Ultrathick Low-Stress Poly-Silicon Film for MEMS Prepared by LPCVD Process

25 μm thick poly-Si with low stress and low stress gradient was deposited using a LPCVD processing. The stress is only -6.5 MPa and the stress gradient is almost negligible, -0.65 MPa/μm. Such low stress characteristic has been enabled by "inhibition layer inserted structure" (ILIS). The inhibition layer initializes crystal growth every 250 nm thick cycle, minimizing the stress gradient. Using 25 μm thick poly-Si, cantilevers were fabricated by DRIE and SiO
2
sacrificial vapor HF etching. A 700 μm long cantilever shows only 0.8 μm downward deflection at the tip, which corresponds to a stress gradient as small as -0.65 MPa/μm. This ultrathick poly-Si will be a new MEMS material, which can compete with epitaxial polysilicon (epi-poly-Si).