7 March 2008 Automated method of detecting SRAF and sidelobe printing with automated CD-SEM recipes
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In development of optical proximity correction (OPC) for new technology nodes, optimization of assist features requires multiple placement scenarios for each line/space or hole combination. Additionally, illumination and process conditions are varied to determine the optimal process window. Under some illumination and process conditions, optimal printing of the desired features is attained; however, undesired printing of sidelobes or sub-resolution assist features (SRAFs) also occurs. Currently, CD sizes are measured for the desired feature and images are hand checked for unwanted features (sidelobe or SRAF printing). This takes a large amount of time, given the hundreds to thousands of CDSEM measurements required to generate a given OPC model. This problem is multiplied if several passes of data collection are needed to optimize each OPC model and each layer. An automated method has been developed to quickly screen a large number of SEM images for unwanted features, and if they exist, flag the measurement point so it can be easily identified as an undesirable area of the process window. This method employs edge placement measurement capabilities available with automated SEM recipe generation software to identify the presence of an unwanted feature within a given image. A simple Boolean filter is used to exclude this process area as SRAF or sidelobe printing process space so it may be excluded from the OPC model and from the operational process space. This automated method for identification of SRAFs or sidelobes provides significant engineering time savings and allows characterization of the onset of undesirable features to assist in optimization of OPC within a given process window.
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Mary Coles, Mary Coles, Yong Seok Choi, Yong Seok Choi, Kyoungmo Yang, Kyoungmo Yang, Cindy Parker, Cindy Parker, Andy Self, Andy Self, } "Automated method of detecting SRAF and sidelobe printing with automated CD-SEM recipes", Proc. SPIE 6924, Optical Microlithography XXI, 692430 (7 March 2008); doi: 10.1117/12.775808; https://doi.org/10.1117/12.775808

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