JPH06251739A - Electrostatic lens - Google Patents

Abstract

PURPOSE:To provide an electrostatic lens which can be controlled at high speed in the electrostatic lens upon which high voltage is impressed. CONSTITUTION:An electrostatic lens is formed in a three-pole structure of a central electrode 30 and outside electrodes 31 and 32. The outside electrodes 31 and 32 are connected electrically to each other, and high voltage is impressed upon the central electrode 30 from a high voltage circuit 33, and high voltage is impressed upon the outside electrodes 31 and 32 from a high voltage circuit 34. When strength of the electrostatic lens is changed minutely, voltage impressed upon the outside electrodes 31 and 32 from the high voltage circuit 34 is changed within a range of several kVs from several hundred Vs. Since an electric potential difference between the central electrode 30 and the outside electrodes 31 and 32 changes microscopically according to this voltage change, an ion beam focusing degree can be changed microscopically.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic lens most suitable for a focused ion beam device such as an ion microscope.

[0002]

2. Description of the Related Art FIG. 1 shows a general ion microscope, 1 is an ion emitter, 2 is an extraction electrode,
A high voltage is applied from the high voltage circuit 3 between the emitter 1 and the electrode 2. The ion beam IB generated from the extraction electrode 2 is finely focused on the sample 6 by the condenser lens 4 and the objective lens 5. The condenser lens 4 and the objective lens 5 are Einzel-type electrostatic lenses, and have center electrodes 7 and 8 and outer electrodes 9 and 10 at ground potential, respectively. A high voltage is applied to the center electrode 7 from the high voltage circuit 11, and a high voltage is applied to the center electrode 8 from the high voltage circuit 12. It should be noted that the lens of the ion microscope cannot focus on an electromagnetic lens using a magnet because the object to be focused is an ion and its mass is 2000 times or more that of an electron. Therefore, such an electrostatic lens is used.

Reference numeral 13 is an alignment electrode, to which an alignment voltage is applied from the alignment circuit 14 to align the axis of the ion beam IB. Reference numeral 15 is a deflection electrode, to which a scanning signal for scanning the ion beam on the sample 6 is supplied from the scanning circuit 16. Reference numeral 17 denotes an astigmatism correction electrode, to which an astigmatism correction voltage is applied from the astigmatism correction circuit 18. Each circuit 3, 11, 12, 14, 16, 18 described above
From the CPU 19 to the interfaces 20, 21, 2
Controlled via 2, 23, 24, 25. The operation of such a configuration will be described below.

The ion beam IB is extracted from the extraction electrode 2 and finely focused on the sample 6 by the condenser lens 4 and the objective lens 5. The irradiation position of the ion beam on the sample 6 is scanned by supplying a scanning signal from the scanning circuit 16 to the deflection electrode 15. Secondary electrons and secondary ions generated based on the irradiation of the sample 6 with the ion beam are detected by a detector (not shown). This detection signal is stored in the frame memory 26. The signal stored in the frame memory 26 is read out as appropriate,
It is supplied to a display device such as a cathode ray tube to display a scan image of the sample.

The axis of the ion beam with which the sample 6 is irradiated is aligned with the alignment electrode 13 by the alignment circuit 1.
4 is applied by applying a necessary voltage, and the astigmatism of the ion beam is corrected by applying a correction voltage from the astigmatism correction circuit 18 to the astigmatism correction electrode 17.

[0006]

In the above apparatus, the voltage applied to the central electrodes 7, 8 of the electrostatic lenses 4, 5 becomes higher as the acceleration voltage of the ion beam IB is increased. This voltage is usually about 10 kV to 100 kV. However, as the applied voltage becomes higher, the frequency characteristics of the circuit deteriorate due to the capacity of the electric circuit and the voltage supply cable that apply the voltage, and it becomes difficult to control the ion beam at high speed.

For example, in a high voltage power supply of about 100 kV, the response is 20 even if the voltage is changed.
It is about 0 msec to 500 msec. On the other hand, the response of the electromagnetic lens used in a normal scanning electron microscope is a few msec when a coil with a core is used, and on the order of a few μsec when an air-core coil is used, enabling extremely fast control. Is. Therefore, in the above device, the automatic focusing operation of the ion beam, the dynamic focus operation of observing the entire field of view of the tilted sample with just focus, and the voltage axis of the lens barrel, which are performed in a normal scanning electron microscope, are performed. It becomes very difficult to perform matching at high speed.

