RU2572806C1 - Magnetic immersion lens for emission electron microscope - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: magnetic immersion lens for emission electron microscope comprises a housing with upper and lower pole tips made of magnetically conducting material with a longitudinal channel on the optical axis of the system, in the gap between an object holder with an object is placed. The upper pole tip is an anode, which is insulated from the housing and is made of two parts with a gap in between in the form of a slit in a plane perpendicular to the optical axis. The lower pole tip can move axially. The lower part of the upper pole tip is attached to the housing through an insulator. The upper pole tip is placed in a shielding electrode, which is made of nonmagnetic material in the form of a truncated cone, coaxial to the optical axis, mounted on the housing. End surfaces of the lower part of the anode and the cone are bounded by a single plane.

EFFECT: high electrooptical magnification while maintaining the optical base of the microscope, improved quality of the emission image and wider range of analysed objects.

1 dwg

Description

The invention relates to electronic lenses, and more specifically to immersion magnetic lenses, and can be used in the formation of the emission image of the investigated object on the luminescent screen of the emission electron microscope.

The immersion magnetic lens is designed to form a high-quality emission picture with a large electron-optical magnification when studying the surface topology, for example, thermal cathodes.

Known immersion magnetic lens for emission electron microscope [1]. The lens contains a sealed housing with upper and lower pole tips made of magnetically conductive material, an object holder and an excitation coil.

The main disadvantage of such a lens is the presence of a gap in the magnetic circuit to accommodate an insulator in it, which fastens the upper pole tip, which leads to a large loss of magnetic field strength in the object placement gap and does not allow focusing the emission image quite clearly. Therefore, it does not provide electron-optical magnification when observing emission objects with small sizes of emission zones.

Known immersion magnetic lens emission electron microscope - prototype [2]. The lens contains a sealed housing with upper and lower pole lugs of magnetically conductive material, an object holder with an object. The upper pole tip is an anode and is made of two parts with a gap between them in the form of a gap in a plane perpendicular to the optical axis. Two parts of the upper pole piece are interconnected by a ring of non-magnetic material. The lower pole piece is axially movable. The increase in electron-optical magnification is achieved due to the appearance on the optical axis of an additional magnetic lens formed in the gap.

The disadvantages of this lens are:

- insufficient electron-optical magnification and image quality in the study of products with small dimensions of the emitting surface;

- the possibility of electrical breakdown between the grounded object of study and the lower part of the upper pole piece when examining objects having pointed protrusions.

The technical result of the invention is to increase the electron-optical magnification while maintaining the optical base of the microscope, improving the quality of the emission image and expanding the range of objects under study.

The technical result is achieved by the fact that the immersion magnetic objective of the emission electron microscope comprises a housing with upper and lower pole tips of magnetically conductive material with a longitudinal channel along the optical axis of the system, in the gap between which an object holder with an object is placed. The upper pole tip is an anode, isolated from the housing and made of two parts with a gap between them in the form of a gap in a plane perpendicular to the optical axis. The lower pole piece is axially movable. The lower part of the upper tip is fixed to the housing through an insulator. The upper tip is placed in a shielding electrode, which is made of non-magnetic material in the form of a truncated cone, coaxial to the optical axis, mounted on the housing. Moreover, the end surfaces of the lower part of the anode and cone are bounded by a single plane.

The lower part of the upper tip is fixed to the housing through an insulator, which allows to supply electric potentials of different magnitude to each part of the anode. In the case where a high potential is applied to the upper part of the anode (upper part of the upper tip), and lower potential to the lower part of the anode (lower part of the upper tip), a dissipating electrostatic lens is formed in the lens slit, increasing the emission image on the microscope screen. And if the potentials are applied on the contrary, a collecting electrostatic lens is formed, which reduces the emission image on the microscope screen.

To improve the quality of the emission image by reducing the ion bombardment of the test object, an electric potential lower than the potential on the lower part of the anode is supplied to the upper part of the anode.

The upper tip is placed in a shielding electrode made of non-magnetic material in the form of a truncated cone, coaxial to the optical axis, and mounted on the housing. The screening electrode, like the object, is under the ground potential. This allows you to eliminate the electrical breakdown that may occur during the study of objects with tip parts.

