JPH0982253A - Field emission type electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a correction for the vibration of an electron beam source for an electron beam holography or the like, regarding the optical device of a field emission type electron microscope. SOLUTION: Regarding a support body 21 with an electron beam source 1 mounted on one end thereof, an X-direction position adjusting piezoelectric device 14 and a Y-direction position adjusting piezoelectric device 15 are provided at the side of the other end of the support body 21 in directions different from each other at 90 degrees. The free ends of the piezoelectric devices 14 and 15 are fixed to a support part 25 used for securing a takeout electrode 12 to an outer cylinder 20. The support body 21 is provided with an X-direction tunnel current measurement chip 16 having a position adjusting piezoelectric device 18, as well as a Y-direction tunnel current measurement chip 17 having a position adjusting piezoelectric device 19 on the side near the electron beam source 1, in parallel to the X direction position adjusting piezoelectric device 14 and the Y direction position adjusting piezoelectric device 15. The X direction position adjusting piezoelectric device 14 and the Y direction position adjusting piezoelectric device 15 are controlled by the output of these tunnel current measurement chips 16 and 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device for a field emission electron microscope such as an electron microscope for electron holography.

[0002]

2. Description of the Related Art For example, in an optical device for electron holography, an electron beam hologram of a sample is created. Since all the information of the electron beam after passing through the sample is recorded in this hologram, irradiating the hologram with laser light can reproduce the image of the sample as a wavefront of light on the optical bench. it can. Therefore, it becomes possible to observe an interference microscope image, a phase microscope image, and the like that cannot be obtained with an electron microscope.

FIG. 1 is a schematic view of a conventional electron beam holographic optical device for producing an electron beam hologram. An electron beam emitted from an electron gun composed of the electron beam source 1 and the extraction electrode 12 is irradiated onto a sample 3 whose irradiation condition is adjusted by a condenser lens 2. Between the objective lens 4 and the intermediate lens 5, an electron beam prism 8 composed of a parallel plate electrode 6 having a ground potential and a thin core wire 7 stretched in the center thereof is provided. When a positive voltage is applied to the core wire 7, the electron beams passing through both sides of the core wire are bent toward the core wire and are superposed below. At this time, if an electron beam that does not pass through the sample 3 is passed through one side of the core wire and an electron beam that has passed through the inner portion of the sample is passed through the other side, two electron beams are superposed below and an interference pattern 9 is formed. It This is further magnified by the intermediate lens 5 and the projection lens 10 below and recorded on the film 11. This becomes a hologram. The entire device is an outer cylinder 2 as a vacuum container.
It is provided in 0.

In the hologram, not only the contrast of light and dark according to the transmittance of the sample (information of the intensity of the electron beam),
Information on the phase change received by the electron beam while passing through the sample (electron beam phase information) is also recorded. The phase information is recorded as a change in the fringe spacing of the fundamental periodic interference fringes in the hologram.

[0005]

In such a holographic optical device, when the electron beam source 1 vibrates, not only does the image become blurred, but the position of the interference fringes moves, resulting in a decrease in the contrast of the interference fringes. . When the vibration is large, the contrast of the interference fringes disappears and it becomes impossible to create a hologram. Therefore, in order to create a high quality hologram, it is necessary to minimize the vibration of the electron beam source.

[0006]

The present invention is realized by supporting the vibration of an electron beam source by a supporting means that expands and contracts relative to the vibration.

[0007]

By supporting the vibration of the electron beam source by the supporting means that expands and contracts relatively to the vibration, the vibration of the electron beam source is substantially canceled.

[0008]

An embodiment of the present invention will be described below with reference to FIG. FIG. 2 mainly shows the portions of the electron beam source 1 and the extraction electrode 12 in FIG. The field emission electron gun is composed of the extraction electrode 12 fixed to the outer cylinder 20, the field emission electron beam source 1, and the support 21 that holds the electron beam source 1. Of course, since a voltage for drawing out electrons must be applied between the electron beam source 1 and the extraction electrode 12, a suitable insulation is provided between them.
To simplify the drawing, these displays are omitted.

