JPH04192245A - Electron beam device - Google Patents

Abstract

PURPOSE:To prevent magnetic fields from leaking into a sample chamber, and thereby prevent electron beams from being incorrectly deflected by connecting the upper section of the sample chamber to an electron beam column with low magnetic permeable material, and thereby closely joining high magnet permeable material in a ring shape onto the upper and lower sections of the upper wall of the sample chamber at the connecting section. CONSTITUTION:Focusing electron beams are radiated onto a sample 6, and the electron beams are scanned in response to scanning signals to a deflection coil 7. Secondary electrons are generated from the sample 6, and detecting signals synchronized with scanning are supplied to a cathode ray tube, so that the secondary electron image of the sample can thereby be obtained. When outside magnetic fields are applied to a sample chamber 1, the magnetic fields pass through the wall of the sample chamber 1. Because of low magnet permeable material 8, the magnetic fields passing through the upper wall 1a of the sample chamber 1 are introduced at a place close to a column 2 into ring shaped disc plates 9 and 10 which are stretched over the upper and lower sections of the upper wall 1a, for having the magnetic fields passed through the disc plates 9 and 10, and the magnetic fields leak out of the edge section of the chamber 1 via the upper wall 1a again. This thereby permits the magnetic fields at the connecting section of the upper wall 1a to leak extremely little, thereby preventing the electron beams from being incorrectly deflected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electron beam apparatus such as a scanning electron microscope suitable for use in inspecting the manufacturing process of VLSI circuits.

(Prior art) In electron beam length measuring machines, scanning electron microscopes, etc., an electron beam is irradiated onto a sample, secondary electrons and reflected electrons obtained from the electron beam are detected, and an image of the sample surface is created based on this detection signal. I'm trying to get it.

In such a device, since it is necessary to observe the sample in a non-evaporated state, it is necessary to prevent the sample from being charged up by the irradiation beam. Therefore, the electron beam is used at a low accelerating voltage (06~X, 2KV). It is said that On the other hand, the width of lines and patterns to be inspected or observed has become 1 μm or less, and observation magnification must be as high as 50,000 to 100,000 times.

(Problem to be Solved by the Invention) In such a device, the lower the accelerating voltage, the more the influence of the electron beam on the external magnetic field increases.

It is known that the influence of the magnetic field increases in inverse proportion to the square root of the ratio of acceleration voltages when the acceleration voltage is changed. For example, when comparing acceleration voltage of 25KV and IKV,
The influence of the magnetic field is f) 57go, and when the acceleration voltage is IKV, the influence of the magnetic field is five times greater than when the acceleration voltage is 25KV. That is, under the same conditions, 25KV
In order to have the same magnetic field influence as IKV,
Is it necessary to set the external magnetic field to 115?

In other words, if the external magnetic field, which is an external factor, cannot be changed, it is necessary to have a magnetic field shielding ability five times as large.

By the way, the size of wafers to be inspected for VLSI circuits is increasing from 6' to 8'. In order to observe the entire surface of an 8" workpiece horizontally or tilted at a high angle, a sample chamber of about 50 cm cube is required. In this case, the force exerted by the atmosphere on the top, bottom and four sides of the sample chamber is: Since it is 1 kg per IC, it is approximately 2500 kg for 50 (7) squares.
g. Therefore, in order to minimize the mechanical strain (warpage) on each surface of the sample chamber, it is necessary to select a material with high mechanical strength for each surface. In addition to mechanical strength, the material for the sample chamber wall is also required to have a high magnetic shielding effect and to be inexpensive.

From the above viewpoint, rolled steel, forged steel, or the like is selected and used for the sample chamber. Even when such a steel material is used, the plate thickness must be approximately 5 cm in order to ensure mechanical strength between vacuum and atmosphere. That is, the size of the wall material is 50 cm x 50 cm x 5 cm. Steel materials that have been processed to this size are subject to stress distortion due to processing and magnetization due to electromagnetic chucking, so they do not have a sufficient magnetic shielding effect. In order to remove incorrect magnetization or increase the magnetic shielding effect, it is also possible to perform magnetic heat treatment to heat the steel material to a high temperature above the Curie point. However, if this large, thick steel material is heat treated, the machining dimensions may be distorted, making it impossible to simply attach the column. Furthermore, heating steel materials requires a large heating furnace and sieve, and for this reason, it is not possible to heat-treat the wall materials, but it is necessary to expect a magnetic shielding effect from the sample chamber walls. I can't.

FIG. 2 shows a cross section of a sample chamber 1 made of steel as described above. When an external magnetic field B is applied to this sample chamber 1, the magnetic field passes through the walls of the sample chamber 1, which have high magnetic permeability. Near the center of the ceiling of the sample chamber is a circular hole H into which the column C section is inserted. When we measured the magnetic field at each part under these conditions, we found that the magnetic field was higher at the edges circled in the figure. In other words, the magnetic field passing through the sample chamber wall leaks to the outside from the edge portion. This leakage magnetic field has a large effect on the electron beam between the objective lens and the sample.

