Novel Processes for Modular Integration of Silicon-Germanium MEMS with CMOS Electronics

Equipment control, process development and materials characterization for LPCVD poly-SiGe for MEMS applications are investigated in this work. In order to develop a repeatable process in an academic laboratory, equipment monitoring methods are implemented and new process gases are explored. Approaches to reduce the strain gradient of LPCVD poly-SiGe are investigated. Correlation between the strain gradient and film microstructure is found using stress-depth profiling and cross-sectional TEM analysis. The effects of film deposition conditions on film microstructure are also determined. Boron-doped poly-SiGe films generally have vertically oriented grains -- either conical or columnar in shape. Films with conical grain structure have large strain gradient due to highly compressive stress in the lower (initially deposited) region of the film. Films with small strain gradient usually have columnar grain structure with low defect density. It is also found that the uniformity of films deposited in a batch LPCVD reactor can be improved by increasing the deposited film thickness, using a proper seeding layer, and/or depositing the film in multiple layers. the effects of post-deposition annealing and argon implantation on mechanical properties are also studied. While the as-deposited film can achieve the desired mechanical properties, post-deposition processing at elevated temperatures can degrade the strain gradient. The original document contains color images.