U.S. patent number 3,889,115 [Application Number 05/341,846] was granted by the patent office on 1975-06-10 for ion microanalyzer.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Toshio Kondo, Hifumi Tamura.
United States Patent |
3,889,115 |
Tamura , et al. |
June 10, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Ion microanalyzer
Abstract
An ion microanalyzer which detects and mass analyzes the
secondary ions emitted from a specimen surface when it is scanned
with an ion beam, comprising a cathode ray tube the electron beam
of which is scanned synchronously with the scanning of the
above-mentioned ion beam, the intensity of the electron beam being
modulated by the directly detected signal of the secondary
ions.
Inventors: |
Tamura; Hifumi (Hachioji,
JA), Kondo; Toshio (Sagamihara, JA) |
Assignee: |
Hitachi, Ltd.
(JA)
|
Family
ID: |
12196934 |
Appl.
No.: |
05/341,846 |
Filed: |
March 16, 1973 |
Foreign Application Priority Data
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Mar 17, 1972 [CH] |
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26561/72 |
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Current U.S.
Class: |
850/43; 250/309;
250/397 |
Current CPC
Class: |
H01J
37/256 (20130101); H01J 49/142 (20130101) |
Current International
Class: |
H01J
37/252 (20060101); H01J 37/256 (20060101); H01J
49/14 (20060101); H01J 49/10 (20060101); H01j
037/26 () |
Field of
Search: |
;250/309,307,306,310,397 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Ion Microprobe Mass Analyzer," Liebl, Journal of Applied Physics,
Vol. 38, No. 13, 5277-5283, Dec. 1967..
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Primary Examiner: Lawrence; James W.
Assistant Examiner: Church; C. E.
Attorney, Agent or Firm: Craig & Antonelli
Claims
What we claim is:
1. An ion microanalyzer comprising:
means for producing an ion beam;
means for scanning the surface of a specimen with said ion
beam;
means for directly detecting a first portion of the secondary ions
emitted from said specimen;
a cathode ray tube having means for scanning the electron beam
thereof synchronously with the scanning of said ion beam;
a mass spectrometer for mass-analyzing a second portion of said
secondary ions and for providing a signal representative of the
mass-analysis;
means for modulating the intensity of the electron beam of said
cathode ray tube by the detected signal from said means for
directly detecting a first portion of the secondary ions emitted
from said specimen; and
means for superimposing the signal obtained from said mass
spectrometer on the signal obtained from said means for directly
detecting a first portion of the secondary ions emitted from said
specimen.
2. An ion microanalyzer according to claim 1, further, comprising
shielding means surrounding the specimen.
3. An ion microanalyzer according to claim 2, in which the
secondary ion detecting means is provided outside the shielding
means.
4. An ion microanalyzer according to claim 1, wherein said means
for directly detecting a first portion of the secondary ions
emitted from said specimen is a secondary electron multiplier.
5. An ion microanalyzer according to claim 1, further comprising
deflection means for deflecting the secondary ions to direct them
to said means for directly detecting a first portion of the
secondary ions emitted from said specimen.
6. An ion microanalyzer according to claim 5, wherein said
deflection means for deflecting the secondary ions consists of a
pair of electrodes one of which is made of a conductive film
deposited on a scintillator, and said means for directly detecting
a first portion of the secondary ions emitted from said specimen is
constituted by said deflection means and a photomultiplier opposed
to said scintillator.
7. An ion microanalyzer according to claim 6, wherein said ion
microanalyzer includes means for maintaining one of said electrodes
at the same electric potential as said specimen and shielding means
surrounding said specimen, and further includes means for changing
over the polarity of an electric potential applied to the other of
said electrodes.
8. In an ion microanalyzer including:
first means for producing an ion beam;
second means for scanning the surface of a specimen with said ion
beam;
a cathode ray tube having means for scanning the electron beam
thereof in synchronism with the scanning of said ion beam; and
third means receiving a principal ion beam which includes a portion
of the secondary ions emitted from said specimen for mass-analyzing
said principal ion beam and for providing a first signal
representative of the mass-analysis thereof;
the improvement comprising
fourth means, disposed separately from said third means, for
directly detecting secondary ions emitted from said specimen
separate from the portion of the secondary ions included in said
principal ion beam and for providing a second signal representative
of the directly detected secondary ions; and
fifth means, coupled to said fourth means and said cathode ray tube
for modulating the intensity of said electron beam in accordance
with said second signal provided by said fourth means, and
including means for superimposing said first signal on said second
signal for modulating the intensity of said electron beam in
accordance with said superimposed signals.
9. The improvement according to claim 8, wherein said fourth means
comprises a secondary electron multiplier.
