In-situ characterization of charge-carrier kinetics in multilayers during plasma growth and etching of amorphous silicon films

Abstract

Transient Reflected Microwave Conductivity (TRMC) measurements after laser pulse excitation have been performed during processing of thin film semiconductors. In particular PECVD-deposition of hydrogenated amorphous silicon (a-Si:H) and etching of the a-Si:H films in a hydrogen plasma has been studied by this non-invasive technique for the determination of excess charge carrier concentrations, mobilities, and lifetimes. During the growth of two intrinsic amorphous silicon layers deposited under different plasma conditions on top of each other, the comparison of the photoconducting properties of these layers already during deposition is shown and compared to conventional ex-situ characterization. By analyzing the interference fringes seen in the TRMC-amplitude during amorphous silicon growth and etching on crystalline silicon wafers covered by a dielectric layer an in-situ thickness control of the a-Si:H film has been achieved. Interface characterization in double layer structures with amorphous silicon deposited on top of crystalline silicon gave an estimation of the interface recombination rate and its change during the a-Si:H growth. An evaluation of the plasma induced damage in the initial stage of the silane plasma process is demonstrated. It has been found that already a very thin layer of a-Si:H inhibits the further defect creation at the surface of the crystalline silicon.