Scatterometry based CD and Profile Metrology of Chrome-less masks using Optical Digital Profilometry

Control of line width and profile is gaining more importance in photomask processes as the industry moves toward 45nm node and beyond. In this paper we report scatterometer measurements of CD and profile data from chrome-less mask profile processed using Intel's 65nm and 45nm node technology. As opposed to the highly charging nature of chrome-less plate during CD SEM measurements, scatterometry provides a non-charging optical alternative to measure critical CDs. As for trench depth measurement, scatterometry has big advantage over AFM with its much higher throughput (about 5 seconds vs. >2min). Since quartz plate is very transmittive to lights, we use eliipsometer-based scatterometry instead of conventional reflective-photometer based one. Parameters characterized in this study include line/space CD, contact CD, and trench depth. Correlation to top-down CD-SEM, cross-sectional SEM, and AFM is reported. Line CD uniformity reduction is more than 30% compared to that from CDSEM, due to averaging effect of scatterometry as well less lack of charging during measurements. Depth bias to AFM was around 3nm in both DCCD and FCCD height measurements we performed. The data show that Scatterometry provides a nondestructive way to monitor basic etch profile combined with relatively little time loss from measurement step.