In some manufacturing applications the alignment of fine structures formed on the surface of a part such as micro-scribed patterns on solar panels can be critical to the panel performance. Variations in pattern uniformity may degrade the efficiency of the solar panel if the pattern deviates significantly from designed parameters. This paper will explore the use of moire patterns to interpret the angular alignment of such structures on 3 dimensional non-planar shapes. The moire interferometry pattern creates a beat between the scribed pattern and a reference pattern that is a function of both the shape of the part as well as the shape of the scribed pattern. Both the part shape variations and the patterns of interest are typically much smaller than can be seen visually. Similar challenges exist when inspecting specular models or testing low quality optics. The moire effect allows small displacements to be measured from patterns that are well below the resolution of the camera systems that are used to view the patterns. Issues such as the separation of the shape of the part from the alignment of the fine structure as well as resolution and robustness of the technique will be explored in this paper.

Moire interferometry patterns for rotational alignment of structures

The relative position of wafer and mask can be calculated by information of Moire fringe during alignment, a maskless
lithography alignment method based on circular gratings Moire fringes phase-shifting technique is proposed in this paper.
Circular grating Moire fringes have characteristics of measuring simultaneously angular displacement and line
displacement. Location information of wafer in alignment can be real-time reflected in spatial phase of Moire fringes. A
digital micromirror device controlled by a computer is used to generate phase-shifting grating labels, and phase-shifting
Moire fringes will be formed by superposition of phase-shifting grating labels with grating label on the wafer. The
position information of wafer can be abstained by phase analysis using Fourier transform method combined with
phase-shifting technique，and gives feedback to the displacement stage to realize alignment. The theory basis of this
method is emphatically introduced. Also, application of this method in maskless lithography alignment is analyzed in
detail. Simulation results show that this method is high in accuracy, simple in operation and simple in algorithm. It
provides a feasible method for lithography alignment technique.

Jungshen Yu

Papers

Maskless lithography alignment method based on phase-shifting Moiré fringes technique