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EUV lithography is one of the hot candidates for the 22nm node. A well known phenomenon in EUV lithography is the impact of non-telecentricity and the mask topography on printing performance. Due to oblique illumination of the mask, layout, the printed features are shifted and biased on the wafer with respect to their target dimension up to several nanometers. This effect is inherent to EUV imaging systems. In order to maintain CDU, overlay and registration requirements, these effects need to be compensated for as part of the lithographic manufacturing process. Conventional compensation techniques, such as OPC compensation, significantly increase the complexity of the litho process.In this paper we discuss pattern shift, which is induced by mask-side non-telecentricity of the EUV ring field system. In particular, we show how the mask position relative to the focal plane of the projection system impacts pattern shift. It is shown that mask focus shift allows for a compensation of pattern shift, independent on angle of incidence, pattern type, pattern pitch, pattern orientation, and slit position. Thus it is seen that placement error is not an effect related to mask topography (not a shadowing effect) but arises purely from the mask non-telecentricity.A geometric interpretation of this effect is given and shown to be consistent with results of rigorous simulations. A method to simulate the shift of the mask focus position is briefly discussed. The mask focus shift for which the pattern shift vanishes in the aerial wafer image at best focus is determined using rigorous simulations. The amount of mask focus shift to compensate for the pattern shift is found to be approximately 136nm. This mask focus shift is then applied to investigate the through focus and dose behavior of the pattern shift in the resist. It is shown that the pattern shift is a function of wafer focus position and that this is a result of the image tilt in EUV systems. While the pattern shift is fully compensated at one wafer focus position, the shift at other positions is very small. The impact of the mask focus position on process window is investigated.

Articles you may be interested inHydrogen silsesquioxane on SOI proximity and microloading effects correction from a single 1D characterization sample J. Vac. Sci. Technol. B 32, 06F511 (2014); 10.1116/1.4901567 Three-dimensional proximity effect correction for large-scale uniform patterns J. Vac. Sci. Technol. B 29, 06F314 (2011); 10.1116/1.3660785 True three-dimensional proximity effect correction in electron-beam lithography Proximity effect correction using blur map in electron projection lithography J. Vac. Sci. Technol. B 23, 3188 (2005); 10.1116/1.2101791 Dose, shape, and hybrid modifications for PYRAMID in electron beam proximity effect correctionThe authors present a general approach to combine model-based dose modulations and shape modifications into a hybrid proximity effects correction (PEC) scheme for electron beam lithography. The authors simplify this scheme significantly by using an appropriate dose correction strategy. This allows us to use an existing optical proximity correction tool for the shape adjustments. This hybrid PEC scheme is demonstrated by computing corrections for simple test patterns as well as a more complex pattern. The model used corresponds to an electron multibeam tool with an acceleration voltage of 50 kV. It predicts resist contours from a written dose distribution. The authors evaluate the quality of the results both for nominal process conditions and in the presence of process variations. The results are compared against the corresponding results for a correction using only dose modulation. The authors also use the hybrid scheme to compensate intentional overexposure by shape adjustments and include these results in the comparison so that the impact of overexposure on robustness against process variations can be determined.

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Electron beam lithography (EBL) requires conducting substrates to ensure pattern fidelity. However, there is an increasing interest in performing EBL on less well-conducting surfaces or even insulators, usually resulting in seriously distorted pattern formation. To understand the underlying charging phenomena, the authors use Monte Carlo simulations that include models for substrate charging, electron beam-induced current, and electric breakdown. Simulations of electron beam exposure of glass wafers are presented, exposing regular patterns which become distorted due to charge-induced beam deflection. The resulting displacements within the patterns are mapped and compared to experimental displacement maps obtained from patterns in PMMA resist on glass substrates. Displacements up to several hundreds of nanometers were observed at a primary beam energy of 50 keV. Also, various scan strategies were used to write the patterns, in the simulations as well as the experiments, revealing their strong effect on pattern distortion, in shape and in magnitude. A qualitative, in some cases even quantitative, good agreement was found between the simulations and the experiments, providing enough confidence in Monte Carlo simulations to predict charge-induced pattern displacement and shape distortion and to find smart scan strategies to minimize the effects of charging.