JPH09147774A - Objective lens for scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the inclination angle of a sample by using an objective lens with conical magnetic poles, and machining into a planar configuration the outer surface of at least that magnetic pole which is opposite to the inclined sample. SOLUTION: An exciting coil 3 supported by a coil frame 2 is provided inside a magnetic pole 6, and a focusing magnetic field for an electron beam is formed by passing current through the coil 3. The electron beam is focused by the magnetic field and applied to a sample 4, and secondary electrons produced by the application are detected by a secondary electron detector 5 involving a photomultiplier. The portion 7 of the objective-lens conical magnetic pole 6 which faces the inclined sample 4 is machined into a planar configuration. Because of this machining, the sample 4 is kept from colliding with the magnetic pole 6 and can be inclined further. Also, the distance between the sample 4 and the objective lens can be reduced, making it possible to observe a secondary-electron image at higher resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope objective lens capable of increasing the tilt angle of a sample.

[0002]

2. Description of the Related Art In order to observe a semiconductor wafer or the like with a scanning electron microscope, an objective lens has been developed in which a sample is formed in a conical shape so that it can be greatly tilted. FIG. 1 shows a conventional single pole type conical objective lens. In the figure, reference numeral 1 denotes a conical objective lens magnetic pole on the outer side, which is made of a magnetic material such as permalloy.

Inside the magnetic pole 1, an exciting coil 3 supported by a coil frame 2 is provided.
A focusing magnetic field of the electron beam is formed by applying an electric current to the electron beam. The electron beam is focused by this magnetic field and irradiated on the sample 4. Secondary electrons generated by irradiating the sample 4 with the electron beam are detected by the secondary electron detector 5 including a photomultiplier tube.

[0004]

In the above-mentioned objective lens, the magnetic pole 1 is formed in a conical shape because the sample 4 needs to be tilted greatly. The tilt angle θ of the sample needs to be as large as possible, but if the sample 4 is tilted too much, it collides with the magnetic pole 1 of the objective lens, and therefore the tilt angle θ is naturally limited.

The present invention has been made in view of the above points, and an object thereof is to realize an objective lens for a scanning electron microscope capable of achieving a larger tilt angle of a sample.

[0006]

An objective lens for a scanning electron microscope according to the invention of claim 1 is an objective lens having a conical magnetic pole, wherein at least the outer surface of the magnetic pole facing the tilted sample is provided. It is characterized by being made into a flat surface.

According to the first aspect of the present invention, the outer surface of the magnetic pole facing the tilted sample is ground into a flat state to increase the tilt angle of the sample. The objective lens for a scanning electron microscope based on the invention of claim 2 is characterized in that, in addition to the invention of claim 1, the outer surface of the conical magnetic pole is made axially symmetrical and in a planar state.

According to the second aspect of the present invention, the outer surface of the magnetic pole facing the tilted sample is ground into a flat state to increase the tilt angle of the sample and to form a uniform axially symmetrical objective lens magnetic field.

An objective lens for a scanning electron microscope according to a third aspect of the present invention is characterized in that the central axis of the cone outside the magnetic pole and the optical axis of the electron beam are decentered. According to the third aspect of the invention, the central axis of the outer cone of the magnetic pole and the optical axis of the electron beam are eccentric to increase the tilt angle of the sample.

An objective lens for a scanning electron microscope according to the invention of claim 4 is characterized in that it has a polygonal pyramidal magnetic pole. In the invention of claim 4, the magnetic pole is formed in a polygonal pyramid shape, and the inclination angle of the sample is increased.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 shows an example of the present invention, and the same reference numerals as those in the conventional apparatus of FIG. 1 indicate the same components. In this embodiment, reference numeral 6 denotes a conical objective lens magnetic pole on the outer side, which is formed of a magnetic material such as permalloy.

An exciting coil 3 supported by a coil frame 2 is provided inside the magnetic pole 6, and a current is passed through the exciting coil 3 to form a focused magnetic field of an electron beam. The electron beam is focused by this magnetic field,
The sample 4 is irradiated. Secondary electrons generated by irradiating the sample 4 with the electron beam are detected by the secondary electron detector 5 including a photomultiplier tube.

