JPS61104549A - Electron microscope - Google Patents

Abstract

PURPOSE:To carry out the rotation of an image in a relatively wide range with the small change of magnification by reversing an excitation current code supplied to a projection lens, using an excitation current, in which a rotational angle is 180 deg., as a boundary. CONSTITUTION:When a rotational angle theta is specified by a rotary encoder 11, in the case of theta<=180, a CPU 12 reads out an excitation specifying signal corresponding to theta from a memory 13 to supply it to an excitation power source 9. Further, in the case of theta>180, the CPU reads out a signal corresponding to 360-theta and supplies a high level signal for reversing polarity to a porality switching circuit 10 through a DA converter 15. Accordingly, the relationship between the rotational angle theta and a magnetomotive force J supplied to a projection lens 7 is shown in a line K, and for example, the magnification corresponding to each angle theta which is based on the magnification in the excitation of 5585 ampere.turn is shown in a curve U. Namely, it is possible to restrain the change of magnification accompanied by the rotation of an image projected on a fluorescent plate 8 to about + or -10%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electron microscope in which an image is rotated on a fluorescent screen for image observation using the image rotation effect of an electromagnetic lens.

[Prior Art] An electron microscope image is rotated so that an image portion of interest is placed at a desired angle within a rectangular photographic field of view. Rotation of the electron microscope image can also be performed by mechanically rotating the sample holder, but in mechanical rotation, the center of rotation of the sample boulder is generally different from the center of the image part of interest. The movements must be done together. Therefore, it has been considered to rotate the image by utilizing the image rotation effect of an electromagnetic lens, which will be described below.

That is, Denshi no Silence 11: Q&A mo (KO>, Denshi'!
Assuming that the load is e′ < Coulomb), U* is the relativistically corrected accelerating voltage (V), and B (z) is the magnetic field (Gauss) at the coordinate Z along the optical axis of the lens, the magnetic field type electron lens is as follows. Rotate the image by an angle 0 expressed by the equation.

The right-hand side of the above equation (1) is expressed as 0.3377 J/ff, where Φ is the magnetomotive force (ampere turn) of the lens, and this value is 0.3377 J/ff at the commonly used acceleration voltage of 100 KV. It becomes .0322J.

[Problems to be Solved by the Invention] By the way, when the magnetomotive force of the electron lens is changed, the focal length f changes, and therefore the observation magnification changes.

This change in observation magnification is undesirable, so the electron lens is recommended! It is desirable to use it near the maximum magnetomotive force, where the rate of change in focal length with respect to changes in the amount of current is small, but since the intermediate lens is primarily used to change magnification, it is suitable for high-magnification observation conditions. It is used only at the maximum excitation current value.

Therefore, it is not suitable as an image rotation lens, and the objective lens must also be changed by a minute amount for focusing. It is not suitable as an image rotating lens because it is used with almost a fixed current. Of course, the object.

The magnetomotive force of each nons in the middle and projection changes in a complex manner 1! In this case, image rotation can be performed with almost no change in magnification, but there is a problem in that the manufacturing cost of the apparatus increases.

The present invention was made in order to solve these conventional problems, and it is possible to perform image rotation over a relatively wide range with a slight change in magnification. The purpose is to provide

[Means for solving the problems] In order to achieve such an object, the present invention provides a projection lens for projecting an electron microscope image formed by an objective and an intermediate lens onto an image observation screen, and a projection lens for projecting an electron microscope image formed by an objective and an intermediate lens onto an image observation screen. In a device equipped with a power source for supplying excitation current to a lens,
The means for specifying the rotation angle θ of the image projected on the screen by the projection lens, etc., when the specified rotation angle θ is 18
It is determined whether or not it is greater than 0 degrees, and if it is less than 180 r & θ, an excitation current corresponding to 3-1 to θ is supplied to the projection lens, and if it is larger, the absolute value is equal to the excitation current corresponding to 360 - θ. The present invention is characterized in that it includes means for supplying excitation currents of different signs to the projection lens.

