Seth Kruger

Fluorinated Acid Amplifiers for EUV Lithography

Five new compounds were synthesized for use as acid amplifiers in EUV (13.5 nm) photoresists. Four compounds act as acid amplifiers and decompose by autocatalytic kinetics to generate fluorinated sulfonic acids, essential for the simultaneous improvement of resolution, sensitivity, and line edge roughness (LER) in EUV photoresists. The decomposition rates were studied using (19)F NMR in the presence and absence of 1.2 equiv of tri-tert-butylpyridine. Three acid amplifiers decomposed 490, 1360, and 1430 times faster without base than with base. Preliminary lithographic evaluations show that cis-1-methyl-2-(4-(trifluoromethyl)phenylsulfonyloxy)cyclohexyl acetate simultaneously improves the resolution, LER, and sensitivity of an EUV photoresist.

RLS tradeoff vs. quantum yield of high PAG EUV resists

The effect of higher film quantum yields (FQYs) on the resolution, line-edge roughness, and sensitivity (RLS) tradeoff was evaluated for extreme ultraviolet (EUV, 13.5 nm) photoresists. We determined the FQY of increasingly high levels of an iodonium photoacid generator (PAG) using two acid detection methods. First, base titration methods were used to determine C-parameters for acid generation, and second, an acid-sensitive dye (Coumarin-6) was used to determine the amount of acid generated and ultimately, to determine absorbance and FQYs for both acid detection methods. The RLS performance of photoresists containing increasing levels of PAG up to ultrahigh loadings (5-40 wt% PAG) was evaluated. RLS was characterized using two methods: • KLUP resist performance •Z-Parameter (Z = LER2*Esize*Resolution3)

Investigation of Sensitivity of Extreme Ultraviolet Resists to Out-of-Band Radiation

A method to evaluate the sensitivity of photoresists used for extreme ultraviolet (EUV) lithography has been developed. EUV sources produce out-of-band radiation and the reflective optics used in EUV tools reflect some of this out-of-band light on the wafer plane. The effect of exposing these photoresists to this unwanted light can reduce the image contrast on the wafer, and thereby reduce the image quality of the printed images. To examine the wavelengths of light that may have an adverse effect on these resists, a deuterium light source mounted with a monochromator has been designed to determine how sensitive these photoresists are to light at selected wavelengths in the range 190-650 nm.

Can Acid Amplifiers Help Beat the Resolution, Line Edge Roughness, and Sensitivity Trade-Off?

In this paper, we describe the structures of several new acid amplifiers and of extreme ultraviolet (EUV) resist formulations prepared from them. We have synthesized and lithographically evaluated eleven new compounds specifically designed for use as acid amplifiers in EUV resists. We make direct comparisions between resolution, line-edge roughness (LER) and sensitivity using the common resolution, line-edge roughness, and sensitivity (RLS) analysis technique of Z-parameter. We show that acid amplifiers are capable of simultaneously improving resolution, LER, and sensitivity.

Mass spectrometer characterization of reactions in photoresists exposed to extreme ultraviolet radiation

The development of resists that meet the requirements for resolution, line edge roughness and sensitivity remains one of the challenges for extreme ultraviolet (EUV) lithography. Two important processes that contribute to the lithographic performance of EUV resists involve the efficient decomposition of a photoacid generator (PAG) to yield a catalytic acid and the subsequent deprotection of the polymer in the resist film. We investigate these processes by monitoring the trends produced by specific masses outgassing from resists following EUV exposure and present our initial results. The resists tested are based on ESCAP polymer and either bis(4-tert-butylphenyl)iodonium perfluoro-1-butanesulfonate or bis(4-tert-butylphenyl)iodonium triflate. The components originating from the PAG were monitored at various EUV exposure doses while the deprotection of the polymer was monitored by baking the resist in vacuum and detecting the cleaved by-product from the polymer with an Extrel quadruple mass spectrometer.

Options for high index fluids for third generation 193i lithography

Successful fluids for use in 3rd generation 193 nm immersion lithography must have refractive indices of ≥ 1.80 at 193 nm, ≤ 0.15/cm absorbance at 193 nm, and be photochemically inert to 193 nm radiation. Various classes of organic compounds were prepared and evaluated for use as 3rd generation 193 nm immersion fluids. Functional groups that were evaluated included: sulfones, sulfoxides, sulfonic acids, ammonium sulfonate salts, alkanes, alkyl chlorides, alkynes, and nitriles. Several compounds were synthesized including three sulfone and three sulfonic acid compounds. Other commercially available compounds of interest underwent extensive purification prior to evaluation. Although this work did not lead to any specific solutions to the challenge of identifying 3rd generation 193 nm immersion fluids, it can be concluded that high density hydrocarbons based on cubane may have the best chance of meeting these goals.

Lithographic evaluation and chemical modeling of acid amplifiers used in EUV photoresists

This paper describes the lithographic properties of fifteen acid amplifiers (AAs) and the chemical modeling approach used to predict their thermal stability in an ESCAP polymer resist system at 70 and 110 °C. Specifically, we show how added AAs affect the sensitivity (Eo and Esize), resolution, line edge roughness (LER), exposure latitude, and Z-parameter of ESCAP resists. We find that acid amplifiers that generate fluorinated sulfonic acids give the best combination of sensitivity, LER, and exposure latitude. Additionally, we show that these compounds are not photochemically active. Combining thermodynamic and kinetic modeling has allowed us to predict the relative enthalpies of activation for catalyzed and uncatalyzed decomposition pathways and compare the results to experimental thermal stability tests.

Models for Predicting the Index of Refraction of Compounds at 193 and 589 nm

A simple empirical model is presented that predicts the index of refraction at 589 nm (D-line) and 193 nm for molecules based solely on chemical structure. The model was built by comparing literature values of refractive indices (sodium D-line 589 nm) of compounds with representative functionalities and has 18 adjustable parameters. Published values for nD and n193 were used to extrapolate the predictions from values of nD to values of n193. These simple, accessible models can be run using only Excel software on a laptop computer.