KR100239748B1 - Method for measuring accumulation of charge using electronic-microscope - Google Patents

Abstract

The present invention relates to a method for measuring the degree of charge accumulation of an electron microscope to confirm the degree of charge accumulation of a sample to improve measurement accuracy and to improve the reliability of an integrated circuit fabrication process.

An object of the present invention is to provide a method for measuring the degree of charge accumulation of an electron microscope to improve the measurement accuracy by evaluating the degree of charge accumulation of a sample generated in the electron microscope.

In order to achieve the above object, a method of measuring charge accumulation degree of an electron microscope according to the present invention scans electrons at a high magnification only in a central portion of a sample, and then scans electrons at a low magnification in all areas of the sample and calculates a difference in brightness between the two areas. In comparison, the degree of charge accumulation is accurately evaluated.

Description

Method for measuring accumulation of charge using electronic-microscope

The present invention relates to the charge accumulation of an electron microscope, and more particularly, to a method of measuring the charge accumulation degree of an electron microscope to improve the measurement accuracy and improve the reliability of an integrated circuit fabrication process by checking the charge accumulation degree of a sample. will be.

In general, when a person observes an object, the microstructure of about 0.1 mm or less is difficult to analyze. Therefore, in order to magnify and observe the smaller, an auxiliary means such as a magnifying glass or an optical microscope is used. However, optical microscopes, which are mainly used, have a limit to their magnification due to the wavelength of light, which is about 0.2 mm. The electron microscope was developed to overcome this limitation.

The electron microscope generates electrons in an electron gun section to form an image of an observation sample in a cathode ray tube (CRT), and scans a thinly collected electron beam on a sample. The beam is scanned on the fluorescent surface and the images are synchronized by synchronizing both. At this time, the electrons incident on the sample are lost due to heat generation of the placenta, and some of the sample members excite, ionize and scatter the sample signal, and various signals are emitted from the sample, mainly secondary electrons are used as detection signals. do. When measuring a sample with an electron microscope, a charge-up phenomenon by the home appliances occurs on the surface of the sample.

1 is a graph showing a secondary electron generation rate (yield) according to the change in the electron gun voltage of a general electron microscope.

As shown in FIG. 1, the secondary electron generation rate (%) increases as the electron gun voltage (V) increases and decreases after reaching the highest point. The secondary electron generation rate is '100' at the voltages of V1 and V2, the secondary electron generation rate is '100' or more at the voltage between V1 and V2, and the secondary electron generation rate is '100' or less at the voltage of V1 or lower or V2 or higher. Charges with an incidence of 100 or more are called positive charges and charges with an incidence of 100 or less are called negative charges.

The charge accumulation phenomenon varies depending on the material type of the sample and the conditions of the electron microscope, and the degree is slightly different according to the manufacturer and model name of the electron microscope.

It is difficult to observe the sample in the state of the charge accumulation phenomenon, and in particular, it is known that it is very difficult to measure the pattern dimension of the photoresist, which is the material most sensitive to the charge accumulation. Therefore, the pattern dimension of the photosensitive film which determines the line width of the metal wiring in the state of charge accumulation phenomenon is likely to be measured differently from the original dimension.

Despite the error in the pattern dimension of the photoresist film measured in the state of the charge accumulation phenomenon, only the color change of the image has been visually evaluated to evaluate the occurrence of the charge accumulation phenomenon.

However, conventionally, although the degree of charge accumulation varies due to an abnormality in the facilities of the electron microscope, the degree of charge accumulation has not been evaluated. Therefore, it is difficult to evaluate the effect of the charge accumulation on the integrated circuit fabrication process, so the conditions of the following processes after the measurement using an electron microscope cannot be accurately determined. As a result, an error occurs in the dimension of the final formed pattern, and a bad error occurs more than the allowable range, and product defects frequently occur.

In addition, although the degree of charge accumulation varies depending on the manufacturer or model name of the electron microscope, the degree of charge accumulation for each of the electron microscopes cannot be evaluated. Therefore, the equipment review of the electron microscope could not be made accurately.

Accordingly, it is an object of the present invention to provide a method for evaluating the degree of charge accumulation of an electron microscope to improve the measurement accuracy by evaluating the degree of charge accumulation of a sample generated in the electron microscope.

1 is a graph showing the secondary electron incidence (yield) according to the change in the electron gun voltage of a typical electron microscope.

Figure 2 is a cross-sectional structural view showing a sample applied to the method of measuring the charge accumulation degree of the electron microscope according to the present invention.

3 is a plan view showing two regions scanned at different magnifications on the sample surface of FIG.

4 is a graph showing negative charge accumulation for the sample of FIG.

