Izumi Tsukamoto

Mask blanks warpage at 130-nm node

Semiconductor device technology is now making transition from 150 to 130 nm node. Lithography tools for 130 node that employ KrF and ArF as light sources have finished being developed. Also, mask drawing and inspection tools are ready. However, for actual processes, there is an issue to be solved from realistic DOF or overlay accuracy acquisition point of view.

New distortion metrology using reticle coordinate error

There are several ways to measure distortion of lithography exposure equipment, and with each of the distortion metrology technique, coordinate errors of distortion measurement pattern on the reticle affect distortion measurements. The most common way to remove the impact of the reticle coordinate error is to measure such errors in advance using a pattern placement metrology tool and correct distortion measurements based on the coordinate error. We have found, however, that when measuring distortion using two different reticles on the same exposure tool, the two measurement results did not agree with each other with a difference at a 20 nm level (3 sigma) even after being corrected according to the measured reticle coordinate error. After studying this problem, we successfully had distortion measurements on the wafer using two different reticles agree with each other at a 10 nm level (3 sigma) by introducing a technique called STofs., system offset, method. This paper reports that exposure tool distortion can be extracted with more precision by applying the new reticle coordinate error measurement technique.