Charged particle beam apparatus and its control method

Abstract

The present invention provides a charged particle beam apparatus and a control method thereof that can reduce the effects of vibration on charged particles that have passed through a sample. [Solution] A charged particle beam apparatus comprising a sample holder for holding a sample, an electron source for emitting a charged particle beam to irradiate the sample, a detector for detecting transmitted particles which are charged particles that have passed through the sample, and a control unit that generates an observation image of the sample based on a detection signal output from the detector and controls each part, further comprising a vibrometer for measuring the vibration of the sample holder, an upper deflector disposed between the electron source and the sample holder for deflecting the charged particle beam, and a lower deflector disposed between the sample holder and the detector for deflecting the transmitted particles, wherein the control unit controls the upper deflector and the lower deflector based on the measurement value from the vibrometer and corrects the deflection of the transmitted particles together with the charged particle beam.

Description

Technical Field

[0001] The present invention relates to a charged particle beam device.

Background Art

[0002] A charged particle beam device typified by a transmission electron microscope is a device that irradiates a sample with a charged particle beam such as an electron beam and obtains an observation image of the sample by detecting particles emitted from the sample. In a charged particle beam device, various vibrations, for example, vibrations of a refrigerator that cools the sample, have an adverse effect on the observation image.

[0003] Patent Document 1 discloses a scanning electron microscope that reduces the influence of vibrations by deflecting and correcting the charged particle beam irradiated on a sample based on a correction signal generated from vibrations of a sample stage that holds the sample and vibrations of a lens barrel that emits a charged particle beam.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in Patent Document 1, no consideration is given to the adverse effect of vibrations on charged particles that have passed through the sample. Even if the charged particle beam irradiated on the sample is deflected and corrected, the image quality of the observation image will deteriorate unless the influence of vibrations on the charged particles that have passed through the sample is reduced.

[0006] Therefore, an object of the present invention is to provide a charged particle beam device and a control method thereof that can reduce the influence of vibrations on charged particles that have passed through a sample.

Means for Solving the Problems

[0007] To achieve the above objective, the present invention provides a charged particle beam apparatus comprising: a sample holder for holding a sample; an electron source for emitting a charged particle beam to irradiate the sample; a detector for detecting transmitted particles, which are charged particles that have passed through the sample; and a control unit for generating an observation image of the sample based on a detection signal output from the detector and for controlling each part thereof, further comprising: a vibrometer for measuring the vibration of the sample holder; an upper deflector disposed between the electron source and the sample holder for deflecting the charged particle beam; and a lower deflector disposed between the sample holder and the detector for deflecting the transmitted particles, wherein the control unit controls the upper deflector and the lower deflector based on the measurement value from the vibrometer and corrects the deflection of the transmitted particles together with the charged particle beam.

[0008] The present invention also relates to a control method for a charged particle beam apparatus comprising: a sample holder for holding a sample; an electron source for emitting a charged particle beam to irradiate the sample; a detector for detecting transmitted particles, which are charged particles that have passed through the sample; a control unit for generating an observation image of the sample based on a detection signal output from the detector and for controlling each part of the apparatus; a vibration meter for measuring the vibration of the sample holder; an upper deflector disposed between the electron source and the sample holder for deflecting the charged particle beam; and a lower deflector disposed between the sample holder and the detector for deflecting the transmitted particles, characterized in that the upper deflector and the lower deflector are controlled based on the measured value from the vibration meter, and the transmitted particles are deflected and corrected along with the charged particle beam. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a charged particle beam apparatus and a control method thereof that can reduce the effect of vibration on charged particles that have passed through a sample. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of the charged particle beam apparatus of Example 1. [Figure 2] This diagram illustrates deflection correction in response to sample vibration. [Figure 3]This figure shows an example of the processing flow in Example 1. [Figure 4] This figure shows an example of the process flow for generating a learning model used for bias correction. [Figure 5] This is a diagram illustrating vibration analysis based on observed images. [Figure 6] This figure shows an example of a screen for setting machine learning conditions. [Figure 7] This figure shows an example of a screen for setting the polarization correction conditions. [Figure 8] This is a schematic diagram of the charged particle beam apparatus in Example 2. [Figure 9] This is a schematic diagram of the charged particle beam apparatus of Example 3. [Modes for carrying out the invention]

[0011] The charged particle beam apparatus of the present invention will be described below with reference to the drawings. A charged particle beam apparatus is a transmission electron microscope or scanning transmission electron microscope that generates an observation image of a sample by irradiating the sample with a charged particle beam such as an electron beam. In the following, a transmission electron microscope will be described as an example of a charged particle beam apparatus. In the following description and attached drawings, components having the same functional configuration will be denoted by the same reference numerals to avoid redundant explanations. In addition, the XYZ coordinate system will be indicated in each figure to show its orientation. [Examples]

