Evaluation of high-numerical-aperture wide-field steppers for 0.35-micron design rules

Abstract

Many lithographic approaches to achieving 0.35 micron IC design rules have been proposed. Several years ago, the primary candidate was x-ray lithography. Today it is generally acknowledged that an optical approach will be used for such design rules. Both deep UV and i-line stepper technologies have progressed with capability to achieve O.35im design rules. High NA, wide-field lenses now exist for both deep UV and i-line [1]. With the renewed interest in phase shift technology, i-line capability at O.35im design rules is comparable to deep UV technology.The development of a stepper architecture that allows both wide-field i-line and deep UV lenses to be accommodated in the same body and using thru-the-lens, direct-reticle-referenced alignment. method [2] is reported. Common improvements in the areas of stage, die-by-die leveling and environmental control allow exceptional overlay performance to be achieved for both i-line and deep UV. The use of common architecture and the same alignment method facilitates the optimum mix and match combination of i-line and deep UV at O.35jim design rules Experimental investigation of stepper performance is reported in comparison to criteria established for design rules at O.35im. Overlay is evaluated on substrates typical of CMOS IC manufacturing. Lithographic performance is investigated using conventional techniques as well as more advanced techniques including phase shift reticles.Results indicate that overlay performance on tested substrates meets the requirements for O.35jim design rules. Lithographic results indicate that O.35im lines/spaces are achievable using both conventional i-line and deep Uv techniques, however, the implementation of phase shift reticles enhances the process latitudes for i-line at O.35im.