Electron beam metrology of 193-nm resists at ultralow voltage

Abstract

Resist slimming under electron beam exposure introduces significant measurement uncertainty in the metrology of 193 nm resists. Total critical dimension (CD) uncertainty of up to 10 nm can arise from line slimming through a combination of the line slimming during the initial measurement pass and the variation of line slimming across the wafer. For a 100 nm process, the entire CD error budget, can be consumed by line slimming. This research examines the uncertainty that results from the use of offset techniques to account for resist slimming in the process control of 193 nm resist CDs. The uncertainty associated with such offset techniques can be as great as 10 nm, depending upon the 193 nm resist and landing energy evaluated. Data are presented to demonstrate that 193 nm resist CD features experience line slimming greater than 5 nm at 500 eV landing energy during the initial measurement pass. Further, subsequent measurements demonstrate greatly reduced slimming and as a result are not indicative of the true magnitude of line slimming. Experiments conducted using CD-AFM pre- and post-analysis, demonstrate that ultra low landing energies significantly decrease the line slimming, reducing it to 1 nm or less.