JPS5981849A - Beam irradiator for charged particle - Google Patents

Abstract

PURPOSE:To make a beam diametral characteristic selectable in a state of being desired as well as to simplify the changeover control of a diaphragm aperture, by securing a large aperture diaphragm upon rigid positional adjustment, while making a small aperture diaphragm free of going in and out at will. CONSTITUTION:Requirements for making an objective diaphragm turn to a small aperture is the case alone that one wants to secure the high resolution image of a sample surface by the secondary electron emitted out of a sample, in general so that positional slippage in the objective diaphragm toward an optical axis is inconsiderable indeed. Therefore, although positional adjustment in case of using the small aperture diaphragm is required, it is enough to merely use a positioning stopper at the most. A large aperture objective diaphragm B is secured upon rigid positional adjustment in time of assembling a beam irradiator for charged particle. A small aperture objective diaphragm B2 is made to be free of going in and out in a direction at a right angle to the optical axis and can be controlled from the outside of a vacuum device's wall and its positioning in time of application takes place in a way of hitting the stopper. For your information, the small aperture diaphragm B2 may be situated at the lower side of the large aperture diaphragm B, if necessary, but the nearer to an objective lens L2 the smaller in the influence of positional errors.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analytical device such as an electron beam microanalyzer or a scanning electron microscope that converges and irradiates a charged particle beam onto a sample surface, and particularly relates to an objective aperture variable aperture device thereof. It is related to.

The above-mentioned charged particle beam irradiation apparatus usually uses a large aperture aperture, and particularly uses a rear aperture aperture when it is necessary to obtain high resolution. A reduced image of the charged particle beam source is formed on the sample, and the positional resolution of the analysis is determined by the size of this reduced image.

The size of the reduced image is determined by the reduction ratio of the electron (or ion) optical system, but if the diameter of the aperture is large, even if the reduction ratio in the paraxial region is increased due to the aberration of the optical system, The beam diameter cannot be made smaller than the limit.

Therefore, when higher resolution is required, a small aperture aperture is used.The aperture aperture is changed for the reasons mentioned above, but in the past, it was done by replacing apertures of multiple sizes, small and large. I was changing the aperture diameter.

However, according to this method, it is necessary to align the optical axes of the apertures each time the aperture is switched to a large aperture aperture or to a small aperture aperture, and the aperture switching operation is extremely complicated. Furthermore, even slight insufficiency in position adjustment in commonly used large-diameter apertures has a large negative impact on device performance, as will be described later.

The present invention has been made with the object of solving the above-mentioned problems regarding switching the aperture pD diameter of a charged particle beam irradiation device.

The present invention secures a large-diameter diaphragm after precisely positioning it,
By making the fore-end rear aperture freely removable and removable, the above-mentioned problem regarding aperture diameter switching has been solved.

The large-diameter diaphragm is fixed, but when the small-diameter diaphragm is moved onto the optical axis, the large-diameter diaphragm is covered by the small-diameter diaphragm, so it is the same as if there is no large-diameter diaphragm.
If the small diameter diaphragm is removed from the optical axis, the large diameter diaphragm remains fixed, so it is possible to switch to the large diameter diaphragm without the need for position adjustment.

According to the present invention, since the large-diameter diaphragm 9 is fixed, there is no need for any position adjustment associated with switching the aperture diameter, and there is no problem of performance deterioration due to slight positional deviation. On the other hand, since the small diameter diaphragm is movable, it is necessary to adjust its position when using the small diameter diaphragm.However, the small diameter diaphragm is used especially when high resolution is desired, and the normally used large diameter diaphragm is used. B-diameter diaphragm 9 Small-diameter diaphragm #) Even if it takes a lot of effort to adjust the position for convenience, it does not significantly reduce the operability of the charged particle beam irradiation device. The advantage in terms of operability that there is no need to adjust the position when returning to the diaphragm is far greater because large-diameter diaphragms are more susceptible to misalignment.

The present invention will be further explained in detail. FIG. 1 shows the general configuration of a charged particle beam irradiation device. G is a charged particle beam source device such as an electron gun, Ll- is a condenser lens, L2 is an objective lens, and S is a sample. C is a concave curved crystal for X-ray spectroscopy, D is X
It is a beam detector, and the beam irradiation point O2 spectroscopic crystal C of the sample S
C and D are arranged so that the center of the X-ray detector and the front slit of the X-ray detector are located on one Roland mounting plate, and spectroscopy of X-rays emitted from the sample by charged particle irradiation is performed. P is a detector that detects secondary electrons emitted from the sample. The condenser lens L1 forms a reduced image of the charged particle beam source on a, and the objective lens L2 forms a reduced image of the image a on the sample S.
formed on top. B is the objective aperture. In this configuration, if you change the focal length of condenser lens L1, the position of image a will move downward by 200 degrees, and as the focal length is increased and image a is brought closer to aperture B, the beam flow cut by aperture B will decrease. Then, the sample irradiation beam current is added.

