Date of Award

Spring 1988

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering - (M.S.)

Department

Electrical Engineering

First Advisor

Kenneth Sohn

Second Advisor

Roy H. Cornely

Third Advisor

W. H. Warren Ball

Abstract

Thin films of silicon nitride and amorphous hydrogenated silicon were prepared by radio frequency reactive sputter deposition and their properties optimized for their use as low temperature passivation coatings for optoelectronic devices. The effect of various sputter deposition parameters on the conduction and optical properties were studied. Infrared spectrophotometry and ellipsometry were used to determined the optical properties of the films whereas the electrical properties were determined from current-voltage measurements of MIS capacitors.

Typical parameters of a sputter deposition run for the best Si3N4 films were: base pressure, 1-2x10-6 torr; sputtering pressure, 5 mtorr; nitrogen partial pressure, 16.5%; cathode anode gap, 10 cm; target power density, 1.97watts/cm2; and cathode voltage, 1.0 kvolts. Films of thickness 50-120nm, refractive index 1.94-2.2, and low conductivity (resistivity of 1011 Ω-cm) were obtained. The deposition rate was in the ranged of 5-8 nm/min depending on the sputtering pressure, the appied target power, and the nitrogen partial pressure. It was concluded that the quality of the silicon nitride films is strongly dependent on the total deposition pressure, nitrogen partial pressure, applied target power voltage, and possibly cathode voltage. It was also concluded that the water vapor background was the major factor in increasing the conductivity of the best films to values about three orders of magnitude above those for the best bulk silicon nitride material.

Typical sputtering parameters for depositing a-Si:H films were: base pressure, 1-2x10-6 torr; sputtering pressure, 7 mtorr; hydrogen partial pressure, 5-20%; cathode anode gap, 7.6 cm; r.f. target power density, 1.58-1.82 watts/cm2; cathode voltage, 1.8-1.9 kvolts. Films of thicknesses 78-150 nm, refractive index 3.25 - 4.0, and strong absorption at 2000 cm-1 of infrared spectra were obtained. It was concluded that stoichiometric a -Si:H films can be prepared by reactive sputtering of a silicon target in the environment of argon and hydrogen.

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