Fabrication of large UV transmission blazed gratings for slitless spectral sky survey

Slitless spectral sky survey is a critical direction of international astronomical research. Compared with ground-based sky survey, space-based sky survey can achieve full-band observation, and its imaging quality and resolution capability are restricted by the efficiency and size of dispersive elements. Transmission blazed gratings are often used as the dispersive elements in the UV band. Holographic interference lithography produces the photoresist mask of a grating, and the ion beam etching vertically transfers the pattern to the substrate to form the SiO2 mask of a grating. To reduce the effect of ion beam divergence on the uniformity of the groove shape, the grating mask is etched tilted by the ion beam passing through a narrow slit to obtain a blazed grating with consistent structural parameters. Moreover, two-dimensional scanning of the sample stage enables the etching of large-size samples. A UV transmission blazed grating with a linear density of 333 lines mm−1, a blazing angle of 11.8°, and a dimension of 99.2mm × 60.0mm × 6.0mm was successfully fabricated with an average diffraction efficiency of 66%, a PV diffraction wavefront of 0.169λ (λ = 632.8 nm) and low stray light.

К 125-летию со дня рождения лауреата Нобелевской премии академика Николая Николаевича Семенова Архитектура мезы и эффективность InGaP/Ga(In)As/Ge солнечных элементов

It has been shown that the mesa architecture and achieved quality of the mesa sidewall of concentrator multijunction solar cells ensured increasing their efficiency up to 36.7% at the sunlight concentration before 100 (AMO; 0.136W/cm²). Creation of the mesa structure architecture with following separation of epitaxial plates of monolithic InGaP/GaAs/Ge nanoheterostructure into chips was carried out by single step chemical wet etching in the HBr:H2O2:H2O (8:1:100) through a photoresist mask to the depth of 12-18µm. Conditions of single step etching, which ensure formation of a smooth and even side surface of the InGaP/Ga(In)As/Ge nanoheterostructure mesa containing different in composition and thickness layers have been determined. Determination of the activation energy has shown that etching occurs in the diffusion region of the heterogeneous process. In raising etchant temperature from 2 to 36˚C, a change of the tilt angle in the Ge substrate region from 4.5 to 25 angular degrees is observed, what allows optimizing the amount of concentrator solar cells and their quality at final mechanical separation of the epitaxial plate into chips.

Basic approaches to photoresist mask formation modeling in computational lithography

The article gives an overview of the main currently used models for the formation of photoresist masks and the problems in which they are applied. The main stages of «full physical» modeling of mask formation are briefly considered in the case of both traditional DNQ photoresists and CA photoresists. The concept of compact models (VT5 and CM1), which predict the contour of the resist mask for a full-sized device topology is considered. Examples of some calculations using both full physical modeling and compact models are given. Using a full physical modeling of the resist mask formation the lithographic stack was optimized for a promising technological process. The optimum thickness ratios for the binary BARC used in the water immersion lithographic process are found. The problem of determining the optimal number of calibration structures that maximally cover the space of aerial image parameters was solved. To solve this problem, cluster analysis was used. Clustering was carried out using the k-means method. The optimal sample size was from 300 to 350 structures, the mean square error in this case is 1.4 nm, which slightly exceeds the noise of the process for 100 nm structures. Using SEM images for calibrating the VT5 model allows reducing the standard error of 40 structures to 1.18 nm.