[Operation of the invention] The basic idea of the present invention will be explained below.

The focal length of the projection lens is ``, the gap distance between the magnetic pole pieces of the lens is S, the hole diameter of the 111 pieces is ``, the magnetomotive force of the projection lens is J (ampere turns), and the relativistic correction value of the accelerating voltage is t.
If we write J* (KV), we get "/(S+b) and J2/
The relationship with U* is shown in Figure 5. From this figure, it can be seen that if the projection lens is used at the maximum magnetomotive force, that is, around J2/lJ*-200, even if J is changed and the image is rotated, f It can be seen that the change in , and therefore the change in magnification, is small. Furthermore, when the magnetomotive force J of the projection lens is changed near the maximum, how does the rotation angle θ (degrees) of the image change, and J2 /U* = 2
When we investigated how the magnification ratio changed with reference to the magnification in 84, we found that the unity shown in FIG. 6 was obtained. From this unity, the excitation of the projection lens is J2/U*=
It was found that by changing the image rotation angle from 112 to 284 degrees, the image rotation angle can be changed by about 67 degrees, and the change in magnification associated with this change is within a range of about ±10%, which is not a problem in practice. In FIG. 6, the vertical axis represents the magnification ratio (%), and the horizontal axis represents the image rotation angle θ or J2/U*.

Furthermore, in a magnetomotive force where the image rotation angle θ due to the projection lens is 180 degrees, if the polarity of the excitation current supplied to the projection lens is switched, the image rotation angle becomes -180 degrees, so the image rotation angle θ becomes -180 degrees, so the image rotation angle θ becomes -180 degrees. If the image can be maintained and the absolute value of the excitation current is decreased in this state, the change in magnification can be reduced to the above 10.
%, the image can be further changed by about 67 degrees.

E Example] Hereinafter, examples of the present invention based on the above-mentioned idea will be described in detail.

FIG. 1 is for showing one embodiment of the present invention.
is an electron gun, and the electron gun 1 generates 100K V
The electron beam EB accelerated to 1. second focusing lens 2,
3 and irradiates the sample 4. The electron beam transmitted through sample 4 is objective, intermediate.

and is imaged onto the fluorescent screen 8 by the projection lens 5.6.7. Reference numeral 9 denotes an excitation power source for the projection lens 7 , and an excitation current from the excitation power source 9 is supplied to the projection lens 7 via a polarity switching circuit 10 . Is the polarity switching circuit 10 electric? This is a circuit for switching the polarity by switching the terminal of the lens coil connected to the positive terminal of lI9. 11 is the relative rotation angle ω of the image ranging from 0 degrees to 134 degrees (rotation angle θ−113
The rotary encoder 11 is a rotary encoder for instructing the rotation angle (with reference to degrees), and the output signal from the rotary encoder 11 is supplied to the central processing unit 12. 1
3 is a storage device connected to the central processing unit 12, and this storage device 13 stores data from ω-0 to 134/2=6
7. Signals specifying the excitation current value of the projection lens corresponding to each value of ω are stored as a table. Storage device 13
The excitation designation signal read from the excitation designation signal is supplied to the excitation power supply 9 via the DA converter 14, and the excitation power supply 9 generates an excitation current based on this excitation designation signal. Further, a switching control signal is supplied from the central processing unit @12 to the polarity switching circuit 10 via the DA converter 15.

