Photoelectron microscope

Abstract

To provide a photoelectron microscope which facilitates acquisition of high-contrast photoelectron images.SOLUTION: A photoelectron microscope provided herein is configured to start irradiation with a pulsed electron beam 13 by an irradiation electron optical system 10 superimposed on excitation light 2 after the lapse of predetermined time from the start of irradiation of a sample 4 with the excitation light by an excitation optical system 1, and start capturing photoelectron images using a camera 6 when the pulsed electron beam irradiation by the irradiation electron optical system is started, or thereafter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a photoelectron microscope. [Background technology]

[0002] A photoelectron emission microscope (PEEM) is an instrument that forms an image using photoelectrons generated by irradiating the surface of a sample with ultraviolet light or X-rays (excitation light), and can obtain a photoelectron image with contrast due to the surface structure of the sample.

[0003] Patent Document 1 relates to an emission electron microscope and discloses that, in order to suppress charging of the sample surface that occurs when observing an insulating sample, an electron beam is irradiated onto the sample surface to neutralize the charging. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-165155 A Summary of the Invention [Problem to be solved by the invention]

[0005] As shown in Patent Document 1, when a sample containing an insulator is observed with a photoelectron microscope, the sample becomes charged. As a result of the study by the inventors, when the sample has a structure containing an insulator, the contrast of the obtained photoelectron image changes depending on the charging state of the sample, and a photoelectron image in a state where charging is suppressed does not necessarily show the structure of the sample with high contrast. In order to obtain a photoelectron image with the desired contrast, it is necessary to charge the sample to a predetermined charging state and to continuously maintain that charging state during the period of imaging by the camera. [Means for solving the problem]

[0006] A photoelectron microscope as one embodiment of the present invention comprises an excitation optical system which irradiates a sample with excitation light, a camera which captures a photoelectron image formed by photoelectrons emitted from the sample irradiated with the excitation light, an imaging electron optical system including an objective lens which focuses the photoelectrons on a detection surface of the camera, an irradiation electron optical system which irradiates the sample with a pulsed electron beam, and a control unit, wherein the control unit starts irradiating the pulsed electron beam by the irradiation electron optical system superimposed on the excitation light a predetermined time after the start of irradiation of the excitation light by the excitation optical system, and starts capturing a photoelectron image by the camera at the same time as or after the start of irradiation of the pulsed electron beam by the irradiation electron optical system. Effect of the Invention

[0007] The present invention provides a photoelectron microscope that can easily obtain a high-contrast photoelectron image. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Brief description of the drawings]

[0008] [Figure 1] 1 is a configuration example of a photoelectron microscope. [Diagram 2] FIG. 2 is a diagram illustrating a sample being irradiated with excitation light and a pulsed electron beam. [Figure 3A] FIG. 2 is a diagram for explaining the principle of the present embodiment. [Figure 3B] FIG. 2 is a diagram for explaining the principle of the present embodiment. [Figure 3C] FIG. 2 is a diagram for explaining the principle of the present embodiment. [Figure 4] FIG. 2 is a diagram illustrating a part of an excitation optical system, an imaging electron optical system, and an irradiation electron optical system of a photoelectron microscope. [Diagram 5] 4 is a time chart of a control signal for acquiring a photoelectron image. [Figure 6] 13 is an example of a recipe setting screen. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Fig. 1 shows a PEEM that obtains an image (photoelectron image) by photoelectrons generated by irradiating the surface of a sample with excitation light such as laser light or X-rays. The main components of the device main body 15 include a stage 3 on which a sample 4 is placed, an excitation optical system 1 that irradiates the sample 4 with excitation light 2, an irradiation electron optical system 10 that irradiates the sample 4 with a pulsed electron beam 13, a camera 6 that captures a photoelectron image, and an imaging electron optical system 9 that forms the photoelectron image on the camera 6. The excitation optical system 1 may include optical elements such as lenses and mirrors in addition to an excitation light source that generates the excitation light 2. The irradiation electron optical system 10 includes an electron gun 11 that emits an electron beam, a blanker 12 that pulses the electron beam emitted from the electron gun 11, and a pulsing circuit 14 that controls the blanker 12.

