A study on chromium thin film with positive photoresist as a masking layer towards the wet bulk micromachining of Borofloat glass

Abstract

Bulk micromachining is commonly used to fabricate microstructures such as deep cavities, through-holes, and microchannels in glass wafers, which have diverse applications in the areas of science and technology. The methods for glass bulk micromachining include mechanical, dry, and wet etching; among them, wet etching is widely used due to its multifaceted advantages. Masking layer plays an eminent role in wet etching. In the current study, Cr thin film combined with positive photoresist (AZ1512HS) is investigated as the masking layer to develop deep cavities in Borofloat glass wafers via wet etching route. Initially, DC magnetron sputtered Cr thin film is deposited at room temperature, 200 °C, and 400 °C, respectively, on three different glass wafers, followed by spin coating of photoresist on it. Photolithography process is used for patterning, and then selective etching of Cr is performed. Thereafter, wet etching of glass wafers is executed in 10% hydrofluoric acid (HF) solution. This work shows that the sustainability of the masking layer is highly dependent on the deposition temperature of Cr thin film, and the sustainability increases with the increase in the deposition temperature. The high temperature (400 °C) deposited Cr thin film along with photoresist exhibits superior sustainability as a masking layer, and it relatively provides a longer etch time of 380 min, excellent etch depth of  ~  245 µm with negligible surface defects and well-defined structures on glass wafer when etched in 10% HF solution.