SiH radicals

The SiH radical is tlie dominant growtli precursor for tlie fonnation of tlie a-Si H films in a low-temperature silane plasma [32]. Silane molecules are dissociated by energetic plasma electrons ... 

The SiH radical physisorbs on tlie a-Si H surface and recombines tliere witli anotlier SiH radical to fonn disilane Si2 Hg, or abstracts H from tlie surface to fonn a dangling bond and SiH. The film growtli is detennined by tlie chemisoriDtion of tlie SiH radical on a free dangling bond site by fonnation of a Si-Si bond. The cross-linking of... 

Optical emission is a result of electron impact excitation or dissociation, or ion impact. As an example, the SiH radical is formed by electron impact on silane, which yields an excited or superexcited silane molecule (e + SiHa SiH -t-e ). The excess energy in SiH is released into the fragments SiH SiH -I-H2 + H. The excited SiH fragments spontaneously release their excess energy by emitting a photon at a wavelength around 414 nm. the bluish color of the silane discharge. In addition, the emission lines from Si. H, and H have also been observed at 288, 656, and 602 nm, respectively. 

Nowadays, it is generally accepted that device quality a-Si H is obtained under PECVD conditions where the SiH radical is the predominant growth precursor [123, 137, 192]. At typical deposition temperatures and pressures the a-Si H surface is almost completely terminated by hydrogen atoms. The SiHj radical... 

The electronic spectrum of the SiH radical was first investigated by Jack-son15) and Rochester16). Subsequently Douglas17), Verma18) and Herzberg et a/.4) extended the analysis of the electronic states. The presence of SiH in the solar photosphere has been firmly established19). 

Attempts to isolate the SiH radical at low temperature in an Ar matrix by vacuum UV photolysis of SiH4 and various deuterosilanes provided data for Si2, SiH2 and SiH3, but were not conclusive for the identification of SiH7. ... 

Fig. 2. Two-dimensional illustration of the geometric definition of the pore size distribution [25]. Point Z may be overlapped by all three circles of differing radii, whereas point Y is accessible only to the two smaller circles and point X is excluded from all but the smallest circle. The geometric pore size distribution is obtained by determining the size of the largest circle that can overlap each point in the pore volume. (Reproduced with permission from S. Ramalingam, D. Maroudas. and E. S. Aydil. Interactions of SiH radicals with silicon surfaces An atomic-scale simulation study. Journal of Applied Physics, 1998 84 3895-3911. Copyright 1998, American Institute of Physics.)...

The detailed interactions between the SiH radicals and silicon surfaces can be captured by MD simulations of radical impingement at a grid of locations on the surface with varying radical molecular orientation with respect to the surface. Tlie reactions of SiH with the pristine Si(001)-(2 x 1) surface can be classified broadly into two classes (Ramahngam et al., 1998b). The radical either adsorbs dissociatively onto the surface or penetrates below the top surface layer into the substrate also resulting in dissociation. The H atom that is released upon radical dissociation becomes an interstitial impurity of the substrate Si lattice and it can migrate rapidly or channel deeper into the substrate. These reactions can be represented as... 

An important factor in determining the morphology of the amorphous film grown through MD simulations is the observed mobility of the SiHs radical on the amorphous growth surface as the deposition proceeds (Ramalingam, 2000). The dynamics of the radical on the surface is... 

In conclusion, the MD simulations of a-Si H him growth from the SiHa, SiH2, and SiH radicals as the sole deposition precursors support that SiHa is the dominant deposition precursor and have elucidated its role in determining the detailed him structure and him surface morphology and composition (Ramalingam, 2000). 

In spite of the role of the dominant deposition precursor in determining the structure and composition of the deposited him, it is also worth examining the possible roles of minority species that are present at low concentrations in the plasma and are not expected to have signihcant quantitative contribution to the hhn growth process. Of particular interest are species that are very reactive with the growth surfaces, such as SiH radicals and small Si H, clusters with n > 1. Indeed, such species may have both benehcial and detrimental effects on the structural quahty of the deposited him. 

Ohira, T., Ukai, O., Adachi, T, Takeuchi, Y, and Murata, M., Molecular-dynamics simulations of SiHs radical deposition on hydrogen-terminated Si(lOO) surfaces. Phys. Rev. B 52, 8283-8287 (1995). 

Ramalingam, S., Maroudas, D., and Aydil, E. S., Visualizing radical-surface interactions in plasma deposition processes Reactivity of SiHs radicals with Si surfaces. IEEE Trans. Plasma Sci. 27,104-105 (1999a). 

Von Keudell, A., and Abelson, J. R., Direct insertion of SiH radicals into strained Si-Si surface bonds during plasma deposition of hydrogenated amorphous silicon films. Phys. Rev. B 59,5791-5798 (1999). 

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