Measurement of Surface Shape and Residual Stress of Thin Film Deposited on Large-Size Wafers By Using Fringe Reflectometry and Wavelet Transform

We present a fast and full field measurement system to measure the surface profile and residual stress in single-layer and multilayer thin films deposited on large substrates. The principle of the optical measurement system is based on the combination of the projection fringe reflection method and wavelet transform. This method obtains the 3D surface profile and radius of curvature of the 8-inch silicon wafer before and after the coating to calculate the residual stress in the multilayer coating. MgF2 single layer and SiO2/Ge/SiO2 multilayer thin films were fabricated by dual electron-beam evaporation technique. The three-layer SiO2/Ge/SiO2 thin film with a thickness of 976 nm was deposited on an 8-inch silicon wafer. The results show that the measured curvature radii before and after film deposition were -87.086 m and -165.726 m, respectively. The average residual stress of SiO2/Ge/SiO2 thin-film was 17.3 MPa by using the modified Stoney's formula. This residual stress value is positive, indicating a tensile stress state. The proposed fringe reflection measurement method can quickly measure the surface shape and residual stress of thin films deposited on large-size wafers.