EUV actinic imaging tool aerial image evaluation of EUVL embedded phase shift mask performance

Extreme Ultraviolet Lithography (EUVL) embedded phase shift mask (EPSM) can further extend lithography resolution limit and provide better pattern fidelity as compared to that of EUVL binary mask for 16nm node technology and beyond generations. In our previous study, we have demonstrated in wafer printing that EUVL EPSM can provide improved process window for both the dense lines and contacts and the low shadowing effect when compared to that of the EUVL binary mask. Due to limitation of current EUVL resist performances, certain advantages of EUVL EPSM, such as line width roughness (LWR) improvement, cannot be readily seen at wafer resist level. This is because that the aerial image quality improvement in LWR is over shadowed by the current large resist intrinsic and process induced LER. We believe that when EUV resist and wafer process improves in future, mask induced pattern fidelity difference will start to play an observable role in wafer printing. In this study, we focused on comparing EUV actinic aerial image performance of a EUVL EPSM and a binary mask for both lines and contacts. Without convoluting with resist effect, the mask aerial image performance comparison of two different masks can better reflect all the effects that are due to mask differences. Our analysis of the EUV actinic aerial images of a EUVL EPSM and a binary mask showed not only the process window advantages of the EPSM as demonstrated previously, but also the improved LWR performance of EUVL EPSM when compared to that of the EUVL binary mask. The matrix used to analyze the aerial images includes aerial image contrast, LWR, process windows (focus-exposure plot), etc. Our detailed analysis is performed for various line and contact features.