Support 21 having electron beam source 1 at one end
An X-direction position adjusting piezo device 14 and a Y-direction position adjusting piezo device 15 are provided on the side surface of the other end portion thereof in directions different in angle by 90 °. These piezo devices 14,
The other end of 15 is fixed to a support portion 25 for fixing the extraction electrode 12 to the outer cylinder 20. Further, the support 21 is provided on the side surface close to the electron beam source 1 with an X direction tunnel current measuring chip 16 having a position adjusting piezoelectric device 18 and a position adjusting piezoelectric device 19 for measuring a Y direction tunnel current. The chip 17 is arranged in parallel with the X-direction position adjustment piezo device 14 and the Y-direction position adjustment piezo device 15. These tunnel current measuring chips 16 and 17 are placed in a state of facing the inner surface of a supporting portion 25 for fixing the extraction electrode 12 to the outer cylinder 20.

If the tunnel current measuring chips 16 and 17 and the supporting portion 25 are brought close to each other to such an extent that a tunnel current flows, the vibration of the electron beam source 1 will be vibrated.
Since the relative position between the extraction electrode 12 and the field emission type electron beam source 1 which are rigidly fixed to the outer tube 20 via the change, the tunnel current flowing in the tunnel current measuring chips 16 and 17 is changed. It will be. That is, the X-direction fluctuation component of the relative position fluctuation between the extraction electrode 12 and the field emission electron beam source 1 is detected as a change in the tunnel current of the X-direction tunnel current measurement chip 16, and similarly, the position fluctuation Y is detected.
The direction fluctuation component is the Y direction tunnel current measuring chip 17.
It is detected as a change in the tunnel current flowing through.

When the voltage applied to the position adjusting piezoelectric devices 14 and 15 of the electron beam source 1 is changed in the direction of canceling the change in the tunnel current to expand and contract the piezoelectric elements,
The relative position between the extraction electrode 12 and the support 21 of the field emission electron beam source 1 can be changed in the direction opposite to the direction of change due to vibration. That is, if the voltage applied to the X-direction position adjusting piezo device 14 is adjusted so that the tunnel current flowing through the X-direction tunnel current measuring chip 16 becomes constant, fluctuations in the distance between the chip 16 and the extraction electrode, that is, It is possible to compensate the X-direction fluctuation component of the relative position between the electron beam source and the extraction electrode. Similarly, by adjusting the voltage applied to the Y-direction position adjusting piezo device 15 so that the tunnel current flowing through the Y-direction tunnel current measuring chip 17 becomes constant, the Y-direction fluctuation component can be compensated.

An example of initial setting of the position adjusting piezo devices 14 and 15 and the tunnel current measuring chips 16 and 17 and control circuits thereof will be described below.

FIG. 3 shows voltage-expansion / contraction characteristics of the position adjusting piezoelectric devices 14 and 15 and the position adjusting piezoelectric devices 18 and 19 of the tunnel current measuring chips 16 and 17. That is, these piezo devices have the characteristic of expanding and contracting according to the positive and negative of the voltage. When creating an optical device for holography,
Since no voltage is applied to these piezo devices,
In the state where the voltage is zero, in this state, the position adjusting piezo devices 18 and 19 are connected to the tunnel current measuring chips 16 and 17, respectively.
The length including the above is manufactured to be slightly shorter than the length of the position adjusting piezo devices 14 and 15, and one end is attached to the support 21. The other ends of the position adjusting piezo devices 14 and 15 are further fixed to the support portion 25. That is,
The support body 21 is fixed to the support portion 25 by the position adjusting piezo devices 14 and 15 so that the tunnel current measuring chips 16 and 17 face the support portion 25.

FIG. 4 shows an example of an X direction control circuit.
4, 18 and 16 are the position adjusting piezo device 14, the position adjusting piezo device 18 and the tunnel current measuring chip 16 shown in FIG. A similar circuit is provided for Y-direction control as well, but description thereof will be omitted. Reference numerals 31 and 32 are control power supplies for the position adjusting piezo device 14 and the position adjusting piezo device 18, respectively. Both power supplies 31 and 32 are as shown in FIG. 3 according to signal voltages of adder circuits 33 and 34 to be described later. It is supposed to output a voltage that changes to both positive and negative polarities. The adder circuits 33 and 34 add the signal input voltages with the polarities attached to the input terminals.

