Line-edge roughness (LER) is often measured from top-down critical dimension scanning electron microscope (CD-SEM) images. The true three-dimensional roughness profile of the sidewall is typically ignored in such analyses. We study the response of a CD-SEM to sidewall roughness (SWR) by simulation. We generate random rough lines and spaces, where the SWR is modelled by a known power spectral density. We then obtain corresponding CD-SEM images using a Monte Carlo electron scattering simulator. We find the measured LER from these images, and compare it to the known input roughness. We find that, for isolated lines, the SEM measures the outermost extrusion of the rough sidewall. The result is that the measured LER is up to a factor 2 less than the true on-wafer roughness. The effect can be accurately modelled by making a top-down projection of the rough edge. Our model for isolated lines works fairly well for a dense grating of lines and spaces, as long as the trench width exceeds the line height.
Dip-pen nanolithography (DPN) is a low-cost, versatile, bench-top technology for direct patterning of materials over surfaces. Our study reports on the production of two-dimensional optical grating nanostructures based on polymers, using DPN. The influence of both the ink composition and the dwell time were investigated. Prototypes of phase masks were manufactured, and their main characteristics were analyzed. The results in our work may contribute to improving the fabrication process of optical structures, including the production of microlenses with controlled focal length.
Background: In-line metrology for three-dimensional (3D) profiling high-aspect-ratio (HAR) features is highly important for manufacturing semiconductor devices, particularly for memory devices, such as 3D NAND and DRAM. Aim: Our purpose was to obtain the cross-sectional profiles of the HAR features from top-view critical dimension scanning electron microscopy (CD-SEM) images. Approach: Based on Monte Carlo simulation results, we proposed a method for 3D profiling of HAR features using backscattered electron (BSE) signal intensities. Several kinds of HAR holes with different taper angles and bowing geometries were fabricated. High-voltage CD-SEM was used for experiments to determine the feasibility of our approach. Results: Using the BSE line-profile, we constructed cross sections of the taper holes and estimated sidewall angles (SWAs), which were approximately the same as those observed using field-emission scanning electron microscopy (FE-SEM). The constructed cross sections of the bowing holes and the trends of the geometric variance, which were estimated by the middle CD and its depth, were consistent with the cross sections observed by FE-SEM. Conclusions: The results demonstrate that the variation in the HAR holes, such as SWA and bowing geometry, can be measured and monitored using the BSE images.
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.
JM3 Co-Editor-in-Chief Harry Levinson introduces new guidelines regarding materials for lithography.
