Focusing method and apparatus
US8204298B2 · kind B2 · utility
Assignee
Inventor
Key dates
| Filing date | Jul 11, 2011 |
| Grant date | Jun 19, 2012 |
| Priority date | — |
| Expiry date | Jul 11, 2031 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N21/9501
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
Methods and apparatus for placing wafers axially in an optical inspection system. A “best worst” focus method includes a series of through-focus images of a test wafer acquired using full field of view of the inspection optics. The value of the worst quality in each image is associated with the respective axial location, forming a locus of “worst” values as a function of axial location. The axial location is chosen which optimizes the locus, giving an axial location that provides the “best-worst” image quality. A “video focus” method includes a series of through-focus images generated using reduced field of view. A figure of merit is associated with each image, providing through-focus information. The “video focus” can be calibrated against the “best worst” focus. Further, a point sensor can be used to generate a single z-value for one (x,y) location that can be calibrated with “video focus”.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.