JPS63225465A - Focusing lens in scanning electron microscope or the like - Google Patents

Abstract

PURPOSE:To obtain a function equivalent to multi-stage configuration of focusing lenses with small bore diameters by fixing a plurality of annular magnetic material pieces, which have taper parts on their inner surfaces, inside a yoke so as to form lens gaps and configuring a vacuum shield pipe, which has a conical outer surface along the taper parts, inside the magnetic material pieces. CONSTITUTION:A plurality of annular magnetic material pieces 3 to 7 which have taper parts on their respective inner surfaces are surrounded with a lens yoke 1 and configured coaxially. These annular magnetic material pieces 3 to 7 are fixed with non-magnetic material spacers 8 so that magnetic lens gaps A to F are formed between adjacent annular magnetic material pieces themselves or between the yoke terminal parts 1a and 1b. A vacuum shield pipe 9 having a conical outer surface along the taper parts on the inner surfaces of the respective annular magnetic material pieces 3 to 7 is configured inside the magnetic material pieces 3 to 7, and a single excitation coil 2 is assembled in the lens yoke 1. Thus, a focusing lens which functions equivalently to multi- stage configuration of a focusing lens having a small magnetic gap and a small bore diameter can be obtained easily in manufacture and profitably in cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focusing lens for a scanning electron microscope or the like for continuously varying the diameter of an electron beam irradiated onto a sample.

[Prior Art] In a scanning electron microscope, it is possible to continuously change the diameter of an electron beam irradiated onto a sample or the irradiation current while keeping the diameter of an objective aperture fixed.

Therefore, multiple stages of focusing lenses are used as focusing lenses, and the opening angle of the electron beam incident on the objective aperture is controlled by changing the excitation current of each stage of the focusing lens. When the lens is changed, the focal point of the focusing lens system moves, so the focusing of the objective lens and the adjustment of the stigmator must be adjusted each time. Therefore, it has become necessary to ensure that the focusing point hardly moves even if the excitation current of the focusing lens at each stage is changed. In order to meet this requirement without narrowing the variable range of the diameter of the electron beam, the focusing lens should be provided in multiple stages (in practice, two or more stages), and the lens strength of each stage of the focusing lens should be increased as it approaches the objective lens. must be made stronger. For this purpose, we manufacture a large number of focusing lenses with different magnetic pole gaps and bore diameters, and attach these focusing lenses to the upper stage of the objective lens so that the closer to the objective lens the focusing lenses with smaller magnetic pole gaps and smaller bore diameters are placed. It is possible to do so.

[Problems to be Solved by the Invention] However, it is not easy to manufacture a large number of focusing lenses with different bore diameters and mount them on each lens, and it also causes a large increase in cost.

The present invention solves these conventional drawbacks and provides a focusing lens for scanning electron microscopes, etc., which functions substantially the same as the above-mentioned multi-stage focusing lens arrangement, is easy to manufacture, and is advantageous in terms of cost. It is an object.

[Means for Solving the Problems] In order to achieve such an object, the focusing lens of the scanning electron microscope according to the present invention includes a plurality of annular magnetic pieces each having a tapered inner surface surrounded by a lens yoke. each of the annular magnetic pieces is fixed with a non-magnetic spacer so as to have a magnetic field lens gap between adjacent annular magnetic pieces or yoke ends; A vacuum shield pipe having a conical outer surface along the taper of the inner surface of each annular magnetic material piece is disposed inside the magnetic material piece, and a single excitation coil is assembled to the lens yoke. It is said that

[Example code] Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

The drawings are diagrams for showing one embodiment of the present invention, and in the drawings 1
is the yoke of Tokyo Lens L. 3, 4°, 5.6.7 are annular magnetic pieces fixed to the circumferential shaft, and the inner surfaces (surfaces on the optical axis Z side) of these magnetic pieces are tapered. The magnetic pieces 3, 4, 5, and 6°7 are fixed so as to be surrounded by the yoke by a spacer 8, and are fixed on the lens side (lower side) of the smaller diameter magnetic pieces. The spacer 8 is made of a non-magnetic material, and by being fixed by the spacer 8, the magnetic piece 3 forms a 1-nons gap A between the adjacent yoke end 1a, and the magnetic piece 7 A lens gap F is formed between the lens and the yoke end portion 1b. Similarly, there is also a lens gap 8 between adjacent pieces of magnetic material. C,
D and E are formed. Each of the magnetic pieces 3 to 7 is fixed by the spacer 8 so that the gap becomes narrower from the lens gap A to the gap F. Furthermore, a vacuum shield pipe 9 having a conical outer surface that follows the taper of the inner surface of each annular magnetic material piece is arranged inside each of the annular magnetic material pieces 3 to 7. This vacuum shield pipe is made of non-magnetic material. 2 is an excitation coil, and 10.11 is an O-ring for vacuum sealing.

In such a focusing lens, when an excitation current is passed through the excitation coil 2, each gap A, B, C, D, E.

A lens magnetic field is formed at F. The gaps Δ to F are narrower as they get closer to the objective lens, and the diameters of the annular magnetic pieces 3 to 7 are also smaller, so the bore diameter of each lens formed in the gaps A to F is also smaller than the objective lens. It gets smaller towards the lens. Therefore, the focusing lens of this embodiment works in the same way as a multi-stage arrangement of focusing lenses with smaller magnetic pole gaps and bore diameters as they approach the objective lens, but it is possible to use a plurality of annular magnetic pieces as described above. , by carefully arranging these and fixing them to the yoke, and by inserting and fixing the vacuum shield pipe, it can be easily manufactured, so it is easy to manufacture and is cost-effective for focusing devices such as scanning electron microscopes. Lenses are provided.

Note that the above-described embodiment is only one embodiment of the present invention, and the present invention can be modified and implemented.

For example, in the embodiment described above, the lens gaps are made narrower as they approach the objective lens side, but each lens gap may be made to have the same width.

Further, in the above-mentioned embodiment, six lens gaps A to F were provided, but it is better if there are three or more.

Further, the portion of the spacer 8 outside the coil 2 can be omitted.

[Effect of the invention] As is clear from the above explanation, the present invention has the following effects:
A plurality of annular magnetic pieces each having a tapered inner surface are fixed inside the yoke by spacers so as to form a lens gap, and a vacuum shield pipe having a conical outer surface along the taper is placed inside the magnetic pieces. This makes it possible to create a focusing lens for scanning electron microscopes that is easy to manufacture and cost-effective, and has the same function as a multi-stage arrangement of focusing lenses with smaller magnetic pole gaps and bore diameters as they approach the objective lens. can be provided.

[Brief explanation of the drawing]

The drawings are intended to illustrate one embodiment of the invention. 1: Yoke 2: Excitation coil 3.4, 5.6, 7: 'Ej A-shaped magnetic material piece 8 varnish spacer A, B, C, D, E, F: Lens gap 9: Vacuum shield pipe 10.11: 0 ring

Claims (1)

[Claims] A plurality of annular magnetic pieces each having a tapered inner surface are surrounded by a lens yoke and arranged around the circumferential axis, and each of the annular magnetic pieces has an adjacent annular magnetic piece or a yoke end. A vacuum shield pipe, which is fixed with a non-magnetic spacer so as to have a magnetic field lens gap therebetween, and has a conical outer surface that follows the taper of the inner surface of each annular magnetic material piece is arranged inside the magnetic material piece. A focusing lens for a scanning electron microscope, etc., characterized in that a single excitation coil is assembled to the lens yoke.