JPS6363111B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a scanning electron microscope (hereinafter referred to as SEM)
This invention relates to an improvement of a magnification display device.

In a scanning electron beam device such as an SEM, a finely focused electron beam is scanned over the sample surface, and detection signals such as secondary electrons obtained from the sample are detected as brightness modulation signals of a cathode ray tube that deflects and scans in synchronization with this scanning operation. By using this, a sample scanned image is displayed on a cathode ray tube screen. The magnification of the scanned image in this case is determined by the following equation and is normally displayed on a magnification display.

Magnification M = Electron beam scanning width D on the cathode ray tube screen / Electron beam scanning width d on the sample Recently, a device has also been developed that can display this magnification value on the cathode ray tube screen and imprint it on the photograph at the same time as the image. There is. In such an apparatus, there is no problem when the developed photograph is the same size as the cathode ray tube screen, but there is a problem when the film size is different from the cathode ray tube screen. For example, in the case of a device that is adjusted so that when shooting with Polaroid film whose film size is 4 x 5 inches, it will be the same size as the cathode ray tube screen, the commonly used 95
When using 72mm Polaroid film, the actual magnification on the photo will be 0.8 times the magnification value. On the other hand, negative film may be used to enlarge the image to a size larger than that of a cathode ray tube, but in this case a similar situation occurs. In other words, the size of the final photo is CRT (hereinafter referred to as CRT).
If the screen is not the same as the one shown in the image (denoted as ), problems arise such as the photographing magnification and the display magnification becoming different.

Figure 1 is a block diagram of a conventional SEM. The electron beam generated and accelerated by the electron gun 1 is focused by a focusing lens 2 and a final stage lens 4, and is deflected by a deflection coil 3 to irradiate and scan the surface of a sample 5. Secondary electrons 15 generated from the surface of the sample 5 are detected by the detector 12, and then passed through the amplifier 13.
It is given to the CRT 14 as a brightness modulation signal. At this time, the CRT is synchronized with the electron beam scanning on sample 5.
Since the beam is deflected and scanned onto the CRT 14, a sample image is obtained on the CRT 14.

As mentioned above, the image magnification on the CRT 14 is related to the electron beam scanning width on the CRT screen and the electron beam scanning width on the sample 5, but since the electron beam scanning width on the CRT 14 screen is generally constant, The magnification is determined by the scanning width on the sample 5. Further, the scanning width on the sample 5 is proportional to the deflection coil current flowing through the deflection coil 3. This deflection coil current is transmitted to the deflection waveform generator 7.
A deflection current control circuit 6 in which the degree of amplification of the scanning signals generated by X and 7Y is changed by a magnification switcher 9.
It is controlled by passing X, 6Y.

The magnification switch 9 is connected to a magnification display circuit 10, and the magnification display circuit 10 calculates the magnification based on the output signal of the magnification switch 9. The result is displayed on the display 11 and displayed on the CRT. Display circuit 1
6 and is also displayed on the CRT14. In addition, 8X,
8Y is a CRT deflection circuit that outputs to the deflection coil of the CRT 14.

FIG. 2 is a circuit diagram showing an example of the magnification calculation circuit surrounded by the broken line in FIG. 1. The magnification switch 9 includes deflection coil current detection resistance changeover switches 17X, 17Y and a variable resistor 18 for continuously variable deflection coil current.
It is composed of X, 18Y, etc. The peak value of the current supplied from the deflection current control circuit 6X to the deflection coil 3 is I ₀ , the deflection coil current detection resistance value is R _fo , and the resistance values of the variable resistor 18X for continuously variable deflection coil current are R ₁ , R ₂ , R ₀ , and the peak value of the waveform voltage input from the deflection waveform generating circuit 7X is V _i , I ₀ ={(R ₀ +R ₂ )/R·R _fo }V _i (1). However, R=R ₀ +R ₁ +R ₂ .

Furthermore, the resistance R _fn of the magnification display mantissa switch 17S is selected to be inversely proportional to R _fo , and the resistance of the variable resistor 18S for continuously variable magnification display is set to the same value R ₁ , as that of the variable resistor 18X for continuously variable deflection coil current. R ₂ , R ₀ and the input voltage of the mantissa part of the magnification display is V _i2 , then the output voltage V ₀ is: V ₀ = {R・R _fp /R _fn (R ₀ + R ₂ )} V _i2 = {K・R・R _fo / (R ₀ + R ₂ )}V _i2 = (K・V _i・V _i2 )・(1/I _p ) ...(2). K is a proportionality constant, in this case R=R ₀ + R ₁
+ _R2 .

The above V _i and V _i2 are constant values, and since the magnification is inversely proportional to I ₀ , V ₀ is proportional to the magnification. In this example, instead of making R _fn proportional to the entire range of changes in R _fo , R _fo is set to a value in which the same significant figure is repeated every three steps (for example, 1Ω, 2Ω, 5Ω, 10Ω, 20Ω,
50Ω, 100Ω…), while R _fn repeatedly uses three types of resistance values (for example, 5KΩ, 2.5KΩ, 1KΩ), and increases the exponent part of the magnification display value every 3 steps using another switch. . This is to ensure accuracy of A/D conversion.

