SOIウエハによる平面測定用5点法MEMS変位計デバイスの高精度化

抄録

In the 5-point method, the straight profile measurement of one line is performed using the sequential three point method, and the relation between the lines is simultaneously measured by two sensors arranged on the next scan line. Using this relation, straightness measurement results of each line, which is acquired by the three-point method, are connected to obtain a planar shape. In order to realize the on-machine measurement by this principle, the authors have prototyped a 5-point MEMS displacement sensor device for measuring a planar shape with five cantilever displacement sensors in a 20 mm square silicon wafer. Each displacement sensor has a probe of a quadrilateral frustum with a height of 250 μm at the tip of the cantilever and detects the strain generated at the root portion as a resistance value change of the piezo resistor according to the displacement. With bulk silicon wafers, when fabricating a probe by etching, they were difficult to control the thickness of the cantilever after etching and the height of the probe according to the target values. Therefore, the authors adopted the Silicon-on-insulator (SOI) wafer to improve dimensional accuracy by using etching stopped at the SiO2 layer. With the fabrication process adopting the SOI wafer, variations in height of the probe are reduced compared with conventional fabrication process using bulk silicon wafer and the size of the tip of the probe can be controlled independently. Therefore, efficiency of fabrication process using the SOI wafer is confirmed.