[0012] The transmission electron microscope of Example 1 will be described using Figure 1. The transmission electron microscope illustrated in Figure 1 is used for observing a sample 105 cooled to an extremely low temperature, and comprises a microscope body 100, a refrigerator 120, and a control unit 140. The microscope body 100 has a sample holder 109, an electron source 101, a first lens 103, a second lens 104, an objective lens 106, a magnifying lens 107, a detector 108, an upper deflector 111, and a lower deflector 112, and its interior is evacuated to a vacuum.

[0013] The sample holder 109 holds the sample 105 and is connected to the refrigerator 120. The electron source 101 emits an electron beam 102 that irradiates the sample 105. The first lens 103 and the second lens 104 are lenses that adjust the size of the electron beam 102 irradiating the sample 105. The objective lens 106 and the magnifying lens 107 are lenses that form an image of the transmitted electrons, which are the electrons that have passed through the sample 105, at the detector 108. The detector 108 detects the transmitted electrons and outputs a detection signal.

[0014] The upper deflector 111 is disposed between the electron source 101 and the sample holder 109 and deflects the electron beam 102, and is, for example, a deflection coil. The lower deflector 112 is disposed between the sample holder 109 and the detector 108 and deflects the transmitted electrons, and is, for example, a deflection coil.

[0015] The refrigerator 120 is a device that cools the sample 105 via the sample holder 109, and includes a compressor 121, a refrigerant circulation path 122, and a thermal insulation tube 123. The compressor 121 cools by compressing a refrigerant such as helium gas and then adiabatically expanding it. The refrigerant circulation path 122 is a circulation path connecting between the compressor 121 and the sample holder 109, and the refrigerant cooled by the compressor 121 circulates therein. The thermal insulation tube 123 is a tube made of a thermal insulator that covers the refrigerant circulation path 122 and protects the cooled refrigerant from the outside air temperature.

[0016] The control unit 140 is a device that generates an observation image of the sample 105 based on the detection signal output from the detector 108 and controls each part of the microscope body 100, and is a so-called computer. A display unit 141 such as a liquid crystal display is connected to the control unit 140. The observation image generated by the control unit 140 is displayed on the display unit 141.

[0017] Incidentally, in the compressor 121 of the refrigerator 120, vibrations are generated due to compression and expansion. The vibrations generated in the compressor 121 are transmitted to the sample holder 109 via the refrigerant circulation path 122 and the heat insulating tube 123, and vibrate the sample 105 held by the sample holder 109. The vibration of the sample 105 has an adverse effect on the observed image.

[0018] Therefore, in the first embodiment, in response to the vibration of the sample 105, the electron beam 102 irradiated on the sample 105 is deflected and corrected, and the transmitted electrons transmitted through the sample 105 are deflected and corrected, thereby reducing the influence of the vibration. In order to measure the vibration of the sample holder 109, a first vibration meter 131 is attached to the sample holder 109. Also, a second vibration meter 132 is attached to the compressor 121 to measure the vibration of the compressor 121. Furthermore, a thermometer 133 is attached to the sample holder 109 to measure the temperature of the sample holder 109.

[0019] The deflection correction of the electron beam 102 and the transmitted electrons in response to the vibration of the sample 105 will be described using FIG. 2. In (a) of FIG. 2, the case where the sample 105 moves in the positive direction of the X axis due to vibration is shown, and in (b) of FIG. 2, the case where the sample 105 moves in the negative direction of the X axis is shown.

[0020] In (a) of FIG. 2, as the sample 105 moves, the electron beam 102 is deflected and corrected in the positive direction of the X axis, and thus irradiates the center of the sample 105. Further, the transmitted electrons that have passed through the center of the sample 105 are deflected and corrected in the negative direction of the X axis, and thus enter the center of the detector 108.

[0021] Also, in (b) of FIG. 2, as the sample 105 moves, the electron beam 102 is deflected and corrected in the negative direction of the X axis and irradiates the center of the sample 105, and the transmitted electrons that have passed through the center of the sample 105 are deflected and corrected in the positive direction of the X axis and enter the center of the detector 108. The deflection correction of the electron beam 102 is performed by the upper deflector 111, and the deflection correction of the transmitted electrons is performed by the lower deflector 112. The operations of the upper deflector 111 and the lower deflector 112 are controlled by the control unit 140 based on the measured value of the first vibration meter 131.

