JP2000208087A - Electron probe micro-analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform line analysis and mapping analysis without interrupting automatic height correction even when the surface shape of a sample changes and provide high-reliability measurement data in an electron probe micro- analyzer. SOLUTION: This analyzer is provided with: an optical focus position detection device 2; a Z-axis drive means 13 for driving a sample stage 12 in the Z-axis direction; and a control switch means 3 for setting the Z-axis control data of the Z-axis drive means by switching over an approximate value of the Z-axis coordinate to the Z-axis coordinate value provided by the optical focus position detection device 2 according to a focusing signal level from the optical focus position detection device 2. Thereby, continuous automatic height correction can be carried out by switching over the Z-axis control data, and the reliability of the measurement data can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electron probe microanalyzer, and more particularly, to position control of a sample in a Z-axis direction.

[0002]

2. Description of the Related Art In an electron probe microanalyzer (EPMA) using a wavelength dispersive spectroscope, a sample, a dispersive crystal, a detection crystal, and a detector are set as light-collecting conditions for detecting characteristic X-rays emitted from the sample by electron beam irradiation. It is required that the X-ray spectrometer of the instrument be accurately arranged on the circumference of the Rowland circle. Usually, the focusing condition of the X-ray spectroscope is performed by adjusting the height of the sample surface.

[0003] In the analysis using an electron probe microanalyzer, a point analysis for analyzing one point on a sample surface or an X-ray signal is detected by changing an analysis position on the sample surface one by one each time. There are line analysis and mapping analysis to obtain one-dimensional or two-dimensional distribution. In order to accurately perform point analysis, line analysis, and mapping analysis on an uneven sample surface, the sample should always be sampled so that the height of the sample surface at each analysis position satisfies the X-ray spectrometer focusing conditions. It is necessary to perform automatic height correction for correcting the height of the stage.

Conventionally, positioning of an electron probe microanalyzer in the height direction (Z-axis direction) is performed by (a) autofocus control by an optical focus position detecting device, and the current height information of a sample surface is analyzed for each analysis point. And returning it to the sample stage, and adjusting the height position of the sample stage so that the analysis point on the sample surface satisfies the focusing condition, or (b) obtaining the shape of the sample surface in advance, A method of approximating the Z-axis coordinate value of the sample surface from the shape and adjusting the height position of the sample stage based on the obtained Z-axis coordinate value has been performed.

FIG. 9 is a flowchart for explaining a measurement procedure of an electronic probe microanalyzer for performing positioning in the Z-axis direction by autofocus control.
The electron probe microanalyzer moves the sample stage in the X and Y-axis directions to set the irradiation position of the electron beam (step S101), and then uses the optical image of the sample at the irradiation position to execute the Z-axis coordinate by the autofocus function. Is obtained (step S102), and the height position of the sample stage is adjusted by moving the Z-axis using the obtained Z-axis coordinate value (step S10).
3). Adjustment of the height position of the sample stage satisfies the light-collecting conditions of the X-ray spectrometer, and performs measurement (step S10).
4).

[0006]

When point analysis, line analysis, and mapping analysis are performed by a conventional electron probe microanalyzer, the characteristic of the optical focus position detecting device is used in the Z-axis control by the above-mentioned auto focus (a). In some cases, good control becomes difficult. In the optical focus position detection device, the focus position is detected based on the optical image of the sample surface, so if the amount of light detected depending on the condition of the sample surface decreases, the processing time until the focus position is detected increases. In addition, it is difficult to perform automatic height correction following a shape change.

FIG. 10 is a diagram for explaining Z-axis control of a conventional electron probe microanalyzer. When the processing time becomes longer due to the decrease in the detected light amount, FIG.
The Z-axis position of the surface shape of the sample indicated by reference symbol A in FIG. 10B is denoted by reference symbol B in FIG. When the height position of the sample stage is adjusted based on the Z-axis coordinate value obtained by the approximation calculation of (b) above, reference numeral C in FIG.
An error occurs in the Z-axis height due to the approximate calculation.

