Process bias control with thin Cr film blanks for 90nm-node reticle fabrication

For today's advanced reticle production, process bias should be reduced as possible, and be "zero" ideally, because of its negative impacts on CD control and pattern fidelity against minute features. In this paper, blanks with Cr film thinner than 100 run were examined as promising materials to meet this demand. Results from two aspects, reticle production and lithographic performance, are presented. Dry etching properties such as etching bias, CD Linearity, impact on pattern-pitch were investigated. Thin Cr film blanks showed excellent results in process bias less than 50 % of conventional ones with proper etching conditions. They also showed about 50 %'s decrease of etching bias variations for pattern-pitch with smaller CD error in CD Linearity at the same time. Results of aerial image simulations showed possibilities of them as substitute of conventional binary blanks in ArF lithography. There was no impact of Cr film thinning on depth of focus and optical proximity effect with optimized exposure condition. These experimental results imply that Cr film thickness plays an important role to decide the qualities of reticle CD. Thinner Cr film blanks have capability to realize a 90 nm-node reticle with minimized process bias enough to produce fine OPC features.