Processing silane

There are two types of deposited films known as siUcon nitride. One is deposited via plasma-enhanced CVD at temperatures <350° C (18). In this process silane and ammonia react in an argon plasma to form siUcon imide [14515-04-9] SiNH. 

Covalent bond formation is not an immediate process. Silane coating layers consist of physisorbed as well as chemisorbed molecules. Physisorbed molecules go into condensation only slowly and chemical stabilization of the coating layer requires a post-reaction curing step. In this step the modified substrate is thermally treated at temperatures generally in the 353 - 473 K range. 

Silane-Based Adhesion Promotion (Oxide Alternative Treatments). The silane-based process is an alternative to the copper oxide process. Silane can be used to bond epoxy to other materials. One end of the silane molecule bonds to the epoxy. If the other end of the molecule is modified to bond to the secondary material, the silane can serve as a bridge, greatly enhancing adhesion. It is commonly used in this mode to enhance the adhesion of epoxy to glass. It can be also used to enhance the adhesion of epoxy to copper. 

Silane can be provided in many types of mixtures. Mixed gases can include inert, flammable or toxic supplied in the same cylinder. Unless critical to the process, silane should not be mixed with toxics. New processes should be designed to prohibit this mixing. It should only occur in very few existing processes. When silane is mixed with toxics, the users must also follow all ordinances for the handling of toxic gases. 

The acid monolayers adsorb via physical forces [30] however, the interactions between the head group and the surface are very strong [29]. While chemisorption controls the SAMs created from alkylthiols or silanes, it is often preceded by a physical adsorption step [42]. This has been shown quantitatively by FTIR for siloxane polymers chemisorbing to alumina illustrated in Fig. XI-2. The fact that irreversible chemisorption is preceded by physical adsorption explains the utility of equilibrium adsorption models for these processes. 

Viswanathan R, Thompson D L and Raff L M 1984 Theoretical investigations of elementary processes in the chemical vapor deposition of silicon from silane. Unimolecular decomposition of SiH J. Chem. Phys. 80 4230 0... 

The deposition of amoriDhous hydrogenated silicon (a-Si H) from a silane plasma doped witli diborane (B2 Hg) or phosphine (PH ) to produce p-type or n-type silicon is important in tlie semiconductor industry. The plasma process produces films witli a much lower defect density in comparison witli deposition by sputtering or evaporation. 

Manufacture of P-Silicon Carbide. A commercially utilized appHcation of polysdanes is the conversion of some homopolymers and copolymers to siHcon carbide (130). For example, polydimethyl silane is converted to the ceramic in a series of thermal processing steps. SiHcon carbide fibers is commercialized by the Nippon Carbon Co. under the trade name Nicalon (see Refractory fibers). 

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. 

The primary process of SiH decomposition is electron impact which produces a large number of different neutral and ionic species as shown in Table 1. The density of S1H2 and SiH neutral species produced has been found to be much larger than the density of the ions. For example, mass spectrometric data for silane discharges indicate that the density of ionic species is lower by 10 compared with the density of neutral species. Further, mass spectrometer signals of ionic species, such as SiH SiH 25 SiH", SiH", and Si2H , increase by more than two orders of magnitude as the r-f power is increased, eg, from 2 to 20 W. A rapid rise in the population of ions, with power, implicitly means an increase in electron density. 

Table 1. Electron Impact Dissociative Processes Operative in Silane Plasma ...

The production of vitreous siUca from chemical precursors was first described in patents filed in 1934, including a fabrication method in which fine, high purity powders were produced by decomposing silanes (39). Forms were then cast from aqueous sHps. More importantiy, a dame hydrolysis process which used SiCl as the chemical precursor was described (40). This latter approach led to a marked improvement in glass purity and served as the basis for the processes used in the 1990s to make synthetic vitreous siUca. 

Feasibility of the Silane Process for Producing Semiconductor Grade Silicon,]e.. Propulsion Laboratory Contract 954334, June 1979. 

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). 

The most common catalysts in order of decreasing reactivity are haUdes of aluminum, boron, zinc, and kon (76). Alkali metals and thek alcoholates, amines, nitriles, and tetraalkylureas have been used (77—80). The largest commercial processes use a resin—catalyst system (81). Trichlorosilane refluxes in a bed of anion-exchange resin containing tertiary amino or quaternary ammonium groups. Contact time can be used to control disproportionation to dichlorosilane, monochlorosilane, or silane. 

Dialkylanaino-substituted silanes have also been obtained by a similar process (149—151). 

The production of sihcon tetrachloride by these methods was abandoned worldwide in the early 1980s. Industrial tetrachlorosilane derives from two processes associated with trichlorosilane, the direct reaction of hydrogen chloride on sihcon primarily produced as an intermediate for fumed sihca production, and as a by-product in the disproportionation reaction of trichlorosilane to silane utilized in microelectronics. Substantial quantities of tetrachlorosilane are produced as a by-product in the production of zirconium tetrachloride, but this source has decreased in the 1990s owing to reduction in demand for zirconium in nuclear facihties (see Nuclearreactors). The price of tetrachlorosilane varies between l/kg and 25/kg, depending on grade and container. 

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