JP3454052B2 - Electron beam analyzer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam analysis method and apparatus, and more particularly to an electron beam analysis method and apparatus for accurately analyzing the elemental composition of a sample.

[0002]

2. Description of the Related Art The elemental composition of a sample can be analyzed by irradiating the sample with an electron beam and measuring the energy spectrum of characteristic X-rays or Auger electrons generated from the sample. To improve the position resolution of the analysis,
It is necessary to irradiate the sample with an electron beam as a very small probe. In an electron microscope equipped with a field emission electron gun, the size of the electron beam probe can be narrowed down to 1 nm or less, so that the elemental composition in the 1 nm region can also be analyzed. However, since the detected signal is weak, a large amount of time was required for measurement for high precision analysis.

[0003]

Therefore, due to insufficient stability of the sample table and the electron beam, the sample irradiation position of the electron beam may be displaced from the analysis start position during analysis. Furthermore, since the analysis signals such as characteristic X-rays and Auger electrons are weak, it is almost impossible to detect the change in the analysis position from the analysis signals themselves. Therefore, there has been a problem that accurate analysis with high position resolution cannot be performed.

[0004]

According to the present invention, the amount of displacement of a sample is measured in a short time to correct the analysis position by means of detecting secondary electrons or transmitted electrons having a higher detection efficiency than characteristic X-rays or Auger electrons. It is characterized by that.

[0005]

DETAILED DESCRIPTION OF THE INVENTION

<Embodiment 1> FIG. 1 shows an electron beam analyzer according to an embodiment of the present invention. In this embodiment, a scanning transmission electron microscope using a field emission electron source as an electron source is used. The electron beam emitted from the field emission electron source 1 is accelerated by the electrostatic lens 2 to a desired accelerating voltage, and then is irradiated onto the sample 7 by the condenser lens 3 and the objective lens 5. The electron beam is two-dimensionally scanned on the sample 7 by the deflector 4.

The transmitted electrons 14 transmitted through the sample 7 are detected by the detector 1.
After being detected by 5, the signal is amplified by the signal amplifier 21. The amplified video signal is supplied to the display device 25 through the control unit 24 and becomes a brightness modulation signal. The deflection scanning of the electron beam is performed by the control unit 24 by controlling the electron beam with the deflection signal sent from the deflection signal generator 10. at the same time,
A deflection signal synchronized with electron beam scanning is supplied to the display device 25, and a sample scan image is formed on the display device 25. The above is the basic configuration of the scanning transmission electron microscope.

Next, the analysis procedure according to the present invention will be described with reference to FIG. First, the electron beam is scanned on the sample at a predetermined magnification by the deflection signal supplied to the deflector 4 through the deflection signal generator 10 by the control unit 24, and the display device 25 is displayed as shown in FIG. A sample scan image as shown is obtained. The scanning time for obtaining this scanning image is 1
Within seconds, the analysis sample is observed from this image.

On the scan image, a cross marker as shown in FIG. 2B is displayed so as to be superimposed on the luminance modulation signal, and the analysis position is determined by aligning the cross marker with the analysis position. This scanning image is, for example, 1024 in the control unit 24.
It is stored in a video memory A (not shown) of pixels × 1024 pixels.

Next, when an analysis start signal is sent to the control unit 24, the control unit 24 irradiates the sample with the electron beam kept stationary at the position corresponding to the address of the cross marker, that is, the analysis position (FIG. 2 (c)). ). The characteristic X-ray 12 generated from the sample by the excitation by the electron beam irradiation is detected by the X-ray detector 13 to obtain the characteristic X-ray spectrum as shown in FIG. 5, for example. Information on the element distribution can be obtained from the intensity ratio of the characteristic X-ray corresponding to the element of interest.

In order to measure the energy resolution of the X-ray detection system under high conditions, it is usually necessary to set the X-ray count rate to about 1000 cps. On the other hand, since the fluctuation of the counting rate is represented by the square root of the counting rate, for example, 100,000 counts are required for analysis with an accuracy of 0.3%, and the measurement time is at least about 100 seconds. If the drift amount of the sample stage is 0.02 nm / sec, in order to correct the positional deviation of 0.2 nm, it must be corrected at 10-second intervals.

