JPS58119146A - Electron microscope - Google Patents

Abstract

PURPOSE:To accurately perform focusing and astigmatic correction with a simple device, by providing a small lens between an objective lens and intermediate lens and fixing a focus current value and astigmatic correction current value of the objective lens. CONSTITUTION:An objective lens 1, small lens 4, intermediate lens 2 and projecting lens 3 are arranged on the same axis from the side of a sample (a) in said order and respectively provided with coils 1a, 4a, 2a, 3a and yokes 1b, 4b, 2b, 3b. The lens 1 is controlled to a fixed current value to align an image face to an object face b1 of the lens 2 in case of maximum magnification and fix a position of the image face. Then in case of imaging at maximum magnification, an electric current is not conducted in the lens 4 but the image of the lens 1 is imaged in a position of the image b1 and the lens 2 is adjusted to a maximum current value and imaged. Then to decrease the magnification from this condition, the current value of the lens 1 is left as fixed, and the current value of the lens 2 is decreased, interlocking to this decrease, the current value of the lens 4 is increased to correctively image the image of the lens 1 to a position b2 by lens action of the lens 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission electron microscope, and more particularly to an electron microscope in which focusing and astigmatism correction can be performed appropriately when changing magnification in an imaging lens system.

In the imaging lens system of a transmission electron microscope, when increasing or decreasing the magnification, the magnification is adjusted by increasing or decreasing the current value of the intermediate lens or projection lens. It is necessary to perform focusing and astigmatism of the objective lens accordingly.

Figures 1 and 2 are image formation diagrams of a conventional transmission electron microscope using a six-stage lens system (objective-intermediate-projection lens system) for medium-high magnification. In this case, FIG. 2 shows the case at high magnification.

In the drawings, 1 is the objective lens, 2 is the intermediate lens, 6 is the projection lens, a is the sample, b is the image plane of the objective lens 1 and the object plane of the intermediate lens 2, and C is the image plane of the intermediate lens 2 and the projection lens 6. , and d is the image plane (screen) of the projection lens.

In such an imaging lens system, in order to increase the magnification from the medium magnification imaging state shown in Figure 1 to the high magnification imaging state shown in Figure 2, the current value of the intermediate lens 2 is increased and the objective lens 1 is increased. It is necessary to lower the current value.

FIG. 5 is a graph showing the relationship between current and magnification in the conventional imaging lens system as described above.

IL are the objective and intermediate lens curves, M
indicates the range of fold change. As is clear from the curve IL in FIG. 5, in order to increase the magnification from M1 to M2, it is necessary to increase the current value of the intermediate lens 2.

In this case, as shown in FIG. 2, the object plane of the intermediate lens 2 moves to bl and approaches the intermediate lens 2. Therefore, it is necessary to align the image plane of the objective lens 1 with the partial position, and as shown by the curve OL in FIG. 5, it is necessary to slightly reduce the current value of the objective lens 1.

For this reason, it is necessary to readjust the focus current value and astigmatism correction current value of the objective lens 1. Conventionally, a magnification-linked focusing circuit, an automatic astigmatism correction circuit, etc. have been used.
The drawback was that sufficient performance could not be obtained due to large errors due to variations in precision of the half-plane resistor, which required a complicated device.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and by placing a small lens between the objective lens and the intermediate lens, the focus current value and astigmatism correction current value of the objective lens can be adjusted. It is an object of the present invention to provide an electron microscope that is fixed and capable of accurate focusing and astigmatism correction using a simple device.

The present invention includes an objective lens having a fixed current value, and a small lens provided between the objective lens and an intermediate lens for correcting the image plane of the objective lens to match the object plane of the intermediate lens. It is an electron microscope.

Hereinafter, the present invention will be explained with reference to embodiments of the drawings.

FIG. 6 is an image diagram showing an electron microscope according to an embodiment of the present invention, FIG. 4 is a vertical sectional view thereof, FIG. 6 is a graph showing the relationship between current and magnification, and FIGS. The same reference numerals as in FIG. 5 indicate the same or corresponding parts. 4 is a small lens provided between the objective lens 1 and the intermediate lens 2.

