CD error budget analysis in ArF lithography

Abstract

As for CD (Critical Dimension) control, we classified factors of CD variations in each process. We quantified the factors occurred in the devices such as exposure tool, coater/developer and CD-SEM in 193nm lithography. In the coater/developer, influence of PEB (Post Exposure Bake) on CD variation was notably found and made up about 70% of the Track-related factors. This fact indicates that a great importance of PEB in 193nm process. Regarding the exposure tool, we quantified the CD variations caused by Flare using Kirk method. We determined that this issue was influenced by the exposure field layout, and the variation of intra wafer was 1.58nm. As for a CD-SEM, we measured the CD variations caused by the electron beam-induced CD shrink, and LWR (Line Width Roughness). The LWR accounts for about 40% of the total measurement errors, and affects CD variations higher as finer line pattern. We reduced influence of LWR on CD variations by extending measurement points and averaging. Thus we acquired the CD uniformity close to the actual CD.