JP7126914B2 - Electron microscope apparatus, control method for electron microscope apparatus - Google Patents

Description

The present invention relates to an electron microscope apparatus and a control method for an electron microscope apparatus.

In a scanning electron microscope (SEM), the amount of signal in an image obtained greatly affects the quality of the image.
In general, the level of the signal amount of the image is determined by the operator's intuition.

In addition, in scanning electron microscopes (SEM), in order to measure non-conductive samples without conductive coating, low-vacuum mode, in which measurements are performed in a low vacuum of several tens to several hundred Pa, is widely used. (See, for example, Patent Document 1.).
In the low vacuum mode, the number of gas molecules increases by creating a low vacuum of several tens to several hundred Pa. Then, the gas molecules are ionized by the electrons, become positive ions, reach the sample, and can neutralize the charge of the non-conductive sample.

In the low-vacuum mode, the signal amount changes subtly depending on the pressure value.
Also, the optimum pressure value for removing the charge differs depending on the sample and measurement conditions.

Conventionally, when measuring in low-vacuum mode, setting the optimum pressure value based on subtle changes in the amount of signal, or setting the optimum pressure value by judging the degree of electrification depends on the experience of the operator. has been subject to judgment.

JP 2005-285485 A

However, a certain level of skill is required for the operator to understand the sharpness of the image, the measurement accuracy, the degree of charging, and the signal amount of each detector, and to determine the optimum pressure conditions.
Therefore, the burden on the operator is heavy, and it is difficult for an inexperienced operator to determine the optimum conditions.

Furthermore, depending on conditions, such as simultaneous acquisition of a backscattered electron image and a low-vacuum secondary electron image, the degree of difficulty in determining optimum conditions is further increased.

In order to solve the above-described problems, the present invention provides an electron microscope apparatus and an electron microscope apparatus control method that can reduce the burden on the operator and determine optimum conditions even if the operator has little experience. It is.

The electron microscope apparatus of the present invention includes an electron beam irradiation unit for irradiating a sample with an electron beam, a sample chamber in which the sample is placed, and a detection unit for detecting the radiation emitted from the sample by the electron beam irradiation. a processing unit that processes radiation detection signals detected by the detection unit; an image generation unit that generates an image based on the detection signals processed by the processing unit; and a display unit that displays the image generated by the image generation unit. It has
In the electron microscope apparatus of the present invention, the processing section quantifies the signal amount of the detection signal, quantifies the charge state of the sample, and, based on the results obtained by the quantification, the sample chamber. Perform processing to determine the optimum internal pressure value.
In one electron microscope apparatus of the present invention, the detection unit detects electrons, and the processing unit creates a histogram using gradation regarding the detection signal of the electrons detected by the detection unit, and calculates the standard deviation from the histogram. By calculating the value, the signal amount is quantified.
In another electron microscope apparatus of the present invention, the detection unit detects X-rays, and the processing unit obtains the maximum energy of continuous X-rays based on the X-ray detection signal detected by the detection unit. Quantification of the state of charge of the sample is performed.

A control method for an electron microscope apparatus according to the present invention includes an electron beam irradiation unit that irradiates an electron beam onto a sample, a sample chamber in which the sample is placed, and radiation emitted from the sample by the irradiation with the electron beam is detected. a detection unit that processes the radiation detection signal detected by the detection unit; an image creation unit that creates an image based on the detection signal processed by the processing unit; and displays the image created by the image creation unit. A method for controlling an electron microscope apparatus having a display unit for displaying images.
Then, at each pressure within a predetermined pressure range, the detection unit detects a radiation detection signal emitted from the sample, and based on the radiation detection signal detected by the detection unit at each pressure, the processing unit detects Quantification of the signal amount of the signal and quantification of the charged state of the sample are performed.
Furthermore, the processing unit determines the optimum pressure value inside the sample chamber based on the results obtained by performing the quantification.
Then, in a state in which the pressure inside the sample chamber is set to the determined optimum pressure value, the detection unit detects radiation, and the image creation unit creates an image of the sample.
In one control method for an electron microscope apparatus of the present invention, the detection unit detects electrons, and the processing unit creates a histogram using gradation regarding a detection signal of the electrons detected by the detection unit, and from the histogram The amount of signal is quantified by calculating the value of the standard deviation.
In another method of controlling an electron microscope apparatus of the present invention, the detector detects X-rays, and the processor determines the maximum energy of continuous X-rays based on the X-ray detection signal detected by the detector. Thus, the charge state of the sample is quantified.

According to the electron microscope apparatus of the present invention and the control method of the electron microscope apparatus of the present invention described above, the optimum pressure value can be automatically determined in consideration of the signal amount of the detection signal and the charged state of the sample. can. Therefore, even a person unfamiliar with the electron microscope apparatus can perform observation at the optimum pressure value.
This greatly reduces the burden on the operator, reduces human error, and improves the quality of measurement results.

