JPH11237230A - Method and equipment for specimen measuring in electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce influence of contamination and charging-up phenomenon of a specimen, concerning characteristic values characterizing the specimen. SOLUTION: In this specimen measuring method, a portion where dimension is measured is selected on the basis of an image (secondary electron image) of a secondary electron signal, and the dimension of the portion is repeatedly measured by using a dimension measuring apparatus 15. The results are stored in a measurement results storing equipment 16. On the basis of the stored measurement results, a correction function computing equipment 17 obtains a correction function by using, e.g. a method of least squares, and further estimates a dimension measurement value zero number of measurement time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring a sample in an electron microscope, and more particularly to a circuit pattern for a semiconductor device.
The present invention relates to a method and an apparatus for measuring a sample in an electron microscope suitable for measuring the size of a minute portion such as an electron beam.

[0002]

2. Description of the Related Art An electron microscope is often used for measuring the dimensions of a circuit pattern of a semiconductor device. This is based on irradiating the sample with an electron beam and detecting secondary electrons and the like generated from the sample by the irradiation, and the measured value is usually used as it is as a value representing a dimension.

[0003]

However, when a sample is irradiated with an electron beam, contamination mainly composed of hydrocarbons occurs on the surface thereof, and a charge-up phenomenon in which electrons accumulate on the surface occurs. For this reason, when the same part of the sample is repeatedly measured, the measured value changes each time. Such fluctuations cannot be ignored as the miniaturization of circuit patterns of semiconductor devices progresses rapidly.

An object of the present invention is to provide a method and an apparatus for measuring a sample in an electron microscope which are suitable for reducing the influence of the characteristic value characterizing the sample due to the contamination or charge-up phenomenon of the sample.

[0005]

According to the present invention, a sample is irradiated with an electron beam, whereby an information signal generated from the sample is detected. The characteristic values characterizing the sample are obtained at different times based on the detection information signal,
Then, a characteristic value correction function is obtained based on the characteristic values obtained as described above.

[0006]

FIG. 1 shows an embodiment according to the present invention. A primary electron beam 2 generated from a filament 1 as an electron source is controlled and accelerated by a Wehnelt 3 and an anode 4. The accelerated primary electron beam 2 is focused on a sample 9 by a focusing lens 5 and an objective lens 8.
The astigmatism generated in the primary electron beam 2 is reduced by the stigma coil 6
Can be corrected using

[0007] A scanning signal generator 12 generates scanning signals in the X and Y directions, and is provided to the deflection coil device 7. As a result, the primary electron beam 2 is two-dimensionally deflected, so that the sample 9 is two-dimensionally scanned by the focused maintenance electron beam 2. The scanning width of the primary electron beam 2 and thus the magnification of the obtained image, which will be described later, are set by the magnification setting unit 13.

[0008] Secondary electrons and reflected electrons are generated from the sample 9, for example, the secondary electrons 10 are detected by the secondary electron detector 11 and converted into electric signals. This electric signal is introduced into the image capturing device (memory) 14, but the X and Y direction scanning signals from the scanning signal generator 12 are also introduced into the image capturing device 14, so that the secondary electron detector 11 Is stored in the corresponding memory area of the image capturing device 14 in synchronization with the scanning of the sample 9 by the primary electron beam 2. Therefore, the secondary electron image of the sample 9 is stored in the memory. Of course, this stored image can be read out and displayed on the display 19. The size measuring device 15 measures the size of a desired portion of the sample 9 as a characteristic value characterizing the sample 9 based on the image signal read from the image capturing device 14. Since this point is well known, its detailed illustration is omitted.

The same portion of the sample 9 is repeatedly measured, and the resulting dimensional measurements at different times of the portion are stored in the measurement result storage device 1 connected to the dimensional measurement device 15.
6 is stored. A correction function calculator 17 as a feature value correction function calculator connected to the measurement result storage device (memory) 16 is a feature value correction function based on the dimension measurement values at different points in time stored in the measurement result storage device 16. Is calculated, and based on the correction function, the dimension value which is the characteristic value of the sample 9 when there is no irradiation by the primary electron beam 2, and therefore the contamination and the contamination of the sample 9 by the irradiation of the electron beam. Estimate the dimension value without the effect of charge-up. The obtained result is displayed on the display 18 and printed by the printer 19.

