Experimental Study On Processing Resigual Stresses In The Film And Base-wafer Of MEMS

The processing level is a core question which confines the design, manufacture and application of the most MEMS/NEMS today. Residual stress introduced during processing affect both the quality and the dependability of MEMS/NEMS greatly. It is necessary, and difficult as well, to detect the residual stress of MEMS induced by each preparing process through some nondestructive methods with high accuracy and high resolution.In the thesis, the conception and equipment of Micro-Raman spectroscopy, X-ray diffraction and neutron diffraction were introduced briefly. And then, the principles and advantages on the microscopic measurement of residual stresses by applying these three methods are discussed. Furthermore, since it is a hard work to achieve information, such as frequency shift, intensity and peak width, from thousands of spectra by treating them one by one, a software is developed to get those information from the spectra automatically, which makes the data processing of Raman spectrum efficiently and precisely.As the main part of this work, the processing residual stress inside the films and their base-wafer of the bi-material cantilever, used in UIRFPA (uncooled infrared focal plane arrays), is investigated by applying Micro-Raman Spectroscopy and X-ray Diffraction. The experimental results show that the films on both sides of the base wafer are introduced residual stresses,nearly to GPa, during the preparing process of bi-material film structures. These residual stresses are mainly composed by the thermal stresses, due to the difference of thermal expansion coefficient between the films and their base wafer, and the intrinsic stress induced during Si converting to SiO2. In macro scale, the stresses distribute linearly in the substrate and obey the plane hypothesis of elastic mechanics. However, in the meso/micro scale, in the vicinity of Si-SiO2 interface, the distributions of stress, strain and even material component change in gradient, not linearly, which do not follow the plane hypothesis.The experiments and analyses in this work indicate that the residual stresses of MEMS materials and structures introduced during each process scheduling can be detected precisely by applying Micro-Raman Spectroscopy and coupling with X-ray diffraction.