JPH04118847A - Automatic focus detecting device for electron beam microanalyser - Google Patents

Abstract

PURPOSE:To make it possible to detect the focusing of electron beams with no special focus detector by calculating the difference between densities of a central pixel and peripheral pixels and detecting the position of Z axis direction in which the difference becomes maximal. CONSTITUTION:A difference calculating means 25 samples pixel data of one frame stored in a buffer memory 24 dividing into matrixes S1-S9, and multiplies a factor (8) to the density of a central pixel and a factor (-1) to the density of peripheral pixels to calculate the total sum to obtain the difference. This procedure is carried out for every region P1-Pn in one frame to calculate the difference, and when the procedure is completed for one frame a sample table is displaced by a micro distance in Z axis direction, and similar calculations are carried out to store the results in a calculated results storing means 26 together with position data of the sample table in Z axis direction. Then for a region of interest, for instance, for instance, for a central portion, adjacent regions and corner regions factors (4), (1) and (1/2) are allocated respectively, and differences for every position in Z axis direction are read out from the memory means 26 to calculate evaluation values and to obtain the position of Z axis in which the evaluation value becomes maximal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an automatic focusing device suitable for an electron beam probe microanalyzer.

(Prior Art) An electron beam probe microanalyzer is a device that observes the properties near the sample surface by irradiating the sample surface with a focused electron beam and detecting the X-rays emitted from the sample surface. An important factor is that the electron beam is focused on the sample surface.

For this reason, the axis for moving the sample parallel to the electron beam irradiation direction, the so-called Z axis, is adjusted so that the electron beam is always focused on the surface of the sample. To detect such a focus, a focus detector is incorporated into the zero body image.
This is done by controlling the sample stage using signals from this.

(Problem to be Solved by the Invention) For this reason, it is necessary to incorporate a focus detector into the main body drawing, which causes a problem that the apparatus becomes complicated.

The present invention was made in view of the above-mentioned problem 1, and its purpose is to be able to detect the degree of convergence of electron ζ-me without the need for a special focus detector. An object of the present invention is to provide a new automatic focus detection device suitable for an electron beam microanalyzer.

(Means for Solving Section M) In order to solve such problems, in the present invention, an electron beam is irradiated while scanning, and the radiation from the sample is synchronized with the scanning, thereby creating a frame memory 1. In the electron beam microanalyzer, a buffer memory stores image data in the frame memory for each relative Z-axis direction position of the sample, and image data I in the buffer memory.
The present invention includes means for sampling each area of M×N pixels and calculating the difference between the density of the center pixel and the density of surrounding pixels, and means for detecting the position II% in the Z-axis direction at which the difference value is maximum.

(Operation of the invention) By calculating the difference value of the density between the center point and its surroundings based on the image data, the difference value becomes large when the focus is in focus. Focus point can be detected.

(Example) The details of the present invention will be described below based on illustrated examples.

FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 is an electron beam generator, in which thermoelectrons from a filament 2 are focused by a focusing lens 3, and an objective aperture lens 4 is used.
The light is made incident on the objective lens 5 through the beam, and the sample on the sample stage 6 is irradiated.

Reference numeral 6 denotes a sample stage, and a fine movement drive mechanism 7 moves the sample within a plane and in the direction of the electron beam irradiation axis. Reference numeral 8 denotes a radiation detector. In this embodiment, in order to detect the X-rays emitted from the sample surface, the X-ray detector is used to receive X-rays via the X-ray spectrometer 9. Signal processing bag M1o whose detection signal will be described later
This is what is output to.

Reference numeral 10 denotes a signal processing device consisting of the aforementioned microcomputer, which generates an image signal based on the signal from the X-ray detector 9 and stores it in the memory 11, as well as sends the image signal to a display 12 such as a cathode ray tube, and roughly displays the image signal. It is configured to output a signal to the Z-axis drive circuit 13 of the fine movement drive mechanism 7 during focus adjustment.

is configured to drive.

FIG. 2 shows the functions that the microcomputer should perform, and creates a density histogram by calculating the density of each pixel of image data in the frame memory 21 constituted by the memory 11 and its frequency. The histogram calculating means 22 performs density conversion from the density histogram.
density conversion means 23 which creates image data with improved density based on the image data and outputs it to the buffer 24; Attention is focused on the difference calculation means 25 that calculates the difference between the density of the pixel at the center point of the area and the density of the surrounding pixels, and outputs the result to the calculation result storage means 26 along with the position on two axes. It is programmed to include evaluation score calculation means 27 for calculating the position on the Z axis where the difference between regions is maximum.

Next, the operation of the apparatus configured as described above will be explained based on the flowchart shown in FIG.

