Electron beam application apparatus and control method for said apparatus

Abstract

Provided are: an electron beam application apparatus capable of improving the spatial resolution of an observation image; and a control method for said apparatus. The present invention relates to an electron beam application apparatus comprising: a first light source that emits first excitation light which is pulse excitation light; a photocathode that emits a first pulse electron beam as a result of being irradiated with the first excitation light; an objective lens that focuses the first pulse electron beam; a detector that detects signal electrons which are emitted from a sample as a result of the sample being irradiated with the first pulse electron beam; and a control unit that controls each unit. The electron beam application apparatus is characterized by also comprising a second light source that emits second excitation light which is pulse excitation light different from the first excitation light, wherein the control unit causes the sample to be irradiated with a second pulse electron beam at a different timing from that of being irradiated with the first pulse electron beam, the second pulse electron beam being emitted from the photocathode as a result of the photocathode being irradiated with the second excitation light.

Description

Electron beam application apparatus and control method therefor

[0001] The present invention relates to an electron beam application apparatus that measures electrical characteristics of a sample by irradiating the sample whose surface charge amount is controlled with an electron beam, and a control method therefor.

[0002] For failure analysis of semiconductor devices, a method is used in which, while periodically applying a voltage to a sample surface with a probe, pulsed electron beams are irradiated at a specific phase to detect signal electrons emitted from the sample, thereby measuring electrical characteristics of a local region. In particular, to measure electrical characteristics in a high-frequency band, it is necessary to shorten the pulse width of the pulsed electron beam.

[0003] Patent Document 1 discloses use of a photocathode, which is a photoexcitation emission type electron source that facilitates shortening the pulse width of a pulsed electron beam. That is, by irradiating a sample, to which a voltage is periodically applied by a probe, with a pulsed electron beam emitted from the photocathode by pulsed excitation light, electrical characteristics of the sample in a high-frequency band can be measured.

[0004] International Publication No. 2024 / 257200

[0005] However, in Patent Document 1, since the probe that applies a voltage to the sample is disposed between the objective lens and the sample, it is difficult to bring the objective lens close to the sample surface, and there is a limit to improving the spatial resolution of an observed image.

[0006] Therefore, an object of the present invention is to provide an electron beam application apparatus capable of improving the spatial resolution of an observed image, and a control method therefor.

[0007] To achieve the above objective, the present invention provides an electron beam application apparatus comprising: a first light source that emits first excitation light, which is pulsed excitation light; a photocathode that emits a first pulsed electron beam upon irradiation with the first excitation light; an objective lens that focuses the first pulsed electron beam; a detector that detects signal electrons emitted from a sample upon irradiation with the first pulsed electron beam; and a control unit that controls each part, further comprising a second light source that emits second excitation light, which is pulsed excitation light different from the first excitation light, and the control unit irradiates the sample with a second pulsed electron beam emitted from the photocathode upon irradiation with the second excitation light at a timing different from that of the first pulsed electron beam.

[0008] The present invention also relates to a control method for an electron beam application apparatus comprising: a first light source that emits a first excitation light which is pulsed excitation light; a photocathode that emits a first pulsed electron beam upon irradiation with the first excitation light; an objective lens that focuses the first pulsed electron beam; a detector that detects signal electrons emitted from a sample upon irradiation with the first pulsed electron beam; a second light source that emits a second excitation light which is pulsed excitation light different from the first excitation light; and a control unit that controls each part, wherein the control unit irradiates the sample with a second pulsed electron beam emitted from the photocathode upon irradiation with the second excitation light at a timing different from that of the first pulsed electron beam.

[0009] According to the present invention, it is possible to provide an electron beam application device capable of improving the spatial resolution of observed images and a control method therefor.

[0010] Figure 1 shows an example of the overall configuration of the electron beam application device. Figure 2 shows an example of the configuration of the excitation optical system. Figure 3 shows the case where the measurement electron beam and the charge control electron beam are irradiated at the same position and with the same beam diameter. Figure 4 shows the case where the measurement electron beam and the charge control electron beam are irradiated at different positions and with the same beam diameter. Figure 5 shows the case where the measurement electron beam and the charge control electron beam are irradiated at the same position and with different beam diameters. Figure 6 shows another example of the configuration of the excitation optical system. Figure 7 shows an example of the overall configuration of the electron beam application device of Example 2. Figure 8 shows an example of the timing chart between the pulse deflection field, the charge control electron beam and the measurement electron beam. Figure 9 shows another example of the timing chart between the pulse deflection field, the charge control electron beam and the measurement electron beam. Figure 10 shows an example of the processing flow of Example 2. Figure 11 shows an example of the setting screen of Example 2. Figure 12 shows an example of the overall configuration of the electron beam application device of Example 3.

