Role of Ellipsometry in DPT Process Characterization and Impact of Performance for Contact Holes

We analyzed the lithographic performance of a double patterning technology (DPT) with resist freeze (LFLE) process for printing dense contact holes (CH). For the first time, we quantified the contribution of the substrate - frozen resist and topography effects. The impact on image contrast, and NILS was studied through-pitch. In comparing to the case of a uniform L/S, the image through-pitch performance is degraded in LFLE CH. This is resulted from diffraction by the underlying topography and materials. The process steps (between first-and-second Litho) cause additional challenges in the fabrication of CHs using DPT. Current inspection of the process effects only observes the reflected signal for position alignment. We have introduced simulations of a phase change in polarized signal (ellipsometry) after first and second lithography steps for suggesting a new methodology for detection and validation of topography changes in DPT flow. In DPT the first Litho result is fabricated in substrate, so the analysis of ellipsometry signal can be applied to sensitively detect correlations between two steps. The spectroscopic ellipsometry simulation results were shown; alpha and beta parameters demonstrate the sensitivity w.r.t. substrate topography, by changing the incident optical direction from x-z to y-z plane. This represents the correlation between parameters observed by respective Litho steps of perpendicular orientation. Furthermore, ellipsometry signal was used to optimize the "frozen" resist n and k values w.r.t aerial image performance, which can be fed back to DPT design. Concluding, the information obtained by ellipsometry is useful to characterize substrate topography in DPT design.