SEM metrology for advanced lithographies

For many years, lithographic resolution has been the main obstacle for keeping the pace of transistor densification to meet Moore's Law. The industry standard lithographic wavelength has evolved many times, from G-line to I-line, deep ultraviolet (DUV) based on KrF, and 193nm based on ArF. At each of these steps, new photoresist materials have been used. For the 45nm node and beyond, new lithography techniques are being considered, including immersion ArF lithography and extreme ultraviolet (EUV) lithography. As in the past, these techniques will use new types of photoresists with the capability of printing 45nm node (and beyond) feature widths and pitches. This paper will show results of an evaluation of the critical dimension-scanning electron microscopy (CD-SEM)-based metrology capabilities and limitations for the 193nm immersion and EUV lithography techniques that are suggested in the International Technology Roadmap for Semiconductors. In this study, we will print wafers with these emerging technologies and evaluate the performance of SEM-based metrology on these features. We will conclude with preliminary findings on the readiness of SEM metrology for these new challenges.