WO2007093082A1

WO2007093082A1 - A process of producing silicon wafer employing float method and apparatus thereof

Info

Publication number: WO2007093082A1
Application number: PCT/CN2006/000229
Authority: WO
Inventors: Yonggang Jin
Original assignee: Yonggang Jin
Priority date: 2006-02-16
Filing date: 2006-02-16
Publication date: 2007-08-23
Also published as: CN101133194B; CN101133194A

Abstract

The invention provides a process of float method producing silicon wafers, which employs the successive process of melting, crystallizing for molding, burnishing and cutting. The process comprises: adding silicon raw material into a crucible (2) through a feeding unit (1), the temperature in the crucible being set above silicon melting point-1421, the solid silicon raw material being melt to liquid silicon above the temperature of 1421 ; argon gas or the other inert gases being discharged continuously via a feeding inlet over the liquid silicon ; a crystallization region slot (4) communicating with a crucible drain mouth (3),the slot filled with liquid tin metal or other alloys as carrier whose melting point are lower than that of silicon; the temperature near the discharge port being higher than the silicon melting point-1421, the temperature of the other end being between 1421 and 400 ; when liquid silicon moving to the end of float method molding region, liquid silicon would solidify to solid state; a buffer (5)being set at top of crystallization region adjacent the crucible drain mouth (3) to regulate the silicon wafer thickness ; after the molding crystallized silicon wafer being subjected to cooling part (6), burnishing and polishing part (7), cutting the wafer at the wafer cutting region (8) as required. It is suitable for float method producing solar cell and semiconductor silicon wafer.

Description

Fabrication process and equipment for float silicon wafer

Technical field

The invention belongs to crystal growth, and in particular relates to a manufacturing process and equipment for a silicon wafer.

Background technique

Silicon is a non-metal, with an atomic number of 14, and an atomic weight of 28.0855 g.mol- ¹ . Silicon materials are widely used in industries such as semiconductors and solar cells. Production of semiconductor grade silicon wafers or CZochralski (CZ method) or zone melting methods for the fabrication of solar cell wafers. Single crystal silicon is often used for semiconductor silicon materials, and single crystal silicon or polycrystalline silicon is used for solar cells.

In the known technology, there are many methods for preparing polycrystalline silicon, mainly a reduction method using silicon tetrachloride as a raw material, a chlorine reduction and thermal decomposition method using silicon trichloride as a raw material, and a thermal decomposition method using silane. The single crystal silicon fabrication process mainly uses a Czochralski (CZochralski, CZ) method and a floating zone melting method (FZ method). The crystal pulling method, for example, US Pat. No. 3,679,370 (CRYSTAL GROWER WITH EXPANDABLE CHAMBER), CN1150355 (Crystal continuous pulling method and apparatus), is basically used to put a raw material polycrystalline silicon in a quartz crucible in a single crystal furnace. After heating and melting, a rod-shaped seed crystal (called seed crystal) having a diameter of only 10 mm is immersed in the melt. At a suitable temperature, the silicon atoms in the melt form regular crystals at the solid-liquid interface along the arrangement of the silicon atoms of the seed crystal, becoming a single crystal. By slightly increasing the rotation of the seed crystal, the silicon atoms in the melt continue to crystallize on the previously formed single crystal and continue its regular atomic arrangement. If the entire crystallization environment is stable, crystals can be formed in a recurring manner, and finally a cylindrical silicon single crystal crystal in which the atoms are arranged neatly, that is, a silicon single crystal ingot is formed. When the crystallization is accelerated, the crystal diameter becomes thicker, and the increase in the speed can make the diameter thinner, and the increase in temperature can suppress the crystallization rate. On the other hand, if the crystal becomes slower and the diameter becomes thinner, it is controlled by lowering the pulling speed and lowering the temperature. After seeding and crystal pulling, a narrow neck with a diameter of 3 to 5 mm is taken out to eliminate crystal dislocations. This process is called seeding. The single crystal diameter is then amplified to the process requirements and entered into the equal diameter growth stage until most of the silicon melt crystallizes into a single crystal ingot, and then a small amount of residual material remains. The floating zone melting method (FZ method), for example, similar to the CN1139678 patent (method of single crystal growth), is to vertically fix the pre-treated polycrystalline silicon rod and the seed crystal together in the zone melting furnace to sense the polycrystalline silicon rod by high frequency. The heating is directed from the beginning to the end to form a crystal of the molten zone, and the silicon rod is repeatedly purified several times. The technical solution disclosed in the patent of CN1095505 (the straight-pull zone melting method for producing single crystal silicon) combines the above two methods.

Confirmation The above technical solutions are all discontinuous production, low efficiency, large equipment investment and long time. After the single crystal rod is made, it needs to be sliced, polished and polished to increase the process and increase the loss.

