JPS63252347A - Electrostatic lens - Google Patents

Abstract

PURPOSE:To suppress effects of an external electric field and to obtain an electrostatic lens which is excellent in its optical characteristics by disposing electrodes serially on a matter surface side and/or an image surface side and next making at least two of these electrodes equipotential to each other. CONSTITUTION:A lens is composed by dependent disposal of five parallel electrodes, that is, a first electrode 11 to a fifth electrode 15, which respectively have apertures in axis symmetry to an optical axis 1. Two of the first electrode 11 and the second electrode 12, which are disposed serially on an object surface side, and two of the fourth electrode 14 and the fifth electrode 15, which are disposed serially on an image surface side, are made equipotential (earth potential) to each other. A lens voltage is applied to the third electrode 13 by a power source 6. When charged beams 5 incident on an optical axis 1 pass through the apertures of the respective electrodes 12 to 14, they receive lens actions. When the voltage applied to the third electrode 13 is controlled, the lens actions can be regulated, and deterioration in optical characteristics can be prevented without disturbance of an external electric field and also effects of the external electric field can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrostatic lens used for focusing a charged beam.

(Prior Art) A typical conventional electrostatic lens is a unipotential lens (also known as an Einzel lens).

FIG. 4 shows a cross section of a schematic configuration of a unipotential lens.

The lens is constituted by a subordinate arrangement of three parallel electrodes having apertures that are axially symmetrical with respect to the optical axis 1, namely a first electrode 2, a second electrode 3, and a third electrode 4. The charged beam 5 incident above is subjected to a lens action when passing through the apertures of the respective electrodes 2, 3.4.

The first electrode 2 and the third electrode 4 are kept at the same potential, usually the ground potential, and the lens action can be adjusted by controlling the voltage applied to the second electrode 3 from the voltage R6.

By the way, in a charged beam device that performs processing by irradiating a charged beam onto a sample, in addition to electrostatic lenses such as the aforementioned unipotential lens that focuses the charged beam, a deflector that deflects the beam, and a beam blocking and passing device are used. A beam blanking device and other devices that control this are essential elements.

When the unipotential lens is mounted on the charged beam device, the electric field formed inside the unipotential lens from the first electrode 2 to the third electrode 4 is as follows.
It leaks out through the openings of the first electrode 2 and the third electrode 4, affecting the electric field outside the unipotential lens, and conversely, the electric field formed inside the unipotential lens increases the external electric field. The problem arises that it is easy to be influenced.

In other words, if another electrostatic lens or electrostatic deflector is installed near the unipotential lens, the electric field formed by these lenses will be disturbed by the electric field seeping out from the unipotential lens. However, there is a problem in that the quality of the charged beam is reduced by deteriorating the optical properties or deflection properties.Furthermore, on the contrary, the electric field formed by another electrostatic lens or deflector affects the electric field inside the unipotential lens. There is a problem in that the electric field is disturbed and the optical characteristics are deteriorated.

So to solve these problems, each electrostatic lens,
It would be possible to install the deflectors etc. at a sufficient distance from each other, but this would increase the optical path length of the charged beam.
On the contrary, it becomes more susceptible to the effects of disturbances and the space charge of the charged beam itself.Furthermore, the electrostatic lens for focusing requires a lens with a long focal length commensurate with the long optical path length, which adversely affects the optical properties. As a result, the problem of degrading the quality of the charged beam is unavoidable.

(Objective of the Invention) An object of the present invention is to solve the above problems and provide an electrostatic lens with excellent optical properties.

(Means for Solving the Problems) The first invention of the present application is an electrostatic lens constructed by arranging a plurality of electrodes having axially symmetrical apertures in a subordinate arrangement with the axis in common. The above object is achieved by setting at least two consecutive electrodes placed on the image plane side or either side to the same potential.

The second invention of the present application provides an electrostatic lens configured by arranging a plurality of electrodes having axially symmetrical apertures in a subordinate arrangement with the axis in common, the object plane side and the image plane side disposed on the outermost side. Alternatively, the above object can be achieved by hollowing out the inside of the aperture of one of the electrodes to form a shape having two apertures at the front and rear.

(Example) FIG. 1 shows an example of the first invention of the present application, and the lens has five parallel electrodes having apertures axially symmetrical with respect to the optical axis 1. 2nd electrode 12) 3rd electrode 13
, the fourth electrode 14, and the fifth electrode.

Here, the two consecutive first electrodes 11 and second electrodes 12 on the object side) and the two consecutive fourth electrodes 14 and fifth electrodes 15 on the image side are at the same potential, and in this embodiment, It is ground potential.

Further, a lens voltage is applied to the 371st E pole 13 by the power source 6.

