JP3350555B2 - 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 a scanning electron microscope capable of always observing a sample in an optimum state so that an image signal of the electron microscope is not saturated.

[0002]

2. Description of the Related Art For example, a circuit for adjusting brightness and contrast of a conventional scanning electron microscope is shown in FIG. One of the detectors for detecting information obtained from a sample, that is, electrons or electromagnetic waves, is a secondary electron detector 1. The output of the detector 1 is a PMT 2
, And further amplified by the preamplifier 2a. The signal control unit 5 generates a signal for setting the brightness, and outputs the signal to the CRT 3 via the brightness setting circuit 4.
To enter. As shown in FIG. 4, the image signal 6 thus obtained is composed of a DC component D and an AC waveform A superimposed on the DC component D. The signal is input to the CRT 3 to display an image.

[0003] In a signal control section 5, based on a brightness target value setting section 5a, a brightness setting value calculating section 5b calculates, and a brightness setting value storing section 5c stores the calculated value.
The DC component is output by performing D / A conversion by the A converter 4a. The output signal output from the preamplifier 2a is superimposed on the DC component by the adder circuit 4b to form an image signal, which is converted into a digital value by the AD converter 4c and input to the frame memory 4d. The data is converted into an analog signal by the DA converter 4e, input to the CRT 3, and displayed. The numerical value in the frame memory 4d is detected by the brightness contrast level measuring unit 7, and is fed back to the brightness target value setting unit 5a to adjust the brightness.

The contrast of the image detected by the brightness contrast level measuring section 7 is determined by the signal control section 5.
Is fed back to the contrast target value setting unit 8a, and is calculated by the contrast setting value calculation unit 8b, and is stored in the contrast setting value storage unit 8c.
The signal is input from the high voltage generation circuit 9 of the contrast adjustment circuit to the PMT 2 via the DA converter 9a, and the contrast of the sample image is adjusted.

[0005]

In such a conventional automatic brightness and contrast adjusting apparatus, the image signal 6 detected by the brightness / contrast level measuring section 7 is the image signal whose brightness is measured. And the contrast is measured as the intensity of the image signal. However, if the upper value of the image signal 6 exceeds the maximum value that can be measured by the brightness contrast level measurement unit 7,
Is lower than the brightness contrast level measurement unit 7.
If the value is below the minimum value that can be measured by the above, the value exceeding the maximum value is measured as the maximum value, and the value below the minimum value is measured as the minimum value.

In this case, the average value and the intensity of the image signal are obtained based on the values different from the actual values, and the brightness and contrast set values are calculated. Since the correct values are not set, an image having an incorrect brightness contrast is displayed. There was a problem. The present invention has been made in view of such a conventional problem, and the upper value and the lower value of the image signal fall within the range of the maximum value and the minimum value that can be measured by the brightness contrast level measuring unit 7. It is an object of the present invention to obtain a scanning electron microscope capable of always obtaining a correct image display.

[0007]

According to the present invention, as a means for solving the above-mentioned problems, a structure for detecting information obtained from a sample and outputting an output signal, and an output of the detector are provided. An image display unit that generates an image based on an image signal obtained by adding a DC value to a signal, and the image signal has a predetermined brightness and contrast based on a measured value of a brightness contrast level of image data of the image display unit. A scanning electron microscope having a signal control unit for controlling, a saturation discriminating device for discriminating whether or not the image signal is saturated, and the signal control when the saturation discriminating device detects saturation of the image signal. A control unit that performs control in a direction in which the image signal does not saturate, wherein the signal control unit stores an average value of the image signal. A brightness control unit that controls brightness so as to have a value, and a contrast control unit that controls contrast so that the intensity of the image signal becomes a predetermined value. Contrast control which is connected to a contrast control unit and performs control so as to reduce contrast when it is determined that the image signal is saturated upward and downward and when it is determined that the image signal is saturated only upward. A device and a brightness control device that is connected to the brightness control unit and controls to increase the brightness when it is determined that the image signal is saturated only downward are provided.

