JPH0992193A - Electronic probe microanalyzer provided with auto focus device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly obtain focusing at that point even if an analysis point is changed by a particular range order by means of an electron beam. SOLUTION: A focusing area γ in a specified range is so restricted as to select an area whose center is an irradiation position α in an optical microscope field of view β as a criteria for focusing, based on an electronic microscope irradiation position αdetermined from the current quantity to a shift coil for controlling the irradiation position of an electron beam. The average contrast in the focusing area γ is obtained by means of the sensor of the optical microscope and is regulated by moving up and down a stage on which a regent is placed to a height according to the average contrast at which the height position at the analysis point of the regent is obtained. In addition, when the analysis point is changed by an order of several μm to some ten μm, a focusing area ε in a specified range is newly restricted, based on a new electron beam irradiation position δ determined from the current quantity to the shift coil. Similarly, the height position of the regent analysis point is regulated according to the average contrast in this new focusing area ε. Thus, focusing at the analysis point can be obtained certainly even if the height of the regent surface in the optical microscope field of view β is different.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron probe microanalyzer (hereinafter referred to as EP) for analyzing a sample using an electron beam.
(Also referred to as MA), and particularly to an electron probe microanalyzer equipped with an autofocus device for sample alignment using an optical microscope.

[0002]

2. Description of the Related Art An EPMA equipped with a wavelength dispersive spectrometer (hereinafter also referred to as WDS) is an energy dispersive detector (E
In comparison with the one using DS), higher precision is required for the focusing condition for X-ray detection, that is, the positional accuracy in which the sample (analysis point) -spectroscopic crystal-detector is located on the circumference of the Rowland circle. . The analysis system of the dispersive crystal and the detector is moved by an integrated mechanical system moving device, but the sample stage for mounting the sample analysis position is different from the detection system for determining the sample analysis position. It is designed to perform horizontal movement, vertical movement, tilting and rotation independently. This movement of the sample stage independently of the detection system is
In addition to line analysis, it is a function required as an SEM for morphological observation of the sample surface and elemental analysis using reflected electrons.

In order to locate the analysis point of the sample on the circumference of the Rowland circle, conventionally, the focus position of the optical system for X-ray focusing and the focus position of the optical microscope are made to coincide with each other, and the optical microscope is used at the time of measurement. A method of aligning the analysis point on the Roland circle of the spectroscope is adopted.

In order to align the sample using such an optical microscope, an automatic focusing mechanism has recently been incorporated to measure the direction and amount of deviation of the sample surface from the in-focus position, and based on that information. A material that automatically adjusts the height of the material has been developed.

As the sample alignment using an optical microscope, (1) a method of detecting the contrast projected on the sample by using a pattern in which a transmissive part and a non-transmissive part are combined with an illuminated part, (2) There are a method of utilizing the contrast of the sample itself, (3) a method of irradiating a laser spot at one point on the sample obliquely and detecting the position of the reflection spot.

[0006]

However, all of these conventional sample positioning methods using an optical microscope are focusing methods based on a fixed area or point with respect to a certain visual field. Therefore, when the irradiation position of the electron beam is changed by EPMA to change the analysis point on the order of several μm to several tens of μm, it is difficult to obtain the focus at that point.

The present invention has been made in view of such a problem, and its object is to achieve the same even when the analysis point is changed by an electron beam on the order of several μm to several tens of μm. An object of the present invention is to provide an electronic probe microanalyzer equipped with an automatic focusing device capable of surely obtaining focusing.

[0008]

In order to solve the above-mentioned problems, the invention of claim 1 provides an electron beam emitting means for emitting an electron beam and an irradiation position of the electron beam which is an analysis point on the sample surface. An electron beam irradiation position control means such as a shift coil for controlling, a spectroscope for elemental analysis of the sample based on characteristic X-rays emitted from the sample when the sample surface is irradiated with the electron beam, and a spectroscope for the sample. An optical microscope for detecting a position, a sample moving means for moving the sample, and an analysis point of the sample by controlling the sample moving means based on the position of the sample detected by the optical microscope. An electron probe microanalyzer having at least an automatic focusing device for automatically positioning on a Rowland circle of a spectroscope, further comprising the electron beam irradiation position control means and the sample moving hand. And includes a measurement control unit for controlling the automatic focusing device, respectively, the measurement control unit, and the electron beam irradiation position detecting means for determining an irradiation position of the electron beam from the amount of current flowing in the electron beam irradiation position control means,
On the basis of the obtained electron beam irradiation position, a focusing reference position limiting means for limiting a predetermined focusing reference position within the field of view of the optical microscope, which serves as a reference for focusing by the optical microscope, is provided. I am trying.

