EUV OPC modeling of dry photoresist system for pitch 32nm BEOL

Abstract

As technology nodes further shrink, high yield becomes more and more challenging to achieve. Photoresist resolution (see Figure 2) and CD uniformity are two core yield limiters. This can be improved with the use of Lam's EUV dry photoresist system [1] , where the dry develop technique is used to replace wet develop. This process is also less prone to pattern collapse [1] . Another advantage of this new photoresist system consists in its higher dose sensitivity compared to conventional photoresists which leads to higher throughput [1][2] . High resolution process needs to be combined with optical proximity correction (OPC) to enable cutting edge EUV patterning. OPC relies on the capability of a model to predict accurately the behavior of such an innovative process. The purpose of this study is to provide a comprehensive quantification and characterization of the accuracy of an OPC model fitted for this process ADI and AEI (after carbon open).We generated wafers exposed with an OPC calibration reticle, processed with Lam's dry deposited and dry developed photoresist. The anchor is a horizontal line-space grating at pitch 32nm (Figure 2). We acquired CDSEM images of more than 1800 features ADI (after dry develop) and AEI (after carbon open). A subset of the features were collected through FEM ADI. To better understand the characteristics of the dry photoresist system, we used metrics such as proximity, MEEF, DoF and EL. ADI OPC models were calibrated using ASML Tachyon software. Finally, we evaluated the OPC model accuracy of both Tachyon FEM+ (physically motivated) and Newron (machine-learning) engines, ADI for pitch 32nm BEOL metal layer use case.