JPS60193248A - Method for irradiating electron rays in electron ray device - Google Patents

Abstract

PURPOSE:To vary the angle at which electron rays are irradiated upon a sample by installing a movable diaphragm between a final stage focusing lens and focusing lens which is installed in front of the final stage focusing lens and by correcting the excitation of said final stage focusing lens with that of said focusing lens. CONSTITUTION:A movable diaphragm 13 is installed in an arbitrary position located between a second stage focusing lens 11 and a final stage focusing lens 5. The degree of the excitation of the second stage focusing lens 11 can be varied so that the actual image of point (P) is imaged upon an arbitrary position located between points (Q1) and (On) which are in the back of the lens 11 and on the optical axis. The final stage focusing lens 5 diffracts electron rays 6 the orbits of which are altered by the excitational change of the second stage focusing lens 11. The thus diffracted electron rays 6 are then imaged upon the focus of a front objective 2 by the effect of the front objective 2 which is a part of an objective 1. Accordingly it is possible to vary and control the angle at which electron rays are irradiated while maintaining the focus of an electron probe to be located on a sample 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electron beam irradiation method that enters an electron beam apparatus, and in particular, allows the convergence angle of the irradiated electron beam incident on a sample to be continuously varied while keeping the excitation intensity of the objective lens constant. The present invention relates to an electron beam irradiation method as described above.

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 has one or more focusing lenses 4.5 disposed in front of an objective lens 1 consisting of a front objective lens body 2 and a rear objective lens body 3, and the radiation passing through these focusing lenses 4.5. Irradiation electron 11! i16,
It is configured to focus on a sample 7 placed between the front objective lens body 2 and the rear objective lens body 3, that is, within the gap of the objective lens 1. Further, a diaphragm 8 is disposed near the final stage focusing lens 5, and is configured to vary the focusing angle of the irradiated electron beam 6 incident on the sample 7 while keeping the excitation intensity of the objective lens body 1 constant. ing. That is,
In the electron beam irradiation system shown in FIG. After the image is formed at a point Q that is conjugate with P, the image is formed at a point R on the sample 7 by the front objective lens 2 at a predetermined convergence angle. When varying the convergence angle of the irradiated electron beam 6 incident on the sample 7, this is done by changing the aperture diameter of the aperture 8 from the size shown by the solid line in FIG. 1 to another size. 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 0 can be replaced as needed. It has become.

However, in such a conventional electron beam irradiation method, in order to vary the convergence angle of the electron beam 6 irradiated onto the sample 7, a movable aperture 8 provided with several rows of holes is operated. As a result, 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 in 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 focusing lens 5 without changing the aperture diameter of the aperture 8, but in this case, as shown enlarged in FIG. The angle of incidence of the electron beam 6 entering the sample 7 is different between the outside and inside of the electron beam irradiation circle formed on the sample 7 and the center point, so even if you try to obtain a diffraction image of a crystal, for example, it will not be correct. There was a problem that a diffraction image could not be obtained.

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. It is an object of the present invention to provide an electron beam irradiation method that can be used to irradiate an electron beam, 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 an electron optical system, and among these three stages, the second stage focusing lens is arranged from the side closest to the electron beam source. A movable diaphragm is disposed between the and the final stage focusing lens, and while the excitation of the first film focusing lens is kept constant, the excitation of the second film focusing lens and the final stage focusing lens is related to each other. The gist of the present invention is to fix the imaging point of the final stage focusing lens so as to substantially coincide with the object point of the front objective lens while limiting the sample irradiation angle using the movable diaphragm. Further, in the electron optical system, the second film flux lens and R
In addition to the movable diaphragm, an alignment coil for aligning the axis of the beam incident on the sample is disposed between the final stage focusing lens, and in this state, while keeping the excitation of the first film focusing lens constant, The excitations of the second film focusing lens and the final focusing lens are related to each other, and while the sample irradiation angle is limited by the movable diaphragm, the imaging point of the final focusing lens is almost aligned with the object point of the front objective lens. The gist of the second invention is that it is fixed in such a manner. Therefore, in the second invention, even if the optical axis of the irradiated electron beam is shifted due to the excitation change of the R final stage focusing lens, it is aligned with the optical axis by the operation of the alignment coil. In order to minimize the axis shift of the irradiated electron beam due to excitation changes of the lens, the second
Another major feature of the present invention is that the diameter of the beam transmission hole of the movable diaphragm is varied in response to the imaging point that changes due to changes in the excitation of the film-bundling lens, thereby irradiating the electron beam.

