Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With rotor
Patent
1989-05-09
1991-09-17
Wieder, Kenneth A.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With rotor
324158P, 324717, 324718, G01R 104
Patent
active
050498126
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to devices for the electric characterization of samples and is more particularly applicable to electric mapping of semiconductor samples of large area, in solid or thin layer form. It relates more particularly to the devices for determining the electric conductivity .sigma. (or surface resistance) and/or the mobility .mu. of carriers in the semiconductor material.
Numerous devices are already known for measuring .sigma. and .mu.. Among the non destructive methods, several use closed cavities working in the UHF range. But these solutions are either only applicable to small sized samples, usually less than 5.times.5 mm.sup.2 (X. LE CLEAC'H, rev. Phys. Appl. 17 (1982) pages 481-490) or have only very poor resolution and do not allow a sample to be characterized locally, for it must completely close the end of a wave-guide.
Contactless electric mapping devices are further known which do not use the UHF technique but detection of eddy currents or a Hall voltage. Although this solution (HORIGUCHI et al., Japan Appl. 18, suppl. 18-1 pages 165-171) makes local analysis possible, it has different drawbacks. Since the measurement of .mu. takes place using a metal disk and ring forming capacitors with the sample at a very small distance (about 10.mu.), any variation of distance causes an error which may be considerable in the measurement of .mu.. It is difficult to effect automatic mapping, for manual adjustments are required during experimentation. Finally, the use of eddy currents makes the method unusable when the surface conductivity of the sample is too low, in practice when the squared resistance R exceeds 500 ohms.
The object of the present invention is to provide a device for the electric mapping of samples, of the type using UHF frequencies, answering better than those known heretofore the requirements of practice, particularly in that it makes high resolution possible on a sample which may be of a large area, and in that it is applicable even in the case where the conductivity of the sample is low.
To this end, the invention provides particularly a device comprising a UHF resonator for coupling locally to the sample, characterized in that the resonator is formed by a microstrip or triplate line loop carried by a conducting plane and having a gap of small length with respect to the length of the loop, the edges of the gap being formed so as to permit selective coupling thereof to the sample of material to be studied. With such a device, measurements can be made which are of a kind very different from each other.
In particular, it makes possible electric conductivity mapping of thin layer or solid state semiconductor samples; it also makes possible electric mobility magnetoresistance mapping of semiconductor samples. It also makes possible photoconductance mapping of semiconductor or semi-insulating samples. For that, in the conducting plane and insulator of the line, a passage is formed opening into the gap for sending a light beam on to the sample.
The device can be adapted to surface mapping of semiconductor material, either solid or in thin layer form, for example implanted or epitaxied.
In an advantageous embodiment of the invention, the edges of the gap of the loop are fixed to two electrodes of small area passing through a thin plate of dielectric material having a flat face intended to be applied against the sample. When a device of this kind is to be used for surface homogeneity mapping by photoconductance, the passage formed in the conducting plane and the dielectric of the line opens between the electrodes.
The part of the loop remote from the edges of the gap will generally be at a distance from the surface of the thin plate applied on the sample greater than that of the edges which are fixed directly to the electrodes deposited on the plate. Thus, the high coupling zone between the sample and the loop is limited to the zone immediately surrounding the gap.
The UHF resonator is provided for coupling to a UHF generator and a detector. Lead-in and lead-out microstrips m
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Favennec Pierre-Noel
Le Cleac'h Xavier
Burns William J.
French State, represented by the Minister of Post, Telecommunica
Universite de Rennes
Wieder Kenneth A.
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