Radiant energy – Ionic separation or analysis – Ion beam pulsing means with detector synchronizing means
Reexamination Certificate
1998-01-14
2001-03-06
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Ionic separation or analysis
Ion beam pulsing means with detector synchronizing means
C250S305000, C250S3960ML
Reexamination Certificate
active
06198095
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to devices and processes for detector imaging of a particle beam comprising charged particles having a distinct energy distribution and a distinct angle distribution, and spectrometers with energy and angle resolution.
BACKGROUND OF THE INVENTION
When matter is irradiated, particles from an interactive zone can become irradiated by processes of interaction. From the space (angle) and energy distribution of the irradiated particles, inferences can be drawn about physical or chemical processes during the interaction, or about features of the relevant particle types, or of the interaction zone. Numerous analytical processes have accordingly been developed, for instance using electron diffraction tests or spectroscopic test.
One problem of the known analytical processes is the simultaneous detection of the angle and energy distribution of a particle beam (e.g., electrons, ions or clusters of ions, atoms or clusters of atoms).
In electron spectroscopic diffraction tests (e.g. RHEED), there is interest, for example, in linking the imaging of diffraction patterns with energy filtration in order to separate elastic and inelastic scattering processes. The modeling of the elastic scatterings enables an improved resolution of the structure. In addition, there is interest in angle-resolved auger electron spectroscopy.
Known systems for resolving locus and energy simultaneously using electron spectroscopy can be divided into two groups. One design works by combining conventional fluorescent screen imaging with a raster scanning mechanism, enabling the scanning of sections of the diffraction pattern and the analysis of their energy. The raster mechanism can comprise either a scan unit for the diffraction image or a sensor element which can be moved in the diffraction image (the so called Channeltron). Systems like that, however, suffer from the disadvantage that they are complicated to assemble and only allow quasi-simultaneous resolution of position and energy. Operating the raster mechanism takes a lot of time, so that real time analyses, for example in surface changes of solids, are only possible to a limited extent.
A second design enables the diffraction image to be observed through spherical grids for filtering energy. A system like this is described for RHEED examinations, for instance, by Y. Horio in Jpn. J. Appl. Phys. (Vol. 35, 1996, p 3559 et seq.) and is explained as follows with reference to FIG.
6
.
FIG. 6
shows the use of three spherical grids
61
,
62
and
63
in front of an observation screen
64
in a known RHEED apparatus. The spherical grids act as energy filters to screen (extract) inelastically scattered electrons. A deceleration potential V
+
has been installed between grids
61
and
62
. Grid
63
acts to correct the imaging onto Screen
64
. The grids are configured concentrically at intervals at distances of r
1
, r
2
and r
3
so that the sample is located in the center of the grid spheres.
Filtering energy using spherical grids has several disadvantages. The assembly requires the location of the imaged sample zone from which the diffraction image is emitted to be centered inside of the spherical grids. Therefore, to achieve practicable image sections and/or construction sizes a small operational distance (approximately 20 to 30 mm) is needed between the sample and the analyzer (inlet window).
The operating distance is fixed by the grid radii and cannot be changed. The small operating distance leads, for instance when used in coating equipment, firstly to spatial problems and secondly to unacceptable contamination of the spherical grids. The contamination is caused by the fact that partial pressure of the substances which are to be deposited can develop in the area of the spherical grids on account of the small operating distance, thus resulting in deposits on the grids and insulators.
In addition, spherical grid analyzers are restricted to extremely small grid apertures so that energy resolution of &dgr;E/E<10
−2
which would be of practical interest can be achieved. Since the operating distance is fixed as a field-free space, deceleration (energy selection) can only occur in the area of the spherical grids over a short distance. The stop or deceleration potential must be fully attached to the spherical grids. In order to achieve sufficient energy resolution, however, the grid apertures must be very small (under 40 mm in size). This is disadvantageous to grid transmittance.
In addition, spherical grid analyzers require at least three grids for distortion-free projection onto a flat screen. This leads to further transmittance loss and thus to a transmittance in the whole configuration of approximately 40%. This is disadvantageous to analytical sensitivity.
Apart from lack of space, there is often the problem in coating equipment (e.g. molecular beam epitaxy chambers or MBE chambers) that because of the given neck flanges an optimal analyzer position can often not be achieved. Using spherical grid analyzers with a precise centering relative to the sample is only possible to a limited degree.
DESCRIPTION OF THE INVENTION
It is an object of the invention to provide an improved device and process for angle and energy resolution imaging of a particle beam, using high energy resolution and sensitivity and providing increased operating distance between detector and sample. It is a further object of the invention to provide a spectrometer which is equipped such a device, and processes for operating and applying it.
The invention is a device for imaging a particle beam with charged particles of a definite energy and angle distribution a on detector. The invention operates by influencing the particle beam (or group of particles) emitted from a sample firstly by deflection so that essentially parallel straight paths are formed which are then directed to an energy selective electrode configuration with semi transmissive electrodes. The electrode configuration forms an opposing or counter field analyzer which acts to filter inelastic scatterings in electron diffraction tests. The mutual configuration of the parallel particle paths contains all the information about the original particle beam's angle distribution. The invention preferably has a deflection and deceleration apparatus for decelerating the particle beam before it reaches the filter electrodes. Essentially parallel particle paths are formed in the particle beam such that the mutual distances correspond to the angle distribution of the particles, the parallel particle paths being directed to the filter electrodes.
Deflection devices in accordance with the invention allow the operating distance between the sample and a detector to be increased significantly as compared with the conventional spherical grid analyzers. The increased operating distances are also linked with advantages relating to sensitivity and resolution capabilities, which are described in greater detail below.
The deflector means comprise a multitude of electromagnetic lenses or other suitable electrodes which are powered downstream with increasing stopping potential such that the particle beam with initially divergent particle paths is converted into a particle beam with parallel paths, in the course of which the particles are decelerated and directed to the energy selective electrode configuration. The deflection devices are also referred to as stop lenses.
The stop lenses have at least two field forming elements (electrodes) which are powered downstream with increasing stopping potential. Preferably, there are three field forming elements. By using the third element in the beam direction outer beams can be captured more easily (outer beam correction). Even more elements can, however, be provided.
The potential functions with which the elements of the stop lens are driven can be computed by an artisan with a knowledge of electrostatics (e.g. for field distribution in cylinder lenses) using the concrete design and the necessary precision, or can be determined using appropriate num
Nguyen Kiet T.
Schnader Harrison Segal & Lewis LLP
Staib Instruments GmbH
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