JPH0161228B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron beam irradiation method in an electron beam apparatus, and in particular to a method in which the focusing angle of the irradiated electron beam incident on a sample can be continuously varied while keeping the excitation intensity of an objective lens constant. The present invention relates to an electron beam irradiation method.

In recent years, in research and development of new materials, a method called focused electron diffraction has been adopted to observe the composition of the materials. In this type of observation method, the diffraction image is obtained by varying the convergence angle of the electron beam incident on the sample, and the internal structure of the sample is investigated. The method of irradiating and observing the sample is also useful for obtaining high-resolution images of crystals.

A conventional example of an irradiation system for using such an electron beam irradiation method is shown in FIG. This irradiation system includes one or more focusing lenses 4 and 5 arranged in front of an objective lens 1 consisting of a front objective lens body 2 and a rear objective lens body 3.
The irradiated electron beam 6 passing through the front objective lens body 2
and the rear objective lens body 3, ie, within the gap of the objective lens 1, the beam is focused onto a sample 7. Further, a diaphragm 8 is disposed near the final stage focusing lens 5, and is configured to vary the focusing angle of the irradiation electron beam 6 incident on the sample 7 while keeping the excitation intensity of the objective lens 1 constant. . That is, in the electron beam irradiation system shown in FIG. 1, a real image of the electron beam source is first focused on a point P on the electron beam axis (hereinafter referred to as the optical axis for convenience) O by the focusing lens 4, and then the final stage focusing After the lens 5 forms an image at a point Q that is conjugate with the point P, the front objective lens 2 forms an image at a point R on the sample 7 at a predetermined convergence angle. When varying the convergence angle of the irradiated electron beam 6 incident on the sample 7, the aperture diameter of the aperture 8 is adjusted to the first
This is done by changing the size shown by the solid line in the figure to other sizes. In order to vary the focusing angle in this way, a movable diaphragm with three to four rows of holes is usually used for the diaphragm 8, and the holes aligned with the optical axis O can be replaced from time to time as necessary. I'm starting to be able to do it.

However, in such a conventional electron beam irradiation method, a movable aperture 8 provided with several rows of holes is operated to vary the convergence angle of the electron beam 6 incident on the sample 7. Because of this, the convergence angle of the electron beam 6 had to be changed stepwise, and it was not possible to cause a continuous angle change.
Moreover, the number of stages in which the focusing angle can be varied is determined by the number of holes formed by the aperture 8, and the angle can only be varied up to four stages at most.

Of course, the focusing angle can also be changed by changing the excitation intensity of the final stage focusing lens 5 without changing the hole diameter of the aperture 8, but in this case, as shown enlarged in Fig. 2, the focusing angle can be changed. In addition, the angle of incidence of the electron beam 6 entering the sample 7 is different between the outer edge and the center point of the electron beam irradiation circle formed on the sample 7, and for example, even if you try to obtain a diffraction image of a crystal, the correct diffraction may not be obtained. There was a problem with not being able to get an image.

The present invention was developed in view of these conventional problems, and its purpose is to continuously vary the convergence angle of the irradiated electron beam incident on the sample while keeping the excitation intensity of the objective lens constant. The object of the present invention is to provide an electron beam irradiation method that can be used to irradiate electron beams, and to solve the above-mentioned conventional problems.

In order to achieve the above object, the present invention arranges at least three stages of focusing lenses in the order of the first stage, second stage, and final stage from the electron beam source side in front of the objective lens, and excite the first stage focusing lens. While keeping constant,
The gist is that the excitation of the second-stage focusing lens and the final-stage focusing lens are linked to each other, so that the image point of the final-stage focusing lens almost coincides with the object point of the objective lens. By changing the excitation of the first-stage focusing lens and the final-stage focusing lens in conjunction with each other, the image point of the second-stage focusing lens moves in the front-rear direction of the electron beam axis as the excitation changes, but the image point of the second-stage focusing lens moves in the front-back direction of the electron beam axis as the excitation changes. The image point can be kept stationary at a fixed point. The movement of the image point of the second-stage focusing lens means that the focusing angle of the electron beam after passing through the second-stage focusing lens is varied, and the fixation of the image point of the final-stage focusing lens means that This means that the excitation of the objective lens can be kept constant while the focusing angle of the electron beam is varied. In another aspect of the present invention, an additional electron lens is disposed between the final stage focusing lens and the objective lens, and the real image of the electron beam source by the final stage focusing lens is transferred between the additional electron lens and the front objective lens. The image is formed on the sample by By keeping the combined reduction ratio of the additional electron lens and the front objective lens relatively small, it is possible to suppress the fluctuation range of the image point of the final stage focusing lens due to the unevenness of the sample to a small value.

