Measurement of Alignment Accuracy for Wafer Bonding by Moiré Method

Abstract

A centrosymmetric square grating was developed in this paper. Moire ´fringes produced by the two centrosymmetric square gratings are highly sensitive with the misalignments and misaligned directions. The distance between the mismatched moire fringes are expected to be measured directly by an infrared (IR) microscope without requiring any external reference. Using two pair of the moire ´square gratings, misalignments of bonded wafers are proposed to be measured in the X-Y-axis simultaneously on wafer scale. The measurement accuracy of 0.5 mm in the X-Y axis and 3 Â 10 À4 deg in the -axis is presented as an example, which is sufficient for the alignment accuracy of currently available wafer bonding. Moreover, the measurement accuracy by this moire ´method can be improved to nanometer level if the fabrication errors and IR microscope resolution are allowed.

Moiré-Based Alignment Using Centrosymmetric Grating Marks for High-Precision Wafer Bonding

“…In recent years, we demonstrated a moiré fringe assisted alignment method using centrosymmetric gratings, which exhibited many advantages over conventional moiré gratings [15,16]. For instance, small planar misalignments and misaligned directions can be easily measured without requiring any external reference.…”