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For what is to our knowledge the first time, electric-field-induced optical second-harmonic generation (SHG) is studied at the Si-SiO(2) interface by the use of a metal-oxide-semiconductor (MOS) structure. The crystallographic anisotropy of this phenomenon is studied for MOS structures. Experimental results indicate that the MOS technique of dc electric-field application to the Si-SiO(2) interface can be effectively used for studying electroinduced effects on SHG.

Interference lithography ͑IL͒ ͓Yen et al., Appl. Opt. 31, 2972 ͑1992͔͒ based on reflective optics, and utilizing extreme ultraviolet ͑EUV͒ light from an electron storage ring, can be used to pattern structures with periods below 70 nm ͓Solak et al., Appl. Phys. Lett. 75, 2328 ͑1999͒; Ali et al., Microelectron. Eng. 65, 454 ͑2003͔͒. Previously achromatic interferometers with EUV transmission diffraction gratings were also used for this purpose ͓Wei et al., J. Vac. Sci. Technol. B 12, 3648 ͑1994͔͒, and recently we have printed sub-50 nm high quality periodic structures in poly͑methylmethacrylate͒ exposed with transmission-grating EUV interference lithography ͑EUV-IL͒ ͓Solak et al., Microelectron. Eng. 61, 77 ͑2002͒; Solak et al., ibid. 67-68, 56 ͑2003͔͒. With this technique, two-dimensional patterns are easily achievable using multiple diffraction gratings. Both types of EUV-IL have been implemented on one of the undulator beam lines at the University of Wisconsin-Madison Synchrotron Radiation Center electron storage ring because this undulator source provides a tunable and coherent beam of radiation well suited for IL studies. In this article, both exposure methods were applied to explore the ultimate resolution of two positive-tone chemically amplified resists supplied by the Shipley Corporation. We have demonstrated the printing of features as small as 26 nm line and space in Shipley XP9947W-100 resist. The present results demonstrate the fine quality of the above-mentioned EUV-IL techniques to test resist formulations for high-resolution patterning, and we provide the experimental setup and discuss the observed results.

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