The present invention will be explained in detail below based on embodiments shown in the accompanying drawings.

FIG. 3 is a diagram showing an embodiment of an electron beam irradiation system for carrying out the first invention. This irradiation system includes a first-stage focusing lens 10 and a second-stage focusing lens 11 located in front of the objective lens 1 in order from the electron beam source side.
At least three stages of focusing lenses are arranged so as to form a second stage focusing lens 1 and a final stage focusing lens 5.
A diaphragm 13 having a predetermined aperture diameter for regulating the cross section of the electron beam bundle is installed near the opening 1. The first stage focusing lens 10 converts the real image of the electron beam source into an optical axis O in FIG.
The excitation is set so that the image is formed on point S above.
The second stage focusing lens 11 converts the real image of the point S into the second stage focusing lens 11.
It can be excited to form an image at any position on the optical axis O behind the stage focusing lens 11 from point _P1 to point Pn. The third stage focusing lens 5 focuses the electron beam 6 whose trajectory has been changed by the excitation change of the second stage focusing lens 11 on a fixed point Q on the optical axis O, and forms a real image of the electron beam source at this position. In order to
The excitation can be changed in conjunction with the stage focusing lens 11. The objective lens 1 consists of a front objective lens body 2 and a rear objective lens body 3, and a sample 7 is disposed between both the objective lens bodies 2 and 3. It is preferable to use a short focus lens as the front objective lens 2, and this lens has a fixed point Q as an object point,
The electron beam 6 emitted from this point is focused on a point R on the sample 7, and excitation is set to form a real image of the electron beam source at this position. A fixed aperture may be used for the aperture 13 provided near the second stage focusing lens 11, or a movable aperture may be provided. Note that several more focusing lenses may be arranged in front of the first stage focusing lens 10.

In the irradiation system having such a configuration, the electron beam is focused by the first stage focusing lens 10 to a point S on the optical axis O, and the real image of the electron beam source is formed at this position. The light is focused on a predetermined range of points on the optical axis O between the second-stage focusing lens 11 and the final-stage focusing lens 5. In this case, when the second stage focusing lens 11 is set to the weakest excitation within its variable range, the electron beam is
It focuses on point P ₁ as shown in . On the other hand, when the second stage focusing lens 11 is set to the strongest excitation within its variable range, the electron beam is focused at a point Pn, as indicated by 6b. If the excitation of the second stage focusing lens 11 is changed continuously or stepwise from the weakest excitation to the strongest excitation, the path of the electron beam changes from the one indicated by the symbol 6a to the one indicated by the symbol 6b. The imaging point P changes from point _P1 to point Pn.

Next, in the third stage focusing lens 5, the excitation intensity is varied functionally with respect to the excitation strength of the second stage focusing lens 11, and the image point of the third stage focusing lens 5 is always on the optical axis O. Since the electron beam 6 is kept at the fixed point Q, the electron beam 6 is focused at the fixed point Q no matter how the excitation of the second stage focusing lens 11 is changed. Further, the electron beam 6 emitted from this fixed point Q is connected to a point R on the sample 7 by the front objective lens body 2. Since the electron beam 6 entering the front objective lens body 2 is always emitted from a fixed point Q, the excitation intensity of the objective lens 1 can always be kept constant.

If electron beam irradiation is also performed in this way, for example, if the second stage focusing lens 11 is excited at the weakest within its excitation variable range and focused on point _P1 , the electrons obtained thereby While the line 6a is imaged on the sample 7 at an extremely small focusing angle, when the second stage focusing lens 11 is excited to the maximum and the image is formed on the point Pn,
The electron beam 6b thus obtained forms an image on the sample 7 at a relatively large convergence angle. Then, while the imaging point P by the second stage focusing lens 11 moves from point _P1 to point Pn, the focusing angle of the electron beam incident on the sample 7 is
It is sequentially and variably controlled in the range of 10 ^-4 rad to 10 ^-1 rad.

