JPS59103255A - Alignment device for charged particle beam apparatus - Google Patents

Abstract

PURPOSE:To facilitate the alignment of a charged particle beam by providing a deflection element for alignment that deflects the charged particle beam and applying modulated deflection signals and then phase-detecting, integrating, and displaying the current of the charged particle beam or the signals that correspond to the current. CONSTITUTION:A deflection signal for alignment overlaps a small sinusoidal wave with a frequency f1 with the DC output of a potentiometer 8X and the central line of the electron beam in a diaphragm 15 oscillates in the X direction. If the central axis of the electron beam is aligned with the center of the diaphragm hole, the electron beam intensity applied to the diaphragm 15 is minimized. The relationship between the displacement of the control line of the electron beam in the X direction, current applied in the diaphragm 15, and the output of a phase detector is as shown in the figure. It is detected at a high S/N ratio by a narrow band amplifier 17X and a phase detection circuit 18X and signals that correspond to the current value which is applied to the diaphragm 15 in a smoothing circuit 19X and are displayed on a display means 20X. As a result, if the value adjusts the potentiometer 8x to indicate zero, the correct alignment with regard to the X direction can easily be adjusted and the same can apply with regard to the Y axis.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for easily aligning the axis of a charged particle beam in a charged particle beam device.

In a charged particle beam device, it is necessary to guide the charged particle beam emitted from the charged particle beam source to many lenses and apertures. At this time, the center line of the charged particle beam emitted from the charged particle beam source is It is necessary to adjust it so that it coincides with the center line connecting the centers of the aperture and the aperture, that is, the optical axis Z.

FIG. 1 is a schematic diagram showing an example of the intensity distribution in the divergence direction of a charged particle beam emitted from a charged particle beam source. 1st
In the figure, the horizontal axis X represents the direction perpendicular to the electron beam optical axis Z of the charged particle beam device, and the vertical axis represents the charged particle beam intensity at each X position.The intensity distribution is not uniform and the charged particle beam It can be seen that it shows a bell shape with the center P as the apex. FIG. 2 shows a state in which the charged particle beam 1 having the intensity distribution shown in FIG. 1 irradiates the aperture plate 2 placed on the xy plane perpendicular to the optical axis Z of the lightning particle beam device. In this J state, the center P of the charged particle beam does not coincide with the optical axis Z or the center of the aperture hole 3, so the charged particle beam device can only use a charged particle beam with weak intensity. Therefore, most charged particle beam devices are equipped with an alignment means to align the center of the charged particle beam with the optical axis, but the adjustment often requires cumbersome operations and is inconvenient. Often only precise adjustments could be made.

The present invention aims to solve such problems, and the present invention includes an axial alignment deflection element that deflects a charged particle beam in a direction perpendicular to the electron beam optical axis Z of a charged particle beam device, A variable DC signal generation circuit that supplies a deflection signal to the element;
two modulation oscillators that modulate the deflection signal supplied to the deflection element, a detection means that detects the current of the charged particle beam irradiated to the aperture plate placed in the optical axis Z, or a signal corresponding to the current; The present invention is characterized by comprising a phase detection circuit to which the output of the detection means is input and a reference signal is supplied from the modulation oscillator, and means for integrating and displaying the output of the phase detection circuit.

FIG. 3 is a schematic diagram showing the essential parts of an embodiment of an apparatus in which the present invention is applied to an electron beam apparatus such as a scanning electron microscope or an X-ray microanalyzer. In FIG. 3, numeral 4 represents an electron gun, and the intensity distribution of the electron beam emitted from the electron gun shows the same distribution as in FIG. 1, with the center line being 5. Therefore, in order to align the center line 5 with the optical axis Z of the scanning electron microscope, it is necessary to supply a deflection current to the two-stage deflection mirror (3x, 7x) and deflect it as shown in the figure. As a deflection signal for this purpose, a deflection power supply 9X whose output current is controlled according to the output of a potentiometer 8x is used.In addition, an oscillation circuit 11X with a frequency of 11 is connected to the input of the deflection power supply 9X via a capacitor 10. A sine wave is supplied from the deflection coil 6x.

The electron beam deflected in the X direction by 7x is sequentially focused by two focusing lenses 12 and 13 and irradiates the sample 14. An aperture plate 15 is inserted between the focusing lenses 12 and 13, and the current of the electron beam flowing into the aperture plate 15 is detected by a resistor 16 and supplied to a narrowband amplifier 17x. Further, the output of the narrowband amplifier 17x is transmitted to a phase amplifier 18x to which a reference signal is supplied from the oscillator 11x and a smoothing circuit 1.
9x and then displayed on the display means 20x.

In the apparatus shown in FIG. 3, the deflection signal for axis alignment has a waveform in which a minute sine wave of frequency f1 is superimposed on the potentiometer 8x (DC flow rate)]Io, so the center of the electron beam at the aperture plate 15 is The line will vibrate in the X direction.

