Electron trapping: a mechanism for acid production in extreme ultraviolet photoresists

Background: Stochastic defects are becoming major concern in the future extreme ultraviolet (EUV) lithography as their probability P d exponentially increases with decreasing feature size and is highly sensitive to variations in process/mask conditions. Photon shot-noise and discrete/ probabilistic nature of materials have been blamed as their causes. Aim: We introduce models for relating P d to photon and resist statistics under various exposures and material conditions and analyze their impact in future EUV lithography. Approach: Three-dimensional reaction distribution is calculated by a fully coupled Monte Carlo simulation including discrete photon, photoelectron scattering, and resist stochastics. Then probability models predict P d from statistical data extracted from Monte Carlo results. Results: Stochastic defect generation is enhanced by cascade and/or cluster of correlated reactions among nearby polymers/molecules due to secondary electrons (SE)/acid diffusion and SEs generated along scattered photoelectron trajectories. P d decreases with increasing reaction density, suppressing effective image blur, and introducing quenchers, where reaction density is limited by SE, photoacid generator, and reaction site. Defect probability increases with decreasing target size for the same k1-factor, while strongly dependent on image slope and defocus. Conclusions: Our analyses suggest that applying EUV lithography to smaller target requires careful material choice, extremely precise process control, and further EUV power enhancement.

Section: Monte Carlo Methodsmentioning

confidence: 99%

Cascade and cluster of correlated reactions as causes of stochastic defects in extreme ultraviolet lithography

Fukuda

2020

“…Electron affinity and its effect on PAG performance have been studied 27 showing that, if a PAG can be reduced more easily in a cyclic voltammetry, resists consisting of that PAG have a lower dose to clear. 28 To estimate the electron affinity computationally, we compute the lowest unoccupied molecular orbital (LUMO) energy of the four onium PAGs used in Ref. 28 and use it as a proxy for electron attachment affinity.…”

Section: Electron Attachmentmentioning

confidence: 99%

“…28 To estimate the electron affinity computationally, we compute the lowest unoccupied molecular orbital (LUMO) energy of the four onium PAGs used in Ref. 28 and use it as a proxy for electron attachment affinity. In Ref.…”

Section: Electron Attachmentmentioning

confidence: 99%

Investigating extreme ultraviolet radiation chemistry with first-principles quantum chemistry calculations

Heidkamp

Wang

Neureuther

et al. 2020

In extreme ultraviolet (EUV) lithography, chemistry is driven by secondary electrons. A deeper understanding of these processes is needed. However, electron-driven processes are inherently difficult to experimentally characterize for EUV materials, impeding targeted material engineering. A computational framework is needed to provide information for rational material engineering and identification at a molecular level. We demonstrate that density functional theory calculations can fulfill this purpose. We first demonstrate that primary electron energy spectrum can be predicted accurately. Second, the dynamics of a photoacid generator upon excitation or electron attachment are studied with ab-initio molecular dynamics calculations. Third, we demonstrate that electron attachment affinity is a good predictor of reduction potential and dose to clear. The correlation between such calculations and experiments suggests that these methods can be applied to computationally screen and design molecular components of EUV material and speed up the development process.

“…In CAR, [13][14][15][16] photoacid generator molecules generate photoacid upon absorbing photon energy for DUV exposure or SE energy for EUV exposures. 17 Here, we include the discrepancies between the locations of acid generation and photon absorption/SE generation in randomness of photon absorption or SE generation as approximation. Acids promote acid-catalytic reactions to flip the polarity of polar moieties in resist matrix polymers or molecules within the diffusion range of acid.…”

Section: Statistical Model Of Resist Reactionsmentioning

confidence: 99%

Localized and cascading secondary electron generation as causes of stochastic defects in extreme ultraviolet projection lithography

Fukuda

2019

Projection lithography using extreme ultraviolet (EUV) light at 13-nm wavelength is expected to achieve production of integrated circuits below 10 nm design-rules. In pursuit of further miniaturization, however, stochastic pattern defect problems have arisen. Here, we discuss the possible impact of spatially inhomogeneous secondary electron (SE) generation on stochastic defects. Two mechanisms are investigated: (1) accidental connections of photon shot noises enhanced by densely localized SE generation and (2) cascading SE generation along photoelectron trajectory traveling from pattern edge into a dark region. Since such defect probabilities are extremely low (typically 10 −4 to ∼10 −12), results of Monte Carlo simulation based on classical optical image and electron scattering simulations are converted into probability functions for densities of physical/chemical events such as photon absorption, SE generation, and elementary reaction in chemically amplified resists. Probabilities of pattern formation and of defect generation are modeled using these functions. Results of performance optimization using a multiobjective genetic algorithm show higher stochastic defects probability in EUV than in conventional deep-UV exposure due to larger spatial inhomogeneity in reaction density and existence of SE generation strings. Defect probabilities are strongly dependent on absolute pattern sizes in the two mechanisms, regardless of the resolution capability of imaging systems. Guidelines for suppressing stochastic defects are suggested, such as homogenization of reaction density, material composition for increasing scattering crosssection, and suppression of pattern edge fluctuation.