The following two signal voltages are applied to the adder circuit 33 with the polarities shown. From the signal line 35, for example,
A voltage of positive or negative magnitude is manually applied. The circuit composed of the resistor 36 and the power supply 37 is a circuit therefor. The midpoint of the resistor 36 is connected to the extraction electrode potential, and the support portion 25 and the outer cylinder 20 are also set to the same potential. Signal line 38
As described later, a voltage corresponding to the tunnel current detected by the chip 16 is applied from. Reference numeral 39 is an adder circuit, and the following two signal voltages are applied with the polarities shown in the figure, and the signal line 38 is used as an output line. A voltage corresponding to the tunnel current is directly applied from the input signal line 41, and a voltage storing the voltage corresponding to the tunnel current is applied from the input signal line 42. Reference numeral 43 is a hold circuit for that purpose, and 44 is a switch for applying or cutting a voltage corresponding to the tunnel current to the hold circuit 43. How to use the hold circuit 43 will be described later. Four
Reference numerals 5, 46 and 47 are a resistance and a power supply for detecting a tunnel current. The switch 44 is turned on at the initial stage of the adjustment as described later, but is turned off at the time of measurement by the holographic optical device.

The following two signal voltages are applied to the adder circuit 34 with the polarities shown. From the signal line 50, for example,
A voltage of positive or negative magnitude is manually applied. The circuit composed of the resistor 51 and the power supply 52 is a circuit therefor, and the middle point of the resistor 51 is connected to the extraction electrode potential.
From the signal line 53 to the chip 1 via the non-linear circuit 54.
A voltage corresponding to the tunnel current detected by 6 is applied. The non-linear circuit 54 outputs zero when the voltage corresponding to the tunnel current is equal to or lower than a predetermined value, and outputs a voltage that rapidly increases when the voltage exceeds the predetermined value or a predetermined constant voltage.

Prior to the measurement by the holographic optical device, the length of the piezo device 14 is controlled while the voltage of the signal line 35 is manually controlled, and the electron beam source 1 and the extraction electrode 12 are controlled.
The relative positional relationship in the X direction is adjusted, which is essentially the same as the positioning operation of the electron beam source 1 prior to the conventional measurement. After the adjustment, the voltage of the signal line 35 is fixed.
After the position of the electron beam source 1 in the X direction is determined, the signal line 50
Voltage is manually controlled to add a positive voltage to the addition circuit 34 so that the piezoelectric device 18 is extended,
Allow tunnel current to flow. At this stage, since the non-linear circuit 54 has no output, the piezo device 18 is expanded and contracted in response to the manual operation.

At the stage of adjusting the tunnel current by the piezo device 18, the switch 44 is turned on so that the voltage appearing at the resistor 46 due to the tunnel current does not affect the adding circuit 39. That is, the voltage corresponding to the tunnel current appearing in the resistor 46 is directly applied to the adder circuit 39 via the signal line 41, and
By applying the reverse polarity to the adder circuit 39 via the switch 44 and the hold circuit 43, the voltage appearing in the resistor 46 due to the tunnel current has no effect on the adder circuit 39. When the voltage that appears in the resistor 46 reaches a predetermined value due to the tunnel current, the voltage of the power supply 32 is fixed and the switch 44 is turned off. The voltage appearing in the resistor 46 when the switch 44 is turned off is held in the hold circuit 43.

Therefore, if the electron beam source 1 vibrates thereafter and the relative positional relationship between the electron beam source 1 and the extraction electrode 12 shifts in the X direction, the tunnel current changes, which causes the output voltage of the adder circuit 39 to change. Appears as a change. For example, when the electron beam source 1 vibrates and the relative positional relationship between the electron beam source 1 and the extraction electrode 12 shifts in the direction in which the electron beam source 1 and the support portion 25 approach each other, the tunnel current increases and the signal line 41. Voltage increases. However, since the voltage of the hold circuit 43 does not change, the output voltage of the adder circuit 39 increases positively. If the gain of the adder circuit 39 is appropriately increased, as a result,
Since the voltage of the adding circuit 33 increases in the positive direction, the voltage of the control power supply 31 of the piezo device 14 controlled by this increases in the positive direction, and the piezo device 14 extends. As a result, the electron beam source 1 moves in a direction away from the support portion 25.
Of course, as a result of this, the tunnel current decreases, so that the electron beam source 1 settles stably at the initial position, and the deviation of the relative positional relationship between the electron beam source 1 and the extraction electrode 12, that is, the vibration of the electron beam source 1 is compensated. It Similarly, the electron beam source 1 is attached to the supporting portion 2
When oscillating in the direction away from 5, the tunnel current decreases and the voltage of the signal line 41 decreases. Since the voltage of the hold circuit 43 does not change, the output voltage of the adder circuit 39 decreases. As a result, the voltage of the control power supply 31 of the piezo device 14 decreases and the piezo device 14 contracts. As a result, the electron beam source 1 moves toward the supporting portion 25, and the vibration is compensated.

