Source Optimization Based on the Partially Coherent Imaging Model

Extreme Ultraviolet Lithography (EUVL) has been utilized in the manufacturing of integrated circuit with 5nm node and beyond. Free Electron Laser (FEL) has the potential to substitute traditional Laser Produced Plasma (LPP) source in the EUV scanners for its high power ability. However, FEL has the characteristic of high spatial coherence, which would affect the results of computational lithography. This paper proposes source optimization (SO) method for EUVL, which takes into account the coherence of the light source. After considering the coherence among the source points in the "effective source", the partially coherent imaging model is firstly established. Then, an efficient SO method is discussed based on the gradient-based algorithm. Finally, the effectiveness of SO method is demonstrated from the simulation. Results illustrate that the proposed SO can reduce the lithographic pattern errors caused by the spatial coherence.