Mechanical properties of high deposition rate SiO2 films

Abstract

Thick overcoats of SiO2 sputtered at high deposition rates in a radio-frequency (rf) diode system are being considered as alternatives to Al2O3 and photoresist as passivation and planarization layers in the fabrication of thin film magnetic recording heads. The mechanical properties of 7-μm thick SiO2 films sputtered onto silicon substrates were examined as functions of bias voltage and O2 gas flow. A high rate of 3.69 μm/h was achieved in a production system at substrate temperatures below 40 °C. The addition of O2 decreased the deposition rate to 1.65 μm/h. The decrease in deposition rate produced an improvement in the p-etch rate, hardness and stress, but no change in the film density or morphology. The addition of a bias voltage during deposition was found to have the biggest effect on film properties. Bias sputtered films were found to be completely devoid of the columnar structure found in films deposited without bias. The addition of a small bias voltage reduced the film stress from −16×108 dyn/cm2 to −0.4×108 dyn/cm2. However, increasing the bias voltage further caused the film stress to increase to −3.6×108 dyn/cm2 at −160 V bias. This effect can be correlated with the increased Ar content of the films. The p-etch rates of bias sputtered films dropped two orders of magnitude to 10 Å/s. The Knoop hardness increased from 423 without bias to 663 with bias and the film density increased slightly.