From amorphous to microcrystalline silicon: Moving from one to the other by halogenated silicon plasma chemistry

Abstract

Amorphous and microcrystalline silicon thin-films have been deposited on a large variety of substrates including crystalline silicon, Corning glass and polyimide, exploiting SiF4–H2–He radiofrequency (13.56 MHz) plasma-enhanced chemical vapor deposition. Spectroscopic ellipsometry has been mainly applied to investigate the optical and structural characteristics of the deposited films and to investigate the microstructure depending on experimental parameters, such as H2 and He dilution of plasmas, deposition temperature and substrate plasma treatment prior to deposition. Film growth dynamics have also been investigated by analyzing films with different thicknesses. The peculiarities of the SiF4 chemistry involved in heterogeneous processes during film deposition, and responsible for the amorphous to microcrystalline transition are presented. It is demonstrated that the SiF4-H2 chemistry leads to tailoring of film microstructure from amorphous to fully and dense microcrystalline silicon films without any amorphous incubation layer at temperatures as low as 100°C on any substrate, including Corning glass 7059 and polyimide, independently of film thickness. These results and peculiarities of SiF4-based plasmas are discussed within the framework of the literature debate on SiH4 versus SiF4 as silicon precursor.