FIG. 2 shows the case where the horizontal axis represents the sample irradiation beam 1 current and the vertical axis represents the upward slope of the sample surface. When the focal length of the condenser lens Ll is lengthened in order to increase the beam current, the projection reduction ratio of the electron (ion) optical system decreases and the source image on the sample becomes larger, so the curve is in the upper right corner. In X-ray spectroscopy, when a large aperture objective aperture is used and the focal length of the condenser lens is lengthened in order to obtain a large sample irradiation beam current, a slight shift in the position of the objective lens aperture causes a phenomenon as shown in Figure 3. The charged particle beam is partially cut by the aperture, and the cross section of the beam is no longer a perfect circle, and the projection reduction ratio is still small. This appears as a misalignment of the irradiation point, which causes a shift in the X-ray focus of a concentrating X-ray spectrometer using a concave curved crystal as shown in Fig. 1, which impairs analytical accuracy, especially quantitative accuracy. This results in a decrease in condition analysis accuracy. Each part' in FIG. 3 is given the same reference numeral as in FIG. 1, and this figure shows a state in which the objective diaphragm B has been shifted to the right and has been rotated seven degrees. The charged particle beam shown by the dotted line is shown by the solid line when the power of the condenser lens Ll is set to −1 to reduce the projection reduction ratio by 1, and the beam current is narrowed down to 7. The charged particle beam shown by the solid line obtains a large beam current. Therefore, the power of the condenser lens Ll is lowered. Since the objective diaphragm 5B is shifted to the right, a part of the left side from the optical axis of the charged particle beam is cut off, and the diaphragm B is not effective at all on the right side. For example, to obtain the maximum beam current, the power of the condenser lens is lowered so that the convergence point a is located near the objective aperture, but at this time, the diameter of the objective aperture (dog-diameter objective aperture) is If it is 300 p m, the aperture position will be 150 μm laterally.
If it deviates, the convergence point will be on the edge of the aperture, and most of the beam current will be cut off. Moreover, a mechanical deviation of the aperture position f6 of about 150/1 m can realistically occur. If there is no aberration in the objective lens (not visible in Figure 3), there will be no change in the position or shape of the beam irradiation point on the sample surface even if the cross section is no longer a perfect circle centered on the optical axis. However, in situations where the aperture aperture is set to 100 mm and the aberration of the objective lens cannot be ignored, if the beam is asymmetrical with respect to the optical axis, the convergence will also be asymmetrical with respect to the optical axis, and the effective beam irradiation point on the sample will be aligned with the optical axis. It will be shifted from the intersection with .

As mentioned above, when the objective diaphragm has a dog-shaped aperture, positional deviation in the direction perpendicular to the optical axis of the diaphragm causes various adverse effects, so there is a high requirement for positional accuracy.

On the other hand, the objective aperture is generally set to a small diameter when it is desired to obtain a high-resolution image of the sample surface using secondary electrons emitted from the sample, and the secondary electron detection method is a condensing X-ray spectrometer. is sensitive to changes in the position of the X-ray generation point, whereas 2
In addition to being unaffected by the movement of the secondary electron generation point, the projection reduction ratio of the optical system is increased in order to obtain high resolution, so the positional deviation on the source side is also reduced, and the positional deviation of the objective diaphragm in the optical axis direction is reduced. Misalignment does not need to be a problem. Therefore, when using a small-diameter diaphragm, it is sufficient to use a positioning stopper for position adjustment.

FIG. 4 shows a main part of an embodiment of the present invention. Ll is a condenser lens, B2 is an objective lens, B1' is a large diameter objective diaphragm, and B2 is a small diameter objective diaphragm.

B1 is precisely positioned and fixed during assembly of the charged particle beam irradiation device. B2 can be freely moved in and out in a direction perpendicular to the optical axis and can be operated from outside the wall of the vacuum chamber of the apparatus, and is positioned during use by bringing it into contact with the stopper fI.

The figure shows a state in which a small diameter aperture B2 is used. In this embodiment, the small diameter diaphragm 9B2 is placed above the large diameter diaphragm B1, but it may be placed below, and the influence of positional errors will be further reduced if it is closer to the objective lens.

Further, the large-diameter objective diaphragm B1 is also located above the objective lens L2, but since this diaphragm is also placed close to the objective lens or is fixed, it may be placed inside the objective lens L2.

According to the present invention, when the charged particle irradiation device is used as a scanning electron microscope, the switching operation in the X-ray microanalyzer usage is greatly simplified.

[Brief explanation of the drawing]

Fig. 1 is a side view showing the general configuration of a charged particle irradiation device, Fig. 2 is a graph showing the relationship between the minimum beam diameter and beam current, and Fig. 3 is a graph showing the positional relationship between the charged particle beam flux and the aperture. Side View FIG. 4 is a side view of one embodiment of the present invention. G...Charged particle beam source device, Ll...Condenser lens, B2...Objective lens, B...Objective aperture, B1...
...Large diameter objective aperture 9, B2...Small diameter objective aperture, S.
...Sample, C...Concave curved crystal for X-ray spectroscopy, D...
X-ray detector, P... secondary electron detector. Agent Patent Attorney Kosuke Agata

Claims (1)

[Claims] Fix the large-diameter objective diaphragm and set the small-diameter objective diaphragm on the same optical axis.
A charged particle beam irradiation device characterized in that it can be installed in and out of F.