JPS5966042A - Electrostatic type focusing deflection device - Google Patents

Abstract

PURPOSE:To deflect charged particle rays largely as left focused so thinly intact, by having a device made up of a first electrostatic lens focusing an image formation point far away than a sample surface and a second electrostatic lens focusing the charged particle rays on the sample surface, besides a deflector existing between them. CONSTITUTION:Charged particle rays 2 out of an object point 1 are focused to a point 8 far away than an image surface 3 by a first electrostatic type lens 6 and also focused on the image surface 3 by a second electrostatic type lens 7, while deflected by a deflector 5 disposed between lenses 6 and 7. As a result, since magnification of the lens 7 comes to a smaller negative value than 1, aberration on the axis of the lens 7 is made to be very smaller and the aberration on the image surface 3 due to the lens 6 can be made small as well, making the rays 2 focusable so thinly, while deflecting aberration is produced by aberration at the outside axis between the deflector 5 and the lens 7 but this aberration can be compensated with each other so that large deflection can be achieved.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an electrostatic lens and a deflector, and particularly to a focusing/deflecting system suitable for greatly deflecting a charged particle beam while focusing it narrowly. be.

[Prior art]

In conventional electrostatic focusing/deflecting systems, a deflector is placed on the object side as shown in Figure 1, or on the image plane side as shown in Figure 2, with respect to the lens that focuses the charged particle beam. It was very difficult to find what I had set up. In the figure, IFi is an object point, 2 is a charged particle beam, 3 is an image plane, 4e is an electrostatic lens, and 5 is a deflector.

The former is not suitable for large-angle deflection because the particles can be narrowed down on the axis or the deflection aberration is large. The latter has the disadvantage of not being able to stop down quickly enough on the axis because the lens has a long focal point7
Do 5i.

[Purpose of the invention]

The purpose of the present invention is to solve the problem of whether the 11 particles are loaded even on the axis or when deflected sharply. The object of the present invention is to provide an electrostatic focusing/deflecting system that can focus finely.

[Detailed description of the invention]

In the present invention, in order to narrow the aperture on the axis, the deflector is used at the object point 1 of the lens.
11]. At this time, in the conventional method, the deflection aberration increases, but by actively making the particle beam that has passed through the deflector pass outside the axis of the lens, the deflection aberration caused by the deflector can be canceled out by the off-axis aberration of the lens. Configure it as follows.

That is, since the outer lens does not have the effect of rotating the particle beam within the lens, no anisotropic aberration occurs at all, and only isotropic aberration occurs. Therefore, even if the lens and the deflector are arranged independently, it is possible to cancel the deflection aberration.

〔Example〕

An embodiment of the present invention will be explained below with reference to FIG. The charged particle beam 2 emitted from the object point 1 is focused by an electrostatic lens 6.
An image is formed at a point 8 at a distance from the image plane 3, and an image is formed on the image plane 3 by the lens 7.

A deflector 5 is arranged between the lenses 6 and 7.
The particle beam is operated to be deflected to a desired degree of 1Δ above the station.

In this optical system, since the lens 70 magnification has a negative value smaller than 1, the axial aberration of the lens 7 can be made very small. On the other hand, although the aberration coefficient of the lens 6 is large, the aberration on the image plane 3 due to the lens 6 can be made sufficiently small because the convergence angle 9 of the particle beam is small and the lens 7 is a reduction system.

Therefore, the aberration caused by the lenses 6 and 7 is small, and the particle beam can be narrowed down.

On the other hand, deflection aberrations are caused by off-axis aberrations of the deflector 5 and the lens 7, but they can cancel each other out. As an example of explanation, deflection chromatic aberration will be explained using FIG. 4. That is, particle beams 10 and 11 having different speeds (10 is faster) deflected by the deflector 5 are deflected at the deflection point 1 on the sample surface 3.
The fact that 2 matches is described below.

The particle beam emitted from the object point 1 has a trajectory 13 when viewed from the lens 7, but the particle beam with a low velocity has a trajectory 14.
An image is formed on a shifted imaging plane 15-A. Accordingly, according to geometrical optical construction, particle beams 10 and 11 are refracted by lens 7 so as to pass through points 12 and 16, respectively.

When , the particle beams 10 and 11 coincide on the sample surface 3. In other words, no polarization chromatic aberration occurs. It can be proven that other aberrations can be canceled in the same way.

In FIG. 4, the characteristics of the lens 7 and the position of the deflector 5 are set under special conditions (the front focal position of the lens 7) so that not only the deflection aberration but also the particle beam 10 is perpendicularly incident on the sample surface 3. Under these conditions, electrodes 6-2 and 7 of lenses 6 and 7 are
-2 potentials can be made to match, and a single lens power source can be used. In the embodiment of FIG. 3, the lens 6
and 7 are fixed on a unipotential lens, but they can be done similarly with a pipotential lens. In addition, the lens electrode 6
-3 and 7-3' (r- It goes without saying that the electrodes of the deflector 5 may be used instead.

[Effect of departure]

According to the present invention, since the deflection aberration can be reduced, there is an effect that the charged particles can be largely deflected while remaining tightly focused. Furthermore, since the incidence on the sample surface can be made perpendicular, there is also a feature that the direction sensitivity does not deteriorate even when the height of the sample surface changes.

[Brief explanation of the drawing]

Is Figure 1.2 the basic configuration for explaining the conventional technology? This is a drawing shown. FIG. 3 is a diagram showing an embodiment of the present invention. Figure 4 is a drawing to demonstrate that deflection aberrations are canceled by ``kB''. ・1...object point, 2...charged particle beam, 3...image plane, 4
, 6゜7... Seiko type lens, 6-1 to 6-3.7-1
~7-3... Electrode, 5... Deflector, 8... Imaging point of lens 6, 9... Convergence angle of particle beam by lens 6,
1.0.11...Particle beam with different speed, 12...Deflection point, 13°14...Particle trajectory after passing through lens 7, 1
5... Image plane of particle trajectory 14, 16... Particle beam 11
passing point. Agent Patent Attorney Toshiyuki Usuda, 1. ．． ．． layer,
. ', 1:12. i・、、゛

Claims (1)

[Claims] 1. A device that focuses a charged particle beam emitted from an object point,
a first electrostatic lens whose imaging point is far away from the sample surface; and a second electrostatic lens that focuses all of the particles f# from the first lens onto the sample surface. and a deflector that is located between the first and second electrostatic lenses and deflects the charged particle beam. 2. The static one-section type focusing/deflecting device according to claim 1, wherein the first and second electrostatic lenses are driven by the same force S. 3. The electrostatic focusing/deflecting device according to claim 1, wherein the deflector is arranged near the front focal point of the electrostatic lens described in 2 above.