IMPROVEMENT OF THE POROUS SILICON SACRIFICIAL-LAYER ETCHING FOR MICROMACHINING APPLICATIONS

Using porous silicon (PS) as a sacrificial layer, freestanding structu res with a large distance to the bulk can be obtained. The very high s pecific surface area of PS allows its removal using dilute alkaline so lutions. However, a critical equilibrium between a non-violent and a c omplete etch reaction is necessary. A solution to this problem is a mu lti-step etching process using solutions of different concentrations. To avoid this disadvantage, different technological conditions are stu died in order ro optimize the removal of the PS by using a one-step pr ocess with a 0.1% KOH solution. The effects of adding ethanol, ultraso nic stirring and polarization during the etching process are evaluated . Optimization of the etching procedure allows good-quality freestandi ng polysilicon structures featuring a smooth substrate surface to be o btained. (C) 1997 Elsevier Science S.A.