JPH11224640A - Electron microscope, its resolution evaluating method and manufacture of semiconductor therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure, evaluate and adjust resolution by incorporating an arithmetic processor evaluating the image of an acquired deposition sample by a frequency analysis or the like in a scanning electron microscope, quantifying the signal characteristic from the result of the frequency analysis, and calculating the resolution. SOLUTION: Generated secondary electrons are detected by a secondary electron detector 15, the intensity is inputted to an image input device 16, and a two-dimensional gray image is obtained and inputted to an arithmetic processor 19. Two-dimensional Fourier transformation is applied to multiple images to obtain a power spectrum, averaging is made for each frequency, and a smoothing process, e.g. moving averaging and median filtering, is applied. The intersection of the obtained power spectrum and a resolution calculating curve calculated in advance is obtained, and the resolution is calculated based on the frequency. If the resolution is unsatisfactory, the condition set value controlling an electromagnetic lens 14 is inputted to a control computer 20, and the focus condition is optionally changed to make an adjustment until the desired resolution is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample for the purpose of making the resolution, resolution, etc. of a scanning electron microscope uniform, a scanning electron microscope incorporating the sample, and the scanning electron microscope. The present invention relates to a semiconductor manufacturing method.

[0002]

2. Description of the Related Art Conventionally, the resolution of an electron microscope has been evaluated based on the distance between two points of a sample that can be visually confirmed.
A sample obtained by depositing gold particles on carbon as in Japanese Patent No. 45265 is observed with an electron microscope, and the minimum gap between two separated gold particles is defined as the resolution. The resolution of the electron microscope is evaluated based on the degree of blurring of the grain boundaries.

[0003]

In the conventional resolution evaluation, when an image captured by an electron microscope captures gold particles and the like, the size and shape of the gold particles vary, and individual differences occur in the measurement. Furthermore, since the same sample cannot be reproduced, accurate quantitative evaluation cannot be expected. In addition, since the evaluation of the gap between the gold particles during observation with an electron microscope is performed visually, high reproducibility cannot be obtained. Further, the resolution of an electron microscope varies from machine to machine. For this reason, when measuring the dimensions of each part of the semiconductor using a plurality of electron microscopes in a semiconductor product manufacturing process, the observed images differ among these electron microscopes, and defects and the like are visible or invisible by the observed electron microscope. However, there is a problem that manufacturing cannot be performed based on a unified and fixed control value.

An object of the present invention is to provide a sample for measuring the resolution of an electron microscope, a method for evaluating the resolution of an electron microscope, and a method for adjusting the same in order to solve the above-mentioned problems.

[0005]

In order to achieve the above-mentioned object, the present invention provides a vapor deposition sample on an SEM, an image input device for acquiring an SEM image, and an arithmetic processing device for evaluating the acquired image by frequency analysis or the like. And so on. The signal characteristics are quantified from the frequency analysis result, and the resolution of the electron microscope is calculated. A plurality of electron microscopes incorporating such a sample can be adjusted to the same resolution and resolution by adjusting the focus voltage and the like of each electron microscope.
Observations under the same conditions can be made with different types of electron microscopes.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A schematic diagram of a scanning electron microscope (hereinafter, referred to as SEM) as an example of an embodiment of the present invention will be described with reference to FIG. The electron optical system shown in FIG. 1 can focus the electron beam emitted from the electron gun 13 by the electromagnetic lens 14 and scan the sample surface in an arbitrary order. Secondary electron signals generated on the surface of the sample 1 by the irradiation of the electron beam are detected by the secondary electron detector 15 and input to the image input device 16 as image data. Sample 1 which is the inspection object is X-
The YZ stage 17 can move in all three-dimensional directions. The irradiation of the electron beam and the image input synchronized with the movement of the stage are possible, and the movement of the stage is controlled by the control computer 20. Although FIG. 1 shows an example of the SEM using the secondary electron image, the means for observing the sample may use an image of backscattered electrons, reflected electrons, transmitted electrons, and the like in addition to the secondary electrons.

A sample for evaluating the resolution of the SEM will be described. When gold particles having a large atomic number are vapor-deposited on a material to be vapor-deposited such as carbon, an image having a clear contrast as shown in FIG. 2 is obtained. 1 shows a conventional resolution evaluation method. When the schematic view of the carbon surface and the deposited gold particles as viewed from the side is shown in FIG. 3, the smallest gap W is searched from the SEM image and defined as the resolution.

In the present invention, the resolution of the SEM is measured by performing frequency analysis on such an image by a technique such as two-dimensional Fourier transform. Figure 1 shows the means for acquiring images
Will be described. The gold vapor-deposited particles are placed on the sample holder 24, irradiated with an electron beam from the electron gun 13, and scanned two-dimensionally. Electrons generated from the sample surface when scanning are detected by the secondary electron detector 15 and the intensity is input to the image input device 16 to obtain a two-dimensional gray image. The obtained grayscale image is converted into digital image data by the arithmetic processing unit 1.
Enter 9

The image data is transferred to the control computer 2 if necessary.
0, or the acquired image data can be displayed on the display device 30 via the control computer 20. Further, since the size of the vapor deposition particles on the sample surface is not uniform, different portions on the sample are repeatedly obtained. At this time, if the measurement site is near the sample, the electromagnetic lens 14
The measurement field can be changed by adjusting the magnetic field generated in step (1). When the measurement site is largely changed, the XYZ stage 17 is driven. The measurement accuracy of the resolution can be improved by repeatedly measuring the sample and averaging the results of the frequency analysis.

