<title>Strong phase shifter mask application to 0.25-um and 0.35-um technologies</title>

Abstract

Subhalf micron lithography suffers severely from optical proximity correction problem. Although the feature sizes are the same on the mask, as the pitch changes (different packing density), the critical dimension (CD) on wafers will change as well. Therefore, different packing densities of line and space will require different exposure energies to resolve individual patterns to their nominal width. This optical proximity effect is difficult to be corrected effectively and drastically reduces the focus process latitudes. Strong phase shifter mask includes sized rim and chromeless shifters and it can compensate for optical proximity correction without sacrificing defocus process latitude. Strong phase shifter mask, applied on DUV lithography (NA equals 0.53) to pattern 0.25 micrometers line widths with various pitch sizes, can deliver a depth of focus of 1.50 micrometers . If a binary mask is used to print 0.25 micrometers of equal line and space pattern, the depth of focus is reduced to 0.80 micrometers . The focus latitude can thus be improved by almost 100% with strong phase shifter mask. Similarly, strong phase shifter mask, applied on I-line lithography (NA equals 0.54) to pattern 0.30 micrometers of line and space with various pitch sizes, can produce 1.20 micrometers of depth of focus. Using the same I-line lithography process with a binary mask, 0.45 micrometers of equal line and space patterns can be printed with 1.10 micrometers depth of focus with no 0.30 micrometers features resolved. The experimental results of strong phase shifter mask applicable to both 0.25 micrometers and 0.35 micrometers technology will be described in detail.