[0008]

[0009]

[0010]

Next, the operation of the present invention will be described. The saturation determination device determines whether or not the image signal is saturated. When the saturation of the image signal is detected, the saturation release control device controls the image signal in a direction in which the image signal is not saturated separately from the control by the signal control unit. Do. When it is determined that the image signal is saturated upward and downward, and when it is determined that the image signal is saturated only upward, control is performed to reduce the contrast, and it is determined that the image signal is saturated only downward. Then, the brightness is controlled to increase.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of the present invention, in which a secondary electron detector 1 for detecting secondary electrons in information obtained from a sample, a PMT 2 for doubling the output electrons, a preamplifier 2a for amplifying the same,
It has a display CRT 3, a brightness modulation circuit 4 serving as an input unit thereof, and a signal control unit 5 for generating a DC component with respect to an AC waveform output from the preamplifier 2a.

The signal control section 5 includes a brightness target value setting section 5a for setting a brightness target value, a brightness setting value calculation section 5b for calculating the brightness setting value,
It has a brightness setting value storage unit 5c for storing it,
A DA converter 4a for converting the stored value into a DC signal, and an addition circuit 4b for synthesizing the signal output from the preamplifier 2a and the DC signal are provided. The A / D converter 4c for converting the combined image signal 6 into a digital value again, a frame memory 4d for storing the value, a D / A converter 4e for converting the value into an analog signal, and the numerical values of the frame memory 4d are detected. Brightness target value setting unit 5a
The brightness contrast level measurement unit 7 that feeds back is provided.

The contrast of the image detected by the brightness contrast level measuring section 7 is determined by the signal control section 5.
Is fed back to the contrast target value setting unit 8a, is calculated by the contrast setting value calculation unit 8b, is stored in the contrast setting value storage unit 8c, and is stored in the DA converter 9a.
Through the high-voltage generation circuit 9 of the contrast adjustment circuit
Input to MT2, the contrast of the sample image is adjusted. Up to this point, it is the same as the prior art of FIG. 3, and the same members are denoted by the same reference numerals.

If the upper and lower values of the synthesized image signal 6 are within a value that can be measured by the brightness contrast level measuring unit 7, the brightness target value of the signal control unit 5 is not changed. The image is fed back to the setting unit 5a or the contrast target value setting unit 8a, and is calculated and stored, and an image having a correct brightness contrast is displayed on the CRT 3. However, the upper value can be measured by the brightness contrast level measuring unit 7. When the value and the minimum value are exceeded, it is necessary to prevent an image having an incorrect brightness contrast from being displayed on the CRT 3.

Therefore, a saturation determining device 11 for determining whether or not the image signal 6 is saturated is provided at the brightness contrast level measuring section 7. When the saturation determination device 11 detects the saturation of the image signal 6, a saturation release control device 12 that performs control in a direction in which the image signal 6 does not saturate is provided separately from the control by the signal control unit 5.

The signal control section 5 includes a brightness target value setting section 5a for setting a brightness target value, and a brightness setting value calculation section 5 for calculating the brightness setting value.
b, a brightness control unit 13 including a brightness setting value storage unit 5c for storing the same, a contrast target value setting unit 8a for setting a contrast target value, a contrast setting value calculation unit 8b for calculating the contrast setting value,
It is formed by a contrast control unit 14 including a contrast set value storage unit 8c for storing the stored value.

Next, the saturation release control device 12 comprises a brightness control device 15 and a contrast control device 16,
The brightness control device 15 of the saturation release control device 12 controls the brightness so that the saturation is released, and the contrast control device 16 of the saturation release control device 12 controls the contrast so that the saturation is released.

