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The deposition of SiO2 films from novel alkoxysilane/O2 rf plasmas has been investigated using tetraethoxysilane and the novel alkoxysilanes, triethoxysilane, tetramethoxysilane, and trimethoxysilane. We have demonstrated that high quality SiO2 films can be deposited from each of these alkoxysilanes under similar conditions. For all precursors, film deposition rates decrease with the addition of O2. Using 20:80 alkoxysilane/O2 plasmas, film deposition rate decreases with increasing substrate temperature and plasma power, while the SiO2 film quality increases, as determined by Fourier transform infrared spectroscopy, ellipsometry, and wet etch rates. Substrate temperature appears to be the most influential deposition parameter, significantly affecting both composition and properties of the deposited SiO2 films. Measured apparent activation energies for SiO2 deposition from alkoxysilane/O2 plasmas are negative for all precursors. This suggests an adsorption/desorption-limited deposition mechanism controls film formation in all systems. Additional data for SiO2 films deposited from the halogenated alkoxysilanes triethoxyfluorosilane and triethoxychlorosilane are also presented.

Advanced materials processing involves active control of fabrication and real-time monitoring of the final product. Sensors must be an integral part of the overall material processing system. ITN Energy Systems, Inc. and the Colorado School of Mines have developed a Parallel Detection, Spectroscopic Ellipsometer (PDSE) sensor for in-situ, real-time characterization and process control of multi-layered vapor deposited films. By measuring changes in the polarization state of reflecting light as a function of wavelength (250 to 5000 nm), the PDSE sensor determines the complex reflectance and/or the ellipsometric amplitude and phase. The PDSE provides cost-effective in-line sensing for film process control through detection of critical product variables that directly relate to film performance including: film thickness, optical excitation states, impurity concentrations, conductivity/resistance, intermixing at interfaces, microstructure, surface roughness, void fraction, defects, and grain size. The PDSE sensor is an optical probe with no moving parts that can measure the optical properties of thin films in as little as 3 msec with sensitivity to films less than a monolayer in thickness. We will use this PDSE system to provide real time process control of vapor deposited CuInGaSe2 (CIGS) films on a continuous flexible substrate. Initial results from CIGS films indicate that the PDSE has the sensitivity and accuracy to provide intelligent process control. The remaining challenge is to develop interpretive algorithms; the amount and quality of information required will determine their complexity. In addition, with the inception of in-situ, real-time monitoring, we hope to enable minimal data analysis approaches1 that provide extremely useful information with minimum interpretive algorithm development.

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