JPS62217549A - Electrostatic lens - Google Patents

Abstract

PURPOSE:To obtain good beam focusing with low impression voltage without impeding observation of a beam source by having a construction wherein diameters of the openings are simply increased from one end electrode to another end electrode. CONSTITUTION:A captioned lens has a construction wherein the diameters of openings of the electrostatic lenses arranged by placing plural sheets of electrodes 1-3 mutually in parallel while the centers of the openings of the respective electrodes in a straight line simply increase from their one end electrode 1 to another end electrode 3 whereby each opening diameter is not enlarged more than required. For example, the electrode, wherein an opening diameter of said electrostatic lens is the smallest, is placed on the incident side of a beam while the electrode having the largest opening diameter is placed on the outgoing side of the beam. Thereby, when observing an ion emission pattern, a visual field is not narrowed by the electrostatic lens while enabling to realize good beam focusing with low voltage.

Description

[Detailed Description of the Invention] [Summary] The present invention provides an electrostatic lens in which a plurality of electrodes each having an aperture are arranged parallel to each other, and the diameter of the aperture is changed from one end of the electrode to the other end. By adopting a structure that increases monotonically toward the center, good beam focusing can be achieved with a low applied voltage without interfering with beam source observation, etc.

[Industrial application field]

The present invention relates to improvements in the structure of electrostatic lenses.

Compared to electron beams, ion beams have almost no proximity effect due to scattering in solids, and have very high sensitivity to resists.Ion beams are used in lithography, implantation, and etching, which are essential for the manufacture of semiconductor devices. Alternatively, focused ion beams are expected to be used in processes such as deposition.

Conventionally, liquid metal ion sources have been widely used as ion sources, but in order to obtain a deeper range, hydrogen and
Gaseous ion sources such as helium have been developed. With gas ion sources, it is necessary to observe the ion emission state.
Optimization of the focusing electrostatic lens close to the ion source is desired.

[Conventional technology]

Figure 2 shows the field ionization type helium (H) developed by the present inventors.
e) Schematic diagram of a column with an ion source.

In the figure, 11 is a field ionization type He ion source, 12 is a gimbal support mechanism, 13 is a first electrostatic lens, 14 is a microchannel plate and screen, 15 is a reflector, 16 is an observation window, 17 is an aperture, 18 is a second electrostatic lens, 19 is a deflector, and 20 is a stage.

In this apparatus, first, in order to align the ion beam axis and the optical axis of the column, the center of the microchannel plate 14 is positioned on the optical axis, and the observation window 16 is
e Observe the ion release pattern, e.g.
The gimbal support mechanism 12 is adjusted so that the center of the image, which is about mm in size, coincides with the microchannel plate 14.

The ion beam axially aligned in this manner is focused onto the sample surface on the stage 20 by the first electrostatic lens I3 and the second electrostatic lens 18, and is projected to a desired position on the sample surface by the deflector 19. Ru.

As the first electrostatic lens 13, a so-called Einzel lens having a configuration shown in FIG. 3 has conventionally been used. That is, this electrostatic lens includes three electrodes 21, 22, and 23, each of which has a thickness of 3 mm and an aperture diameter of 1.
They have the same dimensions of 4 mm, the interval between them is 5 mm, and the central electrode 22 is placed at a position 25 mm from the ion source 11o in a narrow sense.

The electrodes 21.23 at both ends of the first electrostatic lens 13 are grounded to set Vz+ = OV, Vzz = OV, and a voltage of, for example, v2□ = 63 kV is applied to the central electrode 22, for example, to reduce the diameter of the ion source 11°. Do' = 208 m, applied voltage Vo = 50 kV, ion beam energy distribution ΔE = 10 eV, extraction half angle α0 = l mr
When ad, the diameter D of the circle of least confusion of the focused beam
i#47nm, which is about 3711 from the center electrode 22
It is in position II+.

[Problem that the invention seeks to solve]

In order to focus the ion beam as in the above example, it is not necessary to make the aperture diameter of each electrode 21 to 23 of this first electrostatic lens as large as 141, and when observing the ion emission pattern described earlier, In order to enable observation of a large solid angle without narrowing the field of view by the first electrostatic lens 13, the aperture diameters of all the electrodes 21 to 23 are made large in this way.

However, if the aperture diameter of the electrostatic lens is increased (the applied voltage increases, the insulation between the electrodes, etc., and the power supply must support this), and each part in the front of the ion source where many parts are crowded The layout is cramped.

