AVS 45th International Symposium
    Plasma Science and Technology Division Wednesday Sessions
       Session PS-WeA

Paper PS-WeA3
Atomistic Simulation of Plasma Enhanced Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films

Wednesday, November 4, 1998, 2:40 pm, Room 318/319/320

Session: Plasma-Surface Interactions I
Presenter: S. Ramalingam, University of California, Santa Barbara
Authors: S. Ramalingam, University of California, Santa Barbara
D. Maroudas, University of California, Santa Barbara
E.S. Aydil, University of California, Santa Barbara
Correspondent: Click to Email
Hydrogenated amorphous Si (a-Si:H) and microcrystalline Si grown by plasma deposition through SiH@sub 4@ containing discharges are widely used in solar cells and thin film transistors for flat panel displays. Developing deposition strategies for improving film quality requires a better fundamental understanding of the radical-surface interaction mechanisms. Atomic-scale computer simulations of the deposition process allow monitoring of the events that occur on the surface on a microscopic scale and help elucidate reaction mechanisms that lead to film deposition, defect formation and H incorporation. We present a systematic atomic scale analysis of the interactions of SiH@sub x@ (1@<=@x@<=@) radicals with pristine and H-terminated Si(001)-(2x1) surfaces as well as a-Si:H surfaces with varying H coverage. Hydrogen coverage of the surface is the key factor that controls both the surface reaction mechanism and the reaction probability. The radicals are most reactive when they impinge on pristine c-Si surfaces or surfaces of a-Si:H films with low H concentration, which have high density of Si dangling bonds. In contrast, they are less reactive on H-terminated c-Si and on a-Si:H films with high H coverage. Deposition of a-Si:H from SiH@sub 3@ radicals has also been simulated by repeatedly impinging SiH@sub 3@ radicals onto Si (001)-(2x1) surfaces. The key reactions that occur on the surface during the deposition can be grouped into three classes: (i) SiH@sub 3@ adsorption, (ii) H abstraction, and (iii) disilane formation. We have observed that the dominant mechanism of H removal from the surface is through abstraction by SiH@sub 3@ radicals, which return subsequently to the gas phase in the form of silane and leave behind a dangling bond. The dangling bond created upon H abstraction becomes an adsorption site for the SiH@sub 3@ radicals impinging at this location and the film grows by repeated abstraction and adsorption events which bring Si to surface and remove H.