INSITU INFRARED MEASUREMENTS OF FILM AND GAS PROPERTIES DURING THE PLASMA DEPOSITION OF AMORPHOUS HYDROGENATED SILICON

This research has performed preliminary in situ Fourier transform infrared (FTIR) measurements during the plasma deposition of amorphous silicon (a-Si:H).Experiments demonstrate both gas phase and film measurements within a simple SiH4 Plasma reactor using a specially modified FTIR spectrometer. Films are deposited on substrates of either gold (mirror finish) or stainless steel (matte finish). In particular, in situ emission/reflection FTIR of the film yields information about surface temperature, film thickness, and film composition. We have measured surface temperature to +/- 5 K and detected the onset of poor film growth at a thickness of 500-1000 angstrom using the 2080 cm-1 absorption feature. A simple model for the reflectance of a film on a metal is employed to determine the thickness of the films. In situ emission/transmission FTIR of the plasma determines the gas composition and average gas temperature. Measurements show that the silane conversion is approximately 11% within the plasma region for a typical deposition at 250-degrees-C and roughly doubles for a deposition at room temperature. The FTIR spectra show that most of this converted silane reappears as disilane (Si2H6). Before starting the plasma, the silane gas is approximately 30 K cooler than the nominal substrate temperature of 250-degrees-C; starting the plasma raises the average temperature another 20-degrees-C.