The alignment method based on substrate profile for multiple exposure

When using a combination of contact lithography and laser interferometric lithography for multi-exposure in separate areas, alignment errors between the mask and the substrate can lead to splicing errors in the photoresist pattern. This can seriously affect the quality of photoresist patterns. In this paper, we propose a substrate profile-based alignment method to mitigate the effect of the alignment error between the mask and the substrate by calibrating the relative displacement between the mask plate and the substrate. We design a brightfield mask that includes one central processing area and four scale mark areas. The scale mark areas consist of alternating normal and serrated lines, with the line spacing determined by the cell spacing of the processing pattern. Before each exposure, the substrate contour is aligned with the mark lines. Before the next exposure, fine alignment is achieved by observing through a microscope and driving a displacement stage to align the substrate contour with different types of mark lines. With this method, both the offset error and displacement error are reduced to less than 1μm, the photoresist pattern is of good quality, and there is no overlap in the exposure area. This method has wide applicability in multiple exposure processes combining contact lithography and laser interference lithography.