JPH0836986A - Charged particle beam device - Google Patents

Abstract

PURPOSE:To provide a charged particle beam device that safely performs automatic focusing of an optical microscope in a short time. CONSTITUTION:Excitation strength of an objective lens 3 obtained by automatic focusing of an electron beam becomes a value matching the distance (it is called working distance) between the objective lens 3 and a sample. The excitation strength signal is supplied to the computer 14, the computer 14 finds the working distance from the supplied signal, and the results are stored in a memory 22. The computer 14 which already found the working distance can efficiently perform automatic focusing of an optical microscope based on this value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle beam apparatus such as an electron beam microanalyzer for irradiating a sample with an electron beam and detecting X-rays generated from the sample for elemental analysis. .

[0002]

2. Description of the Related Art In an electron beam microanalyzer, an electron beam from an electron gun is focused on a sample and irradiated, and the characteristic X-ray generated from the sample is analyzed by a wavelength dispersive X-ray analyzer or the like. The wavelength is analyzed, and qualitative analysis and quantitative analysis such as identification of elements in the sample are performed. In such an electron beam microanalyzer, an electron beam is two-dimensionally scanned in a specific region of a sample, secondary electrons generated by this scanning are detected, and a detection signal is a cathode ray line synchronized with the scanning of the electron beam. It can also be supplied to a tube to display a scanning secondary electron image of the sample.

Further, in the electron beam microanalyzer,
When performing analysis, it is necessary to accurately place the analysis position of the sample, the dispersive crystal, and the X-ray detector on the Rowland circle. Therefore, the height of the sample to be analyzed is adjusted by an optical microscope that is coaxial with the electron beam. That is, the position of the optical microscope and the X of the dispersive crystal or X-ray detector.
The positional relationship of the line spectroscopic system is mechanically adjusted accurately,
When focusing is performed with an optical microscope, the height position of the sample becomes an optimum position for the X-ray spectroscopic system.

In the Auger electron analyzer and the secondary ion analyzer, an optical microscope is used to identify the positional relationship between the electron or ion generation source and the analyzer.
In an apparatus using such an optical microscope, the operator manually operates the vertical movement of the analysis sample while observing the image of the optical microscope. However, recently, with the advancement of the technology of the automatic focusing function of the optical microscope,
A device for automatically focusing the sample by moving it up and down has also been developed.

[0005]

In the above-mentioned apparatus having the automatic focusing function of the optical microscope, it is difficult to determine where the height of the first analytical sample is when focusing, so that the analytical sample is The focus position is searched by moving the sample stage up and down within a range (several mm). In such a method, since there is a possibility that the entire range of the vertical movement of the sample stage may be searched, unnecessary time is required. In addition, when the inserted analytical sample happens to jump out above the sample holder, when the sample stage is driven upward, the sample collides with the objective lens and parts around it,
An accident occurs where the collision part is damaged.

The present invention has been made in view of the above circumstances, and an object thereof is to realize a charged particle beam apparatus capable of safely and automatically focusing an optical microscope in a short time. .

[0007]

The charged particle beam according to the present invention continuously changes the focus of the charged particle beam with which the sample is irradiated, and the charged particle beam is based on the signal obtained from the sample. It is equipped with a charged particle beam focusing means for performing the focusing of the sample and an optical focusing means for performing the focusing of the optical microscope by moving the sample in the height direction. It is characterized in that it has means for controlling the range of movement of the sample in the height direction during focusing of the optical microscope based on the focusing signal.

Further, the charged particle beam device according to the present invention performs the focusing operation of the charged particle beam focusing means by the charged particle beam focusing means based on the signal in the height direction of the sample obtained by the optical focusing means. It is characterized by having means for controlling.

Further, the charged particle beam system according to the present invention is characterized in that it has means for automatically focusing the other on the basis of the focusing signal obtained by the one focusing means.

[0010]

The charged particle beam according to the present invention controls the range of movement of the sample in the height direction during focusing of the optical microscope based on the focusing signal obtained by the charged particle beam focusing means, and The focusing operation of the charged particle beam by the charged particle beam focusing means is controlled based on the signal in the height direction of the sample obtained by the optical focusing means, and the charged particle beam focusing means and the optical focus are controlled. The other focus is automatically adjusted based on the focus signal obtained by one of the focus adjustment means.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an example of an electron beam microanalyzer for carrying out the method of the present invention. 1 in the figure
Is an electron gun, and the electron beam generated and accelerated by the electron gun 1 is finely focused by the focusing lens 2 and the objective lens 3, and is irradiated onto the sample 4. The electron beam with which the sample 4 is irradiated is appropriately deflected by the deflection coil 5, and the desired region of the sample 4 is scanned with the electron beam.

