JPS5824726B2 - Scanning length measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention displays an image of the surface of the object to be measured on a display device by two-dimensionally scanning the surface of the object to be measured, which has an extremely small length figure to be measured, with a charged particle beam. , relates to an apparatus for measuring the length of the figure to be measured displayed on the display device.

In recent years, exposure and processing techniques using charged particle beams have made remarkable progress and have become indispensable for integrated circuit manufacturing techniques.

In the integrated circuit manufacturing process, it is sometimes necessary to observe the shape and measure the length of formed elements.

In such a case, shape observation can be performed using a scanning electron microscope or the like, but there is no conventional device that can easily measure the length of the element etc. with sufficient accuracy.

These conventional problems are a big problem now that the dimensions that need to be measured with high precision are on the order of 0.1 μm due to the rapid development of integrated circuit technology, and the emergence of a new device has been strongly desired.

The present invention has been made in response to such demands, and embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram schematically showing an apparatus according to an embodiment of the present invention. In the drawing, 1 is a vacuum casing, and an electron gun 2 is provided on the top of the casing 1.

The electron beam 3 generated by the electron gun is focused by first and second focusing lenses 4 and 5, then deflected by horizontal and vertical deflection systems 6 and 7 and projected onto the surface of an object to be measured 8.

As a result, secondary electrons are generated from the surface of the measurement object 8, and 2
It is detected by the secondary electron detector 9.

The signal from the detector 9 is sent to the cathode ray tube 1 via an amplifier 10.
1 cathode 12.

A horizontal scanning signal, as shown in FIG. The vertical deflection system 7 also includes a vertical scanning signal generation circuit 1.
6, a vertical scanning signal as shown in FIG.

Further, the output doubles of the horizontal and vertical scanning signal generating circuits 13.16 are supplied to the horizontal and vertical deflection systems 20.21 of the cathode ray tube 11 via amplifiers 18.19, respectively.

Therefore, the electron beam 3 two-dimensionally scans a rectangular area on the object to be measured 8, and the electron beam 22 of the cathode ray tube 11 is also scanned in synchronization with this.

Therefore, a scanned secondary electron image of the object to be measured 8 is displayed on the cathode ray tube 11 based on the signal obtained from the secondary electron detector 9.

23 is a voltage generating circuit that generates a voltage for superimposing and displaying a reference vertical line for length measurement on the scanning secondary electron image displayed on the cathode ray tube 11, and the generating circuit 23 has a constant voltage at both ends. It has first and second resistors 24 and 25 to which voltage E is applied, and any voltage below voltage E can be taken out through terminals 26 and 27 that slide on the resistors.

The voltage E corresponds to the peak value of the sawtooth wave of the horizontal scanning signal supplied to the cathode ray tube 11.

Reference numeral 28 denotes a power source for applying voltage E to the resistor 25.

The voltage detected at the sliding terminals 26 and 27 can be supplied to the comparator 30 via a switch circuit 29, but depending on whether the switch circuit 29 is switched, only one of the voltages can be supplied to the comparator 30. supplied to

The comparator 30 is supplied with the horizontal scanning signal that is supplied to the horizontal deflection system 20 of the cathode ray tube 11, and the voltage signal from the voltage generation circuit 23 that has been selected by the switch circuit 29 is supplied to the comparator 30. is compared with the horizontal scanning signal, and at the moment when the signal values of both signals match, a bi-level rectangular signal is output.

That is, for example, when the comparator 30 is supplied with a horizontal scanning signal as shown by the solid line A in FIG. A rectangular wave signal as shown in FIG. 2d is generated.

The signal from the comparator 30 is supplied to the monostable multi-bi break-31, and as a result, the mono-stable multi-bi break-31 generates a negative voltage pulse having a short constant time width as shown in FIG. 2e, The generated pulses are supplied to the cathode 12 of the cathode ray tube 11.

As a result, a bright spot is displayed on the surface of the cathode ray tube 11 because the amount of electron beam reaching the fluorescent surface increases only at the moment when the pulse is supplied.

Since such bright spots appear at the same position on each horizontal scanning line, they are displayed as vertical bright lines on the surface of the cathode ray tube 11.

Returning to the voltage generation circuit 23, the voltage difference between the output voltage of the slider 26 and the output voltage of the slider 27 of the circuit 23 is applied to both ends of the third resistor 32. ,
The differential voltage is applied to a calibration slider 33 that slides on the third resistor 32.
After being taken out as a voltage V via the calibration fine adjuster 34, it is supplied to the digital voltmeter 35.

The digital voltmeter is linked to the variable magnification circuit 14, and the amplifier 15.17 of the variable magnification circuit 14
For example, the object to be measured 8 is imaged by changing the amplification factor of 1,0
The decimal point position on the display section of the digital voltmeter moves one by one as the value changes in three stages: 00 times, 10,000 times, ioo, and ooo times.

The calibration fine adjuster 34 is also linked to the variable magnification circuit 14, and when there is an error between the magnification set by the variable magnification circuit 14 and the actual magnification, the differential voltage is adjusted to an amount corresponding to the amount of error. This is a circuit for only compensation.

That is, for example, if the magnification set by the variable magnification circuit 14 is 10
When the actual magnification is 998 times when the voltage is 00 times, the voltage (1) is multiplied by the calibration fine adjuster 34 to 000 times and then supplied to the digital voltmeter 35.

Since the error between the set magnification and the actual magnification differs depending on the set magnification, the compensation rate by the calibration fine adjuster 34 is automatically switched in accordance with each set magnification.

Assume that such an apparatus is used to image an object having a very small length-measurable figure A as shown in FIG. 3, for example, and measure the width of the length-measuring figure A.

