In the field of lithography technology, EUV lithography can be a leading candidate for sub-30 nm technology node. EUVL expose system has different characteristics compared to DUV exposure system. EUV source wavelength is short and no material is transparent to the source. So off-axis reflective optic system is used for patterning in place of on-axis refractive system of DUV system. And different reticle design is needed that consists of 40 pair of Mo/Si multi layer and absorber layer in place of conventional mask. Because of the oblique incidence on the mask, shadowing effect is occurred such as pattern asymmetry, shift and pattern bias depending on pattern orientation. For non-telecentric characteristics of EUV scanner, shadowing effect produces CD variation versus field position[1] [2]. Besides, it is well known that EUV scanner has bigger flare than conventional DUV scanner. Therefore, the correction of mask shadowing effect and flare level are one of the important issues for EUV lithography.In this paper, process window and MEF of EUV lithography has been examined by 3D mask simulation. CD variation by shadowing is simulated for various pattern orientations. A shadowing correction method has been calculated due to field position to reduce shadowing effect. And the correction effect is examined by simulation and Experimental results. Principle of radial overlay shift due to field position is verified then the shift length of line and space pattern is calculated.
We have studied several factors having an effect on LER in terms of resist chemistry, resist process, CD-SEM metrology, numerical aperture and sigma settings ofthe exposure tool, and the mask pattern. LER is extracted from the developed resist profile. In ArF lithography process, development and rinse process is very critical because ArF resist is relatively hydrophobic compared to KrF resist. It causes heterogeneous interaction at interface of resist and aqueous solution (developer or deionized water). We improved roughness at contact hole pattern by the introduction of wetting process prior to development. Clear and homogeneous rinsing is also needed to remove scum and swelled resist generated at development step. On the other hand, the roughness of mask pattern is one of the important factors of LER on wafer. We confirmed that this global dislocation is a potent influence but local edge roughness ofmask is insignificant to wafer LER. This dislocation ofpattern is originated from the lack of shot accuracy in E-beam writer using variable shaped beam.
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