1. Loading
Place the coated quartz crucible on the heat exchange table, add silicon raw material, then install heating equipment, insulation equipment and furnace cover, evacuate the furnace to reduce the pressure in the furnace to 0.05-0.1mbar and maintain vacuum. Introduce argon as a protective gas to keep the pressure in the furnace basically at around 400-600mbar.
2. Heating
Use a graphite heater to heat the furnace body, first evaporate the moisture adsorbed on the surface of graphite parts, insulation layer, silicon raw materials, etc., and then slowly heat up to make the temperature of the quartz crucible reach about 1200-1300℃. This process takes 4-5h.
3. Melting
Introduce argon as a protective gas to keep the pressure in the furnace basically at around 400-600mbar. Gradually increase the heating power to adapt the temperature in the crucible to about 1500℃, and the silicon raw material begins to melt. Keep about 1500℃ during the melting process until the melting is completed. This process takes about 20-22 hours.
4. Crystal growth
After the silicon raw material is melted, the heating power is reduced to make the temperature of the crucible drop to about 1420-1440℃, which is the melting point of silicon. Then the quartz crucible gradually moves downward, or the insulation device gradually rises, so that the quartz crucible slowly leaves the heating zone and forms heat exchange with the surroundings; at the same time, water is passed through the cooling plate to reduce the temperature of the melt from the bottom, and crystalline silicon is first formed at the bottom. During the growth process, the solid-liquid interface always remains parallel to the horizontal plane until the crystal growth is completed. This process takes about 20-22 hours.
5. Annealing
After the crystal growth is completed, due to the large temperature gradient between the bottom and the top of the crystal, thermal stress may exist in the ingot, which is easy to break again during the heating of the silicon wafer and the preparation of the battery. Therefore, after the crystal growth is completed, the silicon ingot is kept near the melting point for 2-4 hours to make the temperature of the silicon ingot uniform and reduce thermal stress.
6. Cooling
After the silicon ingot is annealed in the furnace, turn off the heating power, raise the heat insulation device or completely lower the silicon ingot, and introduce a large flow of argon gas into the furnace to gradually reduce the temperature of the silicon ingot to near room temperature; at the same time, the gas pressure in the furnace gradually rises until it reaches atmospheric pressure. This process takes about 10 hours.
Post time: Sep-20-2024