[0011] Hereinafter, an embodiment of the electron beam application apparatus according to the present invention will be described with reference to the attached drawings. The electron beam application apparatus is a device that detects signal electrons emitted by irradiating a sample with an electron beam and generates an observation image of the sample surface.

[0012] An example of the overall configuration of the electron beam application apparatus of Example 1 will be explained using Figure 1. The electron beam application apparatus comprises a first light source 21, a second light source 31, a microscope body 11, and a control unit 13.

[0013] The first light source 21 emits a first excitation light 22, which is pulsed excitation light. The second light source 31 emits a second excitation light 32, which is pulsed excitation light, but different from the first excitation light 22.

[0014] The microscope body 11 comprises a viewport 4, a focusing lens 3, a transparent substrate 1, a photoelectric film 2, a deflector 6, an objective lens 7, a sample stage 10, and a detector 16, and its interior is evacuated to a vacuum. The viewport 4 is a window through which the first excitation light 22 and the second excitation light 32 are taken in. The focusing lens 3 focuses the first excitation light 22 and the second excitation light 32 taken in from the viewport 4 onto the lower surface of the transparent substrate 1.

[0015] The transparent substrate 1 is a plate material that transmits the first excitation light 22 and the second excitation light 32, and a photoelectron film 2 is formed on its lower surface. The photoelectron film 2 is a photocathode with, for example, p-type gallium arsenide (GaAs) as the active layer, and emits a first pulsed electron beam 24 when irradiated with the first excitation light 22, and emits a second pulsed electron beam 34 when irradiated with the second excitation light 32. The photoelectron film 2 is not limited to GaAs. The first pulsed electron beam 24 is a measurement electron beam used to generate an observation image of the sample 9, and the second pulsed electron beam 34 is a charge control electron beam used to control the charge amount of the sample 9. The measurement electron beam and the charge control electron beam are irradiated onto the sample 9 at different timings by operating the first light source 21 and the second light source 31 at different timings.

[0016] The energy of the first pulsed electron beam 24 and the second pulsed electron beam 34 is controlled by the voltage applied to the photoelectron film 2. The intensity of the first pulsed electron beam 24 and the second pulsed electron beam 34 is controlled by the intensity of the first excitation light 22 and the second excitation light 32. The beam diameter of the first pulsed electron beam 24 and the second pulsed electron beam 34 emitted from the photoelectron film 2 is controlled by the focusing diameter of the first excitation light 22 and the second excitation light 32 in the photoelectron film 2. The pulse width of the first pulsed electron beam 24 and the second pulsed electron beam 34 is controlled by the pulse width of the first excitation light 22 and the second excitation light 32.

[0017] The deflector 6 deflects the first pulsed electron beam 24 and the second pulsed electron beam 34 using a magnetic field or electric field. The objective lens 7 forms an objective lens magnetic field 8 and focuses the first pulsed electron beam 24 and the second pulsed electron beam 34 onto the upper surface of the sample 9 held on the sample stage 10. The sample stage 10 holds the sample 9 and is moved to adjust the position of the sample 9. The detector 16 detects signal electrons 18 such as secondary electrons and backscattered electrons emitted from the sample 9 by irradiation with the first pulsed electron beam 24 and the second pulsed electron beam 34, and transmits the detection signal to the control unit 13.

[0018] The control unit 13 is a device that controls the operation of each part, and is, for example, a general-purpose computer. The computer is equipped with a processor such as a CPU (Central Processing Unit) and memory such as RAM (Random Access Memory) and ROM (Read Only Memory). The control unit 13 also generates an observation image of the sample 9, such as an SEM (Scanning Electron Microscope) image, based on the detection signal transmitted from the detector 16.

[0019] An example of the configuration of the excitation optical system formed between the first light source 21 and the second light source 31 and the focusing lens 3 will be explained using Figure 2. The excitation optical system in Figure 2 includes a first collimator lens 25, a first stage 26, a second collimator lens 35, a second stage 36, a regulator 62, and an optical path coupling unit 5.

