Proceedings Article | 26 May 1995
Tracy Lindsay, Neal Sullivan, Sasha Dass, Gregory Pollard, Bill Jones
KEYWORDS: Deep ultraviolet, Semiconducting wafers, Lenses, Monochromatic aberrations, Metrology, Manufacturing, Photoresist processing, Distortion, Scanning electron microscopy, Reticles
DUV stepper technology has progressed to the point of practical implementation in the deep submicron lithography regime. A comparison of two state-of-the-art DUV lenses, a GCA Thistle and an ASML 5500/90, will be presented. Lens performance parameters of interest to lithographers, e.g., focus and exposure latitude, astigmatism, coma, focal plane deviation, dense to isolated bias, distortion and linewidth uniformity across lens, are reported. These lenses demonstrate the process latitude and resolution capability required for a production-worthy 0.35 micrometers process. In order to derive a meaningful assessment of lens performance, a rigorous lens analysis procedure is required. Using an automated metrology SEM, the Metrologix Metrostep 2002, and a statistical analysis of software package, SAS, the components of variability in lens performance resulting from the specification, measurement and data analysis methods, along with the physical lens design and manufacture, are examined. For example, wafer nonflatness, can have a major impact on focal plane deviation and useable depth-of-field (UDOF). Lens specification can also greatly influence the perceived lens performance. Differences in the description of an acceptable resist profile contributed to a difference of 0.6 micrometers in UDOF values. Several external factors must be carefully considered when performing lens evaluations. The components of variability in lens performance have been identified and methods to account for these components are described.
