Distortion and overlay performance of UV step and repeat imprint lithography

Abstract

High-resolution overlay is considered to be an important challenge for imprint lithography processes. A key advantage of Step and Flash™ Imprint Lithography (S-FIL™) is that it uses low-pressures (<1/40th of an atmosphere) at room temperature during the imprint processes. This makes it specifically suited for overlay as compared to other thermal or high pressure processes. To obtain high resolution overlay, it is critical to minimize in-plane distortions in both the template and substrate. This article presents a detailed budget of the various distortions that affect the S-FIL process. These distortions include: (i) 1X template e-beam pattern distortions; (ii) template distortions due to post-processing steps; and (iii) wafer processing distortions. Distortions associated with template patterning were measured prior to Cr removal using a Leica LMS tool. Field-to-field distortion variations were measured using 27 imprints on three wafers from a step and repeat imprint tool without control of thermal environment. Thermal effects on the imprint tool showed up as uniform magnification errors. Using the field-to-field distortion data, a first order correction scheme was implemented numerically to significantly lower the imprint-related distortion. Related issues such as XY– Θ alignment is also discussed briefly.