1 is a schematic configuration diagram of an embodiment of an electron microscope apparatus of the present invention; FIG. 2 is a flowchart of a method for determining optimum pressure values for the electron microscope apparatus of FIG. 1; FIG. 10 is a diagram showing the relationship between the irradiation current and the standard deviation of the histogram in each of the three fields of view of the sample of Experiment 1; A is a backscattered electron image obtained at a pressure of 10 Pa in Experiment 2. FIG. B is a backscattered electron image obtained at a pressure of 40 Pa in Experiment 2; FIG. 10 is a diagram showing the relationship between the pressure in Experiment 2 and the number of pixels at the 256th gradation; 4 is a diagram showing the relationship between pressure and the standard deviation of a histogram obtained as a result of quantifying the signal amount of the backscattered electron detector in Example 1. FIG. 4 is a diagram showing the relationship between pressure and standard deviation of a histogram obtained as a result of quantifying the signal amount of the secondary electron detector in Example 1. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in the following order with reference to the drawings.
1. Outline of the present invention2. Embodiment 3. Example

<1. Outline of the present invention>
First, the outline of the present invention will be explained.

The electron microscope apparatus of the present invention includes an electron beam irradiation unit for irradiating a sample with an electron beam, a sample chamber in which the sample is placed, and a detection unit for detecting the radiation emitted from the sample by the electron beam irradiation. and a processing unit that processes a radiation detection signal detected by the detection unit.
Further, the electron microscope apparatus of the present invention includes an image creating section that creates an image based on the detection signal processed by the processing section, and a display section that displays the image created by the image creating section.
In the electron microscope apparatus of the present invention, the processing unit quantifies the signal amount of the detection signal and the charged state of the sample based on the radiation detection signal, and is obtained by performing the quantification. Based on the result obtained, the optimum pressure value inside the sample chamber is determined.

In the electron microscope apparatus described above, the electron beam irradiation section and the sample chamber constitute the electron microscope main body.
The detector is provided in the sample chamber and detects radiation emitted from the sample.
The processing section, image forming section, display section, and control section can be integrated with the electron microscope main body, but can be provided separately from the electron microscope main body.
Further, the detection unit and the processing unit, the processing unit, the image generation unit and the control unit, and the image generation unit and the display unit can be connected by wire such as wiring or wirelessly. As a result, signals such as detection signals and data signals can be transmitted between the connected units.

The electron microscope apparatus of the present invention is configured to irradiate the sample with an electron beam from the electron beam irradiation unit and detect the radiation emitted from the sample by the detection unit, so it corresponds to the scanning electron microscope (SEM) described above. do.

Further, in the electron microscope apparatus of the present invention, the processing unit quantifies the signal amount of the radiation detection signal and the charged state of the sample, and based on the results obtained by the quantification, the sample Processing is performed to determine the optimum pressure value inside the chamber.
As a result, the optimum pressure value inside the sample chamber is determined according to the radiation detection signal and the charged state of the sample.

Then, the pressure inside the sample chamber is set to the determined pressure value, the sample is irradiated with an electron beam, the radiation emitted from the sample is detected by the detector, and an image is obtained based on the detection signal detected by the detector. An image can be created in the creation unit. At this time, the sample is in an uncharged state and the signal amount is sufficiently large, so that a good image of the sample can be obtained in the low-vacuum mode for non-conductive samples.
Therefore, even those who are unfamiliar with electron microscopes can observe at the optimum pressure value, which greatly reduces the burden on the operator, reduces human error, and improves the quality of measurement results. .

More preferably, the electron microscope apparatus further comprises a control unit for controlling the pressure inside the sample chamber, and the control unit controls the inside of the sample chamber to the optimum pressure value determined by the processing unit. . With this configuration, the control unit automatically controls the pressure inside the sample chamber to the optimum pressure value determined by the processing unit, further reducing the burden on the operator.

As a specific configuration of the electron microscope apparatus, for example, the electron microscope apparatus may be configured to have an "automatic setting of optimum measurement pressure" button.
In the case of this configuration, by pressing the "automatic setting of the optimum measurement pressure" button, from the process of detecting radiation such as electrons at each pressure in a predetermined pressure range to the process of the control unit controlling the pressure value to the optimum value , so that each process is automatically executed.

Instead of the configuration in which the controller automatically controls the pressure inside the sample chamber as described above, the configuration may be such that the pressure inside the sample chamber is manually controlled. For example, the optimal pressure value determined by the processing unit is displayed on the display unit, and the operator sees the optimal pressure value displayed on the display unit and determines the pressure inside the sample chamber to the optimal pressure value. should be set to a value. The controller then controls the pressure inside the sample chamber to the optimum pressure value set by the operator.

As described above, the electron microscope apparatus of the present invention can obtain a good image of the sample in the low vacuum mode for non-conductive samples, greatly reducing the burden on the operator, reducing human error, and improving the measurement results. It has the effect of improving quality. Therefore, the electron microscope apparatus of the present invention can be applied to an electron microscope apparatus used in both high vacuum mode and low vacuum mode, or an electron microscope apparatus used only in low vacuum mode.

In the electron microscope apparatus of the present invention, the radiation emitted from the sample detected by the detection unit includes, for example, electrons such as backscattered electrons and secondary electrons, and X-rays.
The detection unit is provided with detectors corresponding to the radiation to be detected.
For example, when detecting backscattered electrons, secondary electrons, and X-rays, a backscattered electron detector, a secondary electron detector, and an X-ray detector are provided.
Further, for example, when only backscattered electrons are to be detected, a configuration in which only a backscattered electron detector is provided can be employed.