Then, after the electron beam is stopped and analyzed for about 10 seconds, the acquisition of the X-ray detection signal is stopped, the sample is scanned with the electron beam at the same magnification, and the sample scan image is obtained again.
Video memory B of 1024 pixels x 1024 pixels in 4
It is stored in (not shown) (FIG. 2 (d)). The positional deviation from the previous scan image can be calculated by calculating the cross-correlation between the sample scan images stored in the video memory A and the video memory B, for example, to obtain the drift amount of the sample.

In the next analysis, an exciting current corresponding to the calculated drift amount is added to the scanning coil and supplied to correct the electron beam irradiation position as shown in FIG. 2 (e). By performing this correction every 10 seconds of analysis, it is possible to perform accurate analysis without displacement.

<Embodiment 2> The second embodiment relates to position correction for X-ray surface analysis. The analysis procedure according to the present invention will be described with reference to FIG.

First, the analysis position is observed by the sample scanning image as shown in FIG. 3A to determine the surface analysis position. The scanning time for obtaining this scanning image is within 1 second. The scanning image is, for example, a video memory A of 1024 pixels × 1024 pixels.
Memorized in.

Next, for example, an area of 64 nm × 64 nm is scanned with an electron beam at intervals of 1 nm, and this area is analyzed in about 40 seconds. The signal amount between the energy regions E1 and E2 corresponding to the characteristic X-ray energy of the specific element x is stored in the video memory M1 of 64 pixels × 64 pixels in association with the address and the display unit 25 is brightness-modulated. It is displayed (FIG. 3 (b)).

At this point, the analysis is stopped and the sample is scanned to confirm the analysis position. This scan image is 1024 pixels x
It is stored in the video memory B of 1024 pixels (see FIG. 3).
(C)). For example, the cross-correlation of the sample scan images stored in the video memories A and B can be used to calculate the drift amount d of the sample.

In the next analysis, an exciting current corresponding to the calculated drift amount is added to the scanning coil and supplied, so that the electron beam irradiation position is shifted as shown in FIG. Correct the deviation of the analysis position. By performing this correction at predetermined time intervals, it is possible to perform accurate analysis without positional deviation (FIG. 3 (e)).

<Third Embodiment> A third embodiment relates to position correction for X-ray surface analysis. The analysis procedure according to the present invention will be described with reference to FIG.

First, the analysis position is observed by the sample scanning image to determine the surface analysis position. Then, the sample is scanned and irradiated with an electron beam. A video memory M1 of 128 pixels × 128 pixels in which the signal amount between the energy regions E1 and E2 corresponding to the characteristic X-ray energy of the specific element z is associated with an address.
Is stored in the display unit 24 and is displayed on the display unit 24 with brightness modulation. Further, the transmission scan images obtained at the same time are also stored in the video memory A1 of 128 pixels × 128 pixels (see FIG. 4).
(A)).

Next, the sample is similarly scanned, and the sample scan image is again stored in the video memory A2 of 128 pixels × 128 pixels.
Video memory M2 with X-ray image of 128 pixels x 128 pixels
Are stored in the memory (FIG. 4B). Such scanning is performed N times, and the Nth sample scan image has 128 pixels × 12.
X-ray image is 128 pixels x 1 in 8-pixel video memory An
It is stored in each of the 28-pixel video memory Mn (FIG. 4C).

Regarding the drift amount of the sample, first, the drift amount d2 of the sample with respect to A1 is calculated by cross-correlating the transmission scanning image A1 with A2. Transmission scan image A1
Is calculated up to An, and the drift amount dN of the Nth transmission scanning image An with respect to A1 is calculated. Next, a desired region of the X-ray image M1 of 128 pixels × 128 pixels, for example, 64 pixels × 64 pixels at the center is selected, and this image is shifted by the drift amount d2 to obtain X pixels of 64 pixels × 64 pixels.
The line image M2 is superimposed. This operation is performed N-1 times, and the Nth X-ray image Mn is superimposed on the X-ray image M1 with a shift of dn (FIG. 4 (d)).

The above operation may be performed each time a new image is captured, or after all images are captured. By these operations, an X-ray image with good SN can be obtained under the condition that there is no displacement of the analysis position, and highly accurate two-dimensional elemental analysis can be performed.

In this embodiment, the number of pixels of the video memory for storing the transmission scanning image and the number of pixels of the video memory for storing the X-ray image are made equal, but for the purpose of increasing the number of X-ray counts detected per unit pixel, The number of pixels of the video memory storing the X-ray image may be smaller than the number of pixels of the video memory storing the transmission scanning image.

