Contrast transfer function measurements of deep ultraviolet steppers

Abstract

The aerial image contrast is a key parameter for the evaluation of the performance of optical projection systems. State-of-the-art deep ultraviolet steppers and some i-line steppers were investigated for comparison by measuring the contrast transfer function, i.e., contrast versus linewidth. Examples are shown how specific weaknesses of an imaging system like astigmatism and sensitivity from internal reflections can be quantified with this technique. For comparison the contrast transfer functions were also calculated, assuming ideal, purely diffraction limited image transfer of the optics, and with the numerical aperture and partial coherence as parameters. Interestingly none of the steppers meet the imaging performance which can be expected from theory.

Hybrid lithography process for nano-scale devices

“…PEB temperature was also optimized to smooth out standing wave effects by homogenizing the photo acid concentration in the resist film [18], but in the best cases a ''footing'' effect was present (Fig. 8).…”

Review of resist-based flare measurement methods for extreme ultraviolet lithography

“…14 In 2002, LaFontaine and other researchers measured flare with this method. 15,16,29 The MTF is measured directly at various spatial frequencies instead of the PSF measured in other methods.…”

“…9,10 However, it is more practical for end users to measure flare using a resist-based method, which means measuring flare patterns exposed on a resist-coated wafer with a CD scanning electron microscope (CD SEM). Four resist-based flare measurement methods have been proposed including Kirk,[11][12][13] modulation transfer function (MTF), [14][15][16][17] double exposure, 18,19 and zonal ring approximation method (ZRAM), 20 and all four methods will be reviewed in this article. Knowledge of the flare point spread function (PSF) is important when modifying the mask patterns to compensate for flare.…”

Lithographic aerial-image contrast measurement in the extreme ultraviolet engineering test stand

“…͑1͒ can be simplified in terms of exposure doses. 6 The aerial-image contrast measured by the resist-clearing method can, thus, be written as dose max and dose min for a given feature size can be obtained by analyzing scanning electron microscopy ͑SEM͒ images, as shown in Fig. 1.…”

“…The resist is used as a threshold detector with the dose to clear as threshold. 6 At a certain dose the lines are developed to the substrate as Fig. 1͑a͒, from which I max can be evaluated.…”