This paper introduces a novel concept, "comeless phase-shifting', that eliminates the need for the use of chrome to form patterns in optical lithography. Chromeless phase-shifting uses 180° phaseshifters on transparent glass to define patterns. The method relies on the destructive interference between phase-shifters and clear areas at the edges of the phase-shifters to define dark or opaque areas on the mask. Gratings sufficiently small will produce sufficient interference to completely inhibit the transmission of light (these gratings are thus named dark-field gratings). The combination of these effects makes it possible to form a wide range of patterns, from line-space patterns to isolated bright or dark areas.In this study, the lithography simulators SPLAT and SAMPLE were used to understand the principles behind this new scheme, and to verify various pattern designs. Simulation and experimental results are presented to demonstrate the concept. tional chrome mask. A phase-shift layer delays the light from a pattern so that it arrives 1800 out of phase with the light through a clear area. By careful placement of the phase-shifting material, the light from the phase-shifted and non-phase-shifted areas can be made to interact coherently, thus producing a

Chromeless phase-shifting is a novel concept that completely avoids the use of chrome for pattern formation in optical lithography. This scheme uses 1800 phase-shifters on transparent glass to define patterns. The method relies on the destructive interference between phase-shifters and clear areas at the edges of the phase-shifters to define dark or opaque areas on the mask. Gratings sufficiently small (named dark-field gratings) will produce sufficient interference to completely inhibit the transmission of light. The combination of these effects makes it possible to form a wide range of patterns, from line-space patterns to isolated bright or dark areas. The lithography simulators SPLAT and SAMPLE were used to understand the principles behind this new scheme, and to verify various pattern designs. Simulation and experimental results are presented to demonstrate the concept.

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Simulation has been used to systematically investigate the effects of phase-shifters on dark-field patterns (openings in a dark-field mask), and to determine the phase-shifter configurations that are most effective for different mask patterns. This study has resulted in a design methodology based on the distance between the centers of clear features and the surrounding phase-shifters. A key verification is that isolated phase-shifted patterns print best when the distance from the center of the phase-shifter to the center of the feature is approximately 0.7 ?JNA. At this optimal spacing, the peak image intensity, image slope and resist wall-angle of the printed pattern is maximized. Optimally-aligned phase-shifters will also have the best focus-exposure behavior of all the different dark-field phase-shifter configurations. However, dark-field phase-shifters will only provide a resolution increase on the order of 0.05 -0.10 A/NA. Different dark-field mask configurations will print with different amounts of bias; the amount of print bias is dependent on the width of the phase-shifters and the distance between the phase-shifters and the feature. Response curves of resist opening as a function of feature size and phase-shifter/feature separation can be used to keep track of the amount of bias required in a given phase-shifter configuration.

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