The present invention has been made in view of these points, and its purpose is to provide an electron beam device that can prevent magnetic field leakage into a sample chamber and eliminate incorrect deflection of an electron beam irradiated onto a sample. The aim is to realize this.

(Means for Solving the Problems) An electron beam device based on the present invention includes a focusing means that is arranged in an electron beam column and focuses an electron beam on a sample, and a focusing means that focuses an electron beam on a sample in a sample chamber. In an electron beam apparatus equipped with a scanning means for scanning the sample chamber, the upper part of the sample chamber and the column are connected with a low magnetic permeability member, and a ring-shaped high permeability member is installed above and below the upper wall of the sample chamber at the connecting part. It is characterized by having magnetic members in close contact with each other.

(Function) In the electron beam device based on the present invention, the upper part of the sample chamber and the column are connected with a low magnetic permeability member, and ring-shaped high magnetic permeability members are installed above and below the upper wall of the sample chamber at the connection part. They are placed in close contact with each other, and the magnetic field passing through the earthen wall of the sample chamber is passed through this ring-shaped high permeability member, thereby preventing leakage of the magnetic field into the sample chamber.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 shows one embodiment of the present invention, and 2 is an electron beam column attached to the sample chamber 1. In FIG. An electron gun 3 is provided above the column 2, and the electron beam generated from the electron gun 3 is passed through a focusing lens 4. The objective lens 5 narrowly focuses the light onto the sample 6 in the sample chamber 1 . The electron beam irradiation position of the soil sample 6 is changed according to a signal supplied to the deflection coil 7. The deflection coil 7 includes:
A scanning signal is supplied from a scanning signal generation circuit (not shown). 2 generated by irradiating the sample 6 with the electron beam
The secondary electrons are detected by a secondary electron detector (not shown). The signal detected by the detector is supplied to a cathode ray tube, which is supplied with a scanning signal.

A low magnetic permeability member 8 made of brass or the like is provided at the connection portion of the sample chamber 1 with the column 2 to shield the column 2 from the magnetic field path. At the top and bottom of the upper wall 1a of the sample chamber 1 near the column 2, ring-shaped disks 9 and 10 made of a high magnetic permeability material such as permalloy or μ metal are installed on the wall portions of the sample chamber, respectively. It is attached tightly.

Further, a shield plate 11 made of a high magnetic permeability material such as permalloy is provided below the objective lens 5. The operation of the electron beam device having such a configuration is as follows.

As described above, the sample 6 is irradiated with a finely focused electron beam, and this electron beam is scanned in accordance with a scanning signal sent to the deflection coil 7. For example, secondary electrons generated from the sample 6 in response to this scanning are detected, and a secondary electron image of the sample is obtained by supplying this detection signal to a cathode ray tube synchronized with the scanning. Now, when an external magnetic field is applied to the sample chamber 1, the magnetic field passes through the walls of the sample chamber 1. The magnetic field passing through the upper wall 1a of the sample chamber 1 is generated by a link-shaped disk 9.10 attached above and below the upper wall 1a at a position close to the column 2.
The liquid is guided inside, passes through this disk, enters the earthen wall 1a again, and leaks out from the edge of the sample chamber to the outside of the sample chamber.

Therefore, the magnetic field leaking from the column connection portion of the upper wall 1a of the sample chamber is extremely reduced, and the electron beam is prevented from being improperly deflected by this leaking magnetic field. Note that even if a slight magnetic field leaks at the connection with the column 2 of the sample chamber, this leaked magnetic field will enter the shield plate 11 provided at the bottom of the objective lens 5 and will not affect the path of the electron beam. Therefore, the influence of the leakage magnetic field on the electron beam can be more completely prevented.

Although the present invention has been described in detail above, the present invention is not limited to this embodiment. For example, the shield plate 11 may be omitted. Furthermore, the present invention can be applied not only to devices such as scanning electron microscopes, but also to electron beam lithography devices and the like.

(Effects of the Invention) As explained above, in the electron beam device based on the present invention, the upper part of the sample chamber and the column are connected by a low magnetic permeability member, and at the top and bottom of the upper wall of the sample chamber at the connection part, A ring-shaped high magnetic permeability member is placed in close contact with the earthen wall of the sample chamber, and the magnetic field passing through the earthen wall of the sample chamber is passed through this link-shaped high magnetic permeability member to prevent the leakage of the magnetic field into the sample chamber. This can prevent unauthorized deflection due to leakage magnetic fields.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an electron beam apparatus based on the present invention, and FIG. 2 is a diagram showing a leakage magnetic field from a sample chamber. 1...Sample chamber 2...Column 3/electron gun
4...Focusing lens 5...Objective lens 6
···sample

Claims (1)

[Claims] In an electron beam apparatus that is disposed in an electron beam column and includes a focusing means for focusing an electron beam on a sample, and a scanning means for two-dimensionally scanning the electron beam over a sample in the sample chamber, the sample chamber An electron beam device characterized in that the upper part of the column and the column are connected by a low magnetic permeability member, and ring-shaped high magnetic permeability members are closely attached to the top and bottom of the upper wall of the sample chamber at the connecting portion.