ELECTRON INTERACTION WITH SOLIDS SINGLE SCATTERING MONTE CARLO SIMULATION SOFTWARE

Transcription

1 ELECTRON INTERACTION WITH SOLIDS SINGLE SCATTERING MONTE CARLO SIMULATION SOFTWARE Version 3.0 J. Bausells, 2004 (v. 1.0) (v. 3.0). 1. Overview EISS is a computer program that simulates the interactions between energetic electrons and solids. It is focused on describing the trajectories of a beam of electrons, and it can therefore be applied to fields such as electron beam lithography or electron microscopy. The electron trajectories are simulated by using a Monte Carlo (or random sampling) method. Each electron enters the solid with a given energy, and its trajectory is followed until it comes to rest or exits the sample. To simulate a beam, the process is repeated for a large number of electrons. The electron-solid interactions are approximated by a model in which the electron-atom interactions are elastic, and the electron energy loss is continuous between elastic processes. The elastic interactions are described by the relativistic Mott cross section, which includes spin-orbit coupling and remains accurate for low beam energies and high-atomic-number targets. Secondary electrons are generated and tracked within the "fast secondary" model. The program has been written from scratch in Java, but its physical content is mainly based in the approximations and algorithms described in the book "Monte Carlo modeling for electron microscopy and microanalysis", by David C. Joy (Oxford University Press, New York, 1995). The program can manage planar samples with up to three layers, with arbitrary thicknesses. A number of materials, typical for electron beam lithography applications, are predefined, but the program allows the user to define new materials for all three layers. 1 / 9

2 2. How to use the program The program is written in Java language, which generates an executable file (.JAR) than can be run in any computer platform. It requires, however, that the computer has an updated Java Runtime Environment, version at least Installation The program is provided in a compressed ZIP file ("Eiss3.zip"), which includes the executable Java file "Eiss3.jar", the "Help" HTML file (this file, "Eiss_help.htm") and a folder ("eiss_help_archivos") containing the images used in the help file. To install the program, the user should only decompress the ZIP file and copy the JAR and HTM files and the folder into the same directory. Download the EISS3.ZIP file Run the program To run the program, simply execute the "Eiss3.jar" file, by for example double-clicking it (in Windows) Input window 2 / 9

3 When running the program, the Input Window opens. The following figure shows the input window in the Windows "look and feel". In EISS the look and feel is supplied by the native window system of the computer. 3 / 9

4 The "Cancel" button exits the program. The user must supply the following data: 1) Input beam energy in kev. The default value is 10. 2) Beam width(standard deviation) in Å, assuming a gaussian beam profile. The default value is 0. 3) The structure of the target. The target may have up to three layers. Layer 1 is the first that the beam encounters. For each layer, the user must provide: 4 / 9

5 a. Target material. A number of predefined materials are available in the ComboBoxes labelled "Target X", where "X" is the layer number. Alternatively, the user may select the "User defined X" button, which allows to define a new material. A new window is opened in this case, which prompts the user to enter the atomic number (mean atomic number for compounds), the atomic weight (mean atomic weight form compounds)(in atomic mass units) and density (in g/cm 3 ). The defaults for all three parameters are 1.0: b. Thickness. In Å. 5 / 9

6 c. A CheckBox allows defining the layer as "bulk", so that it is "infinitely thick". In this case the program calculates an effective finite depth for that layer in order to plot the simulation results. The "Cancel" button closes the window and returns to the Input Window. The "OK" button enters the material data into the program. 4) Number of trajectories. The number of primary electrons that are calculated. The default is ) Plot final positions only. If this checkbox is selected, the primary electron trajectories are not plotted. Only the final positions of the primary electrons and the trajectories of the secondary electrons are shown. The "OK" button proceeds with the simulation of the electron trajectories Output window 6 / 9

7 After the "OK" button is pressed in the Input Window, the electron trajectories are calculated. A small window opens showing the % of trajectories calculated in real time. When 100 % is reached, the Output Window opens. If the "Plot final positions only" CheckBox is NOT selected, it looks like: 7 / 9

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9 The In File: Save:Saves existing Print:Opens options, Exit: the this both final secondary directory case: cases positions the where electron contents simple of the the trajectories Menus primary of executable the Output have electrons are program the Window shown following are file shown into red. is options: located. a graphics blue. Help:Opens About:Shows Exits file and the with printing the the program. the system name same the default contents of name. the program, internet "Print" of the window, browser Output its version Window. which and number shows allows and this It selecting will file its file. overwrite author. named the printer "Saved.png", a previously and itslocated 9 / 9