JPS61147525A - Charged particle beam applying device - Google Patents

Abstract

PURPOSE:To sufficiently reduce an apparent deflection distortion by providing three or more auxiliary lenses for reregulating the focus of charged particle beam at every deflecting point. CONSTITUTION:Charged particle beam emitted from an article point is focused through a main lens 5 on the center 2 of a sample surface 3. Charged particles deflected by a deflector 4 become an orbit 11, and further pass the out of the axis of a main lens to be deflected to become an orbit 12. Auxiliary lenses 61, 62, 63 are provided, focused, and corrected for the distortions of x- and y-directions. The orbits become 15, 16, 17 and can be freely controlled including the rotation around the optical axis.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a charged particle beam application device that narrows a charged particle beam and performs deflection scanning with high precision. Regarding particle beam application equipment.

[Background of the invention]

Deflection distortion correction for conventional charged particle beam application equipment.

This is accomplished by applying a deflection signal corresponding to the amount of correction to the deflector (for example, see Japanese Patent Laid-Open No. 56-59445).

This method has a limit in fully satisfying the required positional accuracy. That is, since the amount of deflection distortion is proportional to the cube of the amount of deflection, as the amount of deflection increases.

The amount of correction becomes dramatically large. Therefore, the amount of correction for the required position accuracy becomes large, reaching the correction limit, and further deflection becomes impossible.

[Purpose of the invention]

The present invention sufficiently reduces the apparent deflection distortion inherent in such an optical system by utilizing positional deviations during focusing (hereinafter referred to as dynamic focusing) performed at each deflection point. The purpose is to provide a means.

[Summary of the invention]

Deflection distortion is expressed by the amount of distortion and its direction, and is proportional to the cube and square of the amount of deflection, respectively. On the other hand, the amount of dynamic focusing is
The amount of positional deviation is proportional to the square of the amount of deflection, but the amount of positional deviation and its direction are proportional to the cube and square, respectively (however, if there is at least ! deflection inside the main lens or on the object point side) (Limited to cases where equipment is available) Therefore, one aspect of the present invention is to make the amount of positional shift match the amount of deflection distortion, reverse the direction, and perform focusing at the same time. Since there are three parameters, this is possible with at least three auxiliary lenses.

First, the principle of the present invention will be explained using FIGS. 1 and 2.

It is assumed that the charged particle beam emitted from the object point 1 is imaged onto the center 2 on the sample surface 3 by the main lens 5. The charged particles deflected by the deflector 4 become orbits 11, and further pass outside the axis of the main lens to receive the deflection action and become orbits 12. At this time, the focus is generally out of focus, so focusing is performed using the auxiliary lens 6 (referred to as dynamic focusing), and the deflection point 7 moves to the point 8. FIG. 2 shows this situation from the viewpoint of deflection distortion. The deflection area is x,
It is divided into four parts in the y direction, and the amount of distortion at each intersection is shown enlarged. When the deflector 4 is located inside the main lens 5 or on the object point 1 side, the deflection distortion generally becomes a barrel-shaped distortion as shown in FIG. For example, deflection point 21 is deflected to the position of point 22 due to deflection distortion. At this time, the deflection point 23 is moved by the action of the auxiliary lens 6. That is, the amount of deflection distortion unique to the optical system is the distance a between points 21 and 22, and the amount of positional shift during dynamic focusing is the distance between points 22 and 23. Therefore, the apparent amount of deflection distortion is at point 21
is the distance of point 23. Since a and b each have a direction (xt y) as well as a size, in the configuration shown in Figure 1, when controlling focusing, the size and direction of b are uniquely determined and cannot be controlled. . In order to control these as well, it is easy to understand that three auxiliary lenses 6 may be used as shown in FIG. 3 from the fact that there are three control parameters (focusing, deflection distortion xyy). In this case, the orbits are 15, 16, and 17, and can be freely controlled including rotation around the optical axis.

Although three auxiliary lenses were used in the above embodiments, it goes without saying that the same effect can always be expected with three or more auxiliary lenses. However, even if only two are placed.

A similar effect can be obtained if the size is extremely moderate, but the conditions are very strict. Considering that it can be done easily in practice, it is effective to provide at least three auxiliary lenses.

In the embodiment described above, the auxiliary lenses 61, 62, and 63 were all placed inside the main lens 5, but due to the nature of dynamic focusing, at least one auxiliary lens is placed inside the main lens 5 or very close to it. The other auxiliary lenses need not be located inside the main lens, as long as the direction of the magnetic field is opposite to that of the main lens.

According to the present invention, with the correction lens for dynamic focus correction,
Apparent deflection distortion can be made extremely small.

Therefore, there is an effect that the correction function for deflection distortion is not necessary, or even if it is necessary, the amount of correction remaining is extremely small. It is also possible to eliminate positional deviation of the charged particle beam at the same time as focusing.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the trajectory of the charged particle beam before and after dynamic focusing, and Figure 2 shows the deflection distortion inherent in the optical system configured in Figure 1 and the deflection distortion during dynamic focusing. FIG. 3 is a sectional view showing an optical system according to an embodiment of the present invention and charged particle trajectories at that time. l...object point, 3...sample surface, 4...deflector, 5...
...Lens, 61-63...Correction lens. Agent: Patent Attorney Masaru Ogawa

Claims (1)

[Scope of Claims] 1. In an apparatus equipped with a main lens for focusing a charged particle beam generated from a charged particle source, and a deflector for deflecting and scanning the charged particle beam in two dimensions, at each deflection point. A charged particle beam application device comprising at least three auxiliary lenses for readjusting the focus of the charged particle beam. 2. The charged particle beam application device according to claim 1, wherein at least one of the auxiliary lenses is disposed inside the main lens.