Method for improved photomask alignment after epitaxial process through 90° orientation change

Abstract

A method for alignment to an alignment mark array within a patterned electronic material layer, formed on a substrate employed in a microelectronics fabrication, with improved registration accuracy of a subsequent step-and-repeat photomask pattern. There is first provided a substrate upon which is formed a patterned microelectronics layer containing an alignment mark array. There is then formed over the substrate and patterned layer, covering over the alignment marks, a subsequent layer or layers which may be of opaque material. In order to align properly a patterned photomask for patterning the overlying layer by means of conventional photolithography, the alignment mark array is located by first scanning with a laser light source contained within a step-and-repeat apparatus containing the patterned photomask and detecting the optical radiation signal scattered from the alignment mark array. The accuracy of location may be enhanced by rotating the orientation of the alignment mark array with respect to the direction of scanning with the laser light source by 90 degrees to render the subsequent orientation orthogonal to the first orientation, and then repeating the scanning operation. The altered nature of the back-scattered light signal from the orthogonal scanning direction provides additional information for improving the precision of location and alignment.