Assessment of the Mask Composed of Sputtered Si Thin Film and Positive Photoresist for Wet Bulk Micromachining of Borofloat Glass

The current study evaluates the effectiveness of the mask consisting of RF-sputtered silicon (Si) thin film in combination with a positive photoresist (AZ1512HS) for wet bulk micromachining of Borofloat glass wafers in 20% HF. The research begins by optimizing the mask via systematically varying the thickness of the Si thin film (200 nm, 400 nm, 600 nm, and 800 nm), keeping the photoresist thickness constant. The sustainability of the mask during glass etching in 20% HF is significantly improved with enhanced Si thin film thickness. Among all masks, the one with an 800 nm-thick Si film and photoresist shows the longest durability and good adhesion to the wafer during etching, yielding an etch depth of$\sim$152 μm in$\sim$65 min of etching, thereby establishing it as the optimal mask. The study further aims to employ the optimized mask to fabricate microchannels with a$\sim$100 μm depth. This successfully facilitates the fabrication of microchannels with the desired depth without any prominent defects on the glass wafer within 45 min of etching. Notably, the present work stands as the first to employ RF-sputtered Si thin films as the mask material for the bulk micromachining of Borofloat glass, whereas most previous studies primarily utilized chemical vapor deposited Si thin films for this purpose.