Liu Hongzhong

Theory and simulations of peel demolding for large-area nanoimprint lithography

Nanoimprint lithography (NIL) is an emerging nanopatterning approach for producing large-area micro/nano scale structures with low cost, high throughput and high resolution. Demolding has now been considered as one of the most challenging issues for large area NIL, and a bottleneck hindering the industrialization of full wafer NIL. Peel demolding mode has been proven to be an effective way implementing large area nanoimprinting. This paper investigated the theoretical model and numerical simulation of peel demolding for large are NIL. A general model estimating demolding force was established based on the combination of the strain energy method and the conservation of energy in demolding stage. The required separating force for vertical demolding of grating patterns was achieved using the proposed model. Furthermore, the influence of the properties of mold materials and the aspect ratio of feature patterns for peel demolding was revealed by numerical simulation using ABAQUS software. These findings are valuable in providing a theoretical basis for large area NIL, optimizing demolding process and further enhancing the performance of full wafer NIL tool.

Design of high precision imprint tool

Imprint lithography technique is introduced in this paper. Imprint tool is one of the key steps of imprint lithography process. In consideration of the fact that the imprint process control is performed in room temperature, replicating patterns is realized by press system and the nanometer positioning driving system of imprint tool is illustrated. Combine ball screw with PZT, Macro-Micro two-level control is accomplished. The developed imprint tool is characterized by simple structure, low cost and the ability of replica with different feature sizes. The several results of imprint are exhibited.

Low-Temperature (< 100°C) Poly-Si Thin Film Fabrication on Glass

Polycrystalline silicon (poly-Si) thin-film is fabricated on Al-coated planar glass substrates at the temperature below 100 °C, using aluminium-induced crystallized (AIC) amorphous silicon (a-Si) deposited by dc-magnetron sputtering under an electric field. The properties of NA poly-Si films (AIC of dc-magnetron sputtered silicon non-annealing) are characterized by Raman spectroscopy and x-ray diffraction (XRD) spectroscopy. A narrow and symmetrical Raman peak at a wave number of about 521 cm−1 is observed for samples, showing that the films are fully crystallized. XRD spectra reveal that the films are preferentially (111) oriented. Furthermore, the XRD spectrum of the sample prepared without electric field does not show any XRD peaks for poly-Si, which only appears at about 38° for Al (111) orientation. It is indicated that the electric field plays an important role in crystallization of poly-Si during the dc-magnetron sputtering. Thus, high quality poly-Si film can be obtained at low temperature and separate post-deposition step of AIC of a-silicon can be avoided.

Nanopositioning and Nonlinearity Compensation for Step Imprint Lithography Tool

In this paper, the motion mode and nanopositioning accuracy in the step imprinting lithography process are presented, and the positioning errors different from the traditional errors, such as the gap error existing in the hinges of the stage structure and the random error produced during the process of the stage position adjustment, are analyzed. To avoid and eliminate these nonlinearity errors, radial basis function-proportional integral derivative and position control algorithms are introduced into the macro- and microdriving processes, respectively. The innovation of this driving method is that the motion locus is monotone, nonoscillatory, and a multistep approaching target, which eliminates the root of the random error by single direction driving mode and avoids the backlash error through preloading function. Driving experiments of different motion ranges prove that this nonlinearity compensation is very effective and the positioning accuracy during the step imprinting process can be improved up to 10-nm.