JPH0133898B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission electron microscope, and more particularly to an apparatus for easily adjusting focus when projecting an image of a hole in a selected area diaphragm onto a fluorescent screen.

Selected area diffraction is used when analyzing metallic samples using a transmission electron microscope. Such selected area diffraction is when a selected area diaphragm is installed at the image plane of the objective lens, and the diffraction image formed on the back focal plane of the objective lens is magnified and focused onto a fluorescent screen using an intermediate lens and a projection lens. It is something that makes you imagine. By doing so, a diffraction image corresponding to an electron microscope image at an arbitrary point on the sample can be obtained.

However, in such selected area diffraction, if the image plane of the objective lens and the selected area aperture are misaligned, the correspondence between the obtained diffraction image and the limited field of view (electron microscope image) will be inaccurate. . Therefore, in order to prevent such inconvenience, first, an image of the hole of the selected area diaphragm (hereinafter simply referred to as the selected area diaphragm image) is formed on the fluorescent screen using an intermediate lens and a projection lens, and in this state, the objective lens is Therefore, a method is generally used in which the position of the image plane of the objective lens and the selected area diaphragm are aligned by simultaneously forming the sample image on a fluorescent screen on which the selected area diaphragm image is projected.

However, when forming a selected area aperture image, it is very difficult to adjust the selected area aperture image on the fluorescent screen to just focus because the aperture angle of the electron beam is small. Conventionally, focus alignment has been carried out by using a sample that scatters easily and increasing the aperture angle of the electron beam that forms a selected area aperture image, but such operations are extremely difficult for beginners and require skilled workers. It takes.

In view of these points, the present invention provides an apparatus that can easily perform focus adjustment of a selected area aperture image without requiring any skill, and will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and numeral 1 indicates an electron gun. The electron beam 2 generated by the electron gun 1 is focused by two stages of focusing lenses 3 and 4 and irradiated onto a sample 5. The electron beam transmitted through the sample 5 passes through an objective lens 6, an intermediate lens 7, and a projection lens 8.
The image is enlarged and the final image is formed on the fluorescent screen 9.
10 is an objective lens power supply, and the power supply and the objective lens 6
A switch 11 is provided between the two. 12 is an intermediate lens power supply. 13 is a selected area diaphragm placed between the objective lens 6 and the intermediate lens 7. 14 and 15 are two-stage deflection coils placed between the focusing lens 4 and the sample 5; the first-stage deflection coil 14 is supplied with a sweep current from a power source 16 via a changeover switch 17; Also, the second stage deflection coil 15 is connected to a power source 16 by a changeover switch 18.
A sweep current is supplied directly or through a resistor 19. The changeover switches 17 and 18 are interlocked, and the changeover switches 17 and 18 are interlocked with the switch 11.

In such a configuration, the deflection angle of the deflection coil 15 is made larger than that of the deflection coil 14 by, for example, increasing the number of coil turns, and the deflection directions of the two deflection coils are opposite to each other. Further, when the changeover switches 17 and 18 are switched to the terminal c side, the electron beam 2 is fixed at one point on the sample 5 as shown in FIG. 2b, and its direction of incidence changes periodically and alternately. Furthermore, selector switch 1
7 and 18 are switched to the terminal b side, the electron beam 2 is fixed at one point in the hole of the selected area diaphragm 13, and its direction of incidence changes periodically and alternately, as shown in Figure 2a. It is structured as follows.

Selected area aperture 13 is now placed on the electron beam path.
In order to match the image plane of the objective lens 6,
First, the objective aperture (not shown) inserted into the center of the objective lens 6 is removed from above the electron beam path. Next, when the switch 11 is opened, the changeover switches 17 and 18 are switched to the terminal b side in conjunction with the operation.
As a result, the objective lens 6 is turned off (non-excited), and the electron beam 2 is fixed at the center of the hole in the selected area diaphragm 13 by the deflection coils 14 and 15, as shown in FIG. 2a. The direction of incidence is periodically and alternately changed. At this time, the beam diameter of the electron beam 2 that irradiates the selected area aperture 13 is made larger than the hole diameter of this selected area aperture. However, as the irradiation direction of the electron beam 2 changes, the electron beams 2 that have passed through the selected area aperture 13 are 2a and 2b.
The intermediate lens 7 is
The image is magnified by the projection lens 8 and a selected area aperture image is projected onto the fluorescent screen 9 . At this time, when the electron beams 2a and 2b are out of focus, the positions on the fluorescent screen 9 are different, and a double image appears.
In addition, when the focus is completely aligned, the electron beams 2a and 2b are focused on the same location on the fluorescent screen 9, and the images become completely single, as shown in the figure. Therefore, by varying the excitation current of the intermediate lens 7 so that the selected area aperture images formed on the phosphor screen 9 are unified, a just-focused selected area aperture image can be easily obtained.

