Study on the etching mechanism of quartz using dual-frequency (60 MHz/400 KHz) capacitively coupled C4F8/Ar/O2 plasma

The etching characteristics of quartz (SiO2) materials were investigated in a dual-frequency (60 MHz/400 KHz) capacitively coupled C4F8/Ar/O2 plasma environment by adjusting the oxygen flow rate, and the etching behaviors of quartz with smooth and rough surfaces were comparatively studied. The experimental results indicate that as the oxygen flow rate increased from 0 to 30 SCCM, the relative concentration of F radicals gradually increased, resulting in a higher etching rate and surface roughness. When the oxygen flow rate reached 40 SCCM, the relative concentration of F radicals decreased, causing the etching rate and surface roughness to decrease accordingly. The fluorocarbon polymer layer on the smooth quartz surface was thicker, causing a slower etching rate and resulting in the formation of etching pits and spikelike protrusions. In contrast, the thinner fluorocarbon polymer layer on rough quartz, likely due to its higher surface roughness, facilitated enhanced ion bombardment, leading to uneven deposition of the fluorocarbon layer. The higher roughness of rough quartz also allowed F atoms to penetrate surface grooves more easily, resulting in a higher etching rate than that of smooth quartz and the formation of numerous small spherical particles and etching pits. These findings demonstrate that surface roughness has a significant impact on the etching behavior of quartz materials.