Gray level mask
US5334467A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 25, 1993 |
| Grant date | Aug 2, 1994 |
| Priority date | — |
| Expiry date | Feb 25, 2013 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F1/50
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
A gray level mask suitable for photolithography is constructed of a transparent glass substrate which supports plural levels of materials having different optical transmissivities. In the case of a mask employing only two of these levels, one level may be constructed of a glass made partially transmissive by substitution of silver ions in place of metal ions of alkali metal silicates employed in the construction of the glass. The second layer may be made opaque by construction of the layer of a metal such as chromium. The mask is fabricated with the aid of a photoresist structure which is etched in specific regions by photolithographic masking to enable selective etching of exposed regions of the level of materials of differing optical transmissivities. Various etches are employed for selective etching of the photoresist, the metal of one of the layers, and the glass of the other of the layers. The etches include plasma etch with chloride ions to attack the chromium of the opaque layer, compounds of fluorine to attack the glass layer, and reactive ion etching with oxygen to attack the photoresist structure. Also, developer is employed for etching on hardened regions of resist in th…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.