[0010] Photoelectrons 5 generated by irradiating the sample 4 with the excitation light 2 are focused on the detection surface of the camera 6 by the objective lens 7 of the imaging electron optical system 9. In FIG. 1, the objective lens 7 and the beam separator 8 are shown as elements constituting the imaging electron optical system 9, but the imaging electron optical system 9 may include one or more stages of electron lenses and other electron optical elements. Here, the beam separator 8 is provided to deflect the pulsed electron beam 13 from the irradiation electron optical system 10 so that it travels toward the sample 4, while the photoelectrons 5 generated from the sample 4 travel toward the camera 6. Such a beam separator can be realized by, for example, a Wien filter or a magnetic sector. The camera 6 may detect and photograph the photoelectrons themselves, or may include a scintillator, convert the electrons into light by the scintillator, and detect and photograph the converted light.

[0011] The device body 15 is connected to a control unit 20. The control unit 20 controls the device body 15 in response to instructions from a user inputted from a GUI (Graphical User Interface) device 22, and also performs image processing of the photoelectron image captured by the camera 6. The control unit 20 includes a storage unit 21, in which control parameters of the device body 15 and the photoelectron image are stored.

[0012] FIG. 2 shows a schematic diagram of how the excitation light 2 and the pulsed electron beam 13 are irradiated onto the sample 4. The field of view of the PEEM is determined by the irradiation range of the excitation light 2, and has a diameter of approximately several hundred μm. The irradiation electron optical system 10 irradiates the pulsed electron beam 13 in accordance with the irradiation range of the excitation light 2. That is, the irradiation positions of the excitation light 2 and the pulsed electron beam 13 are adjusted, and the irradiation ranges are controlled so that they are of the same size. To irradiate such a planar pulsed electron beam 13, the irradiation electron optical system 10 may be provided with a lens that converts the electron beam into a parallel beam upstream of the beam separator 8. In the configuration of FIG. 1, since the pulsed electron beam 13 is affected by the objective lens 7, it is difficult to make the pulsed electron beam 13 into a completely parallel beam, but it is sufficient that the intensity in the irradiation area of ​​the pulsed electron beam 13 is controlled to be as uniform as possible. In addition, the irradiation area of ​​the pulsed electron beam 13 is rectangular in FIG. 2, but this shape is not limited to a rectangle, and it may be circular, elliptical, or other shapes. The shape of the irradiation region is determined by the shape of the aperture of the diaphragm provided in the irradiation electron optical system 10. The pulse interval of the pulsed electron beam 13 is assumed to be on the order of nanoseconds to microseconds.

[0013] The principle of this embodiment will be described with reference to Figures 3A to 3C. The sample 4 has a layered structure in which an electrode 33 is provided on a Si (silicon) substrate 31 via an insulator 32, as shown in Figure 3A, and a photoelectron image of such a sample is to be acquired. At this time, the amount of photoelectrons 5 generated (signal amount) from the electrode 33 decreases with the measurement time, as shown in Figure 3B. This is because the electrode 33 is insulated from the substrate 31 by the insulator 32, and there is no source of charge supply to the electrode 33, so the amount of charge decreases due to the emission of photoelectrons, and the amount of emitted photoelectrons also attenuates with time.

[0014] As a result, the brightness of the electrode 33 in the photoelectron image is determined according to the area of ​​the region 36 surrounded by the decay waveform 35, assuming that the imaging time of the camera 6 is between Ts and Te. On the other hand, the region of the substrate 31 that is not irradiated with the excitation light 2 serves as the source of charge, so the brightness of the substrate 31 in the photoelectron image hardly changes regardless of the measurement time. Therefore, the contrast of the photoelectron image changes depending on the setting of the imaging time of the camera 6. For this reason, it is necessary to set an optimal imaging time of the camera 6 (imaging start time Ts and imaging end time Te) for the sample 4 having the structure shown in FIG. 3A in order to obtain a high-contrast photoelectron image. However, especially at a stage where not much time has passed since the start of irradiation with the excitation light 2, the decay rate of the signal amount of the electrode 33 is also large, and a deviation in control has a significant effect on the contrast of the photoelectron image. If a sufficient amount of time has passed since the start of irradiation with the excitation light 2, the decay rate of the signal amount of the electrode also becomes small, but since the signal amount has decreased, it takes a long time to obtain a photoelectron image, and there is no guarantee that the imaging time of the camera 6 set in this way will give the optimal contrast.

[0015] Therefore, in this embodiment, the pulsed electron beam 13 is superimposed on the excitation light 2 and irradiated. Time period 37 shown in FIG. 3C is a time period during which one pulse of the pulsed electron beam 13 is irradiated to the sample 4. In time period 37, the amount of charge increases as a result of the supply of charge to the electrode 33, and as a result, the amount of photoelectrons emitted by the electrode 33 increases. On the other hand, in time period 38 during which the electron beam is not irradiated, the amount of photoelectrons emitted by the electrode 33 decreases. As a result, for example, as shown in FIG. 3C, the charged state of the sample is controlled between the imaging time of the camera 6 and the set Ts-Te, and the change in the signal amount of the electrode can be suppressed to a range of Smin or more and Smax or less. In this way, in this embodiment, the pulsed electron beam 13 is superimposed on the excitation light 2 and irradiated, and various control parameters of the pulsed electron beam 13, the camera 6, etc. are controlled, making it possible to easily obtain a photoelectron image with optimal contrast for observing the sample 4.

