Transparent-block encoder head with isotropic wedged elements

US10488228B2 · kind B2 · utility

Assignee

• NIKON CORPORATION · JP

Inventor

• Eric Peter Goodwin · Oro Valley, US

Key dates

• Filing date: Jan 10, 2018
• Grant date: Nov 26, 2019
• Expiry date: Jan 10, 2038

Classification

• Technology area (CPC H): Electricity
• CPC primary: H01L21/681
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

An encoder head configured for use with a lithographic exposure tool. The head is devoid of a multiplicity of stand-alone optical retroreflectors. The head includes a single, geometrically substantially perfect optically-isotropic cuboid complemented with optically-isotropic prismatic elements to form a contraption that, in combination with a diffraction grating disposed on a wafer-stage of the exposure tool, splits a single input beam of light delivered to the contraption into four measurement (sub-)beams of light (two in xz-plane, two in yz-plane) and causes each of these sub-beams traverse two prismatic elements and be retro-reflected internally within the cuboid to exit the encoder head at a non-zero angle with respect to the input beam of light, thereby solving problems of (i) structural complexity of a conventional encoder head for use in an exposure tool, (ii) burdensome alignment of the multitude of optical prisms in the process of forming such encoder head, and (iii) cyclic non-linear errors associated with measurements involving conventional corner-cubes-based encoder heads while, at the same time, reducing the geometrical footprint of the encoder head (without reducing t…