As another method, the above electrostatic lens is used as a main lens, an auxiliary electrostatic lens is arranged close to the main lens, the lens strength of the auxiliary electrostatic lens is changed, and the focus of the ion beam is changed. It is also possible to make adjustments. However, when the main electrostatic lens and the auxiliary electrostatic lens are used, the axial misalignment between the two lenses poses a problem and cannot be put to practical use.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrostatic lens capable of controlling the lens at high speed in an electrostatic lens to which a high voltage is applied. It will be realized.

[0010]

The electrostatic lens according to the present invention comprises a first electrode to which a relatively high voltage is applied, and a first electrode.
A second electrode to which a voltage lower than that of the first electrode for performing the electrostatic lens action integrally with the electrode is applied, and by controlling the voltage applied to the second electrode, It is characterized in that the electrostatic lens strength is changed.

[0011]

In the electrostatic lens according to the present invention, a relatively high voltage is applied to one of the two electrodes for performing the electrostatic lens action, a low voltage is applied to the other electrode, and the other electrode is applied. The electrostatic lens strength is changed by controlling the applied voltage.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows an embodiment of an electrostatic lens according to the present invention, which has a three-pole structure of a center electrode 30 and an outer electrode 31.32. Each electrode is formed in a disk shape, and an ion beam passage opening is formed in the center of each electrode. The outer electrodes 31 and 32 are electrically connected, and the high voltage circuit 33 is connected to the center electrode 30.
From the high voltage circuit 34 is applied to the outer electrodes 31 and 32. The operation of such a structure will be described below.

A high voltage of, for example, about 50 kV is applied to the center electrode 30 from the high voltage circuit 33, and the outer electrodes 31 and 32, which are conventionally at the ground potential, are fed from the high voltage circuit 34.
For example, a relatively low high voltage of about 1 kV is applied. This electrostatic lens acts as an electrostatic lens according to the potential difference between the center electrode 30 and the outer electrodes 31 and 32, and focuses the ion beam IB passing through the center aperture of each electrode.

Here, when the electrostatic lens strength is finely changed, the voltage applied from the high voltage circuit 34 to the outer electrodes 31 and 32 is changed within the range of several hundreds of volts to several kV. In accordance with this voltage change, the potential difference between the center electrode 30 and the outer electrodes 31, 32 changes minutely, and the degree of ion beam focusing can be changed minutely. This high voltage circuit 34
Generates a voltage of about 1 kV, which not only facilitates the withstand voltage of the cable that supplies the voltage and circuit design, but also makes its frequency characteristic on the order of several msec. As a result, by changing the voltage applied to the outer electrodes 31 and 32, the automatic focusing operation of the ion beam, the dynamic focusing operation of observing the entire field of view of the tilted sample by just focus, the voltage axis of the lens barrel, and the like. It becomes possible to perform the matching and the like at high speed.

FIG. 3 shows another embodiment of the present invention,
In this embodiment, the high voltage circuits 34 to 50 are connected to the center electrode 30.
A high voltage of about kV is applied, one electrode 31 of the outer electrodes 31, 32 is set to the ground potential, and a voltage of about 1 kV is applied to the other electrode 32 from the high voltage circuit 34. Even in such a configuration, the high voltage circuit 34 is connected to the outer electrode 32.
The electrostatic lens strength can be changed at high speed by minutely changing the voltage applied to. The outer electrode 32 is set to the ground potential, and the high voltage circuit 34 is connected to the outer electrode 31.
The control voltage may be applied from the above.

Although the embodiment of the present invention has been described in detail above, the present invention is not limited to this embodiment. For example, although the electrostatic lens having a three-electrode configuration has been described as an example, in the electrostatic lens having a two-electrode configuration, a relatively high voltage is applied to one electrode and a relatively low control voltage is applied to the other electrode. It may be done.

[0017]

As described above, in the electrostatic lens according to the present invention, a relatively high voltage is applied to one of the two electrodes for performing the electrostatic lens action, and a low voltage is applied to the other electrode. Is applied, and the electrostatic lens strength is changed by controlling the voltage applied to the other electrode. Therefore, in the electrostatic lens to which a high voltage is applied,
It is possible to control the lens at high speed. As a result, the automatic focusing operation of the ion beam, the dynamic focusing operation of observing the entire field of view of the tilted sample with just focus, and the voltage axis alignment of the lens barrel can be performed at high speed.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional ion beam device.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

 30 center electrode 31,32 outer electrode 33,34 high voltage circuit

Claims (1)

[Claims] 1. A first electrode to which a relatively high voltage is applied, and a second voltage to which a voltage lower than that of the first electrode for performing an electrostatic lens action integrally with the first electrode is applied. An electrostatic lens comprising an electrode and configured to change the electrostatic lens strength by controlling the voltage applied to the second electrode.