Optimization of Poly-SiGe Deposition Processes for Modular MEMS Integration
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Optimization of Poly-SiGe Deposition Processes for Modular MEMS Integration Blake C.-Y. Lin, Tsu-Jae King, and Roger T. Howe1 Dept. of Electrical Engineering and Computer Sciences, Berkeley Sensor and Actuator Center1, University of California at Berkeley, Berkeley, CA 94720, U.S.A. ABSTRACT This paper describes a bi-layer deposition technique to reduce the strain gradient of polycrystalline silicon-germanium (poly-SiGe) thin films without the use of any post-deposition annealing. By adjusting deposition conditions such as temperature, pressure, and/or flow rates of reactants, poly-SiGe films with required low average stresses can be obtained. Using the bi-layer technique, a strain gradient of 1.1×10-5µm-1 (equivalent to 88 mm radius-of-curvature) has been achieved in 3.9 µm-thick poly-SiGe. This strain gradient would cause only 0.055 µm tip deflection for a 100 µm-long cantilever. The thermal budget was ~10 hours at 425°C, and no post-deposition annealing was required. The bi-layer film also exhibits low compressive average stress (-36 MPa) and low resistivity (0.55 mΩ-cm).
INTRODUCTION The monolithic integration of MEMS devices with driving and controlling electronics is advantageous for improving system performance and lowering cost. Polycrystalline silicongermanium (poly-SixGe1-x, where 0
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