Influence of Mask Feature on the Diffracted Light in Proximity and Contact Lithography

Abstract

Simple nanolithography methods, which provide increasing resolution at a fraction of the cost of conventional steppers, are of major interest. Methods, such as nano-imprint lithography, interferometric and laser direct-write techniques and the evanescent near-field optical lithography, are becoming increasingly important. Those low-cost optical contact lithography techniques can produce below 45-nm features by using ultraviolet radiation without a complex optical system. In this paper, for the usability of the proximity printing applications, diffraction effects are analyzed with the rigorous electromagnetic calculations when the ratio of mask pattern to the incident wavelength is below one. For this purpose, an analytical model and two models of a rigorous coupled-wave analysis are described and analyzed. The simulated results show good agreement with the experimental results. When the ratio of the pitch to the wavelength is small, the transverse electric (TE) and the transverse magnetic (TM) polarizations with the nonspecular (+1 and -1 orders) harmonics are small in comparison to those with the specular (0 order) harmonic and the variance of the TE and the TM polarizations is produced. When the pitch is smaller than incident wavelength, according to the incident angle, the variation in the diffraction efficiency with the 0 order is decreased. The variance of the TE and the TM polarizations and the diffraction efficiency can degrade the resolution of pattern formation for patterns smaller than the incident wavelength.