JP2007078537A - Electron beam dimension measuring device and electron beam dimension measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron beam dimension measuring device and an electron beam dimension measuring method capable of measuring a sample accurately by fixing the electric potential of the sample surface without depending on a sample material. <P>SOLUTION: The electron beam measuring device has: an electron beam irradiation means for irradiating an electron beam to the sample surface; a detection means for detecting electrons discharged from the sample; and a control means for allowing the electron beam irradiation means to irradiate the electron beam with a lower acceleration voltage than a voltage with which secondary electrons are discharged from the sample, and to stop irradiation of the electron beam when determined that the fixed electric potential is generated on the sample surface based on a signal from the detection means. The control device may allow the electron beam irradiation means to irradiate the electron beam to the whole surface of the sample, or may allow the electron beam irradiation means to irradiate the electron beam to a prescribed range centered at a measuring portion of the sample. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electron beam size measuring apparatus and an electron beam size measuring method for observing a sample by irradiating the sample with an electron beam.

  In the manufacturing process of a semiconductor device, observation of a sample by an electron beam apparatus such as an electron microscope and measurement of a line width of a pattern are performed. In the observation and measurement of a sample using an electron beam device, scanning is performed while irradiating the observation portion with an electron beam, and the amount of electrons such as secondary electrons is converted into luminance and displayed on the display device as an image.

  In this way, when observing or measuring a sample, an electron beam is irradiated, and a phenomenon occurs in which the surface of the sample is charged by the irradiation of the electron beam. Charging is a phenomenon in which an irradiation surface becomes positive or negative depending on a difference between charged particles incident on a sample and emitted charged particles. When the sample surface is charged, the secondary electrons emitted from the sample are accelerated or pulled back, changing the efficiency of secondary electron emission, resulting in unstable image quality on the sample surface. Further, when the charging of the sample surface proceeds, the primary electron beam may be deflected and the image may be distorted.

  Various methods for preventing charging on the sample surface have been proposed for such problems.

As a technique related to this, Patent Document 1 discloses a method for uniformizing the charging of the sample surface by using a voltage at which the yield of secondary electrons is greater than 1 and a voltage at which the yield is less than 1. Patent Document 2 discloses a method of neutralizing charging by irradiating a sample surface with ultraviolet rays. Patent Document 3 discloses a method for making the surface of a sample uniform using secondary electrons and ultraviolet rays. Further, Patent Document 4 discloses a method for neutralizing the charging of the observation site using an external flood gun.
Japanese Patent Laid-Open No. 2003-142019 Japanese Patent Laid-Open No. 2005-174591 JP 2005-164451 A JP-A-8-508776

  As described above, in the observation of the sample in the electron beam apparatus, the phenomenon that the sample surface is charged occurs. For example, when the sample can be electrically connected like a wafer, the sample is electrically connected to the electrically connected wafer. By grounding the conductor, the charging phenomenon of the sample can be prevented, and there is no particular problem.

  However, if the sample is non-conductive or cannot be grounded even if a conductive material is used, a charging phenomenon of the sample surface occurs. For example, when measuring the dimensions of a photomask used as a master for semiconductor exposure, charging occurs.

  The following two states can be considered as states in which the dimensions of the photomask need to be measured and managed. One is a state in which there is a conductor such as chrome on the entire glass substrate, which is in the process of manufacturing the wiring, and a resist wiring for etching the wiring on the chrome on the conductor. The second is a state in which the manufacturing process of the wiring is completed, and there is a state where there is a wiring made of a conductor such as chromium on the glass substrate.

  In particular, in the state immediately before etching chrome, there is a conductor layer such as chrome on the entire glass substrate. Therefore, when charging occurs by irradiating an electron beam at a certain place, the entire conductor layer on the substrate is charged. Therefore, it will affect the observation of other places and the dimension measurement. Even if the charge at one place is very small, if you irradiate hundreds to thousands of places with an electron beam, it will eventually become a large charge, with the first measured dimension and the last measured dimension. Correlation becomes impossible.

  In the above-described method of making the surface of the sample uniform using secondary electrons, the potential is adjusted in consideration of the generation efficiency of secondary electrons depending on the material of the sample, and the surface of the sample is made uniform. Yes. However, since the generation efficiency of secondary electrons depends on the sample material, if the sample surface is composed of different materials, the potential between different samples differs even if the charge of each sample is uniform. End up. For this reason, the electric field changes between different samples, and the force acts on the primary electron beam to change the size of the irradiation region, so that the size management cannot be performed with high accuracy.

