JPS62271338A - Convergence electron beam diffraction instrument - Google Patents

Abstract

PURPOSE:To eliminate the necessity of the adjustment of irradiation angle every time it is changed and improve the operativeness, by providing a means of automatically controlling the excitation intensity of 1st and 2nd convergence lenses so that the ratio of the irradiation angle to electron beam wavelength can remain always constant. CONSTITUTION:A pushbutton 19b is provided, which switches irradiation angle alphain step form according to a formula, alpha=Ki.lambda(i=1, 2, ..., t, u, v, ..., z), assuming theta as diffraction angle and lambda as electron beam wavelength. A CPU 16 sends data of address which corresponds to the acceleration voltage Vk, among the data groups corresponding to Ku in excitation current designating data groups for 2nd and 3rd convergence lenses 6, 7 stored in a memory 18, to respective DA converters 14, 15 through a bus line 17. As a result with a gord to electron beam 3, the crossover position by the 2nd convergence lense 6 moves, as shown by dashed line 3' and at the same time, object point position of the 3rd convergence lense 7 moves in harmonizing with the above moved crossover position. Consequently, electron beam irradiation angle alpha is changed to Ku.lambdak, while the value of theta/alpha remains at the valve before to said change.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention irradiates a microscopic part of a sample with a focused electron beam,
The present invention relates to a convergent electron diffraction apparatus that displays a convergent electron diffraction image based on an electron beam transmitted through a sample.

[Prior Art] Observation of convergent electron diffraction using an electron microscope has become widespread.

Figure 4 shows the electron beam irradiation system of such a convergent electron beam diffraction device. Line 3 is accelerated by anode 4. The electron beams accelerated by the anode 4 are first, second, . Third focusing lens 5, 6
．． 7 and the front magnetic field lens 9a of the objective lens 9, and the crystalline sample 10 is irradiated with an aperture angle of 2α. For simplicity, α, which is half of the opening angle 2α, will be referred to as the opening angle. The electron beam irradiated onto a minute portion of the sample 10 and transmitted through the sample 1o is guided to an imaging lens system (not shown), and is projected onto the fluorescent screen 11 as a convergent electron beam diffraction image of the sample 10. Note that D represents a diffraction disk (or diffraction spot), and 8 is an aperture.

In the conventional apparatus with such a configuration, when the grating spacing determined by the sample is d and the wavelength of the electron beam 3 is λ, the diffraction angle θ, which is the amount corresponding to the spacing between the diffraction disks D, is d and λ. is expressed as follows.

θ=λ/d (1) On the other hand, it is known that the radius of each diffraction disk D is proportional to the irradiation angle α.

Therefore, for example, if the excitation current of the second and third focusing lenses 6.7 is set to be α-θ/2, then the
As shown in Figure (a), the disks can be enlarged to the maximum extent within a range where the disks do not overlap, which is convenient for observing the fine structure inside the disk.

By the way, if the accelerating voltage of the electron beam is changed during observation in this manner, the wavelength λ of the electron beam changes to λ', and therefore the above-mentioned θ changes. however,
Conventionally, the excitation current of the irradiation lens system is automatically set so that the electron beam irradiation angle α does not change regardless of changes in the acceleration voltage of the electron beam. As shown in (b), the diffraction disks overlap and when the accelerating voltage is decreased, the fifth
As shown in FIG. 5(C), the image leaves room for enlargement of the diffraction disk, and in any case, it is no longer an optimal image as shown in FIG. 5(a).

Therefore, in the past, the irradiation angle α had to be adjusted each time the accelerating voltage was changed, which was cumbersome to operate.

The present invention solves these conventional drawbacks and provides a convergent electron diffraction device that can automatically maintain the ratio of the distance between the diffraction disks and the diameter of the diffraction disks regardless of changes in the acceleration voltage of the electron beam. is intended to provide.

[Means for Solving the Problems] Therefore, the present invention provides an electron gun and a first method for focusing an electron beam from the electron gun. a second focusing lens; a means for switching the accelerating voltage of the electron beam; In an apparatus in which an electron beam focused by a second focusing lens is applied to a minute portion of a sample at an illumination angle α, and a convergent electron beam diffraction image of the electron beam transmitted through the sample is projected onto a screen, The first. Automatically adjust the excitation intensity of the second focusing lens
It is characterized by having a control means for @.

[Example j Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, and the same components as in FIG. 3 are designated by the same numbers.

In FIG. 1, 12.13 is the second. It is a lens power supply for the third focusing lens 6.7, and 14.15 is a DA converter. 16 is a CPU, and the DA converters 14 and 15 are connected to the CPU 16 via a pass line 17 and respective 1.10 ports (not shown). It is continued. Further, a storage device 18 is connected to the CPU 16 via a pass line 17, and an input device is also connected thereto. The input table 9 is provided with a push button 19a for specifying the acceleration voltage, and a push button 19b for switching the illumination angle α stepwise according to the following formula.
is provided.

α=Ki ・λ (However, i= 1. 2...
・,(.

u, v, ..., 2) ... (2) Also, a DAf converter 20 is connected to the electron gun power supply 2,
This DA converter 20 passes through the pass line 17 to
Connected to U16.