Further, the invention of claim 2 is characterized in that the focusing reference position is a region limited to a predetermined range with the electron beam irradiation position as a center in the visual field of the optical microscope.

Further, in the invention of claim 3, the focusing reference position is within a predetermined range of a predetermined pattern projected from the optical microscope to a region including the electron beam irradiation position in the visual field of the optical microscope. It is a limited area.

[0011]

In the electron probe microanalyzer provided with the automatic focusing device of the present invention having such a structure, the height of the surface of the sample in the visual field of the optical microscope is different depending on the stepped surface, the uneven surface or the curved surface. Also, the measurement control device limits the in-focus position within a predetermined range based on the electron beam irradiation position within the field of view of the optical microscope. Then, the height position of the analysis point is adjusted on the basis of the contrast in the focused area detected by the optical microscope, and the adjustment of the height position of the analysis point is affected by the change in the height of the surface of the sample. There is no such thing. This ensures that the focus at the analysis point is obtained. Therefore, even for samples with a rough surface, samples with steps, or samples with a sloped surface, the height position of the analysis point can be adjusted easily and more accurately on the Roland circle, and good analysis can be performed more efficiently. It will be easier and more reliable.

Further, when the analysis point is changed in the order of several μm to several tens of μm, the focusing position within a predetermined range is limited with the new electron beam irradiation position as a reference. Thereby, focusing at a new analysis point can be easily and surely obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing an embodiment of an electronic probe microanalyzer provided with an autofocus device according to the present invention.

As shown in FIG. 1, the EPMA 1 includes a filament 3 which is an electron beam emitting means for emitting an electron beam 2,
The sample stage 5 on which the sample 4 is placed and the electron beam 2
The shift coil 6 that controls the irradiation direction of the electron beam 2 so as to scan the analysis region on the surface of the WDS 7 and the WDS 7 that receives the X-rays emitted when the sample 4 is irradiated with the electron beam 2.
And a dispersive crystal 9 in the WDS 7 composed of a crystal lattice that collects the X-rays emitted from the sample 4 and disperses it into the characteristic X-rays 8 of the specific wavelength, and the characteristic X of the specific wavelength dispersed by the dispersive crystal 9.
The detector 10 in the WDS 7 for detecting the line 8, a WDS measuring system 11 consisting of an amplifier, a timer, and a counter, which is a coefficient of the characteristic X-ray 8 detected by the detector 10, and an incident light 14a from the optical microscope illumination 13 are provided. The optical microscope 15 that emits light and receives the reflected light 14b from the sample 4, and the incident light 14a from the optical microscope illumination 13 is reflected so as to irradiate the sample 4 and the reflected light 14b from the sample 4 is reflected by the optical microscope 15. OM reflecting mirror 16 for reflecting light in a certain direction, sensor 17 for guiding reflected light 14b received by optical microscope 15 and outputting a control signal based on this reflected light 14b, stage 5 driving control, and sample movement of the present invention. Means for driving the stage, and an automatic focusing device 19 for controlling the stage driving mechanism 18 by a control signal from the sensor 17.
, A controller 20 for controlling the stage drive mechanism 18 by manual operation, a WDS control system 11, an automatic focusing device 19
And controlling the stage drive mechanism 18 and controlling the amount of current flowing through the shift coil 6 to determine the electron beam irradiation position within the field of view of the optical microscope 15 and the position of the sense region within the field of view through the autofocus device 19. Control device 2
1 and.

Further, the measurement control device 21 includes a shift coil 6
Based on the electron beam irradiation position detecting means 22 for determining the irradiation position of the electron beam 2 from the amount of current flowing through the device, and the predetermined position within the field of view of the optical microscope 15 serving as a reference for focusing by the optical microscope 15. And a focusing reference position limiting unit 23 for limiting the focusing reference position.

The optical axis of the electron beam 2 is adjusted so as to coincide with the optical axis of the optical microscope 15, and the WDS
The focus of 7 is also adjusted so as to match the focus of the optical microscope 15. The electron beam 2 is focused by an electron lens (not shown) and adjusted so as to be focused on the surface of the sample 4.

Next, the operation for obtaining the focus at the analysis point in this EPMA 1 will be described. FIGS. 2A and 2B are views for explaining the focusing operation by the method of extracting the image edge of an arbitrary restricted area in the visual field of the optical microscope 15 by image processing.

