Liquid immersion lithography, especially at 193 nm, is a serious candidate for extending projection optical lithography to the 65 nm node and beyond. This article reviews the status of this technology, the potential pitfalls that it may still encounter, and also the potential to extend it to 157 nm and to higher-index liquids. At 193 nm, no fundamental obstacles have been found yet, although defect control and materials compatibility must still be worked out. At 157 nm, significant progress has been made in developing suitable liquids. The next hurdle is to increase their refractive index, in order to make the transition in wavelengths cost-effective.
Photodeposition of organic films on transparent substrates irradiated in the presence of trace levels ͑ppb to ppm͒ of hydrocarbons has been experimentally investigated and a model is presented that describes the film growth behavior. The efficacy of a given organic precursor at forming a deposit is proportional to the product of its surface coverage ͑as governed by its partial pressure relative to its saturation partial pressure͒ and by its photon absorption cross section. These measurements are important in predicting the transmission characteristics of lithographic optics operating at 157, 193, and 248 nm wavelength. For example, a lens element irradiated continuously for 1 yr ͑1 kHz, 0.1 mJ/cm 2 /pulse͒ in the presence of 1 ppb of t-butyl benzene would exhibit a transmission of ϳ87% at 193 nm. The effects of oxygen-containing ambients are also documented, and methods for elimination and/or prevention of organic contamination are suggested.
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