Study of particulate formation and its control by a radio frequency power modulation in the reactive ion etching process of SiO2 with CF4/H2 plasma

Abstract

Particulate formation in the reactive ion etching process of SiO2 with a CF4/H2 plasma was studied with the laser light scattering (LLS) method. The LLS onset time decreases drastically as the hydrogen percentage increases which indicates that the particulate formation was stimulated by the increase of the unsaturated fluorocarbon species as a result of the hydrogen addition. The onset time was also dependent on the substrate material. The measured onset time with a Si wafer was shorter than that with a SiO2 wafer. The onset time decreases very rapidly with the increase of the radio frequency (rf) power. A decrease of the LLS peak intensity was observed with the square wave modulation process of rf power. The change of the etch rate and the LLS peak intensity according to the change of the duty ratio shows that the optimal process condition, which satisfies high selectivity, high etch rate, and low particulate growth level, can be obtained with the rf modulation method. In the rf modulation process, both an increase in the off period and a decrease in the on period resulted in a decrease of the LLS signal in the particulate trap. It was observed that a change in the off period has a more pronounced effect on the change of the LLS signal intensity.