Crystal silicon preparation method

Monocrystalline silicon material is a crystalline silicon material for very traditional Chinese medicine shops. According to the different growth patterns, it can be divided into single crystal silicon and single crystal silicon. Single-crystal silicon is mainly used in high-power devices, accounting for only a small part of the monocrystalline silicon market, accounting for about 10% in the international market; and Czochralski silicon is mainly used in microelectronic integrated circuits and solar cells On the other hand, it is the subject of monocrystalline silicon. Compared with single-crystal silicon that is zone melted, Czochralski silicon has a relatively low manufacturing cost, high mechanical strength, and easy preparation of large-diameter single crystals. Therefore, in the field of solar cells, Czochralski silicon is mainly used instead of zoned monocrystalline silicon.

The manufacturing process of Czochralski silicon generally includes:

1, polysilicon charging and melting, 2, seed crystals, 3, necking, 4, shoulder, 5, equal diameter growth, 6, ending, etc. 1 polysilicon charging and melting first of all high-grade polysilicon crushed to appropriate The size, and the outer surface of the mixture of nitric acid and hydrofluoric acid wash to remove possible metal impurities, and then placed in a high-purity quartz crucible. After the charging is completed, the crucible is placed in a single crystal furnace, and then the single crystal furnace is pumped into a certain vacuum, and a protective gas with a certain flow and pressure is injected. Finally, the furnace body is heated and heated, and the heating temperature exceeds the melting point of the silicon material. To melt it.

2. After the seed polycrystalline silicon is melted and kept warm for a certain period of time, the temperature and flow of the molten silicon are stabilized, and crystal growth proceeds. When the crystal grows, the single crystal seed is first fixed on the rotating seed crystal axis, and then the seed crystal is slowly lowered and suspended for several moments from the liquid surface, so that the seed crystal temperature is as close as possible to the temperature of the molten silicon, so as to reduce possible Thermal shock; the seed crystals are then gently immersed in fused silica, so that the head is first slightly dissolved, and then forms a solid-liquid interface with the molten silicon; subsequently, the seed crystal gradually rises, and the temperature of the silicon connected to the seed crystal and leaving the solid-liquid interface decreases Single crystal silicon is formed and this stage becomes a seed crystal.

3. After the necking seed crystals are completed, the seed crystals will rise rapidly and the crystal growth speed will increase. The diameter of the newly crystallized single crystal silicon will be smaller than that of the seed crystals, which can reach about 3 mm, and the length is about the crystal diameter at this time. 6-10 times, became a "necked" stage.

4. After the shoulder is “necked”, the growth rate of crystalline silicon is greatly slowed. At this time, the diameter of crystalline silicon increases rapidly, from the diameter of the seed crystal to the required diameter, forming a nearly 108°. The angle, this stage becomes "put shoulder."

5. Equal-diameter growth When the predetermined crystal diameter reached by the shoulder is reached, the crystal grows faster and maintains a nearly constant velocity, allowing the crystal to maintain a constant diameter growth. This stage becomes a "equal path."

6. At the end of the crystal growth, the growth rate of crystalline silicon is accelerated again, while the temperature of the silicon melt is increased, so that the diameter of the crystalline silicon is continuously reduced to form a conical shape, eventually the crystalline silicon leaves the liquid surface, and the single crystal silicon grows. Completed, the final stage is called "closing."