JPH0992191A - electronic microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously perform observation of high resolution and high- quality image at a wide range of magnification by one type by providing a gap for a yoke on the pole piece lower side of an object lens and setting an auxiliary lens where an energizing coil is set. SOLUTION: In a focusing lens system of an electronic microscope, a gap is provided for a yoke on the pole piece lower side of an object lens, and an auxiliary lens 3 where an energizing coil is arranged in the yoke internal part of the gap lower side is provided. This focusing lens system is provided with energizing power supplies 18 to 23 and a computer 17 for controlling these power supplies. According to this constitution, a magnetic field is generated in the pole piece and the gap by means of energizing the object lens. Control of the magnetic field in the gap is made possible by energizing the auxiliary coil incorporated on the gap lower side. For the object lens, image observation of high resolution at a constant regent position and at a low to high magnification is made possible by switching the polarity of energizing current of the auxiliary coil.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a transmission electron microscope.

[0002]

2. Description of the Related Art In a conventional transmission electron microscope, a low magnification image is distorted or its field of view is limited in an imaging mode for obtaining high resolution. Therefore, the minimum magnification that can be used for image observation was only about 1000 times. For this reason, in order to obtain several hundreds of times, it was necessary to equip the electron microscope with an objective lens pole piece having a long focal length with low resolution, or to use the objective lens with extremely weak excitation.

[0003]

When the image forming mode aiming at high magnification and high resolution as in the conventional system is a low-magnification image, the image forming lens system is used with low excitation, so that the magnification is less than 1,000 times. At magnification, distortion occurs and the field of view is limited. Therefore, the minimum magnification that can be used for image observation was about 1,000 times. Therefore, in order to obtain several hundreds of times, the objective lens pole piece with a long focal length is provided in the electron microscope, or the excitation of the objective lens is extremely weakly used to reduce the magnification of the objective lens. This objective lens has a poor resolution, and it has been impossible to obtain a high magnification of several million times. For this reason, the conventional electron microscope has different models for high resolution and low magnification.

An object of the present invention is to provide an electron microscope capable of simultaneously observing a wide field of view with a high resolution and a high image quality even with a wide range of magnifications from a low magnification to a high magnification while improving the observability and operability. To provide.

[0005]

In the present invention, as shown in FIG. 2, an auxiliary lens in which a gap is provided in a yoke below a pole piece of an objective lens and an exciting coil is installed inside the yoke below the gap. And an excitation power source for the objective lens and each imaging lens, and a computer for controlling them.

According to the above structure, a magnetic field is generated in the pole piece and the gap by exciting the objective coil. Further, by exciting the built-in auxiliary coil below the gap, the magnetic field generated in the gap can be controlled. The magnetic field generated in the pole piece was used as the objective lens, and the magnetic field generated in the gap was used as the auxiliary lens, and these were combined to form a compound lens. The composite focal length of the compound lens can be expressed by the following equation.

[0007]

1 / f ₃ = 1 / f ₁ + 1 / f ₂ + 2d / f ₁ f ₂ (Equation 1) f ₃ : composite focal length, f ₁ : objective lens focal length,
f ₂ : Focal length of auxiliary lens, d: Distance between lenses FIGS. 3 and 4 show the relationship between the excitation of the objective lens and the electro-optical characteristics (sample position, focal length, spherical aberration coefficient, chromatic aberration coefficient). FIG. 3 shows electron optical characteristic data when the objective coil and the auxiliary coil have the same polarity. The magnetic fields of the two lens coils are added to the lower side of the gap, and the auxiliary lens is strongly excited. For this reason, the focal length of the auxiliary lens becomes shorter, and the focal length of the compound objective lens becomes longer than that of the expression (1). Further, the compound objective lens can obtain a long focal length and a low spherical aberration coefficient and chromatic aberration coefficient. This is because the incident angle of the electron beam incident on the auxiliary lens is very small, so that the aberration of the auxiliary lens can be ignored. Next, FIG. 4 shows electron optical characteristic data when the exciting current of the auxiliary coil has a reverse polarity. Since the polarity of the auxiliary coil is reversed,
The magnetic field generated in the gap of the auxiliary lens is canceled and becomes smaller. For this reason, the focal length of the auxiliary lens becomes long, and the focal length of the compound objective lens becomes shorter than that of the expression (1). As described above, the compound objective lens can easily control the long and short focal lengths with a low spherical aberration coefficient and a chromatic aberration coefficient. The magnification of the objective lens can be determined from this focal length. The relationship between focal length and magnification is shown below.

