INTERACTION OF ELECTRON BEAM WITH CCD SENSOR
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The topic of this work is the study of direct detection of electrons by Charge-Coupled-Devices (CCD). The aim is to design a detector for the angle and energy-selective detection of signal electrons in very low energy scanning electron microscopy (VLESEM), using an
electron-bombarded CCD sensor (EBCCD). We concentrate upon two problems - the design of appropriate electronics and determination of an appropriate energy of the signal electrons for the CCD sensor.
Summary of the Current State of the Low Energy Microscope
Considerable attention has been paid in the last ten years to the development of low voltage scanning electron microscopy (LVSEM) in order to reduce the radiation damage of some sensitive specimens (e.g., some biological or semiconductor structures) and possibly also to reduce the local charging of a semi-insulating specimen. A radical change in LVSEM has been made by the use of very low energy electrons, with the energy below 10 eV.
The essential element of a low energy electron microscope (LEEM) that makes it different from the classical microscope (TEM) is the cathode lens. The advantages of the immersion objective (magnetic lens plus cathode lens) were fully recognized only recently. So far, experiments demonstrating capabilities of very low energy scanning electron microscopy (VLESEM) have been realized in ISI Brno. A deteriorated function of classical SEM detectors was proved by these experiments. Secondary and backscattered electrons are reaccelerated in the cathode lens and their trajectories are similar to those of the primary beam electrons. The Wien filter is suitable for the separation of the primary and the signal electron beams.
Detection of the Angular Distribution of the Signal Electrons in VLESEM
A schematic arrangement of the optics with an immersion objective, Wien separator and electron bombarded CCD (EBCCD) detector is shown in Figure. The primary electron beam (up to 10keV) from the source of electrons passes through the Wien filters, which are balanced so that the axial ray with the nominal energy is not affected. Next, the primary beam passes through the deflection system, is focused by the magnetic lens, decelerated to the desired energy by the cathode lens, and scanned over the specimen. The beam of signal electrons accelerated by the cathode lens, approximately to the primary energy, passes through immersion objective lens, and it is deflected by the Wien filter to the region of the electrostatic transpotr optics shielded from the primary beam. The transport optics directs the signal beam to the suitable detector.
The arrangement employing the Wien filter makes the angle and energy-selective detection of signal electrons possible and gives rise to the corresponding sort of contrast, if the signal is properly collected. The use of CCD technology is very suitable for this purpose. The planar CCD sensor converts the angular distribution of electrons of the signal beam into the electrical signal that can be further processed, which makes it possible to form the image corresponding to the signal electrons from the selected area of the CCD sensor.
More detailed information is available in:
- Detection of the Angular Distribution of the Signal Electrons in VLESEM
Journal of Computer-Assisted Microscopy, March 1998, Vol. 10, No. 1, pp. 23-32.
(Available in PDF format)
- Detection of the Angular Distribution of the Signal Electrons in VLESEM.
Report on the Ph.D. Thesis, Faculty of Electrical Engineering and Computer Science of Technical University in Brno, Czech Republic, 1999.
(Available in PDF format)
- Direct detection of electrons by area array CCD.
Radioelektronika 99 - 9th International Czech-Slovak Scientific Conference, Brno, April 27-28, 1999. Conference Proceedings, pp. 78-81.
(Available in PDF format)
- Detection of the angular distribution of the signal electrons in VLESEM.
12th European Congress on Electron Microscopy EUREM 12, Brno, Czech Republic, 9-14 July 2000. Proceedings, Volume III, Instrumentation and Methodology, pp. I477-I478.
(Available in PDF format)
- Acquisition of angular distribution of signal electrons in VLESEM.
5th Multinational Congress on Electron Microscopy MCEM 5, Lecce, Italy, 20-25 September 2001. Proceedings, pp. 521-522.
(Available in PDF format)
- Acquisition of multi-dimensional image in the scanning electron microscope.
8th Seminar Recent Trends in Charged Particle Optics and Surface Physics Instrumentation, Skalsky Dvur, Czech Republic, 8-12 July 2002. Proceedings, pp. 37-38.
- Area selective detector of low energy electrons.
15th International Congress on Electron Microscopy ICEM 15, Durban, South Africa, 1-6 September 2002. Proceedings, Volume 3, Interdisciplinary, pp. 111-112.
(Available in PDF format)
- Charge-coupled device area detector for low energy electrons.
6th Multinational Congress on Electron Microscopy - European Extension - MCM 6, Pula, Croatia, 1-5 June 2003. Proceedings, pp. 476-477.
- Charge-coupled device area detector for low energy electrons.
Review of Scientific Instruments, July 2003, Vol. 74, No. 7, pp.3379-3384.
(Available in PDF format)
- Design of the low-voltage SEM.
Recent Trends in Charged Particle Optics and Surface Physics Instrumentation - 9 th Seminar, Brno, July 12-16, 2004. Proceedings, pp. 75-76.
- Modulation transfer function of electron-bombarded CCD.
13th European Microscopy Congress EMC 2004, Antwerp, Belgium, August 22-27, 2004. Proceedings, Volume I, Instrumentation and Methodology, pp.81-82.
(Available in PDF format)
- Detection of angular distribution of signal electrons in low-voltage SEM.
13th European Microscopy Congress EMC 2004, Antwerp, Belgium, August 22-27, 2004. Proceedings, Volume I, Instrumentation and Methodology, pp. 337-338.
(Available in PDF format)
- Design of low energy SEM with electrostatic optics and matrix detector.
7th Multinational Congress on Microscopy - MCM 2005, Portoroz, Slovenia, June 26-30, 2005. Proceedings, pp. 365-366.
(Available in PDF format)
- Design of detector optics for a low energy SEM.
Microscopy Conference 2005 - MC 2005, Davos, Switzerland, August 28-September 2, 2005. Proceedings, p. 59.
(Available in PDF format)
- Modulation transfer function and detective quantum efficiency of electron bombarded charge coupled device detector for low energy electrons.
Review of Scientific Instruments, September 2005, Vol. 76, No. 9, pp.093704-1-6.
(Available in PDF format)
- Wien filter electron optical characteristics determining using shadow projection method.
Recent Trends in Charged Particle Optics and Surface Physics Instrumentation - 11 th Seminar, Brno, July 14-18, 2008. Proceedings, pp. 47-48.
(Available in PDF format)
- Wien filter electron optical characteristics determining using shadow projection method.
14th European Microscopy Congress EMC 2008, Aachen, Germany, September 1-5, 2008. Proceedings, Volume I, Instrumentation and Methods, pp. 551-552.
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