In situ infrared measurements of film and gas properties during the plasma deposition of amorphous hydrogenated silicon

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Abstract
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 Å 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 ∼11% within the plasma region for a typical deposition at 250 °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 ∼30 K cooler than the nominal substrate temperature of 250 °C; starting the plasma raises the average temperature another 20 °C.

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