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Background: One of the challenges for extreme ultraviolet (EUV) lithography is the mitigation of mask threedimensional effects arising from the oblique incident angle and the mask topography. As the scanners' numerical aperture and the pattern aspect ratio increase, these effects become more prominent. A potential solution to reduce them consists in replacing the current TaBN absorber for a higher-k material. Aim: We demonstrate the potential of a mask inspection platform to evaluate the impact of different absorber materials on actinic defect inspection. Approach: We evaluate the performance of a reflective-mode EUV mask scanning microscope (RESCAN), our actinic lensless inspection tool, with three different absorber materials (hydrogen silsesquioxane, TaBN, and Ni). We study the effect of these materials on the image formation and compare the defect maps. Results: The Ni absorber mask exhibits a better contrast compared to the TaBN one, even though the thickness of the layers differs only by 10 nm. Programmed defects are localized and detected with a high signal-to-noise ratio (SNR). Conclusions: The gain in contrast for the Ni absorber being significant, the SNR is higher for a smaller defect in a TaBN absorber photomask. RESCAN allows the evaluation of the performance of absorber materials in defectivity and image formation on small samples. [ABSTRACT FROM AUTHOR]

Background: The purpose of EUV pellicles is to protect the surface of EUV lithography masks from particle contamination. It is important to ensure that the optical characteristics of the pellicle membrane do not critically affect the reticle image quality. Aim: We want to verify the possibility to integrate pellicle inspection and characterization capabilities in reflective-mode EUV mask scanning microscope (RESCAN), our actinic mask inspection platform based on coherent diffraction imaging. Approach: We studied the impact of a few selected EUV pellicle prototypes on the quality and the contrast of the reticle image obtained with RESCAN. Results: We measured the scattering distribution of the pellicles, and we correlated it with the mask image contrast and fidelity. We also detected the presence of a 6.5-µm-diameter fiber on the pellicle surface. Conclusions: We demonstrated that RESCAN is suitable for through-pellicle actinic mask inspection and can be also used to characterize and monitor the pellicle quality. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet interference lithography (EUV-IL) is a relatively simple and inexpensive technique that can pattern high-resolution line/space and has been successfully used for the resist performance testing. While the aerial image in EUV-IL formed by two beams is straightforward to understand and has contrast of 1, the aerial image formed by four beams providing contact holes is rather complicated. The beam polarization and relative phases of the individual beams play a significant role in the aerial image formation in four-beam interference lithography. In particular, controlling the relative phase of the beams is very difficult to achieve due to short wavelength. To circumvent this problem, we propose an effective double exposure four-beam interference lithography method, by intentionally designing the grating with a slightly different pitch to create an optical path difference that is longer than the coherence length of the EUV light (13.5 nm). We numerically prove the effective double exposure four-beam interference is not sensitive to the phases difference and verify our analytical model by printing both positive tone chemically amplified resist and a negative tone inorganic resist. [ABSTRACT FROM AUTHOR]

Actinic mask defect inspection is an essential process step for the implementation of extreme ultraviolet (EUV) lithography in high-volume manufacturing. The main challenges for any mask defect inspection platform are resolution, sensitivity, and throughput. The reflective-mode EUV mask scanning lensless imaging microscope (RESCAN) is being developed to provide actinic patterned mask inspection capabilities for defects and patterns with high resolution and high throughput for node 7 and beyond. Namely, the goal of the RESCAN project is to develop a tool capable of inspecting an EUV reticle in 7 h and detect mask defects down to a size of 10 nm × 10 nm. The lensless imaging concept allows overcoming the resolution limitations due to the numerical aperture and lens aberrations of conventional mask imaging systems. With the increasing availability of computational power and the refinement of iterative phase reconstruction algorithms, lensless imaging became a powerful tool to synthesize the complex amplitude of the reticle image providing us also with extremely valuable information about phase and mask three-dimensional effects. Here, we present a brief description of the current prototype of the RESCAN platform and illustrate a few experimental examples of programmed defect detection. [ABSTRACT FROM AUTHOR]

Background: Reliable photomask metrology is required to reduce the risk of yield loss in the semiconductor manufacturing process as well as for the research on absorber materials. Actinic pattern inspection (API) of EUV reticles is a challenging problem to tackle with a conventional approach. For this reason, we developed RESCAN, an API platform based on coherent diffraction imaging. Aim: We want to verify the sensitivity of our platform to absorber and phase defects. Approach: We designed and manufactured two EUV mask samples with absorber and phase defects, and we inspected them with RESCAN in die-to-database mode. Results: We reconstructed an image of an array of programmed absorber defects, and we created a defect map of our sample. We inspected two programmed phase defect samples with buried structures of 3.5 and 7.8 nm height. Conclusions: We verified that RESCAN, in its current configuration, can detect absorber defects in random patterns and buried (phase) defects down to 50 × 50 nm2. [ABSTRACT FROM AUTHOR]