Radiant energy – Electron energy analysis
Patent
1995-06-12
1997-01-14
Berman, Jack I.
Radiant energy
Electron energy analysis
H01J 4948
Patent
active
055942440
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electron spectrometers.
Electron spectrometers are in widespread use for the study of gases, liquids and solids in both academic and industrial contexts. Their most widespread use is in the characterisation and quantitative analysis of the surfaces of solids. In the semiconductor technology industry, they are used to estimate the state of cleanliness of a surface before, during and after a large variety of different kinds of process steps during the production of integrated circuits. They are used also in the chemical industry to help establish manufacturing processes for catalysts and polymers, and in the metallurgical industries to establish conditions for surface treatments for low friction coefficients, low corrosion in hostile ambient conditions and production of strongly adhering coatings.
The dominant spectrometer in these areas is the coaxial mirror analyser (or CMA). This is a relatively simple instrument which consists essentially of a pair of coaxial metal cylinders which are maintained at different electrostatic potentials. A sample is mounted on the common axis of these cylinders and is bombarded by electrons or photons from a source which can be mounted within the inner cylinder. Electrons excited by the photo-electric effect or the Auger effect leave the sample and enter the coaxial cylinders. If they have a kinetic energy appropriate to the dimensions of the structure and the voltages applied, then they are focused onto an aperture and pass through to an electron multiplier where they are converted into an electrical signal which can be as analog current or pulses which can be counted. The energy distribution of the electrons leaving the sample can be observe by sweeping the voltage on the outer cylinder of the CMA so that electrons of varying kinetic energies are detected at the electron multiplier. Only one narrow range of kinetic energies is detected at one time and so the spectrum is swept sequentially.
This type of spectrometer has been very successful because: to manufacture. leads to a compact structure which can be secured to an experimental chamber by a single flange. This means that the whole assembly can be accurately prealigned during manufacture so giving good control of the properties of the entire instrument. added with a straight line path from the sample to the additional apparatus.
EP 0 470 478 discloses a type of CMA spectrometer.
A second kind of spectrometer, the concentric hemispherical analyser (CHA), has also become popular over the last few years. This is based upon a pair of concentric hemispheres or sections of hemispheres accessed by coaxial cylinder electrostatic lenses. This is a much more complex type of spectrometer, which may require anything between 5 and 15 voltages to be varied as a spectrum is collected. However, it has better energy resolution than the CMA, gives more space around the specimen and can be configured electrically to operate in a variety of modes. The CHA has found favour in research and development laboratories because of this flexibility and the excellent energy resolution that is possible. CHA instruments normally collect a single kinetic energy and at one time and so are swept sequentially like a CMA to collect an electron spectrum. Since this kind of spectrometer is double focusing, it is possible to place an array of electron multipliers at its output and collect several kinetic energies (or channels) simultaneously and so speed up the acquisition of data. This was first done by placing nine channel electron multipliers at the output of a CHA, so speeding up acquisition by a factor of nine. Subsequently, manufacturers have included either separate multipliers (e.g. five) or micro-channel plates with multiple collectors (e.g. sixteen) is order to improve the single channel restriction of the simplest form of CHA. However, it has not been possible to span more than about 50 eV of a spectrum at one time by adding such multiple detectors. This is because of the maximum energy range presented by the hemispheres t
REFERENCES:
patent: 3735128 (1973-05-01), Palmberg
patent: 4126781 (1978-11-01), Siegel
patent: 4983864 (1991-01-01), Murai et al.
D. F. C. Brewer, "A Coaxial Cone Electrostatic Velocity Analyzer 1, Analysis of Electron Optical Properties" Journal of Physics E. Scientific Instruments, vol. 13, 1980, Bristol GB, pp. 114-122. no month.
S. Yavor, et al., "Optics of Conical Electrostatic Analysing and Focusing System", Nuclear Instruments and Methods, vol. A298, 1990, Amsterdam NL. pp. 421-425. no month.
International Search Report, dated Jan. 13, 1994, Appl. No. PCT/GB93/01957.
International Search Report, Appl. No. PCT/GB93/01957.
D. F. C. Brewer, et al., "A Coaxial Cone Electrostatic Velocity Analyzer I. Analysis of Electron Optical Properties", The Institute of Physics, 1980. no month.
S. Ya. Yavor, et al., "Optics of Conical Electrostatic Analysing and Focusing Systems", Nuclear Instruments and Methods in Physics Research A298 (1990), pp. 421-425. no month.
Berman Jack I.
University of York
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