AVS 46th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThM

Paper PS-ThM3
An In Situ Study of Plasma Deposition of Hydrogenated Amorphous Silicon Using Multiple Total Internal Reflection Infrared Spectroscopy

Thursday, October 28, 1999, 9:00 am, Room 609

Session: Plasma-Surface Interactions II
Presenter: D.C. Marra, University of California, Santa Barbara
Authors: D.C. Marra, University of California, Santa Barbara
W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
B.F. Hanyaloglu, University of California, Santa Barbara
E.S. Aydil, University of California, Santa Barbara
Correspondent: Click to Email
Multiple total internal reflection Fourier transform infrared spectroscopy (MTIR-FTIR) was used to study plasma enhanced chemical vapor deposition of hydrogenated amorphous silicon in situ and in real time. Several methods using MTIR infrared spectroscopy are combined to study the hydrogen bonding on a-Si:H surfaces as well as the spatial distributions of hydrides in the bulk film. A new technique for identifying surface adsorbates on plasma deposited films combines the sensitivity of in situ attenuated total reflection FTIR with Ar ion assisted desorption of surface species. The dependence of the silicon hydride coverage on the substrate temperature between 40 and 370@degree@C as a function of discharge power and pressure is investigated. As expected, fewer higher hydrides exist on the surface at elevated deposition temperatures. However, this observation is not universal and depends strongly on the discharge pressure and the power. In fact, the temperature dependence of the surface hydrides is less critical to the coverage than the ion bombardment. A careful study of the effect of Ar ion bombardment on a-Si:H surfaces and near surfaces has enabled experimental observation of isolated H at Si-Si bond center sites. Hydrogens at bond center sites appear to be created during deposition and are metastable. During the first 30 minutes after deposition, Si-H-Si bonds are broken and at least some of these H form more stable SiH, SiH@sub 2@and SiH@sub 3@ bonds either in the film and/or on the surface. Hydrogen concentration distribution and bonding as a function of depth in plasma deposited a-Si:H films were also studied using MTIR-FTIR in conjunction with in situ spectroscopic ellipsometry. Immediately below a hydrogen rich surface layer there is a few hundred Angstrom thick subsurface region that is depleted in H compared to the bulk film. Ion bombardment is shown to be responsible for this hydrogen-depleted layer.