Monocrystalline silicon production process
Monocrystalline silicon is a good semiconducting material. Used in the manufacture of semiconductor devices, solar cells, and the like. It is made of high-purity polycrystalline silicon in a single crystal furnace. The specific production process is as follows:
1.Feeding
The polycrystalline silicon raw material and impurities are placed in a quartz crucible, and the type of impurities depends on the N or P type of the electric resistance. The impurities are boron, phosphorus, antimony and arsenic.
2. Melting
After the polycrystalline silicon raw material is added to the quartz crucible, the crystal growth furnace must be closed and evacuated, and then filled with high-purity argon gas to maintain a certain pressure range, and then the graphite heater power source is turned on and the melting temperature (1420 ° C) or higher is heated. Until the polysilicon material melts.
3. Neck growth
After the temperature of the silicon melt is stabilized, the seed crystals are slowly immersed in the silicon melt. Due to the thermal stress of the seed crystal contacting the silicon melt field, the seed crystal is dislocated and these dislocations must be removed by necking growth. Neck growth is a rapid increase in seed crystals, reducing the diameter of the growing seed crystal to a certain size (4-6 mm). Since the dislocation line forms an angle with the growth axis, the dislocation can be long as long as the neck is long enough. Outside the crystal surface, a crystal with zero dislocations is produced.
4. Shoulder growth
After stretching the neck, the temperature and stretching speed must be lowered to gradually increase the diameter of the crystal to the desired size.
5. Equal diameter growth
After completing the neck and shoulders, the diameter of the ingot can be maintained between plus and minus 2 mm by continuously adjusting the pulling speed and temperature. The fixed portion of the diameter is referred to as the equal diameter portion. The single crystal silicon wafer is taken from an equal diameter portion.
6. Tail growth
After the equal diameter portion is completed, if the ingot is immediately separated from the liquid surface, thermal stress will cause dislocations and slip lines in the ingot. Therefore, in order to avoid this problem, it is necessary to gradually reduce the diameter of the ingot until it is a sharp point and is separated from the liquid surface. This process is called tail growth. The permanent ingot is lifted to the upper chamber for a period of time and then removed, ie the growth cycle is complete.
