Investigation of Resolution Enhancement by Using Interferometric Immersion Lithography with a Lloyd Mirror

The minimum feature size of semiconductor devices will be smaller and smaller because of the increasing demand for high integration of such devices. The resolution limit of an optical lithography system is described by Rayleigh's criterion. While it is hard to achieve a small critical dimension by reducing the illumination wavelength and the processing-dependent factors, the critical dimension can be reduced by increasing the refractive index of the material between the lens and the wafer. We have used an interferometric immersion lithography system. This system uses a Lloyd mirror for interference between the 1st and the -1st diffraction order and deionized water with a refractive index of 1.437 at 193 nm. The experimental result, showed that immersion lithography, compared to conventional dry lithography, improved not only the resolution but also the depth of focus. The simulation result confirmed this behavior, showing a larger depth of focus for immersion compared to dry lithography. Also, the linewidth with immersion lithography was smaller than the linewidth with dry lithography.