Silane SiH

Germane is used, along with silane, SiH, to make amorphous or crystalline siUcon solar cells having an extended solar energy absorption range to increase conversion efficiency. 

Polysilicon. Polysihcon is used as the gate electrode material in MOS devices, as a conducting material for multilevel metallization, and as contact material for devices having shallow junctions. It is prepared by pyrolyzing silane, SiH, at 575—650°C in a low pressure reactor. The temperature of the process affects the properties of the final film. Higher process temperatures increase the deposition rate, but degrade the uniformity of the layer. Lower temperatures may improve the uniformity, but reduce the throughput to an impractical level. 

Dielectric Deposition Systems. The most common techniques used for dielectric deposition include chemical vapor deposition (CVD), sputtering, and spin-on films. In a CVD system thermal or plasma energy is used to decompose source molecules on the semiconductor surface (189). In plasma-enhanced CVD (PECVD), typical source gases include silane, SiH, and nitrous oxide, N2O, for deposition of siUcon nitride. The most common CVD films used are siUcon dioxide, siUcon nitride, and siUcon oxynitrides. 

In RF discharges of silane, SiH usually is the most abundant ion, but others (SiH, and Si H+ with 1 < n < 9) also are present [319]. The relative abundance of SiH ions increases with increasing pressure, while that of SiH decreases [319]. The ionization cross section of SiHt is higher than that of SiHj [320], but SiH is lost via the reaction SiH -1- SiH4 —> SiHj -F SiH3 [305], At pressures lower than 0.1 Torr SiHt becomes the dominant ion. 

All of the atomic species which may be produced by photon decomposition are present in plasma as well as the ionized states. The number of possible reactions is therefore also increased. As an example, the plasma decomposition of silane, SiH/j, leads to the formation of the species, SiH3, SiH2, H, SiHj, SiH3+ and H2+. Recombination reactions may occur between the ionized states and electrons to produce dissociated molecules either directly, or through the intermediate formation of excited state molecules. 

Figure 8.1.12 shows a schematic illustration of laser-induced CVC (63). For the synthesis of silicon nitride, the reaction between silane (SiH,) and ammonia... 

The compound we use as a reference sample is usually tetramethylsilane, TMS. This is silane (SiH with each of the hydrogen atoms replaced by methyl groups to give Si(CH3)4- The four carbon atoms attached to silicon are all equivalent and, because silicon is more electropositive than carbon, are fairly electron-rich (or shielded), which means they resonate at a frequency a little less than that of most organic compounds. This is useful because it means our reference sample is not bang in the middle of our spectrum ... 

Two conditions can give rise to the spontaneous combustion of a fuel. One condition involves contact of the material with air. The other is the spontaneous ignition of an unstable self-reactive substance when it is kept at a sufficiently high temperature. Silane (SiH 4 ) and phosphine (PH 3 ) are the examples of the former case, and a mixed atmosphere of air and nickel carbonyl(Ni(CO) 4 ) or carbon disulfide (CS 2 ) are examples of the latter. 

The bond angles of silicon in the molecules of its compounds are more readily distorted than the corresponding bond angles of carbon in isostructural organic analogs Thus, a tetrahedral molecule of silane SiH (T ) can be transformed... 

Oxidation and hydrolysis reactions are widely used for the deposition of oxide materials. In these systems, oxygen or water is added to the system to oxidize the main precursor, removing hydrogen or halide atoms from the element of interest. A classic example is the oxidation of silane SiH + 2 Si02(s) +... 

Divalent silicon species react with HjO, forming silanes. Dilute aq HF (10%) reacts with SiO or SiO-GeO mixtures producing silanes (SiH, SijH, SijHj, Si Hj, SijHj, Si,H,) or ternary Si-Ge hydrides (SiGeHg, Si GeHg, etc.), respectively. Dimeth-ylsilylene, obtained by photolysis of (MejSi), upon insertion into the OH bonds of HjO yields siloxane ... 

Ionized silanes SiH + (n= 1-5) have been studied both theoretically9 and experimentally10, and all species are found to exist in potential minima. For SiH (protonated silane)... 

The possibility of synthesizing alkyl and alkenyl silanes from olefins and acetylenes with silane, SiH, has been investigated by White and Rochow (128). With ethylene various ethyl derivatives of silane and disilane were obtained under conditions suggestive of a free-radical mechanism ... 

Figure 17.3. Examples of the structures of silicide and silane nanotubes with (8,0) (left panel) and (8,8) (right panel) chirality. From top to bottom are shown pure silicide (Si ) and the silanes (SiH-io) and (SiH-sf), in each case in top and side views (taken from ref...

There are numerous applications where cure reaction by-products are not acceptable as they may contaminate other sensitive areas of the devices, and where fast deep section cure is required. These constraints have directed the choice to the platinum-catalyzed hydrosilylation addition cure system. The reaction involves the addition of a hydrido silane (SiH) to an alkenyl organic group (-CH=CH2), typically the vinyl or hexenyl groups. The product of the reaction is the ethylenic bridge (-CH2-CH2-). The alkenyl groups are usually placed at the end of the polymer base chains in structures such as The SiH groups are usually placed in a combed structure within the polymeric or copolymeric chains called cross-linker M-D -M or M-D -Dy-M. (The M, D, etc. nomenclature is explained in Silicones structures.) Typical values of n cover a wide range from 100 to 1000, while the values of x and y vary from 3 to 100. 

Silane, SiH, is a colorless gas. Phosphine, PHj, is also a gas it catches fire spontaneously when exposed to air, is very toxic, and has a bad odor. Hydrogen sulfide, H2S, is a toxic gas with a foul, rotten-egg odor. Natural gas contaminated with hydrogen sulfide is said to be sour, and the hydrogen sulfide must be removed before the natural gas can be used as a fuel. Fortunately, HjS is readily converted to elemental sulfur or to sulfuric acid, for which there are ready markets. Hydrogen chloride, HCl, gas has a sharp odor and is very soluble in water. Solutions of hydrogen chloride in water are called hydrochloric add. About 2.5 million tons of hydrochloric acid are produced for industrial applications in the U.S. each year. 

The use of silicon tetrachloride SiCU leads to highly corrosive HCl as a byproduct so that silane, SiH, despite being expensive and flammable in air, is generally preferred as the reactant. For Si3N4 production, NH3 is used because N2 is fairly unreactive. 

---