Controlling phase induced CD non-uniformity effects of PSM photo-masks

Abstract

Abstract Aggressive line width and other features of interest in advanced-technology node desi gns are achieved by using pattern-related resolution enhancement techniques (RET) coupled with mask transmission effects. Mask transmission effects, such as phase sh ift, are controlled by physical parameters, including mask blank material characteristics and mask archit ecture. In the case of advanced phase shif t masks, the uniformity of transmitted phase, affected by both material properties and thickness, can become a dominant factor in achieving the final wafer CD targets. While traditional mask inspection tools are capable of detecting geometrical variation, detecting phase non-uniformity effects requires complementary, slow analytical tools. AMAT’s IntenCD TM is a novel application for advanced PSM masks which can be used for CD variation control in mask qualification. IntenCD captures mask CD variations in the aerial image regardless of the geometrical or physical aspect of its origin, producing a high-definition CDU map of the reticle. In this paper, we focus on a case study encountered at MP Mask where a PSM mask was sent to the fab to confirm large CD variations on a printed wafer due to mask etching process issues. Conventional defect inspection was not capable of de tecting this excursion. The effect was clearly related to phase layer thickness as verified using an Atomic Force Microscope (AFM) tool. We show how the novel IntenCD application integrated into the aerial image mask inspection tool enables accurate prediction of CD variation in the aerial image due to mask phase errors. Keywords: Mask, Phase Monitoring, IntenCD