Under the above-mentioned circumstances, there is a demand for optimization of electrostatic lenses used for such purposes.

[Means for solving problems]

The problem is that a plurality of electrodes are arranged parallel to each other and in a straight line with the centers of the openings provided in each electrode, and the openings extend from the electrode at one end to the electrode at the other end. This is solved by an electrostatic lens according to the invention whose diameter increases monotonically.

[For production]

According to the present invention, the diameter of the aperture of the electrostatic lens, in which a plurality of electrodes are arranged parallel to each other and the center of the aperture of each electrode is arranged in a straight line, varies from the electrode at one end to the electrode at the other end. The structure is such that the diameter of each opening increases monotonically toward the end, and the diameter of each opening is not made larger than necessary.

For example, in the usage example described above, the electrode with the smallest aperture diameter of this electrostatic lens is the beam incident side, and the electrode with the largest aperture diameter is the beam exit side.

With this structure, for example, when observing the ion emission pattern mentioned above, the field of view is not narrowed down by this electrostatic lens, and as will be explained in the examples below, it is possible to realize good beam focusing with a low voltage. It becomes possible.

〔Example〕

The present invention will be specifically explained below with reference to an example schematically shown in FIG.

In Fig. 1, 1.2.3 are the electrodes of the electrostatic lens, which are arranged in this order with electrode 1 on the ion source 11o side, with the center axis being the Z axis, and the origin 2 = 0 being the center of the central electrode 2. , the coordinates of the ion 5ilo are Zo, and the coordinates of the circle of least confusion of the focused beam are Zi.

Note that also in this embodiment, the diameter Do of the ion source 11o = 2
0 om, applied voltage ν0 = 50 kV, energy distribution ΔE of ion bee 11 = 10 eV, extraction half angle cro
= l mrad.

In this example, each electrode 1 to
As the diameter d, at, d3 of the opening of 3, d+ =
7mm, dz = 10mn+, d+
= 14 ohm, and the thickness of each electrode 1 to 3 is 3 m111, and the interval 5 mm is the same as in the conventional example. Note that the electrodes 1 at both ends
．． 3 is grounded so that V+ = OV and V3 = OV.

This embodiment and the conventional example (dl=dz=d3=14mm
), the beam was tracked for an electrostatic lens, and the following example results were obtained.

First, for the electrostatic lens of the conventional example, the following is obtained by selecting the voltage v2 applied to the central electrode 2 of this embodiment so that the position of the circle of least confusion is approximately equal to this.

Compare each data and set ν to Vz=49.50, then Z
.

= -30, -35, -40 vs. Vt = 49.
If it is 45kV, then for Zo=-20,-25,
It is known that although Zi matches better with the conventional example, the diameter Di of the circle of least confusion tends to be slightly smaller than that of the conventional example.

In this example, it is possible to achieve the same or better beam focusing as described above by lowering the applied voltage v2 of the central electrode 2 by 49.50 to 49.45 kV, which is 13.5 kV compared to 63 kV in the conventional example. It is.

It should be noted that the dimensions of each part, applied voltage, etc. in the above embodiments are merely examples, and these values can be selected to meet various imaging conditions, apertures, etc. requirements.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to achieve good beam focusing at low voltage without narrowing down the field of view, for example, when observing the ion emission pattern described above, etc. This will bring great benefits to the expected use of ion beams.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIG. 2 is a schematic diagram of a column equipped with a He ion source, and FIG. 3 is a schematic diagram of a conventional example. In the figure, 1.2.3 is an electrode of an electrostatic lens, 11 is a field ionization type He ion source, 11o is an ion source in a narrow sense, 12 is a gimbal support mechanism, 13 and 18 are electrostatic lenses, and 14 is a microchannel plate. and screen, 15
16 is a reflecting mirror, 16 is an observation window, 17 is an aperture, 19 is a deflector, and 20 is a stage. 1 OK=OlL gu 4 H Go 4 On J Ministry ε I Kirika] The Beast Adventures of Utojin 2 @

Claims (1)

[Claims] 1) A plurality of electrodes are arranged parallel to each other and in a straight line with the center of the opening provided in each electrode, from the electrode at one end to the electrode at the other end. An electrostatic lens characterized in that the diameter of the aperture monotonically increases. 2) The static electrode according to claim 1, characterized in that the electrode with the smallest diameter of the aperture is on the beam incidence side, and the electrode with the largest diameter of the aperture is on the beam exit side. Electric lens.