JPH035022B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electron beam device capable of displaying electron channeling patterns.

[Prior Art] As shown in Fig. 1, the bragging condition can be satisfied by sequentially scanning the electron beam in two directions θx and θy while fixing the incident point P of the electron beam on the sample S. Two lines parallel to the crystal plane are displayed on the display screen as loci of the angles that satisfy the crystal plane. Furthermore, OL
indicates the objective lens. An image consisting of two lines and a set of two lines is called an electron channeling pattern, and by analyzing this electron channeling pattern, we can determine the surface habit of the crystal, the grain boundaries, and the crystal orientation between different phases. Observation of this pattern has recently become widespread because it allows us to understand relationships, etc. As mentioned above, angular scanning is necessary to obtain this electron channeling pattern, but in an apparatus that performs angular scanning by scanning the front focal plane of the objective lens with an electron beam, Due to the spherical aberration of the objective lens, the focal length F deviates by ΔF= _CS・θ ² _∝CS・(Xi ² +Yi ² ) (1). However, in equation (1), C _S represents the spherical aberration coefficient, θ represents the locking angle of the electron beam, and Xi and Yi represent the X and Y direction scanning signals generated by the scanning signal generating circuit. Therefore, in conventional devices, a dynamic focus lens is provided near the objective lens, and a signal proportional to Xi ² + Yi ² is supplied to the dynamic focus lens in synchronization with the angular scanning of the electron beam EB. In this way, the above-mentioned ΔF is canceled out. By the way, the spherical aberration coefficient C _S in equation (1) is a function of the focal length F of the objective lens, so when trying to change the working distance W, which is the distance between the objective lens and the sample, the focal length F of the objective lens is changed. When changed, C _S
Since the value of ΔF changes, the value of ΔF changes. Similarly, in order to change the maximum value α of the rocking angle θ of the electron beam EB, ΔF also changes when the amplification factor of the variable magnification circuit is changed, and the spherical aberration coefficient also changes when the accelerating voltage E is changed. If the value of C _S or the focus shift amount δF of the dynamic focus lens changes and the dynamic focus lens is left in the same excited state, the dynamic focus lens will change the focus of the objective lens. Distance deviations cannot be corrected accurately.

[Problems to be Solved by the Invention] Therefore, in the conventional apparatus, the focal length F (or working distance W) of the objective lens, the maximum rocking angle α (or the observation magnification value M of the variable magnification circuit)
Xi ² + Yi ² supplied to the dynamic focus lens each time the accelerating voltage E is changed.
The amplification gain of the signal had to be adjusted by trial and error, making the operation extremely complicated.

The present invention solves these conventional drawbacks and
Even if the focal length F, the maximum locking angle α of the electron beam, or the acceleration voltage E is changed, the dynamic focus lens automatically offsets the focal shift of the objective lens expressed by the equation (1) with high precision. The purpose is to provide an electron beam device that can perform

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

The excitation current value supplied to the dynamic focus lens is I, L is the distance between the objective lens and the main surface of the dynamic focus lens, E ^* is the relativistic correction value of the accelerating voltage of the electron beam, A and n are Assuming that the constant is unique to the dynamic focus lens, the dynamic focus lens can shift the focal length by the amount given by the following equation.

δF=A・(W+L) ⁿ・I/√ ^* (2) If this equation is transformed, the following equation (3) is obtained.

I=A・√ ^*・δF ^* /(W+L) ⁿ …(3) Therefore, the focal length of the objective lens when the focal length F of the objective lens, the maximum locking angle α of the electron beam, and the acceleration voltage E are varied. Measure the maximum value ΔFmax of ^the deviation ΔF ^of Calculate the gain, store the signal values to the variable amplification factor amplifier necessary to realize this amplification gain as a table in a storage device for each set of F, α, and E,
The focal length of the objective lens (or working distance W),
Reading out a corresponding amplification gain control signal from among the signals stored in this storage device based on the signals corresponding to the maximum rocking angle α and the acceleration voltage E;
By controlling the amplification gain of the variable amplification factor amplifier based on this read signal, optimal correction can be performed without making complicated adjustments.

