JPS5821064Y2 - Denshisenouchi - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a scanning electron microscope for analyzing or observing a minute portion of a sample.

In other words, it is a device that converges an electron beam onto an extremely small point on a sample using a lens, scans the sample surface, and captures various types of radiation emitted from the sample.

In this type of device, the smaller the electron beam is focused, the higher the resolution, that is, the higher the magnification image can be obtained.

This type of electron beam device is divided into two-stage convergence type and three-stage convergence type depending on the configuration of the lens system that converges the electron beam, and the latter has a higher magnification because it is easier to converge the electron beam to a smaller point than the former. Suitable for this equipment.

On the other hand, the two-stage type allows easier adjustment of the axis alignment of the lens system than the three-stage type, and is therefore easier to use.

There is also a demand for this type of device to be able to be used with a single device from relatively low to high magnifications.

However, as mentioned above, each of the two-stage and three-stage types has advantages and disadvantages, so whether a two-stage or a three-stage type is adopted, it is not possible to obtain a fully satisfactory device. .

In view of this situation, the present invention aims to provide a scanning electron microscope that has a three-stage lens structure, yet has easy axis adjustment, and can cover a range from relatively low to high magnifications. .

Figure 1 compares the two-stage type and the three-stage type, with the vertical axis representing the convergence diameter of the electron beam and the horizontal axis representing the electron beam current (sample current). A is the characteristic curve of the two-stage type. , the mouth is a three-stage characteristic curve.

As can be seen by extrapolating the curve A to the electron beam current O, the two-stage type is inferior to the three-stage type in its ability to narrow down the electron beam.

Expressing the characteristics of an electron beam device such as a scanning electron microscope as a relationship between electron beam current and electron beam diameter as shown in FIG. 1 is convenient for the following reasons.

Figure 2 shows the electron optical system of a scanning electron microscope, 1.2
．． 3 is number 1 from the top. Second. In the third lens, G is an electron beam source and S is a sample.

Now, assuming that the amount of electron beam transmitted through the second lens 2 is constant, trying to reduce the diameter of the electron beam will reduce the reduction ratio of the reduction projection, so the convergence point of the electron beam flux by the second lens will move upward and It becomes close to 2 lenses.

As the spread angle of the electron beam at this convergence point increases, the amount of electron beam that can pass through the aperture of the third lens 3 (shown below the third lens, no reference numeral) decreases.
Electron beam current decreases.

In other words, there is a functional relationship between the electron beam diameter and the electron beam current.On the other hand, when an image is constructed using detection signals of secondary electrons emitted from the sample, the electron beam current may be small, but the A large electron beam current is desired when spectroscopically detecting and generating a video signal.

Therefore, one concern is how much electron beam diameter can be obtained with the electron beam current.

Furthermore, as mentioned above, when trying to reduce the electron beam diameter, the electron beam current decreases, but when comparing the two-stage type and the three-stage type, the dotted line in Figure 2 is explained using Figure 2. The solid line shows the electron beam flux when the first lunus is not used, and the solid line shows the electron beam flux when the first lunus is used. The opening angle is expanded to angle a at point g.

In general, each lens has an aperture, and the outer peripheral portion of the electron beam whose aperture angle is expanded to a is canted by the aperture F of the second lens. As a result, the electrons contained within the aperture angle θ looking from the point G to the aperture F Even though the beam flux could pass through the second lens without the first lens, the outer peripheral part cannot pass through the second lens, and even if the reduction ratio is the same, the electron beam current will be smaller than that of the two-stage type (and the first lens will pass through the second lens). The relationship is as shown in Figure A9.

By the way, in Figure 1, the vertical axis is the electron beam diameter, but since the limit magnification at which a sharp image can be obtained is determined by the electron beam diameter, the vertical axis also represents the magnification, and higher magnification can be achieved towards the bottom. .

Therefore, it can be seen that above the electron beam diameter at point A marked with a black circle at the left end of the characteristic curve A in the figure (ie, on the low magnification side), there is no point in using the three-stage type, and the two-stage type is sufficient.

Also, without considering continuously varying the magnification below point A (on the high magnification side), only the magnification corresponding to the electron beam diameter at point B, which is marked with a black circle at the left end of the characteristic curve opening, is realized. In this case, one of the three-stage lenses can only be switched between passing current through it (excitation current of the electromagnetic lens), and on the lower magnification side than A, it is essentially used as a two-stage lens,
If we decide to obtain only the magnification corresponding to B in the three-stage type,
Adjustment of axis alignment at least on the low magnification side becomes as easy as with the two-stage type.

