Extending current lithography capability in the case of severe topography is desired in trench-first dual-damascene process. We demonstrate a solution of applying the RELACS process on DUV bi-layer resist system to provide a planarization material with CD shrinkage ability. By combining these two commercially available processes, the cost saving of contact-reducing techniques can be realized on wafers with aggressive topography. The main results presented in this study include (1) process window of the bi-layer/RELACS is comparable with that of the bi-layer only process. (2) Across wafer CD uniformity of the bi-layer/RELACS process is improved compared to that of the bi-layer process alone. Further etch steps does not degrade CD uniformity either. Nice post etch across CD uniformity and cross-section photos from post etch show the image resist still retains enough etch resistance after RELACS process. (3) Among all geometry in this study, the maximum difference from two orientations is 2nm in width and 5 nm in length. (4) Geometry size shows a bigger effect on shrinkage, for the ellipse contacts with aspect ratio 2, it shrinks 14nm more in length direction than in width direction. For contacts with aspect ratio 1.3, the shrinkage difference between width and length is relative small (about 2nm). (5) Total CD shrinkage in the range of 40 to 60nm has been achieved. Baking temperature sensitivity is measured to be about 1.3 nm/ degree(s)C. The value of temperature sensitivity suggests possible lot-to-lot, wafer-to-wafer and across wafer CD control for mass production. (6) A set of horizontal contacts is employed for pitch dependency studies. From pitch size changes from 450nm to 700nm in length direction, the length shrinkage changes by 8% of the target CD. And for pitch size changes from 450nm to 850nm in width direction, the width shrinkage changes by 9% of the CD target. Post RELACS OPC may be necessary for critical cases to compensate the pitch dependency of CD changes.
A phase only grating consisting of equal lines of 0 and 90 degree phase is imaged into a highly absorbing photoresist forming a surface relief grating that is measured with a dark- field optical microscope and a CCD array. The resulting images are analyzed to determine spherical aberration, +-0.001 wave RMS, and focus variations of +-2.0 nm. This method of measurement and analysis is applied to both 248 and 193 nm photolithography lenses.
A technique for the evaluation of scanner lens aberration is described and analyzed. The method is based on the reconstruction of aerial image distribution using a double exposure technique: A first exposure of the mask feature of interest is followed by uniform background exposure. The topdown images in resist at increasing background exposure dose are analyzed using suitable threshold algorithms to obtain a set of aerial image intensity contour lines. This technique has been applied to the analysis of aerial images formed by isolated contacts using an attenuated PSM. Of particular interest in this case is the aerial image intensity present on the first sidelobe and its angular dependence. In the absence of lens aberrations the sidelobe intensity has no angular dependence whereas the presence of aberrations in the lens generally results in a non-uniform angular sidelobe intensity distributions. A detailed theoretical analysis of the capabilities of this method is being presented: Linearity, zero response and expected results in the presence of various Zernike terms have been studied. We were not only able to separate Zernike terms based on their angular dependence but we also propose a method to assess the order of the radial component.
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