For this reason, in the conventional Z-axis control, if automatic height control becomes difficult or a position error occurs in the Z-axis direction, the reliability of the obtained line analysis and mapping analysis data decreases. Become.

Accordingly, the present invention solves the above-mentioned conventional problems and provides an electronic probe microanalyzer with:
Even if the sample surface shape changes, it is possible to continuously perform line analysis and mapping analysis without breaking automatic height correction, and to obtain highly reliable measurement data. .

[0010]

SUMMARY OF THE INVENTION The present invention relates to an electron probe microanalyzer for performing elemental analysis of a sample surface by characteristic X-rays emitted from the sample by irradiation with an electron beam. And an approximate value of the Z-axis coordinate and a Z-axis coordinate value obtained by the optical focus position detection device according to the focus signal level from the optical focus position detection device. A switching unit for switching the Z-axis control data, and a continuous automatic height correction by switching the Z-axis control data, thereby improving the reliability of the measurement data.

The optical focus position detecting device has an auto-focus function for taking in an optical image of a sample position irradiated with an electron beam and automatically obtaining a focus position of the optical image, and a focus signal for focus detection. And a Z-axis feedback control signal forming means for forming a control signal for controlling the Z-axis stage using the focus signal. Z
The axis driving means includes a stage mechanism for driving the sample stage in the Z-axis direction, and a Z-axis drive control means for driving and controlling the stage mechanism. Further, the stage mechanism includes X and Y axis drive control means in addition to the Z axis drive control means, and can move in the X and Y axis directions to perform line analysis and mapping analysis of the sample.

The control switching means is means for switching Z-axis control data used for controlling the Z-axis driving means, and the switching is performed in accordance with a focus signal level from the optical focus position detecting device. The Z-axis control data to be used by switching is an approximate value of the Z-axis coordinate and a Z-axis coordinate value obtained by an autofocus function of the optical focus position detecting device.

The control switching means sets a threshold value for switching, and when the level of the in-focus signal exceeds the threshold value, it is obtained by an autofocus function of the optical focus position detecting device. Switching to the Z-axis coordinate value, the Z-axis coordinate value is sent to the Z-axis driving means as a Z-axis feedback control signal, and Z-axis control is performed. On the other hand, when the focus signal level is lower than the threshold value due to the condition of the sample surface, the surface shape of the sample is measured in advance, and the value is switched to the approximate value of the Z axis coordinate obtained by the approximate calculation. The approximate value of the coordinate value is sent to the Z-axis driving means to perform Z-axis control.

The threshold value is determined from the relationship between the tracking speed of the autofocus function of the optical focus position detecting device and the focusing level, and a focusing level corresponding to an allowable following speed is obtained. Is the switching reference level.

According to the present invention, by switching the Z-axis control data in accordance with the focus level which changes depending on the condition of the sample surface, the tracking speed of the autofocus function of the optical focus position detecting device is sufficiently high. Can perform high-precision Z-axis control following the surface shape of the sample using the Z-axis coordinate value by the autofocus function.
When the tracking speed of the autofocus function of the optical focus position detection device is slow, line analysis and mapping analysis can be performed using the approximate Z-axis coordinate values without stopping automatic height correction.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic block diagram of a configuration example of the electronic probe microanalyzer of the present invention. In the electron probe microanalyzer 1 shown in FIG. 1, a sample placed on a sample stage 12 is irradiated via an electron beam condenser lens or an objective lens generated from an electron beam source 11 such as a filament.
The X-rays emitted from the sample are analyzed by an X-ray signal detection unit 16 including a spectroscopic element that separates the light according to wavelength and a detector that detects the separated characteristic X-rays. Note that X obtained from the sample
Not only the line but also other signals can be detected.

The sample stage 12 is driven in the Z-axis direction by a Z-axis stage drive control means 13, and is driven in the X and Y-axis directions by an X and Y axis drive control means 14. The Z-axis stage drive control means 13 and the X- and Y-axis stage drive control means 14 adjust the height in the Z-axis direction and X, Y
Performs axial positioning.