This is the first principle of this invention.

Next, in this invention, the first lens is a lens that is energized only when the magnification is high.
Lens 1 was chosen as the lens closest to the electron gun.

In this configuration, the first lunus is normally not energized and the second lunz is not energized. It is used as a two-stage type with only the third lens, and alignment adjustment is performed only for the electron gun and the second lens.

(The third lens is fixed to the lens barrel).

Next, when power is applied to the second lun, since the axis of the first lun is not strictly aligned, the image of the electron beam source by the first lun will be slightly shifted from the optical axis connecting the electron beam source and the second and third lenses. However, since each stage of the first to third lenses is a reduction projection system, the effect of this shift is not a problem because it is reduced each time it passes through the second and third lenses.

The divergence angle of the electron beam converged by the second lens is large (because it is projected in a reduced size), so even if there is the above-mentioned deviation, the second beam is reliably converged by the second lens. The third lens and the electron beam can pass through it.

This relationship is shown in FIG.

The electron beam flux shown by the dotted line is when the 1st lunus is not used, and the electron beam shown by the solid line is when the 1st lunus is also used.Since the axis adjustment of the 1st lunula is insufficient, the image of the source G is formed at g. , is shifted by e from the optical axis X.

Also, since it is a reduced projection system, the divergence angle a of the electron beam at g is larger than the divergence angle of the electron beam at the electron beam source G, so even if there is a shift in e, the electron beam flux will be the second. It can pass through the third lens.

Also, the deviation of e is the second. The projection reduction ratio of the third lens is 1/A.
, 1/B, the deviation on the sample is only e/A-B.

Next, the present invention will be explained by examples.

In FIG. 3, 4 is an electron gun outer cylinder, 5 is a filament, and 6 is an accelerating electrode, which constitute an electron beam source section.The electron beam source section and the first lens 1 are integrally connected, and the lens barrel 7
It is fixed in an adjustable position.

The first lens 1 has magnetic poles that are vertically asymmetrical and has a strong power despite its relatively large aperture.

The second lens 2 has a position fine adjustment mechanism with respect to the lens barrel 7.

A magnet may be used instead of this mechanism. The third lens 3 is fixed to the lens barrel 7, and serves as a position reference when adjusting the positions of the other radiation source sections and the second lens.

The first run is the second run. It is connected to the power source E by a switch 8 independent of the third lens 2.degree. 3, and the switch 8 switches between a two-stage type and a three-stage type.

With the above configuration, alignment adjustment is performed by finely adjusting the positions of the combination of the electron beam source and the second lunion 1 and the second lens 2 in a two-stage state in which the second lunion 1 is not energized. The position between the part 4 and the first lunula 1 is fixed relative to each other by fitting depending on the machining accuracy.

The present invention has the above-mentioned configuration, and the first stage of the three-stage lens is an on-off type, and in the low magnification range, the first lens is not energized and is used as a two-stage type, thereby making it possible to adjust the axis alignment in the three-stage lens. It is possible to eliminate the difficulties, obtain a three-stage high magnification, and obtain an electron beam device that can cover a wide magnification range with simple adjustment.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the diameter of a convergent electron beam and the electron beam current, FIG. 2 is a diagram illustrating the operation of the present invention, and FIG. 3 is a side view of an apparatus according to an embodiment of the present invention. 1... Second lens, 2... Second lens,
3... Third lens, 4... Electron gun outer cylinder, I... Lens barrel, 8... Two-stage, three-stage switching of electron beam device. Switch, G...Electron beam source, S...
·····sample.

Claims (1)

[Scope of utility model registration request] An electron beam reduction projection system is constructed by arranging the electron beam source, the second lun, the second lens, and the third lens in this order, and the electron beam source and the second lun are integrally combined. The alignment position of the body and the second lens can be adjusted with respect to the lens barrel, and the second lens is adjustable. The third lens is connected to a power source via a switch independent of the third lens; Second. Each of the third lenses is energized, and only the third lens is de-energized, and the excitation current for the third lens is only allowed to have a current value of 1-'). A scanning electron microscope in which the excitation current of the third lens is adjustable.