In pursuit of Moore’s Law: polymer chemistry in action

Abstract

We present a focused review of photoresist strategies that have been studied over the past few decades driven by the demands of Moore's law. Selected results are discussed with emphasis on the choice of photoresist chemistry depending on the particulars of each radiation type or patterning strategy, while we present special architectures of photoresists that have attracted a great interest in the semiconductor field. We adopt an approach that allows for easy comparison between the different photoresist categories and we include brief discussions of a number of important preparation and property issues pertaining to key characteristics affecting resist performance. Polymer Journal (2018) 50, 45-55; doi:10.1038/pj.2017.64; published online 1 November 2017Photoresists are a workhorse tool for the semiconductor industry; they enable creation of small-scale structures using continuously evolving strategies to form objects of the nanoscale dimensions are needed to stay on the technology path of Moore's law. Simply put, photoresists transfer information using a light-driven process that makes them (often a polymer) either more or less soluble in the exposed region of the film. As dimensions have changed, so too have the chemistry and materials sets used in lithography. Originally requiring critical features of microns, photoresists such as cyclized polyisoprene were used. 1 Subsequently, novolac photoresists were developed and formed a water-soluble exposed material, avoiding the need for organic solvents that swelled the photoresist during development while operating at a shorter wavelength than prior resists, thus enabling smaller, more uniform features. 2 The creation of novolac resists set up a trend in photoresist design: a water developable material, working at a shorter and shorter wavelength to enable a finer feature size and adjusted composition to maintain sufficient transparency for pattern formation. This approach has carried forward through several generations of photoresists built around the principle of chemical amplification.A team of researchers with expertise in photoresists, polymersupported chemistry and protein synthesis worked at the IBM Almaden Research (San Jose, CA, USA) to tackle a new challenge in photolithography: to develop a photoresist that needed very little radiation to cause the solubility change needed during the patterning step. 3 Their concern was that the mercury light source being used to create UV radiation was increasingly weak as shorter wavelengths were used. Hence, a new process was needed that made better use of the imaging radiation.By using acid catalysis driven by a proton created in a light-induced decomposition of a photoacid generator, a single photon was shown to initiate hundreds of reactions. The resulting chemical amplification caused by that single photon was shown to overcome the limited radiation present in light sources of the time. However, the process also did something else arguably more important; it enabled a solubility change from the oil-soluble polymer ...

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