Extreme ultraviolet ͑EUV, ϭ13 nm͒ lithography is considered to be the most likely technology to follow ultraviolet ͑optical͒ lithography. One of the challenging aspects is the development of suitable resist materials and processes. This development requires the ability to produce high-resolution patterns. Until now, this ability has been severely limited by the lack of sources and imaging systems. We report printing of 38 nm period grating patterns by interferometric lithography technique with EUV light. A Lloyd's Mirror interferometer was used, reflecting part of an incident beam with a mirror at grazing incidence and letting it interfere with the direct beam at the wafer plane. High-density fringes ͑38 nm pitch͒ were easily produced. Monochromatized light of 13 nm wavelength from an undulator in an electron storage ring provided the necessary temporal and spatial coherence along with sufficient intensity flux. This simple technique can be extended to sub-10 nm resolution. © 1999 American Institute of Physics. ͓S0003-6951͑99͒02841-7͔Extreme ultraviolet lithography ͑EUVL, ϭ13.4 nm͒ is one of the candidate technologies pursued for printing semiconductor devices with critical dimensions of 70 nm and below.1 The approaches currently developed are based on the use of 4ϫ reduction optics and reflective masks. The reflectivity of near-normal incidence optics is enhanced to ϳ60%-70% by multilayer interference coatings ͑/4 stacks͒. In this spectral region, all materials have high absorption coefficients bringing some special requirements on EUVL optical systems and materials. For example, photoresist thickness has to be limited to less than ϳ0.1 m in order to obtain a sufficiently uniform exposure along the film thickness.Evaluation of resist materials require the ability to expose patterns in order to obtain measurements of exposure dose sensitivity, contrast and resolution using a given material. A prototype EUV projection camera has been built at the Sandia National Laboratory that is capable of printing sub-0.1 m lines and spaces but access is limited. 2 We have developed a system using EUV-interferometric lithography ͑EUV-IL͒ for studying imaging at EUV wavelengths, and for testing photoresist materials in which we have demonstrated unprecedented printing of features with periods as small as 38 nm. IL was not used before to print such small features in the EUV regime, and the features are the smallest ever printed using a photon-based lithography. Fabrication of quantum confinement devices is a clear application, and another is the study of the properties of materials confined in ultrasmall structures ͑polymeric resists in particular͒.