Then, using the backscattered electron detection signal detected by the backscattered electron detector, the processing unit can quantify the signal amount and quantify the charged state of the sample.
In addition, using the secondary electron detection signal detected by the secondary electron detector, the processing unit can quantify the signal amount and quantify the charged state of the sample.
In addition, the charged state of the sample can be quantified in the processing unit using the X-ray detection signal detected by the X-ray detector.

When the detection unit has a configuration in which a plurality of types of detectors are provided, the processing unit uses detection signals from the plurality of types of detectors, quantifies the signal amount from the detection signals, and detects the sample Quantification of the state of charge can be performed to determine the optimum pressure value.
For example, by using the detection signal of reflected electrons and the detection signal of secondary electrons, the signal amount of each electron is quantified, and the detection signal of reflected electrons or the detection signal of X-rays is used to determine the charging of the sample. It is possible to quantify the state.

(Optimal pressure value setting in low vacuum mode)
Next, setting the optimum pressure value in the low vacuum mode will be described in more detail.
In the low-vacuum mode, the optimum pressure value that can remove charge differs depending on the sample and measurement conditions.
Furthermore, the backscattered electron detector and the low-vacuum mode secondary electron detector differ in the pressure value at which a large amount of signal is obtained in each detector.
In terms of electrification, the higher the pressure, the more positively charged nitrogen molecules ionized by the electron beam, which electrically neutralizes the surface of the charged sample. Become stronger.
Considering the primary electron beam, the lower the pressure, the less the scattering, and the sharper the image and the more accurate the analysis by EDS (Energy Dispersive X-ray Spectrometer).
Considering the backscattered electron detector, the lower the pressure, the easier it is for the signal to reach the detector and the greater the amount of signal.
Considering the secondary electron detector for low-vacuum mode, the secondary electrons emitted from the sample are amplified by the electron avalanche phenomenon using nitrogen molecules in the sample chamber, so if the pressure is too low, the signal will not be sufficiently amplified. On the other hand, if the pressure is too high, it will be difficult for the signal to reach the detector, and the amount of signal will decrease. Therefore, the optimum pressure value lies in between.

In the processing unit, the optimum pressure value in the low-vacuum mode is determined in consideration of changes in pressure such as the amount of signal and the state of electrification.
As the optimum pressure value, a pressure that suppresses electrification of the sample and obtains a large amount of signal is selected.
Then, in the processing unit, the signal amount of the detection signal and the charge state of the sample are quantified, and based on the results obtained by the quantification, the optimum pressure in the low-vacuum mode is determined. Perform processing to determine the value.

Images obtained by an electron microscope include a backscattered electron image based on a backscattered electron detection signal and a secondary electron image based on a secondary electron detection signal.
If only one of these images is to be acquired, select the pressure that maximizes the amount of signal for that image within the range of pressures that suppress charging of the specimen as the optimum pressure value. do.
When acquiring both a backscattered electron image and a secondary electron image, there are two methods: selecting the optimal pressure value independently for each image, and selecting the same pressure as the optimal pressure value. , any method is possible.
By adopting the method of selecting the optimum pressure value for the same pressure, it becomes possible to simultaneously acquire both the backscattered electron image and the secondary electron image at that pressure, but the optimum pressure value can be selected independently. The signal amount may be lower than the selected method.
In the method of selecting the same pressure as the optimum pressure value, the optimum pressure value of one of the images may be selected preferentially, or the intermediate pressure value between the optimum pressure values of both images may be selected. is also possible. At this time, the operator can decide in advance which pressure value is to be selected as the optimum pressure value.

(Method for quantifying signal amount of detected signal)
Quantification of the signal amount of the detection signal can be performed, for example, by the following method.
(Procedure 1) Set measurement conditions and contrast.
(Procedure 2) Brightness (luminance) is adjusted so that the peak of the black-and-white gradation histogram is near the center. For example, if the horizontal axis is a histogram of 256 gradations and the vertical axis is a histogram of the number of pixels, the peak of the histogram should be around 128 gradations. Note that the gradation of the histogram is not limited to 256 gradations, and other gradations are possible.
(Procedure 3) Electrons emitted from the sample are detected under the adjusted brightness (luminance) condition, and an image is created based on the detected signal.
(Procedure 4) A black-and-white gradation histogram is obtained from the created image.
(Procedure 5) A value of standard deviation is obtained from the obtained histogram.

Since the value of the standard deviation obtained in this manner has a correlation with the amount of signal, the amount of signal can be quantified from the value of the standard deviation.
In (Procedure 3) and (Procedure 4), an image based on the detection signal was created, and a black-and-white gradation histogram was obtained from the created image. It is also possible to obtain a histogram of gradations of . In either case of creating an image and obtaining a histogram from the image or obtaining a histogram directly from the detection signal, a histogram relating to the detection signal is obtained.

Then, by changing the pressure inside the sample chamber and creating an image at each pressure and quantifying the signal amount, the relationship between the pressure and the signal amount can be obtained. The optimum pressure value can be determined using this relationship between pressure and signal amount.

