Interferometry of double-sided polished wafer and error analysis

An interferometric measurement method is proposed to measure the Total Thickness Variation (TTV) and the Bow and Warp in the deformation of a double-sided polished wafer. Two phase-shifting Fizeau interferometers with reference mirrors are used to measure the topography of the front and back surfaces of the wafer simultaneously, and the measured topography of the front and back surfaces of the wafer are combined with the cavity topography of the two interferometers when the wafer is not placed to obtain the surface parameters of the double-sided polished wafer which are not affected by the reference mirror error. In the combined operation, the mapping error is introduced because the two reference mirrors are not precisely aligned, which affects the measurement results of the relevant parameters. To this end, before wafer measurement, the three-point positioning device is fixed between the two reference mirrors, and the position of the two reference mirrors is continuously adjusted based on the three-point circular theorem, which can make the mapping error extremely small, thereby reducing the influence of the mapping error on the measurement results. The experimental results show that the mapping errors of 50 mm wafer transverse and longitudinal directions are 21.592 & mu;m and 37.480 & mu;m, respectively, and the TTV, Bow and Warp are 0.198 & mu;m, -0.326 & mu;m and 1.423 & mu;m, respectively. In order to further verify the effectiveness of the adjustment method, a single interferometer was used to flip the wafer for measurement, and the TTV, Bow and Warp of wafer are 0.208 & mu;m, -0.326 & mu;m and 1.415 & mu;m, respectively. The proposed interferometric method can be easily and quickly used for the measurement of large quantities of large-sized wafers after adjusting the position of two reference mirrors, which improves wafer inspection efficiency. At the same time, it has a superior measurement accuracy.