Moire Method for Nanoprecision Wafer-to-Wafer Alignment: Theory, Simulation and Application

The two dimensional (2D) moire centrosymmetric grating is developed to assist realization of high-precision wafer-to-wafer alignment and non-destructive measurement of misalignments for wafer bonding. Using these moire patterns the misalignments in the order of +/- 64 nm in X-Y axis can be resolved by a simple IR microscopy (5x objective) images. This value can be further improved to sub-10 nm range if the sub-pixel estimation is performed. For current status, the limit of the minimum resolved misalignment using moire gratings is similar to 0.2 nm according to theoretical analysis. It can be applied for not only the future 3D integration of wafer-scale, but also the fabrication of 3D nanostructures and advanced lithography techniques.