Note that the method for quantifying the signal amount of the detection signal is not limited to the method described above. Other methods can be employed as long as they can quantify the signal amount of the detection signal.

(Experiment 1)
Here, in order to confirm that there is a correlation between the value of the standard deviation of the histogram and the amount of signal, the irradiation current (PC: Probe Current) was changed to examine the change in the value of the standard deviation.

Zinc oxide powder was used as a sample.
The measurement conditions were as follows.
Detector: Backscattered electron detector BED-C, acceleration voltage: 5 kV, magnification: 10,000 times, irradiation current (PC: Probe Current): 0 to 40 (relative value), working distance: 10 mm, pressure value: 10 ^- About ² Pa (high vacuum mode), aperture: 20 μm, load current (LC): 100 μA, number of pixels: 2560×1920, scanning method: slow scan (no CF), scanning time for one frame: 80 seconds

Under the above measurement conditions, the irradiation current (PC) was varied from 0 to 40 at intervals of 5 (relative values), and an image (backscattered electron image) was acquired at each irradiation current. When acquiring the image, the set value of contrast was maximized in order to fix it, and the peak position of the distribution was adjusted to the vicinity of the center by adjusting the brightness (luminance).
Then, the signal amount of the obtained image was quantified. Specifically, the standard deviation was obtained from the distribution of the 256-gradation histogram of the image.
Under the above conditions, even if the contrast is maximum, the amount of signal is small, so the image does not become saturated (brightness is blown out) and exhibits a shape close to a normal distribution.

Then, images were acquired for three different fields of view of the sample (field of view 1, field of view 2, and field of view 3), and the signal amount of the acquired images was quantified.

FIG. 3 shows the relationship between the irradiation current and the standard deviation of the histogram for each of three different fields of view (fields 1, 2, and 3).
As shown in Fig. 3, the standard deviation of the histogram also increases with an increase in the irradiation current, corresponding to the increase in the signal amount with an increase in the irradiation current, and the difference in the signal amount is quantified by the standard deviation of the histogram. I know it's done.
Moreover, it can be seen from FIG. 3 that there is no significant change even if the field of view changes.

(Method 1 for quantification of charged state)
Quantification of the charged state of the sample can be performed, for example, by the following method.
(Procedure 1) Set measurement conditions and contrast.
(Procedure 2) Brightness (luminance) is adjusted so that the peak of the black-and-white gradation histogram is near the center. For example, if the horizontal axis is a histogram of 256 gradations and the vertical axis is a histogram of the number of pixels, the peak of the histogram should be around 128 gradations. Note that the gradation of the histogram is not limited to 256 gradations, and other gradations are possible.
(Procedure 3) Electrons emitted from the sample are detected under the adjusted brightness (luminance) condition, and an image is created based on the detected signal.
(Procedure 4) A black-and-white gradation histogram is obtained from the created image.
(Procedure 5) From the obtained histogram, the number of pixels with the brightest contrast is obtained. For example, in the case of a histogram of 256 gradations, the number of brightest pixels in the 256th gradation is obtained.

Since the value of the number of pixels with the brightest contrast obtained in this way correlates with the state of charge, the state of charge can be quantified from the value of the number of pixels with the brightest contrast. If the value of the number of pixels with the brightest contrast is sufficiently small or close to zero, it can be considered that charging is suppressed.
In (Procedure 3) and (Procedure 4), an image based on the detection signal was created, and a black-and-white gradation histogram was obtained from the created image. It is also possible to obtain a histogram of gradations of . In either case of creating an image and obtaining a histogram from the image or obtaining a histogram directly from the detection signal, a histogram relating to the detection signal is obtained.

By changing the pressure inside the sample chamber and creating an image at each pressure to quantify the charge state of the sample, the relationship between the pressure and the charge state of the sample can be obtained. The pressure range in which charging is suppressed can be seen. For example, the pressure range in which the number of pixels with the brightest contrast is sufficiently small or close to zero can be set as the pressure range in which charging is suppressed.

The method for quantifying the charged state of the sample is not limited to the method described above. Other methods can be employed as long as they can quantify the charge state of the sample.

(Method 2 for quantification of charged state)
In the above-described method, an image obtained by detecting electrons is used to quantify the charged state of the sample.
On the other hand, as another method of quantifying the charged state of the sample, it is also possible to use the detection result obtained by detecting X-rays.

When using detection results obtained by detecting X-rays, the state of the sample can be quantified by, for example, the following method.
(Procedure 1) Set the measurement conditions.
(Procedure 2) X-rays emitted from the sample are detected to obtain an energy distribution based on the detected signals.
(Procedure 3) A terminal value (maximum energy value) of continuous X-rays is obtained from the obtained energy distribution.
The terminal value (maximum energy value) of the continuous X-rays obtained in this manner correlates with the charged state of the sample. The state of charge can be quantified.

Then, by changing the pressure inside the sample chamber and obtaining the energy distribution of the X-rays at each pressure and quantifying the charged state of the sample, the relationship between the pressure and the charged state of the sample can be obtained. Therefore, the pressure range in which charging is suppressed can be known.

(Experiment 2)
Here, it was confirmed that the charge state of the sample can be quantified by each of the methods for quantifying the charge state of the sample described above.

