Using unflatness information of the substrate table or mask table for decreasing overlay
US7239368B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Nov 29, 2004 |
| Grant date | Jul 3, 2007 |
| Priority date | — |
| Expiry date | Jul 3, 2025 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F7/707
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
A lithographic system includes an illumination system for providing a projection beam of radiation, a mask table for supporting a mask, the mask serving to impart the projection beam with a pattern in its cross-section, a substrate table for holding a substrate, and a projection system for projecting the patterned beam onto a target portion of the substrate. The system also comprises a processor arranged to calculate overlay corrections using a reference height map representing a surface of the substrate table or the mask table. Feed forward correction of non-flatness induced wafer grid distortion is allowed during alignment and during exposure, thereby reducing overlay errors caused by differences in flatness characteristics. It provides an indirect qualification method for overlay accuracy related to exposure chuck flatness based on height map information.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.