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Microprobe and molecular beam mass spectrometry in plasma-enhanced chemical vapor deposition
Abstract
Concentrations of stable molecules and of free radicals have been measured from a methane plasma during plasma-enhanced chemical vapor deposition of carbon films. A novel PECVD reactor was designed and constructed with capabilities for both microprobe and molecular-beam mass spectrometric sampling of the gas phase. With the microprobe technique, spatially resolved concentrations of CH$\sb4$, H$\sb2$, C$\sb2$H$\sb2$ and C$\sb2$H$\sb6$ were measured for eight sets of operating conditions. Effects of reactor pressure, inlet gas flowrate and RF power were examined. The concentration profiles exhibited a one-dimensional region in radius in the outer areas of the reactor, away from the gas inlet, due to dominance by steady-state radial diffusion. The stable species concentrations were also measured with molecular-beam mass spectrometry and shown to agree well with the corresponding microprobe measurements. The molecular-beam sampling also allowed detection and concentration estimation of both CH$\sb2$ and CH$\sb3$ radicals impinging on the lower electrode. Films were collected on 3-inch silicon wafers for all sets of operating conditions, and were analyzed for thickness, composition and refractive index. Film growth rates compared well with literature values. The refractive index and IR absorption spectra of the films also indicated that the films were soft and polymer-like; these properties were similar to those from literature studies of carbon deposition on a grounded electrode. In parallel with the experimental work, a method for estimating the rate constants of electron-molecule reactions was developed. Based on Bimolecular Quantum-RRK, this model was shown to predict overall electron-impact-decomposition cross sections of CH$\sb4$ and SiH$\sb4$ to within a factor of three. Also, relative cross-sections for individual radical production channels were shown to agree with literature data on the relative population of CH$\sb3$ and CH$\sb2$ radicals produced by reaction of CH$\sb4$ and 100-eV electrons.
Subject Area
Chemical engineering
Recommended Citation
Pugliese, Roberto Amarando, "Microprobe and molecular beam mass spectrometry in plasma-enhanced chemical vapor deposition" (1993). Doctoral Dissertations Available from Proquest. AAI9316708.
https://scholarworks.umass.edu/dissertations/AAI9316708