Mask errors impact on grayscale lithography patterning

Impact of mask CD errors on microlens and pillar structures fabricated using grayscale lithography technique is studied. CD errors were evaluated from the mask SEM images using contour based metrology. Mask error enhancement factor for grayscale lithography is proposed based on mask (or design) chromium density for given 3D structure to be patterned. Impact of mean-to-target CD mask error and local CD variations on target critical parameters were studied separately. For grayscale lithography, the global mask error enhancement factor calculated to study impact of mask CD errors were found to be non linear and highly dependent on the mask (or layout) chromium density. Surface topography of given grayscale target was found to be highly dependent on the local CD variations. We also found that intentional local CD variation can be used to effectively tune certain target parameters.