Depth of focus (DOF) and line width roughness (LWR) performance of novel surface conditioner solutions for immersion lithography

As lithographic technology goes beyond the 45nm node, depth of focus (DOF) and line width roughness (LWR) for poly gates have become critical parameters. There is a growing interest in applying surface conditioner solutions during the post-develop process to increase DOF and reduce LWR. Surface conditioners interact with resist sidewall selectively, causing surface plasticization effect and smoothing the sidewall profile. As a result, the LWR can be reduced and the poor pattern profile located in the focus marginal area due to poor image contrast will be improved so that the depth of focus (DOF) can be increased significantly. In this paper, the features of lines/spaces patterned for the 45nm node by immersion lithography were used to evaluate surface conditioner performance with regards to DOF increase and LWR reduction. The results demonstrate there is about 1.5 nm LWR reduction, as well as a significant improvement on the process window for DOF, for which there is 37.5% increase for ISO poly gates and 36% increase for DENSE poly gates. No negative impact on the effect of optical proximity correction (OPC) and resist profile were observed with the new process. In addition, etch testing was conducted to determine how much post-develop LER reduction has been retained through etch by comparing post-etch and post-develop LER for both baseline and surface conditioner processes.