For acquiring high-contrast and high-brightness images in hard-x-ray optics, Fresnel zone plates with high aspect ratios (zone height/zone width) have been constantly pursued. However, knowledge of aspect ratio limits remains limited. This work explores the achievable aspect ratio limit in polymethyl methacrylate (PMMA) by electron-beam lithography (EBL) under 100 keV, and investigates the lithographic factors for this limitation. Both Monte Carlo simulation and EBL on thick PMMA are applied to investigate the profile evolution with exposure doses over 100 nm wide dense zones. A high-resolution scanning electron microscope at low acceleration mode for charging free is applied to characterize the resultant zone profiles. It was discovered for what we believe is the first time that the primary electron-beam spreading in PMMA and the proximity effect due to extra exposure from neighboring areas could be the major causes of limiting the aspect ratio. Using the optimized lithography condition, a 100 nm zone plate with aspect ratio of 15/1 was fabricated and its focusing property was characterized at the Shanghai Synchrotron Radiation Facility. The aspect ratio limit found in this work should be extremely useful for guiding further technical development in nanofabrication of high-quality Fresnel zone plates.

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We are now beginning to see the application of extreme ultraviolet (EUV) lithography to the mass production of 7 nm node logic devices, primarily for smartphones. This lithography technology currently attracts the most interests due to its expected use in upcoming mass production of 5nm node and beyond for semiconductor devices. The development of EUV resists are one of the key research areas. However, EUV exposure instruments are extremely costly, and there are currently no tools that can be used for resist development. To promote the development of EUV resists, we investigated an evaluation method based on EB exposure for EUV resist. Due to similar exposure reaction mechanisms to EUV exposure, EB exposure offers a practical alternative. This paper examines the use of EB exposure simulations to advance EUV resist development.

In this paper, grayscale electron beam lithography is applied to generate multistep Aztec profiles (MAPs) for angle-resolved spectral applications such as microspectrometers. Monte Carlo simulations taking into consideration the proximity effect are carried out to calculate the spatial dose distributions for desired profiles, using actual dissolution rates measured on the same resist. The MAPs in PMMA resist with step heights from 50 to 200 nm and step widths from 0.1 to 5 μm are achieved by high-resolution electron beam lithography, and high-resolution scanning electron microscopy and atomic force microscopy are used to characterize the quality of the MAPs. Angle-resolved spectra of the reflectance are obtained using a finite-difference time-domain simulator and by experimental measurements. A distinct angle selection of the wavelengths is demonstrated, though the high surface roughness measured on the deeper steps may cause broadening of the spectral peaks. Initial investigations into the origin of the surface roughness are carried out, and further improvements are discussed.

Electron beam lithography shot-pattern design technologies and a dedicated algorithm for patterning and miniaturization of the exposure area were investigated. Beam step-size fracturing was used to optimize the fill pattern at the designed pattern edges, and propagation loss was reduced for a 500-nm-wide Si wire waveguide with a 30°tilt angle from 4.7 to 3.0 dB/cm using a conventional process. Furthermore, proximity effect correction technology allowed the integration of different trench widths for a 5 µm spot-size converter and 1 µm Si wire waveguide. The propagation loss was reduced to 2.1 dB/cm due to optimization of the dose density for each exposure area, and runtime was reduced to less than half.