Wet bulk micromachining of Borofloat glass towards the fabrication of through‐holes in different concentrations of hydrofluoric acid

Abstract Glass through‐holes are essential for wafer‐level packaging of microelectromechanical systems (MEMS) devices and are often fabricated through wet bulk micromachining. For efficient through‐hole fabrication, there is a need for the development of cost‐effective masking layers and faster etching processes. This work presents an economical method for fabricating through‐holes of various dimensions in 500 µm‐thick Borofloat glass wafers with a relatively high etch rate using wet bulk micromachining. The process employs wet isotropic etching in 25% and 30% hydrofluoric acid (HF), utilizing a masking layer of sputter‐deposited Cr thin film and spin‐coated positive photoresist. The masking layer revealed strong adhesion to the wafers during the entire etching process, enabling the fabrication of through‐holes with sharp edges. Additionally, the masking layer delivered excellent resistance to both HF concentrations, establishing effective protection, and subsequently resulting in minimal defects on the wafer surface. Through‐holes are fabricated in 190 min using 25% HF and in 150 min using 30% HF, with the latter facilitating comparatively faster fabrication due to its higher HF concentration. The present work demonstrates the best output in terms of faster etching time for through‐holes fabrication in glass wafers using a Cr thin film combined with a photoresist as a masking layer.