In this submission, we introduce the performance and attributes of our broadband EUV source, which is generated using a copper-based laser-produced plasma. This source is currently operational in EUV Tech’s HVM reflectometer and multi-angle reflectometer / scatterometry (ENK) tools.
EUV lithography is rapidly being pushed to its resolution limit, where tradeoffs are heightened between resolution, throughput, and stochastics. Mitigation strategies include attenuated phase shift masks (aPSMs) and thinner high-k absorbers. Furthermore, multilayer bandwidth and phase shift may need to be reassessed. All these improvements relate to mask 3D effects (M3D), arising from several causes: First, phase shift vs pitch, which sets the aPSM target phase shift around 1.2pi instead of pi. Second, absorber thickness effects which directly relate to the promise of high-k absorbers. And third, multilayer effects like bandwidth and phase vs angle. We propose to quantify these effects in simulation for different EUV scanner generations (0.33 NA, high-NA, or hyper-NA). Finally, we will propose measuring these effects with the EUV Tech ENK (EUV n/k tool) using actinic scatterometry. The complexity of M3D suggests that new metrics of multilayer and absorber performance beyond reflectivity will need to be considered. Actinic scatterometry provides a promising route to measuring M3D due to its sensitivity to wavelength, angle, and feature size.
In extreme ultraviolet lithography, multilayer roughness effects are a key contributor to mask-induced pattern roughness1. In particular, replicated roughness from the mask substrate results in a spatially dependent phase error that ultimately manifests as aerial image roughness at the wafer. In this paper, we utilize Monte Carlo methods to study the impact of multilayer roughness on the printing of two-dimensional patterns. We focus on the impact of multilayer roughness on both TaN absorber masks as well as attenuated phase shift masks, comparing roughness impact on each architecture at both 0.33 and 0.55 NA EUV lithography. We examine whether the modeled multilayer roughness explains observed patterning phenomena, with a focus on what level of remedy would be required for multilayer roughness effects to become negligible components of the patterning error budget.
With EUV attenuated phase shift absorbers rapidly approaching maturity, actinic metrology soon will be required to ensure phase accuracy, uniformity, and stability. The target phase shift for these absorbers is carefully optimized to a value typically around 1.2pi for optimal printing. The additional 0.2pi is necessary due to mask 3D effects (M3D), which increasingly distort the near-field scattering and phase as the feature size is reduced. Therefore, EUV attenuated phase shift masks require phase metrology not only for large-area multilayer and absorber, but also for feature-dependent in-pattern phase. We demonstrate in-pattern phase measurement using spectroscopic variable angle scatterometry with the commercially available EUV Tech ENK (EUV n/k tool). We describe experiments validating the accuracy and precision of actinic scatterometry-based pattern phase measurements conducted on the ENK platform through direct comparison to synchrotron reference scattering measurements.
With EUV Attenuated Phase Shift Masks (aPSMs) rapidly approaching maturity, actinic metrology soon will be required to ensure phase accuracy, uniformity, and stability. The target phase shift is carefully designed to an optimized value, which is not 𝜋, but typically around 1.2𝜋 for optimal printing at critical feature sizes. The additional 0.2𝜋 phase shift is necessary due to mask 3D effects (M3D), which increasingly distort the nearfield scattering and phase as the feature size is reduced. Therefore, EUV attenuated phase shift masks require metrology, not only for the relative Fresnel phase shift between large-area multilayer and absorber regions, but also for the feature-dependent pattern phase shift in the near-field scattering. We demonstrate a metrology solution for measuring the in-pattern phase shift using spectroscopic variable angle scatterometry. The measurements are performed using the commercially available EUV Tech ENK (EUV n/k tool), based on a compact continuously tunable laser-produced plasma light source. In this presentation we describe experiments validating the accuracy and precision of actinic scatterometry-based pattern phase measurements conducted on the ENK platform on seven samples of EUV attenuated phase shift absorbers of varying thickness. We demonstrate good agreement with simulation on measurements of phase vs absorber thickness and phase vs grating pitch, validating the suitability of this measurement for measuring the actinic phase shift of an EUV mask.
With the coming adoption of EUV phase shift absorbers in high-volume manufacturing, it soon will be critical to ensure phase uniformity across the mask and stability over time. Synchrotron-based EUV variable angle spectroscopic reflectometry has been demonstrated to be a highly sensitive metrology technique for the measurement of phase. More recently, this phase measurement technique has been successfully implemented as a fab-scale tool based on a laser produced plasma source. The metrology enabled by this tool supports the continual monitoring of phase stability in a manufacturing environment, which can provide invaluable knowledge about best practices for mitigating or reversing phase drift resulting from effects such as contamination and mask aging. In this presentation we report on such phase drift measurements on real EUV masks looking at various sources of phase change on the mask.
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