10. The improvement according to claim 8, wherein said third means
comprises a mass analyzer and a comparator having first and second
inputs and an output, said first input being connected to said mass
analyzer, said second input being connected to a reference voltage
and said output being coupled to the output of said fourth
means.
11. The improvement according to claim 8, wherein said fourth means
comprises deflection means for deflecting the secondary ions and
directing the secondary ions into an ion detector.
12. The improvement according to claim 11, wherein said deflection
means comprises a pair of electrodes, one of which is made of a
conductive film deposited on a scintillator, and said ion detector
comprises a photomultiplier disposed opposite said
scintillator.
13. The improvement according to claim 12, further comprising
shielding means surrounding said specimen with said fourth means
located outside said shielding means.
14. The improvement according to claim 13, further comprising means
for maintaining one of said electrodes at the same electric
potential as said specimen and means for reversing the polarity of
the electric potential applied to the other of said electrodes.
15. A method of analyzing a specimen surface by an ion
microanalyzer comprising the steps of:
a. generating a primary ion beam;
b. continuously scanning a specimen surface with said primary ion
beam;
c. directly detecting a first portion of the secondary ions emitted
from said specimen;
d. scanning the electron beam of a cathode ray tube synchronously
with the scanning of said primary ion beam;
e. mass-analyzing a second portion of the secondary ion emitted
from said specimen and providing a signal representative
thereof;
f. modulating the intensity of the electron beam of said cathode
ray tube by the detected signal of said mass-analyzed secondary
ions; and
g. superimposing the signal obtained from said mass-analyzing of
said second portion of the secondary ions on the signal obtained by
directly detecting the first portion of the secondary ions emitted
from the specimen.
Description
The present invention relates to an ion microanalyzer, and more
particularly to an ion microanalyzer which can display the image of
the secondary ions emitted by a specimen on the face plate of a
cathode ray tube.
The ion microanalyzer of the type described is for the purpose of
obtaining an image of the surface of a specimen, potential
distribution, atomic number contrast (the contrast resulting from
the difference in the secondary ion emitting power of elements), or
the like on the face plate of a cathode ray tube and/or on the
recorder by detecting secondary ions emitted from a specimen by
being scanned with an ion beam.
A prior art ion microanalyzer for the preparation of a description
of the present invention and a preferred embodiment of the present
invention will be described with reference to the accompanying
drawings, in which
FIG. 1 is a schematic construction of a prior art ion
microanalyzer;
FIG. 2 is a schematic construction of an ion microanalyzer
according to the present invention;
FIG. 3 is a secondary ion image on the face plate of a cathode ray
tube; and
FIG. 4 is a photograph of a secondary ion image.
As a preparatory description for the present invention a prior art
ion microanalyzer will first be described with reference to FIG. 1.
The prior art ion microanalyzer shown in FIG. 1 includes a primary
ion irradiation system, a double focussing type mass-spectrometer,
a secondary ion detecting system, and a cathode ray tube. The
primary ion irradiation system consists of an ion source 1, a
primary ion separator 3 for ions 2 emitted by the ion source 1, a
condenser lens 4, an objective lens 6 and deflection electrodes 5.
An ion beam emitted by the ion source 1 is converged by the
condenser lens 4 onto a specimen 7 to a diameter of several microns
or less, and scanned by the deflection electrodes 5 synchronously
with a cathode ray tube 18 for observation. A part of the secondary
ions emitted by the specimen 7 passes through an electrostatic lens
9 and enters the mass-spectrometer which consists of an electric
field device 10, a magnetic field device 12 and slits 16 and 17.
The mass-analyzed ions pass through a deflector 13, are detected
and amplified by a detector such as a secondary electron multiplier
14, and supplied as a video signal to the cathode ray tube 18 and a
recorder 15 to provide an image for the concentration distribution
of a particular element in the surface of the specimen 7.
This ion microanalyzer can display an image of a particular element
as described above, but the image is not clear and distinct because
the intensity of the video signal for forming the image is low due
to the fact that the video signal is obtained by detecting the ions
analyzed by the mass-spectrometer. That is, this image forming
method has the following disadvantages:
1. Though this method is relatively effective for an element having
a high secondary ion emissivity (the ratios of emitted ions to
atoms) and having a concentration of several percent to 100 percent
in a specimen such Al, Fe, Cr, Na or K, other elements are only
with difficulty observed as images.
2. It is difficult to distinguish between the image of the surface
of a specimen and the atomic number contrast due to the
concentration of the element because the contrast due to the
unevenness of the surface of the speciman is observed superposed on
a particular element.
3. It is not practical to utilize the secondary ion image for the
location of the analyzing position because the intensity of signal
is low for that purpose.