First, in order to confirm that the charging state of the sample correlates with the change in the number of brightest contrast pixels in the histogram, the change in the value of the brightest contrast standard deviation was examined by changing the pressure.

Filter paper was used as a sample.
The measurement conditions were as follows.
Detector: backscattered electron detector BED-C, acceleration voltage: 10 kV, magnification: 100 times, irradiation current: 150 pA, working distance: 10 mm, pressure: 10 to 150 Pa, number of pixels: 2560 × 1920, scanning method: slow scan ( No CF), scan time for 1 frame: 40 seconds

Under the above measurement conditions, the pressure was changed in the range of 10 to 150 Pa, and an image (backscattered electron image) was acquired at each pressure. When acquiring the images, the visual field and contrast settings were fixed at each pressure, and the peak position of the distribution was adjusted to the vicinity of the center by adjusting the brightness.
Then, the charged state of the sample was quantified from the obtained image. Specifically, the number of pixels at the 256th gradation, which is the brightest in the histogram of the image, was obtained.

A backscattered electron image obtained at a pressure of 10 Pa is shown in FIG. 4A, and a backscattered electron image obtained at a pressure of 40 Pa is shown in FIG. 4B.
FIG. 5 shows the relationship between the pressure and the number of pixels at the 256th gradation.
At a pressure of 10 Pa in FIG. 4A, the backscattered electron image has several bright spots, indicating that the film is charged. On the other hand, at the pressure of 40 Pa in FIG. 4B, the backscattered electron image has almost no high-brightness portions seen in FIG. 4A, and it is considered that charging is suppressed.
Also, from FIG. 5, it can be seen that as the pressure increases, the number of pixels in the 256th gradation of the image decreases, and charging is suppressed. At a pressure of about 40 Pa, the number of pixels of the 256th gradation of the image becomes sufficiently small, and it can be seen that charging is substantially suppressed.

In addition, in order to confirm that the above-described quantification of the charged state of the sample is effective, an energy dispersive X-ray spectrometer (EDS) was used as another quantification method, and the pressure value was set in the range of 10 to 150 Pa. , and continuous X-rays were measured at each pressure value.
However, when the measurement was performed using the same sample and under the same measurement conditions as the acquisition of the image described above, only about 500 counts of X-rays per second could be acquired, and the number of counts was small.
Therefore, the time was extended to 500 seconds, and the sample and other measurement conditions were the same as those for obtaining the above-described image. Then, the terminal value (maximum energy value) was examined for the continuous X-rays obtained by the measurement.

Table 1 below shows the relationship between the pressure (Pa) and the terminal value (eV) of continuous X-rays measured using EDS.

As can be seen from Table 1, similarly to the change in the number of pixels at the 256th gradation shown in FIG.
That is, it was confirmed that the charge state of the sample can be quantified by the number of pixels in the 256th gradation shown in FIG. It was confirmed that the state can be quantified.

(Inspection method for electron microscope device)
The electron microscope apparatus according to the present invention can be inspected by utilizing the fact that the signal amount can be quantified based on the detection signal acquired by the detector.

An electron microscope apparatus to be inspected includes an electron beam irradiation unit that irradiates a sample with an electron beam, a sample chamber in which the sample is placed, and radiation emitted from the sample by the electron beam irradiation is detected. A detection unit, a processing unit that processes radiation detection signals detected by the detection unit, an image creation unit that creates an image based on the detection signal processed by the processing unit, and an image created by the image creation unit is displayed. It is configured to have a display unit.

Then, the inspection is performed by the method described below.
(Procedure 1) First, radiation is detected and the signal amount of the detection signal is quantified in advance under measurement conditions for a reference sample, and a reference value for the signal amount of the detection signal is set.
It is desirable that the measurement for setting the reference value is performed when the electron microscope apparatus is in good and stable condition, such as when the electron microscope apparatus is delivered. Then, for example, in the case of delivery, the delivery worker can respond.
(Procedure 2) During the inspection, the reference sample used in (Procedure 1) is used to detect radiation and quantify the signal amount of the detection signal under the same measurement conditions as in (Procedure 1). Then, the processing unit compares the value obtained by quantification with the reference value set in (Procedure 1) and determines whether or not it is within a predetermined normal value range.
If the values obtained are within the predetermined normal range, the device is used normally.
If the value obtained is outside the predetermined normal range, the device is serviced. In this case, the display may be configured to display a notification recommending maintenance.

In this way, the signal amount is quantified, and the value obtained by quantification is compared with the reference value to determine whether or not it is within a predetermined range of normal values. Maintenance can be performed at appropriate timing. As a result, it is possible to maintain the performance of the electron microscope apparatus and operate it efficiently.

In this inspection method, either one or both of the backscattered electron detector and the secondary electron detector may be used for quantifying the signal amount. (Procedure 2) may be performed using the same detector as that used in (Procedure 1).

<2. Embodiment>
Next, specific embodiments of the present invention will be described.
FIG. 1 shows a schematic configuration diagram of an embodiment of an electron microscope apparatus of the present invention.