Reference numeral 6 denotes an electron beam automatic focusing unit. From this unit 6, an exciting current which changes stepwise during automatic focusing is supplied to the objective lens 3.
Further, the unit 6 supplies the deflection coil 5 with a scanning signal which is synchronized with the stepwise excitation current supplied to the objective lens 3. Further, the unit 6 is supplied with a signal from a detector 7 which detects secondary electrons generated by the irradiation of the sample 4 with the electron beam. Although not shown, an X-ray spectroscope for analyzing X-rays generated by irradiating the sample with an electron beam is arranged above the sample 4.

The sample 4 is placed on a horizontal moving mechanism 8 which can move in the two-dimensional directions of x and y. The horizontal movement mechanism 8 is mounted on the vertical movement mechanism 9 that can move in the z direction. The horizontal moving mechanism 8 is driven by the pulse motor 10, and the vertical moving mechanism 9 is driven by the pulse motor 11. Reference numeral 12 is a drive control circuit for the pulse motor 10, and 13 is a drive control circuit for the pulse motor 11. The two types of drive control circuits 12 and 13 are controlled by the computer 14.

Reference numeral 15 is an objective lens of an optical microscope. The optical objective lens 15 is generated from a light source 16, and the lens 1
The light that has passed through 7, the semitransparent mirror 18, and the reflecting mirror 19 is focused on the sample 4. The light reflected from the sample 4 is the optical objective lens 15
Is imaged by and is projected on the imaging surface of the image pickup device 21 via the reflecting mirror 19, the semitransparent mirror 18, and the relay lens 20. Since the optical objective lens 15 and the reflecting mirror 19 are arranged on the optical path of the electron beam, an opening for passing the electron beam is formed in the optical axis of the electron beam. The signal obtained by the image pickup device 21 is supplied to the computer 14. Reference numeral 22 is a memory connected to the computer 14, and 23 is a cathode ray tube. The operation of such a configuration will be described below.

First, in the usual X-ray analysis as an electron beam microanalyzer, the electron beam from the electron gun 1 is focused finely on the sample 4 and, as a result, the characteristic X generated from the sample is obtained.
The X-ray spectrum is obtained by dispersing the rays with an X-ray spectrometer (not shown). Before this electron beam irradiation,
The sample 4 is irradiated with light from the light source 16, an optical image of the sample is obtained by the imaging device 21, and the optical image is displayed on the cathode ray tube 23. The optical image is observed, the pulse motor 11 is driven through the drive control circuit 13 so that the image is in focus, and the vertical movement mechanism 9 adjusts the height position of the sample. The positional relationship between the position of the optical microscope and the X-ray spectroscopic system is mechanically preliminarily adjusted, and when focusing is performed by the optical microscope, the height position of the sample becomes the optimum position for the X-ray spectroscopic system.

The above-mentioned focusing of the optical microscope can be automatically performed. That is, the signal of the optical image of the sample obtained by the image pickup device 21 is stored in the computer 1
Sent to 4. The computer 14 differentiates the image signal, and the computer 14 further controls the vertical drive circuit 13 to move the vertical movement mechanism 9 within a certain range, and compares the differential values of the image signal at the vertical position of each sample. When this differential value is the largest, it is the vertical position of the focused sample. Therefore, the computer 14 controls the drive control circuit 13 to drive the pulse motor 11 to position the sample 4 at the vertical position where the focus is achieved.

Next, the focusing operation of the electron beam will be described. From the automatic focusing unit 6 to the objective lens 3
Is supplied with an exciting current that changes stepwise, and as a result, the focus changes stepwise. Each time the objective lens 3 changes stepwise, the deflection coil 5 is supplied with a scanning signal for scanning a predetermined region on the sample. Secondary electrons generated from the sample due to the scanning of the electron beam are detected by the secondary electron detector 7. The detection signal of the detector 7 is supplied to the automatic focusing unit 6, and the signals of the scanning period of the predetermined area are integrated. The unit 6 compares the signal intensities accumulated for each excitation state of the objective lens 3 and sets the objective lens 3 to the excitation intensity when the maximum signal intensity is obtained. In this way, the automatic focusing operation of the electron beam is executed.

The excitation intensity of the objective lens 3 obtained by the above-mentioned automatic focusing of the electron beam has a value corresponding to the distance between the objective lens 3 and the sample (referred to as working distance). This excitation intensity signal is supplied to the computer 14, and the computer 14 obtains the working distance from the supplied signal and stores the result in the memory 23. Next, since the computer 14 is required to have the working distance, the automatic focusing of the optical microscope can be efficiently performed based on this value.

That is, the computer 14 changes the position of the sample 4 in the height direction by controlling the drive control mechanism 13 during the automatic focusing of the optical microscope. The specified range. As a result, the focusing operation of the optical microscope can be executed in a remarkably short time, and the height of the sample is inadvertently changed to prevent the sample and the like from colliding with the peripheral components.

It should be noted that the variation width in the height direction of the sample at the time of focusing of the optical microscope is sufficiently narrow as long as it covers the depth of focus of the scanning image by the electron beam (for example, ± 20 μm at an observation magnification of 1000 times). Becomes However, this search range can be set arbitrarily.

