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The trend in microelectronics toward printing features 0.25 [mu]m and below has motivated the development of lithography at the 193-nm wavelength of argon fluoride excimer lasers. This technology is in its early stages, but a picture is emerging of its strengths and limitations. The change in wavelength from 248 to 193 nm requires parallel progress in projection systems, optical materials, and photoresist chemistries and processes. This paper reviews the current status of these various topics, as they have been engineered under a multiyear program at MIT Lincoln Laboratory.
Introduction
The relentless drive in the integrated circuit industry toward greater packing density and higher speeds has served as the impetus for optical lithography to reduce printed image sizes from 2 [mu]m twenty years ago to less than 0.5 [mu]m today. This remarkable progress has been made possible by improved lens quality, increases in numerical aperture, improved resist processes, and the use of increasingly shorter exposure wavelengths. Today's photolithography uses wavelengths of 365 or 248 nm for imaging the smallest possible feature sizes, thus employing aggressively low lithographic k^sub1^factors of 0.5 to 0.6. However, as image dimension requirements drop below 0.25 [mu]m in the next few years, it will be necessary to consider even shorter exposure wavelengths. An obvious candidate for extension to shorter wavelengths is the 193nm laser line produced by the argon fluoride (ArF) excimer laser. Indeed, the recent Semiconductor Industry Association roadmap lists 193 nm as one of the options for printing 0.18 [mu]m, along with extensions of 248 nm. While each of the alternatives has its own advantages and risks, only those of 193 nm are discussed here.
The change to 193 nm poses challenges and opens up new possibilities, as new photoinduced processes take place at this shorter wavelength. Specifically, optical materials that are nominally transparent have weak absorption and also undergo laser-induced changes, and few organic polymers are transparent enough to serve as single-layer resists. On the other hand, efficient photoinduced cross-linking of polymers or oxidation of silicon-containing polymers may enable new near-surface resist processes.
This paper reviews the progress that has been made at MIT Lincoln Laboratory toward a production-worthy 193nm technology at sub-0.25-[mu]m resolution [1]. The Lincoln Laboratory program has addressed in parallel both the construction of a...