In such a configuration, when the operator specifies a certain rotation angle ω using the rotary encoder 11, the central processing unit 12 determines whether ω>67 (that is, θ>180), and determines whether ω≦67 (0≦180). In this case, the storage device 13
The excitation designation signal corresponding to ω stored in is read out and supplied to the excitation power supply 9 via the DA converter 14. Further, in the case of ω>67 (θ>'180), the central processing unit 12 reads the excitation designation signal at the address of the storage device 13 corresponding to 134-ω (hit 360-θ) and sets the excitation power supply 9 At the same time, a high-level bindoff signal is supplied to the polarity switching circuit 10 via the DA converter 15 to reverse the polarity. Therefore, when the rotation angle θ or ω is specified by the rotary encoder 11, the excitation 1 lightning source 9
The relationship between the excitation designation signal supplied to the pole switching circuit 10 is as shown in FIG. 2, and the relationship between the rotation angle θ(a)) and the level of the signal supplied to the pole switching circuit 10 is as shown in FIG. Becomes a fairy tale. Therefore, the relationship between the rotation angle θ (ω) and the magnetomotive force J (ampeta-turns) supplied to the projection lens 7 is as shown by the straight line in FIG. The A8 ratio corresponding to each angle polishing θ(ω) based on the magnification of O() is as shown by curve J in the figure. In addition, in Fig. 4, the horizontal axis is 0 or ω (degrees)
The left vertical axis represents the magnetomotive force (ampere turns), and the right vertical axis represents the magnification ratio (%). As is clear from this graph, the image projected onto the fluorescent screen 8 is approximately 1
It can be rotated 34 degrees, and the change in magnification associated with this can be kept to about 110%.

The present invention is not limited to the embodiments described above, and can be modified in many ways.

For example, in the embodiment described above, in order to reverse excite the projection lens, the terminal of the lens coil connected to the positive terminal of the power supply 9 is switched, but instead of switching the terminal, the sign of the current value generated from the power supply is changed. It may be reversed.

Furthermore, it goes without saying that the present invention can be applied to cases where the accelerating voltage of the electron beam is other than 100 KV, and in the case of the accelerating voltage U*, the magnetomotive force of the projection lens is approximately 112≦J2/ It is sufficient to vary within the range defined by lJ*≦284.

[Effect of the invention] 1-As is clear from the above d1 light, the present invention has J3
In the present invention, the excitation current (Y) supplied to the projection lens is reversed at the boundary of the excitation current that causes the rotation angle of the projection lens to be 180 degrees. To provide an electron microscope that can rotate an image by a large amount without moving, has a simple structure, and is inexpensive to manufacture.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing one embodiment of the present invention, Fig. 2 is a diagram showing the relationship between each rotation angle and the excitation designation signal supplied to the excitation power supply, and Fig. 3 is a diagram showing the relationship between each rotation angle and the excitation designation signal supplied to the excitation power supply. Figure 4 is a diagram showing the relationship between the switching signals supplied to the polarity switching circuit. Figure 4 is a diagram showing changes in the magnetomotive force and multiplication factor of the projection lens with each rotation angle. Figure 5 is the diagram for projection. Diagram 6 showing the relationship between magnetomotive force and focal length near the maximum magnetomotive force of a lens
The figure is a diagram showing the relationship between the magnetomotive force or image rotation angle of the projection lens and the magnification value. 1: Electron gun, 2, 3: Focusing lens, 4: Testing, 5: Objective lens, 6: Intermediate lens, 7: Projection lens, 8: Fluorescent screen, 9: Excitation power supply, 10: [I bamboo switching circuit, 11 : Rotary encoder, 12: Central processing unit, 13: Storage device, 14.15: DA transformer.

Claims (2)

[Claims] (1) In an apparatus equipped with a projection lens for projecting an electron microscope image formed by an objective and an intermediate lens onto an image observation screen, and a power supply for supplying excitation current to the projection lens, means for specifying a rotation angle θ by the projection lens of an image projected on the image; and determining whether the specified rotation angle θ is larger than 180 degrees;
If it is less than 0 degrees, an excitation current corresponding to θ is supplied to the projection lens, and if it is larger, an excitation current having an equal absolute value and a different sign from the excitation current corresponding to 360-θ is supplied to the projection lens. An electron microscope characterized by comprising means. (2) J is the magnetomotive force of the projection lens (ampere turns)
, U^* is the relativistically corrected accelerating voltage (KV), then the magnetomotive force J of the projection lens is approximately 112≦J^2/U^*≦284 ((ampere-turn)^2/KV) The electron microscope according to claim (1), wherein the electron microscope is changed within the range defined by (1).