[0020] The first collimator lens 25 focuses the first excitation light 22. The first stage 26 moves in a direction perpendicular to the optical axis of the first excitation light 22, thereby changing the position in which the first excitation light 22 irradiates the photoelectric film 2.

[0021] The second collimator lens 35 focuses the second excitation light 32. The second stage 36 changes the position in which the second excitation light 32 irradiates the photoelectrode 2 by moving in a direction perpendicular to the optical axis of the second excitation light 32. The adjuster 62 controls the focal diameter of the second excitation light 32 at the photoelectrode 2 by moving the second collimator lens 35 in the optical axis direction of the second excitation light 32. If the second collimator lens 35 is a variable-focus lens, the focal diameter of the second excitation light 32 at the photoelectrode 2 is controlled by changing the refractive index of the lens without using the adjuster 62.

[0022] The optical path coupling unit 5 couples the optical path of the first excitation light 22 and the optical path of the second excitation light 32. When the wavelengths of the first excitation light 22 and the second excitation light 32 are different, for example, when the wavelength of the first excitation light 22 is 650 nm and the wavelength of the second excitation light 32 is 780 nm, a dichroic mirror is used. By using a dichroic mirror in the optical path coupling unit 5, intensity loss between the first excitation light 22 and the second excitation light 32 can be avoided.

[0023] The excitation optical system illustrated in Figure 2 controls the position at which the first pulsed electron beam 24, which is used for measurement, and the second pulsed electron beam 34, which is used for charge control, are irradiated onto the sample 9, as well as the beam diameter at the sample 9.

[0024] Figure 3 illustrates a case where the measurement electron beam and the charge control electron beam are irradiated onto the sample 9 at the same position and with the same beam diameter. Figure 3(a) shows a cross-sectional view parallel to the optical axis, and Figure 3(b) shows the first spot 23, which is the spot of the first excitation light 22 irradiated onto the photoelectric film 2, and the second spot 33, which is the spot of the second excitation light 32. By irradiating the photoelectric film 2 at the same position with the same focusing diameter, the measurement electron beam and the charge control electron beam are irradiated onto the sample 9 at the same position with the same beam diameter.

[0025] Figure 4 illustrates a case in which the measurement electron beam and the charge control electron beam are irradiated onto the sample 9 at different positions but with the same beam diameter. Figure 4(a) is a cross-sectional view parallel to the optical axis, and Figure 4(b) shows the first spot 23 and the second spot 33 on the photoelectric film 2. By irradiating the first spot 23 and the second spot 33 at different positions on the photoelectric film 2 with the same focusing diameter, the measurement electron beam and the charge control electron beam are irradiated onto the sample 9 at different positions with the same beam diameter. The irradiation position of the first spot 23 is controlled by the first stage 26, and the irradiation position of the second spot 33 is controlled by the second stage 36.

[0026] Figure 5 illustrates a case where the measurement electron beam and the charge control electron beam irradiate the sample 9 at the same position but with different beam diameters. Figures 5(a) and 5(b) show diagrams similar to those in Figures 3 and 4. By irradiating the same position on the photoelectric film 2 with different focusing diameters using the first spot 23 and the second spot 33, the measurement electron beam and the charge control electron beam irradiate the same position on the sample 9 with different beam diameters. The focusing diameter of the second spot 33 is controlled by the regulator 62. Furthermore, by controlling the beam diameter of the charge control electron beam on the sample 9, the range over which the charge amount is controlled can be changed.

[0027] Figure 6 illustrates a case where the measurement electron beam and the charge control electron beam irradiate the sample 9 at different positions and with different beam diameters. Figures 6(a) and 6(b) show diagrams similar to those in Figures 3 and 4. By irradiating the first spot 23 and the second spot 33 at different positions on the photoelectric film 2 with different focusing diameters, the measurement electron beam and the charge control electron beam irradiate the sample 9 at different positions with different beam diameters.

[0028] Another example of the excitation optical system configuration will be explained using Figure 7. The excitation optical system in Figure 7 has a fiber coupler 51 and a collimator lens 61. The fiber coupler 51 combines multiple optical fibers into one, coupling the first excitation light 22 from the first light source 21 and the second excitation light 32 from the second light source 31, and guiding them to the collimator lens 61. The collimator lens 61 focuses the first excitation light 22 and the second excitation light 32. In the excitation optical system of Figure 7, the first excitation light 22 and the second excitation light 32 have the same wavelength and are irradiated onto the same position on the photoelectric film 2 with the same focusing diameter. That is, the measurement electron beam and the charge control electron beam are irradiated onto the same position on the sample 9 with the same beam diameter. Note that the first light source 21 and the second light source 31 are operated at different timings, and the measurement electron beam and the charge control electron beam are irradiated onto the sample 9 at different timings.

