Focusing system with filter for open or closed loop control
US9903806B2 · kind B2 · utility
Assignee
Inventor
Key dates
| Filing date | Dec 17, 2013 |
| Grant date | Feb 27, 2018 |
| Priority date | — |
| Expiry date | Feb 5, 2035 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG02B7/28
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An optical metrology device, such as an ellipsometer, includes a focusing system that adjusts the focal position of the metrology device in real time so that focus may be maintained during movement of the measurement locations on the sample, e.g., using closed loop control. A filtered focus signal may be used to adjust the focal position while moving to a measurement location. Additionally, the focus signal may be coarsely filtered and finely filtered, where a coarse filtered focus signal is used to adjust the focal position while moving to a measurement location and a fine filtered focus signal is used to adjust the focal position when at the measurement location. An open loop control may be used in which once at the measurement location, a filtered focus signal is used to adjust the focal position when the filtered focus signal has no offset with respect to the focus signal.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.