Craig Higgins

Evaluation of EUV resist materials for use at the 32 nm half-pitch node

The 2007 International Technology Roadmap for Semiconductors (ITRS)1 specifies Extreme Ultraviolet (EUV) lithography as one leading technology option for the 32nm half-pitch node, and significant world wide effort is being focused towards this goal. Readiness of EUV photoresists is one of the risk areas. In 2007, the ITRS modified performance targets for high-volume manufacturing EUV resists to better reflect fundamental resist materials challenges. For 32nm half-pitch patterning at EUV, a photospeed range from 5-30 mJ/cm2 and low-frequency linewidth roughness target of 1.7nm (3σ) have been specified. Towards this goal, the joint INVENT activity (AMD, CNSE, IBM, Micron, and Qimonda) at Albany evaluated a broad range of EUV photoresists using the EUV MET at Lawrence Berkeley National Laboratories (LBNL), and the EUV interferometer at the Paul Scherrer Institut (PSI), Switzerland. Program goals targeted resist performance for 32nm and 22nm groundrule development activities, and included interim relaxation of ITRS resist performance targets. This presentation will give an updated review of the results. Progress is evident in all areas of EUV resist patterning, particularly contact/via and ultrathin resist film performance. We also describe a simplified figure-of-merit approach useful for more quantitative assessment of the strengths and weaknesses of current materials.

Film quantum yields of EUV& ultra-high PAG photoresists

Base titration methods are used to determine C-parameters for three industrial EUV photoresist platforms (EUV- 2D, MET-2D, XP5496) and twenty academic EUV photoresist platforms. X-ray reflectometry is used to measure the density of these resists, and leads to the determination of absorbance and film quantum yields (FQY). Ultrahigh levels of PAG show divergent mechanisms for production of photoacids beyond PAG concentrations of 0.35 moles/liter. The FQY of sulfonium PAGs level off, whereas resists prepared with iodonium PAG show FQYs that increase beyond PAG concentrations of 0.35 moles/liter, reaching record highs of 8-13 acids generated/EUV photons absorbed.

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)

Resolution, Line-Edge Roughness, Sensitivity Tradeoff, and Quantum Yield of High Photo Acid Generator Resists for Extreme Ultraviolet Lithography

Ultrahigh loadings of photoacid generators (PAGs) in phenolic extreme ultraviolet (EUV) resists have generated the highest known film quantum yields (FQYs). We evaluate the performance of these resists in terms of resolution, line-edge roughness (LER), and sensitivity and collectively evaluate these three parameters (known as RLS) in terms of KLUP and Z-Parameter figures of merit. An analytical model describing the kinetics of photodecomposition was developed to explain the relationship between film quantum yield and PAG concentration. Resists were prepared using a broad range of concentrations of iodonium (DTBPI-PFBS), sulfonium (TPS-PFBS), and non-ionic (NDI-PFBS) PAGs. The model fits the experimental data (correlation coefficient R2 = 0.998, 0.994, and 0.995) and compares the rate at which electrons react with PAGs or recombine with holes. Resists prepared with 15–20 wt % of iodonium nonaflate PAG exhibit both high quantum yields and the best RLS performance as determined using both KLUP and Z-Parameter methodologies. The improvement in RLS performance correlates with the increase in FQY at higher PAG concentrations.

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.

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.