A quantitative evaluation method of the resolution will be described with reference to FIGS. FIG. 2 shows an image of a gold vapor deposition particle at 512 pixels × 5.
This is a digital image composed of 12 pixels. This image is subjected to a two-dimensional Fourier transform to obtain a sum of squares of a real part and an imaginary part.
FIG. 4 shows an image obtained by taking the logarithm of the value of each pixel. For example, FIG. 5 shows a result obtained by taking a profile of a portion of the horizontal axis A passing through the center of FIG. This is the frequency spectrum in the horizontal direction in the image of FIG. 2 and is called a power spectrum. FIG. 5 shows SEs corresponding to the three images in FIG. 2 which were determined to have resolutions of 4 nm, 4.5 nm, and 5 nm by visual classification and the like.
The power spectrum of M is displayed. The power spectrum can be obtained at any plane passing through the center. Therefore, a resolution at an arbitrary angle can be obtained.

In FIG. 5, the vertical axis represents signal strength and the horizontal axis represents frequency. The frequency in this case is one cycle of light and dark in the image. Therefore, the highest frequency in the horizontal direction is 51
In the case of an image of 2 pixels × 512 pixels, there are 256 periods.
In the state of FIG. 5, the power spectra of the SEMs determined to have resolutions of 4 nm, 4.5 nm, and 5 nm overlap each other, and it is difficult to evaluate the resolution. For this reason, the image of the gold vapor deposition particles is repeatedly obtained, and the average value of the power spectrum is obtained. Further, when processing such as smoothing processing such as moving average or median filter is performed, as shown in FIG.
Can be easily separated due to the difference in resolution.

Through experiments, the resolution of the SEM was previously set to 4 nm, depending on the conventional method and the appearance of the cross section of the thin film layer.
4.5 nm, 5 nm, etc. are defined, the values are converted to the frequency of the power spectrum, and the value of the power spectrum at that frequency is plotted on the resolution. A determination straight line can be obtained. For example, assuming that the resolution R in the horizontal direction is the wavelength, the relationship with the frequency F is the width of the image (512 pixels).
Is L, the following relationship is established.

[0013]

F = L / R (Equation 1) Next, when the minimum gap between the gold particles is defined as the resolution R,
Since the minimum gap between the gold particles is a dark portion, and one cycle of light / dark repetition is one cycle, the wavelength is doubled to obtain a wavelength of one cycle. By dividing this total length by the wavelength of the resolution R, it is possible to calculate the corresponding frequency in the two-dimensional Fourier transform for an arbitrary resolution. The formula for calculating the frequency is

[0014]

F = L / (2 × R) (Equation 2) Conversely to this formula, the formula for calculating the resolution R

[0015]

R = L / (2 × F) (Equation 3) holds, and the resolution of an arbitrary SEM can be measured. For example, in FIG. 6, L is 1140 nm,
When the resolutions of 4 nm, 4.5 nm, and 5 nm are converted into frequencies from the values, they are 114 Hz, 126 Hz, and 142 Hz. However, Hz defined here is the number of waves existing in the entire length L.

The procedure for calculating the resolution is shown in the flowchart of FIG. First, a plurality of gold-deposited sample images at different sites are obtained (100). Next, two-dimensional Fourier transform is performed on a plurality of images to obtain a power spectrum (102). The obtained power spectrum is averaged for each frequency (10
4). Further, smoothing processing such as a moving average and a median filter is performed (106). The intersection of the power spectrum obtained as a result and the previously calculated resolution calculation curve is calculated (108). The frequency is represented by F in [Equation 3].
And the resolution R of the corresponding SEM is calculated (11
0).

Thus, if the sample is mounted on the SEM, the apparatus itself can always manage the resolution of the SEM.

Although the above description has been made in one dimension (X-axis direction), it is apparent that the present invention can be applied to two dimensions individually. It is clear that changing the acceleration voltage also changes the resolution.

If the resolution is not satisfactory, the condition setting value for controlling the electromagnetic lens 14 is changed to the control computer 20.
, The focus condition can be arbitrarily changed and the optimum adjustment can be made so that a desired resolution can be selected. Further, by inputting condition setting values for controlling the vacuum control system, the degree of vacuum can be adjusted so that a desired resolution can be selected by arbitrarily changing the vacuum control conditions. Since the condition of the electron gun 13 may be bad, it is necessary to adjust the voltage applied to the electron gun 13 so that a desired resolution can be selected.

Since the storage device connected to the arithmetic processing unit 19 stores the history data relating to the resolution, the user can be notified at any time by using the control computer 20 and the display device 30, for example.

