Stress in thin films is one of the mayor technological problems of silicon micromachining. Therefore stress reduction by a compensation method increases the technological use of a material. Three methods to obtain stress free films are investigated:
1. Stress in SiO2 and Si3N4 can be compensated by ion implantation.
2. Sandwich layers of SiO2 and Si3N4 can be made internally stress compensated by variation of the thickness ratio.
3. Polysilicon is stress reduced by appropriate doping and annealing.
The film stress is evaluated by the measurement of the bending of the substrate. Examples of processed membranes, bridges and cantilevers made of stress compensated films are given.