19 July 1989 Lens Matching And Distortion Testing In A Multi-Stepper, Sub-Micron Environment
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Step and repeat camera optical systems today exhibit greater resolution, numerical aperture and field sizes than in the past. It has become necessary to control lens distortion and matching errors to less than one-tenth micron across the entire usable field. The quality of the optics has risen to the point that fifth order distortion modeling has become a necessary component of the stepper matching procedure. Methods of data gathering and analysis vary significantly in the industry. In this paper we investigate four methods of overlay measurement including electrical, optical coherence probe, automated optical and optical vernier techniques. Precision to tolerance ratios and throughput for the measurement methods are discussed. Three methods of data analysis are compared including KLASS II for KLA 2020* data, EM1** for electrical data and SASO*** for both. A novel multi-substrate calibration technique is presented. In any matching situation the required sample size for accurate estimation of the lens components is important. Our study reviews the results of analyses of variances due to daily repeatability, wafer films, the number of measurement sites on each wafer and stepped field. Two methods of artifact generation were investigated, that of stage referenced matching and matching to a 'golden standard'. Finally, the expansion of the model to include seventh order distortions and the significance of this for the now emerging high numerical aperture, large field g-line lens designs is discussed.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Alan Yost, Wei Wu, Terrence Zavecz, Faris Modawar, "Lens Matching And Distortion Testing In A Multi-Stepper, Sub-Micron Environment", Proc. SPIE 1087, Integrated Circuit Metrology, Inspection, and Process Control III, (19 July 1989); doi: 10.1117/12.953096; https://doi.org/10.1117/12.953096


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