UV optical fluoride crystal elements for λ < 200nm laser lithography and methods therefor
US6894284B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Dec 11, 2002 |
| Grant date | May 17, 2005 |
| Priority date | — |
| Expiry date | Jun 7, 2023 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N21/3563
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
This invention provides a method of detecting sub-ppm lead impurity levels in a below 200 nm transmitting optical calcium flouride crystal. The method includes providing a below 200 nm wavelength transmitting optical flouride crystal having a crystal light transmission path length, providing a 200-210 nm spectrophotometer having a light source for producing a transmission test wavelength in the range 200 to 210 nm and a transmission detector for measuring transmission of the test wavelength, and transmitting the transmission test wavelength in the range of 200 to 210 nm through the below 200 nm wavelength transmitting optical flouride light transmission path length and measuring the transmission of the 200 to 210 nm test wavelength through the path length to provide a lead ppb impurity level measurement less than 500 ppb. The invention provides for improved manufacturing of below 200 nm wavelength optical elements and optical fluoride crystals such as ultralow lead contaminated calcium flouride.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.