Historically, in the mass production of semiconductor devices, exposure tools have been repeatedly replaced with those with a shorter wavelength to meet the resolution requirements projected in the International Technology Roadmap for Semiconductors issued by the Semiconductor Industry Association. After ArF immersion lithography, extreme ultraviolet (EUV; 92.5 eV) radiation is expected to be used as an exposure tool for the mass production at or below the 22 nm technology node. If realized, 92.5 eV EUV will be the first ionizing radiation used for the mass production of semiconductor devices. In EUV lithography, chemically amplified resists, which have been the standard resists for mass production since the use of KrF lithography, will be used to meet the sensitivity requirement. Above the ionization energy of resist materials, the fundamental science of imaging, however, changes from photochemistry to radiation chemistry. In this paper, we review the radiation chemistry of materials related to chemically amplified resists. The imaging mechanisms from energy deposition to proton migration in resist materials are discussed.

https://iopscience.iop.org/article/10.1143/JJAP.49.030001/pdf

Radiation Chemistry in Chemically Amplified Resists

Early studies on the radiolysis of water suggested a wide variety of precursors, and mechanisms, for the formation of the observed yield of molecular hydrogen. Molecular hydrogen yields have been measured in the {gamma} radiolysis of aqueous solutions with a wide variety of scavengers of the hydrated electron and its precursors. A decrease in molecular hydrogen yield with increasing scavenging capacity of the hydrated electron is found with all solutes. Scavengers with particularly high rate coefficients for reaction with the precursors to the hydrated electron compared to the hydrated electron, such as selenate and to a lesser extent molybdate, show a more rapid decrease in hydrogen yields with increasing scavenging capacity than is observed with the other solutes. The yield of molecular hydrogen is better parameterized by the scavenging capacity for the precursors to the hydrated electron than by the scavenging capacity for the hydrated electron. Good scavengers of precursors to the hydrated electrons do not exhibit a nonscavengable hydrogen yield in the high scavenging capacity limit. These results suggest that the previously accepted nonscavengable yield of molecular hydrogen is due to precursors of the hydrated electron and it can be lowered with appropriate scavengers.

Dependence of Molecular Hydrogen Formation in Water on Scavengers of the Precursor to the Hydrated Electron

The chemistry of muonium, a light isotope of hydrogen, is investigated for the time period immediately after stopping of its precursor, the positive muon, in the condensed phase. Information is extracted from the initial amplitudes of the muon precession signals arising from muonium and muon-substituted diamagnetic compounds. In liquid water part of the initial spin polarization cannot be accounted for in terms of existing models of muonium formation and reaction. This missing fraction is postulated to arise via a spin exchange interaction of muonium with a hydrated electron. It is also suggested that the chemical fate of the muon is determined by reactions with transient species created in the terminal spur of the muon track.

Radiolysis effects in muonium chemistry

Polyfluorenes (pF) were synthesized having anthraquinone (AQ) or naphtylimide (NI) end caps that trap electrons or di-p-tolylaminophenyl (APT2) caps that trap holes. The average lengths of the pF chains in these molecules varied from 7 to 30 nm. End capping was found not to be complete in these molecules so that some were without caps. Electrons or holes were injected into these polymers in solution by pulse radiolysis. Following attachment, the charges migrated to the end cap traps in times near 2 ns in pF12AQ or 5 ns in pF35NI. From these observations, electron mobilities for transport along single chains to the end caps in THF solution were determined to be smaller by a factor of 100 than those observed by microwave conductivity. Despite this, the mobilities were sufficiently large to provide encouragement to the use of such single chains in solar photovoltaics. Most charges were observed to transport over substantial distances in these polymers, but 23, 18, and 37% of the charges attached to pFNI, pFA...

Electron and hole transport to trap groups at the ends of conjugated polyfluorenes.

The one-electron reduction product of nitrate, the NO{sub 3}{sup 2-} radical, was reinvestigated because of the contemporary interest in its reactivity in high-level liquid radioactive systems Indirect observations suggest that the same dianion is produced by the precursor to the solvated electron The redox potential of the couple NO{sub 3}{sup -}/NO{sub 3}{sup 2-} was calculated, using several ab initio approaches combined with semiempirical solvation models, to be E{sup o} {approx} -11 V vs NHE Using the theoretical prediction to guide the experiment, we find a value of E{sup o} = -089 V at zero ionic strength Kinetic and free-energy-relationship arguments are used to question the acid-base equilibria and reaction mode that converts the NO{sub 3}{sup 2-} to the oxidizing NO{sub 2} radical It is proposed that the reaction of the dianion with various general acids is an O{sup 2-} (ie, water or OH-) transfer to the acid and not proton transfer to NO{sub 3}{sup 2-} Implications of the highly negative redox potential of the dianion and the existence of the protonated forms to practical systems are discussed

K.Y. Lam

Papers

Picosecond pulse radiolysis—VI. Fast electron reactions in concentrated solutions of scavengers in water and alcohols