FIG. 2 shows a flow of the sample measurement based on the present invention in the embodiment of FIG. Steps 1 to 5 are generally performed. Step 1
In step (2), an image (secondary electron image) is formed by a secondary electron signal, and in step 2, a portion for measuring a dimension is selected. In step 3, a smoothing process is performed in order to cause the measurement value to fluctuate due to noise included in the image. In step 4, a measurement position is selected based on the signal obtained in step 3, and a dimension measurement value of the position selected in step 5 is calculated in consideration of the magnification.

In the embodiment of the present invention, in addition to such processing, the measured value is temporarily stored in step 6, and the processing from step 1 to step 5 is repeated a plurality of times. This saves the measurements at the same point at different times.
In step 7, a correction function is determined based on the number of measurements or the measurement time point based on the plurality of measurement values stored in step 6, and in step 8, the time t (t ≧ 0) or the number of measurements n is calculated from the correction function. The dimension value at the time of (n ≧ 0) is calculated as an estimated value.

Table 1 shows the results of dimension measurement based on the present invention. This measurement result was obtained by continuously measuring the same portion of the sample 10 times.

[0013]

[Table 1]

FIG. 3 shows an approximate curve as a correction function obtained with respect to the fluctuation of the measured value, with the number of measurements taken on the x-axis and the measured value taken on the y-axis from the obtained measurement results. This is obtained by performing a linear approximation by the least squares method on the fluctuation of the measured value. From the obtained approximate curve, a measured value of 0.4467, which was not affected by contamination and the like, was obtained.

In the embodiment, a straight line approximation by the least squares method is performed on the fluctuation of the measured value. However, even when the measured value has a sudden fluctuation, a characteristic curve as a correction function is obtained in the same manner as in the embodiment. An approximation can be made.

In the embodiment, the information signal generated and detected from the sample is a secondary electron signal, but the detection target may be a reflected electron or the like.

In the embodiment, the characteristic value characterizing the sample is the dimension value of the sample, but is not limited thereto.
For example, an elemental analysis value of the sample by X-rays generated from the sample may be used.

[0018]

According to the present invention, there is provided a method and an apparatus for measuring a sample in an electron microscope suitable for reducing the influence of a characteristic value characterizing the sample due to contamination or charge-up phenomenon of the sample.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of one embodiment based on the present invention.

FIG. 2 is a flowchart of sample measurement based on the present invention in the embodiment of FIG. 1;

FIG. 3 is a diagram showing an approximate curve as a correction function obtained based on an obtained measurement result.

[Explanation of symbols]

1: filament, 2: primary electron beam, 3: Wehnelt, 4: anode, 5: converging lens, 6: stigma coil, 7: deflection coil device, 8: objective lens, 9: sample, 10: secondary electron, 11: secondary electron detector, 12: scanning signal generator, 13: magnification setting device, 14: image capturing device (memory), 15: dimension measuring device, 16: measurement result storage device (memory), 17: Correction function calculator, 18: display, 19: printer.

Claims (9)

[Claims] A step of irradiating a sample with an electron beam to detect an information signal generated from the sample; and a step of obtaining characteristic values characterizing the sample at different times based on the detected information signal. Obtaining a characteristic value correction function based on the characteristic values obtained in this manner. 2. A sample in an electron microscope according to claim 1, further comprising a step of estimating a feature value of said sample when said sample is not irradiated with said electron beam based on said feature value correction function. Measuring method. 3. The method according to claim 1, wherein the characteristic value correction function is a linear approximation function by a least squares method. 4. The sample measuring method according to claim 1, wherein said characteristic value represents a size of said sample. 5. A means for irradiating a sample with an electron beam, thereby detecting an information signal generated from the sample, and obtaining characteristic values characterizing the sample at different time points based on the detected information signal. Means for obtaining a characteristic value correction function based on the obtained characteristic value. 6. An apparatus according to claim 5, further comprising means for storing said characteristic value. 7. An apparatus according to claim 5, wherein said characteristic value correction function is a linear approximation function by a least squares method. 8. The apparatus according to claim 5, wherein said means for calculating the characteristic value correction function estimates a characteristic value of the sample before irradiation of the sample with the electron beam based on the characteristic value correction function. Sample measuring device in electron microscope. 9. An apparatus according to claim 5, wherein said characteristic value represents a size of said sample.