When the selected area aperture image of the just focus is obtained, the switch 11 is closed and the excitation current is supplied to the objective lens 6 to turn it on, and the changeover switches 17 and 18 are switched to the terminal c side. 2
As shown in Figure b, the electron beam 2 is fixed at one point on the sample 5, and its direction of incidence is periodically and alternately changed. As a result, the sample image is simultaneously projected into the selected area aperture image projected on the fluorescent screen 9, and since the sample image appears double when the focus is not adjusted, the double images are made to become one. The excitation current of the objective lens 6 is adjusted. By performing such an operation, the image plane of the objective lens 6 and the selected area diaphragm 13 can be accurately aligned. Therefore, if the excitation current of the intermediate lens 7 is changed and the diffraction image formed on the back focal plane of the objective lens 6 is enlarged and imaged on the fluorescent screen 9, the field of view limited by the selected area diaphragm 13 can be accurately focused. A corresponding selected area diffraction image can be obtained.

In the above description, when the direction of incidence of the electron beam on the selected area diaphragm is periodically changed, the sample remains on the electron beam path, but it goes without saying that it may be moved out of the path.

With the above configuration, the present invention eliminates the need to use the electron beam scattered by the sample when performing focus adjustment of the selected area aperture image, as in the past, and even beginners can easily adjust the focus without requiring any skill. You can get the statue of Orcus. Furthermore, since there is no need to use a sample, by increasing the excitation intensity of the projection lens, focus alignment can be performed with sufficient brightness even if the selected area aperture image is projected at a high magnification. Furthermore, the ratio of the sweep currents supplied to the two-stage deflection coil can be fixed at a constant value by periodically changing the direction of incidence of the electron beam to the selected area diaphragm while the excitation current of the objective lens is stopped. This makes operation very easy. Furthermore, by installing two stages of deflection coils above the sample, focus alignment between the selected area aperture image and the sample image can be performed using one set and two stages of deflection coils, thereby simplifying the configuration. Can be done.

In the above embodiment, two stages of deflection coils are installed above the sample, but two stages of deflection coils may be installed above the sample and between the sample and the selected area aperture.

Further, although the excitation current supply to the objective lens was stopped when focusing the selected area aperture image on the fluorescent screen, it is not necessarily necessary to stop the supply.

Further, although it has been described that when the switch 11 for turning the objective lens 6 on and off is opened, the changeover switches 17 and 18 are changed from terminal a to terminal b, the changeover switch 1 is not limited to this.
It may be configured such that 11 is opened only when 7 and 18 are switched to the terminal b side.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention, and FIGS. 2a and 2b are diagrams for explaining the operation, respectively. 1: Electron gun, 2: Electron beam, 3 and 4: Focusing lens, 5: Sample, 6: Objective lens, 7: Intermediate lens, 8: Projection lens, 9: Fluorescent screen, 10: Objective lens power supply, 11: Switch, 12: Intermediate lens power supply, 13: Selected field diaphragm, 14 and 15: Deflection coil, 16: Power supply, 17 and 18: Selector switch, 19: Resistor.

Claims (1)

[Claims] 1. In an apparatus in which a selected area diaphragm is inserted into an imaging lens system and a selected area diffraction image is obtained by adjusting the excitation current of the imaging lens system behind the selected area diaphragm, the selected area diaphragm is A transmission electron microscope is equipped with a deflection system to periodically change the direction of incidence of an electron beam with the electron beam fixed in a hole.