JPS61176810A - Size measuring instrument - Google Patents

Abstract

PURPOSE:To measure efficiently the size of a sample with high accuracy without receiving the influence of the material of the sample by measuring the size of the sample by a method for superposing a cursor line and setting the threshold value of the pulse waveform obtd. when the sample surface is subjected to linear scanning in accordance with the measured value thereof. CONSTITUTION:The pulse waveform obtd. by linear scanning of the sample surface by using a linear scanning circuit 19 is amplified by an amplifier 14 and is then inputted to a threshold setting circuit 21. The signal of the measured value of the sample size measured by the method for superposing the cursor line using a cursor matching circuit 18 and a length measuring circuit 20 is inputted to the circuit 21 from the circuit 20 in this stage. The threshold value of the circuit 21 is set by the output signal from the circuit 20. The threshold value of the circuit 21 is automatically set in accordance with the measured value if the operation for measuring just once the sample size by the method for superposing the cursor line is carried out even if the sample material is different. The subsequent size measurement is automatically carreid out by using such threshold value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a dimension measuring device that measures minute dimensions such as the width of a circuit pattern on a semiconductor wafer using an electron beam.

[Background of the invention]

Conventionally, as this type of dimension measuring apparatus, one using a scanning electron microscope as shown in FIG. 2 is known.

In this conventional apparatus, an electron beam 4 emitted from an electron gun 1 and accelerated by anodes 2 and 3 is narrowly focused by a converging lens 5 and an objective lens 6, and then irradiated onto the surface of a sample 8. At this time, the electron beam 4 is two-dimensionally deflected by the deflector 7 and passes over the surface of the sample 8 at 4a, 4b.
Scan like this.

A sample signal of secondary electrons 9 generated from the surface of the sample 8 by the irradiation of the electron beam 4 is transmitted to a detector 10 and an amplifier 14.
After being amplified as an image signal by
By inputting it to the grid electrode 17 of No. 5, it is projected as a sample image on the screen of the display 15. In addition, 11
1 is a high-voltage power source for generating an electron beam, 12 is a lens power source, and 13 is a deflection power source, and this deflection power source 13 is connected to the polarizer 7.
The deflector 16 of the display 15 is also driven in synchronization with this.

Now, when a wafer pattern with a pattern width Ω and a cross-sectional shape as shown in FIG. 3(a) is observed with a scanning electron microscope, the shape shown in FIG. 2(b) is obtained by two-dimensional scanning of the electron beam.
When a part of the pattern is line-scanned in the direction of the arrow in FIG. 2(b), a back image as shown in FIG. 2(b) is obtained.
A pulse waveform as shown in c) is obtained.

Therefore, the surface image shown in Fig. 2(b) was photographed and its dimensions were determined. or display 1 as shown in Figure 4(a).
Project the cursor line 16 on the screen of step 5, move the position of this cursor line 16 as indicated by the arrow, and superimpose it on the edge part of the sample surface image as shown by symbol 16a. The dimensions of the wafer pattern can be measured by determining this distance and further dividing this distance by the observation magnification M (Crte/M).

On the other hand, the threshold value Tk of the pulse waveform shown in FIG. 2 (Q) is set appropriately, and this threshold value T is used to
By determining the pulse width of the pulse waveform as shown in b), the dimension a1 of the wafer pattern can be measured.

However, the measurement method using cursor lines has the advantage that the dimensions of the wafer pattern can be measured with high precision by overlapping the cursor lines 16 with high precision; The problem is that it is inefficient.

On the other hand, the method of measuring based on the pulse width of the pulse waveform has the advantage that the rest of the measurement work can be automated by only setting the threshold value T, but on the other hand, depending on how the threshold value T1 is set, the measurement value An error occurs, and the cross-sectional shape of the wafer pattern changes as shown in Fig. 4 (c), (d),
If the pulse waveform is as shown in Figure 4 (f) or due to the influence of the material of the wafer pattern,
), there were problems such as measurement being impossible. [Objective of the Invention] The present invention provides high precision, unaffected by the material of the sample.
Moreover, it is an object of the present invention to provide a dimension measuring device that can efficiently measure the dimensions of a sample.

[Summary of the invention]

In the present invention, the sample dimensions are measured by a method of superimposing cursor lines, and the threshold value of the pulse waveform obtained when the sample surface is line-scanned is set based on this measurement value.

(Example of the invention) The present invention will be described in detail below based on examples.

FIG. 1 is a block diagram showing one embodiment of the present invention, and the same parts as in FIG. 2 are indicated by the same symbols.

In FIG. 1, the difference from the conventional configuration is that the cursor alignment circuit 18. Line scanning circuit 19. A length measuring circuit 20, a threshold setting circuit 21, and a display selection circuit 22 are added.

In this configuration, the sample size is measured using the cursor alignment circuit 18 and the length measurement circuit 20 by a method of overlapping cursor lines. This measured value is input to the grid electrode 17 of the display 15 via the display selection circuit 22, so that it is displayed numerically instead of the sample image.

On the other hand, the pulse waveform obtained by line-scanning the sample current surface using the line-scanning circuit 19 is amplified by the amplifier 14 and then input to the threshold setting circuit 21. At this time, the threshold setting circuit 21 receives a signal of the measured value of the sample dimension measured by the cursor line superimposition method.
Input from The threshold value T of the threshold setting circuit 21 is as shown in FIG. It is set by the output signal of the measuring circuit 20 to be 1,000 n, l. The threshold value T1 set at this time is transmitted to the display 15 via the display selection circuit 22.
It is displayed by inputting it to .

When the threshold value T is set in the threshold setting circuit 21,
The pulse width range of the pulse waveform obtained by line scanning is measured using this threshold value Th as a reference, and the display selection circuit 22
The information is input to the display 15 via the .

Therefore, even if the specimen materials are different, if the specimen dimensions are measured only once using the method of overlapping cursor lines, the threshold value of the threshold setting circuit 21 can be set based on the measured value at this time. It is automatically fixed, and subsequent dimension measurements are automatically performed using this threshold T-.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the dimensions of a sample can be measured with high precision and efficiently without being affected by the material of the sample.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. Figure 2 is a block diagram showing the configuration of a conventional device, Figure 3 is a diagram showing the cross-sectional shape of a wafer pattern, its secondary electron image and pulse waveform during line scanning, and Figure 411 shows the types of cross-sectional shapes of the wafer pattern. FIG. 3 is a diagram showing a conventional measurement method. 4... Electron beam, 7... Deflector, 8... Sample, 9...
... Secondary electron, 10 ... Detector, 13 ... Deflection power supply, 15 ... Display device, 16 ... Deflector, 17 ... Grid electrode, 18 ... Cursor alignment circuit, 19・・・
- Line scanning circuit, 20... Length measurement circuit, 21... Threshold setting circuit, 22... Display selection circuit.

Claims (1)

[Claims] 1. A first circuit that scans the sample surface with an electron beam and extracts a sample surface image and a pulse waveform corresponding to this surface image using secondary electrons generated from the sample surface, and superimposes a cursor line on the surface image. A second circuit measures the dimensions of the sample surface, and a threshold value is set based on the measured value of this second circuit, and the pulse waveform is compared based on this threshold value to determine the size of the sample surface. A dimension measuring device comprising: a third circuit for measuring dimensions.