An electron microscope apparatus 1 shown in FIG.
Among them, the body of the electron microscope is constituted by the lens barrel 2 and the sample chamber 3 .
An electron gun 11 is provided above the lens barrel 2, and the lens barrel 2 and the electron gun 11 constitute an electron beam irradiation section for irradiating the sample with an electron beam.
The sample chamber 3 is provided with a backscattered electron detector 13 and a secondary electron detector 14 as detectors for detecting electrons in the radiation emitted from the sample. A sample 12 to be measured is placed inside the sample chamber 3 .
In addition, the sample chamber 3 is provided with an exhaust pump 4 and a gas introduction section 5 to control the intake and exhaust of the sample chamber 3 . The gas introduction part 5 may be a gas introduction valve that simply introduces the air into the sample chamber 3 .
Further, the electron microscope apparatus 1 includes a processing section 21 , a control section 22 , an image creation section 23 and a display section 24 .

In this electron microscope apparatus 1, an electron beam EB emitted from an electron gun 11 is irradiated onto a sample 12 arranged in a sample chamber 3. As shown in FIG. Backscattered electrons and secondary electrons emitted from the sample 12 are detected by a backscattered electron detector 13 and a secondary electron detector 14, respectively.

If the X-rays emitted from the sample 12 are also to be detected, the electron microscope apparatus 1 is further provided with an X-ray detector in the sample chamber 3 .

The processing unit 21 processes detection signals based on electrons detected by the backscattered electron detector 13 and the secondary electron detector 14, respectively. The processing unit 21 also quantifies the signal amount and the charged state of the sample 12 based on the detection signal. Then, the processing unit 21 determines the optimum pressure value based on the quantification of the signal amount and the quantification of the charged state of the sample 12 .

The control unit 22 controls the operations of the exhaust pump 4 and the gas introduction unit 5 to adjust the internal pressure of the sample chamber 3 . Although not shown, the control unit 22 also controls the coils, lenses, etc. within the lens barrel 2 .
Based on the optimum pressure value determined by the processing unit 21, the control unit 22 controls the operation of the exhaust pump 4 and the gas introduction unit 5 while detecting the internal pressure of the sample chamber 3 with a pressure sensor or the like (not shown). Thereby, the pressure inside the sample chamber 3 can be automatically controlled to an optimum pressure value.

The image creating section 23 creates an image based on the detection signal processed by the processing section 21 .
The display section 24 displays the image created by the image creating section 23 .
By observing the image displayed on the display unit 24, the state of the sample can be observed.

In addition to the image created by the image creation unit 23, the display unit 24 may display various information such as the state of the electron microscope apparatus 1. FIG. For example, a warning may be displayed when there is an abnormality.

The processing unit 21, the control unit 22, and the image creation unit 23 can be configured by a computer (for example, a microcomputer or a personal computer) that executes a computer program.
The processing unit 21 and the control unit 22 are connected to the main body of the apparatus, which includes the lens barrel 2 and the sample chamber 3, by wire such as wiring or wirelessly.
Also, the display unit 24 is configured to be connected to the image creation unit 23 by wire or wirelessly.

Next, a specific method for determining the optimum pressure value in the electron microscope apparatus 1 of this embodiment will be described.
A flow chart of one form of method for determining the optimum pressure value is shown in FIG.

In the flowchart shown in FIG. 2, first, in step S11, measurement conditions and image contrast are set. Measurement conditions include, for example, irradiation current, acceleration voltage, magnification, scan time, and the like.

Next, in step S12, a pressure range and a pressure interval are set.
Note that if the optimum pressure value is always determined in the same pressure range and pressure interval, this step S12 is omitted.

Next, in step S13, the pressure in the sample chamber 3 is set to the minimum pressure within the set pressure range.

Next, in step S14, brightness is adjusted. Specifically, by adjusting the brightness, the peak of the black-and-white gradation histogram is brought to the vicinity of the center. For example, if the histogram has 256 gradations, the peak should be around 128 gradations.

Next, in step S15, an image is acquired. Specifically, electrons are detected by the detector, the detection signal is processed by the processing unit 21 , and an image is generated by the image generation unit 23 based on the detection signal processed by the processing unit 21 . As a detector, either or both of the backscattered electron detector 13 and the secondary electron detector 14 of FIG. 1 are used.
Note that the image created by the image creation unit 23 is temporarily stored in a storage unit (memory or the like) not shown.

Next, in step S16, it is determined whether the pressure is the maximum pressure.
If the pressure is not the maximum pressure, go to step S17.
If the pressure is the maximum pressure, go to step S18.

In step S17, the pressure is increased by one step according to the pressure interval set in step S12, and the process returns to step S14.
Then, the brightness is adjusted again in step S14 with the pressure increased by one step.

In step S18, the signal amount is quantified from the acquired image. The acquired image is read out from the storage section in which it was temporarily stored, and used for quantification of the signal amount.
For example, as described above, the signal amount is quantified by obtaining the standard deviation of the histogram. By quantifying the amount of signal for each image acquired at each pressure, the relationship between pressure and amount of signal is obtained.

Next, in step S19, the charged state is quantified from the acquired image. Specifically, for example, as described above, the charging state is quantified by determining the number of pixels with the brightest contrast in the histogram. By quantifying the state of charge for each image acquired at each pressure, the relationship between pressure and signal amount can be obtained.

