JP2006126054A - Cathode luminescence analyzing method and cathode luminescence analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode luminescence analyzing method inexpensively obtaining the original signal component (net component), and also to provide a cathode luminescence analyzer. <P>SOLUTION: The cathode luminescence analyzer is constituted so as to irradiate a sample 5 with electron beam not only to detect the light emitted from the sample 5 by the irradiation with the electron beam by a photodetector 11, but also to obtain the wavelength spectrum of the detected light, and equipped with: a cut-off means for preventing the irradiation of the sample 5 with the electron beam; and an operation control means 13 for comparing the count value, which is detected by the photodetector 11 in a state that the cut-off means is opened, with the count value detected by the photodetector 11 in a state of the sample 5 being irradiated with the electron beam by operating the cut-off means to calculate the cathode luminescence characteristics of the sample. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for cathodoluminescence analysis.

  The cathodoluminescence analyzer is an apparatus for irradiating a sample with a finely focused electron beam, detecting light excited by the electron beam, and performing emission analysis of a minute region of the sample. This cathodoluminescence analyzer irradiates one point on the sample with an electron beam, decomposes the light generated from the electron beam irradiation point with a monochromator to obtain a wavelength spectrum, or fixes the monochromator to a certain wavelength. The state of light emission distribution can be obtained while scanning the sample with an electron beam. The emission intensity includes, for example, a photon (photon) counting method and a method obtained from the output of a CCD detector.

  As this type of cathodoluminescence analyzer, an apparatus is known in which a spectrum for each wavelength obtained from a sample by cathodoluminescence is displayed on a display unit with a color for each spectrum (for example, a patent). Reference 1).

  Although the cathodoluminescence analyzer detects light excited by an electron beam from a sample, it may be difficult to measure weak cathodoluminescence. Specifically, in the filament type electron gun that is widely used due to its price and simplicity of operation, the light emitted from the filament is reflected by the sample surface and enters the detector, or a photomultiplier tube or CCD. The dark noise of the detector is the cause of the difficulty. Therefore, removal of the filament light emission component and noise component from the measured value is performed.

As a specific configuration, a beam blanking device that blocks the beam and a lock-in amplifier (which puts a periodic signal and performs phase detection in accordance with the cycle) are incorporated into the electron gun to detect the phase. And a method of using a cold FE (field emission type) electron gun having a low operating temperature and no filament emission has been employed. In addition, a method of reducing the influence of filament light emission by reducing the hole diameter of the objective aperture, a method of suppressing the generation of dark noise by cooling the detector, and the like are performed.
JP 2001-91461 A (second page, third page, FIG. 2)

In the conventional apparatus described above, it is necessary to use an expensive circuit or mechanism in any method in order to suppress the influence of noise or the like by measuring weak cathodoluminescence.
The present invention has been made in view of such a problem, and provides a cathodoluminescence analysis method and apparatus capable of obtaining an original signal component (net component) at a low cost even when measuring weak cathodoluminescence. It is aimed.

  In the present invention, the photon counting measurement and the background count value when the irradiation current is zero and the irradiation current are irradiated by the axis correction function of the electron optical system or the variable function of the focusing lens in synchronization with the CCD detector. Each count value can be taken in.

  The invention according to claim 1 irradiates the sample with an electron beam using an electron optical system, detects light generated from the sample by the electron beam irradiation with a photodetector, and thereby obtains a wavelength spectrum of the detected light. In the cathodoluminescence analysis method described above, the background count value by the photodetector when the electron beam is controlled by the axis correction function of the electron optical system or the variable function of the focusing lens and the sample is not irradiated with the electron beam, and the sample In this case, the wavelength spectrum of the sample is obtained by subtracting the background count value from the count value when the sample is irradiated with the electron beam and subtracting the background count value from the count value when the sample is irradiated with the electron beam. To do.

  The invention according to claim 2 applies the maximum current to the axial alignment coil of the electron gun, obtains the cathode luminescence intensity at the time of blanking without irradiating the sample with the electron beam, and obtains the cathode luminescence when the sample is irradiated with the electron beam. Determine the intensity, and determine the net intensity of the cathodoluminescence at each sampling point from the cathodoluminescence intensity at the time of blanking at each sampling point and the cathodoluminescence intensity when the sample is irradiated with the irradiation current. It is characterized in that it is requested.

The invention according to claim 3 is characterized in that mapping by beam scanning becomes possible by controlling a scanning coil of an electron beam so as to be synchronized with the sampling.
The invention described in claim 4 is characterized in that the sample movement is controlled so as to synchronize with the sampling so that mapping by the sample scan becomes possible.

