Sub-diffraction-limited patterning using evanescent near-field optical lithography

Patterning at resolution below the diffraction limit for projection optical lithography has been demonstrated using evanescent near-field optical lith ography with broadband illumination (365-600 nm). Linewidths of 50 nm and g ratings with 140 nm period have been achieved. Ultrathin photoresist layers in conjunction with conformable photomasks are employed and a reactive ion etching process using SF6 has been developed to transfer the patterns to a depth of more than 100 nm into silicon. Full electromagnetic field simulat ions of the exposure process show that a high contrast image is present wit hin the resist layer, and that the exposure is dominated by one polarizatio n for the grating structures studied. (C) 1999 American Institute of Physic s. [S0003-6951(99)00148-5].