High contrast, low noise alignment mark for laser trimming of redundant memory arrays

摘要

An improved alignment mark used by a laser trimming tool to locate fuses in an underlying integrated circuit is formed using conventional processing sequences. The design features high resolution and improved low noise characteristics. The alignment mark is etched in a shallow layer over a metal layer rather than in the metal itself. The edges which are sensed by the scanning alignment laser of the trimming tool have their elevated portions external to the alignment mark. The improved design replaces a prior art design in which the metal mark protruded from a deep area in the site region. Debris in deep areas adjacent to alignment marks etched in metal, is avoided by the improved design. The absence of this debris virtually eliminates noise in the alignment scan thereby greatly reducing alignment errors.