  Further, the method of neutralizing the charge of the sample by irradiating with ultraviolet rays cannot be applied when the measurement target is a resist material. This is because the resist material changes due to ultraviolet irradiation.

  In addition, when an external flood gun is used, it is difficult to uniformly neutralize charging over a wide range centering on the observation site. This is because the distance between the sample and the electron microscope column is narrow, it is difficult to guide the electron irradiation from the flood gun to the measurement site, and uniform neutralization cannot be performed.

  The present invention has been made in view of the problems of the prior art, and provides an electron beam size measuring apparatus and an electron beam that can accurately measure a sample with a constant potential on the surface of the sample without depending on the material of the sample. An object is to provide a dimension measuring method.

  The above-described problems include an electron beam irradiation unit that irradiates the surface of the sample with an electron beam, a detection unit that detects electrons emitted from the sample, and a voltage at which secondary electrons are emitted from the sample to the electron beam irradiation unit. Control means for irradiating the electron beam at a lower acceleration voltage and stopping the irradiation of the electron beam when it is determined that the surface of the sample is at a constant potential based on a signal from the detection means. This is solved by a characteristic electron beam size measuring device.

  In the electron beam size measuring apparatus, the control unit may cause the electron beam irradiation unit to irradiate the entire surface of the sample with the electron beam irradiation unit, or the electron beam may be applied to the measurement site of the sample. You may make it irradiate to the predetermined range centered.

  In addition, the above-described problems include a step of obtaining an electron beam acceleration voltage based on a charged potential of a sample to be measured, a step of irradiating the surface of the sample with an electron beam at the acceleration voltage, and a surface of the sample being constant. An electron beam size measuring method comprising: stopping irradiation of the electron beam when a potential is reached; and switching the potential of the electron beam to a potential at which secondary electrons are emitted from the sample. To solve.

  In the above-described electron beam size measuring method, instead of the step of obtaining the acceleration voltage of the electron beam and the step of irradiating the surface of the sample with the electron beam at the acceleration voltage, the step of charging the sample to be measured to a positive potential And irradiating the surface of the sample with an electron beam at a predetermined negative potential.

  In the present invention, the electron beam is irradiated with an acceleration voltage that is lower than the potential at which the sample is charged on the surface of the sample to be measured and does not emit secondary electrons. By irradiating such an electron beam, the negative charge of the electron beam is absorbed by the sample, but by continuing to irradiate the electron beam, the sample is charged to the same potential as the acceleration voltage of the electron beam. As a result, the potential of the sample surface is kept constant, the trajectory of the electron beam is constant, and the irradiation range is constant.

  Further, in the present invention, the potential of the electron gun (electron beam irradiation means) of the electron beam dimension measuring device is controlled to be constant without providing an electrode for controlling charging specifically in order to make the surface potential of the sample constant. A potential electron beam is generated. For this reason, even when the process of making the potential constant is performed, an electron image of the sample surface can be easily obtained by a normal operation. Thereby, it is possible to confirm the process in which the electric potential becomes constant by an electronic image.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, the configuration of the electron beam dimension measuring apparatus will be described. Next, a process for making the potential of the sample surface constant, which is a feature of the present invention, will be described. Next, an electron beam dimension measuring method using the electron beam dimension measuring apparatus will be described. Finally, an embodiment in which the surface of the sample is set to a constant potential by the electron beam size measuring apparatus according to the present invention will be described.

(Configuration of electron beam size measuring device)
FIG. 1 is a configuration diagram of an electron beam dimension measuring apparatus according to the present embodiment.

  The electron beam size measuring apparatus 100 is mainly used for an electronic scanning unit 10, a signal processing unit 30, a display unit 40, and a control unit 20 that controls the electronic scanning unit 10, the signal processing unit 30, and the display unit 40. Separated. Among these, the electronic scanning unit 10 includes an electron column (column) 15 and a sample chamber 16. The electron column unit 15 includes an electron gun (electron beam irradiation means) 1, a condenser lens 2, a deflection coil 3, and an objective lens 4, and the sample chamber 16 includes a wafer stage moving unit 5 and a wafer stage 6. is doing. The sample chamber 16 is connected to a motor (not shown) for moving the wafer stage 6 and an evacuation pump (not shown) for maintaining the inside of the sample chamber 16 in a predetermined reduced pressure atmosphere.