In the configuration of this embodiment, the second electrode 12), the third electrode 13, and the fourth
Focusing on the electrodes 14, the operating principle is equivalent to the conventional unipotential lens shown in FIG. 4, and the charged beam 5 incident on the optical axis 1 passes through the apertures of each electrode 12, 13, and 14. The lens effect can be adjusted by controlling the voltage applied to the third electrode 13.

By the way, the inventor of the present application has discovered that the first electrode 11 and the second electrode 12
The space between the two electrodes is almost equivalent to a space surrounded by a ground potential, which blocks the influence of external electric fields to some extent, and is formed from the second electrode 12 through the third electrode 13 to the fourth electrode. Through experiments, we have found that the electric field generated inside the electrostatic lens is blocked to a considerable extent from the outside, and as a result, the electric field formed inside the electrostatic lens is less likely to be disturbed by the external electric field, and as a result, the optical characteristics deteriorate. In addition, it is possible to suppress the influence of the electric field inside the electrostatic lens on the external electric field.

Furthermore, it has been found that the above-mentioned effect is greater when the opening of the first electrode 11 is smaller than the opening of the second electrode 12.

The effects of the fourth electrode 14 and the fifth electrode 15 are also similar, so their explanation will be omitted here.

FIG. 2 shows an embodiment of the invention in Box 2, in which the lens has three parallel electrodes having apertures that are axially symmetrical with respect to the optical axis (i.e., a first electrode 21 and a second electrode 22). Third electrode 23
It is composed of dependent arrays of .

Here, the first electrode 21 and the third electrode 23 on the outside have a shape in which the inside of the opening is hollowed out and has two openings at the front and back.

The first electrode 21 and the third electrode 23 are at the same potential, here the ground potential, and a lens voltage is applied to the second electrode 22 by the power source 6.

The operating principle of this lens is the same as that of the conventional unipotential lens shown in FIG. This is what you are trying to obtain.

The effects of the invention in Box 2 of the present application are almost the same as those of the invention of Box 1 of the present application, so a description thereof will be omitted here.

It has also been found that in a shape in which the inside of the opening is hollowed out, the effect of the invention is greater when the outside opening is smaller than the inside opening.

Incidentally, if it is difficult to manufacture the electrode hole in a hollow shape in one piece, it may be manufactured in two parts as shown in FIG. 3, and then they may be joined together.

In the embodiments of the present invention, an electrostatic lens in which the operating principle of a unipotential lens is established is explained.
The present invention is not limited to the embodiments, and the same effect can be obtained even if the present invention is applied to any electrostatic lens constructed by arranging a plurality of electrodes having axially symmetrical openings in a subordinate arrangement.

In addition, as another effect of the present invention, when it is desired to differentially pump the inside of an electrostatic lens with respect to the outside of the lens, or when it is desired to differentially pump the object side and image side through the electrostatic lens, This can be realized by using the opening of the outer electrode in the invention of Item 1 as a perforated hole for differential exhaust, and also in the invention of Box 2, the outer opening can be used as a perforated hole for differential exhaust. It also has the feature that it can be realized by using it as

(Effects of the Invention) According to the present invention, an electrostatic lens that has excellent optical properties and is capable of differential pumping can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the invention in Box 1 of the present application. FIG. 2 is a schematic sectional view of an embodiment of the second invention of the present application. FIG. 3 is a sectional view of the first electrode part of another embodiment. Figure 4 shows a conventional electrostatic lens (unipotential lens)
FIG. 1... Charged beam optical axis, 2.11.21... First electrode 3,13°23
2nd electrode, 4.13.23...Third electrode, 5...Charged beam. 6...Power supply.

Claims (4)

[Claims] (1) In an electrostatic lens configured by arranging a plurality of electrodes having axially symmetrical openings in a subordinate arrangement with the axis in common,
An electrostatic lens characterized in that at least two consecutive electrodes placed on the object side and/or the image side are configured to have the same potential. (2) In the electrostatic lens described in claim 1, the hole diameter of the aperture of the at least two consecutive electrodes, which are at the same potential, extends outward from the center of the electrostatic lens. An electrostatic lens that is characterized by becoming smaller as it approaches. (3) In an electrostatic lens configured by arranging a plurality of electrodes having axially symmetrical openings in a subordinate arrangement with the axis in common,
The electrode on the object surface side and the image surface side, or either one of the electrodes disposed on the outermost side, has a shape in which the inside of the aperture of the electrode is hollowed out and two apertures are provided at the front and rear. electric lens. (4) In the electrostatic lens described in claim 3, the hole diameter of the outer hole of the electrode is smaller than the hole diameter of the inner hole. An electrostatic lens characterized by: