Visibility enhancement of first order alignment marks.

摘要

A method of enhancing first order alignment marks (AM1) formed in the respective layers (12) of a processed semiconductor wafer in which critical masking steps are carried out. After a given mark is formed, it is tested for visual contrast. If the contrast is insufficient to provide adequate alignment, a block mask (BM) is formed on the critical mask. The block mask exposes all of the alignment target areas and protects the product regions of the wafer, and the critical mask only exposes the mark to be enhanced. The mark is then etched for a time period which is a function of the measured visual contrast.