Further, the contrast control device 16 of the saturation release control device 12 reduces the contrast when it is determined that the image signal 6 is saturated upward and downward and when it is determined that the image signal 6 is saturated only upward. Control, and the brightness control device 15 of the saturation release control device 12
Controls to increase the brightness when it is determined that the image signal 6 is saturated only downward.

That is, as shown in FIG.
Upper part 6a and lower part 6b are both saturated, and upper limit U and lower limit L
, The upper part 6a of the signal level is lowered,
By lowering the contrast in order to raise the lower part 6b, the upper and lower parts are both reduced and saturation is eliminated.
Further, as shown in FIG. 2B, when only the upper part 6a of the image signal 6 is saturated and exceeds the upper limit U, the upper part 6a of the signal level may be lowered, so that the contrast is lowered. As a result, the upper portion 6a is lowered and saturation is eliminated. Further, as shown in FIG. 2C, when only the lower part 6b of the image signal 6 is saturated and exceeds the lower limit L, the lower part 6b is raised by increasing the brightness so as to raise the lower part 6b of the signal level. Rising saturation disappears.

The present invention is not limited to the above embodiment,
Even when an output signal is obtained by detecting electron or electromagnetic wave information such as reflected electrons and cathodoluminescence from a sample, and an image is displayed based on the signal,
Similar effects can be obtained.

[0021]

As described above, according to this scanning electron microscope, a saturation discriminating device for discriminating whether an image signal is saturated, and the saturation discriminating device detects the saturation of the image signal. In addition, separately from the control by the signal control unit, a saturation release control device that performs control in a direction in which the image signal is not saturated is provided, and the signal control unit has an average value of the image signal to be a predetermined value. A brightness control unit that controls brightness, and a contrast control unit that controls contrast so that the intensity of the image signal becomes a predetermined value. The saturation release control device is connected to the contrast control unit. Then, when it is determined that the image signal is saturated upward and downward, and when it is determined that the image signal is saturated only upward, control is performed so as to lower the contrast. And Cormorant contrast control device, connected to the brightness control unit, since the image signal is provided and a brightness control unit for controlling so as to increase the brightness when it is determined that the saturated only downward,
Even when the upper value and the lower value of the image signal are out of the range of the maximum value and the minimum value that can be measured by the brightness contrast level measurement unit, the saturation release control device controls the brightness contrast level to be an appropriate value. So that the correct image display can always be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a scanning electron microscope of the present invention.

FIG. 2 is a waveform diagram of an image signal output showing an operation of adjusting the brightness contrast of the scanning electron microscope of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional scanning electron microscope.

FIG. 4 is a waveform diagram of a conventional brightness modulation circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Secondary electron detector (detector) 3 Image display part 5 Signal control part 7 Brightness contrast level measurement part 11 Saturation discrimination device 12 Saturation release control device 13 Brightness control part 14 Contrast control part 15 Brightness control device 16 Contrast control device

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01J 37/22 502 G09G 5/10 H01J 37/244

Claims (1)

(57) [Claims] 1. A detector for detecting information obtained from a sample and outputting an output signal; an image display unit for generating an image based on an image signal obtained by adding a DC value to an output signal of the detector; A signal control unit that controls the image signal to have a predetermined brightness and contrast based on the measured value of the brightness contrast level of the image data of the unit. A saturation determination device for determining whether the image signal is saturated,
Aside from the control by the signal control unit, a saturation release control device that performs control in a direction in which the image signal is not saturated is provided, and the signal control unit is configured such that an average value of the image signal becomes a predetermined value. a brightness control unit for controlling the brightness, the image signal intensity is only set a contrast control section for controlling the contrast to a predetermined value of, in the saturated release control device, the contrast control unit
Connect, the image signal is saturated upward and downward
And the image signal is saturated only upward.
Control to reduce contrast when it is determined that
Control device for performing brightness control and the brightness control
The image signal is saturated only downward
Control to increase brightness when it is determined that
A scanning electron microscope comprising a brightness control device .