Study of Poly-SiGe Structural Properties for Modularly Integrated MEMS

Abstract

Approaches to improve the strain gradient of low-temperaturedeposited LPCVD polycrystalline silicon-germanium (poly-SiGe) for MEMS inertial sensor applications are investigated. Correlation between the strain gradient and film microstructure is found, and the effects of film deposition conditions on film microstructure are studied. Boron-doped poly-SiGe films generally have vertically oriented grains, either conical or columnar in shape. Films with small strain gradient usually have columnar grain structure with low defect density. The best strain gradient achieved is 1.1×10-6 µm-1 for a 3.5 µm thick film deposited at 410°C, with a worst-case variation across a 150 mm-diameter wafer of 1.6×10-5 µm-1. 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 muliple layers. Post-deposition annealing and argon implantation can be used to tune the strain gradient so that lower strain gradient can be achieved with proper deposition and annealing/implantation combinations.