Submicron Optical Lithography Using An I-Line Wafer Stepper

Optical lithography using an i-line wavelength (365 nm) has superior resolution compared to longer g- or h-line wave-lengths. This is due to the inverse relationship between the wavelength of the light and the diffraction-limited resolution of an imaging lens. The higher absorptivity of typical positive photo-resists at the i-line wavelength also enhances resolution. The half micron resolution capability of the Zeiss i-line 10:1 projection lens has been reported in a previous papers. This paper describes the performance of the THE 800SLR® Wafer Stepper with an i-line imaging lens. The i-line optics for the wafer stepper have presented difficulties in the areas of illuminator optimization, i-line spec-tral filter development, and wafer-to-reticle alignment. The reduced linewidth (0.5 micron) requires tighter system tolerances in the performance of the wafer stepper for linewidth control. The error budget to achieve these tight tolerances in the optical, mechanical, and electrical areas explained later in this paper. High throughput combined with submicron system capability enables i-line optical lithography to be superior to other non-optical lithography methods in production applications.