Deep wet etching of borosilicate glass using an anodically bonded silicon substrate as mask

Deep wet etching of borosilicate glass using an anodically bonded silicon substrate as mask is presented. Depths of 500 mu m or more can be achieved very easily. The structured glass wafer can be bonded anodically on the same side to another silicon wafer, alter having removed the bonded silicon mask. A lateral underetching 1.5 times larger than the depth was measured. An application using this masking technique is also presented. It consists of using the anodically bonded frame of a resonant silicon structure as a mask for deep glass etching to increase the gap between the glass wall and the resonator, thus yielding a high Q-factor.