Next, in step S20, from the quantified state of charge, that is, the relationship between the pressure and the state of charge obtained in the quantification at step S19, a pressure range in which charging is suppressed is obtained.
For example, as described above, the range in which the number of pixels with the brightest contrast in the histogram is sufficiently small or close to zero is defined as the pressure range in which charging is suppressed.

Note that the steps S18 to S20 are not limited to the order of the flowchart shown in FIG. Other orders (eg, S19->S18->S20, S19->S20->S18, etc.) are also possible.

Next, in step S21, from the relationship between the pressure and the signal amount obtained in the quantification in step S18, the pressure obtained in step S20 that is within the pressure range that suppresses charging and that maximizes the signal amount is determined. Ask.

In this way, it is possible to obtain the pressure at which charging is suppressed and the signal amount is maximized.
The control unit 22 controls the pressure inside the sample chamber 3 by instructing the control unit 22 from the processing unit 21 to use this pressure as the optimum pressure value. In this way, the sample 12 can be observed and measured while the sample chamber 3 is controlled to the optimum pressure value.
As a result, the pressure inside the sample chamber 3 is automatically controlled to the optimum pressure, so that individual differences due to operator experience are eliminated, and even an inexperienced operator can perform good measurements.

(Modification)
In the flowchart shown in FIG. 2, the case of increasing the pressure from the minimum value to the maximum value of the pressure range has been described, but it is also possible to decrease the pressure from the maximum value to the minimum value of the pressure range. In that case, instead of step S13 in FIG. 2, a step of setting the pressure to the maximum pressure is inserted, step S16 is replaced with a step of determining whether the pressure is the minimum pressure, and step S17 is replaced with a step of lowering the pressure by one step. .

In the flowchart shown in FIG. 2, first, images are acquired with a detector for all pressures in the pressure range, and the signal amount and the charging state are quantified from the acquired images. The order of acquisition and quantification of is not limited to the order of the flow chart of FIG.
For example, acquisition of images at each pressure and quantification from the images acquired at each pressure can be performed independently in parallel.
Further, for example, it is possible to perform image acquisition and quantification from the acquired image at one pressure, and then change to the next pressure to acquire an image and perform quantification from the acquired image. In this case, the flow chart has, for example, steps S18 and S19 in FIG. 2 moved between steps S15 and S16.

In the flowchart of FIG. 2, an image is acquired, and the quantification of the signal amount and the sample is performed from the acquired image. That is, an image is created based on the detection signals detected by the detectors 13 and 14, a histogram is obtained from the created image, and quantification is performed.
In the case of quantifying an image created based on the detection signal in this way, in order to share the image creation process, the same image as the image created by observing and measuring the sample at the optimum pressure value should be used. It is desirable to create an image in the range.

On the other hand, it is also possible to directly quantify the signal amount and the charged state of the sample from the detection signal without creating an image. In the case of direct quantification from the detection signal in this way, it is also possible to set the range of the detection signal to be used independently of the range in which the image is created. A histogram can then be created directly from the detected signals within that range to obtain the value of the standard deviation of the histogram and the number of pixels with the brightest contrast in the histogram.

<3. Example>
Next, as an example according to the present invention, quantification of the signal amount and quantification of the charged state of the sample were performed to obtain the optimum pressure value.

(Example 1)
In the measurement of Experiment 2 described above, an image is acquired by the secondary electron detector 14 at the same time as the backscattered electron detector 13 (BED). was also quantified.
FIG. 5 shows the result of quantifying the charging state from the image acquired by the backscattered electron detector 13. FIG. As shown in FIG. 5, the pressure range in which charging is suppressed is the pressure range of 40 Pa or more.
Further, the standard deviation of the histogram was obtained from the same histogram in which the number of pixels at the 256th gradation shown in FIG.
Furthermore, the standard deviation of the histogram was obtained from the image acquired by the secondary electron detector 14 to quantify the signal amount of the secondary electron detector 14 .

FIG. 6 shows the relationship between the pressure and the standard deviation of the histogram as a result of quantifying the signal amount of the backscattered electron detector 13 .
It can be seen from FIG. 6 that the lower the pressure, the larger the standard deviation and the larger the signal amount.
In the pressure range of 40 Pa or higher where charging is suppressed, the standard deviation is the largest at the lowest pressure of 40 Pa within the pressure range, and it is presumed that the signal amount is also the largest.
Therefore, it can be seen from the backscattered electron image that the optimum pressure is 40 Pa.

FIG. 7 shows the relationship between the pressure and the standard deviation of the histogram as a result of quantifying the signal amount of the secondary electron detector 14 .
From FIG. 7, it is presumed that the standard deviation value increases from 40 to 80 Pa, and the signal amount correlated with the standard deviation value also increases. Moreover, when the pressure is increased further, the value of the standard deviation becomes smaller, and it is presumed that the amount of signal correlated with the value of the standard deviation also decreases.
From the results of FIG. 7, it is presumed that, in the pressure range of 40 Pa or more where charging is suppressed, the standard deviation is the largest at a pressure of 80 Pa, and the signal amount is also the largest.
Therefore, it can be seen from the secondary electron image that the optimum pressure is 80 Pa.