The surface of the sample is imaged by an optical microscope 15 equipped with an image pickup device such as a CCD camera, and displayed on a monitor 7 by an optical focus position detecting device 2 having an autofocus function.

The optical focus position detecting device 2 includes a focus signal detecting and forming means 21 and a Z-axis feedback control signal forming means 22. The focus signal detecting and forming means 21 forms a focus signal used for focusing from an optical image signal picked up by the optical microscope 15. The Z-axis feedback control signal forming unit 22 forms a Z-axis feedback control signal using the focusing signal, feeds back to the Z-axis stage drive control unit 13, controls the sample stage 12 in the Z-axis direction, and Focus and acquire sample height data.

Normally, the optical focus position detecting device 2 sets the focus position on the sample so as to coincide with the analysis position on the sample which satisfies the light focusing condition of the X-ray spectroscope, and focuses the optical image. By doing so, the light collecting conditions of the X-ray spectrometer can be adjusted.

The electronic probe microanalyzer 1 of the present invention includes a control switching unit 3 for switching a control signal sent to the Z-axis stage drive control unit 13. Control switching means 3
A focus signal comparing means 31 for comparing the signal level of the focus signal formed by the focus signal forming means 21 with a threshold value;
A threshold value storage means for storing a threshold value; comparing the in-focus signal level with the threshold value; switching a control signal to be input to the Z-axis stage drive control means based on the comparison result; Do. The control signals to be switched are a Z-axis feedback control signal and an approximate Z-axis control signal, and the Z-axis feedback control signal is Z-axis coordinate data fed back from the Z-axis feedback control signal forming means 22. Is Z-axis coordinate data read from the approximate Z-axis coordinate data storage means 4. The approximate Z-axis coordinate data storage unit 4 measures the surface shape of the sample to be measured, obtains approximate Z-axis coordinate data by approximate calculation based on the measurement result, and stores the data.

The detection signal detected by the X-ray signal detector 16 such as an X-ray spectroscope can be stored in the data storage 5 together with the coordinate data. In the present invention, the control switching means 3
Thereby, the control signal of the Z-axis control is switched. Hereinafter, first, a procedure for obtaining approximate Z-axis coordinate data will be described with reference to the flowchart in FIG. 2, and a procedure for setting a threshold will be described with reference to a flowchart in FIG. 3 and a relationship diagram between the focus signal level and the autofocus speed in FIG. After that, two operation examples performed by the electronic probe microanalyzer 1 of the present invention will be described with reference to FIGS.

The procedure for obtaining approximate Z-axis coordinate data is shown in FIG.
In the flowchart of FIG. 7, the height data of the sample surface to be measured is measured by an auto-focus function or the like provided in the optical focus position detecting device (step S31), and approximate interpolation calculation is performed based on the measured data to obtain approximate Z-axis coordinates. Data is obtained (step S32), and the obtained approximate Z-axis coordinate data is stored in the approximate Z-axis coordinate data storage means 4. The approximate Z-axis coordinate data is stored together with the X-axis coordinate value and the Y-axis coordinate value, and read out in accordance with the X and Y-axis coordinate values (step S33).

By obtaining the approximate Z-axis coordinate data, the Z-axis control can be performed on a portion other than the actually measured portion. Further, the measurement data itself can be stored without performing the approximate calculation. When this measurement data is used, the Z-axis control can be performed only for the actually measured portion.

In the procedure for setting the threshold value, the correlation between the signal level L of the in-focus signal and the control speed v of the autofocus is obtained in the flowchart of FIG. FIG.
In the case, when the focus signal level L is high, the control speed v by the autofocus increases, and when the focus signal level L is low, the control speed v by the autofocus decreases (step S41).

If the control speed v by the autofocus becomes slow, a delay occurs in the Z-axis control, and it becomes difficult to follow the sample surface shape with high accuracy. Therefore, an allowable auto focus control speed Vc is determined (step S4).
2) A focus signal level Lc corresponding to the determined autofocus control speed Vc is obtained from the correlation (step S4).
3) The obtained focus signal level Lc is stored in the threshold value storage means 32 as a reference value for comparison (step S44).

