Metal oxide photoresists are recognized as an integral component in the high–numerical aperture future of EUV lithography and the challenging feature sizes required at associated nodes. Many properties of these materials, such as their high EUV absorptivity, etch selectivity, and relatively small molecular size are particularly beneficial for enabling the advancement of lithographic processes. To help ease process development efforts involving these materials, a previously reported rigorous stochastic lithography model has been built using in-depth knowledge of the chemical and material processes that govern the behavior of spin-on metal oxide resists. Experimental data from a series of measurement techniques were used to both define and parametrize the fundamental equations that underlie the lithographic performance of these materials. The resulting parameters were then calibrated to a dataset derived from an extensive series of CD-SEM and open-frame exposures. In this model update, the match between simulated data and experiment has been improved both by more targeted calibration efforts and by the inclusion of more diverse exposure measurements into the calibration dataset. Interrogating the changes necessary to improve performance provides insights into resist behavior and how disparate process steps are interrelated. The updated model is used to simulate a series of exposure conditions outside of the calibration dataset to both validate the model and show its capabilities. Together, the fundamental nature of the model and the insights gained through its calibration provide a powerful tool to drive process optimization for metal oxide materials.
Airborne molecular contaminants (AMCs) in the cleanroom have been known to impact the performance of photoresist materials. Here, we investigate the effect of the environment composition during post-exposure delay (PED) on metal oxide resists (MOR). We applied specific environments during a fixed PED time and measured the impact of each condition on the printed L/S patterns by measuring the change in the final critical dimension (CD) in each case compared to a reference control. We performed chemical analysis to elucidate which chemical changes take place in the resist under the conditions that induced the largest CD changes. Our results suggest that the magnitude of the CD change after a fixed PED time depends on two main variables: the concentration of contaminants and the humidity of the environment. The chemical analysis after a PED in the presence of contaminants and humidity revealed that extra ligand cleavage takes place under these conditions compared to the reference non-delayed conditions. The results show that deviations from the target CD in MOR can be prevented by having control over humidity, contaminant levels, and PED time during processing. Furthermore, new optimized formulations designed to hinder extra chemical reactions during PED show a stable CD even when the PED was applied in environments with humidity and contaminants.
One of the key steps in the pattern formation chain of extreme ultraviolet (EUV) lithography is the development process to resolve the resist pattern after EUV exposure. The traditional development process might be insufficient to achieve the requirements of ultra-high-resolution features with low defect levels. The aim of this paper is to establish a process to achieve a good roughness, a low defectivity at a low EUV dose, and capability for extremely-high-resolution for high numerical aperture (NA) and hyper-NA EUV lithography. A new development method named ESPERT™ (Enhanced Sensitivity develoPER Technology™) has been introduced to improve the performance of metal oxide-resists (MOR). ESPERT™ as a chemical super resolution technique effectively apodized the MOR chemical image, improving chemical gradient (higher exposure latitude (EL)) and reducing scums (fewer bridge defects). This new development method can also keep the resist profile vertical to mitigate the break defects. The performances of the conventional development and ESPERT™ were evaluated and compared using 0.33 NA EUV, 0.5 NA EUV, and electron beam (EB) exposures, for all line-space (LS), contact hole (CH), and pillar (PL) patterns. Using 0.33 NA EUV scanners on LS patterns, both bridge and break defects were confirmed to be reduced for all 32-nm-pitch, 28-nm-pitch, 26-nm-pitch LS patterns while reducing the EUV dose to size (DtS). In the electrical yield (1 meter length) test of breaks/bridges of 26-nm pitch structures, ESPERT™ reduced EUV dose while its combo yield was almost 100% over a wide dose range of 20mJ/cm². For CH patterns, in the case of 32-nm-pitch AEI (after etch inspection), EL was increased 7.5% up to 22.5%, while failure free latitude (FFL) was widened from 1-nm to 4-nm. A 16-nm-pitch LS pattern was successfully printed with 0.5 NA tool, while a 16-nm-pitch PL and an 18-nm-pitch CH patterns were also achieved with an EB lithography by ESPERT™. With ESPERT™, there was no pillar collapse observed for 12-nm half-pitch PL by 0.5 NA and 8-nm half-pitch PL by EB. With all the advantages of having a high exposure sensitivity, a low defectivity, and an extremely-high-resolution capability, this advanced development method is expected be a solution for high-NA EUV towards hyper-NA EUV lithography.
One of the key steps in the pattern formation chain of (extreme ultraviolet) EUV lithography is the development process to resolve the resist pattern after EUV exposure. A simple traditional development process might not be sufficient to achieve the requirements of an ultra-high-resolution feature with low defect levels in high numerical aperture (NA) EUV lithography. In our previous literature, a new development method named ESPERTTM (Enhanced Sensitivity develoPER TechnologyTM) has been introduced to improve the performance of metal oxide resists (MOR) for 0.33 NA EUV lithography by breaking the dose-roughness trade-off. In this work, this development technique was optimised for high-NA lithography to not only keep the advantages of previous ESPERTTM version, but also reduce the defect levels at a higher EUV sensitivity. This is made possible thanks to the capability of the new version of ESPERTTM that can easily remove the residue (undeveloped resist) at low exposure dose area to enhance the developing contrast. Using 0.33 NA EUV scanners at imec on 16-nm half-pitch (HP) line/space (L/S) patterns, with the new development method, EUV dose-to-size (DtS) was reduced roughly 16%, and total after-development-inspection (ADI) defects was reduced by a factor of approximately 7, simultaneously. In another condition, DtS was reduced from 44.2 to 28.4 mJ/cm² (an improvement of 36%), while the number of after-etch-inspection (AEI) single-bridge defects was reduced by half, simultaneously. Using the 0.5 NA exposure tool at Lawrence Berkeley National Laboratory with this new development method, the exposure sensitivity and line-width-roughness (LWR) were both improved by 30% and 21%, respectively. An 8-nm-HP L/S pattern was also successfully printed by this high NA tool. Using a 150 kV electron-beam (EB) lithography system, a 12-nm-HP of pillars was successfully printed on a 22-nm-thick MOR resist with ESPERTTM. With all the advantages of having a high exposure sensitivity, a low defectivity, and an ultra-high-resolution capability, this new development method is expected to be a solution for high-NA EUV lithography.
The unique suitability of metal-oxide (MOx) photoresists for high-NA EUV lithography has been demonstrated by successful imaging of these resists at the resolution limit of high-NA exposure tools.
We utilize the capabilities of the 0.5-NA Berkeley MET5 and a 0.33-NA scanner to explore the RLS impact of specific formulation adjustments, alternative develop chemistries and bake processes, and etch optimization of features from 16-26nm pitch. We investigate the effect of these optimizations on defectivity at aggressive pitches using 0.33-NA exposures. These results validate both fundamental advantages and continued progress of MOx development to align with the introduction of high-NA imaging.
Vibration levels in MET5 exposures were reduced from 1.5 nm RMS to 0.8 nm RMS by tuning the vibration isolation system and removing non-compliant hardware. Frequency doubling exposures were improved by replacing the Fourier synthesis pupil scanner mirror. Focus-exposure-matrix outliers have been solved by patching a bug in the control software. 9 nm half-pitch lines and 8 nm half-pitch lines were printed in 11 nm thick MOx resist.
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