Thermal decomposition silane

Silane, pure or doped, is used to prepare semiconducting siUcon by thermal decomposition at >600° C. Gaseous dopants such as germane, arsine, or diborane maybe added to the silane at very low concentrations in the epitaxial growing of semiconducting siUcon for the electronics industry. Higher silanes, eg, Si H and Si Hg, are known but are less stable than SiH. These are analogues of lower saturated hydrocarbons. 

The thermal decomposition of silanes in the presence of hydrogen into siUcon for production of ultrapure, semiconductor-grade siUcon has become an important art, known as the Siemens process (13). A variety of process parameters, which usually include the introduction of hydrogen, have been studied. Silane can be used to deposit siUcon at temperatures below 1000°C (14). Dichlorosilane deposits siUcon at 1000—1150°C (15,16). Ttichlorosilane has been reported as a source for siUcon deposition at >1150° C (17). Tribromosilane is ordinarily a source for siUcon deposition at 600—800°C (18). Thin-film deposition of siUcon metal from silane and disilane takes place at temperatures as low as 640°C, but results in amorphous hydrogenated siUcon (19). 

A15 nm thick layer of silicon is then deposited by the thermal decomposition of silane at the same temperature and pressure as follows ... 

Beta SiC powder from the decomposition of methyl-trichlorosilane (MTS) in the presence of hydrogen in an argon plasma. Also from the gaseous thermal decomposition of tetramethylsilane, Si(CH3)4, in a flowthrough reactor between 850 and 1500°CP 1 and by the reaction of acetylene and silane. 

Previously, trifluorosilyl groups have been bound to phosphorus (40) and silicon via the SiF (g), fluorine-bond insertion-mechanism (41). The new compound HgCSiFs) is readily hydrolyzed, but it can be stored for long periods of time in an inert atmosphere. It is a volatile, white solid that is stable up to at least 80°C. The preparation of bis(trifluoro-silyDmercury, of course, raises the possibility of (a) synthesis of the complete series of trifluorosilyl, "silametallic compounds, as had previously been done for bis(trifluoromethyl)mercury by using conventional syntheses, and (b) transfer reactions similar to those in Section II, as well as (c) further exploration of the metal-vapor approach. The compound Hg(SiF.,)j appears also to be a convenient source of difluoro-silane upon thermal decomposition, analogous to bis(trifluoromethyl)-mercury ... 

For illustrative purposes, the process of deposition of Si onto graphite is being used as an example. The 15 pm natural graphite precursors were introduced into the industrial size chemical vapor deposition reactor, where a thermal decomposition of silane (SiH4) into the silicon and hydrogen was taking place under inert gas in accordance with the equation (1) ... 

Silane decomposes to its elements at above 400°C. Process (1) is known as direct thermal decomposition, and produces either amorphous or polycrystalline Si (function of reaction temperature and other processing parameters), and is commonly used, for instance, in the solar cell industry to reduce silane to silicon. 

In 1989, Corriu and workers reported the thermal decomposition (85 °C) of the silyl formate 6, having a remote stabilizing amino group, which was prepared by the insertion reaction of the corresponding pentacoordinated functional silane 5 with CO2,... 

It is well known that thermal decomposition of allyl-substituted silanes proceeds by retro-ene reaction with formation of transient species having a Si=C bond, such as silaben-zene, silatoluene and dimethylsilaethylene4b e. The kinetic data on the gas-phase pyrolysis of a similar allyloxysilane derivative, (l,l-dimethylallyloxy)dimethylsilane (16), and the results on thermolysis of allyloxydimethylsilane (17) in a flow system both indicate the participation of an intermediate silanone, (CH3)2Si=0 (10), as shown in Scheme 523. 

Corriu and coworkers have studied the thermal decomposition of hydrosilsesquioxane resins90 (17) and have observed the evolution of silane (18) between 350 °C and 480 °C (equation 10). Above this temperature hydrogen is observed. 

As an alternative to condensation of dichlorosilanes by alkali metals, it is possible to synthesize poly silanes by the reaction of preformed dilithio compounds with dichlorosilanes. An early synthesis of a copolymer by this route is illustrated in equation (19).10 (see also Section 5.9.2). Finally, poly(phenylmethylsilylene) has been made by thermal decomposition of a silyl-mercury polymer36 (equation (20)). 

The 1273 K treated sample (figure 14.9a) shows 2 bands, at 3740 and 2290 cm 1. These may be assigned to surface hydroxyls and silane groups, respectively. Upon thermal decomposition of the alkyl chain, hydrogen gas is formed. The evolved gas may react with the silica surface siloxanes, according to reaction (E). 

Activation by silicon of a P-C-H bond to an intramolecular carbene insertion reaction is exemplified by the silicon-directed Bamford-Stevens reaction.68 For example, thermal decomposition of P-trimethylsilyl /V-aziridinyl imines 72 in toluene (Scheme 8) [with or without Rh2(OAc)4 catalyst] results in the formation of allylic silanes 73 as major or exclusive products by the preferential insertion of the carbene intermediate into the C-H bond P to the silicon substituent. 

Decomposition of complex metal organic molecules are t3 ically endothermic reactions performed in furnace reactors. An example of a furnace decomposition is the thermal decomposition of dimethyl— chloro-silane to give silicon caihide [6] ... 

In some cases two step reactions can take place. An example [18] of such a two step reaction is that observed with the laser synthesis of SiC using the reactants SiH4 and CH4. In this reaction, silane undergoes thermal decomposition giving silicon as follows ... 

This might account for the failure to synthesize FH2CSi derivatives by treatment of (monochloro-methyl)silanes with fluorinating agents like AgF, KF, or SbFs, which led to a breakdown of the (chloromethyl)silicon moiety to give the corresponding fluorosilanes [7]. Additional indications of the reactivity of the C-F bond have been obtained by studying the thermal decomposition of these compounds. 

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