Spectroscopic ellipsometry studies on microstructure evolution of a-Si:H to nc-Si:H films by H2 plasma exposure

Abstract

This paper presents the influence of hydrogen plasma treatment on the growth of nano crystalline silicon phase in a-SiH films. Series of hydrogenated amorphous silicon films were prepared by PECVD technique with intermittent hydrogen plasma treatment for 5 min each time followed by silane plasma, keeping the total silane plasma time fixed at 60 min. The evolution of nanocrystalline Si phase due to intermittent hydrogen plasma treatment is studied through Spectroscopic Ellipsometry(SE), Raman and FTIR absorption spectroscopy. Dielectric function obtained from the SE measurements was used to determine the optical constant, thickness and band gap of the films. The hydrogen plasma treated films have less void fraction and higher density. The growth of nanocrystalline phase is enhanced due to etching of weak SiSi bonds and reduction in bonding disorder during hydrogen plasma. Hydrogen plasma treatment results in nc-Si:H films at high deposition rate and low substrate temperature.