In the first and second inventions described above, the excitation association between the second film focusing lens and the final stage focusing lens may be performed manually or may be performed by automatic interlocking operation.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIGS. 3 and 4 are diagrams showing an embodiment of an electron beam irradiation system for carrying out the invention of ml. This irradiation system has a first lens located in front of the objective lens 1 in order from the electron beam source side.
Film-bundling lens 10°: At least three stages of focusing lenses are arranged such that the second film-bundling lens 11 and the final-stage focusing lens 5 are arranged, and the gap between the second film-bundling lens 11 and the final-stage focusing lens 5 is A movable aperture 13 having a predetermined opening for regulating the cross section of the electron beam bundle is attached at an arbitrary position. The first film focusing lens 10 is set to be excited so as to form a real image of the electron beam source at a point P on the optical axis O in FIG. Second
The film focusing lens 11 is variable in excitation so that a real image of the point P can be formed at any position from a point Q1 to a point Qn on the optical axis behind the second stage focusing lens 11. The final stage focusing lens 5 refracts the electron beam 6 whose trajectory has been changed by the excitation change of the second film focusing lens 11, and
Of the front objective lens 2 and the rear objective lens body 3 that constitute the front objective lens 2, the front objective lens 2 cooperates to form an image on the object point of the front objective lens 2. A sample 7 is disposed between the front objective lens holder 2 and the rear objective lens body 3.

It is preferable to use a single focus lens for the front objective lens body 2, and the front objective lens body 2 and the final stage focusing lens 5 operate as if they were one lens, and the electron beam emitted from the variable focusing point Q is In order to focus the electron beam 6 onto a point R on the sample 7 and form a real image of the electron beam source at this position, the front objective lens 2 is set to a constant excitation value, while the final stage focusing lens 5 is set to variable excitation. Ru. A fixed aperture may be used for the movable aperture 13 provided between the second film convergence lens 11 and the final stage focusing lens 5, or a movable aperture may be provided. Note that, of course, several focusing lenses may be further arranged in front of the first film focusing lens 10.

In the irradiation system having such a configuration, the first film bundle lens 1
The electron beam that is focused at a point P on the optical axis 0 by 0 and formed a real image on the electron beam source at this position is transferred by the second film focusing lens 11 to the second stage focusing lens 11 and the third film focusing lens. 5
It is focused on a predetermined range of points on the optical axis O between the two. In this case, when the second film fluxing lens 11 is set to the weakest excitation within its variable range, the electron beam is
It converges on point Q1 as follows. 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 Qn as shown by reference numeral 6b.

Then, if the excitation of the second and later focusing lenses 11 is changed continuously from the weakest excitation to the strongest excitation (if the excitation is changed stepwise, the path of the electron beam will be shown as 6a and 6b). The imaging point Q changes from point Q1 to point Qn by J°.

Next, in the final stage focusing lens 5, the excitation intensity is varied functionally with respect to the excitation strength of the second and subsequent east focusing lenses 11, and the excitation intensity is kept constant between the final stage focusing lens 5 and the front The imaging point of the electron beam source formed by the combination with the objective lens body 2 coincides with a point R on the sample 7.

Such an electron optical system, especially the configuration of the final stage focusing lens 5, has emerged in recent years with the adoption of an objective lens mode in which the front objective lens has a single focus, and has various utility values, but the present invention This is used for the purpose of limiting the combined reduction ratio of the final stage focusing lens 5 and the front objective lens body 2 to 1 if it is larger than 20 minutes. In order to efficiently limit the sample irradiation angle to a small value in such an electron optical system, it is optimal to set the beam cross-section limiting aperture, that is, the movable aperture 13, at a position where the beam cross-section is at its maximum. That is, by arranging the movable aperture 13 at a position where the beam cross section is maximized, the sample irradiation angle can be minimized with respect to the apertures of the movable aperture having the same diameter. However, the largest beam cross section never appears at the first film focusing lens 10, and the closer it is to the final stage focusing lens 5, the larger the beam cross section becomes. However, considering the purpose of controlling the sample irradiation angle using lens action, at least one lens that can be varied backwards from the diaphragm (corresponding to the movable diaphragm 13 described above) is required.
More than one is required. In the present invention, a movable diaphragm 13 is disposed between the second and subsequent focusing lenses 11 and the final stage focusing lens 5 so as to satisfy the above two conditions.