[0022] Using Figure 3, we will explain an example of the processing flow of Example 1 step by step.

[0023] (S301) The sample 105 for observation is attached to the sample holder 109 and placed inside the microscope body 100. The inside of the microscope body 100 in which the sample 105 is placed is evacuated, and when a predetermined vacuum is reached, the refrigerator 120 starts cooling the sample 105, and the vibrations of the compressor 121 are transmitted to the sample 105 via the refrigerant circulation path 122, the heat insulating tube 123, and the sample holder 109.

[0024] (S302) The first vibration meter 131 measures the vibration of the sample holder 109 and outputs the measured value to the control unit 140. The measured value includes the direction, amplitude, and frequency of the vibration.

[0025] (S303) The control unit 140 controls the electron source 101 and starts irradiating the sample 105 with the electron beam 102. Note that the observation image generated at this stage includes noise due to vibrations of the sample 105.

[0026] (S304) The control unit 140 controls the upper deflector 111 and the lower deflector 112 based on the measurement value of the first vibrometer 131 to correct the deflection of the electron beam 102 irradiated onto the sample 105 and the transmitted electrons that have passed through the sample 105. Since the measurement value of the first vibrometer 131 is different from the vibration of the sample 105, it is preferable that the deflection correction is performed according to a value corrected from the measurement value of the first vibrometer 131. The deflected transmitted electrons are detected by the detector 108.

[0027] (S305) The control unit 140 generates an observation image based on the detection signal output from the detector 108, which has detected the deflection-corrected transmitted electrons. The generated observation image is displayed on the display unit 141.

[0028] The processing flow explained using Figure 3 yields an observation image in which the adverse effects of vibration of sample 105 are reduced. In S304, instead of correcting the measurement value of the first vibrometer 131, a learning model generated by pre-training the relationship between the measurement value of the first vibrometer 131 and the vibration of sample 105 may be used.

[0029] Using Figure 4, we will explain step by step an example of the process flow for generating a learning model used for bias correction.

[0030] (S401) A learning sample 105 is attached to a sample holder 109 and placed inside the microscope body 100. The learning sample 105 may be, for example, an amorphous carbon film in which minute particles of about 10 nm in size are randomly arranged, or a single amorphous carbon film.

[0031] (S402) The first vibration meter 131 starts measuring the vibration of the sample holder 109 and outputs the measured values ​​to the control unit 140. The measured values ​​include the direction, amplitude, and frequency of the vibration. The vibration source is, for example, the refrigerator 120 connected to the sample holder.

[0032] (S403) The control unit 140 controls the electron source 101 and the detector 108 to irradiate the sample 105 with the electron beam 102 and detect transmitted electrons. The electron beam 102 irradiated onto the sample 105 may be pulsed at predetermined intervals or continuously irradiated.

[0033] (S404) The control unit 140 generates an observation image of the training sample 105 when it is vibrating, based on the detection signal output from the detector 108.

[0034] (S405) The control unit 140 performs vibration analysis based on the observation image generated in S404.

[0035] Using Figure 5, we will explain vibration analysis based on observed images. Figure 5(a) is an observed image of the training sample 105 when it is stationary, and Figure 5(b) is the FFT pattern obtained by processing the observed image in Figure 5(a) with FFT (Fast Fourier Transform). Figure 5(c) is an observed image of the training sample 105 when it is vibrating, and Figure 5(d) is the FFT pattern of the observed image in Figure 5(c). The observed image in Figure 5(c) is a double-exposure image obtained by the timing of pulse exposure indicated by the black circles in Figure 5(e). By analyzing the Young's fringe pattern based on the double-exposure image, the amount and direction of image displacement can be obtained. The maximum displacement can be obtained by measuring while changing the phase with respect to the time axis of pulse irradiation. Half the distance of the maximum displacement corresponds to the vibration amplitude. Furthermore, by changing the pulse interval, the vibration frequency of interest can be selected.

[0036] In Figure 5(a), the microparticles are at rest, whereas in Figure 5(c), the microparticles are vibrating in the direction indicated by the double-headed arrow. Also, a Young's fringe, which is not present in Figure 5(b), is present in the circle in Figure 5(d), extending from the upper left to the lower right. Since the Young's fringe originates from the vibration of sample 105, the amplitude, frequency, and direction of the vibration of sample 105 can be obtained and output as the vibration analysis result by performing a pattern analysis of the Young's fringe in Figure 5(d) at various frequencies.

[0037] (S406) The control unit 140 generates a learning model by machine learning using the measured values ​​from the first vibrometer 131 and the results of the vibration analysis in S405. The learning model generated in S406 outputs the vibration values ​​of the sample 105 when the measured values ​​from the first vibrometer 131 are input. The output vibration values ​​include, for example, the amplitude, frequency, and direction of the vibration.