[0029] In the electron beam application apparatus of Example 1, the charge level of the sample 9 is controlled by the second pulsed electron beam 34, which is irradiated onto the sample 9 at a different timing than the first pulsed electron beam 24 used for measurement. As a result, the objective lens 7 can be brought closer to the sample 9. Consequently, the spatial resolution of the observed image of the sample 9, whose charge level is controlled, can be improved.

[0030] The first excitation light 22 and the second excitation light 32 irradiated onto the photoelectric film 2 may be emitted from a single pulsed light source. The pulsed excitation light emitted from a single pulsed light source is split into the first excitation light 22 and the second excitation light 32 via a half mirror, beam splitter, etc., and irradiated onto the photoelectric film 2 at different timings.

[0031] In Example 1, the position at which the first pulsed electron beam 24 and the second pulsed electron beam 34 irradiate the sample 9 is controlled by changing the position at which the first excitation light 22 and the second excitation light 32 irradiate the photoelectric film 2. An anode (not shown) is provided on the sample stage 10 side of the photoelectric film 2, and the first pulsed electron beam 24 and the second pulsed electron beam 34 irradiate the sample 9 through a hole in the anode. When the position at which the first excitation light 22 and the second excitation light 32 irradiate the photoelectric film 2 is changed, the number of electrons reaching the sample 9 may decrease as the first pulsed electron beam 24 and the second pulsed electron beam 34 are shifted from the center of the hole in the anode. In Example 2, the position at which the first pulsed electron beam 24 and the second pulsed electron beam 34 irradiate the sample 9 is controlled by deflecting the first pulsed electron beam 24 and the second pulsed electron beam 34 without changing the position at which the first excitation light 22 and the second excitation light 32 irradiate the photoelectric film 2.

[0032] An example of the overall configuration of the electron beam application apparatus of Example 2 will be explained using Figure 8. Note that Figure 8 is the same as Figure 1 but with the addition of a pulse deflector 41, so the following explanation will mainly focus on the pulse deflector 41.

[0033] The pulse deflector 41 is positioned between the photoelectric film 2 and the objective lens 7, and forms an electric or magnetic field as a deflection field that deflects the first pulsed electron beam 24 or the second pulsed electron beam 34 at the deflection pivot point 42. The deflection field formed by the pulse deflector 41 deflects either the first pulsed electron beam 24 or the second pulsed electron beam 34, so that the first pulsed electron beam 24 and the second pulsed electron beam 34 are irradiated to different positions on the sample 9. Since the pulse deflector 41 deflects either the first pulsed electron beam 24 or the second pulsed electron beam 34, it operates using a pulse signal.

[0034] An example of a timing chart between the pulse deflection field formed by the pulse deflector 41 and the electron beam for charge control and the electron beam for measurement will be explained using Figure 9. In Figure 9, since the pulse signal 43 is input to the pulse deflector 41 in synchronization with the second pulse electron beam 34, which is the electron beam for charge control, the deflection field deflects the electron beam for charge control and does not deflect the electron beam for measurement, which is emitted from the photoelectron film 2 at a different timing than the electron beam for charge control. Furthermore, by using an optical switch to switch the pulse signal 43 on and off, the irradiation position of the second pulse electron beam 34 can be controlled at a higher speed.

[0035] Using Figure 10, another example of a timing chart between the pulse deflection field formed by the pulse deflector 41 and the electron beam for charge control and the electron beam for measurement will be explained. In Figure 10, since the pulse signal 43 is input to the pulse deflector 41 in synchronization with the first pulse electron beam 24, which is the electron beam for measurement, the deflection field deflects the electron beam for measurement but does not deflect the electron beam for charge control, which is emitted from the photoelectric film 2 at a different timing than the electron beam for measurement.

[0036] Furthermore, by setting a delay time as illustrated in the timing charts in Figures 9 and 10, the surface state of the sample 9 is measured by irradiation with a measurement electron beam after the delay time has elapsed following the change in the surface potential of the sample 9 due to irradiation with the charge control electron beam. The delay time is controlled by the control unit 13. Moreover, when the photocathode with p-type GaAs as the active layer is the photoelectron film 2, the charge control electron beam and the measurement electron beam can be irradiated with a pulse width of as little as approximately 1 picosecond, allowing the surface state of the sample 9, whose surface potential has been rapidly changed, to be measured with high temporal accuracy.

