|
|
Trajektorie signálních elektronů v nízkonapěťovém BSE detektoru
Wandrol, Petr ; Autrata, Rudolf
Nowadays the development of the image formation in scanning electron microscope (SEM) is oriented to the use of scanning electron microscopes with low accelerating voltage of the primary beam (LV SEM). Secondary electrons (SEs) for topographical contrast observation and backscattered electrons (BSEs) for material contrast observation are the main components of the detected signal in LV SEM. While the secondary electrons can be detected either by Everhart-Thornley scintillation detector or by the "in lens" SE detector, the detection of backscattered electrons (BSEs) in LV SEM is an unsolved problem yet
|
|
|
Návrh nízkoenergiového REM
Vlček, Ivan ; Lencová, Bohumila ; Horáček, Miroslav
Our aim is to redesign the low-energy SEM (a scanning LEEM) in an UHV apparatus designed in our institute to allow the detection of the angular distribution of signal electrons. For this purpose we have to separate the signal electrons from the primary beam with a Wien filter and project the image of the back-focal plane of the objective lens on an area-sensitive detector (a back-illuminated CCD). Therefore we have to design a new electrostatic optics working in UHV
|
|
|
Experimentální a simulační metody pro optimalizaci scintilačního detektoru
Schauer, Petr ; Autrata, Rudolf
In S(T)EM an image is formed using a focused electron beam, which is scanning across a very small part of the specimen surface. A scintillation detection system consisting of a scintillator, light-guide and photomultiplier (PMT) processes only one pixel of the image at any given moment. Not only efficiency, but also kinetic properties of such a system are of great importance. Scintillation detectors can show a noticeable difference in detective quantum efficiency (DQE) due to the bad electron-photon energy conversion and/or light losses in the optical part of the detector. Up to now, some studies were engaged in measurement of S(T)EM detectors performance ascertaining very low DQE for some detectors, but no suggestion has been made to optimize the detector set-up. To find the neck of a detection system, one must examine the whole detection path step by step
|
|
|
Elektrostatický nízkoenergiový rastrovací elektronový mikroskop pro Augerovu analýzu
Romanovský, V. ; El Gomati, M. M. ; Frank, Luděk ; Müllerová, Ilona
A scanning low energy electron microscope (SLEEM) was realized with a cathode lens in which the negatively biased specimen is used as the cathode. In this arrangement, electrons pass through the microscope at high energy and are decelerated to low energy before landing on the sample. This design brings plenty of signal even in the landing energy range of tens or units of eV. However, the use of the primary electrons with low energy brings some problems e.g. low source brightness, increased aberrations and sensitivity to stray fields. The scanning Auger microscopy (SAM) is well-established experimental method. A combination of SAM and SLEEM in one device would therefore provide a sufficient tool to solve the problems inherent in these individual methods. Although much has already been achieved in the area of detection of slow electrons, none of the methods currently known is suitable to be built into a scanning illumination column for Auger microprobe analysis
|
|
|
Výpočet proudové hustoty svazků nabitých částic
Oral, Martin
A method and a program for calculation of current density profiles was developed. It simulates the propagation of a charged-particle beam in an optical system. Since it requires data of positions of a high number (billions - 109) of particles on a given target, analytical expressions for paraxial position and aberrations are used for calculation, that are very fast to evaluate (millions of particles per second). Ray tracing is slow for this purpose (up to 100 particles per second). The accuracy of the analytical expressions is comparable with ray tracing in a certain space near the optical axis
|
|
|
Tvorba kontrastu při zobrazení dopovaného polovodiče v nízkoenergiovém REM
Mika, Filip ; Frank, Luděk
Functional details of semiconductor structures keep decreasing in size. Among the structure elements the locally doped patterns play crucial role so that tools are needed for their observation. For fast diagnosis and quality check of the semiconductor structures the scanning electron microscope is useful because of its wide range of magnification, availability of different signal modes, speed of data acquisition and nondestructive nature of the technique in general, especially at low voltage operations. The dopant concentration in semiconductor is quantitatively determined via acquisition of signal of the secondary electron (SE) emission in such a way that the image contrast is measured between areas of different type or rate of doping
|
|
|
Vybrané příklady našich výpočtů
Lencová, Bohumila ; Jánský, Pavel ; Zlámal, J.
The paper discusses the properties of the program EOD (Electron Optical Design), which contains interfaces for Windows, integrates all programs for 2D computations by the first order FEM, ray tracing in computed fields, simulation of electron and ion sources, and computation of space charge limited beams. Most parts of the software are in the beta development phase, and they are already used in a number of our projects. For example, it was used to simulate the behavior of ion optical systems for the ion beam deposition at TU Brno by including the plasma creation inside the ion gun as well as space charge effects in ion beams transported in the system. Electron guns with space charge effects can be computed as well, as illustrated on the example of the well-known Pierce electron gun. Graphical possibilities are illustrated on a 3D cut-away view of the electron gun for electron-beam welding
|
|
|
Nejnovější vývoj software pro částicovou optiku
Lencová, Bohumila
The paper gives an overview of the development of software for electron optics in ISI. New problems and applications force us to improve existing programs, to get better results from them, which requires continuous improvements of our own software. We are also trying to improve the user interface, which should run under Windows operating system. For processing of large amount of data, e.g. from the computation of optical properties, it is reasonable to use as much as possible other well-known tools like EXCEL to take over some of the processing of computation outputs
|
|
|
Sběrová účinnost detektoru sekundárních elektronů v REM
Konvalina, Ivo ; Müllerová, Ilona
In order to collect the secondary electrons (SE), scanning electron microscopes (SEM) are equipped with the Everhart-Thornley (ET) type detector. The electrostatic field of the front grid, biased to a positive potential of several hundred volts , is to attract all SE of kinetic energy below 50 eV or at least those from the SE spectrum peak at 1(3 eV. However, the detection quantum efficiency (DQE) of such detectors has been found to be significantly lower than one, which is mainly given by their low collection efficiency. The electrostatic field of the grid cannot sufficiently penetrate toward the specimen and influence the trajectories of SE owing to grounded electrodes surrounding the specimen (specimen alone and its holder, specimen stage, pole piece of the objective lens, etc)
|
|
|
Detekce signálu použitím segmantového ionizačního detektoru
Jirák, Josef ; Černoch, P. ; Autrata, Rudolf
For signal electrons detection at environmental conditions, it is often used a detector that utilizes impact ionization in the gaseous environment of a specimen chamber for a signal amplification. An electrostatic field created in a space between a grounded specimen and a detector electrode provides the energy needed for efficient ionization of secondary electrons. A voltage of several hundred volts is attached to the detector electrode. It was proposed an electrode system of a ionization detector, with several concentric electrodes divided into two halves - right and left. It was shown that the higher diameter of the electrodes brings an increased contribution of backscattered electrons to the detected signal. Different contrast mechanisms were studied
|
guest ::
