SiH4, decomposition

The other SiH4 decomposition pathway involves Hj elimination via a three-center cyclic transition state (Roenigk et ai, 1987) ... 

Figure 6. First-order rate constant for SiH4 decomposition as a function of pressure and temperature. The solid points represent rate measurements by Purnell and Walsh (218). 1 torr = 133.322 Pa.

Fig. 1 compares the Auger electron spectra of poly-Si films grown from different gas mixtures. The spectrum in Fig. la (Si LMM transition, 92 eV) was taken from the poly-Si film grown by the standard process (SiH4 decomposition). The presence of GeH4 during the film growth gives rise to additional peaks, Ge LMM (37 eV) and Ge KLL (109.8 eV) (Fig. lb), attesting to Ge doping of the films, in accordance with XRD results (Fig. 2). The spectra in Figs, lc and Id show the B KLL (81 eV) and P KLL (99.58 eV) transitions, respectively.

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, die plasma decomposition of silane, SiH4, leads to the formation of the species, SiH3, SiHa, H, SiH, SiH3+ and H2+. Recombination reactions may occur between the ionized states and electrons to produce dissociated molecules either direcdy, or tlrrough the intermediate formation of excited state molecules. 

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) ... 

In the early 1970s, Spear and coworkers (Spear, 1974 Le Comber et al., 1974), although unaware of the presence of hydrogen, demonstrated a substantial reduction in the density of gap states (with a corresponding improvement in the electronic transport properties) in amorphous silicon films that were deposited from the decomposition of silane (SiH4) in an rf glow discharge. 

The work of Purnell and Walsh67 will now be compared with previous studies of this decomposition. Hogness et al.12 were the first to undertake a systematic investigation of the kinetics of the SiH4 pyrolysis. They followed the course of the reaction by measuring the increase in total pressure and assumed a stoichiometry corresponding to... 

EXPERIMENTAL CONDITIONS AND RESULTS FOR STUDIES OF SiH4 AND SiD4 DECOMPOSITION... 

Fig. 12. Potential energy diagram for the unimolecular decomposition of SiH4 to SiHj and H, showing the activation energy barrier . The sketch above is a geometrical representation of the events (1 to r) along the reaction coordinate, which is the Si-H distance.

Fig. 21. Unimolecular QRRK predictions for the rate of decomposition of SiH4...

In the previous problem we examined temperature profiles and reactant (SiH4) concentration profiles in a channel-flow chemical vapor deposition (CVD) reactor. At sufficiently high temperatures (and pressures) SM4 undergoes unimolecular decomposition into the species SiH2 and H2. This is followed by numerous reactions of the intermediate species [180]. One such intermediate species formed in the gas phase is Si (i.e., a gas-phase silicon atom). In this problem we consider the gas-phase formation and destruction reactions governing the spatial profiles of Si atoms in a rotating-disk CVD reactor. 

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