Silicon cryo-etching of deep holes

The cryogenic process is used to drill 400 pm thick silicon wafers. It is first studied on single side masked substrates. Holes of 14 mu m in diameter are 210 mu m deep after 30 min, representing an average etch rate as high as 7 mu m min(-1). This process enables the drilling of holes of 12 mu m in diameter within 1 h 06 min. We investigate the effect of the substrate temperature and show that the process is very sensitive to this parameter. It is the main issue in cryo-etching. We use a recent cryogenic chuck with a good temperature uniformity. This last point was characterized using a new method we developed. It is based on the dependencies of columnar microstructures dimensions on the temperature. We have shown that the maximum temperature variation is less than 2 degrees C on the cryogenic chuck. (c) 2007 Elsevier B.V. All rights reserved.