[0016] The method of acquiring a photoelectron image in this embodiment will be described below. FIG. 4 shows a part of the excitation optical system 1, the camera 6, the imaging electron optical system 9, and the projection electron optical system 10 of the photoelectron microscope in this embodiment. The excitation optical system 1 includes an excitation light source 41 and a shutter 42. To stably irradiate the sample 4 with the excitation light 2, it is not desirable to turn on and off the excitation light source 41 itself. Therefore, the shutter 42 is provided to control the irradiation / non-irradiation of the excitation light 2 to the sample 4. The shutter 42 may be a mechanical mechanism or may be an optical crystal that electrically controls the optical crystal. In addition, the projection electron optical system 10 includes an electron gun 11 and a blanker 12. The blanker 12 includes an aperture 46 and a deflector 47. The deflector 47 controls the passage / non-passage of the electron beam from the electron gun 11 through the aperture 46, thereby pulsating the electron beam.

[0017] The imaging electron optical system 9 shows a blanker 43 that pulses the photoelectrons 5 incident on the camera 6. The blanker 43 includes an aperture 44 and a deflector 45, and pulses the photoelectrons 5 in the same manner as the blanker 12. The reason for providing the blanker 43 in the imaging electron optical system 9 will be described with reference to FIG. 3C. As described above, the signal amount of photoelectrons increases when the electron beam is irradiated on the sample 4 in the time period 37. However, secondary electrons are also generated when the electron beam is irradiated on the sample 4 at this time. Since there is not much difference in energy between photoelectrons and secondary electrons, it is difficult to separate them in the imaging electron optical system 9, and in fact, secondary electrons are detected as signal electrons in addition to photoelectrons in the time period 37. For this reason, the imaging electron optical system 9 shown in FIG. 4 is provided with a blanker 43 that blocks the incidence of electrons on the camera 6 in the time period 37. This makes it possible to suppress noise caused by the irradiation of the pulsed electron beam 13. If the signal amount of secondary electrons is negligible compared to the signal amount of photoelectrons in the time period 37, blanking of photoelectrons by the blanker 43 may be unnecessary.

[0018] Fig. 5 is a time chart of control signals for acquiring a photoelectron image in a photoelectron microscope equipped with the optical system shown in Fig. 4. Control signal 51 is a control signal for the blanker 12 that turns irradiating electrons on and off, control signal 52 is a control signal for the blanker 43 that turns photoelectrons on and off, control signal 53 is a control signal for the shutter 42 that turns excitation light on and off, and control signal 54 is a control signal for the camera 6 that captures a photoelectron image.

[0019] The control signal 51 is a rectangular wave with a pulse width t1 and a pulse interval t2. In this example, the electron beam is irradiated onto the sample 4 when the high level of the control signal 51 is input to the blanker 12, and the electron beam is blocked when the low level is input to the blanker 12. Irradiation of the pulsed electron beam 13 onto the sample 4 begins t7 after the shutter 42 is turned on and the excitation light 2 starts to be irradiated onto the sample 4. After the t7 time has elapsed, the electrode 33 is in a predetermined charged state, and thereafter, the electron beam is irradiated in a superimposed state with the excitation light 2 at the timing of the control signal 51, thereby maintaining the charged state of the electrode 33 in the same state (see FIG. 3C).

[0020] The control signal 52 is a rectangular wave with a pulse width t5 that is controlled in synchronization with the control signal 51. As with the control signal 51, when the high level of the control signal 52 is input to the blanker 43, the photoelectrons 5 are incident on the camera 6, and when the low level is input to the blanker 43, the photoelectrons are blocked. Therefore, in order to prevent secondary electrons from being incident on the camera 6, the control signal 51 and the control signal 52 are controlled in synchronization with each other so that the control signal 52 is always at a low level during the period when the control signal 51 is at a high level. Although this example shows an example where the pulse interval t2=pulse width t5, the present invention is not limited to this, and the pulse interval t2>pulse width t5 may also be satisfied.

