Browsing by Author "Kostic I."
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Item Comparative study of the sidewall shape and proximity effect of the AR-N 7520 negative electron beam resist(2022-04-04) Kostic I.; Vutova K.; Koleva E.; Bencurova A.; Konecnikova A.; Andok R.This paper deals with the performance of the AR-N7520 (Allresist) negative electron beam resist (EB resist) which was selected as an etch mask for the fabrication of gratings on GaAs substrates. The developed resist sidewall shape is crucial for this purpose. The required near-to-vertical sidewall shape can be achieved by optimizing the electron beam lithography (EBL) process based on experimental investigations and computer simulations. The sidewall shape dependence on the EBL parameters (exposure dose, resist pattern, etc.) and the proximity effect are studied.Item Dependence of PMMA electron beam resist sidewall shape on exposure dose and resist thickness(2021-11-02) Andok R.; Vutova K.; Koleva E.; Bencurova A.; Kostic I.The influence of electron beam lithography parameters (such as electron energy, resist thickness, the exposure dose) on the resist sidewall shape (profile) was studied for the PMMA (polymethyl-methacrylate) positive resist. The profile of the positive tone resist PMMA was investigated depending on varying exposure doses for the resist thicknesses 600 and 1300 nm, and electron energy 30 keV. Simulation results based on measurements along the resist profile depth are presented and discussed. The results obtained contribute to the knowledge on electron scattering in resist/substrate in electron beam lithography for the case of field emission cathode and Gaussian intensity distribution, and to the development and approval of models for the prediction and precise control of resist profiles in thick PMMA layers for 3D proximity effect simulation, the bilayer resist system, and the lift-off method.Item Modeling approaches for electron beam lithography(2018-10-19) Koleva E.; Vutova K.; Asparuhova B.; Kostic I.; Cvetkov K.; Gerasimov V.In this paper, a study based on the mathematical modelling, applying different process simulation tools (CASINO, TREM, SELID) for characterization of PMMA resist and for the improvement of the resolution concerning the critical dimensions of nano-patterning by electron beam lithography (EBL) is presented. Data for important EBL characteristics (energy deposition function, proximity effect parameters, solubility rate, etc.) are obtained by applying different approaches (Monte Carlo methods, regression models, etc.).Item Optimisation criteria for the process electron beam lithography of negative AR-N7520 resists(2023-01-01) Koleva E.; Kostic I.; Andok R.; Vutova K.; Bencurova A.; Konecnikova A.Experimental investigation of negative electron resist AR-N 7520 profiles using an electron beam lithography system ZBA23 (Raith) is performed at variation of the exposure doses and the exposure patterns. The form of the obtained after the exposure resist profiles is investigated and optimized. Artificial neural networks for the dependence of the overall geometry of the obtained resist profiles on process parameters are trained, tested and validated. Several overall geometry quality criteria for the shape of the developed resist profile cross-sections are defined. An approach, based on the defined overall quality characteristics and multicriterial parameter optimization, is proposed and implemented for fulfillment of the technological requirements for the produced resist profile dimensions.Item Patterning of structures by e-beam lithography and ion etching for gas sensor applications(2014-01-01) Durina P.; Bencurova A.; Konecnikova A.; Kostic I.; Vutova K.; Koleva E.; Mladenov G.; Kus P.; Plecenik A.This work deals with a method of preparation of nanometer structures for a gas detector based on e-beam lithography and ion etching of a thin TiO2 film. The aim was the fabrication of a gas sensor with meander or comb structures of nanometer dimensions. This is of importance since both the size of the contacts and the layer thickness affect the sensor's sensitivity.Item PMMA resist profile and proximity effect dependence on the electron-beam lithography process parameters(2020-06-02) Kostic I.; Vutova K.; Koleva E.; Bencurova A.The study reveals the influence of the electron-beam lithography parameters (such as the exposure dose, resist thickness, depth) on the resist profile shape in the case of the PMMA (polymethyl-methacrylate) positive resist. The experiments are performed using an Elphy Quantum (Raith) e-beam lithography control system installed on an Inspect F50 (FEI) scanning electron microscope with a field emission cathode and a Gaussian intensity distribution. Profiles developed in the PMMA using the MIBK:IPA 1:3 developer and simulation results based on measurements along the resist profile depth for the case of 30-keV electron energy are presented and discussed. The results contribute to the knowledge on electron scattering in the resist/substrate in electron-beam lithography and assist in the development and approval of simulation tools for prediction and control of resist profiles in thick PMMA layers for lift-off nanopatterning.Item Simulation and experimental study on developed profiles in the positive polymer resist PMMA(2018-10-19) Koleva E.; Vutova K.; Kostic I.Theoretical and experimental study on developed profiles in the positive tone PMMA (polymethyl-methacrylate) resist and e-beam lithography process parameters was performed. E-beam lithography control system Elphy Quantum (Raith) installed on Scanning Electron Microscope Quanta FEG (FEI) with a field emission cathode and Gaussian intensity distribution has been used for the conducted experiments. Simulation results obtained by different models concerning the geometry of the developed resist profiles in PMMA were compared and verified with experimental data for improvement characterization of PMMA resist. The estimated models presented are useful for prediction and optimization of the developed resist profiles at electron beam lithography.Item Study and comparison of resist characteristics for different negative tone electron beam resists(2023-01-01) Andok R.; Vutova K.; Bencurova A.; Kostic I.; Koleva E.In this work, four types of negative electron beam resists are investigated. Electron beam lithography (EBL) experiments were conducted using EBL system ZBA23 (Raith) with the variable-shaped electron beam cross-section at 40 keV electron energy. Important electron beam resist characteristics such as sensitivity, dissolution rate, aspect ratio and sidewall developed profiles in the chemically amplified resist (CAR) SU-8 2000, non-CARs ma-N 2410 and ARN-7520, and inorganic negative resist HSQ XR-1514 are studied and compared. This study was motivated by the selection of a suitable resist for practical use such as large area gratings fabrication for optoelectronics.Item Study of the new CSAR62 positive tone electron-beam resist at 40 keV electron energy(2016-04-07) Andok R.; Bencurova A.; Vutova K.; Koleva E.; Nemec P.; Hrkut P.; Kostic I.; Mladenov G.One of the few «top-down» methods for nano-device fabrication is the electron-beam lithography, which allows flexible patterning of various structures with a nanoscale resolution down to less than 10 nm. Thinner, more etching durable, and more sensitive e-beam resists are required for the better control, linearity, and uniformity of critical dimensions of structures for nano-device fabrication. Within the last decade, researchers have made significant efforts to improve the resolution of the nanoscale e-beam lithography. The resist material properties are an important factor governing the resolution. Only the e-beam resist ZEP 520 of the Japanese manufacturer ZEON is characterized by relatively good properties and thus meets most users' expectations. This paper deals with the investigation and simulation of the characteristics of the new less-expensive AR-P 6200 (CSAR 62) positive e-beam resist (available since May 2013, manufactured by Allresist GmbH company).