Summary of the invention

SUMMARY OF THE INVENTION The present invention is directed to an apparatus and process for producing silicon wafers in a continuous, large-scale and low-cost manner in order to increase wafer productivity and reduce production costs. The technical solution adopted by the present invention is as follows:

A manufacturing process of a float silicon wafer, which is obtained by a continuous process of melting, crystal forming, grinding and cutting:

A: The silicon raw material is melted, and the silicon raw material is added to the crucible by a feeding device. The temperature in the crucible is set to be higher than the melting point of the silicon by 1421 ° C, and the solid silicon raw material is melted into liquid silicon at a temperature above 1421 ° C. Argon gas or other inert gas is continuously removed from the top of the silicon through the feeding port;

B: Crystallization molding, the crystallization zone trough is connected with the crucible liquid discharge port, the tank is filled with liquid tin metal or other alloy whose melting point is lower than the melting point of silicon as the carrier, and the temperature near the discharge port is higher than the melting point of silicon 1421 ° C The temperature at the other end is between 1421 ° C and 400 ° C. When the liquid silicon moves to the end of the float forming zone, the liquid silicon solidifies into a solid state, and the upper layer of the corresponding silicon surface in the crystallization zone is relatively close to the drain of the crucible. The plate is adjusted to control the thickness of the wafer, and the temperature is set in a molten state in which the molten metal having a melting point lower than the melting point of the silicon is filled in the bottom of the trough, and the upper layer of the corresponding silicon surface is relatively close to the baffle discharge opening of the crucible discharge port. Control the thickness of the wafer;

C: After the formed crystalline silicon wafer is cooled, polished and polished by the cooling section, the wafer is cut in the dicing wafer area as needed.

The metal having a melting point lower than the melting point of silicon at the bottom of the crystallization zone is tin metal.

The device adopting the manufacturing process of the float silicon wafer, the crucible is rectangular, the feeding port is provided with a gas nozzle in the direction of the pot, and the argon gas or other inert gas is continuously discharged, and the crystallization zone trough is connected with the dip pan discharge port, crystallizing The upper layer of the corresponding silicon surface is provided with a baffle relatively close to the drain port of the crucible. The liquid discharge port of the crucible is set to U shape, and the liquid discharge port is lower than the liquid level of the carrier such as liquid tin in the float crystal region.

The invention adopts a continuous process for preparing polycrystals or single crystals, and in particular, the crystal forming process adopts tin metal which has a large difference from the melting point of silicon, so that the invention achieves an unexpected effect. Tin has a melting point of 292 V and a boiling point of 2270 ° C. The use of tin not only allows the silicon to float on the surface layer of the tin liquid, but also allows harmful heavy metal impurities of the silicon single crystal to diffuse to the surface of the silicon single crystal, and finally to the molten tin. in.

DRAWINGS The drawing is a schematic diagram of the equipment for the production process of a float silicon wafer.

In the figure, 1-feeding device, 2-tank, 3-tank drain, 4-crystallization zone chute, 5-baffle, 6-cooling section, 7-grinding section, 8-cut wafer area.

detailed description

The following are specific embodiments of the invention. The examples are intended to illustrate the invention, and are not intended to limit the invention.

The silicon raw material is added to the crucible 2 through a feeding device, and the temperature in the crucible is set to be higher than the melting point of the silicon by 1421 ° C, and the solid silicon raw material is melted into liquid silicon at 1421 ° C or higher. In order to prevent the reaction of silicon and air with oxygen and nitrogen, the design of the crucible is different from that of ordinary crucibles. Gas nozzles can be installed near the feeding device 1 to continuously remove argon or other inert gases to avoid air contact. The shape of the crucible is rectangular, one end is the feeding device 1, the other end is the crucible liquid discharge port 3, and the crucible liquid discharge port 3 is designed at the bottom of the crucible. Such a crucible design allows continuous feeding and continuous smelting to produce liquid silicon. Unlike the existing Czochralski single crystal method and the casting method, the two can only be intermittently produced, with low productivity and high cost.

The liquid discharge port 3 of the crucible is set to a U shape, and the discharge port is lower than the liquid surface of the carrier such as liquid tin in the float crystal region. Since the density of the liquid silicon is smaller than the density of the liquid carrier, the liquid silicon will automatically float, which can reduce the liquid. Splash caused by discharge.

