Comparison of Acid Generation in EUV Lithography Films of Poly(4-hydroxystyrene) (PHS) and Noria Adamantyl Ester (Noria-AD₅₀)

Abstract

The mechanism for acid production in phenolic extreme ultraviolet (EUV) lithography films containing triphenylsulfonium triflate (Ph(3)S(+)TfO(-)) acid generator has been investigated by electron paramagnetic resonance (EPR) spectroscopy and by use of the acid indicator coumarin 6 (C6). Gamma radiolysis was substituted for the EUV radiation with the assumption that the chemistry generated by ionization of the matrix does not depend on the ionization source. Poly(4-hydroxystyrene) (PHS) was first investigated as a well-studied standard, after which the water-wheel-like cyclic oligomer derivative containing pendant adamantyl ester groups, noria-AD(50), was investigated. EPR measurements confirm that the dominant free radical product is a phenoxyl derivative (PHS-O(•) or noria-O(•)) that exhibits quite slow stretched exponential recombination kinetics at room temperature. Also observed at 77 K was the presence of a significant hydrogen atom product of radiolysis. The G value or yield of acid production in thin lithography films was measured with the C6 indicator on a fused silica substrate. It was found that a significant amount of acid is generated via energy transfer from the irradiated fused-silica substrate to the Ph(3)S(+)TfO(-) in the films. By varying the film thickness on the substrates, the substrate effect on the acid yield was quantitatively determined. After subtraction of the contribution from the substrates, the acid yield G value in the PHS film with 10 wt % Ph(3)S(+)TfO(-) and 5 wt % C6 was determined to be 2.5 ± 0.3 protons per 100 eV of radiation. The acid yield of noria-AD(50) films was found to be 3.2 ± 0.3 protons per 100 eV.

Molecular Glass Photoresists with High Resolution, Low LER, and High Sensitivity for EUV Lithography

“…One practical method to solve this problem is to prepare a new kind of photoresist material which can simultaneously improve pattern's resolution, sensitivity, and LER. Under this RLS restriction and the critical requirements on resolution, LER, and sensitivity in EUVL, previous polymer photoresist system is difficult to satisfy this demand since its large molecular weight, uneven distribution of compositions as well as excessive and inhomogeneous acid diffusion caused by the aggregation of polymer chains …”

Driving Force Dependence of Electron Transfer from Electronically Excited [Ir(COD)(μ-Me2pz)]2 to Photo-Acid Generators

“…PAGs have been studied in detail concerning their mechanism(s) to produce acid upon direct photolysis and sensitization. − Electron transfer to PAG has been proposed to be one excited-state pathway that leads to the production of acid. This pathway may become more important in EUV lithography, as 13.5 nm light (91.8 eV) is proposed to produce high energy photoelectrons which in turn thermalize upon interaction with various components of a photoresist, including the PAGs. − While a correlation has been proposed for the acid generation efficiency to the reduction potential of PAGs, , to date, no studies have been conducted to understand which factors determine the rates at which PAGs are reduced. Therefore, we investigated PAG reduction by employing electronically excited [Ir­(COD)­(μ-Me 2 pz)] 2 (COD = 1,5-cyclooctadiene; Me 2 pz = 3,5-dimethylpyrazolyl) as an electron donor (Figure ).…”

Progresses and Challenges of EUV Lithography Materials

“…Resins for EUV resists are mostly hydroxyl styrene, acrylate and alicyclic polymers of the kinds in use in 248 nm and 193 nm lithographic resists [1,2,3]. The photoacid generators are also based on similar chemistries as those used on 248 nm and 193 nm lithography [4] although they are optimized to tune their sensitivity to EUV radiation.…”