The effect of substrate temperature and bias on the stress, chemical etch rate, and microstructure of high deposition rate sputtered SiO2 films

Abstract

The dependence of the stress, p-etch rate, and microstructure on the substrate temperature and bias voltage were examined for 4-μm thick SiO2 films sputtered at high rates. At a substrate temperature of 111 °C, or less, the stress was a complex function of the bias voltage. High values of the stress and p-etch rate were found when films were sputtered with the substrate grounded. Minimums in the stress and p-etch rates were observed with the application of a substrate bias of −20 V. These correlated well with the transition of the microstructure from one with large fibrous columns separated by regions of open porosity to a dense film with few voids and no distinguishable columns. With more negative values of bias, the stress increased due to incorporation of Ar atoms in the SiO2 and, at voltages more negative than −80 V, to atomic peening of the film by incident Ar ions. At a deposition temperature of 322 °C, the stress was independent of the bias and could be completely accounted for by the difference in thermal expansion coefficients of the substrate and the film. A more dense microstructure was observed for high temperature films even without the application of a bias voltage. The lowest p-etch rates, approximately 3.4 Å/s were obtained at high temperature, and with a bias voltage of −20 V.