Kinetics of silicon film growth and the deposition phase diagram

Abstract Three different surface microstructural transitions have been identified versus accumulated bulk layer thickness d b during the growth of hydrogenated silicon (Si:H) films by plasma enhanced chemical vapor deposition (PECVD): (i) an amorphous growth regime roughening transition, (ii) an amorphous-to-(mixed-phase amorphous + microcrystalline) roughening transition, and (iii) a (mixed-phase)-to-(single-phase) microcrystalline smoothening transition. These transitions are observed using real time spectroscopic ellipsometry, and the results can be summarized succinctly using deposition phase diagrams wherein the transition thicknesses of interest are plotted versus the H 2 -dilution ratio R =[H 2 ]/[SiH 4 ]. For Si:H p–i–n solar cells, a greater understanding of processing-property relations and optimization procedures is possible by correlating cell performance with the corresponding phase diagram for the intrinsic (i) layer obtained, using a relevant substrate material. Here we review previous key results, and as an example present a comparison of phase diagrams for Si:H PECVD obtained at two plasma excitation frequencies, 13.56 MHz (rf) and 60 MHz (vhf).