Hermetical Sealing of Pressure Sensor Diaphragms by CVD of Si_(1-X)Ge_X with Minimized Cavity Deposition

摘要

In this work, the hermeticity of diaphragm structures for later post-CMOS integration is investigated and optimized. The diaphragms were completely made of Si_(1-X)Ge_X, which is a high quality MEMS material that can be deposited at temperatures below 400°C. The hermeticity tests of the diaphragms were performed in a helium atmosphere at 1800 hPa and in a temperature range from 50°C to 100°C. To calculate the diffusion coefficients, the change of diaphragm deflection caused by He-diffusion through the diaphragm is measured optically. In the fabrication process, a variation of the deposition parameters of a CVD Si_(1-X)Ge_X sealing layer on a polycrystalline p~+Si_(1-X)Ge_X diaphragm was investigated regarding the selectivity of the layer growth on different surfaces (p~+Si_(1-X)Ge_X, Si, and SiO_2). An increasing selectivity of the layer growth against Si and SiO_2 was shown, which increases with the GeH_4 ratio in the process gas flow. With a GeH_4 pure gas flow, the best results were observed with the highest selectivity, a minimal diffusion and a minimal intrinsic stress of the Si_(1-X)Ge_X sealing layer.