JP2839732B2 - Automatic brightness / contrast adjuster for scanning electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic brightness / contrast adjusting device in a scanning electron microscope or the like, and more particularly to a device capable of automatically adjusting brightness / contrast even when a range of change of a detection signal is wide.

[0002]

2. Description of the Related Art Conventionally, secondary electron beam images such as a scanning electron microscope (SEM), an electron probe X-ray microanalyzer (EPMA) and a scanning Auger microprobe (SAM) are displayed on an image display device such as a cathode ray tube (CRT). In the apparatus observed above, the brightness and contrast of the CRT are automatically adjusted according to the intensity of the detection signal. FIG. 5 shows a conventional example of an automatic brightness / contrast adjusting device in a scanning electron microscope.

In FIG. 5, an electron beam 32 focused by lenses 30 and 31 is converted into a sample 34 by a deflector 33.
Scanned two-dimensionally above. A secondary electron beam signal 35 emitted from the sample 34 is converted into light by a scintillator 36, and is converted to light via a photomultiplier tube (PMT) 37 and an amplifier 38.
Displayed on RT39. In this case, the average value of the output signal of the amplifier 38 is detected by the average value
Numeral 1 controls the output of the amplifier 38 to a constant value by negatively feeding back a correction voltage generated by comparing the reference voltage 42 to the amplifier 38. The reference voltage 42 is set to an appropriate voltage between the grid 43 corresponding to the maximum luminance and the grid 43 corresponding to the minimum luminance on the CRT 39, and by adjusting the voltage 44 of the photomultiplier tube 37, the optimum luminance and I try to get contrast.

[0004]

SUMMARY OF THE INVENTION However, EPM
In devices such as A and SAM, the beam current value of the primary electron beam is often changed and used, and its variable range is as wide as 10 ^-12 to 10 ^-5 A. For this reason, the dynamic range of the detection signal becomes large, and it is necessary to manually adjust the operating range of the amplifier downstream of the detector each time.

The present invention provides an automatic brightness / contrast adjusting device in a scanning electron microscope or the like which can automatically adjust brightness and contrast even under extremely wide measurement conditions in consideration of the above-mentioned problems. It is intended to be.

[0006]

SUMMARY OF THE INVENTION The present invention provides a detecting means for two-dimensionally scanning a sample surface with an electron beam and detecting information obtained from the sample surface, and an amplifier for amplifying the detection signal. An image display device for displaying an image of a sample surface based on an output signal of the amplifier, and a means for controlling an amplification factor and a level of the amplifier so as to adjust brightness and contrast of an image displayed on the image display device In an automatic brightness / contrast adjusting device in a scanning electron microscope or the like comprising: a means for sweeping a high voltage applied to the detector prior to control of an amplification factor; and a detecting signal detected at the time of the high voltage sweeping. Means for detecting that the set operation level of the amplifier has reached the upper limit and setting the high voltage value; and randomly sampling a detection signal obtained from the sample after setting the high voltage value. Means for comparing the intensity values of all the sampled signals to detect data u having a predetermined number removed from the highest value and data l having a predetermined number removed from the lowest value, and based on the data u and data l. Means for calculating the gain control signal and the level control signal,
The amplification factor and the level of the amplifier are controlled based on the data.

[0007]

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating the configuration of an apparatus for explaining an embodiment of the present invention, and FIGS. 2 and 3 are diagrams illustrating the operation.

In FIG. 1, an electron beam 3 focused by lenses 1 and 2 is two-dimensionally formed on a sample 6 by a deflector 4 driven based on a TV-rate scanning signal generated by a scan generator 5. Scanned. The secondary electron beam signal 7 emitted from the sample 6 is converted into light by a scintillator 8 and supplied to a frame memory 13 via a photomultiplier tube (PMT) 9, a gain adjustment amplifier 10, and a level adjustment amplifier 11. Is stored. Writing and reading of data to and from the frame memory 13 are performed based on an output signal of an address generation circuit 12 which generates a writing and reading address in synchronization with a scanning signal of the scan generator 5. The data read from the frame memory 13 is displayed on a CRT 14 scanned at a TV rate.

In the automatic brightness / contrast adjustment according to the present invention, first, when an electron beam irradiated on a sample is scanned at a high speed at a TV rate, a voltage HV applied to a photomultiplier tube 9 from a high voltage power supply 15 is applied. Is swept from the low pressure side to the high pressure side (or from the high pressure side to the low pressure side). Thus, the voltage HV
Is increased, the gain of the detector is also increased. At this time, the offset value of the amplifier 10 is set to 0 so that the output signal of the detector 9 always changes in the same code region.

