Plasmonic lithography with 100 nm overlay accuracy

Abstract

In this paper, we demonstrate an auto accurate alignment method to align mask-substrate in the prototype of plasmonic lithography (PL), which is essential to multilayer nanostructure fabrication with high resolution, low cost, high efficiency, and high throughput. The alignment method for PL is essential to circuit manufacturing and other multilayer applications. We obtained an alignment signal with sensitivity better than 20 nm by using the Moire fringe image. However, the alignment of Moire fringes just cannot guarantee the alignment of the mask and the substrate because the Moire fringe repeats itself when the mask and substrate are offset by a fixed displacement. To eliminate the ambiguity, boxes and the crosses alignment marks are designed beside the grating marks on the substrate and the mask, respectively. A two-step alignment scheme including coarse alignment and fine alignment is explored in the auto alignment system. In the stage of coarse alignment, the edge detection algorithm based on Canny operator is adopted to detect the edges image effectively. In the process of fine alignment, Fourier transform based on Moire fringe image is obtained to improve the alignment accuracy. In addition, experimental results of overlay indicate that PL can obtain sub-100 nm alignment accuracy over an area of 1 cm2 using the proposed two-step alignment scheme. Via the substrate-mask mismatch compensation, better stages and precise environment control, it is expected that much higher overlay accuracy is feasible in the prototype of PL.