As shown in FIG. 2 (a), in this system, the measurement controller 21 first controls the amount of current flowing through the shift coil 6, and the electron beam 2 which is an analysis point in the field of view β of the optical microscope 15. Irradiation position α is determined. Next, the measurement control device 21 uses the electron beam 2 determined from the amount of current to the shift coil 6.
Based on the irradiation position α, the focusing area γ within a predetermined range is limited so that the area around the irradiation position α in the visual field β of the optical microscope 15 is selected as the focusing reference. Further, the measurement control device 21 determines the position of the sense area of the sensor 17 according to the limited focus area γ through the autofocus device 19.

When the reflected light 14b illuminating the sample 4 is received by the optical microscope 15 and guided to the sensor 17, the sensor 17 reflects the reflected light 14b to the determined sense region.
The average contrast in the in-focus area γ is calculated based on b, and a control signal having a magnitude corresponding to the calculated average contrast is output to the automatic focusing device 19. Autofocus device 1
9 drives the stage drive mechanism 18 by this control signal to move the stage 5 up and down to adjust the height based on the control signal. Then, the autofocus device 19 stops driving the stage drive mechanism 18 when the average contrast in the focus area γ becomes the highest, and the stage 5 is fixed at the height position. In this way, the height of the sample 4 is adjusted so that the analysis point of the sample 4 is located on the Rowland circle.

As described above, in this embodiment, even if the height of the surface of the sample 4 in the field of view β of the optical microscope 15 varies depending on the stepped surface, the uneven surface, the curved surface, or the like, the optical microscope 15
Since the height position of the analysis point is adjusted with reference to the average contrast in the focused area γ within a limited range centered on the irradiation position α in the visual field β of the sample 4, the height of the surface of the sample 4 changes. Will no longer be affected by. Therefore, it becomes possible to accurately obtain the focus at the irradiation position α of the electron beam 2 which is the analysis point.

Next, in order to change the analysis point on the order of several μm to several tens of μm, the amount of current flowing through the shift coil 6 is changed by the measurement control device 21, and as shown in FIG. The irradiation position of 2 is changed to the irradiation position δ. The height position of the surface of the sample 4 at this irradiation position δ is different from the above-mentioned irradiation position α. However, the measurement control device 21
Is based on the irradiation position δ of the electron beam 2 determined from the amount of current to the shift coil 6 in the same manner as described above, a focusing area ε within a predetermined range centered on the irradiation position δ within the visual field β of the optical microscope 15. Restrict new. Then, the automatic focusing device 19 drives the stage drive mechanism 18 on the basis of the average contrast in the new in-focus area ε as described above. The stage drive mechanism 18 moves the stage 5 up and down to adjust the height position of the sample. Thus, even if the analysis point is changed on the order of several μm to several tens of μm in the visual field β of the optical microscope 15, it becomes possible to accurately obtain the focus at the irradiation position of the electron beam 2 which is the analysis point. .

FIG. 3 is a diagram for explaining another focusing operation by the method of projecting a pattern on an arbitrary area within the field of view of the optical microscope 15. In this method, a predetermined pattern is set on the optical microscope 15 so that its position can be adjusted, and this pattern η is projected onto the surface of the sample 4 within the optical microscope field β by the optical microscope illumination 13 as shown in FIG. At this time, when the pattern η is not projected at the irradiation position α of the electron beam 2 which is the analysis point, the operation microscope (not shown) provided in the optical microscope 15 or an adjusting mechanism from the automatic focusing device 19 causes the optical microscope 15 to move. The position of the set pattern is mechanically adjusted so as to come to the irradiation position α.
Similarly, the position of the sensor 17 and the effective area of the sensor 17 are mechanically adjusted manually according to the irradiation position α.

Further, in the pattern η, a portion which does not match the in-focus position cannot be seen due to the difference in height of the sample surface. Therefore, in FIG. 3, the contrast due to the reflected light 14b reflected from the sample surface in the sense region θ within a predetermined range including the irradiation position α is obtained in the same manner as described above,
Based on the obtained contrast, the automatic focusing device 19 drives the stage drive mechanism 18, and the stage drive mechanism 18 moves the stage 5 up and down to adjust the height position at the irradiation position α of the sample surface. In this way, focusing at the analysis point on the sample surface is obtained.

