Angular dependence of SiO2 etch rate at various bias voltages in a high density CHF3 plasma

Abstract

The dependence of the SiO2 etch rate on the angle of ions incident on the substrate surface was studied over a bias voltage range from −20 to −600 V in a high-density CHF3 plasma using a Faraday cage to control the ion incident angle. The effect of the bottom plane on the sidewall etching was also examined. Differences in the characteristics of the etch rate as a function of the ion angle were observed for different bias voltage regions. When the absolute value of the bias voltage was smaller than 200 V, the normalized etch rate (NER) defined as the etch rate normalized by the rate on the horizontal surface, changed following a cosine curve with respect to the ion incident angle, defined as the angle between the ion direction and the normal of the substrate surface. When the magnitude of the bias voltage was larger than 200 V, the NER was deviated to higher values from those given by a cosine curve at ion angles between 30° and 70°, and then drastically decreased at angles higher than 70° until a net deposition was observed at angles near 90°. The characteristic etch-rate patterns at ion angles below 70° were determined by the ion energy transferred to the surface, which affected the SiO2 etch rate and, simultaneously, the rate of removal of a fluorocarbon polymer film formed on the substrate surface. At high ion angles, particles emitted from the bottom plane contributed to polymer formation on and affected the etching characteristics of the substrate.