Study of masking layer behavior towards bulk micromachining of Borofloat glass

Abstract

In this work, a study of different masking materials for the development of deep grooves in a Borofloat glass wafer using bulk micromachining is presented. Masking layers such as photoresist (AZ1512HS), Chromium (Cr)/photoresist, and Chromium (Cr)/Gold (Au)/photoresist are deposited on the Borofloat glass and investigated in 20% hydrofluoric acid (HF) for isotropic etching. Among all the masking layers, the photoresist layer is not sustainable in the etchant solution and is peeled off immediately due to poor surface imperfections. Metal masking layers with the combination of photoresists are therefore investigated for the formation of deep grooves in the Borofloat glass. Here the metal layers are deposited by DC magnetron sputtering. By utilizing thin masking layers of Cr (30 nm)/Au (200 nm)/photoresist and Cr (250 nm)/photoresist over the glass wafer, a significant etch depth with a good etch rate of 5 µm/min is observed along with good sustainability of the masking layer in the etchant. For a longer duration of the etching time, thin metal masking layers are not sufficient to provide a good barrier to the etchant. Further, an etch depth of greater than 400 µm is achieved using a combination of thicker layers of Cr (250 nm), Au (250 nm and 1000 nm), and photoresist with minimal surface imperfection compared to other thin masking layers. The present study of masking layers paves a new way toward the deep cavities and through holes in the Borofloat glass.