JP2851394B2 - Scanning electron microscope - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope, and more particularly to a scanning electron microscope having an image processing means for forming a sample image by integrating information signals emitted from a sample. For a microscope.

[Prior Art] Conventionally, a scanning electron microscope having a configuration as shown in FIG. 2 is known. In FIG. 1, reference numeral 1 denotes an electron gun. An electron beam emitted from the electron gun is focused by a focusing lens 2 and then focused on a sample 5 by an objective lens 3 for irradiation. Reference numerals 6x and 6y denote horizontal and vertical deflecting lenses for scanning the electron beam horizontally and vertically on the sample 5. The horizontal and vertical device signals from the scanning signal generating circuit 7 are set on the lenses 6x and 6y for magnification setting. It is supplied via a circuit 8.

Secondary electrons generated by irradiating the sample 5 with an electron beam are detected by the detector 9. After the output signal from the detector is amplified by the amplifier 10, the A / D converter
The analog-to-digital conversion is performed by 11 and supplied to an image memory 15 via a sampling circuit 12, a coefficient register 13, and an integrator 14. Here, an electron beam scanning signal is supplied from the scanning signal generating circuit 7 to the sampling circuit 12, and a sampling signal is generated at a timing synchronized with the scanning signal. Based on this sampling signal, A
The signal supplied from the -D converter 11 is sampled and stored in the image memory 15 sequentially. Meanwhile, the image memory
The image data stored in the readout circuit 15 is read out onto the image display CRT 17 via the readout circuit 16.
The scanning signal generation circuit 18 of the image display CRT is supplied with a scanning signal, and a reading signal is generated at a timing synchronized with the scanning signal. The image data stored in the image memory 15 is stored in the image display CRT 1 based on the readout signal.
7 and displayed as a scanning electron microscope image.

Now, the signals of the second embodiment emitted from the sample, such as electrons and reflected electrons, differ depending on the material and shape of the sample and the intensity of the irradiated electron beam. If the S / N (detection signal-to-noise ratio) is poor, a clear scanning electron microscope image cannot be obtained.
Therefore, when the sample is stationary, the image memory 15
The data for one frame stored in the
Is supplied to the integrator 14 via the coefficient register 19 of the
In step 14, image data for one frame obtained by repeatedly scanning the same area repeatedly is sequentially added to increase the intensity of the video signal to improve the image quality.

[Problems to be Solved by the Invention] In the scanning electron microscope having the above-described configuration, in order to improve the image quality, the number of times of integration may be increased, and the operator is required to obtain an image having a desired image quality. In the process of predicting the number of times n and adding the image data of one frame before to the new image data, how much weight (how much ratio) should be given to the already acquired image data and added. Is determined and instructed to the integration coefficient registers 13 and 19.

However, as described above, if the number of integrations is increased in order to further improve the image quality, a large amount of processing time is required until a final image is obtained.

Therefore, no problem occurs when the sample is completely stopped, but when the observation target moves during the integration processing time, the images appear to be multi-layered. In particular, since such a phenomenon occurs when the operator moves the sample by driving the stage 20 by the drive mechanism 21 to search for a visual field, a clear sample image cannot be obtained when searching for a visual field.

An object of the present invention is to provide a scanning electron microscope capable of always obtaining a clear image irrespective of a stopped or moving state of a sample in consideration of the above-described problems.

Means for Solving the Problems According to the present invention, a detector that detects a signal emitted from a sample based on electron beam scanning on the sample, and stores a detection signal of the detector as image data. image memory and, the image read out image data stored memory and display means for displaying a new image data X _N and the image memory obtained from the detector for the same position on the specimen And the following equation X _N = α × _N + (1−α) × _N-1 is performed on the basis of the image data X _N-1 stored in the image memory X, and the calculation result is stored in the image memory. In the scanning electron microscope, when the sample is moved, the time required for the sample to move a distance corresponding to one pixel on the display means,
The image capturing time of a frame is compared, and the value of α in the arithmetic processing equation is changed based on the comparison result.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is an apparatus configuration diagram for explaining an embodiment of the present invention. 1, the same components as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. The embodiment shown in FIG. 1 is different from the conventional example in that a moving amount detecting means for detecting the moving speed of the sample stage 20 is, for example, a driving mechanism 21.
A voltage detecting means 23 for detecting a driving voltage of a pulse motor (not shown) engaged with the motor, and a signal detected by the voltage detecting means 23 and information on an image magnification supplied from a magnification setting circuit 8. The point is that an integration controller 24 for setting the number of integrations N and an integration coefficient α and a table memory 25 storing a value of α previously obtained are provided.

In the present invention, in order to improve the image quality of the scanning electron microscope image, the integration of the image is performed as much as possible, and the integration is performed when the stage is stopped in order to follow the integration process even when the image changes when the sample is moved. The number of times is increased, and when the stage is moving, the maximum number of times of integration is determined according to the moving speed of the stage, and the first and second integration coefficients for increasing the weight of the new information signal to be integrated are calculated.
And a new information signal is weighted to form a scanning electron microscope image.