The objective lens 1, the small lens 4, the intermediate lens 2, and the projection lens 6 are arranged coaxially in the above order from the sample a side, and have coils 1a, 4a, 12a, 15a, and yokes 1b, 4b, 2b, and 5b, respectively. . Small size L
/ 7s 4 is 100KV acceleration voltage Te'10DO~15
It is a relatively small lens of about 00AT and is provided in the middle yoke 1C of the objective lens 1.

In the electron microscope configured as described above, the objective lens 1 keeps the current value constant so as to match the object surface of the intermediate lens 2 when the image surface is at the highest magnification, and fixes the image surface position. . When forming an image at the highest magnification,
The small lens 4 is not energized and the image plane of the objective lens 1 is formed at the position bl, the intermediate lens 2 is adjusted to the maximum current value, and the image is formed in the same manner as in FIG.

Next, to lower the magnification from this state, while keeping the current value of the objective lens 1 fixed, lower the current value of the intermediate lens 2 along the curve IL in FIG. Accordingly, the current value of the small lens 4 is increased, and the image plane of the objective lens 1 is made smaller, corrected to the b2 position by the lens action of /, and an image is formed. Here, b2 is the current value of the intermediate lens 2 on the curve I
The curve ML is the object plane of the intermediate lens 2 when moving down along L, and the current value applied to the small lens 4 is determined so that the image plane of the objective lens 1 coincides with the object surface of the intermediate lens 2. As described above, when changing the magnification by changing the current value of the intermediate lens 2, the image plane of the objective lens 1 can be changed by simply changing the current value of the small lens 4 while keeping the current value of the objective lens 1 constant. can be made to coincide with the object plane of the intermediate lens 2. Therefore, it is not necessary to readjust the current value for focusing the objective lens 1 and correcting astigmatism. At this time, small lens 4
Although a circuit for focusing and astigmatism correction is theoretically necessary, the influence on the image is smaller than that of the objective lens 1, so it is virtually negligible and does not pose a problem.

In addition, the magnetomotive force of the objective lens 1 is approximately 4000 to <5OOOA.
T, whereas the magnetomotive force of the small lens 4 is approximately 1000
~1500 AT, which is about 115 to 1/4, and the power consumed by the small lens 4 is extremely small, and the stain flow is also small. This is also clear from the difference in absolute values between the curves ML and OL in FIG. When setting the stain flow value using the same device, the error rate is almost constant, so the smaller the absolute value, the smaller the error and the higher the accuracy. On the other hand, if the same level of accuracy is sufficient, the adjustment device may have a simple structure. Therefore, the setting of the small lens 4 is easier and more accurate than the adjustment of the objective lens 1.

Note that although the above embodiment shows the case where there is one intermediate lens 2, there may be a plurality of intermediate lenses 2. Furthermore, the structures of the imaging lens system and lenses are not limited to those of the above embodiments, and can be modified. Furthermore, the small lens 4 may be placed apart from the objective lens 1.

According to the present invention, the current value of the objective lens is fixed and the image plane position of the objective lens is corrected using a small lens. With a simple device, without changing the current value of
It is possible to accurately adjust the current value of the small lens, correct the image plane position of the objective lens, and change the magnification. Furthermore, since the small lens can be inserted into the middle yoke of the objective lens, there is an advantage that the apparatus does not need to be enlarged.

[Brief explanation of the drawing]

1 and 2 are image formation diagrams of an electron microscope, FIG. 6 is an image formation diagram of an electron microscope according to an embodiment of the present invention, and FIG. 4 is a vertical cross-sectional view thereof. , FIG. 5 is a graph showing the relationship between current and magnification in a conventional imaging lens system, and FIG. 6 is a graph showing the relationship between current and magnification in an imaging lens system according to an embodiment of the present invention. In each figure, the same reference numerals indicate the same or equivalent parts; 1 is an objective lens, 2 is an intermediate lens, 6 is a projection lens, and 4 is a small lens. Representative Patent Attorney Seiku Yanagihara ψ Law ¥! Nobu

Claims (3)

[Claims] (1) An objective lens having a fixed current value, and a small lens provided between the objective lens and an intermediate lens and correcting the image plane of the objective lens to match the object plane of the intermediate lens. electronic microscope. (2) The electron microscope according to claim 1, wherein the current value of the small lens is adjusted in conjunction with a change in the current value of the intermediate lens. (3) The electron microscope according to claim 1 or 2, wherein the small lens is disposed within the yoke of the objective lens.