HCDS – Hexachlorodisilane
Certificate of Analysis (CoA) and specifications for current lot of HCDS – Download PDF (Updated on September 2, 2016)
Over the course of nearly 100 years, HCDS has been used as a precursor for a variety of industrial chemical applications. The last 50 years in particular have seen an acceleration of technological breakthroughs in electronics, specifically in semiconductors, solar cells, and fiber optics, as a result of high purity refining of HCDS. The aerospace industry has been utilizing the benefits of HCSD in aerogel production for many years and overlaps many of the same applications as the electronics industry. Over the past 30 years, fuel cell membranes have been researched and developed, with the most promising being polymer electrolyte membranes (PEMs).
High tech industrial applications require intricate chemical interactions. In the manufacturing of polysilicon, the base raw material of the electronics and solar industries, tetrachlorosilane (Cl4Si) and hydrogen combine resulting in the exhaust gas byproducts Trichlorosilane (SiHCl3) and HCDS. HCDS is separated from SiHCL3 through a process of condensing and distilling, then captured as a liquid vapor. This liquid vapor is used in deposition processes leading to manufacturing of electronic components and solar cells.
There are three purity grades which develop during the processes leading up to the manufacture of polysilicon: low, high, and ultrahigh. Low purity is high in metallic contamination and tends to degrade and decrease efficiency and reliability. High and ultrahigh pure HCDS, on the other hand, have been refined to the point metallic impurities measure approximately 1 ppb. Thin films for solar and microchip applications, as well as base glass for fiber optics, require high to ultrahigh purity.
The capture and distilling of HCDS is extremely beneficial to silicon based industries due to the ability to refine the chemical to the ultrahigh purity necessary for microelectronics. These advancements allow manufacturers to manipulate the chemical and physical properties of HCDS, resulting in efficient and reliable thin films for solar cells and microchips. Base glass production for fiber optics also benefits from these advances. HCDS is of particular interest in fuel cell application as not only do the cells require a thin film membrane for electrical transport, but they are also being designed at the micro level utilizing silicon as the substrate. HCDS also has the ability to improve certain properties of aerogels when applied via the CVD method. The production and refining of HCDS is not without its risks, however. The chemical decomposes easily at high temperatures, is highly volatile in the presence of moisture, and is highly toxic to humans and aquatic life. The advantages lie within its electrical properties, high deposition rates, and lower temperature requirements.
Physical and Chemical Characteristics and Properties
HCDS, an inorganic compound comprised of 2 silanes and 6 chlorines, is a byproduct of the manufacturing of polysilicon, a substrate necessary for the development of electronic devices, fiber optics, and solar cells. Two initial gases are involved in the reactor phase of polysilicon manufacturing: tetrachlorosilane (Cl4Si) and hydrogen. This process results in the formation of several volatile gases, including HCDS. At this production phase, these gases have a high concentration of impurities from the initial silicon feedstock input, specifically titanium and aluminum, making them a low purity gas. For many years, these gases have been disposed of as waste, but over the last two decades their value in high tech manufacturing has been realized. Manufacturers were trying to figure out how to cut down on wasteful emissions and utilize these gases. A refining process, known as the Siemens process, was developed to solve this issue. This process allows for the capture, refining, and purification of HCDS.
The Siemens process is complex yet fairly straightforward: the reaction HCDS develops as a byproduct of heating vaporized CL4Si and hydrogen; hydrogen chloride is introduced to quickly cool the gas in order to freeze any further decomposition (usually takes less than one second); HCDS becomes a condensate liquid which is quickly collected from the bottom of the tower, becoming a valuable raw material of its own.
The two phases of HCDS are gas and liquid. At high temperatures, this chemical maintains a gas state, but as illustrated in the Siemens process, transforms to liquid if cooled quickly. In both states, HCDS is highly corrosive, colorless, explosive upon contact with air, and will convert to hydrochloric acid if exposed to moisture. HCDS has a high level of reactivity and is stable up to a year in airtight storage (it begins to degrade and decompose shortly thereafter). HCDS has boiling point of 145 degrees Celsius, higher than any other chemicals involved in or resulting from the reactor phase process.
HCDS undergoes specific chemical and physical changes during the polysilicon production process which give it the flexibility to be utilized in a multiplicity of fields and applications, especially for use in chemical vapor deposition (CVD) due to its Si-Si bonding properties. These properties serve to stabilize and strengthen these chemical bonds during CVD.
Storage and Transportation
HCDS containers must be kept tightly closed in a cool, dry, well-ventilated place. Handling and storage under inert gas only. HCDS is stable, but reacts violently with water. HCDS is moisture and shock sensitive. HCDS is not compatible with water, moisture, acids, strong bases, oxidizing agents, and alcohols.
Proper Shipping Name: Chlorosilanes, Corrosive, n.o.s. (Hexachlorodisilane)
Hazard Label: Corrosive
Packing Group: II