Encoder with an alignment target

US6958819B1 · kind B1 · utility

Assignee

• Nanometrics Incorporated · US

Inventors

• John D. Heaton · Fremont, US
• Weidong Yang · San Diego, US
• Roger R. Lowe-Webb · Sunnyvale, US

Key dates

• Filing date: Apr 4, 2002
• Grant date: Oct 25, 2005
• Expiry date: Aug 5, 2023

Classification

• Technology area (CPC G): Physics
• CPC primary: G01D5/34746
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

An encoder uses an alignment target that includes periodic patterns on the movable element and the stationary element. The alignment target may include at least two measurement locations, each location having a different offset between the periodic pattern on the movable element with respect to the periodic pattern on the stationary element. Alternatively, two measurements using different polarization states may be made at one location. When the periodic patterns on the movable element and the stationary element are aligned, the difference between the two measurements will produce a minimum, i.e., approximately a zero value plus noise. By counting the minima, the precise position of the movable element with respect to the stationary element can be determined. The resolution of the encoder may be further increased using reference measurements.