EUV photoresist patterning characterization for imec N7/N5 technology

Background: Inorganic resists show promising performances in extreme ultraviolet (EUV) lithography. Yet, there is a need for understanding the exact chemical mechanisms induced by EUV light on these materials. Aim: To gain knowledge on the EUV chemistry of inorganic resists, we investigate hybrid inorganic-organic molecular compounds, metal oxoclusters (MOCs). Their molecular nature allows for the monitoring of specific structural changes by means of spectroscopy and thus for the elucidation of the mechanisms behind pattern formation. Approach: We compare the sensitivity of MOCs based on Zr and Hf, and methacrylate ligands as EUV resists. The chemical and structural changes causing the solubility switch were investigated by ex situ x-ray spectroscopy, infrared spectroscopy, ultraviolet-visible spectroscopy, and grazing incidence x-ray scattering. Results: Higher sensitivity was detected for the Hf-based material, in line with its higher absorptivity. A small fraction of the carboxylate ligands is lost at doses that yield solubility contrast, whereas aggregation of the inorganic clusters was not observed. Conclusions: These results provide evidence that, although the mechanism of solubility switch in these materials starts with decarboxylation reactions, it mainly proceeds through cross linking of the organic shells instead of aggregation of the inorganic clusters.

Section: Introductionmentioning

confidence: 99%

Mechanistic insights in Zr- and Hf-based molecular hybrid EUV photoresists

Baljozović

Portale

et al. 2019

“…The latter point thus demands that the photoresists have high sensitivity and can yield nanopatterns at doses as low as 20 mJ∕cm 2 or below. 2,[10][11][12] Although the standard platform for resist materials has been polymer-based chemically amplified resists, EUV lithography technology requires the development of entirely new resist platforms. 2,[13][14][15] As future nodes are continuously decreasing, the size of polymers traditionally used in photoresists has become a critical point especially with regard to linewidth roughness.…”

Section: Introductionmentioning

confidence: 99%

Stability studies on a sensitive EUV photoresist based on zinc metal oxoclusters

Thakur

Tseng

Vockenhuber

et al. 2019

Background: Hybrid inorganic-organic materials have emerged as promising candidates for EUV resists. However, knowledge on their stability when deposited as thin films is essential for their performance in EUV lithography. Aim: We investigate whether the molecular structure of Zn-based metal oxoclusters is preserved upon thin film deposition and study aging processes of the thin film under different atmospheres, since these chemical changes affect the solubility properties of the material. Approach: A hybrid cluster that combines the high EUV photon absorption cross-sections of zinc and fluorine with the reactivity of methacrylate organic ligands was synthesized. The structural modifications upon thin film formation and after aging in air, nitrogen, and vacuum were studied using a combination of spectroscopic techniques. Preliminary studies on the lithographic performance of this material were performed by EUV interference lithography. Results: The Zn-based compound undergoes structural rearrangements upon thin film deposition as compared to the bulk material. The thin films degrade in air over 24 h, yet they are found to be stable for the duration and conditions of the lithography process and show high sensitivity. Conclusions: The easy dissociation of the ligands might facilitate hydrolysis and rearrangements after spincoating, which could affect the reproducibility of EUV lithography.

“…[11][12] We assume two types of resist materials: chemically amplified resists (CAR) and nonchemically amplified metal-containing resists, such as metal oxide materials (MOx). 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.…”

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.