Growth of Polycrystalline Silicon Films: Grain Size

Transmission electron microscopy has been used to study the structure of polycrystalline films grown on silicon nitride and silicon dioxide substrates by chemical vapor deposition from silane gas. The effects of substrate temperature, type of carrier gas (nitrogen or hydrogen), and gas flow rate were examined. For substrate temperatures of 720°(993°and above, the films were polycrystalline, and under certain conditions a uniform grain size of ca . 30 nm was obtained. At the highest temperatures ( ca . 1040°–1100°K), the films were discontinuous and showed also a type of secondary structure. Results obtained by field emission microscopy have been used to show how incident flux and surface diffusion coefficient may affect grain size in polycrystalline films: it is likely that the observed noncrystalline/polycrystalline transition is affected by recrystallization, decrease in density of preferred sites for nucleation, and change in critical nucleus size.