[0038] As explained using Figure 4, a learning model is generated that outputs the vibration of sample 105 in response to the input of the measurement value from the first vibrometer 131. By using the generated learning model in S304 of Figure 3, more accurate deflection correction becomes possible, and the image quality of the observation image of sample 105 for observation is improved.

[0039] Furthermore, the measurements from the second vibrometer 132 may also be used in the machine learning process to generate the learning model. Since the measurements from the second vibrometer 132 are larger than those from the first vibrometer 131, the SNR (Signal-to-Noise Ratio) improves, and the learning accuracy also improves.

[0040] Furthermore, the measurements from the thermometer 133 may also be used in the machine learning process to generate the learning model. Since the vibration of the sample 105 may change with temperature, the learning accuracy can be improved by using the measurements from the thermometer 133 in the machine learning process.

[0041] An example of a screen used for setting machine learning conditions will be explained using Figure 6. The learning condition setting screen 600 shown in Figure 6 has a frequency range setting unit 601, a temperature range setting unit 602, a sample holder selection unit 603, a learning time setting unit 604, a start button 605, and a save button 606.

[0042] The frequency range setting unit 601 receives the frequency range to be analyzed in S405 of Figure 4. The temperature range setting unit 602 receives the measurement temperature range when the measurement value of the thermometer 133 is used for machine learning. The sample holder selection unit 603 selects the type of sample holder 109. The learning time setting unit 604 receives the upper limit time required for machine learning. The start button 605 is pressed to start machine learning. The save button 606 is pressed to save the results of machine learning.

[0043] An example of a screen used for setting the conditions for deflection correction will be explained using Figure 7. The correction condition setting screen 700 shown in Figure 7 has a model selection section 701, a frequency range setting section 702, a start button 703, and a stop button 704.

[0044] The model selection unit 701 selects a learning model from among several learning models to be used for deflection correction. The frequency range to be corrected is input to the frequency range setting unit 702. The start button 703 is pressed to start deflection correction. The stop button 704 is pressed to stop deflection correction. [Examples]

[0045] Example 1 described a transmission electron microscope that corrects the deflection of the electron beam 102 and transmitted electrons based on the measurement values ​​of the first vibrometer 131. Example 2 describes a transmission electron microscope that can obtain a hologram image. For the same components as in Example 1, the same reference numerals are used to simplify the explanation.

[0046] The transmission electron microscope of Example 2 will be explained using Figure 8. In Figure 8, an electron biprism 800 is added between the lower deflector 112 and the detector 108 compared to Figure 1. The electron biprism 800 obtains a hologram image by interfering an object wave 801 that has passed through the sample 105 (an object) with a reference wave 802 that has passed through a vacuum.

[0047] In Example 2, too, a hologram image with reduced vibration of the sample 105 can be obtained by correcting the deflection of the electron beam 102 and transmitted electrons based on the measurement values ​​of the first vibrometer 131. [Examples]

[0048] Example 1 described a transmission electron microscope that corrects the deflection of the electron beam 102 and transmitted electrons based on the measurement values ​​of the first vibration meter 131. Example 3 describes a scanning transmission electron microscope that obtains a two-dimensional transmission electron image by detecting transmitted electrons while scanning the sample 105 with a narrowly focused electron beam 102. Note that the same reference numerals are used for components that are the same as in Example 1 to simplify the explanation.

[0049] The scanning transmission electron microscope of Example 3 will be described using Figure 9. In Figure 9, the magnifying lens 107 in Figure 1 is replaced by the projection lens 903, and an annular detector 901 is added between the objective lens 106 and the projection lens 903. The annular detector 901 detects high-angle scattered electrons 900 generated in the sample 105. By using the detection signal output from the annular detector 901, the atomic numbers and sample structure of the sample 105 can be obtained. In addition, the electric and magnetic fields in the sample 105 can be analyzed from the amount of position change 902 of the transmitted electrons in the detector 108.

[0050] In Example 3, a two-dimensional transmission electron image with reduced vibration of the sample 105 can be obtained by correcting the deflection of the electron beam 102 and transmitted electrons based on the measurement values ​​of the first vibrometer 131. Furthermore, the deflection correction of the electron beam 102 and transmitted electrons based on the measurement values ​​of the first vibrometer 131 can also be applied to transmission electron microscopes equipped with secondary electron detectors, energy dispersive X-ray detectors, and electron energy loss spectroscopy detectors.

