Defect Avoidance for Extreme Ultraviolet Mask Defects using Intentional Pattern Deformation
Extreme ultraviolet (EUV) lithography has been adopted as the next generation lithography solution to sub 10nm technology node with many companies claiming to be ready for production by late 2018. Despite the technology’s maturity for production, EUV lithography still faces a number of challenges and mask blank defect is a major challenge.
Defect avoidance method has been proposed to allow the mask defects to be tolerated by hiding them under the absorber patterns. By moving the design pattern relative to the defects’ positions, more defects can be mitigated with the given absorber pattern. Past works have demonstrated usefulness of some degrees of freedom, however, pattern deformation has not been a subject of study. Hence, this thesis explores the extended benefits of utilizing pattern deformation, including linear asymmetric magnification and second-order deformation, by using new proposed method based on constraint programming.
In the first part of the thesis, we propose a constraint programming based method that can explore pattern shift, small angle rotation, and deformation for defect avoidance. We model the degrees of freedom as a displacement in relative defect location to the absorber, then construct a constraint programming model that takes inputs of defect location, prohibited regions, and ranges of allowed degree of freedom. The framework returns the maximum number of mitigated defects and corresponding degrees of freedom values.
In the second part of the thesis, we utilized this proposed method to explore the benefit of pattern deformation. We intentionally deform the absorber pattern on the mask to allow for maximum defect avoidance, then this deformation is reversed during its printing on to the silicon wafer through scanner operations. The types of deformation explored in this thesis are linear asymmetric magnification (absorber patterns are magnified to a different x and y value) and second-order deformation where deformation is calculated as a polynomial function of the location on the pattern.