JPS6340018B2 - - Google Patents

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 is
This is done by giving 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, the amount of correction increases dramatically as the amount of deflection increases. Therefore, the amount of correction for the required positional accuracy becomes large, reaching the correction limit, and further deflection becomes impossible.

[Purpose of the invention]

The present invention eliminates such deflection distortion inherent in optical systems.
The object of the present invention is to provide a means for sufficiently reducing apparent deflection distortion by utilizing positional deviations during focusing (hereinafter referred to as dynamic focusing) performed at each deflection point.

[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 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. (only if there is at least one deflector on the object side). Therefore, in the present invention, the amount of positional shift is made to match the amount of deflection distortion, the direction is set in the opposite direction, and focusing is performed 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 have a trajectory 11, and further pass outside the axis of the main lens to undergo a deflection action and become a trajectory 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 divided into four parts in each of the x and y directions, 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. In other words, the amount of deflection distortion unique to the optical system is the distance a between points 21 and 22.
The amount of positional shift during dynamic focusing is the distance b between points 22 and 23. Therefore, the apparent amount of deflection distortion is the distance between points 21 and 23. a,
Since each b has not only a size but also a direction x and y, when controlling focusing in the configuration shown in FIG. 1, the size and direction of b are uniquely determined and cannot be controlled. In order to control these as well, it is sufficient to use three auxiliary lenses 6 as shown in FIG.
This can be easily seen from the fact that there are three deflection distortions (x, y). In this case, the orbits are 15, 16, and 17, which 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, the same effect can be obtained with only two if the arrangement and size are extremely appropriate, but the conditions are very strict. Considering that it can be done easily in practice, at least 3
It is effective to provide several auxiliary lenses.

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

According to the present invention, apparent deflection distortion can be extremely reduced by using a correction lens for dynamic focus correction.
Therefore, there is an effect that the correction function of deflection distortion is not necessary, or even if it is necessary, the remaining amount of correction can be made 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. 1...Object point, 3...Sample surface, 4...Deflector, 5
... Lens, 61-63 ... Correction lens.

Claims (1)

[Claims] 1. A main lens for narrowing a charged particle beam generated from a charged particle source, and at least one deflector disposed inside the main lens or on the object point side for deflecting the charged particle beam and scanning it over a sample. The apparatus includes at least three auxiliary lenses for readjusting the focus of the charged particle beam at each deflection point on the sample, and at least one of the auxiliary lenses is located inside the main lens or inside the main lens. A charged particle beam application device that is characterized by its close proximity.