The invention described in claim 5 is characterized in that a multi-channel photoelectric conversion element is used as the photodetector.
The invention according to claim 6 is characterized in that the mechanical axis of the electron optical system is shifted to block filament light emission of the electron gun so that the sample is not irradiated with an electron beam.

  According to the seventh aspect of the invention, the sample is irradiated with an electron beam from an electron gun, light generated from the sample by the electron beam irradiation is detected by a photodetector, and thereby a wavelength spectrum of the detected light is obtained. In the cathodoluminescence analyzer, a blocking means for preventing the sample from being irradiated with the electron beam, a sample value irradiated with the electron beam with the blocking means being opened, and the detected value detected by the photodetector, and the blocking And a calculation control means for obtaining a cathode luminescence characteristic of the sample by operating the means and comparing the count value detected by the photodetector in a state where the sample is not irradiated with the electron beam. .

  According to the first aspect of the present invention, the net cathodoluminescence spectrum can be obtained from the measured value when the electron beam irradiation current to the sample is zero and the measured value when the sample is irradiated with the electron beam. it can.

  According to the invention of claim 2, the maximum current is applied to the axial alignment coil of the electron gun to block the irradiation of the electron beam to the sample, and the cathode luminescence intensity obtained at that time, the specified irradiation current to the sample, The cathode luminescence intensity of the net can be obtained from the difference in cathode luminescence intensity obtained by irradiating the electron beam.

According to the third aspect of the present invention, mapping by beam scanning can be performed by controlling the scanning coil of the electron beam.
According to the fourth aspect of the present invention, mapping by sample scanning can be performed by controlling the movement of the sample.

  According to the invention described in claim 5, by using a multi-channel photoelectric conversion element as a photodetector, cathodoluminescence in all wavelength regions can be obtained simultaneously.

According to the sixth aspect of the invention, by shifting the mechanical axis of the electron optical system, light emission from the filament coil can be cut off to obtain the light emission characteristic of cathodoluminescence.
According to the seventh aspect of the present invention, the net is calculated from the difference between the count value measured by blocking the electron beam irradiation from the electron gun by the blocking means and the count value measured in a state where the sample is irradiated with a normal electron beam. The cathodoluminescence characteristics can be obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a configuration example of an apparatus for implementing the present invention. In the figure, 1 is a lens barrel, 2 is an electron gun that emits an electron beam EB, 3 is an axial alignment coil that adjusts the optical axis of the electron beam, 4 is a diaphragm, 5 is a sample, and 6 is a sample on which a sample 5 is placed. It is a stage. 7 is a condensing mirror that collects cathode luminescence (CL) light generated from the sample 6 by irradiating the sample 6 with an electron beam, 8 is a light guide that guides CL light, 9 is a monochromator that decomposes incident light, A scanner 10 drives the wavelength of the monochromator 9.

  11 is a photodetector that detects monochromatic CL light from the monochromator 9, 12 is a measurement system that receives the output from the photodetector 11 and measures CL light, and 13 controls the overall operation of the apparatus. A computer, 14 is a measurement program provided in the computer 13, 15 is a keyboard / mouse that gives commands to the computer 13, and 16 is a color display that receives the output from the computer 13 and displays the spectrum of CL light. Reference numeral 17 denotes a keyboard / mouse for inputting coordinates and commands.

  FIG. 2 is a diagram showing an electron optical system of the apparatus shown in FIG. The same components as those in FIG. 1 are denoted by the same reference numerals. In the figure, 2 is an electron gun for emitting an electron beam EB, 3 is an alignment coil, 4 is a diaphragm for focusing the electron beam, 20 is a focusing lens for focusing the electron beam, 21 is an objective diaphragm for focusing the electron beam EB, 23 Is a minute moving coil, 24 is an objective lens, and 5 is a sample. The electron beam EB is controlled by the electron optical system.

  The electron beam EB emitted from the electron gun 2 passes through the alignment coil 3, is narrowed down by the diaphragm 4, narrowed down by the focusing lens 20, narrowed down by the objective diaphragm 21, and then sampled by the objective lens 24. 5 is irradiated. A scanning coil 22 is provided in front of the objective lens 24, and a minute moving coil 23 moves the electron beam EB by a minute amount. The operation of the apparatus configured as described above will be described as follows.

  First, the operator inputs the wavelength driving range (λ1 to λn) of the monochromator 9 and the driving speed of the monochromator 9 from the keyboard / mouse 17 to the computer 13 before starting measurement of the spectrum and the like. When such an input is performed, emission analysis is started, and the electron beam EB emitted from the electron gun 2 is narrowed down by the focusing lens 20 and irradiates the sample 5 mounted on the sample stage 6. The CL light generated from the sample 5 by this electron beam excitation is condensed by the condenser mirror 7 and guided to the monochromator 9 through the light guide 8.

