For the multi-channel collimators employed in SPECT measurements and in gamma probes (for radio guided surgery) an approach to modeling the functioning of collimator is developed. This approach involves the calculation of point source function and the sensitivity field for the considering device. The effect of finite absorption in collimator material is taken into account. The results of modelling for confocal collimator are presented. The calculations were performed for the attenuation length corresponding to the device 3D-printed from metal and in the assumption of infinite absorption. It makes possible to estimate quantitatively the effect of gamma photons partial propagation through the matrix of collimator on the sensitivity and resolution for the specified material and the geometry of the device.
The paper demonstrates that the ion beam milling process can be modelled as a local isotropic etching without taking into account the material re-deposition during the sputtering. It also presents a software, IonRevSim, specifically developed to simulate the 3D ion structuring and thus to validate and if necessary to optimise off-line the processing parameters. In particular, employing the IonRevSim software it is possible to prepare the necessary data for performing 3D ion milling and then to simulate the 3D structuring process in order to validate it. These two main functions and their operating modes are discussed in the paper. Experimental verification based on optimised data prepared by IonRevSim was performed using both FIB tool and multi-beam CHARPAN PMLP tool. For both ion-patterning techniques good coincidence was demonstrated for structures of low aspect ration.
A mathematical model and numerical method are described, which make it possible to simulate ultraviolet ("step and flash") nanoimprint lithography (UV-NIL) process adequately even using standard Personal Computers. The model is derived from 3D Navier-Stokes equations with the understanding that the resist motion is largely directed along the substrate surface and characterized by ultra-low values of the Reynolds number. By the numerical approximation of the model, a special finite difference method is applied (a coarse-grain method). A coarse-grain modeling tool for detailed analysis of resist spreading in UV-NIL at the structure-scale level is tested. The obtained results demonstrate the high ability of the tool to calculate optimal dispensing for given stamp design and process parameters. This dispensing provides uniform filled areas and a homogeneous residual layer thickness in UV-NIL.
The development of an electron resist on PMMA basis was experimentally shown to depend not only on an exposure dose but on current density and exposure sequence as well. Various exposure doses are required to obtain a uniform development rate at different beam currents, with an exposure dose being the lager, the higher the current rate. Maximum dose changes can be as large as several tens of percent. A model is proposed which is a development of the temperature effect model, i. e. the dependence of an absorbed dose on resist temperature. The model supposes that a resist molecule is in an intermediate state after the interaction with an electron, from which state it can either spontaneously break down, or spontaneously return to the unexcited state, or else return to the unexcited state due to the effect of electrons. A model experiment was made which helped determine the model parameters, the time of intermediate state relaxation, and the characteristic current density. Using the values of the model parameters, it was found that the rate of resist development in some areas exposed to equal doses can be different, with the difference being approximately as large as two times.
KEYWORDS: Electrons, Aluminum, Gold, Simulation of CCA and DLA aggregates, Scattering, Laser scattering, Astatine, Monte Carlo methods, Solids, Electron beams
Using developed simulalion program based on Monte-Carlo method in discrete looses approximation
(DLA) we carried out analysis of secondary electrons (SE) energy spectrums (ES). The possibility of determination
of thickness and depth of subsurface structures using ES of SE is shown.
KEYWORDS: Monte Carlo methods, Thin films, Simulation of CCA and DLA aggregates, Scattering, Gold, Computer simulations, Ionization, Chlorine, Solids, Statistical analysis
Problems of secondary electrons (SE) energy spectrum simulation are discussed in present article. It is shown that
secondary electrons shoot energy spectrum (ES) simulated using discrete looses approximation coincides with Landau
distribution function.
KEYWORDS: Simulation of CCA and DLA aggregates, Silicon, Gallium nitride, Monte Carlo methods, Gold, Silver, Electron beams, Optical simulations, Copper, Particles
Problems of simulation of deposited during beam irradiation charge and energy (dose) simulation. Results
obtained using Monte-Carlo method in discrete and continuous looses. Analytical approximations for depth-dose and
charge-dose for Si, Au, Ag, Cu, GaN obtained.
KEYWORDS: Electrons, Monte Carlo methods, Scattering, Gold, Simulation of CCA and DLA aggregates, Solids, Laser scattering, Computer simulations, Photonic integrated circuits, Diagnostics
In this work we discuss the problems of the energy-angular spectrum of backscattered and true secondary
electrons simulation using the discrete (DLA) and the continuous (CLA) loss approximations. The presence of an angular
spectrum artefact - the deviation from the sinusoidal distribution over the range of 177-18O° from the beam direction is
shown.
KEYWORDS: Monte Carlo methods, Solids, Silicon, Electron beams, Optical simulations, Scanning electron microscopy, Ionization, Plasmons, Photonic integrated circuits, Gold
Problems of backscattered and true-secondary spectra as far as transmission spectra simulation using discrete looses approximation are regarded in this article. Developed model allows acquiring the electron energy spectra from samples with complicated 3-d structure. Besides due to higher detailing of the discrete looses method one can evaluate the spatial energy and accumulated charge distributions more accurately. Simulation results are compared with the experimental ones, SEM image simulation examples are given.
On the basis of Monte-Carlo method a new approach to modeling of an electron interaction with a substance is offered. Some phenomena concerned with spatial energy distribution and accumulation of a charge in an irradiated sample are considered. Calculations of distributions of electric potential and resists polarization induced by an injected charge are presented. It is shown that charging is still the essential circumstance, capable to cause significant loss of accuracy in electron-beam lithography.
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