Next, a first operation example of the electronic probe microanalyzer according to the present invention will be described with reference to the flowchart of FIG. 5 and the signal diagram of FIG. 6, and the flowchart of FIG. 7 and the signal diagram of FIG. A second operation example of the electronic probe microanalyzer of the invention will be described. The first operation example switches the control signal of the Z-axis control by one threshold value, and the second operation example switches the control signal of the Z-axis control by two threshold values. Is what you do.

In the first operation example, the electronic probe microanalyzer prepares for analysis such as mapping analysis and line analysis (step S1), and sets the autofocus function of the optical focus position detecting device 2 (step S2). ), And start the analysis (step S3).

The X, Y-axis stage drive control means 14 drives the sample stage 12 in the X-axis direction and the Y-axis direction to align the electron beam with the analysis point on the sample (step S).
4). Focus forming means 21 of optical focus position detecting device 2
Forms a focus signal of an optical image of the sample taken from the optical microscope 15. The comparison means 31 of the control switching means 3 compares the focus signal level L from the focus formation means 21 with the threshold value Lc in the threshold value storage means 32 (step S).
5).

If the focus signal level L is larger than the threshold value Lc, it is determined that a sufficiently high control speed can be obtained in the Z-axis control by the function of autofocus,
The Z-axis feedback control signal forming means 22 of the optical focus position detecting device 2 forms a Z-axis feedback control signal. The Z-axis stage drive control means 13 takes in the Z-axis feedback control signal (step S6), and
The Z-axis is driven based on the axis feedback control signal (Step S8).

On the other hand, when the focus signal level L is smaller than the threshold value Lc, it is determined that a sufficient control speed cannot be obtained in the Z-axis control by the function of the autofocus, and the Z-axis feedback control signal forming means is determined. The control signal for the reference 22 is stopped, and a read signal is output to the approximate Z-axis coordinate data storage means 4. The approximate Z-axis coordinate data storage unit 4 takes in the X-axis coordinate and the Y-axis coordinate from the X and Y-axis stage drive control unit 14 from the time when the read signal is input, and stores the Z-axis coordinate data corresponding to the X and Y coordinates. The readout is output to the Z-axis stage drive control means 13. The Z-axis stage drive control means 13 takes in the Z-axis coordinate data as an approximate Z-axis control signal (step S7), and drives the Z-axis based on the Z-axis feedback control signal. The data storage unit 5 stores the detection signal detected by the X-ray signal detection unit 16 and the coordinate position (Step S8). Steps S4 to S8 are repeated until the mapping is completed (step S9).

The signal diagram of FIG. 6 shows the relationship between the magnitude of the focus level L and the control switching. As shown in FIG. 6, at the threshold Lc, the Z-axis feedback control signal obtained by auto-focusing and the previously obtained Z-axis coordinate data are switched. As a result, when a sufficiently large focus level L is obtained, the control in the Z-axis direction is performed with high accuracy, and even when the focus level L is low, the line analysis can be performed without breaking the automatic height correction. And mapping analysis can be performed continuously.

In the second operation example, two thresholds Lc1,
By using Lc2, switching chattering is prevented. Steps S11 to S14 of the second operation example are the same as steps S1 to S4 of the first operation example, and thus the operation of step S15 will be described below.

The focus forming means 21 of the optical focus position detecting device 2 forms a focus signal, and the comparing means 3 of the control switching means 3
1 compares the in-focus signal level L with the second threshold Lc2 from the threshold storage means 32. The second threshold Lc2 is set to a value smaller than the first threshold Lc1 (step S15).

When the focus signal level L is equal to the second threshold value Lc2
If the value is larger than the threshold value, it is determined that a sufficiently high control speed can be obtained in the Z-axis control by the function of the auto focus, and the Z-axis feedback control signal forming means 22 of the optical focus position detecting device 2 is given a Z-axis feedback control signal. A control signal is formed. The Z-axis stage drive control means 13 takes in the Z-axis feedback control signal (step S1).
6) The Z-axis is driven based on the Z-axis feedback control signal (Step S17).