When a sample is placed on the sample stage 6 and the apparatus is operated, the electron beam from the electron beam generator 1 is focused on the focusing lens system 3.4.
．． 51 is guided to irradiate the sample surface while scanning it two-dimensionally, and emit X-rays from each irradiation point. This X-ray is detected by the detector 8 and stored in the frame memory 21 in synchronization with the scanning of the electron beam.

On the other hand, the histogram calculation means 22 is connected to the frame memory 21.
The density of each pixel of the image data stored in is detected and a histogram \j:W of the pixel density is output. The density conversion means 23 calculates a density conversion curve that is integrated in order from the frequency of the lowest density based on the histogram, and outputs the contrast-enhanced image data to the buffer memory 24.

The difference calculation means 26 converts the image data of one frame, for example, 512 pixels x 512 pixels, stored in the buffer memory 24 into a constant, for example, 3 x 3 pixel matrix matrix S, S2, S3, S4. ...-89C (Figure 4)), and as shown in Figure 5, a factor of 8 is applied to the density of the pixel at the center of the sampling matrix within each sampling area, and the density of the surrounding pixels is to "
-1'' and calculate the total value to obtain the difference value. Such operations are calculated for each sampling area P7, P2, P3, P4...P of one frame, and the results are stored in the calculation result storage means 27 together with the position data of the sample stage 6 in the Z direction. do. Needless to say, when the image is in focus, the contrast becomes high, so the difference value increases in proportion to the degree of focus.

2 when the difference calculation for one frame is completed.
A drive signal is output to the axis drive circuit 13 to move the sample stage 6 minutely in the two-axis directions, and the difference value for one frame is calculated in the same manner as described above to determine the position of the sample stage in the two-axis directions. It is stored in the calculation result storage means 27 together with the data.

In this way, when the computation within a predetermined Z-axis moving node is completed, the factor "," which has the maximum value in the region of interest, for example, the center, is divided into multiple, for example, 3×3 regions. 4J, and set a medium factor of ``1'' in the areas adjacent to this above, below, left and right, and a minimum factor of ``1/2'' in the area located roughly diagonally (Figure 6).
, the difference value for each position in the Z-axis direction is read out from the calculation result storage means 26, and the evaluation score is calculated. As a result of this calculation, when the sample stage 6 is moved to the Z-axis position where the evaluation score is maximum, an image that is focused on the target area will be obtained. By inputting a matrix with coefficients whose maximum value is the region vt of interest,
You can easily get an image that focuses on the desired area.

In this example, the explanation was given using an example where the entire frame is the subject of evaluation, but if there is interest in a specific area, the focusing operation can be sped up by performing calculations on that area. can be done.

In addition, in this example, one frame is divided into 3 x 3 areas, and the calculation area for the difference value is set to 3 x 3 pixels, but it may be changed arbitrarily by the magnification etc., or the coefficients for evaluation may be changed as appropriate. It is clear that the same effect can be achieved even if the changes are made.

Furthermore, in this example, X-rays from the sample are detected, but it is clear that the same effect can be achieved even when applied to detecting reflected electrons and secondary electrons from the sample to create an image. It is.

(Effects of the Invention) As described above, in the present invention, in an electron beam microanalyzer in which an electron beam is irradiated while scanning and radiation from a sample is stored in a frame memory in synchronization with the scanning, the relative A buffer memory stores the image data in the frame memory for each position in the Z-axis direction, and the image data in the buffer memory is sampled for each region of MXN pixels, and the difference between the density of the center pixel and the density of surrounding pixels is calculated. A means of calculation and Z for which this difference value is maximum
Since it is equipped with means for detecting bubbles in the axial direction,
Not only does it become unnecessary to incorporate a special focus detection device into the main body of the snowmaking machine, but it is also possible to easily detect the position where a region of interest other than the center is in focus.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a device showing an embodiment of the present invention, FIG. 2 is a block diagram showing the functions performed by the microcomputer in FIG. 1, FIG. 3 is a flowchart showing the operation of the same device, and FIG. Figure 4 is a schematic diagram showing the divided areas of one frame, Figure 5 is a schematic diagram showing the coefficients of each pixel in the sampling area, and Figure 6 is an example of the coefficients for each frame divided area to obtain evaluation points. FIG.

Claims (1)

[Claims] In an electron beam microanalyzer that irradiates with an electron beam while scanning and synchronizes radiation from a sample with the scanning and stores it in a frame memory, image data in the frame memory is stored for each relative Z-axis direction position of the sample. a buffer memory for sampling image data in the buffer memory for each region of M×N pixels, and means for calculating the difference between the density of the center pixel and the density of the surrounding pixels; An automatic focus detection device for an electron beam microanalyzer consisting of means for detecting the position in the axial direction.