Reticle’s contribution to critical dimension control and overlay in extreme-ultraviolet lithography

Abstract

In order to design an exposure tool for extreme-ultraviolet (EUV) lithography that adheres to technology roadmap requirements, we translated overall system performance requirements to system design specifications by setting up detailed error budgets for critical dimension (CD) control and overlay. In this article we concentrate on the EUV reticle contributions, including surface flatness, hydrocarbon contamination, multilayer d-spacing variations, and mounting in the writer and exposure tool. It is determined that in order to meet the CD-control budget, the reticle multilayer d-spacing variation must be limited to 0.25%, whereas the thickness variation of the hydrocarbon growth should be less than 1.5 nm. The overlay budget requires that the reticle flatness within the site area must be better than ±25 nm, both on the patterned side and on the back side. Also, the chuck of the exposure tool must be flat within ±25 nm. To avoid in-plane pattern distortion, the flatness of the chuck in the e-beam writer must be identical to that of the chuck in the exposure tool, and hence also must be flat within ±25 nm.