Therefore, the deflection coil current detection resistance changeover switches 17X, 17Y, the magnification display mantissa changeover switch 17S, and the magnification display exponent changeover switch 17
In addition, the variable resistors 18X and 18Y for continuously variable deflection coil current and the variable resistor 18S for continuously variable magnification display are operated in conjunction with each other to convert V ₀ to A with an appropriate conversion coefficient. A correct magnification value can be obtained by performing /D conversion. The magnification value calculated here is displayed on the display 11, or as required via the CRT character display circuit 16.
Displayed on CRT14.

However, even if you do this, the size of the final photo will be
If it is not equal to the image plane size of CRT14,
The above-mentioned problem arises in that the photographing magnification and the display magnification become different.

The present invention solves the above drawbacks of the prior art, corrects the display magnification according to the photographing magnification when the size of the final photograph is not the same size as the image plane of the CRT, and always keeps the image magnification and display magnification of the final photograph constant. can be matched
The purpose is to provide a magnification display device for SEM,
The present invention is characterized by means for scanning a sample with an electron beam to generate a signal characterizing the sample from the sample, and displaying an image of the area of the sample scanned by the electron beam based on the signal. means for switching the magnification of the image displayed on the image display means; and means for changing the magnification according to the switching of the magnification.
means for extracting a signal representing the magnification of the image displayed on the image display means and displaying the magnification; and a means for extracting a signal representing the magnification of the image displayed on the image display means, and making the signal representing the magnification correspond to the size of the photograph to be taken of the image displayed on the image display means. means for correcting with a correction coefficient determined by the scanning electron microscope; be.

FIG. 3 is a magnification calculation circuit diagram according to an embodiment of the present invention, and the same parts as in FIG. 2 are given the same reference numerals. In this case, a display magnification correction circuit 20 surrounded by a broken line is added to the circuit shown in FIG. When the resistance value of the correction coefficient changeover switch 19 is R _fk and the feedback loop resistance is R _e , the output voltage of the mantissa part of the magnification display is
V ₀ ′ can be expressed by the following equation.

V ₀ ′=(R _e /R _fk )・V ₀ …(3) Therefore, by appropriately selecting the values of R _fk and R _e , the magnification display can be corrected according to the shooting conditions, and the obtained data The magnification can be set to an accurate value regardless of the type of film.

Generally, images taken with 4 inch x 5 inch film are often taken at the same magnification, and in this case the correction coefficient is 0.8 for 95 mm x 72 mm Polaroid film, 0.6 for Brownie version negative film, etc. In case further enlargement is performed, values such as 2, 3, 4, 5, etc. may be set.
For that, R _k = 0.6, 0.8, 1, 2, 3, 4, 5
... multiplied by R _e . Furthermore, if the operating knob of the correction coefficient changeover switch 19 is marked with the abbreviation of the applicable film, it will be extremely convenient to change the correction coefficient.

The magnification display device of this embodiment has a magnification switch and an A/
By connecting a display magnification correction circuit between the D converter and selecting the resistance value, it is possible to match the magnification of the final photograph with the display magnification. This has the effect of being extremely convenient when printing at the same time.

In the above embodiment, a case has been described in which the image magnification M is defined by D/d, but the actual image magnification is also related to the accelerating voltage, the distance between the final stage focusing lens and the sample (working distance), etc. Normally, the magnification calculation circuit also incorporates these elements, but since they have been widely used in the past, their explanation will be omitted.

The SEM magnification display device of the present invention has the advantage of being able to match the image magnification of the final photograph with the display magnification by adding a relatively simple display magnification correction circuit.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional SEM, Fig. 2 is a circuit diagram showing an example of a magnification calculation circuit surrounded by a broken line in Fig. 1, and Fig. 3 is a magnification calculation circuit diagram of an embodiment of the present invention. be. 3... Deflection coil, 5... Sample, 6X, 6Y...
...Deflection current control circuit, 7X, 7Y...Deflection waveform generation circuit, 8X, 8Y...CRT deflection circuit, 9...
Magnification switcher, 10...Magnification display circuit, 11...Display device, 12...Detector, 13...Amplifier, 14...
...CRT, 15...Secondary electron, 16...CRT character display circuit, 17X, 17Y...Deflection coil current detection resistor switching switch, 17S...Magnification display mantissa switching switch, 17S'...Magnification display exponent switching switch Switch, 18X, 18Y... Variable resistor for continuously variable deflection coil current, 18S... Variable resistor for continuously variable magnification display, 19... Correction coefficient changeover switch,
20...Display magnification correction circuit, _I0 ...Axis deflection coil current, R _fo , R _fn ...Deflection coil current detection resistance value,
R ₁ , R ₂ , R ₀ ...Resistance value.

Claims (1)

[Claims] 1 means 1 for scanning a sample 5 with an electron beam and generating from the sample a signal 15 characterizing the sample;
2, 3, 4, 6X, 6Y, 7X, 7Y, means 8X, 8Y, 14 for displaying an image of the area of the sample scanned by the electron beam based on the signals, and an image displayed on the image display means. Means 9 for switching the magnification of the image; and means 10, 11, 16 for extracting a signal representing the magnification of the image displayed on the image display means and displaying the magnification, which changes in accordance with the switching of the magnification.
and means 19, 20 for correcting the signal representing the magnification with a correction coefficient corresponding to the size of the photograph of the image displayed on the image display means, and the correction coefficient is applied to the image display means. A scanning electron microscope magnification display device selected so that the magnification of the displayed image matches the magnification of that image on the photograph.