[0037] Using Figure 11, an example of the processing flow of Example 2 will be explained step by step.

[0038] (S111) The sample 9 to be observed is set on the sample stage 10.

[0039] (S112) Irradiation conditions for the measurement electron beam and the charge control electron beam are set. The irradiation conditions include acceleration voltage, pulse frequency, delay time, pulse width, beam intensity, etc. The pulse frequency is the reciprocal of the pulse period, and the delay time is the timing difference between the first pulsed electron beam 24 and the second pulsed electron beam 34. Based on the set irradiation conditions, the alignment and focus of the measurement electron beam and the charge control electron beam are adjusted.

[0040] (S113) The irradiation position of the charge control electron beam is adjusted. When adjusting the irradiation position of the charge control electron beam, the irradiation of the first excitation light 22 is stopped, and the intensity of the pulse signal 43 input to the pulse deflector 41 is adjusted such that an SEM image generated by irradiating the sample 9 with the charge control electron beam is at a desired position.

[0041] (S114) The control unit 13 measures the sample 9, the charge amount of which is controlled by the charge control electron beam whose irradiation position has been adjusted in S113, using the measurement electron beam.

[0042] (S115) The control unit 13 determines whether or not the measurement of the sample 9 has been completed. If the measurement has not been completed, the process returns to S112; if the measurement has been completed, the process proceeds to S116.

[0043] (S116) The control unit 13 determines whether or not the sample 9 is to be replaced. If the sample 9 is to be replaced, the process returns to S111; if the sample 9 is not to be replaced, the process flow ends.

[0044] According to Example 2, which executes the processing flow illustrated in FIG. 11, the charge amount of the sample 9 is controlled by the second pulsed electron beam 34 that irradiates the sample 9 at a timing different from that of the first pulsed electron beam 24 which is the measurement electron beam, so the objective lens 7 can be moved closer to the sample 9. As a result, the spatial resolution of an observation image of the sample 9, the charge amount of which is controlled, can be improved.

[0045] Further, since the irradiation position of the first pulsed electron beam 24 or the second pulsed electron beam 34 onto the sample 9 can be controlled without changing the irradiation position of the first excitation light 22 or the second excitation light 32 onto the photoelectric film 2, the number of electrons reaching the sample 9 can be maintained. Note that the irradiation condition setting in S112 and the irradiation position adjustment in S113 may be performed from the setting screen.

[0046] An example of the setting screen according to Embodiment 2 will be described with reference to FIG. 12. The setting screen in FIG. 12 includes a first pulse setting unit 121, a second pulse setting unit 122, an image display unit 123, and a focusing adjustment unit 124.

[0047] In the first pulse setting unit 121, an acceleration voltage, a pulse frequency, and a delay time are set. In the second pulse setting unit 122, on / off switching of the charging control electron beam is performed, and a pulse width, a pulse intensity, and an irradiation position are set. The irradiation position of the charging control electron beam set by the second pulse setting unit 122 is a relative position with respect to the irradiation position of the measurement electron beam. Furthermore, in the second pulse setting unit 122, on / off switching of the measurement electron beam is performed, and the pulse width, pulse intensity, and alignment are adjusted. Further, based on the conditions set by the first pulse setting unit 121 and the second pulse setting unit 122, the pulse waveforms of the charging control electron beam and the measurement electron beam are displayed on the right side of the first pulse setting unit 121.

[0048] The image display unit 123 displays an SEM image generated by irradiation of the charging control electron beam and the measurement electron beam. In the focusing adjustment unit 124, the focus, stigma, and magnification of the charging control electron beam and the measurement electron beam are adjusted.

[0049] In Embodiment 2, a case where one set of the first pulsed electron beam 24 and the second pulsed electron beam 34 is used to measure the sample 9 whose charge amount is controlled has been described. In Embodiment 3, a case where two sets of the first pulsed electron beam 24 and the second pulsed electron beam 34 are used to measure the sample 9 whose charge amount is controlled, thereby acquiring different information, will be described.

[0050] An example of the overall configuration of the electron beam application apparatus of Example 3 will be explained using Figure 13. Note that Figure 13 is the same as Figure 8 but with the addition of a second detector 17, so the second detector 17 will be mainly explained from here on.