When the analysis point is changed on the order of several μm to several tens of μm, the pattern is projected on a new irradiation position in the same manner as described above. Then, similarly to the above, the height position of the sample surface at the new irradiation position is adjusted based on the contrast in the sense region θ in the predetermined range including the new irradiation position. Thus, also with this method, when the analysis point is changed in the field of view β of the optical microscope 15 on the order of several μm to several tens of μm, it is possible to accurately obtain the focus at the irradiation position of the electron beam 2 which is the analysis point. Will be able to.

The focusing method by the autofocus device 19 is not limited to the above-mentioned embodiments, and a method using reflection of a laser spot obliquely incident can be used. In this case, the irradiation position of the spot, the position of the sensor 17 and the like may be controlled according to the analysis point irradiated with the electron beam 2.

[0026]

As is apparent from the above description, according to the electron probe microanalyzer equipped with the automatic focusing device of the present invention, the height of the surface of the sample in the field of view of the optical microscope is a step surface, an uneven surface or Even if it varies depending on the curved surface, etc., while limiting the focusing area within a predetermined range centered on the electron beam irradiation position within the field of view of the optical microscope, the height position of the analysis point is set based on the contrast in this focusing area. Since it is adjusted, it is not affected by changes in the height of the surface of the sample. This makes it possible to reliably obtain the focus at the analysis point. Therefore, even for a sample with a rough surface, a sample with steps, or a sample with an inclined surface, the height position of the analysis point can be easily adjusted so as to be on the Rowland circle, and a good analysis can be further performed. It can be done easily and reliably.

Further, even when the analysis point is changed in the order of several μm to several tens of μm, the focus area within a predetermined range centering on the new electron beam irradiation position is limited so that the focus at the new analysis point is changed. It becomes possible to obtain the focus easily and surely.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an embodiment of an electronic probe microanalyzer provided with an autofocus device according to the present invention.

2A and 2B are diagrams for explaining focusing by an image processing method in the embodiment shown in FIG. 1, FIG. 2A is a diagram for explaining focusing at a certain analysis point in a visual field of an optical microscope, and FIG. It is a figure explaining a focus when changing on the order of micrometers-several tens of micrometers.

FIG. 3 is a diagram for explaining focusing by pattern projection in the embodiment shown in FIG.

[Explanation of symbols] 1 ... Electron probe microanalyzer (EPMA), 2
... Electron beam, 3 ... Filament, 4 ... Sample, 5 ... Stage, 6 ... Shift coil, 7 ... Wavelength dispersive spectrometer (WD)
S), 8 ... Characteristic X-ray, 9 ... Spectroscopic crystal, 10 ... Detector, 1
DESCRIPTION OF SYMBOLS 1 ... WDS measurement system, 13 ... Optical microscope illumination, 15 ... Optical microscope, 16 ... OM reflecting mirror, 17 ... Sensor, 18 ... Stage drive mechanism, 19 ... Automatic focusing device, 20 ... Controller, 21 ... Measurement control device

Claims (3)

[Claims] 1. An electron beam emitting means for emitting an electron beam, an electron beam irradiation position control means such as a shift coil for controlling an irradiation position of the electron beam which is an analysis point on the sample surface, and an electron beam on the sample surface. A spectroscope for elemental analysis of the sample based on the characteristic X-rays emitted from the sample by irradiation, an optical microscope for detecting the position of the sample, and a sample moving means for moving the sample, At least an automatic focusing device for automatically positioning the analysis point of the sample on the Roland circle of the spectroscope by controlling the sample moving means based on the position of the sample detected by the optical microscope. The electron probe microanalyzer further comprises a measurement control device for controlling the electron beam irradiation position control means, the sample moving means, and the automatic focusing device, respectively. The measurement control device includes an electron beam irradiation position detection unit that obtains an irradiation position of the electron beam from the amount of current passed through the electron beam irradiation position control unit, and a combination of the optical microscope based on the obtained electron beam irradiation position. An electronic probe microanalyzer provided with an autofocus device, comprising: an in-focus reference position limiting means for limiting a predetermined in-focus reference position within a field of view of the optical microscope, which is a focus reference. 2. The autofocus device according to claim 1, wherein the focus reference position is a region within a field of view of the optical microscope, which is limited to a predetermined range around the electron beam irradiation position. Equipped with electronic probe micro-analyzer. 3. The focus reference position is a region limited to a predetermined range in a predetermined pattern projected from the optical microscope to a region including the electron beam irradiation position within a field of view of the optical microscope. An electronic probe microanalyzer provided with the autofocus device according to claim 1.