Further, by using a short focus lens for the front objective lens body 2, it is advantageous that the spherical aberration of the front objective lens body 2 can be suppressed to a small value. This is because when the convergence angle of the electron beam 6 incident on the sample 7 increases, the spherical aberration of the front objective lens body 2 increases in proportion to the cube of the convergence angle, and the sample 7
The diameter of the upper irradiation spot increases, and the homogeneity of the focusing angle within the irradiation circle is destroyed. If a short focal length lens is used for the front objective lens body 2, its spherical aberration will be reduced, so that the above-mentioned disadvantages can be avoided.

In addition, in this irradiation system, the excitation intensity of the first stage focusing lens 10 is changed, and the imaging point of the first stage focusing lens 10 is fixed at a point S' different from the point S (for example, a point at the rear). It is also possible to focus the electron beam 6 on a point Q on the sample 7 using a method similar to that described above. Such an operation can only be performed if the diaphragm 13 is installed near the second stage focusing lens 11. This is because, assuming that the aperture 13 is installed at the final stage focusing lens 5 position,
This is because the electron beam hitting the aperture 13 is cut off by the aperture 13, and therefore the convergence angle of the electron beam incident on the sample 7 cannot be varied. On the other hand, if the diaphragm 13 is set at the position of the first stage focusing lens 10, the aperture diameter of the diaphragm 13 necessary to give a certain focusing angle to the electron beam 6 will be one order of magnitude smaller, as is clear from FIG. is necessary, and production problems arise. As described above, the effect of changing the imaging point of the first stage focusing lens 10 from the point S to the rear point S' appears as an increase in the diameter of the irradiation circle at the point R, that is, a decrease in the reduction ratio.

Further, in this embodiment, it is preferable that the reduction ratio of the front objective lens body 2 is used within a range of 1/20 or less (numerically, it becomes larger such as 1/15, 1/10, etc.). This is achieved by increasing the distance between the sample 7 and the front objective body 2. By taking such measures, the positional fluctuation of the point Q with respect to the normal unevenness of the surface of the sample 7 can be suppressed to a small level. In addition, in order to enable the irradiation system to respond to the positional fluctuation of the point Q, an excitation fine adjustment means is connected to any of the first stage focusing lens 10, the second stage focusing lens 11, or the third stage focusing lens 5. It is preferable to make the focusing lens variable within a certain minute width.

FIG. 4 is a diagram showing an embodiment of an electron beam irradiation system for carrying out the second invention. In this irradiation system, an additional electron lens 12 is installed between the final stage focusing lens 5 and the front objective lens body 2, and one composite electron lens is formed by this additional electron lens 12 and the front objective lens body 2. It differs from the irradiation system of the first invention in that it is formed. The other configurations and the effects based on the configurations are the same as in the first invention.

In the irradiation system having such a configuration, the combined reduction ratio of the additional electron lens 12 and the front objective lens body 2 is set to be smaller than 1/20, so that the same effect as in the first invention is performed. . This makes it possible to continuously change the convergence angle of the electron beam 6 incident on the sample 7 while keeping the excitation intensity of the objective lens 1 at a constant value. It becomes possible to appropriately respond to the positional fluctuation of Q in the same manner as in the first invention. The effect of the additional electron lens 12 can be added by simply setting the excitation intensity of the additional electron lens 12 to an appropriate value without changing (replacing) the objective lens magnetic pole piece or changing the position of the sample 7. Since the composite reduction ratio of the electron lens 12 and the front objective lens body can be selected to be 1/20 or less, the structure of the objective lens magnetic pole piece, the position of the sample 7, and the setting of the excitation intensity of the objective lens can be determined exclusively by the imaging system. The reason is that the position with the best resolution can be selected preferentially.

