Bonding properties of glow-discharge polycrystalline and amorphous Si-C films studied by x-ray diffraction and x-ray photoelectron spectroscopy

Abstract

Polycrystalline and amorphous Si-C films were prepared by rf glow-discharge decomposition of silane-methane mixtures at 700 °C. We have demonstrated that polycrystalline SiC films with large grains grow under heavy hydrogen dilution. The bonding properties as a function of film composition and hydrogen dilution were characterized by means of x-ray diffraction and x-ray photoelectron spectroscopy. Crystallization takes place at around C content x=0.5 in Si1−xCx, accompanying some segregation of carbon atoms in grain boundaries, as a result of a preference for heteronuclear bonds. It was shown that C-C(C3−nSin) (n=0–3) bonds appear in the carbidic phase of C-rich films, leading to occurrence of compressive strain in the crystalline SiC grains. In addition, effects of hydrogen dilution were discussed in correlation with the strain.

Ion-beam synthesis of amorphous SiC films: Structural analysis and recrystallization

“…However, the second contribution ͑at 284.2 eV͒ appears at an energy somehow lower than that assumed by Takeshita et al for the C-C 4 one. 12 This disagreement could be related to the high uncertainty related to this contribution, which is very small in almost all the spectra. Moreover, we have to remark that, in contrast with the previous data from Takeshita et al, 12 the results obtained from the Si 2p and C 1s spectra show the same behavior, obtaining the same percentage of heteropolar bonds in both cases.…”

“…12 This disagreement could be related to the high uncertainty related to this contribution, which is very small in almost all the spectra. Moreover, we have to remark that, in contrast with the previous data from Takeshita et al, 12 the results obtained from the Si 2p and C 1s spectra show the same behavior, obtaining the same percentage of heteropolar bonds in both cases. The presence of only two significant contributions in the XPS spectra suggests the existence in our case of a tendency towards partial chemical ordering with phase separation.…”

“…On the other hand, Takeshita et al 12 have interpreted the XPS data from glow discharged amorphous SiC layers in terms of the complete chemical order with the homogeneous dispersion model ͑COHD͒. In this model, the spectra arise from five possible contributions corresponding to the different tetrahedral bonding configurations (Si-Si 4Ϫn C n and C-C 4Ϫn Si n with nϭ0 -4) averaged according to the different bond probabilities predicted for the different models indicated in Sec.…”

“…[11][12][13] In the first case, only homonuclear A-A and B-B bonds are observed, with probabilities (1Ϫx) and x, respectively. The second case corresponds to the absence of chemical order, in which a random distribution of bonds occurs.…”

“…[12][13][14][15][16][17][18][19] These works have involved the use of different techniques such as x-ray scattering, extended x-ray absorption fine structure, x-ray photoelectron spectroscopy, Auger electron spectroscopy, Raman scattering, and infrared spectroscopy, observing a strong dependence of the chemical ordering and crystalline structure of the layers on the deposition conditions. Moreover, some of the experimental results are still not clear, being the subject of controversy.…”