Optimization of microsphere optical lithography for nano-patterning

We present an original approach to realistic modeling of light focusing by microsphere systems to form the photonic jets for nano-patterning of the substrates with high refractive index. In simulations we analyze the photonic jets produced by a single sphere and close-packed array of microspheres on the photoresist layer and Si substrate. We show how the lithographic profiles can be controlled by varying the exposure dose and system geometry in wide ranges of photoresist layer thicknesses and microsphere sizes. The modeling covers the entire lithographic system and accounts for the interference of focused light transmitted through the microlenses and reflected from the Si substrate. We use our approach to optimize the size of the lithographic pattern and confirm the simulation results experimentally. The suggested set of methods is rather universal and may be applied to other microlens and resist materials to minimize lithography lateral resolution.

Плазмохимическое и жидкостное травление в постростовой технологии каскадных солнечных элементов на основе гетероструктуры GaInP/GaInAs/Ge

Investigation and development of a separating mesa-structure creating technology for fabricating multi-junction solar cells based on the GaInP/GaInAs/Ge heterostructure has been carried out. Studied were methods of etching of heterostructure layers: liquid chemical etching in the etchants based on HBr, H2O2, K2Cr2O7 and plasma-chemical etching in the stream of operating gas BCl3. The comparative analysis of etching methods was studied. The protective masks based on photoresist layer and TiOx/SiO2 were developed. Multi-junction solar cells with low parameters of leakage current less than 10-7 A at voltage 0,5-1 V were created.

Application of the Metal Reflector for Redistributing the Focusing Intensity of SPPs

The near-field photolithography system has attracted increasing attention in the micro- and nano-manufacturing field, due to the high efficiency, high resolution, and the low cost of the scheme. Nevertheless, the low quality of the nano-patterns significantly limits the industrial application of this technology. Theoretical calculations showed that the reason for the poor nano-patterns is the sharp attenuation of the surface plasmon polaritons (SPPs) in the photoresist layer. The calculation results suggest that the waveguide mode, which is composed of the chromium-equivalent dielectric layer-aluminum, can facilitate the energy flux density distribution in the photoresist layer, resulting in the enhancement of the field intensity of SPPs in the photoresist layer. This reduces the linewidth of nano-patterns, while it enhances the pattern steepness. Eventually, the focusing energy of the photoresist layer can be improved. The finite-difference time-domain method was employed to simulate and verify the theoretical results. It is found that for the rotational near-field photolithography with 355 nm laser illumination, the linewidths of the nano-patterns with and without the aluminum reflector are 17.54 nm and 65.51 nm, respectively. The robustness of the experimental results implies that the application of the aluminum reflector enhances the focusing effect in the photoresist, which can broaden the application of the near-field photolithography.

Экспериментальные исследования различных полимерных композиций для создания рельефно-фазовых дифракционных решеток для систем дополненной реальности

The possibility of copying high-frequency diffraction gratings obtained in a photoresist layer to glass substrates using polymer compositions (“OKM” and “Tekhnovit”) is shown and their comparative analysis is carried out. The mechanism of copying the relief-phase structure is based on a two-stage process consisting of the following steps: obtaining a nickel master, applying a polymer composition to it and curing under the influence of UV radiation. The copying modes were optimized (time, exposure, thickness of the polymer base), and that allowed to obtain relief phase diffraction gratings with a surface relief depth comparable with the initial structure obtained in the photoresist layer. The diffraction efficiency of the resulting gratings was estimated, as well as the change in the depth of the surface relief of polymer copies obtained from one master.

Formation and Characterization of Hole Nanopattern on Photoresist Layer by Scanning Near-Field Optical Microscope

Patterning of lines of holes on a layer of positive photoresist SX AR-P 3500/6 (Allresist GmbH, Strausberg, Germany) spin-coated on a quartz substrate is carried out by using scanning near-field optical lithography. A green 532 nm-wavelength laser, focused on a backside of a nanoprobe of 90 nm diameter, is used as a light source. As a result, after optimization of parameters like laser power, exposure time, or sleep time, it is confirmed that it is possible to obtain a uniform nanopattern structure in the photoresist layer. In addition, the lines of holes are characterized by a uniform depth (71–87 nm) and relatively high aspect ratio ranging from 0.22 to 0.26. Numerical modelling performed with a rigorous method shows that such a structure can be potentially used as a phase zone plate.

Mask-Based Microsphere Photolithography

Microsphere Photolithography (MPL) uses a self-assembled array of transparent microspheres to focus incident ultraviolet radiation and produce an array of photonic jets in photoresist. Typically, the microspheres are self-assembled directly on the photoresist layer and are removed after exposure during development. Reusing the microsphere array reduces the expense of the process. A mask is formed by transferring the self-assembled microsphere array to a transparent tape. This can be used for multiple exposures when pressed into contact with the photoresist. This paper demonstrates the use of this process to pattern infrared metasurface absorbers and discusses the effects of the mask-based MPL process on the metasurface performance.