Low-temperature plasma deposition of dielectric coatings from organosilicon precursors

Silicon dioxide coatings have been grown with deposition rates up to 0.7 μm/min and substrate temperatures from 80 to 140 °C in a high-density microwave electron cyclotron resonance discharge. The deposition precursors were tetraethoxysilane (TEOS), hexamethyldisiloxane (HMDSO), and hexamethylcyclotrisiloxane (HMCTSO), with oxygen as an additive gas. The O2/precursor flow ratios ranged from 2:1 to 8:1 and the total gas pressure prior to plasma ignition was 1–10 mTorr. The deposited films for all precursors were hard, colorless, and transparent. Maximum deposition growth rates were 0.25 μm/min for TEOS, 0.65 μm/min for HMDSO, and 0.68 μm/min for HMCTSO; final film thicknesses were 3–10 μm. Deposition growth rates increased with increasing precursor gas flow, increasing input power, and decreasing O2/precursor flow ratio. The coatings exhibit Si–O elemental bonding with a small Si–CH3 component. The oxygen-to-silicon ratios are approximately 2:1 with some incorporated carbon.