Electron-beam lithography (EBL) is an important technique in manufacturing high-resolution nanopatterns for broad applications. However, the proximity effect in EBL can degrade the pattern quality and, thus, impact the performance of the applications greatly. The conventional proximity effect correction (PEC) methods, which employ computationally intensive cell or path removal method for development simulation, are very computational lengthy, especially for complex and large-area patterns. Here, the authors propose a novel short-range PEC method by transforming the evaluation of pattern feasibility into the shortest path problem based on the concept of critical-development time. The authors combine this evaluation algorithm with the swarm intelligence which mimics the natural collective behavior of animals to optimize the design of electron dose distribution in EBL. The PEC algorithm is applied for pattern fabrication for U-shaped split-ring resonator and produces optimized exposure pattern that shows excellent agreement with the targeted objectives. Our work on the PEC strategy reduces the computational cost significantly and is particularly suitable for the design of complex pattern with various constraints.

This report deals with the feasibility of carrying out in-situ monitoring of cavity filling in nanoimprints using capacitance measurements with a capacitance circuit built-in on the mold body. A finite element model valid for the numerical description of a parallel-plate capacitor has been developed, and simulations were carried out to predict the influence of cavity filling on capacitance values. On the other hand, in order to measure the continuous variations in capacitance of a parallel-plate capacitor during the course of imprinting, a series of experiments have been performed isothermally, and the capacitance values have been measured at various imprinting stages. The correlation between capacitance values and replicated polymer heights was studied. The preliminary results presented indicate that capacitance measurement is a feasible tool for the monitoring of cavity filling in nanoimprints.

Nanoimprinting has been recognized as a highly potential method of volume production for nanoscale devices. In the nanoimprinting process, the filling process of the mold cavity plays a key role in determining the productivity of the nanoimprinting process and the quality of the final imprint product. A defective filling of the mold affects the uniformity, precision, and throughput of the imprint. The mold filling is subjected to the applied imprinting pressure and temperature, repetitive mold use, mold sticking, or factors regarding mold features. It involves physical contact between the mold and the polymer layer on the substrate surface; thus, how the polymer fills up the cavity is of major interest and is vital in pattern transfer. The proposed study employs a finite element model for the single mold cavity to simulate the nanoimprint process. The mold is assumed to be a linear elastic body and the polymer preheated above its glass transition temperature is considered to be nonlinear elastic, described by the Mooney-Rivlin model. The numerical model is able to predict the mold filling at any nanoimprint stage and the mold cavity with various aspect ratios. To study the effects of pattern density and contact friction existing between the mold and polymer during the mold filling of the nanoimprinting process, an imprint mold with mixed pattern density is simulated and a sensitivity analysis of a contact friction coefficient on the mold filling is performed. Both the cavity feature and pattern density have significant effects on mold filling of the nanoimprinting process, while the contact friction coefficient has a mild effect. The obtained results support the development of a process recipe and automatic large-scale industrial production for nanoimprinting.

In this study, we propose a set of single-spot experiment to construct a comprehensive model of electron-beam lithography to describe the relation among the incident electrons, resist, and the development conditions such as durations and temperatures. Through the experiments, small feature can be achieved by performing a short-time development due to the high acceleration voltage and large depth of focus of electron-beam system. The singular point in the beginning of the development is also observed in our model and supported by the experimental data. In addition, we verify the characteristic region of each incident spot induced by the point spread function of the electron-beam system. We further fabricate the single line with narrow groove width by utilizing the results from single-spot experiment at low developing temperatures. The line is formed by arranging a series of incident points with a distance close to the characteristic radius. This method can eliminate the proximity effect effectively and thus the groove width is scaled down to 8 nm. By adopting the successful experience in the single line formation, dense array with narrow linewidth is also demonstrated under well suppression of the proximity effect. The minimum groove width of 9 nm with 30 nm pitch is achieved with 5 s development time at -10 °C. Finally, the exceptional capability of pattern transfer is presented due to the high aspect ratio of the resist.

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