FIG. 5 is a graph showing positive charge accumulation for the sample region of FIG.

<Description of the symbols for the main parts of the drawings>

DESCRIPTION OF SYMBOLS 1: Substrate 3: Photosensitive film 3a: 1st area | region 3b: 2nd area | region I1: Brightness of 1st area | region I2: Brightness of 2nd area | region

The method of evaluating the charge accumulation degree of the electron microscope according to the present invention for achieving the above object is to scan the electrons only in the central region of the sample, and then to scan the electrons in the entire region of the sample and compare the brightness difference between the two regions It is characterized by accurately assessing the degree of.

Hereinafter, a method of evaluating the charge accumulation degree of the electron microscope according to the present invention will be described in detail with reference to FIGS. 2 to 5.

First, as shown in FIG. 2, a substrate, for example, a cleaned single crystal silicon substrate 1 is prepared, and then a predetermined film, for example, a predetermined thickness, preferably on the entire surface of the substrate 1 using a photographic process. Prepares a sample by forming a photosensitive film 3 having a thickness of 10000 kPa.

Subsequently, as shown in FIG. 3 using an electron microscope (not shown), the second region 3b is scanned at a second magnification immediately after the first region 3a of the photosensitive film 3 is scanned at a first magnification. do. At this time, the first region 3a is an area where charge is accumulated and the second region 3b is an area where no charge is accumulated.

Here, the first region 3a is a central partial region of the photosensitive film 3, the second region 3b is the entire region of the photosensitive film 3, the first magnification is high magnification of 50K, and the second magnification is 20-30K. Low magnification of. In addition, the interval between the syringes of the first region 3a should be kept constant in order to prevent a change in charge accumulation due to variation in scanning time. In addition, the prepared sample should be measured within a certain time to prevent the photosensitive film of the sample from changing.

The profiles for the brightness of the scanned first region 3a and the second region 3b are shown as shown in FIG. 4 or as shown in FIG. 5.

That is, as shown in FIG. 4, the brightness I1 of the first region 3a is greater than the brightness I2 of the second region 3b because of the negative charge accumulation phenomenon. If the difference between the brightness I1 and the brightness I2 with respect to the brightness I1 is large, a large charge accumulation and a small difference between the brightness I1 and the brightness I2 mean that the charge accumulation is small.

As shown in FIG. 5, since the brightness I1 of the first region 3a appears to be smaller than the brightness I2 of the second region 3b, this is because of a positive charge accumulation phenomenon. If the difference between the brightness I1 and the brightness I2 with respect to the brightness I1 is large, a large charge accumulation and a small difference between the brightness I1 and the brightness I2 mean that the charge accumulation is small.

Therefore, scanning the two regions of the photosensitive film at different magnifications to confirm the degree of charge accumulation can accurately evaluate the effect on the following process.

On the other hand, the first region 3a is the entire region of the photosensitive film 3, the second region 3b is the central partial region of the photosensitive film 3, the first magnification is low magnification of 20-30K, and the second magnification is 50K. High magnification may be sufficient.

As described above, the method for evaluating the charge accumulation degree of the electron microscope according to the present invention is to scan the partial region and the entire region of the photosensitive film coated on the substrate at different magnifications and compare the brightness difference between the two regions to determine the degree of charge accumulation. Accurate confirmation can improve measurement accuracy. Therefore, by accurately confirming the degree of change of the charge accumulation of the sample, it is possible to detect an abnormality in the facilities of the electron microscope early and to improve the reliability of the integrated circuit manufacturing process.

Claims (9)

In the method for measuring the charge accumulation formed on the sample using an electron microscope, Forming a predetermined film on the surface of the sample, scanning the first area of the predetermined film at a first magnification and then scanning the second area at a second magnification, comparing the brightness of the two scanned areas Method of measuring the charge accumulation degree of the electron microscope comprising the step of measuring the charge accumulation of the sample. The method of claim 1, wherein the first magnification is high magnification and the second magnification is low magnification. The method of claim 2, wherein the first region is a partial region of the center of the predetermined film, and the second region is an entire region of the predetermined film. 4. The method of claim 3, wherein the first region is a charge accumulated region. The method of claim 1, wherein the first magnification is low magnification and the second magnification is high magnification. 6. The method of claim 5, wherein the first region is an entire region of the predetermined film and the second region is a partial region of the predetermined film. 7. The method of claim 6, wherein the second region is a charge accumulated region. The method of measuring charge accumulation degree of an electron microscope according to claim 2 or 5, wherein the high magnification is 50K magnification and the low magnification is 20-30K magnification. The method of measuring charge accumulation degree of an electron microscope according to claim 1, wherein said predetermined film is a photosensitive film.

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