US 7,420,164 B2Granted

Objective lens, electron beam system and method of inspecting defect

AssigneeEbara Corporation

InventorsMamoru Nakasuji, Tohru Satake, Hirosi Sobukawa, Takeshi Murakami, Kenji Watanabe, Nobuharu Noji

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Abstract

An electron beam system or a method for manufacturing a device using the electron beam system in which an electron beam can be irradiated at a high current density and a ratio of transmittance of a secondary electron beam of an image projecting optical system can be improved and which can be compact in size. The surface of the sample S is divided into plural stripe regions which in turn are divided into rectangle-shaped main fields. The main field is further divided into plural square-shaped subfields. The irradiation with the electron beams and the formation of a two-dimensional image are repeated in a unit of the subfields. A magnetic gap formed by the inner and outer magnetic poles of the objective lens is formed on the side of the sample, and an outer side surface and an inner side surface of each of the inner magnetic pole and the outer magnetic pole, respectively, forming the magnetic gap have each part of a conical shape with a convex having an angle of 45° or greater with respect to the optical axis.

Claims1

Dependent claims

A method for evaluating a pattern on a sample plane with plural beams, comprising the steps of:

(a) forming multiple beams by irradiating plural apertures with an electron beam emitted from an electron gun having a cathode;
(b) forming a cross-over of a beam passed through the plural apertures on an aperture having a dimension substantially larger than a dimension of the cross-over or at a position in the vicinity of the aperture;
(c) focusing a magnified cross-over by a condenser lens at a Z-coordinate position in the vicinity of a principal plane of an objective lens;
(d) forming a reduced image of an image of the multiple beam on the sample plane with at least a reducing lens and an objective lens;
(e) scanning the sample with the multiple-beams by using at least a two-stage deflector disposed between the reducing lens and the objective lens;
(f) accelerating and focussing a secondary electron group emitted from the scanning point on the sample with an objective lens;
(g) deflecting the secondary electron group passed through the objective lens with an electromagnetic deflector and sending it to a secondary optical system;
(h) magnifying a mutual distance of the secondary electron group by the secondary optical system and leading the secondary electron group to plural secondary electron detectors;
and
(i) evaluating a pattern on the sample plane from a signal detected with the detector;
wherein a cross-over to be formed by the electron gun for irradiating the plural apertures has a negative spherical aberration.

8 more elements

Dependencies are inferred from the claim text.