  An electron beam 9 irradiated from the electron gun 1 is irradiated to the sample 7 on the wafer stage 6 through the condenser lens 2, the deflection coil 3 and the objective lens 4.

  The amount of secondary electrons or reflected electrons emitted from the sample 7 after being irradiated with the electron beam 9 is detected by an electron detector (detection means) 8 composed of a scintillator or the like, and the detected amount is detected by the signal processing unit 30 as AD. It is converted into a digital quantity by the converter, further converted into a luminance signal, and displayed on the display unit 40.

  The electronic deflection amount of the deflection coil 3 and the image scan amount of the display unit 40 are controlled by the control unit 20.

  The control unit 20 is configured by a microcomputer, for example, and stores a program for executing length measurement. Further, the control unit 20 determines an acceleration voltage of the electron beam 9 and applies the acceleration voltage to the electrically connected electron gun 1.

  In the electron beam size measuring apparatus 100 configured as described above, prior to the observation of the sample 7 placed on the wafer stage 6, the electron beam 9 having a low potential so as not to emit secondary electrons from the sample 7 is applied to the sample. 7 is irradiated on the surface. After the electron beam 9 is irradiated and the charged potential of the sample 7 becomes constant, the sample 7 is observed or measured.

(Treatment to make the sample surface potential constant)
Prior to the observation or measurement of the sample 7, the above process is performed, so that the potential of the surface of the sample 7 is kept constant. This principle is shown below.

  FIG. 2 schematically shows the relationship between the energy of primary electrons and the secondary electron emission ratio. As shown in FIG. 2, the secondary electron emission ratio increases as the energy of the primary electrons increases from the low energy, and becomes 1 when the energy of the primary electrons becomes E1. When the primary electron energy is further increased, the secondary electron emission ratio becomes maximum when the primary electron energy becomes Em. When the primary electron energy exceeds E2, the secondary electron emission ratio becomes smaller than 1 again. Here, the values of E1, Em, and E2 vary depending on the material of the sample, but it is known that the value of Em is approximately between 500 eV and 1000 eV.

  FIG. 3 schematically shows the relationship between the secondary electron emission ratio and the charged state of the insulating film surface of the sample. FIG. 3A shows a case where the secondary electron emission ratio of the sample is larger than 1. In the range where the secondary electron emission ratio is larger than 1, the number of secondary electrons 52 emitted from the sample 7 is larger than the number of primary electrons 51 incident on the sample, so that the surface of the sample 7 is positively charged. On the other hand, FIG. 3B shows the case where the secondary electron emission ratio is smaller than 1, and corresponds to the case where the primary electron energy is lower than E1 or higher than E2 in FIG. In the range where the secondary electron emission ratio is smaller than 1, many electrons remain on the surface of the sample 7, so that the surface of the sample 7 is negatively charged.

  When the energy of the primary electrons is sufficiently large and the secondary electron emission ratio is smaller than 1, the surface of the sample 7 is negatively charged, so the primary electrons are decelerated near the sample 7. This charging proceeds until the secondary electron emission ratio approaches 1. At this time, the charging voltage is a difference between E2 and the primary electron energy, and there is a case where the charging voltage is charged to a large negative value (for example, a value exceeding −100 V). When such charging occurs, the secondary electron image is greatly distorted and the measurement error increases.

  On the other hand, when the secondary electron emission ratio is greater than 1, the surface of the sample 7 is positively charged, but when charged several V, the secondary electrons 53 having only several eV energy are drawn back to the surface of the sample 7. Become. The incident current, which is a combination of the primary electrons and the secondary electrons withdrawn to the surface, balances with the emission current of the emitted secondary electrons, and charging does not proceed any further. For this reason, the range in which the secondary electron emission ratio is larger than 1 is adopted for observation of the sample 7 and the like.

  In this case, when a plurality of materials are used as the sample 7, the generation efficiency of the secondary electrons 52 varies depending on the material, and thus the potential is not always constant on the surface of the sample 7. Therefore, it is necessary to make the charge uniform, but in the conventional method of making the charge uniform, the secondary electron emission ratio is set to 1, and the acceleration voltage is set so as to prevent the charge. . However, since the acceleration voltage at which the generation efficiency of the secondary electrons 52 is 1 differs depending on the material of the sample 7, the acceleration voltage must be adjusted so that the secondary electron generation efficiency becomes 1 while adjusting the acceleration voltage. Setting the voltage is difficult.

