Patent ID: 7001697

Claim:
A method of manufacturing a photomask, the method comprising: providing a photomask that includes a substrate having a front side and a rear side, and a main pattern located at said front side of the substrate; transferring an image of the main pattern to a wafer by directing illumination onto the wafer through said photomask in an exposure process, and using the image to produce a pattern on the wafer formed of elements having critical dimensions; quantifying the critical dimensions to obtain a distribution of values of the critical dimensions on the wafer; comparing the critical dimension values to a reference critical dimension value in order to as certain the differences therebetween; determining, in relation to localities on the photomask, degrees to which the intensity of the illumination used in the exposure process would need to be decreased in order to reduce the differences, respectively, between the critical dimension values and the reference critical dimension value, to thereby obtain a distribution of said degrees in relation to said localities; selecting transparency-adjusting pattern features that, if provided in a set at a rear side of the substrate of the photomask during the exposure process, would change the intensity of the illumination passing through the photomask during the exposure process due to the density of the features in terms of their size and spacing; obtaining a correlation between the densities of the transparency-adjusting pattern features, in terms of their size and spacing, and the changes that the transparency-adjusting pattern features provided at those densities at the rear side of the substrate-would make in the intensity of the illumination directed therethrough during the exposure process; based on said correlation, ascertaining the densities of the transparency-adjusting pattern features that correspond to said distribution of the degrees to which the intensity of the illumination needs to be decreased, to thereby obtain a distribution of-the densities-of the-transparency-adjusting pattern features in relation to said localities; and providing the transparency-adjusting pattern features at the rear side of the substrate in an arrangement corresponding to said distribution of the densities of the transparency-adjusting pattern features.