Individual Effects of Various Plasma-Related Factors on the High Aspect Ratio Oxide Etching Process at Low-Frequency Bias Power Using an Inductively Coupled Plasma System

초록

In this study, we attempted to investigate individual effects of various plasma-related factors (radical flux, ion flux and ion energy) on high aspect ratio etching characteristics of SiO2 with using the amorphous carbon layer (ACL) mask. Experiments were carried out in an inductively coupled plasma etching system in CF4/C4F8/He gas mixture with both conventional (13.56 MHz) and low-frequency (2 MHz) bias power sources. In order to control changes of internal plasma parameters influencing the etching process, plasma diagnosis by double Langmuir probe and optical emission spectroscopy was applied. In addition, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy delivered the information on properties of etched surface, such as chemical state and profile features. It was found that an increase in the 2 MHz bias power escalates the negative dc bias voltage, but has the negligible effect on radical densities. This accelerated both SiO2 and ACL etching rates, but resulted in no changes in both etching selectivity and profile features. Oppositely, the mixing ratio of fluorocarbon components provided an individual control of CFx/F ratio under the nearly constant ion bombardment intensity. This allowed one to adjust both SiO2 etching rate and SiO2/ACL selectivity, probably through the change in the polymer film thickness.

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