Defect Investigation of the Develop Process on 28nm Contact Mask

Abstract

For 28nm node devices, Photomask feature size has decreased in accordance and been requested strict CD uniformity performance. Considering fan develop mode without distinct develop loading effect would benefit a lot for CD uniformity, it was chosen as baseline process at first. However, one certain defect type occurred on 28nm CT hole mask, and was hard to repair since its deference from normal pattern was limited but its impact would be so sensitive on wafer due to CT mask critical characteristics in high mask error factor (MEF), lower image contrast, or exposure latitude (EL), and reduced common depth of focus (DOF). With defect investigation, we studied puddle develop mode connected with exposure PRC function to achieve acceptable CD uniformity and take advantage of defect free.