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Abstract

A maskless, extreme ultraviolet (EUV) lithography system uses microlens arrays to focus EUV radiation (at an operating wavelength of 11.3 nm) onto diffraction-limited (58-nm FWHM) focused spots on a wafer printing surface. The focus spots are intensity-modulated by means of microshutter modulators and are raster-scanned across a wafer surface to create a digitally synthesized exposure image. The system uses a two-stage microlens configuration to achieve both a high fill factor and acceptable transmission efficiency. EUV illumination is supplied by a 6 kHz xenon plasma source, and the illumination optics comprise an aspheric condenser mirror, a spherical collimating mirror, and two sets of flat, terraced fold mirrors that partition the illumination into separate illumination fields covering individual microlens arrays. (The system has no projection optics, because the image modulator elements are integrated with the microlens arrays.) The printing throughput is estimated to be 62 (300-mm) wafers per hour (assuming a resist exposure threshold of 20 mJ/cm.sup.2), and print resolution is estimated at 70 nanometers for mixed positive- and negative-tone patterns (at k.sub.1 =0.6).

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First Claim