Furthermore, the storage device 18 stores excitation v11 current designation data for the focusing lens 6.7, which is necessary to maintain the irradiation angle α that satisfies the relationship of equation (2) regardless of the switching of the accelerating voltage. There is.

That is, as shown in FIG.
) Excitation current designation data for the focusing lens 6.7 is stored in groups for each value of Ki given by the equation. In Figure 2, DAu (Vk) is Vk as the accelerating voltage.
When selecting , DBu (Vk) represents the excitation 6t1 current specification data of the focusing lens 6 necessary to take the value 1) (U), and DBu (Vk) is the focusing value necessary to satisfy this condition. It represents excitation current designation data for the lens 7.

Other data in FIG. 2 also have the same correspondence as above.

In such a configuration, it is assumed that the lattice spacing of the sample to be observed is ds, and the accelerating voltage is selected to be Vj to observe a convergent electron beam diffraction image.

In this state, the wavelength of the electron beam is λj corresponding to vj, and therefore the value of the diffraction angle θ is λj /ds. In this state, the push button 19 of the input device 19
Assume that as a result of selecting the value of KLI as the value of Ki by manipulating b, a convergent electron diffraction image as shown in FIG. 3(a) is observed. Therefore, the input device 1
When Vk is specified as the acceleration voltage by operating the push button 19a of 9, the CPU 16 sends a control signal to the high voltage power supply 2 via the DA converter 20 based on the instruction signal from the input device 19, and changes the acceleration voltage to that value. Change from Vj to Vk. As a result, the wavelength of the electron beam becomes λk corresponding to Vk, and therefore the diffraction angle θ becomes λk /ds. At this time, the CPU 16 performs the second . Third focusing lens 6.7
Encouragement lif! Among the current specification data group, data DAu (Vk) and DBu (Vk) of the address corresponding to the acceleration voltage Vk are selected from the data group corresponding to the Ku.
are read out and sent to each DA converter 1 via the pass line 17.
Send to 4, 15. As a result, the electron beam 2 is
As shown by - (however, in FIG. 1, the optical diagram of the electron beam on the sample exit side is omitted), as the crossover position by the second focusing lens 6 moves,
The object point position of the third focusing lens 7 moves to match this moved crossover position! II. As a result, the electron beam irradiation angle α is the value KIJ ・λ given by equation (2) above.
k. Therefore, the value of θ/α is 1/(ds
Ku>, and the acceleration voltage is maintained at the value before the change. Therefore, the diffraction image projected onto the fluorescent screen 11 is shown in FIG.
), the ratio between the disk spacing and the disk diameter can be kept unchanged regardless of the switching of the accelerating voltage, and there is no need to adjust the irradiation angle α.

The embodiment described above is only one embodiment of the present invention, and can be modified and implemented.

For example, in the embodiment described above, the second . Although the excitation current designation data for the third focusing lens 6.7 is stored as a data group for each Ki, it may also be stored in a group for each acceleration voltage value.

Furthermore, in the embodiment described above, the second. Although the excitation intensity of the third focusing lens was changed in conjunction,
1st. Second. If the excitation intensity of any two of the third focusing lenses is changed in conjunction so that the total magnification is constant, the other lenses may be changed.

Effect of the Invention 1 As is clear from the above explanation, according to the convergent electron diffraction apparatus based on the present invention, the ratio of the electron beam wavelength λ to the electron beam irradiation angle α is determined by changing the acceleration voltage of the electron beam. Since the illumination angle α is controlled in conjunction with the switching of the accelerating voltage so that it remains at a predetermined value regardless of the switching of the accelerating voltage, the ratio between the diffraction disk interval and the diffraction disk diameter remains constant regardless of the switching of the accelerating voltage. can be automatically maintained at the initially set desired value, making it unnecessary to adjust the irradiation angle each time the acceleration voltage is changed, thereby improving operability.

[Brief explanation of the drawing]

FIG. 1 is a diagram for showing one embodiment of the present invention, FIG. 2 is a diagram for explaining the storage contents of the storage device 18, and FIG. 3 is a diagram for explaining the details of the present invention by illustrating a diffraction image. FIG. 4 is a diagram to show a conventional device, and FIG. 5 is a diagram to explain the drawbacks of the conventional device. 1: Electron gun 2: Acceleration power source 3: Electron beam 5, 6, 7: Focusing lens 8: Aperture 9: Objective lens 10: Sample 11: Fluorescent screen 12. 13: Lens power source 14. 15, 20: DA converter

Claims (1)

[Claims] an electron gun and a first tube for focusing the electron beam from the electron gun;
, a second focusing lens, means for switching the accelerating voltage of the electron beam, and irradiating the electron beam focused by the first and second focusing lenses onto a minute portion of the sample at an irradiation angle α; In an apparatus configured to project a convergent electron beam diffraction image of an electron beam transmitted through a sample onto a screen, the ratio between the irradiation angle α and the wavelength λ of the electron beam is maintained unchanged regardless of switching of the accelerating voltage. A convergent electron diffraction apparatus comprising: a control means for automatically controlling the excitation intensities of the first and second focusing lenses so that the excitation intensity of the first and second focusing lenses is controlled.