In observation and measurement of the sample after setting the optimum pressure value, if it is desired to simultaneously acquire images with the backscattered electron detector 13 and the secondary electron detector 14, either the backscattered electron image or the secondary electron image is selected. The optimum pressure value (40 Pa or 80 Pa) is prioritized, or an intermediate pressure value (eg, 60 Pa) is used.

(Example 2)
Instead of the image acquired by the backscattered electron detector 13 employed in Example 1, continuous X-rays detected using EDS were employed, and the charge state of the sample was quantified by the terminal value of the continuous X-rays. .
In this example, the same sample as in Experiment 2 was used and the same measurement conditions as in Experiment 2 were used.

The results of quantification of the charged state of the samples are shown in Table 1 above.
From the results in Table 1, it can be seen that charging is suppressed at 40 Pa.
That is, by judging from the terminal value of the continuous X-rays, similarly to the first embodiment, it is possible to obtain the pressure range in which charging is suppressed.

1 electron microscope apparatus, 2 lens barrel, 3 sample chamber, 4 exhaust pump, 5 gas introduction section, 11 electron gun, 12 sample, 13 backscattered electron detector, 14 secondary electron detector, 21 processing section, 22 control section, 23 image creation unit, 24 display unit, EB electron beam

Claims (5)

an electron beam irradiation unit for irradiating the sample with an electron beam;
a sample chamber in which the sample is placed;
a detection unit that detects radiation emitted from the sample by being irradiated with the electron beam;
a processing unit that processes a detection signal of the radiation detected by the detection unit;
an image creation unit that creates an image based on the detection signal processed by the processing unit;
A display unit for displaying the image created by the image creation unit,
The processing unit quantifies the signal amount of the detection signal, quantifies the charged state of the sample, and optimizes the pressure value inside the sample chamber based on the results obtained by the quantification. perform processing to determine
The detection unit detects electrons,
The processing unit creates a histogram using gradation for the electron detection signal detected by the detection unit, and calculates a standard deviation value from the histogram, thereby quantifying the signal amount.
Electron microscope equipment. an electron beam irradiation unit for irradiating the sample with an electron beam;
a sample chamber in which the sample is placed;
a detection unit that detects radiation emitted from the sample by being irradiated with the electron beam;
a processing unit that processes a detection signal of the radiation detected by the detection unit;
an image creation unit that creates an image based on the detection signal processed by the processing unit;
A display unit for displaying the image created by the image creation unit,
The processing unit quantifies the signal amount of the detection signal, quantifies the charged state of the sample, and optimizes the pressure value inside the sample chamber based on the results obtained by the quantification. perform processing to determine
The detection unit detects X-rays,
The processing unit quantifies the charged state of the sample by obtaining the maximum energy of continuous X-rays based on the X-ray detection signal detected by the detection unit.
Electron microscope equipment. Further comprising a control section for controlling the pressure inside the sample chamber, wherein the control section controls the inside of the sample chamber to the optimum pressure value determined by the processing section . Electron microscope apparatus as described. an electron beam irradiation unit for irradiating the sample with an electron beam;
a sample chamber in which the sample is placed;
a detection unit that detects radiation emitted from the sample by being irradiated with the electron beam;
a processing unit that processes a detection signal of the radiation detected by the detection unit;
an image creation unit that creates an image based on the detection signal processed by the processing unit;
In an electron microscope apparatus comprising a display section for displaying an image created by the image creation section,
At each pressure within a predetermined pressure range, the detection unit detects a detection signal of the radiation emitted from the sample,
Based on the radiation detection signal detected by the detection unit at each pressure, the processing unit quantifies the signal amount of the detection signal and quantifies the charging state of the sample,
Furthermore, the processing unit determines the optimum pressure value inside the sample chamber based on the results obtained by performing the quantification,
The detection unit detects electrons,
The processing unit creates a histogram using gradation for the electron detection signal detected by the detection unit, and calculates a standard deviation value from the histogram, thereby quantifying the signal amount,
A control method for an electron microscope apparatus, wherein the radiation is detected by the detection unit and an image of the sample is created by the image creation unit while the pressure inside the sample chamber is set to the determined optimum pressure value. an electron beam irradiation unit for irradiating the sample with an electron beam;
a sample chamber in which the sample is placed;
a detection unit that detects radiation emitted from the sample by being irradiated with the electron beam;
a processing unit that processes a detection signal of the radiation detected by the detection unit;
an image creation unit that creates an image based on the detection signal processed by the processing unit;
In an electron microscope apparatus comprising a display section for displaying an image created by the image creation section,
At each pressure within a predetermined pressure range, the detection unit detects a detection signal of the radiation emitted from the sample,
Based on the radiation detection signal detected by the detection unit at each pressure, the processing unit quantifies the signal amount of the detection signal and quantifies the charging state of the sample,
Furthermore, the processing unit determines the optimum pressure value inside the sample chamber based on the results obtained by performing the quantification,
The detection unit detects X-rays,
The processing unit obtains the maximum energy of continuous X-rays based on the X-ray detection signal detected by the detection unit, thereby quantifying the charged state of the sample,
A control method for an electron microscope apparatus, wherein the radiation is detected by the detection unit and an image of the sample is created by the image creation unit while the pressure inside the sample chamber is set to the determined optimum pressure value.

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