Number 2 and number 3 of electron optics

[0009]

(2) (1 / a) + (1 / b) = 1 / f (Equation 2)

[0010]

## EQU00003 ## M = b / a (Equation 3) Object plane distance: a, image plane distance: b, magnification: M, focal length:
f, if the magnification M has a value sufficiently larger than 1

[0011]

[Equation 4] M = b / f (Equation 4) From these, the excitation is used in which the sample positions of the objective lens compounded from the electron optical characteristic data of FIGS. 3 and 4 are the same. Then, there is a lens condition in which the focal length can be changed by changing the curvature of the auxiliary lens while the sample position is constant. Therefore, the magnification of the objective lens can be changed with the change of the focal length. As described above, an observation image with a high resolution and a high image quality can be obtained in a wide range of magnifications from a high-field image to a low-magnification.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to FIG. It should be noted that the number of lens steps of the imaging lens system does not matter, but in this embodiment, a case of using a general four-step imaging lens system will be described. As described in the operation, in the objective lens according to the present invention, by switching the polarity of the exciting current of the auxiliary coil, it is possible to observe an image with a high magnification and a low magnification from a low magnification with a fixed sample position. If the low-magnification mode and the high-magnification mode have the same imaging lens system, the objective lens has a small magnification in the low-magnification mode, and a low total magnification can be obtained. Further, in the high magnification mode, the magnification of the objective lens becomes large, and a high total magnification can be obtained. As described above, a high-field image and a high-resolution image can be observed from low magnification to high magnification.

An embodiment of the objective lens according to the present invention will be described with reference to FIGS. FIG. 3 shows the electron optical characteristics of the objective lens when the auxiliary lenses have the same polarity. The focal length becomes longer as the exciting current becomes larger, but the spherical aberration coefficient and the chromatic aberration coefficient do not change so much. As a result, a high quality image can be obtained even if the magnification of the objective lens becomes small and the total magnification becomes low. FIG. 4 shows the electron optical characteristics of the objective lens when the auxiliary lens has the opposite polarity. As the exciting current increases, the focal length decreases, and the spherical aberration coefficient and chromatic aberration coefficient also decrease. Therefore, the magnification of the objective lens is increased, and a high resolution image can be obtained with a high overall magnification.

Next, an embodiment of the present invention will be described with reference to the flowchart of FIG.

The objective coil 15 is previously provided in the computer 17.
And two imaging modes, a low magnification mode (500 times to 200,000 times) in which the auxiliary coil 16 has the same polarity and a high magnification mode (3 times to 600,000 times) in which the auxiliary coil 16 has the opposite polarity are set. .
Excitation current data and magnification data (excitation current value of each imaging lens) of the objective lens and the auxiliary lens in each mode are stored. The reset data is set to 2000 times that in the low magnification mode. When changing the magnification, the desired magnification is input to the computer 20. If the input magnification is less than 500 times, re-enter, and if it is more than 500 times and less than 200,000 times,
In the low magnification mode, the magnification data is output to the excitation power sources 18 to 23 of each lens. Next, when it is more than 600,000 times, it is input again. Then, the change magnification data is output. When changing the magnification further,
Enter the magnification, and if it is 3,000 times or more and 600,000 times or less, change the magnification in the high magnification mode. If it is less than 3,000 times,
The polarity of the auxiliary coil 16 is switched, the low magnification mode is set, and the magnification data is output. When changing the magnification from 500 times to 200,000 times, input the magnification repeatedly in this mode. Further, the observation may be performed from the beginning in the high magnification mode.

[0016]

According to the present invention, it is possible to observe an image with a high resolution and a wide field of view at a fixed sample position of several hundred to several hundred thousand times, and it is possible to remarkably improve the observability and operability.

[Brief description of drawings]

FIG. 1 is an explanatory view of an electron beam optical path of an imaging lens system of a transmission electron microscope of the present invention.

FIG. 2 is an explanatory diagram of an objective lens of the transmission electron microscope of the present invention.

FIG. 3 is an electron optical characteristic diagram of the transmission electron microscope of the present invention.

FIG. 4 is an electron optical characteristic diagram of the transmission electron microscope of the present invention.

FIG. 5 is a control system flowchart of the transmission electron microscope of the present invention.

[Explanation of symbols]

1 ... Sample, 2 ... Objective lens, 3 ... Auxiliary lens, 4 ... Intermediate lens, 5 ... Intermediate lens, 6 ... Projection lens, 7 ... Projection lens, 8 ... Screen, 9 ... Electron beam, 10 to 1
4 ... Crossover, 15 ... Objective coil, 16 ... Auxiliary coil, 17 ... Computer, 18-23 ... Excitation power supply.

Claims (1)

[Claims] 1. An electron microscope having a mechanism for generating an electron beam, an objective lens, and an imaging lens system for forming an image of the electron beam, wherein a gap is provided in a yoke below a pole piece of the objective lens, An electron microscope comprising an auxiliary lens having an exciting coil arranged inside the yoke below the gap.