High performance source optimization using a gradient-based method in optical lithography

Recently, source and mask optimization (SMO) has been proposed as an effective solution to help extending the life time of conventional 193nm lithography. However, SMO is very computationally intensive. To mitigate this issue, we propose a highly effective and efficient method for source optimization in this paper. Based on the gray-level pixel based source representation, the gradient of the cost function is calculated to guide optimization to improve the wafer image fidelity and depth of focus (DOF). This method is demonstrated using two mask patterns with critical dimension of 45nm, including a periodic array of contact holes and an asymmetric mask pattern from an SRAM layout. Comparing with two recently proposed methods, our method can provide greater improvements in image quality and over 10X running speed enhancement. The robustness of our method is verified using several different initial source patterns. Results show that similar final optimized source patterns and image quality have been achieved.

[1]  Gabriella Kókai,et al.  Genetic Algorithms to Improve Mask and Illumination Geometries in Lithographic Imaging Systems , 2004, EvoWorkshops.

[2]  Harry J. Levinson,et al.  Principles of Lithography , 2001 .

[3]  Alan E. Rosenbluth,et al.  Optimum mask and source patterns to print a given shape , 2002 .

[4]  Eytan Barouch,et al.  Optimization of stepper parameters and their influence on OPC , 1996, Advanced Lithography.

[5]  Eytan Barouch,et al.  Illuminator optimization for projection printing , 1999, Advanced Lithography.

[6]  Kafai Lai,et al.  Benefits and trade-offs of global source optimization in optical lithography , 2009, Advanced Lithography.

[7]  Scott Halle,et al.  Experimental result and simulation analysis for the use of pixelated illumination from source mask optimization for 22nm logic lithography process , 2009, Advanced Lithography.

[8]  Chris A. Mack Optimum stepper performance through image manipulation , 2004 .

[9]  Tsai-Sheng Gau,et al.  Customized illumination aperture filter for low k1 photolithography process , 2000, Advanced Lithography.

[10]  Vikram Tolani,et al.  Source-mask co-optimization (SMO) using level set methods , 2009, Photomask Technology.

[11]  G. Arce,et al.  Pixel-based simultaneous source and mask optimization for resolution enhancement in optical lithography. , 2009, Optics express.

[12]  George E. Bailey,et al.  Effective multicutline QUASAR illumination optimization for SRAM and logic , 2003, SPIE Advanced Lithography.

[13]  D. Fehrs,et al.  Illuminator modification of an optical aligner , 2004 .

[14]  Aasutosh Dave,et al.  Pushing the limits of RET with different illumination optimization methods , 2009, Advanced Lithography.