Continuously varying offset mark and methods of determining overlay
US7440105B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Feb 16, 2005 |
| Grant date | Oct 21, 2008 |
| Priority date | — |
| Expiry date | Feb 3, 2026 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F7/0002
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
The present invention relates to overlay marks and methods for determining overlay error. One aspect of the present invention relates to a continuously varying offset mark. The continuously varying offset mark is a single mark that includes over laid periodic structures, which have offsets that vary as a function of position. By way of example, the periodic structures may correspond to gratings with different values of a grating characteristic such as pitch. Another aspect of the present invention relates to methods for determining overlay error from the continuously varying offset mark. The method generally includes determining the center of symmetry of the continuously varying offset mark and comparing it to the geometric center of the mark. If there is zero overlay, the center of symmetry tends to coincide with the geometric center of the mark. If overlay is non zero (e.g., misalignment between two layers), the center of symmetry is displaced from the geometric center of the mark. The displacement in conjunction with the preset gain of the continuously varying offset mark is used to calculate the overlay error.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.