[0051] Multiple embodiments of the present invention have been described above. The present invention is not limited to the above embodiments, and the components can be modified and implemented without departing from the spirit of the invention. Furthermore, the multiple components disclosed in the above embodiments may be combined as appropriate. In addition, some components may be deleted from all the components shown in the above embodiments. [Explanation of symbols]

[0052] Microscope body 100, electron source 101, electron beam 102, first lens 103, second lens 104, sample 105, objective lens 106, magnifying lens 107, detector 108, sample holder 109, upper deflector 111, lower deflector 112, refrigerator 120, compressor 121, refrigerant circulation path 122, thermal insulation tube 123, first vibrometer 131, second vibrometer 132, thermometer 133, control unit 140, display unit 141, learning condition setting screen 60 0, Frequency range setting unit 601, Temperature range setting unit 602, Sample holder selection unit 603, Learning time setting unit 604, Start button 605, Save button 606, Correction condition setting screen 700, Model selection unit 701, Frequency range setting unit 702, Start button 703, Stop button 704, Electron beam biprism 800, Object wave 801, Reference wave 802, High-angle scattered electron 900, Ring detector 901, Position change amount 902, Projection lens 903.

Claims

1. A vibration meter that measures the vibration of the sample holder that holds the sample, An upper deflector is positioned between an electron source that emits a charged particle beam to irradiate the sample and the sample holder, and deflects the charged particle beam. A lower deflector is positioned between the sample holder and a detector that detects transmitted particles, which are charged particles that have passed through the sample, and deflects the transmitted particles. A charged particle beam apparatus characterized by comprising a control unit that controls the upper deflector and the lower deflector based on the measured values ​​from the vibration meter, corrects the deflection of the transmitted particles together with the charged particle beam, and generates an observation image of the sample based on the detection signal output from the detector.

2. A charged particle beam apparatus according to claim 1, The charged particle beam apparatus is characterized in that the control unit corrects the deflection of the transmitted particles together with the charged particle beam according to the values ​​output by inputting the measured values ​​of the vibration meter into a learning model generated by machine learning in advance by studying the relationship between the measured values ​​of the vibration meter and the vibration of the sample.

3. A charged particle beam apparatus according to claim 2, The charged particle beam apparatus is characterized in that the control unit calculates the vibration of a sample by performing vibration analysis on an image acquired using a training sample while it is vibrating.

4. A charged particle beam apparatus according to claim 2, The charged particle beam apparatus is characterized in that the control unit further uses the measured value of a thermometer attached to the sample holder to generate the learning model.

5. A charged particle beam apparatus according to claim 2, A refrigerator for cooling the sample holder, The refrigerator further comprises a second vibration meter attached to the aforementioned refrigerator, The charged particle beam apparatus is characterized in that the control unit further uses the measured values ​​of the second vibration meter to generate the learning model.

6. A charged particle beam apparatus according to claim 1, A charged particle beam apparatus further comprising an electron biprism that obtains a holographic image by interfering an object wave that has passed through an object with a reference wave that has passed through a vacuum.

7. A charged particle beam apparatus according to claim 1, A charged particle beam apparatus further comprising a ring detector for detecting high-angle scattered electrons from the aforementioned sample.

8. A control method for a charged particle beam apparatus comprising: a sample holder for holding a sample; an electron source for emitting a charged particle beam to irradiate the sample; a detector for detecting transmitted particles, which are charged particles that have passed through the sample; a control unit for generating an observation image of the sample based on a detection signal output from the detector and for controlling each part of the apparatus; a vibrometer for measuring the vibration of the sample holder; an upper deflector positioned between the electron source and the sample holder to deflect the charged particle beam; and a lower deflector positioned between the sample holder and the detector to deflect the transmitted particles, wherein the apparatus comprises: a sample holder for holding a sample; an electron source for emitting a charged particle beam to irradiate the sample; a detector for detecting transmitted particles that have passed through the sample; a control method for a charged particle beam apparatus, wherein the apparatus comprises: a sample holder for holding a sample; an electron source for emitting a charged particle beam to irradiate the sample; a detector for detecting transmitted particles that have passed through the sample; a control unit for generating an observation image of the sample based on a detection signal output from the detector and for controlling each part of the apparatus; a vibrometer for measuring the vibration of the sample holder; an upper deflector positioned between the electron source and the sample holder to deflect the charged particle beam; and a lower deflector positioned between the sample holder and the detector to deflect the transmitted particles. A control method characterized by controlling the upper deflector and the lower deflector based on the measured values ​​from the vibration meter, thereby correcting the deflection of the transmitted particles together with the charged particle beam.

Images