Connected to the drain port 3 of the crucible is a float crystallized zone. The crystal zone is filled with liquid tin metal or other germanium as a carrier. Since the buoyancy of the liquid silicon is smaller than the carrier, the liquid silicon floats on it. The carrier temperature near the discharge port is higher than the melting point of silicon. Liquid silicon will continue to move forward along the crystallization zone along with gravity. When the high temperature resistant baffle 5 passes, the liquid silicon flowing there will be formed to a certain thickness due to the gap between the baffle 5 and the carrier. 5 High-precision stepper motor and computer control can control the gap between the baffle and the carrier to the micron level, and control the thickness of the solidified wafer to 1000 microns. At 10 cm at the other end of the baffle, the carrier temperature drops to 1300 - 1400 °C. At this time, the liquid silicon crystallizes into solid silicon to form a solid silicon plate of a certain thickness. If a single crystal silicon wafer is to be produced, it is necessary to use a flat single crystal seed crystal (seed crystal) to be immersed in the molten metal. At a suitable temperature, the silicon atoms in the molten metal are aligned along the silicon atom arrangement of the seed crystal. A regular crystal is formed on the liquid interface to form a single crystal. The seed crystal is slightly rotated and stretched forward, and the silicon atoms in the melt continue to crystallize on the previously formed single crystal and continue its regular atomic arrangement. If whole When the crystal environment is stable, crystals can be formed repeatedly to form a single crystal silicon wafer. This method is basically similar to the CZ straight pull single crystal method, which requires high purity of raw materials, and usually has less than ppb of impurities. However, since this invention is continuous crystallization, it is only necessary to use the seed crystal once. If a polycrystalline silicon wafer is to be produced, the liquid silicon can be solidified without the need for seed crystals. By controlling the proper temperature gradient, more refined grains are obtained. This method is superior to the casting method and avoids the formation of dendrites around the mold. In this area, an inert gas is used to insulate the silicon material from the air to avoid the formation of undesirable impurities such as silicon oxide and silicon nitride.

The condensed silicon plate is mechanically transferred to the cooling section 6. In this area, the high temperature solidified silicon plate continues to cool until room temperature. In this area, the cooling method is conductive hot plate cooling, or it can be designed as a convection type for airflow cooling. The cooling method affects the shape and size of the grains in the silicon plate.

After cooling, the silicon plate continues to advance to the sanding and polishing section 7, where the entire silicon plate is polished and polished, and the process here is continuous and uninterrupted. The abrasive sheet is mounted on the top and reciprocally moved in the horizontal direction. Different grades of abrasive sheets can be arranged along the direction of advancement of the silicon plate, from rough grinding to precision polishing. Whether it is CZ Czochralski single crystal method or zone melting method, it is first made into ingot, then cut into silicon wafer, and then polished and polished. Since silicon is a brittle material, the cutting method is different from that of metal, and it is technically in the form of sanding. The cutter is used to squeeze the material section. In addition, microcracks are formed on the fracture surface, and it is necessary to remove a certain thickness of the material by grinding to completely eliminate the microcrack. Nearly half of the material is wasted during the production process. The invention is pre-formed to a certain thickness, eliminating the need for cutting, which can greatly reduce the cost of the material, which is about 50% or more.

The polished wafer is cut into silicon wafers of different sizes by a diamond cutter or laser cutter in the cutting zone (8). The wafers are turned away from the production line, polished, and placed in a package.

Claims

Rights request

1. A process for fabricating a float silicon wafer, characterized by extracting, melting, crystal forming, grinding and cutting continuous processes -

A: The silicon raw material is melted, and the silicon raw material is added to the crucible (2) through the feeding device (1). The temperature in the crucible is set to be higher than the melting point of the silicon by 1421 ° C, and the solid silicon raw material is above 1421 ° C. Melting into liquid silicon, and continuously removing argon or other inert gas through the feeding port above the liquid silicon;

B: Crystallization molding, the crystallization zone trough (4) is connected with the crucible liquid discharge port (3), and the tank is filled with liquid tin metal or other alloy having a melting point lower than the melting point of silicon as a carrier, and the temperature near the discharge port is higher than The melting point of silicon is 1421 ° C, and the temperature at the other end is between 1421 ° C and 400 ° C. When liquid silicon moves to the end of the float forming zone (4), the liquid silicon solidifies into a solid state, and the upper layer of the corresponding silicon surface of the crystal region is relatively The baffle (5) provided near the dipper drain port (3) adjusts the thickness of the control wafer;

C: After the shaped crystalline silicon wafer is cooled and polished by the cooling section (6) (7), the wafer is cut in the dicing wafer area (8) as needed.

A process for fabricating a float silicon wafer according to claim 1, wherein the metal having a melting point lower than the melting point of the silicon at the bottom of the crystallization zone chute (4) is tin metal.

3. A device for manufacturing a float silicon wafer, characterized in that: the crucible (2) is rectangular, and the feeding port (1) is provided with a gas nozzle in the direction of the pot, continuously discharging argon gas or other inert gas, and crystallizing. The zone trough (4) is integrally connected with the crucible liquid discharge port (3), and the upper surface of the corresponding silicon surface of the crystallization zone is relatively close to the crucible liquid discharge port (3), and the baffle plate (5) is disposed.

4. Apparatus for fabricating a float silicon wafer according to claim 3, wherein the rear end of the crystallization zone chute (4) is coupled to the cooling section (6), the polishing section (7) and the dicing wafer area (8). ).

5. The apparatus for fabricating a float silicon wafer according to claim 3, wherein the crucible liquid discharge port (3) is set to a U shape, and the crucible liquid discharge port (3) is lower than the float crystallizing area (4) ) The liquid level of the carrier such as liquid tin.