Polysilicon

Polysilicon has gray metallic luster, density is 2.32 to 2.34, melting point is 1410, boiling point is 2355. Can dissolve in mixed hydrofluoric acid and nitric acid, does not dissolved in water, nitric acid and hydrochloric acid. Hardness between germanium and quartz, crisp at room temperature and easily broken while cutting. Heated to above 800 can with ductility, at 1300 show significant deformation. At room temperature is inactive, at high temperature can react with oxygen, nitrogen, sulfur, etc. At high-temperature molten state, have greater chemical reactivity, can react with almost any materials. Have semiconductor properties, is extremely important excellent semiconductor materials, but small amounts of impurities can greatly affect its conductivity. In the electronics industry are widely used as basic materials in manufacturing transistor radios, tape recorders, refrigerators, color TV, VCR, computer, etc. Obtain from dry silicon powder and dry hydrogen chloride gas chlorination, condensation, distillation, reduction under a certain condition.

Polysilicon is a form of elemental silicon. While the molten elemental silicon freezing under subcooled conditions, silicon atoms are arranged in diamond lattice patterns in many crystal nucleus, such as these crystal nucleus grow into different crystal plane orientation crystalline grains, these grains combined can crystallize into polysilicon. Polysilicon can use as the raw materials of monocrystalline silicon, the differences between polycrystalline silicon and monocrystalline silicon mainly in physical properties. For example, in anisotropy of mechanical properties, optical properties and thermal properties, it is far less the monocrystalline obviously; polysilicon crystal’s conductivity also far less than monocrystalline significantly in electrical properties, even almost no conductivity. In chemical activity, the difference is minimal. Polysilicon and monocrystalline silicon can be distinguished from the appearance, but the real differential shall be determined by analyzing the crystal direction of the crystal surface, conductivity type and resistivity.

According to metal powder supplier, polysilicon production for environmental and equipment cleaning requirements is very high. The production process is more complicated. Especially the equipment impact on the quality of the product is extremely important. In order to ensure the quality of products, in the equipment installation process, the cleaning of equipment and piping and other important equipment must be very strict. In the cleaning process, make every aspect of quality are up to par. According to different process requirements, different material of the device as well as different types of devices, cleaning processing requirements and the achieved basic standards (require to achieve no oil, anhydrous and dust-free three requirements).

Polysilicon equipment cleaning is mainly the pickling, degreasing, passivation, drying, etc. wherein the most important is the degreasing process and drying technology. Grease and water have a huge impact on polysilicon products. So that in polysilicon equipment cleaning, degreasing process and drying process is the point. Mainly have cleaning hydrogenation furnace, CDI equipment, reduction furnace, synthesis workshop, reductive hydrogenation plant, distillation systems, intermediate tanks, pipelines and other major equipment. And in order to ensure the quality of degreasing and drying, the polysilicon equipment need to clean on a single piece of equipment and single installation after acceptance.

Device’s residual dirt on the polysilicon have adversely affected, Grease: in the polysilicon producing process, the hazards of the oil molecules for polysilicon is very serious. The actual proven that a few millionths of oil content may cause entire polysilicon reaction process system slower, lower production, even stopping silicon reaction. Therefore, the polysilicon equipment degreasing process is particularly important. Moisture content: the water contained a lot of chlorine ion, chloride ion is very sensitive for polysilicon reactions. Residual chloride ions: the effect of water and other solutions residual chlorine ions in the device surface for polysilicon is very large. Therefore, after cleaning, the process of water rinsing the device is very important. Oxides, dust and other impurities: the presence of other dirt, also have a great impact on polysilicon production. Therefore, in equipment cleaning process, use the pickling process to clean other dirt is necessary.

Source:http://www.mhcmp.com