Method to uni-directionally expand bandwidth of an asymmetric optical system
US6242137A · kind A · utility
Assignees
Inventor
Key dates
| Filing date | Sep 21, 1999 |
| Grant date | Jun 5, 2001 |
| Priority date | — |
| Expiry date | Sep 21, 2019 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F7/70316
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
An optical mask system for improving the bandwidth in the x-direction of an asymmetrical optical mask, wherein the optical mask has a pattern that varies strongly in the x-direction, but slowly in the y-direction, thus occupying a two-dimensional cigar-shaped area in the transformed F.sub.x -F.sub.y two-dimensional frequency domain. The apparatus and method of the present invention are most advantageous for preparing semiconductor devices whose topography varies strongly in one direction but weakly in another direction. The optical mask system includes: (a) a first diffractive light grating, tilted at a tilting angle .omega. relative to an incident light direction, wherein .omega. is about 45 degrees; (b) an asymmetric optical mask; (c) a second diffractive light grating, tilted at a tilting angle .phi. relative to the incident light direction, wherein .phi. is about 45 degrees; and (d) a low-pass filter. The light grating has a two-dimensional band-width that includes a major cluster and two minor clusters diagonally opposing each other. And the low-pass filter is a rectangular light passageway formed between two parallel plates.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.