When electron beam irradiation is performed using the method described above in an electron optical system having the above configuration, for example, the second
If the electron beam 6a thus obtained is focused on the point Q1 with the weakest excitation within its excitation variable range, the electron beam 6a thus obtained will be focused on the sample 7 at an extremely small angle of convergence. When the electron beam 6b obtained by this is imaged at a point Qn with the second or later east focusing lens 11 being most excited, the electron beam 6b thus obtained is imaged on the sample 7 at a relatively large convergence angle. The relationship between the excitation change of the second and subsequent focusing lenses 11 and the focusing angle on the sample 7 will be explained in detail. First, the first film bundle lens 1
0 is strongly excited to create a first reduced point electron beam source image at point P, and at the same time, the second film flux lens is excited to the weakest extent in its excitation range, and the second reduced point electron beam source image is created at point P. 2 focusing lens 11
and the final stage focusing lens 5 at a point Q1. Then, a third reduced electron beam source image, that is, an electron probe is formed on the sample 7 by the combined action of the final stage focusing lens 5 and the front objective lens body 2. The convergence angle at this time is set to 01. Next, the second
Changing the film flux lens to the strongest excitation in its excitation range, creating a second reduced point electron beam source image at point Qn,
Correspondingly, the combining action of the final stage focusing lens 5 and the front objective lens body 2 is readjusted so that the imaging position of the third reduced electron beam source image does not deviate from the surface of the sample 7. do. Let the convergence angle at this time be θn. As is clear from FIGS. 3 and 4, θ1 x θn.

As mentioned above, the third reduced electron beam source image is always placed on the sample 7 when the Q point moves from 01 to Qn.
=, the excitation intensity of the front objective lens 2 is kept constant and the excitation of only the final stage focusing lens 5 is changed.
This is because a change in the excitation of the front objective lens 2, that is, a change in the excitation of the entire objective lens 1, means that the focus of the image on the fluorescent screen changes before and after the change in excitation of the objective lens. As is clear from FIGS. 3 and 4, the focusing point of the second reduced electron beam source image changes from point Q1 to point Q even if only due to the excitation change of the final stage focusing lens 5.
The focus of the electron probe on the sample 7 is kept constant even if it changes to n. As the image forming point changes from point Q1 to point Qn, the electron beam irradiation angle on the sample 7 changes to θ1.
to θn. Therefore, the electron beam irradiation angle is θ1
In this case, the excitation current values of the second film focusing lens 11 and the final stage focusing lens 5 are respectively (I21.131>,
The following sequentially (122, 132), (123, I 33)
,...(I2n, 13n). These sets can be easily obtained through actual measurements. and a second film bundle lens 11
The current value of 121. I22. I23. ...(If I31゜132, I33.I3n are automatically made to correspond to 2n, the electron beam irradiation angle can be changed to θ1, θ2, θ3, etc. while keeping the focus of the electron probe on the sample 7. - Variable control is possible like Qn.In this way, the object of the first invention is achieved.

Next, the second invention will be explained. In the first invention, the focus of the electron probe on the sample 7 is maintained by varying the excitation of the second film focusing lens 11 and the final stage focusing lens 5 while keeping the excitation of the objective lens 1 constant. The electron beam irradiation angle can be varied by
From the viewpoint of such variable operation of the electron beam irradiation angle, the first invention described above has some shortcomings. It is true that in the first invention, the second film bundle lens 1
The electron probe is always imaged on the surface of the sample 7 due to excitation changes between the final stage focusing lens 5 and the final stage focusing lens 5;
It is largely displaced in the direction perpendicular to the optical axis O in the plane. This displacement of the imaging point R in the direction perpendicular to the optical axis is caused by the difference between the final stage focusing lens 5 and the front objective lens 2 because the electromagnetic alignment coil 12 is disposed in front of the final stage focusing lens 5. This is because the configuration is such that the current of the alignment coil 12 is adjusted so that the electron beam that finally enters the sample 7 due to the refraction effect comes to the center of the sample 7. In such a configuration, the final stage If either the focusing lens 5 or the front objective lens 2 (however, in the present invention, the excitation of the front objective lens body 2 is kept constant) changes, the axis will be deviated. Therefore, in order to eliminate the misalignment of the axis, the final stage focusing lens 5
However, if the excitation of the final stage focusing lens 5 is not varied, the electron beam irradiation angle θ incident on the sample 7 will change.
A contradiction arises in that the situation cannot be changed.

