Etching of micro-channels in fused quartz for novel device applications

Abstract

Glass and fused-quartz are commonly used in microfluidic and optical sensor devices due to their chemical inertness and optical transparency. This study focuses on the etching of glass and fused-quartz using chemical etching and electrochemical discharge machining (ECDM) techniques. The aim is to compare their effectiveness and identify the most suitable technique for micro-channel formation. Chemical etching with hydrofluoric acid /Buffered hydrofluoric acid solution is commonly used for deep etching in silicon dioxide, but becomes challenging for long etching periods beyond 100 µm depth. There are primarily two problems: a) the integrity of the mask used for defining micro-channels; b) undercut below the mask edges. These two problems seriously limit the chemical etching process beyond 100 µm depth. A mask made of evaporated Au/Cr has been found effective in protecting borosilicate-glass during etching to a depth of 148 µm. However, etching of fused-quartz is much slower than borosilicate-glass while the mask integrity remains the same. Hence obtaining micro-channels beyond 100 µm depth is extremely challenging in fused-quartz. This study compares our results of chemical etching and ECDM of fused-quartz, concluding that electrochemical discharge machining is the effective and reliable technique for micro-channel formation on fused-quartz. The results showed a significant enhancement in surface quality as proven by UV–vis transmission data obtained after well-optimized BHF treatment on ECDM samples. Specifically, this treatment involved subjecting ECDM etched fused-quartz samples to a 1:1 BHF treatment for duration of 5 min. Following this optimal BHF treatment, the UV–vis transmission data showed an increase from 36% to 44% thereby meaning the surface roughness caused by ECDM has been smoothened during 5 min 1:1 BHF treatment. These findings provide valuable insights into the etching processes, masking materials, and techniques for micro-channel fabrication, with potential applications in microfluidics and optical sensing devices.