[0051] The second detector 17 detects a second signal electron 19 that is different from the signal electron 18 detected by the detector 16. That is, the signal electron 18 is emitted from the sample 9 by a first set of pulsed electron beams 24 and 34, while the second signal electron 19 is emitted from the sample 9 by a second set of pulsed electron beams with a different pulse frequency from the first set. The pulse frequency F1 of the first set may be an integer multiple of the pulse frequency F2 of the second set, or F2 may be an integer multiple of F1.

[0052] According to Example 3, the amount of charge on the sample 9 is controlled by the second pulsed electron beam 34, which is irradiated onto the sample 9 at a different timing than the first pulsed electron beam 24. This allows the objective lens 7 to be brought closer to the sample 9, thereby improving the spatial resolution of the observed image.

[0053] Furthermore, by using two sets of pulsed electron beams, a first pulsed electron beam 24 and a second pulsed electron beam 34 with different pulse frequencies, the sample 9, whose charge level is controlled, can be measured, allowing for the simultaneous acquisition of different information. As a result, the time required to measure the sample 9, whose charge level is controlled, can be reduced.

[0054] The embodiments of the present invention have been described above. The present invention is not limited to the embodiments described above, 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.

[0055] Transparent substrate 1, photoelectric film 2, focusing lens 3, viewport 4, optical path coupling unit 5, deflector 6, objective lens 7, objective lens magnetic field 8, sample 9, sample stage 10, microscope body 11, control unit 13, detector 16, second detector 17, signal electron 18, second signal electron 19, first light source 21, first excitation light 22, first spot 23, first pulsed electron beam 24, first collimator lens 25, first stage 26, second light source 31, second excitation light 32, second spot 33, second pulsed electron beam 34, second collimator lens 35, second stage 36, pulse deflector 41, deflection pivot 42, pulse signal 43, fiber coupler 51, collimator lens 61, adjuster 62, first pulse setting unit 121, second pulse setting unit 122, image display unit 123, focusing adjustment unit 124.

Claims

1. An electron beam application apparatus comprising a first light source that emits first excitation light, which is pulsed excitation light; a photocathode that emits a first pulsed electron beam upon irradiation with the first excitation light; an objective lens that focuses the first pulsed electron beam; a detector that detects signal electrons emitted from a sample upon irradiation with the first pulsed electron beam; and a control unit that controls each part, further comprising a second light source that emits second excitation light, which is pulsed excitation light different from the first excitation light, and characterized in that the control unit irradiates the sample with a second pulsed electron beam emitted from the photocathode upon irradiation with the second excitation light at a timing different from that of the first pulsed electron beam.

2. An electron beam application apparatus according to claim 1, wherein the control unit irradiates the same position of the photocathode with the first excitation light and the second excitation light.

3. An electron beam application apparatus according to claim 2, further comprising a pulse deflector for deflecting one of the first pulsed electron beam and the second pulsed electron beam.

4. An electron beam application apparatus according to claim 3, characterized in that the pulse signal input to the pulse deflector is switched by an optical switch.

5. An electron beam application apparatus according to claim 1, wherein the control unit irradiates the first excitation light and the second excitation light to different positions of the photocathode.

6. An electron beam application apparatus according to claim 1, wherein the control unit controls the beam diameter of the second pulsed electron beam in the sample by changing the focusing diameter of the second excitation light at the photocathode.

7. An electron beam application apparatus according to claim 1, further comprising a second detector that detects a second signal electron different from the signal electron emitted from the sample by a first set of the first pulsed electron beam and the second pulsed electron beam.

8. An electron beam application apparatus according to claim 7, characterized in that the second signal electrons are emitted from the sample by a second set of the first pulsed electron beam and the second pulsed electron beam, the second set having a pulse frequency different from that of the first set.

9. A control method for an electron beam application apparatus comprising: a first light source that emits a first excitation light which is pulsed excitation light; a photocathode that emits a first pulsed electron beam upon irradiation with the first excitation light; an objective lens that focuses the first pulsed electron beam; a detector that detects signal electrons emitted from a sample upon irradiation with the first pulsed electron beam; a second light source that emits a second excitation light which is pulsed excitation light different from the first excitation light; and a control unit that controls each part, wherein the control unit irradiates the sample with a second pulsed electron beam emitted from the photocathode upon irradiation with the second excitation light at a timing different from that of the first pulsed electron beam.

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