Pulse-modulated plasma-enhanced chemical vapor deposition of SiO2 coatings from octamethylcyclotetrasiloxane

Silicon dioxide coatings can be grown at low substrate temperatures in a pulse-modulated microwave electron cyclotron resonance (ECR) oxygen plasma with octamethylcyclotetrasiloxane (OMCTS) as the organosilicon precursor. The 2.45 GHz microwave power was pulse-modulated with repetition frequencies of 20 Hz-20 kHz, duty ratios (pulse on-time/pulse period) from 25 to 100%, and peak microwave power from 800 to 2400 W The coatings are SiO2-like with Si:O ratios of approximately 3:4 and carbon percentages of 20-25%. Pulsed plasma deposition significantly lowers the deposition substrate temperature as the peak power and duty ratio decrease. With 1600 W input continuous microwave power, substrate temperatures were 140-150degreesC after 10 min of deposition, while with a 50% pulse duty cycle and 1600 W peak power the temperature decreased to 90degreesC. The coating hardness decreased with pulsed operation compared to continuous operation, unless the average microwave power levels were made equivalent. Deposition growth-rates depended only weakly on the pulse repetition frequency and duty ratio, but increased strongly as the pulse peak power was raised. Pulsed deposition at 800 W peak power and 50% duty ratio gave a growth rate of 0.5-0.6 mum/min for all frequencies between 20 Hz and 20 kHz, increasing to 0.8-0.9 mum/min at 1600 W peak power. (C) 2003 Elsevier B.V. All rights reserved.