JP3303916B2 - Sample surface mapping device using the principle of electron beam microanalyzer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electron beam micro analyzer.
In particular, the present invention relates to a so-called high-speed mapping apparatus that performs two-dimensional analysis of a sample surface by scanning a stage. (Prior art) An electron beam microanalyzer scans a sample surface two-dimensionally with an electron beam, ionizes the atoms of the sample, and measures secondary radiation such as characteristic X-rays generated at that time, thereby distributing component elements. It is usually equipped with an optical microscope for adjustment between the electron optical system and the X-ray optical system, confirmation of the analysis position on the sample surface, etc. A sample stage that can finely move the XYZ directions with an accuracy of about μm is incorporated. In recent years, large samples have tended to be analyzed in the micro area, and a high-speed mapping device that can perform wide area mapping (plane analysis) by automatically scanning the sample stage in the XY direction in response to this tendency. Is being developed. (Problems to be Solved by the Invention) In the past, since mapping was performed in a narrow area, the inclination and flatness of the sample surface did not significantly affect the analysis accuracy. However, when mapping large samples as described above, the effects of undulations and irregularities on the sample surface cannot be ignored, so finish the sample surface in advance and pay attention to the inclination when setting the sample on the mapping device. It must be set, and the preparation of the measurement is troublesome, and there is a problem that the flatness greatly affects the analysis accuracy because the sample surface may not be finished flat. The tilt of the sample surface can be solved by equipping the sample stage with a simple correction mechanism that can adjust the tilt angle when setting the sample. There is no suitable solution except for the finishing work, and therefore, there is a drawback that a sample having an undulating surface cannot be analyzed with high accuracy by a high-speed mapping apparatus. In view of the above, it is an object of the present invention to provide a high-speed mapping apparatus that can perform highly accurate analysis even on a sample having an undulating surface and that does not affect the high-speed stage scanning. It is. (Means for Solving the Problems) In order to achieve the above object, a sample surface mapping apparatus using the principle of an electron beam microanalyzer according to the present invention includes an electron beam irradiation apparatus 1 and a secondary radiation detection apparatus 2
And an electron beam microanalyzer equipped with an XY stage controller 4 for automatically scanning the sample stage 3 in the XY direction and having an optical microscope 5 for monitoring the sample surface, with a predetermined focal position of the optical microscope 5 interposed therebetween. Two image sensors are arranged before and after on the opposite side on the optical axis, and an auto focus device 6 for calculating a degree of focusing based on a video signal obtained by each image sensor is provided. A control circuit 8 for controlling the sample stage elevating device 7 so that the sample surface is always at a predetermined height by the output of the device 6 is provided. (Operation) According to the above configuration, the shift between the image forming position of the electron beam and the sample surface is optically detected and the output of the sample stage is automatically controlled to raise and lower the sample stage. However, it is possible to perform automatic high-speed mapping over the entire measurement range without deteriorating the analysis accuracy, and to effectively use an optical microscope normally attached to an electron beam microanalyzer to automatically focus an image. Can be configured,
The structure is simple and inexpensive. (Embodiment) FIG. 1 shows an embodiment of the present invention. An electron beam irradiation apparatus 1 is constituted by an electron gun, an electron lens, etc., and forms an irradiation spot of an electron beam B on the surface of a sample A. The characteristic X-rays generated from the sample surface by the electron beam B are detected by the characteristic X-ray detector 2.