  In the present embodiment, attention is paid to the case where the energy of the primary electrons is small and the secondary electron emission ratio is smaller than 1.

  When the primary electron energy is small and the secondary electron emission ratio is smaller than 1, the surface of the sample 7 is negatively charged. While the charged potential of the sample is higher than the potential of the acceleration voltage, the negative charge of the primary electrons is absorbed by the sample, and the charged potential of the sample gradually decreases. Eventually, the charged potential of the sample becomes the same potential as the acceleration voltage of the primary electrons. If the potential of the sample becomes the same as the potential of the acceleration voltage, no more charge is absorbed by the sample.

  For example, when a wiring pattern 7b formed of a conductor on a glass substrate 7a as shown in FIG. 4 is charged to +30 V, an electron beam 9 having an acceleration voltage of −10 V is adjusted by adjusting the power supply 60 to the sample 7. Consider the case of irradiation. As shown in FIG. 4A, the negative charge of the electron beam 9 is absorbed by the sample 7b that is positively charged with respect to the acceleration voltage. As shown in FIG. 4B, the potential of the sample 7b that absorbed the negative charge gradually decreases from + 30V, and the charged potential becomes 0V. When the irradiation with the electron beam 9 is further continued, as shown in FIG. 4C, the potential of the sample 7b drops to −10V, which is the same as the acceleration voltage. At this time, since the charged potential of the sample 7b is the same as the acceleration voltage of −10V, all the charges are pushed back without absorbing the charge of the electron beam 9. At this time, the potential of the sample 7b becomes constant.

  In this way, the method of making the potential constant does not depend on the material of the sample 7. That is, the constant potential is determined only by the value of the acceleration voltage.

  In the above description, the acceleration voltage of the electron beam is set to −10V, but may be a low potential that does not generate secondary electrons. For example, depending on the sample 7, it may be 0V or + 10V. For example, if the acceleration voltage is + 10V, the constant potential is also + 10V.

  In addition, as described above, since the sample absorbs the negative charge of the electron beam and makes the potential constant, the charged potential of the sample before making the potential constant may be higher than the potential after making the potential constant. Necessary.

  In the above description, the potential at which the potential of the sample is constant is assumed to be the same potential as the acceleration voltage. However, actually, the energy of electrons is not only the energy corresponding to the acceleration voltage, but also emitted from the electron gun. It is conceivable that the energy given to be added is added. In this case, the potential becomes constant at a potential corresponding to the energy actually emitted from the electron gun.

  In this way, by setting the acceleration voltage of the electron beam to a voltage that is low enough not to emit secondary electrons from the sample, the potential for making the sample surface constant can be determined only by the value of the acceleration voltage of the electron beam. For this reason, in the case of an accelerating voltage at which secondary electrons are emitted, it has been difficult to control potentials having different secondary electron emission ratios depending on the material, but a constant potential can be easily determined. .

(Electron beam dimension measurement method)
Next, a method for measuring the length of the sample 7 while keeping the potential on the sample 7 constant by using the electron beam size measuring apparatus 100 of the present embodiment will be described with reference to the flowchart of FIG.

  Here, it is assumed that a process of making the potential on the sample 7 constant is performed every time the sample 7 is measured. An electron microscope is used as the electron beam size measuring device.

  First, in step S11, initialization is performed. In this initial setting, the potential on the sample 7 is measured, and the acceleration voltage of the electron beam is determined from the measured value.

  Next, in step S12, the electron beam having the acceleration voltage determined in step S11 is irradiated onto the sample. The electron beam is irradiated over the entire sample.

  It should be noted that the range in which the electron beam is irradiated may be irradiated only in a range that affects the lens of the electron microscope, for example, with the measurement site as the center.

  Next, in step S13, it is determined whether or not the potential on the sample has become constant by the electron beam irradiation in step S12. If it is determined that the potential on the sample has become constant, the process proceeds to the next step S14. If it is determined that the potential on the sample has not become constant, the process returns to step S12 to return the electron beam onto the sample. Continue irradiation.

  Whether or not the potential on the sample has become constant is determined as follows, for example.