A part of the video signal obtained through the amplifiers 10 and 11 is supplied to a central processing unit (CPU) 16 via a sampling circuit 15. The CP
In U16, to set the high voltage HV _G the strength of the video signal reaches about 80% of the gain included in the amplifier 10 is compared with the preset reference value S and the video signal as shown in FIG. 2 Is performed. Then, in that the intensity of the video signal reaches the reference value, the increase in the high pressure value is stopped, the voltage HV _G applied to the photomultiplier tube 9 is fixed. Next, the sampling circuit 17 randomly samples about 2000 video signals during one frame scanning or a period in which repetitive scanning is performed, and the sampled data is stored in a memory (not shown) in the CPU 16. Is stored. The intensity of the data stored in the memory is compared by the CPU 16,
The maximum data u and the minimum data 1 are obtained by removing 100 data (5%) from the maximum value and the minimum value in all the data as shown in FIG. 3, respectively. Then, based on the data, the CPU 16 adjusts the gain adjustment amplifier 10 and the level based on the following equation so that the range of the signal supplied to the CRT 14 matches the value corresponding to the dynamic range set for the CRT. The control signals G and LE supplied to the adjustment amplifier 11 are calculated.

[0011] In a state of performing the setting of the high-pressure value HV _G, the gain G of the gain adjustment amplifier 10 G =
1, that is, there is no amplification effect, and the level of the level adjustment amplifier 11 is also set to LE = 0.

The gain G is determined by the following equation based on the data u and data l. G = (U-L) / (u-l) (1) LE = (U · l -L · u) / (u - l) (2) where, where U and L are set by the CRT The maximum and minimum values of the signal. The data determined by the above calculation is used as a control signal by the gain adjusting amplifier 1.
0, when supplied to the level adjustment amplifier 11, the detection signal (A) is amplified (B) at a predetermined amplification factor as shown in FIG. Shift to correspond to (C)
Is done.

As described above, after the gain of the detector is automatically set to the optimum value based on the detection signal obtained from the sample, the detection signal is randomly sampled, and the predetermined number in the sampled data is obtained. By automatically adjusting the brightness and contrast using only the data of the above, even when the beam current value of the primary electron beam changes variously and the dynamic range of the detection signal greatly changes, Appropriate brightness and contrast adjustments can be made automatically.

The above-described embodiment is merely an embodiment of the present invention, and the present invention can be implemented with various modifications. For example, irregular sampling in the above-described embodiment is particularly effective when scanning a sample at a high speed at a TV rate. For example, when the beam current is as low as 10 ⁻¹¹ A, low-speed scanning is performed. At the same time, it is desirable to perform sampling after interposing a low-pass filter in all stages of the sampling circuit.

[0015]

As is apparent from the above description, according to the present invention, a detecting means for two-dimensionally scanning a sample surface with an electron beam and detecting information obtained from the sample surface, An amplifier that amplifies the detection signal, an image display device that displays an image of the sample surface based on the output signal of the amplifier,
An automatic brightness / contrast adjusting device in a scanning electron microscope or the like comprising means for controlling the gain and level of the amplifier so as to adjust the brightness and contrast of an image displayed on the image display device. Means for previously sweeping a high voltage applied to the detector;
Means for detecting that the detection signal detected at the time of the high voltage sweep has reached the preset upper limit of the operation level of the amplifier and setting the high voltage value; and detecting the high voltage value from the sample after setting the high voltage value. Means for randomly sampling a signal; comparing the intensity values of all the sampled signals; detecting data u which is removed by a predetermined number from the highest value and data 1 which is removed by a predetermined number from the lowest value;
And means for calculating an amplification factor control signal and a level control signal based on the data 1 and controlling the amplification factor and the level of the amplifier based on the data so that the beam current value of the primary electron beam is reduced. Even when the dynamic range of the detection signal changes greatly due to various changes, it is possible to automatically perform appropriate brightness and contrast adjustments using only a predetermined number of data in the randomly sampled image data. it can.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining a gain setting operation of the detector.

FIG. 3 is a diagram showing maximum data u and minimum data 1 out of 100 data (5%) respectively removed from the maximum value and the minimum value in all data.

FIG. 4 is a diagram for explaining an operation of setting a gain and a level of an amplifier.

FIG. 5 is a diagram for explaining a conventional example.

[Explanation of symbols]

1: Lens 2: Lens 3: Electron beam 4: Deflector 5: Scan generator 6: Sample 7: Secondary electron beam signal 8: Scintillator 9: Photomultiplier tube (PMT) 10: Gain adjustment amplifier 11: Level adjustment Amplifier 12: Address generation circuit 13: Frame memory 14: CRT 15: High voltage power supply 16: Central processing unit (CPU) 17: Sampling circuit

Claims (1)

(57) [Claims] 1. A detecting means for two-dimensionally scanning the surface of a sample with an electron beam and detecting information obtained from the surface of the sample, an amplifier for amplifying the detection signal, and an output signal from the amplifier. An image display device for displaying an image of the sample surface by
An automatic brightness / contrast adjusting device in a scanning electron microscope or the like comprising means for controlling the gain and level of the amplifier so as to adjust the brightness and contrast of an image displayed on the image display device. Means for previously sweeping a high voltage applied to the detector;
Means for detecting that the detection signal detected at the time of the high voltage sweep has reached the preset upper limit of the operation level of the amplifier and setting the high voltage value; and detecting the high voltage value from the sample after setting the high voltage value. Means for randomly sampling a signal; comparing the intensity values of all the sampled signals; detecting data u which is removed by a predetermined number from the highest value and data 1 which is removed by a predetermined number from the lowest value;
Means for calculating an amplification factor control signal and a level control signal based on the data l, and controlling the amplification factor and level of the amplifier based on the data. Brightness / contrast adjustment device.