JPH0482151A - Scanning electron microscope - Google Patents

Abstract

PURPOSE:To obtain a constantly clear image by setting the maximum counting frequencies with a counting controller in accordance with the moving speed of a sample stage and the magnification of the image on an image display means and controlling a counting coefficient which is set in the first and the second registers. CONSTITUTION:The maximum value of counting frequencies, available for an image memory 15, can be found by a preset equation. When the maximum value of counting frequencies is N, a counting coefficient a is set by a preset equation as a result of the counting frequencies N. As new data XN only are stored in the image memory 15 in case of alpha=1, a value which attains alpha=1 is set in stopping a sample to allow a clear image. When a stage is moving, the frequencies N at the moving speed (s) of the stage is determined and the coefficient alpha is set to put more emphasis on the new data side. so that a constantly clear image can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a scanning electron microscope, and more particularly to a scanning electron microscope equipped with an image processing means for forming a sample image by integrating information signals emitted from a sample. Regarding microscopes.

[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, and an electron beam emitted from the electron gun is focused by a focusing lens 2, and then focused by an objective lens 3 and irradiated onto a sample 5. 6x and 6y are horizontal and vertical deflection lenses for horizontally and vertically scanning the electron beam on the sample 5, and the horizontal and vertical device signals from the scanning signal generation circuit 7 are applied to the lenses 6x and 6y to set the magnification. It is supplied via circuit 8.

Secondary electrons generated by irradiating the sample 5 with the electron beam are detected by the detector 9. The output signal from the detector is amplified by an amplifier ]O, then converted from analog to digital by an A-D converter 11, and then sent to an image memory 15 via a sampling circuit 12, a coefficient register 13, and an integrator 14. Supplied. Here, the sampling circuit 12 is supplied with an electron beam scanning signal from the scanning signal generating circuit 7, and a sampling signal is generated at a timing synchronized with the scanning signal. Based on this sampling signal, the signal supplied from the A-D converter 11 is sampled and sequentially stored in the image memory 15. On the other hand, the image data stored in the image memory 15 is read out onto the image display CRT 17 via the readout circuit 16. A readout signal is generated at a timing synchronized with the scanning signal. The image data stored in the image memory 15 is read out onto the image display CRT 17 based on the readout signal and displayed as a scanning electron microscope image.

Signals such as secondary electrons and backscattered electrons emitted from a sample vary depending on the material and shape of the sample and the intensity of the irradiated electron beam. /N (detection signal-to-noise ratio) is bad, it is impossible to obtain a clear scanning electron microscope image. Therefore, when the sample is stationary, the image memory 15
Read out one frame of data stored in the second
The signal is supplied to the integrator 14 via the coefficient register 19, and the integrator 14 sequentially adds it to one frame of image data obtained by repeatedly scanning the same area to increase the intensity of the video signal. Improves image quality.

[Problems to be Solved by the Invention] In a scanning electron microscope configured as described above, in order to improve the image quality, it is sufficient to increase the number of integrations. In addition to predicting the number of times n, in the process of integrating the new image data with the image data of one frame before, how much weighting (what ratio) is given to the already acquired image data and added? The integration coefficient α that determines the summation coefficient α 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 will be required to obtain the final image.

Therefore, if the sample is completely stopped, the number of images does not occur, but if the object to be observed moves during this cumulative processing time, the image will appear multiple times. Particularly, such a phenomenon occurs when the operator drives the stage 20 by the drive mechanism 21 to move the sample in order to search the field of view, and therefore a clear sample image cannot be obtained when searching the field of view.

The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a scanning electron microscope that can always obtain clear images regardless of whether the sample is stopped or moving.

[Means for Solving the Problems] The present invention provides a scanning electron microscope that irradiates a sample with a scanning electron beam and displays an image of the sample on an image display means based on an information signal emitted from the sample. , an image storage device that stores at least one frame of the information signal as the image display means; an integrator that sequentially integrates newly detected information signals with respect to the image information stored in the image storage device; an integration controller that controls integration by the integrator;
a first coefficient register for weighting a new information signal supplied to the integrator; and a second coefficient register for weighting an information signal read from the image storage and supplied to the integrator. The integration controller sets the maximum number of integrations based on the moving speed of the sample stage on which the sample is placed and the image magnification on the image display means, and also sets the first and second integration numbers based on the maximum number of integrations. The feature is that the integration coefficient set in the register is controlled.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. 1st
The figure is an apparatus configuration diagram for explaining one embodiment of the present invention. In FIG. 1, the same components as in FIG. 2 are given the same numbers and their explanations are omitted. The embodiment shown in FIG. 1 differs from the conventional example in that, for example, a drive mechanism 21 is used as a movement amount detection means for detecting the movement speed of the sample stage 20.
Based on the voltage detection means 23 that detects the driving voltage of a pulse motor (not shown) that is engaged with the voltage detection means 23 and the image magnification information supplied from the signal detected by the voltage detection means 23 and the magnification setting circuit 8. The difference is that an integration controller 24 for setting the number of integrations N and an integration coefficient α, and a table memory 25 for storing the value of α determined in advance are provided.

