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Degree of purity of more than 99.9999 %. If required, electronic grade also possible.
Silicon is a constituent of many minerals. Indeed it is the second most common element in the earth's crust after oxygen. Elemental silicon is used and classified in various degrees of purity. The solar industry manufactures and processes solar grade silicon (Sisg). Its impurities amount to less than 0.0001 percent. The solar industry is increasingly using even higher purities, even up to electronic grade (Sieg).
The EPC Group's portfolio of services covers not only the planning and provision of equipment for synthesizing TCS and vent gas recovery systems, but also rectification units, which require the know-how of experienced experts. We also provide you with the ancillary plants, infrastructure systems and construction planning services for complete factories. Production methods for TCS and polysilicon Elemental silicon is obtained on an industrial scale by reducing silicon dioxide with activated carbon in a melt. This produces silicon that is sufficiently pure for metallurgical purposes. However, the silicon has to be purified even further to obtain polycrystalline silicon (Sisg). This is done e.g. with the aid of a Siemens method that has been further developed by EPC.
The first step is to mix the metallurgical silicon with gaseous hydrogen chloride. This produces hydrogen, which is removed, and trichlorosilane, which is purified in further distillation stages. In the subsequent CVD process, gaseous TCS is fed into separation reactors in which ultrapure silicon is deposited on up to 54 hot silicon rods. The production cycle of each CVD reactor finishes after about 4 days, after which the polycrystalline silicon is "harvested". Silicofluidizedn tetrachloride is formed as a byproduct. This is converted back to trichlorosilane in a fluidized bed-reactor, and fed back into the production cycle. This conversion reactor can also be designed to be the sole source of TCS.
Polysilicon and TCS
EPC offers turnkey plants for your PolySi production. They have the following advantages:
- A degree of purity greater than 99.9999%, electronic grade is also possible if required
- Intelligent revamping concepts reduce the total per kg cost of producing Si
- Overall energy consumption is reduced by, for example, recovering energy
- In-house TCS production, mainly supplied by hydrogenation conversion, including separation and rectification
- Integration into the existing production location and the existing infrastructure
- Extension of the existing value chain (ingots, wafers, cells)
- Greater competitiveness in the world market
Monosilane
Monosilane has the simplest chemical structure of all the silanes, it is also known as silicon hydride. Silanes are part of a group of chemical compounds that consist of a silicon framework and hydrogen. Monosilane is used to separate silicon and silicon nitride layers in semi-conductor production and in the manufacture of solar cells.
EPC offers technologies for the economical and efficient manufacture and storage of monosilane. Special gases, such as monosilane, are used on account of the high requirements for purity and plant safety. We develop tailor-made and, above all, economical solutions for our customers, and also for new production technologies. Our monosilane tank, filling and distribution systems for our customers set new standards in the semi-conductor supply industry.
EPC Exclusives
Innovative technologies using trichlorosilane and monosilane
The method of producing ultrapure silicon from metallurgic silicon is based on the thermal decomposition of highly pure, rectified chlorosilanes or silanes to form silicon with the separation and recycling of gaseous byproducts. The conventional commercial technology passes through the stage of producing trichlorosilane in a fluidized-bed reactor from metallurgic grade silicon and hydrogen chloride. The trichlorosilane is then subjected to multi-stage rectification until the purity required for the desired application is reached (solar grade or electronic grade). The thermal decomposition of trichlorosilane in a chemical vapor deposition (CVD) reactor to form silicon at 900 °C creates a mixture of gaseous by-products, which have to be prepared for recycling (vent gas recovery) back into the process. We have optimized the process for producing ultrapure silicon from monosilane. It now offers a significantly higher efficiency as temperatures are only around 600 °C, and the collection efficiency has been increased to almost 100% in comparison to the mere 25% achieved by conventional processes. Monosilane is obtained by the disproportionation of trichlorosilane and recirculation of the disproportionation products. Trichlorosilane is thus required in both methods.
Vent gas recovery plants, including rectification units
The gas mixture produced by the thermal decomposition of trichlorosilane in a chemical vapor deposition (CVD) reactor has to be separated into its constituent parts before the individual products can be recirculated. The monosilane method does not need these cycles, however Vent Gas Recovery is still part of our range or products.
Hazardous substance stores, including monosilane storage and handling systems
The monosilane synthesis gas is stored temporarily in vacuum-insulated containers prior to further processing or filling. The containers are equipped with a pressure build-up vaporizer and an internal cooling coil to facilitate cooling. The containers are a special product of our subsidiary company, CRYOTEC, which specializes in special cryogenic applications.
Process control optimized by fluidized bed reactor technology (FBR plants)
Silicon tetrachloride is the main by-product of both the production of trichlorosilane from metallurgic silicon with HCl in a fluidized-bed reactor and the disproportionation of trichlorosilane. The thermal decomposition of trichlorosilane in a CVD reactor also creates large quantities of silicon tetrachloride. The silicon tetrachloride is converted with hydrogen into trichlorosilane in a conversion reactor. This process can be run homogeneously with hydrogen at approximately 1,000 °C in graphite reactors. We use the more elegant heterogeneous method of controlling the process by feeding silicon into a fluidized-bed reactor.