In the above embodiment, the transmitted electron 14 that has passed through the sample serves as the sample position detecting means, and the transmitted electron detector 15
However, the present invention is also implemented in a scanning electron microscope using a secondary electron image obtained by detecting the secondary electron 16 generated from the sample with the secondary electron detector 17 with the same configuration. be able to.

Further, in the above embodiments, the characteristic X-rays 12 generated from the sample are used as the sample analyzing means for the X-ray detector 13.
However, the present invention can be implemented with the same configuration by using the spectrum obtained by detecting the Auger electron 18 generated from the sample with the Auger electron detector 19.

[0026]

As described above, in the electron beam analyzer of the present invention, the displacement amount of the sample is measured by the information detecting means such as the secondary electron or the transmitted electron, which has a higher detection efficiency than the characteristic X-ray or Auger electron. Accurate analysis can be performed by correcting the analysis position.

[Brief description of drawings]

FIG. 1 is a block diagram of an electron beam analyzer showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an analysis procedure of the first embodiment of the present invention.

FIG. 3 is an explanatory view showing an analysis procedure of the second embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an analysis procedure of the third embodiment of the present invention.

FIG. 5 is a spectrum diagram showing a characteristic X-ray spectrum.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Field emission electron source, 2 ... Electrostatic lens, 3 ... Condenser lens, 4 ... Deflector, 5 ... Objective lens, 6 ... Aperture, 7
... sample, 8 ... high-voltage power supply, 9 ... condenser lens drive power supply, 10 ... deflection signal generator, 11 ... objective lens drive power supply, 12 ... X-ray, 13 ... X-ray detector, 14 ... transmission electron,
15 ... Transmission electron detector, 16 ... Secondary electron, 17 ... Secondary electron detector, 18 ... Auger electron, 19 ... Auger electron detector, 20 ... Amplifier, 21 ... Amplifier, 22 ... Amplifier, 2
3 ... Amplifier, 24 ... Control part, 25 ... Display part.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI G01N 23/227 G01N 23/227 (56) References JP-A-2-65045 (JP, A) JP-A-3-291842 (JP , A) JP 2-151749 (JP, A) JP 10-92369 (JP, A) JP 62-229646 (JP, A) JP 63-259949 (JP, A) JP 9-43173 (JP, A) JP 1-102839 (JP, A) JP 10-92354 (JP, A) JP 63-80453 (JP, A) JP 63-190236 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01J 37/252 H01J 37/20 H01J 37/28 G01N 23/225 G01N 23/227

Claims (6)

(57) [Claims] 1. An electron source that emits a primary electron beam, a deflector that scans the primary electron beam onto a sample, an objective lens that irradiates the sample with the primary electron beam deflected by the deflector, and the primary In an electron beam analyzer having an electron beam detector for detecting transmitted electrons transmitted through a sample by irradiation of an electron beam, a control unit for detecting a shift of the transmission scanning image, and a sample by irradiation of the primary electron beam X to detect X-rays generated from
A line detector, and the control unit is obtained by irradiating the sample with a first transmission scan image obtained by irradiating a desired region of the sample with a primary electron beam, and by irradiating the sample with a primary electron beam again. The deviation of the image is detected from the second transmission scan image, the deviation is corrected by deflecting the irradiated primary electron beam, and the first X obtained by irradiating the desired area with the primary electron beam.
An electron beam analyzer characterized by superimposing a line image signal and a second X-ray image signal obtained by irradiating the corrected primary electron beam. 2. The electron beam analyzer according to claim 1, wherein the first storage means stores the transmission scanning image, and the second storage means stores image information of X-rays detected by the X-ray detector. And a storage means for storing the electron beam. 3. The electron beam analysis apparatus according to claim 2, wherein the control unit acquires a transmission scan image and an X-ray image at the same time. 4. The electron beam analyzer according to claim 2, wherein the control unit corrects the deviation from the first X-ray image signal.
An electron beam analyzer, wherein the superimposition with the second X-ray image signal is performed either for each of the corrections or after all the X-ray image signals have been measured. 5. The electron beam analyzer according to claim 1, wherein the control unit detects an image shift by cross-correlating the first transmission scan image and the second transmission scan image. An electron beam analyzer characterized by: 6. The electron beam analyzer according to claim 1, further comprising an Auger electron detector in place of the X-ray detector.