抄録
As the increase in the density of the VLSIs, the circuit patterns become smaller. In the lithographic process, patterning accuracy of a tenth part of the minimum feature size is demanded. Therefore, precision alignment between masks and wafer are important. The methods using moire technique were found to give high alignment accuracy. We have realized an automatic mask alignment, using moire signals controlled by a computer, with accuracy of 4nm. In this paper, the moire signals have been calculated by using computer simulation. The laser beam diameter (number of the slits in the gratings) affects the moire signals. We discuss about the influence of the laser beam diameter on the alignment accuracy for an alignment system using moire signals.
