Characterization of fluorinated tetra ethyl ortho silicate oxide films deposited in a low pressure plasma enhanced chemical vapor deposition reactor

Abstract

Fluorinated silicon dioxide films were deposited in a commercial plasma enhanced chemical vapor deposition reactor using tetra ethyl ortho silicate (TEOS), oxygen, and C2F6. The depositions were carried out using dual rf frequency power at low pressure, 500–750 mTorr. Film properties were investigated as a function of rf power, pressure, gas flows, and wafer temperature. Fluorine content, refractive index, stress, and deposition rate are among the film properties studied. Special attention was paid to the stability of these properties in air, in boiling water, and after subsequent annealing. The base line TEOS process is unusual in that high compressive stress values can be achieved, up to about 300 MPa. It was thought that this high initial stress would lead to improved stability at higher fluorine concentration. Film stress was found to be quite compressive, even at high fluorine concentration. Good film stability was observed for fluorine concentrations up to 10% (Si–F/Si–O peak ratio). Refractive indices as low as 1.40 were measured. This work demonstrates that a stable, production-quality, fluorinated oxide film can be deposited in this reactor.