Thin Film Formation by Coating
Here, the coating of silicon solution to form polysilane films and subsequent conversion of the polysilane films to amorphous Si films via pyrolysis are described. Preparing a uniform film of polysilane on a substrate is not straightforward. Although wetting of the silicon solution on a substrate such as glass, quartz, or silicon is adequate, a film once coated on the substrate tends to break during evaporation of the solvent. As a result, only dotted patterns of polysilane remain on the substrate. This phenomenon of film formation is closely related to molecular forces between the substrate and solute in the solution. Therefore, the molecular force itself and its influence on the formation of silicon films are described in 4.2 after general description of coating phenomena in 4.1.
The observed color change of a coated film during the conversion from polysilane to amorphous Si is interesting. The polysilane film is transparent because of its optical bandgap of approximately 6 eV, whereas that of an amorphous Si film is approximately 1.5 eV. Therefore, the bandgap decreases during heating of the film, leading to the absorption of visible light. Strict control of the conversion process from polysilane to amorphous Si is quite important to obtain a semiconductor-grade film with few defects. The amorphous Si film thus obtained can be converted into a polysilicon film via solid-phase growth or laser annealing. This chapter corresponds to the production steps from Si ink (i, p, n) to amorphous Si film via coating and drying and pyrolysis shown in Fig. 2.2.
KeywordsMolecular force van der Waals interaction Hamaker constant Cauchy plot Polydihydrosilane film
- 2.J. Mahanty, B.W. Ninham, Dispersion Forces (Academic Press, New York, 1976)Google Scholar
- 4.V.A. Parsegian, Physical Chemistry: Enriching Topics in Colloid and Surface Science (Theorex, La Jolla, 1975)Google Scholar
- 5.Handbook of Chemistry and Physics 88th ed. (CRC Press, Boca Raton, 2008)Google Scholar
- 6.The Aldrich Library of FT-IR Spectra (Sigma–Aldrich Co., 1985)Google Scholar
- 7.E.M. Lifshitz, Sov. Phys. Jetp. 2, 73 (1956)Google Scholar
- 9.L.D. Landau, E.M. Lifshitz, Electrodynamics of Continuous Media (Pergamon, Oxford, 1960)Google Scholar
- 13.T. Kogai, H. Yatsuda, Y. Shiokawa, inthe 36th EM Symposium (2007), p. 49Google Scholar
- 15.J.N. Israelachvili, Intermolecular and Surface Forces (Academic Press, New York, 1985)Google Scholar