Method of detecting aberrations of an optical imaging system
US6368763B2 · kind B2 · utility
Assignees
Inventors
Key dates
| Filing date | Jun 12, 2001 |
| Grant date | Apr 9, 2002 |
| Priority date | — |
| Expiry date | Jun 12, 2021 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10S430/143
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
Aberrations of an imaging system (PL) can be detected in an accurate and reliable way by imaging, by means of the imaging system, a circular phase structure (22) on a photoresist (PR), developing the resist and scanning it with a scanning detection device (SEM) which is coupled to an image processor (IP). The circular phase structure is imaged in a ring structure (25) and each type of aberration, like coma, astigmatism, three-point aberration, etc. causes a specific change in the shape of the inner contour (CI) and the outer contour (CE) of the ring and/or a change in the distance between these contours, so that the aberrations can be detected independently of each other. Each type of aberration is represented by a specific Fourier harmonic (Z-), which is composed of Zernike coefficients (Z-), each representing a specific lower or higher order sub-aberration. The new method enables to determine these sub-aberrations The new method may be used for measuring a projection system for a lithographic projection apparatus.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.