In the present invention, in order to improve the image quality of scanning electron microscope images, images are integrated as much as possible, and in order to follow changes in the image when the sample is moved, integration is performed when the stage is stopped. If the stage is moving, the maximum number of times of integration is determined according to the moving speed of the stage, and an integration coefficient that increases the weighting of the new information signal to be integrated is determined by the first and second integration coefficients. A coefficient register is provided to weight the new information signal to form a scanning electron microscope image.

By the way, in the case of an image processing system in which the number of pixels of one frame of the CRT 17 is 512 x 512 pixels in the vertical and horizontal directions, and the image processing system is capable of capturing data at 30 frames per second, the time T required to capture an image of one frame is approximately 33 m5ec. Furthermore, if the width of the display screen is W, then 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 x 512 sections can be determined.

Here, if the time required to move the sample 5 by the width m- of one section by the stage 20 is represented by S, then the S
If the value of is less than the image acquisition time T for one frame, the data accumulated with respect to the original image data will be data of an area shifted by one pixel or more, and as mentioned above, the image will be overlapped several times. A phenomenon that appears to overlap will occur.

Therefore, if the data acquisition time for one frame of the image memory 15 is the width of one pixel on the T1 display image and the stage movement time for one pixel is S, then the maximum possible number of integrations can be obtained. N4.8 can be determined by the following formula.

1≦N1.8≦(m/S)/T (where N is an integer) Furthermore, the integration coefficient α is determined from the maximum value N1.8 of the number of integrations. The integration coefficient α (where α is 1≧α>0) is such that when the maximum number of integrations is N, the result of the Nth integration is such that XN in the following equation becomes 0 (invalid information). Set.

In the above formula, XN indicates data stored in the image memory 15, XN indicates newly obtained image data,
N is the image data of the previous frame read out from the image memory 15. Therefore, in the above equation, when α-1, only new data XN is stored in the image memory 15, so a clear image can be obtained by setting a value of α˜1 when the sample is stopped. On the contrary,
When performing integration processing and the stage is moving, the maximum number of integrations N at the moving speed S of the stage is determined based on the above formula, and then the integration coefficient α that gives more weight to the new data side is determined. By setting , clear images can always be obtained regardless of the movement of the sample.

In the present invention, the value of α is determined for various number of integrations, and the determined value of α is stored in the memory 25 as a table indexed by the number of integrations N. Therefore, when the maximum number of integrations N is determined in the integration controller 24 based on the information on the detected moving speed S of the sample and the image magnification M, the integration coefficient α is stored in the memory 25 based on the information on the number of integrations N. is read out and the integration coefficient α value and (α-1) value are set in the first and second coefficient registers, so a clear image can always be obtained regardless of the movement of the sample.

Note that the embodiment described above is only one embodiment of the present invention, and the present invention can be implemented with various modifications. for example,
In the embodiment described above, the integration coefficient α is stored in the memory in advance, but the value may be calculated each time. In addition, in the above-mentioned embodiments, examples were shown in which the sample stage was moved automatically by motor drive, or the sample stage movement speed could be determined based on a signal detected by an encoder or the like to detect the amount of sample movement. good.

[Effects of the Invention] As is clear from the above description, according to the present invention, a scanning electron beam is irradiated onto a sample, and an image of the sample is displayed on an image display means based on an information signal emitted from the sample. In the scanning electron microscope, the image display means includes an image storage device that stores at least one frame of the information signal, and a newly detected information signal is sequentially displayed with respect to the image information stored in the image storage device. an integrator that performs integration; an integration controller that controls integration by the integrator; a first coefficient register that weights new information signals supplied to the integrator; a second coefficient register for weighting the information signal supplied to the instrument; By setting the number of integrations and controlling the integration coefficients set in the first and second registers based on the maximum number of integrations, a clear image can always be obtained regardless of whether the sample is stopped or moving. A scanning electron microscope capable of

[Brief explanation of the drawing]

FIG. 1 is an apparatus configuration 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: Samples 6x, 6y + deflection lens 7: Scanning signal generation circuit 8: UO: 12: 13° 14: 16: 18: 20 = 23: 25 : Magnification setting circuit 9: Secondary electron detector amplifier
11: A-D converter sampling circuit 19 two-coefficient register integrator 15: Image memory readout circuit 17: CRT CRT scanning signal generation circuit sample stage 21: Drive mechanism voltage detection means 24: Integration controller memory

Claims (1)

[Claims] In a scanning electron microscope that irradiates a sample with a scanning electron beam and displays a sample image on an image display means based on an information signal emitted from the sample, the image display means displays at least one frame of the information signal. an image storage device that stores image information stored in the image storage device, and an integrator that sequentially adds up newly detected information signals to the image information stored in the image storage device;
an integration controller that controls integration by the integrator; and a first integration controller that weights a new information signal supplied to the integrator.
a second coefficient register for weighting information signals read from the coefficient register and the image storage and supplied to the integrator;
a coefficient register, the integration controller sets the maximum number of integrations based on the moving speed of the sample stage on which the sample is placed and the image magnification on the image display means, and also sets the first number of integrations based on the maximum number of integrations. and a second register that controls an integration coefficient set.