The end surfaces of the lower part of the upper tip and the cone are limited by a single plane, which ensures optimal operation of the anode, that is, the object can be approached to the anode at a distance at which electrical breakdown does not occur.

The immersion magnetic objective of the emission electron microscope is illustrated in the drawing.

In FIG. 1 shows an immersion magnetic objective of an emission electron microscope, where:

flange 1;

Pavilion 2;

top pole piece 3;

bottom pole piece 4;

object holder 5;

object 6;

the upper part of the upper pole piece 7;

the lower part of the upper pole piece 8;

insulator 9;

insulator 10;

shielding electrode 11,

focusing coil 12,

bellows actuator 13,

s is the width of the slit,

d is the width of the gap,

Example.

An immersion magnetic objective of an emission electron microscope for studying thermal cathodes comprises a housing 2 mounted on a flange 1 and made of steel 10895 (ARMKO), which is a magnetic circuit. Coaxial between themselves the upper 3 and lower 4 pole pieces made of steel 10895 (ARMCO), with a longitudinal channel along the optical axis of the system. In the gap between the pole pieces 3 and 4, with a width d of about 10 mm, thermal cathodes 6 are fixed on the object holder 5.

The lower pole piece 4 can be moved axially using a bellows actuator 13.

The upper pole piece 3 is divided into two parts 7 and 8 by a slit of width s equal to 2 mm. The upper part 7 of the upper pole piece 3 is attached to the housing 2 by an insulator 9 made of 22XC ceramics, and the lower part 8 of the upper pole piece 3 is attached to the housing 2 by an insulator 10 made of 22XC. The upper tip 3 is placed in the shielding electrode 11, made of stainless steel X18H10T in the form of a truncated cone, coaxial to the optical axis, which is mounted on the housing 2. The end surfaces of the lower part of the anode 8 and the cone of the electrode 11 are bounded by a single plane. The focusing coil 12 is designed to create a magnetic field in the gap and gap.

The lens works as follows.

Flange 1 is attached to the camera emission electron microscope. The thermal cathode 6 is fixed on the object holder 5 and placed in the housing 2. The microscope chamber is pumped out to high vacuum (approximately 1 · 10 ^-5 Pa). Thermal cathodes 6 are heated to obtain thermal emission. A high potential (approximately 20 KV) is applied to the upper part of the anode (upper part 7 of the upper tip 3) and a low potential (approximately 15 KV) is supplied to the lower part of the anode (lower part 8 of the upper tip 3). The focusing coil 12 is turned on and an unfocused emission image is obtained on the microscope screen. By changing the width of the gap d, moving the lower tip 4 with a bellows drive 13, increase the clarity of the image. The gap width d can be from 5 mm to 25 mm, depending on the dimensions of the object under study.

Further, in order to improve the quality of the emission image by reducing the ion bombardment of the test object, an electric potential of 20 kV is left on the upper part 7 of the upper tip 3, and 30 kV is supplied to the lower part 8 of the upper tip 3. Due to the potential difference, the bulk of the ions of the microscope moves toward the screen and only a small part of the ions is directed toward the object.

Using the proposed device in an experimental sample made it possible to obtain a magnetic lens with a 2-fold increased electron-optical magnification while maintaining the optical base of the microscope. With the optical base of the microscope L = 350 mm, the electron-optical magnification with the prototype lens was up to 300 times, and with our sample it was 600 times.

The magnetic lens allows you to explore objects with tip parts.

Ion bombardment in a microscope using the proposed lens decreased by 30 times, which allowed to obtain a better image.

Information sources

1. USSR author's certificate No. 241560, M.Kl. H01J 37/10.

2. Patent RU No. 2002329, IPC H01J 3/20 - prototype.

Claims (1)

An immersion magnetic objective of an emission electron microscope, comprising a housing with upper and lower pole tips of magnetic conductive material with a longitudinal channel along the optical axis of the system, in the gap between which there is an object holder with an object, the upper pole tip, which is an anode isolated from the housing, is made of two parts with a gap between them in the form of a gap in a plane perpendicular to the optical axis, the lower pole tip is made with the possibility of axial movement, different t We note that the lower part of the upper tip is fixed to the housing through an insulator, the upper tip is placed in a shielding electrode made of non-magnetic material in the form of a truncated cone, a coaxial optical axis, mounted on the housing, and the end surfaces of the lower part of the anode and cone are bounded by a single plane.