mm/min, the argon flow rate is adjusted to 25L/h, the crystal rotation is adjusted within 6-30 rpm, and the position of the crucible is kept under the guide tube The distance between the edge and the liquid surface is 15mm, the crucible rotates at 10 rpm, and is adjusted, finished and cooled according to the conventional process. Experimental measurement results: Φ150mm grown under a Φ16″ thermal field device with a feeding capacity of 42 kg, P-type <100> crystal orientation, resistivity of silicon single crystal rod, head ρ≤3Ω·cm, tail ρ≥0.5Ω·cm The interstitial oxygen content is [O _i ]≤17.5ppma, the replacement carbon content is [Cs]≤0.5ppma, the non-equilibrium minority carrier lifetime τ≥150μs, and the dislocation density EPD≤500/cm ² .

Claims (8)

1. the device of a Grown by CZ Method gallium-mixing silicon monocrystal is characterized in that this device comprises protection plate and venting hole at the bottom of single crystal growing furnace, well heater, guide shell, quartz crucible, plumbago crucible, insulation cover, heat-preservation cylinder, pallet, curing heat preservation carbon felt, the curing oven;

Well heater is installed in the described single crystal growing furnace burner hearth, and the graphite heat-preservation cylinder is installed at the peripheral place of well heater, and the heat-preservation cylinder outside is installed and solidified heat preservation carbon felt; The graphite heat-preservation cylinder is located at the bottom of the curing oven under the graphite on the protection plate in the rim of the mouth of pallet, graphite heat-preservation cylinder upper edge is also by the location, following rim of the mouth of graphite upper tray, the guide shell upper edge is by location, rim of the mouth on the graphite upper tray, and last insulation cover is by the location, top outer rim of the mouth of graphite upper tray; Graphite crucible bar supports plumbago crucible, and quartz crucible is located in the plumbago crucible, and the quartz crucible upper edge exceeds the plumbago crucible upper edge.

2. according to the device of the described Grown by CZ Method gallium-mixing silicon monocrystal of claim 1, it is characterized in that the peripheral 15mm of described well heater place's installation graphite heat-preservation cylinder.

3. according to the device of the described Grown by CZ Method gallium-mixing silicon monocrystal of claim 1, it is characterized in that described quartz crucible upper edge exceeds plumbago crucible upper edge 20～25mm.

4. according to the device of the described Grown by CZ Method gallium-mixing silicon monocrystal of claim 1, it is characterized in that described well heater separates the lobe seam by 32 grades, electrode position does not crack, and actual is 30 lobes.

5. according to the device of the described Grown by CZ Method gallium-mixing silicon monocrystal of claim 4, it is characterized in that the described lobe of opening stitches wide 10mm, height 285mm cracks.

6. according to the device of the described Grown by CZ Method gallium-mixing silicon monocrystal of claim 4, it is characterized in that described well heater external diameter 495mm, internal diameter 458mm, electrode spacing 320mm.

7. according to the device of the described Grown by CZ Method gallium-mixing silicon monocrystal of claim 1, it is characterized in that described well heater virtual height in 330～375mm scope, the well heater total height is 480mm.

8. according to the device of the described Grown by CZ Method gallium-mixing silicon monocrystal of claim 1, it is characterized in that described single crystal growing furnace burner hearth internal diameter is φ=620～700mm.

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