Frequency Effects in the Plasma Deposition of Silicon Oxide from TEOS.

We have studied the chemical and physical properties and step coverage of silicon oxide films plasma deposited from TEOS (Tetraethyoyxsilane) at high dilution in helium/oxygen mixtures as a function of discharge frequency (150 kHz and 14 MHz) and O sub 2 flow in a parallel plate reactor operating at low power (~0.1 W/cm sup 2). The typical deposition conditions were 1 torr total pressure, 320C substrate temperature, 1-9% TEOS and 1-80% O sub 2. Films deposited at high frequency with excess oxygen were generally oxygen-rich, unstable and hygroscopic, while films deposited at low frequency were stable to moisture and slightly deficient in oxygen. However an unusual degree of directionality was observed for the profiles of films deposited at high frequency, which would be favorable for coating high aspect ratio featurs. A judicious combination of high and low frequency discharges may improve film properties while maintaining this step profile.