In the above-mentioned embodiment, the focusing of the optical microscope is executed based on the information of the automatic focusing of the electron beam. In addition to this method, other control can be performed using the system of FIG. For example, if the probe current of the charged particle beam of a charged particle beam device such as a scanning electron microscope, the opening angle of the probe (incident angle to the sample), and the observation magnification are determined, the focal depth of the scanned image of the charged particle beam is determined. It Therefore, it is also possible to calculate a search range that covers this depth of focus (for example, twice the depth of focus) from the set values of the observation conditions of the charged particle beam image, and set the search range in the automatic focusing device of the optical microscope. it can.

Further, after the manual focusing operation or the automatic focusing operation of the charged particle beam image and the automatic focusing of the optical microscope by the button operation or the automatic continuous operation, the charged particles due to the movement of the sample stage In order to correct the deviation of the focus state of the beam image, it is possible to continuously and automatically correct the charged particle beam image again by the automatic focusing operation. Further, the working distance recognized by the optical microscope is converted back to the objective lens setting value (focal length or excitation code, etc.) and set in the objective lens of the charged particle beam device, or the charged particle beam is centered around this setting value. It is also possible to set the search range of the automatic focusing function of the device. If the search range is narrow, when the objective lens of the charged particle beam apparatus is an electromagnetic type, the influence of hysteresis and the influence of inductance of the magnetic circuit can be reduced, and the focusing accuracy is improved.

Furthermore, when focusing the charged particle beam image or the optical microscope, if either one of the focusing is performed, the current working distance is automatically recognized and this information is provided to the other focusing mechanism. Tell
Finally, it is possible to automatically set both focus points.

Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment. For example, although the electron beam microanalyzer has been described as an example in the embodiment of FIG. 1, the present invention can be applied to other charged particle beam devices including an optical microscope such as an ion beam device.

[0025]

As described above, the charged particle beam according to the present invention is based on the focusing signal obtained by the charged particle beam focusing means to determine the height direction of the sample at the time of focusing by the optical microscope. The moving range is controlled, and the focusing operation of the charged particle beam by the charged particle beam focusing means is controlled based on the signal in the height direction of the sample obtained by the optical focusing means. The other focus is automatically adjusted based on the focusing signal obtained by one of the beam focusing means and the optical focusing means.

As a result, since the working distance value converted from the excitation current of the objective lens can be set at the start of the search of the automatic focusing function of the optical microscope, it is not necessary to move the sample up and down in a wide range, and the sample is narrow. A search for automatic focusing can be performed by vertically moving the sample in the range, and the search time (focusing time) can be shortened. Further, since the working distance is referenced, the range of vertical movement of the sample can be recognized in advance. Therefore, the search range can be optimized and the search can be stopped. It is possible to prevent an accident that collides with the vehicle.

Further, in the present invention, the working distance can be recognized from the focused state of the optical microscope, an appropriate value can be set in the objective lens of the charged particle beam apparatus, and the search of the automatic focusing apparatus for the charged particle beam can be started. Since the position and the search range can be determined, the charged particle beam image and the optical microscope image can be automatically and efficiently focused.

[Brief description of drawings]

FIG. 1 shows an example of a system for implementing the method according to the invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electron gun 2 Focusing lens 3 Objective lens 4 Sample 5 Deflection coil 6 Automatic focusing unit 7 Secondary electron detector 8 Horizontal movement mechanism 9 Vertical movement mechanism 10, 11 Pulse motor 12, 13 Drive control circuit 14 Computer 15 Optical objective lens 16 light source 17 condensing lens 18 semi-transparent mirror 19 reflecting mirror 20 relay lens 21 imaging device 22 memory 23 cathode ray tube

Claims (3)

[Claims] 1. A charged particle beam focusing means for continuously changing the focus of a charged particle beam with which a sample is irradiated, and focusing the charged particle beam based on a signal obtained from the sample accordingly. It is equipped with an optical focusing means for moving the sample in the height direction and focusing the optical microscope, and when focusing the optical microscope based on the focusing signal obtained by the charged particle beam focusing means. Charged particle beam device having means for controlling the moving range of the sample in the height direction. 2. A charged particle beam focusing means for continuously changing the focal point of the charged particle beam with which the sample is irradiated, and focusing the charged particle beam based on the signal obtained from the sample accordingly. A charged particle beam is provided based on a signal in the height direction of the sample obtained by the optical focusing means, which is provided with an optical focusing means for moving the sample in the height direction and focusing the optical microscope. A charged particle beam device having means for controlling the focusing operation of the charged particle beam by the focusing means. 3. A charged particle beam focusing means for continuously changing the focal point of the charged particle beam with which the sample is irradiated, and focusing the charged particle beam based on the signal obtained from the sample accordingly. It is equipped with an optical focusing means that moves the sample in the height direction and focuses the optical microscope.Based on the focus signal obtained by one focusing means, the other focus is automatically adjusted. A charged particle beam device having a matching means.