Maurizio Dapor

Monte Carlo modeling in the low-energy domain of the secondary electron emission of polymethylmethacrylate for critical-dimension scanning electron microscopy

The main scattering mechanisms governing the transport of electrons in PMMA in an energy domain ranging from the energy of the primary electron beam down to few hundreds of meV are identified. A quantitative Monte Carlo model for the emission of secondary electrons is developed to be applied for critical dimensions extraction from high-resolution scanning electron microscopy (SEM) images. Selected results are presented, which demonstrate the accuracy of the proposed approach.

Modeling secondary electron images for linewidth measurement by critical dimension scanning electron microscopy

Modeling of critical dimensions scanning electron microscopy with sub-nanometer uncertainty is required to provide a metrics and to avoid yield loss in the processing of advanced CMOS technologies. In this paper, a new approach is proposed, which includes a new Monte Carlo scheme, a new Monte Carlo code, as well as the coupling with electrostatic fields to take into account self-charging effects.

Theory of the interaction between an electron beam and a thin solid film

After a brief introduction to scattering processes, a simple theory of the interaction between an electron stream and a thin solid film is described. The energy dependence of the backscattering coefficient is considered in the formulation of the theory. Then the theoretical results are compared with the Palluel, Cosslett and Thomas and Bishop experimental data. The energy dissipation of the electron beam in the solid film and the possibility of evaluating the thickness of thin films deposited on substrates by measuring the backscattering current are discussed.

Elastic scattering of electrons and positrons by atoms: differential and transport cross section calculations

Abstract Differential and transport electron-atom and positron-atom elastic scattering cross sections have been computed for a number of selected atomic targets in the electron energy range 500–4000 eV. The phase shifts have been computed by numerically solving the Dirac equation for a central electrostatic field up to a large radius where the atomic potential becomes negligible. The atomic potential was that of Hartree-Fock for the atomic numbers ≤ 18 and that of Dirac-Hartree-Fock-Slater for the atomic numbers > 18. Good accordance with previous theoretical computations and experimental data has been found.

A novel Monte Carlo simulation code for linewidth measurement in critical dimension scanning electron microscopy

Besides the use of the most sophisticated equipment, accurate nanometrology for the most advanced CMOS processes requires that the physics of image formation in scanning electron microscopy (SEM) being modeled to extract critical dimensions. In this paper, a novel Monte Carlo simulation code based on the energy straggling principle is presented, which includes original physical models for electron scattering, the use of a standard Monte Carlo code for tracking and scoring, and the coupling with a numerical device simulator to calculate charging effects.

Monte Carlo Simulation of Secondary Electron Emission from Dielectric Targets

In modern physics we are interested in systems with many degrees of freedom. The Monte Carlo (MC) method gives us a very accurate way to calculate definite integrals of high dimension: it evaluates the integrand at a random sampling of abscissa. MC is also used for evaluating the many physical quantities necessary to the study of the interactions of particle-beams with solid targets. Letting the particles carry out an artificial random walk and taking into account the effect of the single collisions, it is possible to accurately evaluate the diffusion process. Secondary electron emission is a process where primary incident electrons impinging on a surface induce the emission of secondary electrons. The number of secondary electrons emitted divided by the number of the incident electrons is the so-called secondary electron emission yield. The secondary electron emission yield is conventionally measured as the integral of the secondary electron energy distribution in the emitted electron energy range from 0 to 50eV. The problem of the determination of secondary electron emission from solids irradiated by a particle beam is of crucial importance, especially in connection with the analytical techniques that utilize secondary electrons to investigate chemical and compositional properties of solids in the near surface layers. Secondary electrons are used for imaging in scanning electron microscopes, with applications ranging from secondary electron doping contrast in p-n junctions, line-width measurement in critical-dimension scanning electron microscopy, to the study of biological samples. In this work, the main mechanisms of scattering and energy loss of electrons scattered in dielectric materials are briefly treated. The present MC scheme takes into account all the single energy losses suffered by each electron in the secondary electron cascade, and is rather accurate for the calculation of the secondary electron yield and energy distribution as well.

Reducing Hydrogen Permeation through Metals

Metal–hydrogen systems are of great basic and technological interest in connection to the role of hydrogen as a clean energy carrier. Frequently, metal systems are involved in hydrogen purification, storage, and engines making use of this fuel. The presence of hydrogen in a metallic matrix gives rise to modifications of electrical, optical and mechanical properties. Hydrogen accumulation in metals may cause damage to the material by also producing fracture, thus limiting operating lifetime. Reducing the hydrogen permeation is an important task also for the fusion reactors: it is well known, indeed, that tritium is radioactive so that it is very important to be able to confine tritium during the nuclear fusion process. The theoretical study of permeation is thus of fundamental importance to obtain efficient barriers to permeation. Hydrogen trapping sites have a great influence on the hydrogen permeation through a slab sample. The diffusion of the hydrogen in a crystal is generally described by a parabolic partial differential equation with appropriate boundary conditions. The numerical simulation code PHM (Permeation of Hydrogen through Metals), realized for the study of the permeation of hydrogen in presence of trapping sites, is here described and utilized for the analysis of the influence of reversible and irreversible traps on the diffusion of hydrogen in a metal.