An interferometric analysis tool (iMAT®) for imprint nanolithography that achieves precise registration and mold curing is disclosed in U.S. Patent 7,630,067. Molecular Imprints, Inc. (Austin, TX) inventors Pawan Kumar Nimmakayala, Tom H. Rafferty, Alireza Aghili, Byung-Jin Choi, Philip D. Schumaker, Daniel A. Babbs, and Van N. Truskett developed an interferometric analysis method that determines relative spatial parameters between two coordinate systems, which may be an imprint mold and a region of a substrate in which mold is employed to generate a nanoscale pattern. The method includes sensing relative alignment between the two coordinate systems at multiple points and determines relative spatial parameters there between. The relative spatial parameters include a relative area and a relative shape.
In a typical alignment process the measurements are taken as the distance between mold and region varies, e.g. becoming closer in proximity along the Z-direction. For example, the measurements and control signals may be generated when mold and substrate are spaced-apart a distance of 4 microns, 1 micron or a final distance in which a volume is defined therebetween that is substantially filled with polymeric material. As a result, the spatial parameters may be determined and control signals generated in real time during the imprinting process so as to minimize relative spatial parameters between mold and imprint region that are undesirable in forming nano-scale electronic circuitry.
During curing of imprinting material by hardening or cross-linking, the very photons that are needed for curing may also cause heating of mold and imprint region. If the intensity of curing light is maintained reasonably uniform, mold and substrate may heat up uniformly. The differential heating and/or the differential coefficient of thermal expansion (CTE) can cause alignment mismatches during exposure up to the point where the imprinting material has not jelled to behave like a solid that adheres to the substrate. However, the average misalignment may either be estimated by simulations or by using the alignment measurement systems described here, and the size of the mold or substrate can be pre-corrected in such a way that a desired scaling (magnification) mismatch is achieved using the iMAT just prior to curing. It is desirable that the wavelengths used for alignment metrology need to be substantially different from the curing light.
Referring to FIG. 3, the present invention includes an imprint lithography system 50 that has a template 52, retained within a template stage 54, a substrate 56 supported upon a substrate stage 60 and an interferometric analysis tool (iMAT.TM.) 62 is in optical communication with both template 52 and substrate 56. Also present are a polymeric fluid dispensing system and a source of actinic radiation, both of which are typically included in imprint lithography systems, but are not shown for clarity. An exemplary template stage includes a chucking system (not shown) and an actuator sub-assembly (not shown) coupled to imprint head 20 through a flexure system.
iMAT.TM. 62 is coupled with both stages 54 and 60 to communicate therewith over feedback loop 64 to facilitate proper spatial arrangement between two coordinate systems, one defined by template 52 and one defined by substrate 56 to obtain a desired spatial arrangement therebetween. To that end, iMAT.TM. 62 produces data concerning multiple spatial parameters of both template 52 and substrate 56 and determines signals in response thereto to ensure differences between the spatial parameters are within desired tolerances. To that end, iMAT.TM. 62 is coupled to sense one or more of alignment marks on template 52, referred to as template alignment marks 65, as well as one or more of the alignment marks on substrate 56, referred to as substrate alignment marks 66. iMAT.TM. 62 can determine multiple relative spatial parameters of template 52 and substrate 56 based upon information obtained from sensing alignment marks 65 and 66. The spatial parameters includes misalignment therebetween, along X and Y directions, as well as relative size difference between substrate 56 and template 52 in the X and Y directions, referred to as a relative magnification/run out measurement, and relative non-orthogonality of two adjacent transversely extending edges on either template 52 and/or substrate 56, referred to as a skew measurement. Additionally, iMAT.TM. 62 can determine relative rotational orientation about the Z direction,