The non-linear circuit 54 is not directly necessary for compensating for the vibration of the electron beam source 1, but the length of the piezoelectric device 14 is controlled by controlling the voltage of the signal line 35 prior to the measurement by the holographic optical device. When the relative positional relationship between the electron beam source 1 and the extraction electrode 12 in the X direction is adjusted by controlling the height, it is intended to prevent the tip 16 from being extremely close to the surface of the support portion 25. . At the time of initial adjustment, the tunnel current is monitored, and when it becomes too large, a large negative voltage is generated by the non-linear circuit 54 and the piezo device 18 is contracted, so that the chip 16 is extremely supported. It is possible to prevent access to the surface of 25.

Although the X direction has been described above, the vibration of the electron beam source 1 is similarly compensated for the Y direction.

In the description of the above embodiment, the optical device for electron beam holography for producing an electron beam hologram was described, but the invention of the present application is applicable to all optical devices for electron microscopes of the type having a field emission electron source. It is effective when applied.

The X-direction position adjusting piezo device and the Y-direction position adjusting piezo device are formed in a cylindrical shape, and the X-direction tunnel current measuring chip is provided with the position adjusting piezo device in the hollow portion of the cylinder. It goes without saying that a Y direction tunnel current measuring chip having a position adjusting piezoelectric device may be arranged. With this configuration, there is an effect that the detection position of the vibration point of the electron beam source and the correction position can be the same point.

[0024]

As a result of the above, according to the present invention, the vibration of the electron beam source can be compensated.

[Brief description of drawings]

FIG. 1 is a schematic view of a conventional electron beam holographic optical device that creates an electron beam hologram.

FIG. 2 is a perspective view mainly showing an electron beam source and an extraction electrode portion of an electron beam holography optical device according to an embodiment of the present invention.

FIG. 3 is a voltage of a piezo device used in an example of the present invention-
The figure which shows expansion-contraction characteristics.

FIG. 4 is a diagram showing a circuit for controlling the X direction of the piezo device according to the embodiment of the present invention.

[Explanation of symbols]

1: electron beam source, 2: condenser lens, 3: sample, 1
2: Extraction electrode, 14: X-direction position adjusting piezo device, 1
5: Y direction position adjustment piezo device 15, 16: X direction tunnel current measurement chip, 17: Y direction tunnel current measurement chip, 18: Position adjustment piezo device, 19: Position adjustment piezo device, 20: Outside Cylinder, 21: support, 25:
Support section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Tonomura 2520 Akanuma, Hatoyama-cho, Hiki-gun, Saitama Stock company Hitachi Research Laboratory

Claims (4)

[Claims] 1. A field emission electron microscope in which an electron beam emitted from an electron gun composed of an electron beam source and an extraction electrode is irradiated onto a sample with irradiation conditions adjusted by a condenser lens, and the electron beam source vibrates the electron beam source. Is supported by a supporting means that expands and contracts relatively with respect to vibration. 2. The expanding and contracting supporting means is a piezo device, and the vibration of the electron beam source is detected by a tunnel current detecting means provided between the electron beam source and a means for holding the electron beam source, and the piezo device is detected. The field emission electron microscope according to claim 1, wherein 3. A field emission electron microscope in which an electron beam emitted from an electron gun composed of an electron beam source and an extraction electrode is irradiated on a sample with irradiation conditions adjusted by a condenser lens, wherein the electron beam source is provided at one end. A piezo device for position adjustment in X direction and a piezo device for position adjustment in Y direction, which are provided on the side surface of the other end portion of the support body at angles different from each other by about 90 °, and a field emission electron for fixing the other end of the piezo device. The main body of the microscope, the side surface of the support closer to the electron beam source, so as to face the surface of the main body of the field emission electron microscope in parallel with the piezo device for position adjustment in the X direction and the piezo device for position adjustment in the Y direction. And a Y direction tunnel current measuring chip provided with a position adjusting piezo device and a Y direction tunnel current measuring chip provided with a position adjusting piezo device. Field emission electron microscope and controls the X-direction position adjusting piezo device and a Y-direction position adjusting piezo device by the chip output. 4. A piezoelectric device for position adjustment in the X direction and a Y device.
A direction position adjusting piezo device is formed in a cylindrical shape, and an X direction tunnel current measuring chip having the position adjusting piezo device in the hollow portion of the cylinder and a Y direction tunnel current measuring device having the position adjusting piezo device The field emission electron microscope according to claim 3, wherein a chip is arranged.