  In this embodiment, since the electron beam 9 is irradiated by the electron beam dimension measuring apparatus 100 (electron microscope) itself that performs dimension measurement, an electron microscope image by the electron beam 9 can be observed. For this reason, when the potential of the surface of the sample 7 is not constant, an electron microscope image including information based on the shape and material of the surface of the sample 7 can be acquired. Further, since the electron beam 9 is irradiated, an electron microscope image of a process in which the potential becomes constant by the irradiation of the electron beam 9 can be obtained. When the potential reaches a constant level, the electron beam 9 cannot reach the sample and does not have information such as the shape of the sample surface. Therefore, thereafter, no change is observed in the electron microscope image. Thus, when there is no information obtained from the sample and no change is observed in the electron microscope image, it can be determined that the potential has become constant. For example, when the control unit 20 causes the signal processing unit 30 to perform signal processing on the electron microscope image and there is no change between an image at a certain time and an image after a predetermined time has elapsed, the control unit 20 Is determined to be constant.

  In the present embodiment, since an acceleration voltage is applied so that secondary electrons are not emitted from the sample 7, an image obtained as an electron microscope image is an image obtained mainly from electrons other than the secondary electrons.

  In the next step S14, the electron beam irradiation performed to keep the potential constant is stopped.

  In the next step S15, the electron beam dimension measuring device is switched to the length measuring mode. Here, switching to the length measurement mode includes setting the acceleration voltage set in the process of making the potential constant from an acceleration voltage used in normal length measurement, for example, from 500 V to 2 kV.

  In the next step S16, the sample 7 is actually measured.

  As described above, in the measuring method using the electron beam size measuring apparatus of the present embodiment, the potential on the sample is made constant before measuring the size of the sample. In order to make this potential constant, an electron beam having an acceleration voltage that does not generate secondary electrons is irradiated onto the sample. The electron beam irradiation is performed until the potential of the electron beam and the potential of the sample become the same value. Since all the potentials on the sample have this constant value, the electron beam is not affected by the different potentials on the sample and the irradiation range of the electron beam does not change, and stable measurement can be performed. .

  Further, in this embodiment, since the potential of the sample is made constant with the electron microscope itself that performs dimension measurement, an electron microscope image until the potential on the sample becomes constant can be observed, and only in a necessary part. It is also possible to confirm that the electron beam is irradiated, and it is possible to prevent unnecessary electron beam irradiation.

  In this embodiment, the process of making the potential of the sample surface constant is performed every time the sample is measured. However, the present invention is not limited to this, and when the process of making the potential of the sample surface constant is necessary. You may do it only. FIG. 6 shows a flowchart of an example of an electron beam dimension measuring method including the above processing. As shown in FIG. 6, the charging state of the reference sample is inspected in step S22. In the next step S23, it is determined whether or not the error is within an allowable range. For example, when a length measurement error of 0.1 percent occurs, the process proceeds to step S24, and a process of making the sample surface potential constant is performed. Other processing is the same as the processing described in FIG.

  Further, in the present embodiment, it has been described that a part of the sample is charged to 30 V. First, after charging the entire surface of the sample to an arbitrary positive potential, the acceleration voltage is set to a negative value. You may make it irradiate an electron beam.

  In order to charge the sample positively, for example, it is possible to easily charge the sample positively by generating many secondary electrons with an acceleration voltage of about 1 kV and capturing the secondary electrons.

  Further, the electron beam irradiated for making the potential constant may be irradiated for a few seconds by increasing the beam irradiation amount as compared with the normal case of measuring the sample. By doing so, it is possible to shorten the time until the potential becomes constant.

  In the present embodiment, the case of measuring the length of the sample has been described. However, the present invention is not limited to this. For example, it is stable in a wide range of the SEM field such as confirming that the sample is not contaminated with an image. The sample can be observed.

(Example)
Hereinafter, a specific example in which the potential on the sample 7 is made constant using the electron beam dimension measuring apparatus 100 of the present embodiment will be described. FIG. 7A shows a part (0.5 mm length, 0.5 mm width) of a photomask in which a chrome wiring 72 is formed on a substrate 71. FIG. 7B to FIG. 7D show a process in which a process for making the potential constant is performed before length measurement is performed for this range. The acceleration voltage of the electron beam is −10 V, and this range is irradiated with the electron beam. As an electron microscope image obtained at this time, an image having a low resolution and an image that shows that there is something in the portion where the chromium wiring 72 is formed is obtained. When the electron beam irradiation is continued, as shown in FIG. 7C, the shape in which the chrome wiring 72 is formed is not imaged, and an image different from that in FIG. 7B is obtained. When the electron beam is further irradiated, as shown in FIG. 7D, a circular electron microscope image is obtained at the center. This image is considered not to be information from the sample surface but to indicate the characteristics of the lens. Even if the electron beam was continuously irradiated thereafter, the obtained electron microscope image did not change from FIG. As a result, it is determined that the electron beam no longer reaches the sample surface. That is, it can be determined that the acceleration voltage and the sample surface potential are equal, the electron beam cannot reach the sample surface, and an electron microscope image of the sample surface cannot be obtained.