In order to solve this contradiction (1), the excitation of the final stage focusing lens 5 is varied, but while keeping this variable range as small as possible, the excitation of the final stage focusing lens 5 is kept as small as possible. It is important to keep the range of change in the electron beam irradiation angle as wide as possible. The second invention aims to achieve such an object.

As explained in the first invention, the excitation of the second film fluxing lens 11 is varied within its variable range from the weakest excitation to the strongest excitation, and the imaging point of the second reduced electron beam source image is set to the point Q1. Correspondingly, the electron beam irradiation angle incident on the sample 7 was changed from 01 to Qn, but the aperture diameter of the movable aperture 13 used for this operation was
The diameter of the smallest hole in the row of holes drilled in the movable diaphragm 13 (
Let this be d).

Then, θn/θi=. Since the value of Qn is greater than the value of θ1, the value of θn/θ1 is greater than 1. Based on this K, the diameter of the hole row of the movable diaphragm 13 is adjusted from the smallest hole to the largest hole by d.
, kd, 2d, 3d, and so on.

Then, if the value of the electron beam irradiation angle θ corresponding to point 01 when using a hole of diameter d is expressed as θ1, then θ at points Ql...Qn becomes θ=θ1...kd1. In the next hole kd, θ at Ql...Qn is
θ=θ1...k2 θ, and by sequentially switching the holes from smaller diameter ones to larger diameter ones, θ can be continuously changed to θ1...k+01.

Therefore, the optimum electron beam irradiation angle for any crystal can be selected from the above-mentioned wide range θ.

Further, as for this variation of 0, the greater the number of divisions between Ql and Qn, the greater the number of variable stages of θ, and the crystal can be observed in finer stages.

- As an example, let the minimum hole diameter d of the movable diaphragm 13 be 20 microns in diameter (this is the minimum value for a practical hole), and K be 1
．． 5, the diameter of the hole row of the movable diaphragm 13 is 20.3.
0,45,67.5. ...becomes like a micron. Also, if K is 2, the diameter of the hole row is 20.40.80,16
0. ...becomes like a micron. Furthermore, if K is 3, the diameters of the hole rows are 20.60, 180, 540. ...
It becomes like a micron. The movable diaphragm 13 is used not only for focusing lens electron beam diffraction, but also for normal electron microscope image observation. In the latter case, holes with a diameter exceeding 500 microns are not normally used, so when considering the effective use of the movable aperture, the limit is the hole in the fourth row when = 3 in the above hole row. . Therefore, it is desirable to set the diameter to a value smaller than 3.

In the first and second aspects of the present invention, the case where the point Q is set between the second film focusing lens 11 and the final stage focusing lens 5 has been described. The reason for this is that the farther the point Q is from the movable diaphragm 13, the greater the gap between Ql and Qn required to obtain the same change in the focusing angle, and this increases the amount of change in the excitation current of the final stage focusing lens 5. This is to avoid this. The closer Ql...Qn is to the movable diaphragm 13, the smaller the distance between Q1...Qn, and the smaller the current change in the final stage focusing lens 5 becomes. Also, Q
If the point is moved away from the movable aperture 13 and set at position 1, even if the movable aperture 13 with the same hole diameter is used, the electron beam irradiation angle above the sample 7 will cause the Q point to approach the movable aperture 13 side. Therefore, the hole diameter of the movable diaphragm 13 needs to be set even smaller than 20 microns, which exceeds the practical minimum hole diameter, resulting in manufacturing difficulties. There is also a disadvantage.

Furthermore, in the first and second inventions, the combined reduction ratio of the front objective lens 2 and the final stage focusing lens 5 is 1/20.
It is preferable to use it within the following range (in terms of numerical values, it increases like 1/15.1/10...). This can be achieved by increasing the distance between the sample 7 and the front objective lens 2. By taking such measures, it is possible to suppress the positional fluctuation of the point Q with respect to the normal unevenness of the surface of the sample 7 to a small level. In addition, in order for the irradiation system to respond to the positional fluctuation of the point Q, the first to
It is preferable to connect an excitation fine adjustment means to either the second film focusing lens 11 or the final stage focusing lens 5, so that either of the above focusing lenses can be varied within a certain minute range.

As explained above, according to the present invention, in the irradiation system of an electron beam device, a movable diaphragm is provided between the final stage focusing lens and the focusing lens installed at a position in front of the final stage focusing lens, The excitation with the focusing lens is related to each other, so that the imaging points of the final focusing lens and the front objective lens almost coincide with each other on the sample. It is now possible to vary the irradiation angle of the electron beam. For this reason, the focusing lens electron diffraction method used in research and development of new materials is used to obtain high-resolution images of crystals.
It is easy to operate, and observation images with finely changed angles can be obtained, thereby improving observation accuracy.