Further, by connecting a plurality of SEMs via a control computer 20 in a production line of a semiconductor product or the like via a network, the plurality of SEMs are simultaneously managed,
The performance difference is measured, and if a difference is found, the difference is adjusted by using the above-mentioned resolution adjusting means, so that the difference in production quality between each process can be reduced, and the quality of the product can be stabilized. . In addition, it is possible to communicate with factories located in different places, and similarly produce a product with stable quality. An embodiment of the present invention in a production line for semiconductor products and the like will be described with reference to FIG.

FIG. 8 shows the SEM inspection including wafer input, film formation,
1 is a schematic diagram of a semiconductor product production line performed after or before exposure, etching, wafer test, and the like.

The resolution evaluation is performed in all SEMs on the line, and data such as resolution, focus setting conditions, electron beam setting conditions, electromagnetic lens setting conditions, and vacuum degree setting conditions are sent to the network server 40 via a LAN (Local Arrangement).
ea Network). If the resolutions of all the SEMs do not match, the network server 40 changes the focus setting conditions, electron beam setting conditions, electromagnetic lens setting conditions, and vacuum degree setting conditions for the SEMs that do not match, and controls the SEM. Feedback adjustment is performed until a desired resolution is obtained. Network server 4
For 0, any of the SEMs on the line may be substituted.

Similarly, the resolution of a plurality of SEMs can be adjusted by the network server 40 for a semiconductor product production line at another location.

According to the above invention, SEM between factories and processes
As a result of improving the stability of the inspection, it is possible to reduce the difference in the quality of the produced product, to accurately grasp the abnormality of the production line, and to stabilize the quality of the product.

[0026]

According to the present invention, the resolution of an electron microscope,
By using a gold vapor-deposited sample to quantitatively evaluate the resolution by means of frequency analysis or the like, using a gold-deposited sample, it is possible to accurately grasp the performance difference between different electron microscopes and changes over time. . This is especially true for semiconductor inspection
In a manufacturing process using a plurality of electron microscopes, individual differences between electron microscopes can be reduced, and the accuracy of inspection can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a scanning electron microscope.

FIG. 2 is a view of an electron microscope imaging result of a gold vapor-deposited sample according to an example of the present invention.

FIG. 3 is a schematic view of a gold vapor deposition sample of the present invention.

4 is a diagram showing a result of frequency conversion of an electron microscope image of the gold vapor-deposited sample of FIG.

FIG. 5 is a profile diagram showing the result of frequency conversion of an electron microscope image of a gold-deposited sample of the present invention.

FIG. 6 is a diagram illustrating a method for evaluating the resolution of an electron microscope according to the present invention.

FIG. 7 is a flowchart for evaluating the resolution of the electron microscope of the present invention.

FIG. 8 is an SEM in the semiconductor product manufacturing line of the present invention.
Network schematic diagram.

[Explanation of symbols]

1 ... sample, 8 ... electron beam, 13 ...
Electron gun, 14 ... electromagnetic lens, 15 ... secondary electron detector,
16 image input device, 17 XYZ stage,
19: arithmetic processing unit, 20: control computer, 24: sample holder, 30: display device, 40: network server.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tatsuo Horiuchi 292 Yoshidacho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi, Ltd.Production Technology Research Institute (72) Keisuke Kawame 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Within Hitachi, Ltd. Production Technology Research Laboratories (72) Inventor Goro Shimoma 882 Ma, Hitachinaka-shi, Ibaraki Pref., Ltd.Measurement Division, Hitachi, Ltd. (72) Inventor Tadanori Takahashi 882 Mao, Hitachinaka-shi, Ibaraki Pref. Within Hitachi Measuring Instruments Division (72) Inventor Masayuki Yukiti 882 Ma, Hitachinaka-shi, Ibaraki Prefecture Within Hitachi Instruments Measuring Instruments Division

Claims (4)

[Claims] 1. Resolution of an electron microscope and measurement of the resolution,
Means for imaging the sample on which fine particles are deposited once or more than once for adjustment, means for storing the captured image, and operation for analyzing the data of the stored image using a procedure such as frequency analysis An electron microscope comprising means and means for quantitatively evaluating resolution and resolution from the analysis result. 2. Resolution of an electron microscope and measurement of resolution.
A step of imaging the sample on which fine particles are deposited once or a plurality of times for adjustment, a step of storing the captured image, and an arithmetic step of analyzing data of the stored image using frequency analysis or the like. And a method for evaluating the resolution of an electron microscope, comprising a step of quantitatively evaluating the resolution and the resolution based on the analysis result. 3. A semiconductor manufacturing method for inspecting semiconductor products in a plurality of semiconductor manufacturing processes under the same conditions by using one or more scanning electron microscopes according to claim 1. 4. The method according to claim 2, wherein one or a plurality of scanning electron microscopes having the same adjusted performance are used.
A semiconductor manufacturing method for inspecting semiconductor products in a plurality of semiconductor manufacturing processes under the same conditions.