  The computer 13 operates the measurement program 14 and controls the scanner 10 according to the value previously input by the operator. That is, the computer 13 sends a wavelength driving signal of the monochromator 9 to the scanner 10 so that the monochromator 9 sequentially extracts monochromatic lights having wavelengths λ1, λ2,..., Λn from the CL light. By the scanner control of the computer 13, the monochromator 9 sequentially extracts monochromatic lights having wavelengths λ1, λ2,..., Λn from the CL light.

  The extracted monochromatic light is converted into a CL electric signal corresponding to the light intensity by the photodetector 11, and the CL electric signal is amplified by an amplifier (not shown), and then is input into the measurement system 12. It is digitized by an A / D converter (not shown) provided and sent to the computer 13. The computer 13 reads the CL electrical signal digitized by the A / D converter and acquires the wavelength distribution spectrum of CL while synchronizing with the wavelength driving of the monochromator 9 described above. The acquired wavelength distribution spectrum is displayed on the color display 16.

  However, in the present invention, at a sampling point of each of the wavelengths λ1, λ2,..., Λn, the intensity is measured for a certain time while the sample 5 is irradiated with the electron beam EB. The cathodoluminescence intensity B1 is obtained. Next, the sample 5 is not irradiated with the electron beam EB by flowing a maximum current through the axis alignment coil 3 and the intensity is measured for a certain period of time, and the intensity I1 corresponding to only the background and noise components is obtained. obtain.

Then, by calculating (I1-B1), it is possible to obtain a net intensity that does not include background and noise components.
Here, the switching of the electron beam irradiation current by the control of the axis alignment coil 3 can be performed in a sufficiently shorter time than each sampling time (several ms [milliseconds] to several s [s]). Such mechanical driving can be performed at one time. In addition, the net intensity at the sampling point can be obtained in real time.

  As described above, a spectrum can be obtained by performing sampling with changing the state of the irradiation current together with wavelength driving of the monochromator, but mapping can be performed by performing similar sampling in synchronization with sample movement or beam scanning. it can.

  Thus, according to the present invention, at each sampling point, the count value measured by blocking the electron beam irradiation from the electron gun by the blocking means, and the count value measured in a state in which the normal electron beam is irradiated to the sample, From this difference, the cathodoluminescence intensity (spectrum or map) of the net can be obtained.

Hereinafter, embodiments of the present invention will be described.
(Embodiment 1)
The configuration of the embodiment is the same as that in FIG. In the first embodiment, the CL spectrum can be obtained by scanning the monochromator 9, and the spectral CL can be mapped using the stage driving device 15. That is, it can be seen what distribution of light of a certain wavelength shows on the sample. On the other hand, by giving the maximum current by the axis alignment coil 3 of the electron gun 2, the actual irradiation current can be made small enough to be ignored. Accordingly, the computer 13 measures the CL intensity of the gross (the signal component includes the background component) and the CL intensity of the blank component (noise component) at each sampling point of the spectrum and mapping, respectively. The net strength of each CL can be obtained. Here, the noise component (blank component) is a component caused by light emission of a filament or a dark count component related to a photodetector.

  According to this embodiment, the maximum current is applied to the axial alignment coil of the electron gun to block the irradiation of the electron beam to the sample, and the cathode luminescence intensity obtained at that time and the specified irradiation current to the sample are obtained. The net cathodoluminescence intensity can be obtained from the difference in cathodoluminescence intensity obtained by irradiating the electron beam.

(Embodiment 2)
The configuration of the embodiment is the same as that in FIG. In this embodiment, sample movement or beam scanning and sampling are performed synchronously in order to see the intensity distribution on a sample of a certain wavelength. In order to move the sample, the computer 13 drives the stage driving device 15. Alternatively, mapping by beam scanning can be performed by controlling the scanning coil of the electron beam from the computer 13, and a spectral distribution can be obtained.

  According to this embodiment, the sample stage 6 is driven from the outside (for example, a computer) to perform beam scanning, or the scanning coil is controlled by scanning with an electron beam to enable mapping by beam scanning. An intensity distribution at a certain wavelength can be seen.

(Embodiment 3)
The configuration of the embodiment is the same as that in FIG. In this embodiment, a multi-channel sensor such as a CCD detector is attached to the photodetector 11. For example, the intensity is obtained by a separate CCD detector for each wavelength of light. When such a multichannel sensor is used, the cathodoluminescence distribution in all wavelength regions generated from the sample 5 can be obtained simultaneously.

(Embodiment 4)
The configuration of the embodiment is the same as that in FIG. However, in this case, the monochromator 9 is not used, but a photoelectric conversion element such as a photomultiplier tube and a bandpass filter is used. In this embodiment, since a monochromator is not used, a wavelength spectrum cannot be detected, but mapping by simple spectroscopy can be obtained. In other words, the spectral characteristics of the sample can be obtained by passing the output of the photodetector through a bandpass filter.

(Embodiment 5)
The configuration of the embodiment is the same as that in FIG. In this embodiment, the mechanical axis of the electron optical system is shifted, and the electron beam is irradiated onto the sample by a deflection operation. With this configuration, since the mechanical axis is shifted, the influence on the detection system can be eliminated by blocking the light emission of the filament, so that the CL intensity from which the influence of the light emission of the filament is eliminated can be obtained.

  FIG. 3 is a diagram showing an example of spectral characteristics of a sample. The vertical axis represents the relative intensity of CL (arbitrary unit), and the horizontal axis represents the wavelength [nm]. f1 to f3 show characteristic examples when the probe current is changed. The photon count value increases as the probe current increases. The characteristics shown in the figure indicate that the photon count value is maximum when the wavelength is around 500 nm. f4 is a photodetector output in a state where the electron beam is completely cut off, that is, a so-called background noise component.

  FIG. 4 is a diagram showing the net spectral characteristics of the sample. This figure is obtained by subtracting the background component f4 from the f1 characteristic of FIG. It shows the cathodoluminescence characteristics with the background component removed.

  As described above in detail, according to the present invention, the irradiation current is reduced within the effective time by the axis correction function of the electron gun or the control of the focusing lens, and the noise component is removed during CL spectrum or mapping. The net strength of CL can be determined more easily than before. In addition, a beam blanking device, a cold FE electron gun, or the like, without using a complicated device configuration, an axial alignment coil or a focusing lens that is incorporated as a standard in a general SEM or EPMA (X-ray microanalyzer) is used. Therefore, an inexpensive cathodoluminescence analysis method and apparatus can be provided.

It is a figure which shows the structural example of the apparatus which implements this invention. It is a figure which shows the electron optical system of the apparatus shown in FIG. It is a figure which shows the spectral characteristic of a sample. It is a figure which shows the net spectrum characteristic of a sample.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens barrel 2 Electron gun 3 Axis alignment coil 4 Aperture 5 Sample 6 Sample stage 7 Focusing mirror 8 Light guide 9 Monochromator 10 Scanner 11 Photo detector 12 Measurement system 13 Computer 14 Measurement program 15 Keyboard / mouse 16 Color display

Claims (7)

In a cathode luminescence analysis method in which an electron beam is irradiated onto a sample using an electron optical system, light generated from the sample by the electron beam irradiation is detected by a photodetector, and a wavelength spectrum of the detected light is thereby obtained. ,
The background count value by the photodetector when the electron beam is controlled by the axis correction function of the electron optical system or the variable function of the focusing lens and the sample is not irradiated with the electron beam, and the total time when the sample is irradiated with the electron beam A cathode luminescence analysis method characterized in that a wavelength spectrum of a sample is obtained by taking each numerical value and subtracting the background count value from a count value when the sample is irradiated with an electron beam.   Applying the maximum current to the axial alignment coil of the electron gun, obtaining the cathode luminescence intensity at the time of blanking without irradiating the sample with the electron beam, obtaining the cathode luminescence intensity when irradiating the sample with the electron beam, and at each sampling point The cathode luminescence intensity at each sampling point is obtained from the cathode luminescence intensity at the time of blanking and the cathode luminescence intensity when the sample is irradiated with an irradiation current, thereby obtaining the wavelength spectrum of the sample. The method for analyzing cathodoluminescence according to claim 1.   3. The cathodoluminescence analysis method according to claim 2, wherein mapping by beam scanning is enabled by controlling a scanning coil of an electron beam so as to synchronize with the sampling.   3. The cathodoluminescence analysis method according to claim 2, wherein the movement of the sample is controlled so as to be synchronized with the sampling so that mapping by the sample scan is possible.   5. The cathodoluminescence analysis method according to claim 1, wherein a multichannel photoelectric conversion element is used as the photodetector.   2. The cathodoluminescence analysis method according to claim 1, wherein the electron axis of the electron optical system is shifted to block filament light emission of the electron gun so that the sample is not irradiated with an electron beam. In the cathode luminescence analyzer that irradiates the sample with an electron beam from an electron gun, detects the light generated from the sample by the electron beam irradiation with a photodetector, and obtains the wavelength spectrum of the light detected thereby,
A blocking means for preventing the sample from being irradiated with the electron beam;
The sample was irradiated with an electron beam in the state where the blocking means was opened, and the count value detected by the photodetector was detected, and the sample was detected by the photodetector when the electron beam was not irradiated by operating the blocking means. Computation control means for obtaining the cathodoluminescence characteristics of the sample by comparing with the count value;
A cathodoluminescence analyzer characterized by comprising:

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