Radiant energy – Electron energy analysis
Patent
1984-03-06
1986-05-06
Smith, Alfred E.
Radiant energy
Electron energy analysis
250310, 250397, H01J 4948
Patent
active
045874255
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates generally to electron beam apparatus of the kind in which an electron probe, constituted by a beam of electrons, is caused to impinge on a specimen under examination and information about, for example, the voltage distribution of the specimen surface is obtained by using a detector, including an electron collector, to pick up electrons emanating from the specimen.
Electron beam apparatus of the kind in which or for which the present invention may be used include general purpose scanning electron microscopes but also special purpose apparatus particularly adapted for inspection, quality control and fault diagnosis of integrated circuits.
It is generally known to employ an electron collector which collects secondary electrons emitted from the specimen, mainly as a function of the potential at the point on which the electron beam impinges, so as to develop an output signal which according to the mode of operation chosen for the electron beam apparatus can be used to derive, for example, a voltage contrast image or (particularly if stroboscopic scanning is used) information concerning the dynamic behaviour of the specimen under test. It is known to employ an electron collector which includes an extraction grid which may overcome field distortions above the surface of the specimen and also a control grid which can form a potential barrier of variable height to discriminate between secondary electrons emanating from regions of the specimen's surface of different potential. It is also known to employ a scintillator to collect the secondary electron current and to provide some discrimination between two secondary electrons emitted from the specimen and high energy reflected primary electrons.
SUMMARY OF THE INVENTION
It is the general object of the present invention to provide an improved electron collector or electron beam apparatus including such an improved collector. In particular the present invention concerns an improved system of electrodes which provide discrimination against the collection of unwanted high energy secondary electrons and also make the collection of electrons by or for a scintillator more efficient. As will be explained hereinafter, this aspect of the invention concerns the use of a solid reflective, or "mirror" electrode in combination with a filter electrode which is constituted by a cylindrical electrode of which the inner surface is of conical form. Further features of the voltage measuring electron collector characteristic of the present invention will be set forth hereinafter.
In a preferred form, the invention facilitates the scannng, or vector deflection, of the electron beam within an area up to 10 millimeters square or more on a normal specimen, depending on the working distance, that is to say the distance between the final ends and the specimen. Hitherto only much smaller areas, not more than 1/2 millimeter square can be scanned satisfactorily. The great importance of this is that the electron beam can be moved relative to the specimen, for example a microchip circuit specimen, by electromagnetic means only in order to measure voltages at different points quickly and with great accuracy.
A preferred, though not essential, feature of the voltage measuring electron collector is that it may be embodied by a self-contained structure which can be inserted into most scanning electron microscopes easily through a standard aperture in the chamber wall of the scanning electron microscope. In general, known systems are specific to a particular design of scanning electron microscope and require parts of the scanning electron microscope for their operation. However, it is not hereby intended to exclude structures which are not self-contained. It is feasible to make a voltage measuring electron collector in accordance with the invention in a retractable form which can be completely withdrawn from the path of the primary electron beam to a position which allows the ordinary scanning electron microscope's electron collector to be used in i
REFERENCES:
patent: 4039810 (1977-08-01), Heritage
patent: 4438332 (1984-03-01), Lichtenegger
Patent Abstracts of Japan, vol. 4, No. 185(E38), Dec. 19, 1980, see p. 667, JP, A, 55128242 Hitachi Seisakusho, Oct. 10, 1980.
Soviet Inventions Illustrated, vol. C12, Apr. 30, 1980, Derwent (London, GB) see Abstract No. C6586C/12, SU, A, 556583, Moscow Lomonosov University, Jul. 5, 1979.
Berman Jack I.
Smith Alfred E.
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