On the other hand, if the in-focus signal level L is lower than the second threshold value Lc2, it is determined that a sufficient control speed cannot be obtained in the Z-axis control by the function of the auto focus, and the Z-axis feedback is performed. Control signal forming means 2
2 is stopped, and a read signal is output to the approximate Z-axis coordinate data storage means 4. The approximate Z-axis coordinate data storage unit 4 stores the X-axis coordinate and Y-axis data from the X, Y-axis stage drive control unit 14 from the time when the read signal is input.
The axis coordinates are taken in, the Z-axis coordinate data corresponding to the X and Y coordinates is read, and output to the Z-axis stage drive control means 13. The Z-axis stage drive control means 13 takes in the Z-axis coordinate data as an approximate Z-axis control signal (step S1).
9) The Z-axis is driven based on the Z-axis feedback control signal (Step S20).

If the mapping analysis has not been completed (step S21), after the in-focus signal level L falls below the second threshold value Lc2, the comparing means 31 compares the in-focus signal level L with the first Compare with the threshold value Lc1. When the in-focus signal level L exceeds the first threshold value Lc1, it is determined that a sufficiently fast control speed can be obtained in the Z-axis control by the function of autofocus, and the process proceeds to step S16 (step S22). Switch to Z-axis control by Z-axis feedback control signal. If the focus signal level L does not exceed the first threshold value Lc1 in step S22, control using the approximate Z-axis control signal is continued.

The signal diagram of FIG. 8 shows the relationship between the magnitude of the focus level L and control switching. As shown in FIG. 8, the Z-axis feedback control signal obtained by autofocus and the Z-axis coordinate data are switched at the first threshold Lc1 and the second threshold Lc2. By using the first threshold value Lc1 and the second threshold value Lc2, even when the focus level L fluctuates, switching is not performed when the focus level L is within a predetermined fluctuation range. Chattering of switching can be prevented, and stable switching control can be performed.

[0039]

As described above, according to the present invention,
With the electron probe microanalyzer, even when the sample surface shape changes, line analysis and mapping analysis can be performed continuously without breaking automatic height correction, and highly reliable measurement data can be obtained. Obtainable.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a configuration example of an electronic probe microanalyzer according to the present invention.

FIG. 2 is a flowchart illustrating a procedure for obtaining approximate Z-axis coordinate data.

FIG. 3 is a flowchart illustrating a procedure for setting a threshold.

FIG. 4 is a relationship diagram between a focus signal level and an autofocus speed.

FIG. 5 is a flowchart illustrating a first operation example of the electronic probe microanalyzer of the present invention.

FIG. 6 is a signal diagram illustrating a first operation example of the electronic probe microanalyzer of the present invention.

FIG. 7 is a flowchart for explaining a second operation example of the electronic probe microanalyzer of the present invention.

FIG. 8 is a signal diagram for explaining a second operation example of the electronic probe microanalyzer of the present invention.

FIG. 9 is a flowchart for explaining a measurement procedure for performing positioning in the Z-axis direction by autofocus control.

FIG. 10 is a diagram for explaining Z-axis control of a conventional electron probe microanalyzer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron probe microanalyzer, 2 ... Optical focus position detection device, 3 ... Control switching means, 4 ... Approximate Z-axis coordinate data storage means, 5 ... Data storage means, 10 ... Electron probe microanalyzer body, 11 ... Electron beam Source, 12
... Sample stage, 13 ... Z axis stage drive control means, 1
4 X and Y axis stage drive control means, 15 optical microscope, 16 X signal detection means, 31 comparison means, 32 threshold value storage means.

Claims (1)

[Claims] An electron probe microanalyzer for performing elemental analysis of a sample surface by characteristic X-rays emitted from a sample by irradiation of an electron beam, an optical focus position detecting device, and a Z-axis for driving a sample stage in a Z-axis direction. The approximate value of the Z-axis coordinate and the Z-axis coordinate value obtained by the optical focus position detection device are switched according to the focus signal level from the axis drive device and the optical focus position detection device. An electronic probe microanalyzer comprising: a control switching unit that sets axis control data.