Degree Type

Dissertation

Date of Award

1992

Degree Name

Doctor of Philosophy

Department

Chemical and Biological Engineering

First Advisor

Glenn L. Schrader

Abstract

Thin films of molybdenum oxides were produced on silicon substrates from Mo(CO)[subscript]6 and O[subscript]2 using both a low pressure and plasma enhanced chemical vapor deposition (LPCVD and PECVD). The substrates were heated using a SiC coated graphite susceptor which was inductively coupled to a 200-450 kHz radio-frequency (RF) generator and using a Macor resistive heater. The process variables investigated were temperature, 250-530°C; pressure, 100-1014 mtorr; Mo(CO)[subscript]6 flow rate, 0.56-6.7 mg/min; O[subscript]2 flow rate, 5-15 sccm; H[subscript]2O flow rate of 0.0-0.53 sccm; and RF current, 22-34 amps;Thermodynamic equilibrium calculations were conducted on the system using a computer program, Solgasmix-PV. The calculations indicated that [alpha]-MoO[subscript]3 was the most stable phase for all deposition conditions. [alpha]-MoO[subscript]3 films formed under LPCVD conditions at temperatures greater than 350°C and pressures of 300 mtorr or more depending upon the reactor geometry and the heater used during deposition. The [alpha]-MoO[subscript]3 films were oriented and had a columnar or platelet structure. At lower temperatures under LPCVD conditions reduced molybdenum oxides, MoO[subscript]2 and Mo[subscript]4O[subscript]11, were produced. A quadratic model was developed of the formation of LPCVD [alpha]-MoO[subscript]3 as a function of temperature and pressure. The film uniformity and composition were strongly influenced by transport processes;At high RF currents, the RF generator created an inductively coupled Ar-O[subscript]2 plasma in the system when using the Macor heater. Films deposited under PECVD conditions were oriented [alpha]-MoO[subscript]3; the PECVD films had lower deposition rates and were produced at lower temperatures than LPCVD [alpha]-MoO[subscript]3 films. The deposits contained little carbon (<1%). A model of the [alpha]-MoO[subscript]3 formation as a function of the process variables was developed using experimental design and regression analysis. The model indicated that the process variables act synergistically on the [alpha]-MoO[subscript]3 formation. The films were characterized using profilometry, x-ray diffraction and x-ray photoelectron, Fourier transform infrared, Auger and laser Raman spectroscopy.

DOI

https://doi.org/10.31274/rtd-180813-12003

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Jeffrey Scott Cross

Language

en

Proquest ID

AAI9311485

File Format

application/pdf

File Size

105 pages

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