In this state, if the center axis of the electron beam is aligned with the center of the aperture hole and alignment is performed correctly, the intensity of the electron beam irradiated to the aperture plate 15 is the minimum (the intensity of the electron beam passing through the aperture plate 15 is maximum). The relationship between the displacement of the center line of the electron beam in the X direction and the current flowing through the aperture plate 15 is as shown in FIG. 4(a), and the output of the phase detection record is as shown in FIG. 4(b). Although these changes in the current value flowing through the diaphragm plate 15 are extremely small, they are detected by the narrowband amplifier 17x and the phase detection circuit 18X with a high S/N ratio, and the smoothing circuit 19x generates a signal corresponding to the current value flowing through the diaphragm 15. The obtained value is displayed on the display means 20x. Therefore, so that the value displayed by the C1 display means 20 is zero,
Adjustment of the potentiometer 8x will result in correct alignment adjustment in the X direction.

The above is an explanation of only the configuration and operation necessary for axis alignment in the X direction, but the configurations necessary for alignment in the X direction include deflection coils 6y, 7y, potentiometer 8y, deflection power supply 9y, narrowband amplifier. 17y, phase detection circuit 18y,
Smoothing circuits 19y9 display means 20y are provided, and these are 9x, 8x, 17x, 18x, 19x, 20y, respectively.
It has a function equivalent to x. However, the oscillation circuit 11y
The frequency f2 and phase of the oscillation circuit 11x are different from the frequency f1 and phase of the oscillation circuit 11x. As a result, the X direction and
Directional alignment operations can be performed simultaneously.

Incidentally, since such a signal detection method using a phase detection circuit can generally be performed at an extremely high S/N ratio, it is possible to detect the sample even if the intensity of the modulation signal applied to the deflection coils 6X and 7X is sufficiently weakened. Even if modulation was applied during i52 observation (measurement), there was no problem with observation.

FIG. 5 is a schematic diagram showing another embodiment of the present invention.

In FIG. 5, the same symbols as in FIG. 3 represent the same components, such as the potentiometer 8 and the deflection power source 91.
Oscillator 11. Narrowband amplifier 17, phase detection circuit 18. The smoothing circuit 191 display means 20 are 8x, sy, 9x, respectively.
9y, 17x.

17V, 18x, 1sy, 19x, 19V, 20x
, 20. It has a function equivalent to y. A newly installed switch 21 is used to switch and supply the output of the oscillator 11 to the deflection power supplies 9x and 9y.

Although it becomes impossible to perform axis alignment in the (1) direction at the same time, it becomes possible to further simplify the device.

FIG. 6 shows the main part of yet another embodiment of the apparatus, in which signals whose phases are shifted by 90' to 9X and 9y are supplied from an oscillator 11 through a phase shifter 22. The phase detector 18 has phases of 0', 90°, and 180'.

The configuration is such that an output corresponding to 270° can be obtained.

In this case, the output of the detector is, for example, in the X direction,
The output corresponding to the phase O° is on the + side of Fig. 4(b),
The output corresponding to the phase of 180° is placed on the negative side of FIG. 4(b). With such a configuration, a single oscillator can be used.

Incidentally, the present invention is not limited to the above-described embodiment apparatus, and various modifications are possible. For example, an electrostatic deflection plate may be used instead of a deflection coil as a deflection element for alignment, and it is also possible to apply the present invention to an ion beam device instead of an electron beam device.

As described above, according to the present invention, accurate alignment adjustment can be made by electrical means without incorporating special means for alignment into the optical system of the charged particle beam device. This has a great effect on improving the operability of the alignment device in the equipment.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the intensity distribution of the charged particle beam emitted from the Xun electric particle beam source, FIG. Schematic diagram showing, No. 4
The figure is a schematic diagram for explaining the operation of the device shown in FIG. 3, and FIGS. 5 and 6 are schematic diagrams showing other embodiments of the device of the present invention. 1: Charged particle beam, 2: Aperture plate, 3: Aperture hole, 4: Electron gun, f3x, 7x: Deflection coil, Bx, sy: Potentiometer, 9x, 9y: Deflection power supply, 11x,
IIV: Oscillation circuit, 12.13: Focusing lens, 14: Sample, 15: Aperture plate, 17x, 17y: Narrowband amplifier, 1
8x, 18゛y: phase detection circuit, 19x, 19y: smoothing circuit, 20x, 20y: display means, 22: phase shifter. Patent applicant JEOL Ltd. Representative Ige - Husband

Claims (1)

[Claims] An alignment deflection element that deflects a charged particle beam in a direction perpendicular to the electron beam optical axis Z of a charged particle beam device, a variable DC signal generation circuit that supplies a deflection signal to the deflection element, and a deflection signal supplied to the deflection element. Two modulation oscillators that give modulation to the optical axis Z
a detection means for detecting a current of a charged particle beam irradiated to an aperture plate placed therein or a signal corresponding to the current; a phase detection circuit to which the output of the detection means is input and a reference signal is supplied from the modulation oscillator; , and means for integrating and displaying the output of the phase detection circuit, an alignment device for a charged particle beam device.