Scanning of the sample A in the XY direction is performed by controlling the sample stage 3 at a high speed by the XY stage controller 4. The sample surface is monitored by the automatic focusing device 6 via the optical microscope 5, and the control circuit 8 receives the output from the automatic focusing device 6 and controls the sample stage elevating device 7. FIG. 2 shows a specific configuration example of the automatic focusing device 6, in which an image sensor 9 is installed so as to face an eyepiece of the optical microscope 5, and the eyepiece is always driven in an oscillatory manner by an eyepiece driving circuit 10. ing. Video signal analysis circuit
At 11, the output signal of the image sensor 9 is Fourier-transformed,
The point of time where the highest frequency component is the largest is detected as the focal point, and the processing circuit 12 calculates the drive amount of the sample stage 3 from the position of the eyepiece lens at that point and sends the calculation result to the control circuit 8. Alternatively, two image sensors are arranged before and after each other on the opposite side of the optical axis across a predetermined focal position of the optical microscope,
The degree of focus is calculated for a video signal obtained by each image sensor. When the sample surface is at the correct height, the degree of focus of the two video signals is equal, and when the height of the sample surface is slightly higher or lower than that position, the degree of focus of one of the video signals increases, and Since it decreases, it can be detected whether the sample surface is too high or too low. Therefore, the vertical position of the sample stage may be controlled so that the two video signals have the same degree of focus. According to these configurations, it is not necessary to drive the sample stage elevating / lowering device 7 having a large inertia for trial and error detection for detecting the focal point position, so that the response to the vertical fluctuation of the sample surface is extremely good. FIG. 3 shows the operation of the apparatus of the present invention. In the case of an ordinary flat sample, data is collected through a loop of a → b → c → d → a. That is, by scanning the sample stage 3 in the XY direction at a, scanning is performed for one pixel, and if focus is achieved in that state, characteristic X-rays are immediately detected. If the sample surface has undulation and is not focused in b, the sample stage is moved up and down in a loop of e → f → e → f to focus, and then data is collected in c. In the high-speed mapping apparatus, it takes about 1 ms to move one pixel (for example, 1 μm). This is a restriction for detecting characteristic X-rays,
Normally, if an autofocusing device is used, several μS is enough to correct an error of 1 μm, and the correction amount in the height direction is 1 μm or less for 1 μm in the horizontal direction of the sample surface. For example, it is possible to control the elevation of the sample stage without substantially affecting the high-speed performance of the conventional mapping apparatus. (Effects of the Invention) As described above, the present invention arranges two image sensors before and after each other on the optical axis with a predetermined focal position of the optical microscope interposed therebetween, and applies a video signal obtained by each image sensor to each other. Equipped with an automatic focusing device for calculating the degree of focusing based on the output of the automatic focusing device during scanning of the sample surface, and a control circuit for controlling the sample stage elevating device so that the sample surface is always at a predetermined height by the output of the automatic focusing device. Therefore, the sample surface is controlled so as to be at a predetermined height position, and the function of the automatic focusing function is accurate and quick, so that even if there is unevenness or undulation on the sample surface, the analysis accuracy does not decrease. Since the optical microscope that is usually attached to the electron beam microanalyzer can be used as the optical system, there is an advantage that the structure can be provided simply and at a low cost. Since the power performance is relatively slow due to the restriction for characteristic X-ray detection, there is an advantage that the analysis speed is hardly reduced to improve the analysis accuracy according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the apparatus of the present invention, FIG.
The figure is a block diagram showing the specific configuration of the automatic focusing device,
FIG. 3 is a flowchart showing the above operation. 1 ... Electron beam irradiation device, 2 ... Characteristic X-ray detection device,
3 ... Sample stage, 4 ... XY stage controller, 5 ...
... Optical microscope, 6... Automatic focusing device, 7... Sample stage elevating device, 8... Control circuit, A... Sample, B.

Claims (1)

(57) [Claims] A sample using the principle of an electron beam microanalyzer equipped with an electron beam irradiation device, a secondary radiation detector, and an XY stage controller that automatically scans the sample stage in the XY direction, and with an optical microscope that monitors the sample surface. In the plane mapping device, two image sensors are arranged before and after each other on the optical axis with a predetermined focal position of the optical microscope interposed therebetween, and a degree of focus is calculated based on a video signal obtained by each image sensor. An electron beam micro-controller for controlling the sample stage elevating device so that the sample surface is always at a predetermined height by the output of the auto-focus device during scanning of the sample surface. Sample surface mapping device using the principle of analyzer.