[Structure of the Invention] The present invention is based on this idea, and when the X-direction and Y-direction scanning signals are Xi and Yi, respectively,
Xi and Yi are supplied to the X- and Y-direction electron beam deflectors to scan the front focal plane of the objective lens with the electron beam, and the dynamic focus lens placed near the objective lens is supplied with Xi ² + Yi ² . A proportional current is supplied via a variable amplification amplifier to offset the movement of the electron beam irradiation position based on the spherical aberration of the objective lens, and the electron beam is angularly scanned, and the detection signal accompanying the angular scanning is scanned. In a device that displays an electron channeling pattern by guiding it to a display means that is scanned synchronously with , when the value corresponding to the accelerating voltage of the electron beam is Ek, each value Fi, αj,
storage means for storing a signal for specifying the amplification gain of the variable gain amplifier for a set of Ek; a signal corresponding to the focal length; a signal corresponding to the maximum rocking angle; and a signal corresponding to the accelerating voltage. It is characterized by comprising means for reading the signal stored in the storage means based on the signal and setting the amplification gain of the variable gain amplifier based on the read signal.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 2 is for showing one embodiment of the present invention. In FIG. 2, 1 is an electron gun, and a predetermined high voltage is applied to this electron gun 1 from an acceleration power source 2. In FIG. The electron beam EB from the electron gun 1 is focused by focusing lenses 3a and 3b, passes through an objective aperture 4, and enters a deflection system. This deflection system consists of first-stage scanning coils 5ax and 5ay for scanning in the X and Y directions.
It consists of second-stage scanning coils 5bx and 5by similar to the above. The electron beam EB deflected by these scanning coils is transmitted through a dynamic focus lens 6.
The light is then irradiated onto the sample 8 through the objective lens 7.
Reference numeral 9 denotes an objective lens power source for adjusting the excitation current supplied to the objective lens 7. 10X is Figure 3a
This X-scanning signal generating circuit 10 generates a scanning signal in the X direction as shown in FIG.
The scanning signal from X is sent to the scanning coils 5ax and 5bx via the switch circuit 11
It is now possible to supply 10Y is a Y scanning signal generation circuit that generates a scanning signal in the Y direction as shown in FIG. 3b, and this Y scanning signal generation circuit 1
The scanning signal from 0Y is also sent to the scanning coils 5ay and 5 via the switch circuit 11Y and the variable magnification circuit 12.
It is now possible to supply by. The X and Y direction scanning signals from these scanning signal generation circuits 10X and 10Y are transmitted to the scanning coils 13x and 1 of the cathode ray tube 13.
3y, and the cathode ray tube 13 emits electron beams.
It is designed to be scanned in synchronization with EB scanning. Further, the scanning signals from the scanning signal generating circuits 10X and 10Y are supplied to square circuits 14X and 14Y via switches Sx and Sy, respectively. The output signals of these square circuits 14X and 14Y are output from the adder circuit 1.
The output signal of the adder circuit 15 is supplied to the dynamic focus lens 6 via a variable gain amplifier 16. The amplification gain of the variable amplification factor amplifier 16 can be controlled based on a control signal supplied from the central processing unit 18 via the DA converter 17. This central processing unit 18 includes an objective lens power supply 9
The signal corresponding to the focal length of the objective lens 7 is
It is supplied via the AD converter 19, and
A signal representing an acceleration voltage from the acceleration power source 2 is
It is supplied via an AD converter 20, and furthermore, a signal representing the maximum rocking angle from the variable magnification circuit 12 is supplied via an AD converter 24. 21 is a memory that stores the focal length of the objective lens Fi (i = 1, 2, 3, ..., p) and the maximum value αj of the locking angle of the electron beam EB (j = 1, 2, 3, ...,
q), acceleration voltage as Ek (k=1, 2, 3,..., r)
, this memory 21 stores each Fi, αj, Ek
p×q×r signals for optimally specifying the amplification gain of the variable gain amplifier 16 for the set of are stored. 22 is a secondary electron detector, and the output signal from this detector 22 is supplied to the grid 13g of the cathode ray tube 13 via an amplifier 23.

