Radiant energy – With charged particle beam deflection or focussing – With detector
Reexamination Certificate
2001-12-19
2003-11-25
Lee, John R. (Department: 2881)
Radiant energy
With charged particle beam deflection or focussing
With detector
C250S281000, C250S282000, C250S299000, C250S489000, C378S019000, C378S098800
Reexamination Certificate
active
06653637
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charged particle trap for X-ray analysis so as to analyze a specimen and its constituent elements by sending a beam of charged particles to strike the specimen and detecting the characteristic X-rays from the specimen with least concern about any undesired charged particles.
2. Description of Related Art
A method for analyzing a specimen's elements by sending a beam of charged particles to strike the specimen and detecting the characteristic X-rays emitted from the specimen is known. An example of such method is the X-ray spectrometry of a spatial energy dispersive type in which the composition of a specimen is measured by detecting X-rays emitted from the specimen. This method is advantageous in that the characteristic X-rays from the specimen have energy equal to the electronic transitional energy of the elements constituting the specimen. The measurement of the volume of X-ray emissions per unit time for each X-ray provides information about how the specimen under examination is composed of elements. A semiconductor detector having semiconductor crystal such as silicon, germanium, etc. is generally used for detecting X-rays.
In recent years, as reported in Physics Today, July, 1998, pp. 10-21, an X-ray detector called a micro-calorimeter, which operates at ultra-low temperature (below 100 milli-Kelvin), has been developed. As compared with the above semiconductor detector, the micro-calorimeter detects the X-rays at high-energy resolution.
Along with the above-mentioned X-ray spectrometry of a spatial energy dispersive type, a method called X-ray spectrometry of a wavelength dispersive type using the combination of an X-ray spectrometer and a proportional counter is also known.
The schematic structural drawing of a typical radiation detector using the above-mentioned semiconductor detector is shown in FIG.
16
. For noise reduction purposes, arrangement is made such that an X-ray crystal
101
and a field effect transistor
2
at the input stage of a pre-amplifier circuit block
20
is cooled to low temperature by a cryostat
7
using liquid nitrogen or a Peltier element in conjunction with cooling rods
12
. When a beam of electrons
5
strikes a specimen
9
, X-rays
1
are emitted from the specimen. The X-rays
1
pass through an X-ray window
8
and arrive at the X-ray crystal
101
where they are transformed into positive hole pairs of electrons proportional to the X-ray energy.
A method for processing signals produced by the X-ray crystal
101
will be described below. Electrons that reach at the electrodes of the X-ray crystal further travel through the pre-amplifier circuit block
20
of a charge integral type where they are transformed into pulses of voltage
220
with a height proportional to the number of the electrons. Furthermore, the pulses of voltage
220
are filtered through a shaping amplifier
51
so as to be shaped into pulses of voltage
310
. The pulses of voltage
310
are inputted to a pulse height analyzer
53
where they are subjected to pulse height analysis and mapped in an X-ray spectrum
400
. The X-ray spectrum
400
represents an energy distribution curve of the incident X-rays
1
detected by the X-ray crystal, i.e., how many X-rays of a certain energy level have been detected. The value of energy at a peak of the spectrum determines what is an element (a component) of the specimen and the count of the X-rays forming the spectrum peak determines the quantity of the element content.
Although, in the above description, attention is directed to the X-rays
1
emitted from the specimen
9
when the beam of electrons
5
strikes the specimen
9
, reflected/back-scattered electrons
4
with a diversity of energy less than the energy of the incident electron beam also radiate from the specimen
9
by elastic or inelastic scattering. Such reflected electrons
4
are called backscattered electrons. When the backscattered electrons
4
are detected by the X-ray crystal as the incident rays, they are also transformed into electric signals as for the X-rays and cause background noise. Moreover, the backscattered electrons cause a defect in the X-ray crystal and significantly deteriorate the X-ray detecting performance of the X-ray crystal.
For the reason, a backscattered electron trap
3
is installed between the X-ray crystal
101
and the specimen
9
, as shown in
FIG. 16
, so as to trap the backscattered electrons
4
from entering incidentally. Furthermore, as the backscattered electrons
4
strike against the surface of an object other than the specimen
9
, X-rays are produced and cause more background noise.
Thus, a chamber
6
containing the X-ray crystal
101
is partially made of metal material to be thick enough to attenuate the X-rays so that the X-rays reflected from any objects other than the specimen will not enter into the X-ray crystal incidentally.
Another detector implementation mechanism is to keep the X-ray detector away from the specimen when the X-ray detection is not performed to further prevent the detector from being deteriorated by the backscattered electrons. Hereinafter, the backscattered electron trap will be referred to as an electron trap.
As described in Microscopy and Microanalysis, Vol. 4 (1999) pp. 605-615, for conventional X-ray detectors, a single X-ray crystal is generally used as the detector for detecting X-rays. The electron trap essentially consists of a pair of permanent magnets.
Another conventional electron trap is shown in
FIGS. 17
,
18
, and
19
. This trap has a structure similar to the trap disclosed in JP-A-103379/1981.
FIG. 17
shows a section of the trap including the optical axis and the axis of X-ray detection.
FIG. 18
shows another section of the trap taken along the line XVIII—XVIII in FIG.
17
.
FIG. 19
shows yet another section of the trap taken along the line XIX—XIX in FIG.
18
.
The electron trap
300
includes two permanent magnets
21
and
22
placed above and under a X-ray path hole
11
, a cylindrical support
15
made of soft iron with a magnetic path
13
and a groove
14
, and a cover
16
. A magnetic field
17
is generated in the X-ray path hole
11
so as to turn the incident backscattered electrons
4
to the hole
11
toward a direction perpendicular to the direction in which the electrons
4
travel and the direction of the magnetic field
17
by the Lorentz force. This causes the backscattered electrons to strike against the walls of the groove
14
so that they will not enter the X-ray crystal incidentally.
The groove
14
is formed such that X-rays
18
emitted when the backscattered electrons
4
strike against the walls of the groove
14
as shown in
FIG. 19
will not enter the X-ray crystal
101
(see
FIG. 16
) incidentally. The magnetic flux density of the magnetic field is a few times larger than 0.1 tesla. If the magnetic flux density of the magnetic field is 0.2 tesla, electrons with energy of 20 keV incoming perpendicular to the magnet field is redirected to curve with the radius of curvature of about 2 millimeters.
The conventional X-ray detection by using a single X-ray detecting element has been illustrated above,
FIGS. 20 and 21
illustrative an X-ray detector implementing a plurality of X-ray detecting units as disclosed in JP-A-222172/1996.
FIG. 20
shows the X-ray detector setup on an electron microscope, while four X-ray crystals
101
are set symmetrically on the right and left sides. These X-ray crystals
101
detect characteristic X-rays emitted from the specimen
9
when the beam of electrons
5
strikes the specimen. Reference numeral
107
denotes a collimator for reducing X-rays that travel in random directions.
FIG. 21
is an enlarged perspective view of the collimator shown in
FIG. 20
for explaining two electron traps provided in the collimator for the innermost two X-ray crystals
101
. The collimator
107
is made of tantalum and has an electron beam path hole
700
through which the electron beam
5
is allowed to travel along its axis. The h
Kanda Kimio
Ochiai Isao
Shinada Hiroyuki
El-Shammaa Mary
Hitachi , Ltd.
Lee John R.
LandOfFree
X-ray detector and charged-particle apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with X-ray detector and charged-particle apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and X-ray detector and charged-particle apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3179511