<title>Influence of gas composition and the mask materials on the etch profile of dry-etched structures in silicon</title>

Abstract

In the field of micromachining dry etching processes of silicon are getting more and more important in view of applications. By means of RIE processes it is possible to achieve structures with a very high aspect ratio. This is interesting especially in comparison with the well known but expensive LIGA technique. Unfortunately the anisotropy of the profile in silicon depends strongly on different process conditions. Therefore experiments were carried out with variations in the gas composition, the plasma power and the mask materials. All investigations were made in a 310-type machine from STS. The gas composition was made of SF6, O2 and CHF3. The flow rate of these gases was varied in a wide range. The power of the plasma was hanged from 75W up to 600W at a frequency of 13,56MHz. Aluminium, copper, nickel and chromium were used as masking materials. The width of the patterns was in a range of > 20 micrometers. In contradiction to results known from literature it was not simple to achieve structures with vertical sidewalls. Using aluminium as materials, the sidewalls were rounded independent of the power and the composition of the gas. In some cases a small redeposition was observable at the bottom of the structures. A kind of microgas was observed, too. Copper showed high etch rates in some gas compositions and at defined power conditions. Therefore a complete removing of the masking layer was observed in some cases. Some material was redeposited in the transition zone between the sidewalls and the bottom. The structures showed rounded edges and no vertical sidewalls. A higher redeposition rate was found using nickel as masking material. Unfortunately this redeposition occurred at the bottom of the structures. This is measurable in a decrease of the etch rate. The structures are rounded with a kind of vertical sidewalls. Anisotropic structures with vertical sidewalls were observed with chromium as mask layer. The anisotropic etch behavior with a high aspect ratio was achieved only in a small range of the gas composition and the plasma power.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.