The effects of wafer-scan induced image blur on CD control, image slope, and process window in maskless lithography

In this paper we present analytical and simulation results on the wafer-scan induced image blur and its impact on CD control, image slope and line-edge roughness (LER), and process window in maskless lithography. It is shown that the effects of image blur do not impose serious constraints on lithographic performance in low throughput operation. However, when throughput is high, significant CD enlargement, lower image slope and higher LER, and process window degradation are observed consistently in both coherent imaging analysis and partially coherent lithographic simulations. The dependence of CDs on the wafer's scan speed and the distance between neighboring features will be an important issue of maskless OPC development. We also analyze the potential challenges of image blur to DUV and EUV maskless lithography and propose several solutions to overcome them.