A portion 7 of the magnetic pole 6 of the conical objective lens facing the tilted sample 4 is cut off in a flat shape.
An external view of the magnetic pole 6 is shown in FIG. In this planar cutting, for example, the conical magnetic pole 6 having a wall thickness of 5 mm is processed by a lathe, and the wall thickness of the plane portion 7 is set to about 0.2 mm to 0.5 mm at the minimum portion. .

In this way, the magnetic pole 6 of the conical objective lens
Since the portion 7 facing the inclined sample 4 is shaved off in a plane shape, the sample 4 can be largely inclined without colliding with the magnetic pole 6. Further, when the inclination angle is the same as the conventional one, the distance (working distance) between the sample 4 and the objective lens can be shortened, and the aberration of the objective lens can be reduced to observe a secondary electron image with higher resolution. It will be possible.

In the above embodiment, when considering the axial symmetry of the magnetic field of the objective lens, the magnetic pole 6 itself may be formed to be axially symmetric, and for that purpose, the flat portion 7 is formed.
The surface of the magnetic pole 6 which is axisymmetric with respect to the above may be planar. In this case, the surface of the magnetic pole 6 has two flat portions. The plane portion is not limited to these two places, but may be four or more places as long as it is axisymmetric, and the magnetic pole itself may be formed in a polygonal pyramid shape. By forming the magnetic pole itself in the shape of a polygonal pyramid, the inclination angle of the sample can be increased. However, in this case, it is necessary to dispose the polygonal pyramid surface so as to face the sample surface.

FIG. 4 shows another embodiment of the present invention. FIG. 4 is an external view of the magnetic pole 8 in this embodiment, and the magnetic pole 8 has a conical outer shape. The central axis O1 of the outer cone and the optical axis O2 of the electron beam are eccentric, and the inner surface of the magnetic pole 8 has an optical axis O2 of the electron beam.
And is axisymmetric.

Therefore, the magnetic pole 8 has a thick portion 9 and a thin portion 10. Although not shown, the exciting coil of the objective lens is provided in axial symmetry with respect to the electron beam optical axis O2. Sample 4 is thin part 10
Since the sample 4 is tilted so as to face, the tilt angle of the sample 4 can be increased.

Although the embodiment of the present invention has been described above by taking the single-pole type objective lens as an example, the present invention has, for example, two magnetic poles, an inner magnetic pole (upper magnetic pole) and an outer magnetic pole (lower magnetic pole). It can also be applied to an objective lens. However, in an objective lens having two magnetic poles, it should be noted that the magnetic pole may be magnetically saturated when the outer magnetic pole is thinned.

[0019]

As described above, according to the first aspect of the invention, since the outer surface of the magnetic pole facing the tilted sample is ground to be in a flat state, the tilt angle of the sample can be increased.

According to the second aspect of the present invention, since the outer surface of the magnetic pole facing the tilted sample is ground to be in a flat state, the tilt angle of the sample is increased and an axially symmetrical uniform objective lens magnetic field is formed. You can

According to the third aspect of the invention, since the central axis of the cone outside the magnetic pole and the optical axis of the electron beam are decentered, the tilt angle of the sample can be increased. In the invention of claim 4, since the magnetic pole is formed in a polygonal pyramid shape, the inclination angle of the sample can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional objective lens.

FIG. 2 shows an objective lens according to the present invention.

3 is an external view of a magnetic pole used in the objective lens of FIG.

FIG. 4 is an external view of a magnetic pole according to another embodiment of the present invention.

[Explanation of symbols]

 1, 6, 8 Magnetic pole 2 Coil frame 3 Coil 4 Sample 5 Secondary electron detector 7 Planar processing part

Claims (4)

[Claims] 1. An objective lens for a scanning electron microscope, which is an objective lens having a conical magnetic pole, in which at least the outer surface of the magnetic pole facing the tilted sample is ground to be in a flat state. 2. The objective lens for a scanning electron microscope according to claim 1, wherein the outer surface of the conical magnetic pole is axially symmetrical and is in a planar state. 3. An objective lens for a scanning electron microscope, which is an objective lens having a conical magnetic pole, wherein a central axis of a cone outside the magnetic pole and an optical axis of an electron beam are decentered. 4. An objective lens for a scanning electron microscope having a polygonal pyramidal magnetic pole.