Stable nanodepth and nanogram level material removal in electrochemically induced chemical etching of fused quartz

Abstract

The minimum and stability of material removal are critical determinants of the accuracy limitations in precision engineering. This study explores electrochemically induced chemical etching (ECICE) as a method to achieve nanogram-level, low-cost, stress-free, and stable material removal of fused quartz. A modeling analysis of the etching process coupled with testing of the current, potential, and etching pit topography reveals the key factors affecting removal minimum and stability. It is discovered that the removal minimum and stability are determined by both generation and diffusion of the etching active species HF2−. Due to concentration variation of the electrochemically active species NO2−, the generation rate of HF2− is unstable under constant potential processing. In contrast, constant current processing can produce stable HF2− and thus stable etching. Additionally, a large working distance and small insulation layer radius contribute to achieve precision and stable removal through accelerated diffusion of H+ and HF2−, which decreases the generation rate and concentration of HF2−. The processing current is linearly related to the mass removal over such a small nA-level current range. The proposed method achieves precision stable removal with a 40 nm for maximal etching depth and minimum material removal of 6 ± 0.5 ng at the nanogram level. This work can improve the capability for high-precision fused quartz parts without stress, thermal effects, and sediment contamination.