By the way, the number of pixels in one frame of the CRT 17 is 5
In the case of an image processing system having 12 × 512 pixels and capable of capturing data of 30 frames per second, the time T required for capturing an image of one frame is about 33 msec. If the width of the display screen is W, the width m of one pixel on the display screen is m
= W / 512. By dividing the width m of one pixel by the image magnification M of the electron microscope, the width m 'of one section when the sample surface scanned by the electron beam is divided into 512 × 512 sections is obtained.

Here, the time required to move the sample 5 by the width m 'of the one section by the stage 20 is represented by s, and
Is less than or equal to the image capture time T of one frame, the data integrated with the original image data is data in a region shifted by one pixel or more, and as described above, the image A phenomenon that appears to overlap also occurs.

Therefore, the data capture time for the frame of the image memory 15 is T, and the distance for one pixel on the display image is the stage.
Assuming that the moving time is s according to 20, the maximum value _{Nmax of the} number of possible integrations can be obtained by the following equation.

1 ≦ N _max ≦ s / T (where N is an integer) Further, the integration coefficient α is obtained from the maximum value N _{max of the} number of integrations. When (the proviso α 1 ≧ α> 0) the integration coefficient alpha is the cumulative number of times N, the result of the N th integration is, a value such as the X _N in the following equation to 0 (disabled information) is set You.

In the above formula, Shows the data contained in the image memory 15, X _N image data obtained newly, Is image data of one frame before read from the image memory 15. Thus, since in the above formula when alpha = 1, only the new data X _N is stored in the image memory 15, at the time the sample is stopped it is possible to obtain a clear image by setting a value that is a alpha ≦ 1. On the other hand, when performing the integration process and the stage is moving, the maximum integration number N _max at the stage moving speed S is determined based on the above equation, and the new data is weighted. By setting the increased integration coefficient α, a clear image can always be obtained regardless of the movement of the sample.

In the present invention, the value of α is obtained for various integration times, and the obtained value of α is stored in the memory 25 as a table using the integration number N as an index. Therefore, based on the detected information of the moving speed S of the sample and the image magnification M, the integration controller 24 calculates the maximum integration number N.
_{When max} is obtained, the integration coefficient α is read from the memory 25 based on the _maximum integration number _Nmax information, and the integration coefficient α value and the (1-α) value are stored in the first and second coefficient registers. Because it is set, a clear image can always be obtained regardless of the movement of the sample.

Note that the above-described embodiment is merely an embodiment of the present invention,
The present invention can be implemented with various modifications. For example,
In the above-described embodiment, the integration coefficient α is stored in the memory in advance, but the value may be obtained by calculation each time. Further, in the above-described embodiment, an example in which the sample stage is automatically driven by the motor drive has been described, but the sample stage movement speed is obtained based on a signal obtained by detecting the amount of sample movement by an encoder or the like. Is also good.

[Effects of the Invention] As is apparent from the above description, according to the present invention, a detector for detecting a signal emitted from a sample based on electron beam scanning on the sample, and detection of the detector A new image obtained from the detector at the same position on the sample, comprising: an image memory for storing signals as image data; and display means for reading and displaying the image data stored in the image memory. Using the data _XN and the image data _XN-1 stored in the image memory, an arithmetic processing _XN = α · _XN + (1−α) · _XN−1 is performed, and the operation result is expressed by the image In the scanning electron microscope stored in the memory, when the sample is moved, the time required for the sample to move a distance corresponding to one pixel on the display means, and
By comparing the image capturing time of the frame, and by changing the value of α of the arithmetic processing equation based on the comparison result, it is possible to always obtain a clear image regardless of the stop or moving state of the sample. A scanning electron microscope is realized.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention, and FIG. 2 is a diagram for explaining a conventional example. 1: electron gun 2: focusing lens 3: objective lens 4: lens power supply 5: sample 6x, 6y: deflection lens 7: scanning signal generation circuit 8: magnification setting circuit, 9: secondary electron detector 10: amplifier, 11: A / D converter 12: Sampling circuit 13, 19: Coefficient register 14: Integrator, 15: Image memory 16: Readout circuit, 17: CRT 18: CRT scanning signal generation circuit 20: Sample stage, 21: Drive Mechanism 23: Voltage detection means, 24: Integration controller 25: Memory

Claims (1)

(57) [Claims] A detector for detecting a signal emitted from the sample based on electron beam scanning on the sample; an image memory for storing a detection signal of the detector as image data; and display means for reading and displaying the stored image data, the image stored for the same position on the specimen to the new image data X _N and the image memory obtained from the detector data X _{N In} the scanning electron microscope in which the calculation result X _N = α · X _N + (1−α) · X _N−1 is performed by using the following equation, and the calculation result is stored in the image memory, Time when the sample moves a distance corresponding to one pixel on the display means,
A scanning electron microscope wherein the image capturing time of a frame is compared, and the value of α in the arithmetic expression is changed based on the comparison result.