Image based overlay measurement with finite gratings
US10107621B2 · kind B2 · utility
Assignee
Inventor
Key dates
| Filing date | Feb 13, 2013 |
| Grant date | Oct 23, 2018 |
| Priority date | — |
| Expiry date | Jul 15, 2033 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F7/70633
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An image based overlay measurement is performed using an overlay target that includes shifted overlying gratings. The overlay target is imaged and an asymmetry is measured in the image of the overlaid gratings. The asymmetry is used to determine the overlay error. For each measurement direction, the overlay target may include two or more overlay measurement pads with different offsets between the top and bottom gratings. The measured asymmetries and offsets in the overlay measurement pads may be used to determine the overlay error, e.g., using self-calibration. The pitch and critical dimensions of the overlay target may be optimized to produce a greatest change of symmetry with overlay error for a numerical aperture and wavelength of light used by the image based metrology device.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.