[0021] Camera photography starts after time t8 has elapsed since the shutter 42 was turned on and the excitation light 2 started to irradiate the sample 4. If the relationship of delay time t8≧delay time t7 is satisfied, the electrode 33 is controlled to a desired charged state. Camera photography starts at the photography start time Ts and ends at the photography end time Te. By integrating the photoelectron images captured during the integration period t9 (=Te−Ts), a photoelectron image with a desired contrast can be obtained. After that, the shutter 42 blocks the irradiation of the excitation light 2 to the sample 4.

[0022] The control unit 20 reads a condition file in which shooting conditions for obtaining a photoelectron image with a desired contrast are set in advance, and stores the file in the storage unit 21. The control unit 20 can obtain a photoelectron image by controlling the device main body 15 in accordance with the shooting conditions read into the storage unit 21. FIG. 6 shows a recipe setting screen for setting shooting conditions (recipe) for obtaining a photoelectron image with a desired contrast. The recipe setting screen 60 is a display screen displayed on the GUI device 22.

[0023] The photoelectron image display section 61 displays a photoelectron image captured under predetermined imaging conditions. The position of the sample 4 where the photoelectron image is to be captured is specified in the stage coordinate setting section 62, and the captured photoelectron image 63 is displayed. For example, a histogram of the brightness of a region in which the user wishes to enhance the contrast may be displayed by specifying the region of the photoelectron image 63. The histogram 64 shows the brightness histogram of the region A and region B specified on the photoelectron image 63. The user sets a control parameter for obtaining a photoelectron image with a desired contrast in the parameter setting section 65. In the example of FIG. 6, the parameter name input section 66 allows the control parameter to be selected by a pull-down menu, and when a control parameter is selected, the value at the time when the photoelectron image 63 was captured is displayed in the value setting section 67. The user adjusts the control parameter so as to obtain the desired contrast.

[0024] 5, the control parameters include the irradiation electron beam current (density) c3 as the intensity of the pulsed electron beam 13, and the irradiation electron beam area a4 which is the area on the sample of the pulsed electron beam 13. Also, the photoelectron pulse phase p6 indicates the magnitude of the delay of the rising edge of the pulse of the control signal 52 relative to the rising edge of the pulse of the control signal 51 when the pulse interval t2>pulse width t5.

[0025] When loading a condition file in which shooting conditions have been set in advance from an external source, the user presses a load button 68. In addition, in order to store the shooting conditions adjusted on the recipe setting screen 60, the user presses a save button 69. As a result, the shooting conditions adjusted on the recipe setting screen 60 are stored in the storage unit 21.

[0026] Although the method in which the user adjusts the photographing conditions by visual inspection has been described above, the user may specify an area in the photoelectron image 63 where the contrast is to be enhanced, and the control unit 20 may automatically adjust the contrast of the photoelectron image 63 by feeding it back to the photographing conditions. For example, the contrast of the photoelectron image can be improved by performing either a first adjustment in a direction to increase the amount of charge or a second adjustment in a direction to decrease the amount of charge, and performing an adjustment in the same direction if the contrast improves, or performing an adjustment in a different direction if the contrast decreases.

[0027] The present invention is not limited to the above-described embodiment, and includes various modified examples. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and is not necessarily limited to the embodiment having all of the configurations described. In addition, it is possible to add, delete, or replace part of the configuration of the embodiment with other configurations.

[0028] For example, a photoexcited electron source may be used to generate a pulsed electron beam in the projection electron optical system 10. The photoexcited electron source is an electron source that generates an electron beam by irradiating a photocathode with excitation light. A pulsed electron beam can be generated by irradiating a photocathode with pulsed excitation light. Even when a photoexcited electron source is used, it is possible to adjust the pulse waveform and intensity of the pulsed electron beam by adjusting the pulse waveform and intensity of the pulsed excitation light. In addition, although a beam separator is provided in the configuration of FIG. 1 to irradiate the sample with the pulsed electron beam, if there is sufficient space around the sample, the pulsed electron beam may be irradiated obliquely without providing a beam separator. [Explanation of symbols]

[0029] 1: excitation optical system, 2: excitation light, 3: stage, 4: sample, 5: photoelectron, 6: camera, 7: objective lens, 8: beam separator, 9: imaging electron optical system, 10: irradiation electron optical system, 11: electron gun, 12: blanker, 13: pulsed electron beam, 14: pulsation circuit, 15: device body, 20: control unit, 21: memory unit, 22: GUI device, 31: substrate, 32: insulator, 33: electrode, 35: attenuation waveform, 36: area, 37, 38: time zone, 41: excitation light source, 42: shutter, 43: blanker, 44, 46: aperture, 45, 47: deflector, 51, 52, 53, 54: control signal, 60: recipe setting screen, 61: photoelectron image display section, 62: stage coordinate setting section, 63: photoelectron image, 64: histogram, 65: parameter setting section, 66: parameter name input section, 67: value setting section, 68: load button, 69: save button.

