Sensitivity analysis for accurate determination of PSF parameters

One possible candidate to address future nodes (below 16 nm) is electron beam lithography as sub 10 nm resolution was already demonstrated in PMMA or HSQ resists. If multiple electron beam systems significantly increase the throughput to meet industrial needs, it can be the tool of choice. Nevertheless using a chemically amplified resist (CAR) is mandatory even for systems with a large number of beams. Achieving dense sub 20 nm patterns with CAR is still a challenge as proximity effects degrade the contrast of the aerial image. Bridging, shape rounding or partial development are typical degradation in the desired final pattern shape. Proximity effect correction is needed in order to properly delineate dense features as well as meet the required CD uniformity. Proximity effect correction can only be accurate if a Point Spread Functions (PSF) is precisely determined.In this paper we demonstrate a strategy that allows accurate determination of Point Spread Function parameters. This strategy consists in using sensitivity analysis in order to define conditions where the calibration features and the measured quantities are sensitive enough to the PSF parameters and this without a correlation between the final results.

Figure optionsDownload as PowerPoint slideHighlights
► Design of a specific layout for PSF determination.
► Usage of Latin Hypercube Sampling for sampling the solution space.
► Simulation of the PSFs over the pattern contour with Inscale™.
► Sensitivity analysis and scatter plots of the measurement points.
► Optimal strategy for an accurate determination of the parameters of a PSF.