Optical metrology with small illumination spot size

US9915524B2 · kind B2 · utility

Assignee

• KLA-TENCOR CORPORATION · US

Inventors

• Noam Sapiens · Cupertino, US
• Kevin Peterlinz · San Ramon, US
• Alexander Buettner · Weilburg, DE
• Kerstin Purrucker · Berching, DE
• Andrei V. Shchegrov · Campbell, US

Key dates

• Filing date: May 11, 2015
• Grant date: Mar 13, 2018
• Expiry date: Aug 29, 2035

Classification

• Technology area (CPC G): Physics
• CPC primary: G01N2021/213
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

Methods and systems are presented to reduce the illumination spot size projected onto a measurement target and associated spillover onto area surrounding a measurement target. In one aspect, a spatial light modulator (SLM) is located in the illumination path between the illumination light source and the measurement sample. The SLM is configured to modulate amplitude, phase, or both, across the path of the illumination light to reduce wavefront errors. In some embodiments, the desired state of the SLM is based on wavefront measurements performed in an optical path of the metrology system. In another aspect, an illumination aperture having an image plane tilted at an oblique angle with respect to a beam of illumination light is employed to overcome defocusing effects in metrology systems that employ oblique illumination of the measurement sample. In some embodiments, the illumination aperture, objective lens, and specimen are aligned to satisfy the Scheimpflug condition.