Charged-particle-beam microlithography apparatus and methods exhibiting reduced astigmatisms and linear distortion
AssigneeNikon Corporation
InventorMamoru Nakasuji
Life of this patent
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Abstract
Apparatus and methods are disclosed for making accurate yet simple corrections of astigmatism that would otherwise degrade edge resolution and astigmatism, and cause linear distortion of, a reticle image. Astigmatism that would otherwise degrade edge resolution of the reticle image is corrected by a stigmator lens (including a respective set of stigmator coils) having a principal plane coincident with a plane of a contrast aperture. Linear distortion of the reticle image is corrected by a separate stigmator lens (including a respective pair of stigmator coils) having a principal plane coincident with the principal plane of a projection lens.
Claims20
A charged-particle-beam microlithography apparatus, comprising:
- (a) an illumination-optical system situated and configured relative to a charged-particle-beam source and a pattern-defining reticle so as to direct a charged-particle illumination beam from the source to illuminate a region of the pattern defined by the reticle;
- (b) a projection-optical system situated on an optical axis extending between the reticle and a sensitive substrate, the projection optical system being configured to receive an imaging beam, generated by passage of a portion of the illumination beam through the illuminated region of the reticle, and cause the imaging beam to form an image of the illuminated region on a corresponding region of the sensitive substrate;
- and
- (c) the projection-optical system comprising a stigmator lens comprising at least two stigmator coils each generating, when energized, a respective magnetic-field strength and each exhibiting a respective convergence or divergence of the imaging beam, the stigmator lens having a principal plane at a position on the optical axis, the position being a function of a ratio of the respective magnetic-field strengths and respective degrees of convergence or divergence exhibited by the stigmator coils.
A charged-particle beam microlithography apparatus, comprising:
- (a) an illumination-optical system situated and configured relative to a charged-particle-beam source and a pattern-defining reticle so as to direct a charged particle illumination beam from the source to illuminate a region of the pattern defined by the reticle;
- (b) a projection-optical system situated on an optical axis extending between the reticle and a sensitive substrate, the projection-optical system being configured to receive an imaging beam, generated by passage of a portion of the illumination beam through the illuminated region of the reticle, and cause the imaging beam to form an image of the illuminated region on a corresponding region of the sensitive substrate;
- and
- (c) the projection-optical system comprising first and second projection lenses, a contrast aperture situated and configured to prevent charged particles scattered by the reticle from propagating toward the sensitive substrate, a first stigmator lens, and a second stigmator lens, wherein the first stigmator lens has a principal plane that is coincident with a principal plane of either the first or second projection lens, and the second stigmator lens has a principal plane that is coincident with a plane of the contrast aperture.
In a process for performing microlithography of a reticle pattern onto a sensitive substrate using a charged particle beam that passes, after passing through a region of a reticle illuminated by the charged particle beam, through a projection-optical system to the sensitive substrate, a method for reducing astigmatisms that otherwise would cause linear distortion and degradation of edge resolution of an image of the reticle pattern as projected onto the sensitive substrate by the projection-optical system, the method comprising:
- (a) providing, in the projection-optical system, a stigmator lens comprising at least two stigmator coils and having a principal plane located at a position on an optical axis of the projection-optical system;
- and
- (b) energizing the stigmator coils to cause each stigmator coil to produce a respective magnetic-field strength and a respective convergence or divergence of the charged particle beam, wherein the position of the principal plane of the stigmator lens is a function of a ratio of the respective-field strengths and respective degrees of convergence or divergence exhibited by the stigmator coils.
In a process for performing microlithography of a reticle pattern onto a sensitive substrate using a charged particle beam that passes, after passing through a region of a reticle illuminated by the charged particle beam, through a projection-optical system to the sensitive substrate, a method for reducing astigmatisms that otherwise would cause linear distortion and degradation of edge resolution of an image of the reticle pattern as projected onto the sensitive substrate by the projection-optical system, the method comprising:
- (a) providing, in the projection-optical system, first and second projection lenses, a contrast aperture, and first and second stigmator lenses;
- (b) situating the contrast aperture to prevent charged particle scattered by the reticle from propagating toward the sensitive substrate;
- and
- (c) while passing the charged particle beam through the projection-optical system so as to transfer the reticle pattern to the substrate, causing a principal plane of the first stigmator lens to be coincident with a principal plane of either the first or second projection lens, and causing a principal plane of the second stigmator lens to be coincident with a plane of the contrast aperture, wherein linear distortion is corrected by the first stigmator lens and degradation of edge resolution is corrected by the second stigmator lens.
Dependencies are inferred from the claim text.