As explained above, according to the present invention, in the irradiation system of an electron beam apparatus, the excitation of the final stage focusing lens and the focusing lens installed in a position in front of the final stage focusing lens is linked to each other, and the imaging point of the final stage focusing lens is By making the electron beam almost coincide with the object point of the front objective lens, it became possible to vary the convergence angle of the electron beam incident on the sample without varying the excitation intensity of the objective lens. For this reason, it is easy to operate and allows observation images with finely changed angles to be obtained when using focused electron diffraction, which is used in research and development of new materials, or when obtaining high-resolution images of crystals. It is possible to achieve the effect that observation accuracy can be improved.

[Brief explanation of drawings]

Fig. 1 shows a conventional example of an electron irradiation system in an electron beam device, and Fig. 2 shows the image formation state of the electron beam source when the excitation intensity of the final stage focusing lens is changed in the above-mentioned conventional irradiation system. FIG. 3 is a diagram showing an electron beam irradiation system used for implementing the first invention, and FIG. 4 is a diagram showing an electron beam irradiation system used for implementing the second invention. 1... Objective lens, 2... Front objective lens body,
3... Rear objective lens body, 5... Final stage focusing lens, 6... Electron beam, 7... Sample, 8, 13... Aperture, 10... First stage focusing lens, 11... Second stage focusing Lens, 12...Additional electronic lens.

Claims (1)

[Scope of Claims] 1. In an electron beam apparatus for sample observation having an electron beam source and an objective lens composed of a front objective lens body and a rear objective lens body, in front of the objective lens,
At least three stages of focusing lenses are arranged in the order of the first stage, second stage, and final stage from the electron beam source side, and while the excitation of the first stage focusing lens is kept constant, the second stage focusing lens and the final stage focusing lens are 1. A method for irradiating an electron beam in an electron beam apparatus, characterized in that the excitations of and are linked to each other, and the imaging point of the final stage focusing lens is fixed so as to substantially coincide with the object point of a front objective lens body. 2. An electron beam irradiation method in an electron beam apparatus according to claim 1, characterized in that a diaphragm for regulating the cross section of the electron beam bundle is provided near the second stage focusing lens. 3. Claims 1 or 3, characterized in that the final stage focusing lens changes its excitation in conjunction with the second stage focusing lens, and the final stage focusing lens itself slightly changes the excitation. A method for irradiating an electron beam in the electron beam apparatus according to item 2. 4. An electron beam irradiation method in an electron beam apparatus according to any one of claims 1 to 3, wherein the reduction ratio of the front objective lens body is set to be smaller than 1/20. . 5 The first stage focusing lens is provided with a variable number of multiple steps, and the second stage focusing lens and the third stage focusing lens are controlled in conjunction with each other for any excitation intensity of the multiple steps, so that the third stage is always 5. A method for irradiating an electron beam in an electron beam apparatus according to any one of claims 1 to 4, characterized in that the imaging point of the focusing lens is set at a fixed position. 6. In front of the objective lens of an electron beam apparatus for sample observation, which has an electron beam source and an objective lens composed of a front objective lens body and a rear objective lens body,
At least three stages of focusing lenses are arranged in the order of a first stage, a second stage, and a final stage from the electron beam source side, and an additional electron lens is provided between the final stage focusing lens and the front objective lens body, While keeping the excitation of the stage focusing lens constant, the excitation of the second stage focusing lens and the final stage focusing lens are linked to each other so that the image point of the final stage focusing lens almost coincides with the object point of the additional electron lens. An electron beam device characterized in that the convergence angle of an electron beam incident on a sample is varied by varying the excitation of a second stage focusing lens while keeping the excitation intensities of the electron lens and objective lens constant. electron beam irradiation method. 7. An electron beam irradiation method in an electron beam apparatus according to claim 5, wherein the combined reduction ratio of the additional electron lens and the front objective lens body is set to be smaller than 1/20. 8 A variable number of multiple steps is provided in the first stage focusing lens, and the second stage focusing lens and the third stage focusing lens are controlled in conjunction with each other for any excitation intensity among these multiple steps, so that the third stage is always 8. An electron beam irradiation method in an electron beam apparatus according to claim 6 or 7, characterized in that the imaging point of the focusing lens is set at a fixed position.