In addition, this angle change can be reliably performed by electrical means and switching of the aperture row of the movable diaphragm without causing significant axis deviation due to changes in excitation of the focusing lens. The operational complexity of having to adjust the alignment coil after changing the excitation of the electron beam can be avoided, and various effects such as extremely easy-to-operate electron beam observation can be obtained.

In the above explanation, a three-stage focusing lens system has been described, but if several focusing lenses are added above (that is, in front of) the first film focusing lens, the first reduced electron beam source image can be While maintaining the position of point P at point P, the size of the electron probe on the sample can be freely varied by the interlocking operation of the added focusing lens and the first film focusing lens. This is more desirable in high-performance electron beam equipment.

[Brief explanation of the drawing]

Figure 1 shows a conventional example of an electron irradiation system in an electron beam device, and Figure 2 shows the result of an electron beam source when the excitation intensity of the final stage focusing lens is changed in the conventional irradiation system described above. FIG. 3 is a diagram showing the electron beam irradiation system used to implement the invention shown in FIG. 1, and FIG. FIG. 5 is a diagram showing the electron beam path in detail, FIG. 5 is a diagram showing the electron beam irradiation system used in implementing the second invention, and FIG. 6 is an example of a movable aperture used in the first and second inventions. It is a diagram. 1... Objective lens, 2... Front objective lens body 3...
・Rear objective lens body, 5...Final stage focusing lens 6...
・Electron beam, 7... Sample 10... First stage focusing lens 11... Second stage focusing lens, 12... Axis alignment coil, 13... Movable aperture

Claims (5)

[Claims] (1) In an electron beam apparatus for sample observation that has 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, from the electron beam source side, a first stage, At least three stages of focusing lenses are arranged in the order of the second stage and the final stage, and a movable diaphragm is arranged between the second stage focusing lens and the third stage focusing lens. While keeping the excitation constant, the excitations of the second-stage focusing lens and the final-stage focusing lens are related to each other, and while the sample irradiation angle is limited by the movable diaphragm, the imaging point of the R final-stage focusing lens is set to the front objective. An electron beam irradiation method using an electron beam device, characterized in that a lens body is fixed so as to substantially coincide with an object point. (2) By changing the excitation of the second-stage focusing lens, the focusing point of the reduced light source image by the two-tube focusing lens is set to the closest point to the second-stage focusing lens between the second-stage focusing lens and the third-stage focusing lens. An electron beam irradiation method for an electron beam apparatus according to claim 1, characterized in that the electron beam irradiation method is continuously varied from the farthest point 01 to the nearest point Qn. (3) In an electron beam device for sample observation that has an electron beam source and an objective lens composed of a front objective lens body and a rear objective lens body, a first stage, a second stage, and a final stage are installed in front of the objective lens. At least three stages of focusing lenses are arranged in the order of stages, and a movable diaphragm and an alignment coil for aligning the axis of the beam incident on the sample are arranged between the second stage focusing lens and the third stage focusing lens. While keeping the excitation of the first stage focusing lens constant, the excitation of the second stage focusing lens and the final stage focusing lens are related to each other, and the final stage focusing lens is controlled while limiting the sample heat angle by the movable diaphragm. An electron beam irradiation method for an electron beam device, characterized in that the imaging point of is fixed so as to substantially coincide with the object point of a front objective lens body. (4) By changing the excitation of the second-stage focusing lens, the imaging point of the reduced light source image by the two-tube focusing lens is changed between the second-stage focusing lens and the third-stage focusing lens. 4. An electron beam irradiation method for an electron beam apparatus according to claim 3, characterized in that the electron beam irradiation method can be continuously varied from point 01, which is farthest to the bundle lens, to point Qn, which is closest to the bundle lens. (5) The movable aperture is provided with multiple beam transmission holes,
When the beam convergence angles on the sample obtained corresponding to the focusing points Q1 to Qn of the reduced light source image by the second film focusing lens are θ1 to θn, these transmitted beams have the following relationship: θ1/θn=≦ 3 and the diameter of the beam transmission aperture of the movable diaphragm corresponding to the imaging point Q1 is d, then the diameter of the beam transmission aperture corresponding to the imaging points Ql to Qn is d, kd, and 2d. An electron beam irradiation method using an electron beam apparatus according to claim 3 or 4, characterized in that the number of irradiators is set to one person.