In such a configuration, the acceleration power supply 2 is operated to set the acceleration voltage to Ea, and then the switch circuit 1 is set to Ea.
Scanning signals are supplied to scanning coils 5ax and 5ay via 1X and 11Y. Therefore, after selecting the working distance W and placing the sample 8 at a predetermined position along the optical axis, the excitation power source 9 is operated to
The focal length of the objective lens 7 is set to Fb so that the EB is locked with the point of incidence on the sample 8 fixed. Further, the variable magnification circuit 12 is adjusted to set the maximum value of the locking angle of the electron beam EB to αc. Therefore, the scanning signal generation circuits 10X, 10
When X and Y direction scanning signals Xi and Yi are generated from Y as shown in FIG. scan the surface,
The electron beam EB is locked at the maximum angle αc with the irradiation point on the sample 8 substantially fixed by the objective lens 7. Therefore, when the switches Sx and Sy are closed, the scanning signals Xi and Yi from the scanning signal generation circuits 10X and 10Y are supplied to the squaring circuits ^14X and ^14Y. A signal proportional to is supplied.
On the other hand, the central processing unit 18 receives signals representing the acceleration voltage Ea, the focal length Fb of the objective lens, and the maximum rocking angle αc set by the acceleration power supply 2, the excitation power supply 9, and the variable magnification circuit 12, respectively, from the AD converter 20,
19 and 24, the central processing unit 18 selects one of the signals for specifying the amplification gain of the variable gain amplifier 16 stored in the memory 21 based on these supplied signals.
Read out the signals corresponding to Ea, Fb, and αc, and send this signal to the variable amplification factor amplifier 1 via the DA converter 17.
Supply to 6. Therefore, the amplification factor variable amplifier 16
Under these conditions of Ea, Fb, and αc, the focus shift ΔF of the objective lens expressed by the above equation (1) is canceled out by the focal shift ΔF due to the dynamic focus lens expressed by the above equation (2). As if
Set to optimal amplification gain. Therefore, since the signal amplified by the variable amplification amplifier 16 is supplied to the dynamic focus lens 6, the focal shift of the objective lens 7 is corrected with high precision, and the electron beam due to locking of the electron beam EB is The movement of the irradiation position is extremely small. Therefore, detector 2
The output signal of 2 is sent to the cathode ray tube 13 via the amplifier 23.
, the electron channeling pattern in the extremely small area of the sample 18 can be displayed on the cathode ray tube 13.

Note that since the focal length and working distance of the objective lens have a fixed functional relationship, a signal representing the working distance may be used as a signal representing the focal length.

[Effects of the Invention] As is clear from the above explanation, in the apparatus based on the present invention, even when changing the accelerating voltage, the focal length of the objective lens, or the maximum locking angle of the electron beam, the dynamic adjustment is automatically performed. Optimal correction can be performed using the focus lens, and operability can be improved.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining scanning of an electron beam to obtain an electron channeling pattern.
FIG. 2 is a diagram showing one embodiment of the present invention, and FIG.
This figure is a diagram for illustrating output signals of each circuit of the embodiment shown in FIG. 2. 1: Electron gun, 2: Acceleration power source, 3a, 3b: Focusing lens, 4: Aperture, 5ax, 5ay, 5bx, 5by:
Scanning coil, 6: Dynamic focus lens, 7: Objective lens, 8: Sample, 9: Excitation power supply,
10X, 10Y: Scanning signal generation circuit, 11X, 1
1Y: Switch circuit, 12: Magnification variable circuit, 1
3: Cathode ray tube, 14X, 14Y: Square circuit, 1
5: Adder circuit, 16: Variable gain amplifier, 17:
DA converter, 18: Central processing unit, 19,2
0, 24: AD converter, 22: detector, 23: amplifier.

Claims (1)

[Claims] 1 When the X-direction and Y-direction scanning signals are Xi and Yi, respectively, the X- and Y-direction electron beam deflectors have Xi and Yi.
is supplied to scan the front focal plane of the objective lens with an electron beam, and a current proportional to Xi ² + Yi ² is supplied to the dynamic focus lens placed near the objective lens via a variable gain amplifier. The electron beam is angularly scanned by offsetting the movement of the irradiation position of the electron beam due to the spherical aberration of the objective lens, and the detection signal accompanying the angular scanning is guided to a display means that is scanned in synchronization with the scanning to display the electron beam. In a device designed to display a channeling pattern,
The value corresponding to the focal length of the objective lens is Fi, and the electron beam
When αj is the value corresponding to the maximum locking angle of EB and Ek is the value corresponding to the accelerating voltage of the electron beam, a storage means for storing a signal; a signal stored in the storage means is read out based on a signal corresponding to the focal length, a signal corresponding to the maximum rocking angle, and a signal corresponding to the accelerating voltage; An electron beam apparatus comprising means for setting an amplification gain of the variable amplification factor amplifier based on a read signal.