Etch-back in DDSOG process by ultrasonic agitation and application to tunneling gyroscope fabrication

The etch-back of anodic bonded silicon-on-glass wafer using ultrasonic agitation to obtain uniform silicon film and good surface finish in deeply dissolved silicon-on-glass (DDSOG) process has been studied in KOH solution. Etch-back characteristics of p-type (100) 4 inch SOG wafer have been explored under the different ultrasonic power. It has been observed that the characteristics of etch-back such as the etch rate, etch uniformity and surface roughness were evidently improved under 120 W ultrasonic power agitation. The etching uniformity was less than plusmn1% on the whole wafer. And the root-mean-square roughness (R
_rms
) of 20.6 nm was achieved after 360 mum thickness silicon being etched. Some shortcomings of ultrasonic agitation such as damaging membrane and reducing the bonding intensity are observed and how to overcome these disadvantages in DDSOG process is also discussed. Using this technology, a tunneling gyroscope with an out-of-plane, 30 mum thickness beam was successfully fabricated.