It is a block diagram of the electron beam dimension measuring apparatus used by embodiment of this invention. It is a figure which shows the relationship between the energy of a primary electron, and a secondary electron emission ratio. 3A and 3B are diagrams showing the relationship between the secondary electron emission ratio and the charging of the sample surface. 4A to 4C are diagrams for explaining the principle that the potential on the sample becomes constant. It is a flowchart (the 1) which shows an electron beam dimension measuring method. It is a flowchart (the 2) which shows an electron beam dimension measuring method. FIG. 7A shows a part of the photomask. FIGS. 7B to 7D are schematic views of electron microscope images in the process of making the potential constant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Electron beam dimension measuring apparatus, 1 ... Electron gun (electron beam irradiation means), 2 ... Condenser lens, 3 ... Deflection coil, 4 ... Objective lens, 5 ... Wafer stage moving part, 6 ... Wafer stage, 7 ... Sample, DESCRIPTION OF SYMBOLS 8 ... Electron detector (detection means), 9 ... Electron beam, 10 ... Electron scanning part, 15 ... Electron lens barrel part, 16 ... Sample chamber, 20 ... Control part, 30 ... Signal processing part, 40 ... Display part, 51 ... primary electrons, 52, 53 ... secondary electrons, 60 ... power supply, 71 ... substrate, 72 ... wiring.

Claims (12)

An electron beam irradiation means for irradiating the surface of the sample with an electron beam;
Detection means for detecting electrons emitted from the sample;
When the electron beam irradiation means is irradiated with an electron beam at an acceleration voltage lower than the voltage at which secondary electrons are emitted from the sample, and based on a signal from the detection means, it is determined that the surface of the sample has become a constant potential And an electron beam size measuring device characterized by further comprising a control means for stopping the irradiation of the electron beam. Furthermore, it has a display means for displaying an image,
2. The electron beam size measuring apparatus according to claim 1, wherein the control unit generates an image of the sample based on a signal from the detection unit and displays the image on a screen of the display unit.   The electron beam dimension measuring apparatus according to claim 1, wherein the control unit causes the electron beam irradiation unit to irradiate the entire surface of the sample with the electron beam.   3. The electron beam dimension measuring apparatus according to claim 1, wherein the control unit causes the electron beam irradiation unit to irradiate the electron beam to a predetermined range centering on a measurement site of a sample.   5. The electron beam size measuring apparatus according to claim 1, wherein the constant potential is lower than a charging potential of the sample.   6. The electron beam dimension measuring apparatus according to claim 1, wherein a value of an irradiation electron quantity of the electron beam is larger than a value of an irradiation electron quantity when performing dimension measurement.   The said control means irradiates an electron beam with the predetermined electric potential which a secondary electron generate | occur | produces from the said sample, after stopping irradiation of the said electron beam. The electron beam dimension measuring apparatus as described. Obtaining the acceleration voltage of the electron beam based on the charged potential of the sample to be measured;
Irradiating the surface of the sample with an electron beam at the acceleration voltage;
Stopping the irradiation of the electron beam when the surface of the sample is at a constant potential;
And switching the potential of the electron beam to a potential at which secondary electrons are emitted from the sample.   9. The electron beam dimension measuring method according to claim 8, wherein the acceleration voltage is lower than a charging potential of the sample. Instead of obtaining the acceleration voltage of the electron beam and irradiating the surface of the sample with the electron beam at the acceleration voltage,
Charging the sample to be measured to a positive potential;
The method according to claim 8, further comprising: irradiating the surface of the sample with an electron beam at a predetermined negative potential.   The electron beam dimension measuring method according to claim 8 or 10, wherein the electron beam is applied to the entire surface of the sample.   The electron beam size measuring method according to claim 8 or 10, wherein the electron beam is applied to a predetermined range centering on a measurement site of the sample.

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