If the imaging magnification of the object to be measured 8 is appropriately selected by the variable magnification circuit 14 and the object to be measured 8 is scanned by the electron beam 3 and the image of the object to be measured 8 is displayed on the cathode ray tube 11, the image on the tube surface is Fourth
An image as shown in Figure a is displayed.

Here, A' is the figure image to be measured. Next, when the switch circuit 29 is connected to the terminal a, the voltage signal from the sliding terminal 26 is supplied to the comparator 30, and the above-described operation causes a vertical bright line as shown by B in FIG. 4 to be displayed.

When 26 is adjusted, the voltage to the comparator 30 changes, and the bright line moves in a direction perpendicular to it, so that the bright line B coincides with the right end of the length figure image A to be measured (dotted line H1 in Figure 4). ).

Next, the switch circuit 29 is switched to the b terminal so that the voltage taken out from the slider 27 is supplied to the comparator 30.

When the slider 27 is moved in this manner, the bright line in the vertical direction as indicated by B in FIG. 4 also moves in parallel in the horizontal direction.

While observing the bright line B, the bright line B becomes the length-measured figure image A'.
When the slider 27 moves to a position corresponding to the left end of the slider 27 (indicated by the dotted line H2 in FIG. 4), the slider 27 stops moving.

The voltage difference between the voltages taken out by the terminals 26 and 27 of the voltage generating circuit 23 is detected by the slider 33 of the resistor 32 and supplied to the digital voltmeter 35 via the calibration fine adjuster 34. .

As a result, a count value representing the width of the length figure to be measured is displayed on the digital voltmeter.

As described above, according to the present invention, the observation magnification is selected according to the size of the length figure to be measured, and after the length figure to be measured is displayed on the display device at the optimal size, the mark can be moved. By simply aligning it with the length of the object to be measured, extremely minute figures can be measured easily and with high precision.

In the above embodiment, the position of the calibration slider 33 is set as follows.

That is, first, an object to be measured having a reference figure whose length has been measured in advance by a known length measuring device such as a laser length measuring device is imaged at an appropriate magnification, and the image obtained by this imaging and the above-mentioned bright line are The length measurement results are displayed on the digital voltmeter 35 through the same process as described above while observing the length.

Compare the displayed value with the previously obtained length measurement value, and if the two values do not match, move the calibration slider 33 by a small amount so that the value displayed by the digital voltmeter 35 matches the previously obtained measurement value. The position where the matching is completed becomes the set position of the calibration slider 33.

Further, the fine adjustment by the calibration fine adjuster 34 is actually performed after the position setting by the calibration slider 33 is completed, and once these settings are set, there is almost no need to reset them.

It should be noted that the embodiment described above is only one basic embodiment of the present invention, and many modifications can be made.

For example, in the above-described embodiment, the bright line is displayed in the vertical direction to measure the width, but the bright line can also be displayed in the horizontal direction to measure the vertical length of the figure to be measured.

Further, when the length measurement figure image is oblique, the length measurement can be performed by rotating the displayed image obliquely or by rotating the bright line obliquely.

In addition, as shown in Fig. 5a, a circle C whose center position and radius can be freely adjusted is displayed on the surface of the cathode ray tube, and this circle C is used to measure the length of the length-measuring figure image indicated by D in the same figure. It is also possible to change the center position and radius until they coincide with the ends, and then take out the radius of the circle C as, for example, a voltage signal difference and display it on a digital voltmeter or the like to measure the length.

Further, as shown in Fig. 5, the image of the figure to be measured is placed between concentric circles CI and C2 whose center position and radius are variable, and the voltage corresponding to the difference in radius between the circles CI and C2 is displayed. The length may be measured by

Similarly, it is also possible to measure by displaying other figures or elements such as points constituting the figure as a reference.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing output signals of various circuits of the apparatus according to the embodiment shown in FIG. Figure 4 is a diagram showing the figure to be measured, and Figure 4 is a diagram to show the relationship between the image of the figure to be measured and the reference bright line displayed on the cathode ray tube surface, and Figure 5 is the image of the figure to be measured. FIG. 4 is a diagram for illustrating the relationship between and a reference circle. 1... Vacuum housing, 2... Electron gun, 3,
22...Electron beam: 4,5...Focusing lens, 6,20...Horizontal deflection system, 7,21...
...Vertical deflection system, 8...Object to be measured, 9...
...Secondary electron detector, 10, 18, 19...
Amplifier, 11...Cathode ray tube, 12...
Cathode, 13...Horizontal scanning signal generation circuit, 1
4...Magnification variable circuit, 15, 17...
Variable gain amplifier, 16... Vertical scanning signal generation circuit, 23... Voltage generation circuit, 24, 25, 3
2...Resistance, 26,27. 33...Slider, 28...Power supply, 29
...Switch circuit, 30...Comparator, 31...Monostable multi-vibration break-
134... Fine adjuster for calibration, 35...
Digital voltmeter.

Claims (1)

[Claims] 1. A means for two-dimensionally scanning the surface of an object having a length figure to be measured by supplying a scanning signal to a deflector for deflecting a charged particle beam; means for changing the amplification factor of an amplifier for switching the observation magnification; means for detecting information generated from the object to be measured during the scanning and converting it into an electrical signal; a display means that scans in synchronization with the scanning for displaying an image of the surface of the object to be measured based on the scanning;
means for displaying reference mark elements for indicating both ends of the i-length measurement figure image on the screen of the display means; means for moving the mark on the image; and means corresponding to the distance between the marks on the image. It is characterized by comprising means for generating a signal, means for changing the magnitude of the generated signal in conjunction with changes in the amplification factor of the amplifier, and means for displaying the output signal from the means. A scanning length measuring device.