Continuously adjustable neutral density area filter
US6744494B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Dec 7, 2001 |
| Grant date | Jun 1, 2004 |
| Priority date | — |
| Expiry date | Jul 11, 2022 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F7/70558
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
An apparatus for compensating light exposure on different, subsequently irradiated target areas (11, 12) in a photosensitive medium (2) on a semiconductor wafer (1). In order to improve exposure dose uniformity the apparatus comprises a mask filter (9) with a plurality of oblong transparent (31) and oblong opaque elements (32; 41) inserted between a light source (3) and said photosensitive medium (2) so that light (4) traverses through said plurality of transparent elements (31) to expose the photosensitive medium. Each of said plurality of oblong opaque elements (32; 41) is rotatable around a longitudinal axis (42) so as to define the area masked by the projection of the opaque element on the photosensitive medium and to continuously adjust a ratio between irradiated and non-irradiated areas on the photosensitive medium.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.