Objective with lenses made of a crystalline material

US6842284B2 · kind B2 · utility

Assignee

• Carl Zeiss SMT GmbH · DE

Inventors

• Michael Gerhard · Aalen, DE
• Daniel Krähmer · Aalen, DE

Key dates

• Filing date: Dec 17, 2003
• Grant date: Jan 11, 2005
• Expiry date: Dec 17, 2023

Classification

• Technology area (CPC G): Physics
• CPC primary: G03F7/70966
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

An objective (1), in particular for a microlithography projection apparatus, has lenses or lens parts falling into at least two groups. The first group (3) is made of a first crystalline material and the second group (5) is made of a second crystalline material. In the first group (3), an outermost aperture ray (15) is subject to a first optical path difference between two mutually orthogonal states of linear polarization; and the same outermost aperture ray is subject to a second optical path difference in the second group (5). The two different crystalline materials are selected so that the first and second optical path difference approximately compensate each other. A suitable selection consists of calcium fluoride for the first and barium fluoride for the second crystalline material.