Claims

1. an excitation optical system that irradiates the sample with excitation light; a camera for capturing a photoelectron image of photoelectrons emitted from the sample irradiated with the excitation light; an imaging electron optical system including an objective lens that focuses the photoelectrons onto a detection surface of the camera; an irradiation electron optical system for irradiating the sample with a pulsed electron beam; A control unit, The control unit starts irradiating the excitation light by the excitation optical system and a predetermined time later, starts irradiating the pulsed electron beam by the irradiating electron optical system in a manner superimposed on the excitation light, and starts capturing the photoelectron image by the camera at the same time as or after the irradiation of the pulsed electron beam by the irradiating electron optical system starts.

2. In claim 1, the imaging electron optical system includes a beam separator; The beam separator is a photoelectron microscope that causes the pulsed electron beam from the irradiation electron optical system to travel toward the sample and causes the photoelectrons from the sample to travel toward the camera.

3. In claim 1, the imaging electron optical system includes a blanker that pulses photoelectrons incident on the camera; The control unit performs synchronous control so that the blanker blocks the photoelectrons from entering the camera during a period in which the sample is irradiated with an electron beam from the irradiation electron optical system.

4. In claim 1, The projection electron optical system is a photoelectron microscope that projects the planar pulsed electron beam onto the sample.

5. In claim 1, the control unit includes, as imaging conditions for the photoelectron image, a pulse width, a pulse interval, an intensity and an area on a sample of the pulsed electron beam, a delay time from the start of irradiation of the excitation light to the start of irradiation of the pulsed electron beam, a delay time from the start of irradiation of the excitation light to the start of imaging by the camera, and an imaging time by the camera; A photoelectron microscope, wherein the photographing conditions are determined based on the contrast of the photoelectron image.

6. In claim 3, the control unit includes, as imaging conditions for the photoelectron image, a pulse width, a pulse interval, an intensity and an area on a sample of the pulsed electron beam, a pulse width of the photoelectrons, a pulse phase of the photoelectrons, a delay time from the start of irradiation of the excitation light to the start of irradiation of the pulsed electron beam, a delay time from the start of irradiation of the excitation light to the start of imaging by the camera, and an imaging time by the camera; A photoelectron microscope, wherein the photographing conditions are determined based on the contrast of the photoelectron image.

7. an excitation optical system that irradiates the sample with excitation light; a camera for capturing a photoelectron image of photoelectrons emitted from the sample irradiated with the excitation light; an imaging electron optical system including an objective lens that focuses the photoelectrons onto a detection surface of the camera; an irradiation electron optical system for irradiating the sample with a pulsed electron beam; A control unit; A GUI device, the control unit causes the irradiation of the pulsed electron beam by the irradiating electron optical system to start superimposed on the excitation light a predetermined time after the start of irradiation of the excitation light by the excitation optical system, and causes the camera to start capturing the photoelectron image at the same time as or after the start of irradiation of the pulsed electron beam by the irradiating electron optical system; The GUI device displays the photoelectron image acquired by the camera along with the photographing conditions of the photoelectron image, and displays a recipe setting screen for adjusting the photographing conditions.

8. In claim 7, A photoelectron microscope, wherein the conditions for capturing the photoelectron image include the pulse width, pulse interval, intensity and area on the sample of the pulsed electron beam, the delay time from the start of irradiation of the excitation light to the start of irradiation of the pulsed electron beam, the delay time from the start of irradiation of the excitation light to the start of imaging by the camera, and the imaging time by the camera.

9. In claim 7, the imaging electron optical system includes a blanker that pulses photoelectrons incident on the camera; The control unit performs synchronous control so that the blanker blocks the photoelectrons from entering the camera during a period in which the sample is irradiated with an electron beam from the irradiation electron optical system.

10. In claim 9, A photoelectron microscope, wherein the conditions for capturing the photoelectron image include the pulse width, pulse interval, intensity and area on the sample of the pulsed electron beam, the pulse width of the photoelectrons, the pulse phase of the photoelectrons, the delay time from the start of irradiation of the excitation light to the start of irradiation of the pulsed electron beam, the delay time from the start of irradiation of the excitation light to the start of imaging by the camera, and the imaging time by the camera.

Images