An object of the present invention is to provide an ion
microanalyzer which overcomes the above-described disadvantages of
the prior art ion microanalyzer.
According to the present invention the above-described
disadvantages are overcome by directly detecting secondary ions
emitted by a specimen to supply a video signal.
To achieve this purpose, the present invention provides an ion
microanalyzer comprising means for producing an ion beam, means for
scanning the surface of a specimen with the ion beam, means for
detecting secondary ions emitted by the specimen, a cathode ray
tube having means for scanning the electron beam thereof
synchronously with the scanning of the ion beam, means for
mass-analyzing the secondary ions, and means for modulating the
intensity of the electron beam of the cathode ray tube by the
detected signal from the secondary ion detecting means.
There is another prior art ion microanalyzer which displays a
secondary electron image instead of a secondary ion image. However,
the secondary ion emissivity of an element is far higher than the
secondary electron emissivity. Consequently, according to the
present invention which employs secondary ions a very clear and
distinct atomic number contrast can be observed. Also, since a
secondary ion image is far less affected by scattered electrons
than a secondary electron image, the present invention can provide
an essentially low noise image.
An embodiment of the present invention will now be described with
reference to FIG. 2. A primary ion irradiation system consists of,
similarly to the prior art one described with reference to FIG. 1,
an ion source or gun 1, a condenser lens 4, an objective lens 6,
and deflection electrodes 5 for scanning. A cathode ray tube 18 for
the observation of a specimen image and a mass-spectrometer are the
same as those of the prior art.
To directly detect secondary ions 24 emitted from a specimen 7
placed on a support 8, a secondary ion detector consists of a
photosensitive surface 20 and an electrode 19 for secondary ion
deflection maintained at the same potential as a shielding
electrode (mesh or perforated metal electrode) 25 arranged around
the specimen 7. Though the shielding electrode 25 is not always
necessary, it has the function of maintaining the frontal space of
the specimen 7 at zero electric field to prevent an adverse effect
by the deflection of secondary ions. In some cases, to perform
energy analysis of the secondary ions to be detected a variable
electric source 26 is connected to the shielding electrode 25 so
that the potential Va of the shielding electrode 25 is made
variable over a range of from several volts to several hundreds of
volts relative to the specimen 7. The photosensitive surface 20
consists of a scintillator coated with an electrically conductive
film. The output light of the photosensitive surface 20 is received
by a photomultiplier 21 to be subjected to photoelectric
conversion. The electric signal produced by the conversion is
amplified by an amplifier 22 and modulates the intensity of the
electron beam of the cathode ray tube 18. The photosensitive
surface 20 is arranged such that it cannot directly be viewed from
the beam irradiated point on the specimen 7 so that the reduction
of the sensitivity of the photosensitive surface 24 due to the
deposition thereon of particles sputtered by the specimen 7 is
prevented. For this purpose an electric source 27 is connected to
the electrically conductive film on the photosensitive surface 20
so that a negative potential -Vs is applied thereto relative to the
opposing electrode 19 when positive secondary ions are to be
detected, and a positive potential +Vs is applied thereto when
negative secondary ions are to be detected to deflect the ions so
that they impinge upon the photosensitive surface 20.
Instead of the scintillator and photomultiplier 21 a secondary
electron multiplier may be used.
By the above-described structure according to the present invention
an amount of secondary ions about 10.sup.3 times as high as that
provided by a prior art apparatus could be detected for primary
argon ions Ar.sup.+ having an energy of 10 Kev and an ion current
of 10.sup.-.sup.8 A. As a result, a clear and distinct secondary
ion image of a resolution of 0.5 micron or less could be observed
on the cathode ray tube.
The thus obtained secondary ion image represents the atomic number
contrast between different kinds of elements present in the surface
of a specimen, which could not be observed by the prior art
apparatus.
In the apparatus according to the present invention the output of
the secondary electron multiplier 14 may be superimposed on the
output of the amplifier 22 through a comparator 28. By doing so an
element having a particular mass, for example M.sub.3, can be
specially brightly displayed on a cathode ray tube as shown in FIG.
3. Consequently, an image of the entire surface of a specimen can
be displayed brightly irrespective of the composition of the
specimen surface, and yet it is possible by scanning the
mass-spectrometer to know which regions of the image corresponds to
what mass. In FIG. 2, reference numeral 23 designates a power
source for scanning.
FIG. 4 is a photograph of a secondary ion image of a specimen
consisting of an iron plate and an aluminum film evaporated thereon
to a thickness of about 200 Angstroms. The atomic number contrast
between aluminum and iron is clearly observed in FIG. 4.
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