Achromatic spatial frequency multiplication: A method for production of nanometer-scale periodic structures

Fabrication of periodic structures with resolution below 100nm is required in many emerging applications such as subwavelength optical components, self-assembly templates, or patterned magnetic media. The achromatic spatial frequency multiplication technique that we have developed uses wideband illumination and self-imaging property (Talbot effect) of gratings to create periodic structures. The depth of field is practically unlimited, unlike the Talbot images obtained with monochromatic illumination. The technique requires limited spatial coherence making it suitable for use with sources other than lasers or synchrotrons which are normally used in interference lithography. We demonstrated the feasibility of the method using simulations and exposures in the extreme ultraviolet (EUV) region. One- and two-dimensional patterns with 50nm feature sizes were obtained. The technique is especially suitable for use with EUV light where the newly developed sources (laser or discharge produced plasma) have a rather wide bandwidth and limited spatial coherence. The technique is extendible to the production of much higher-resolution structures with the fundamental limit for the pattern period being equal to one-half of the wavelength.