Narrow band gas discharge laser with gas additive
US6188710A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 27, 1999 |
| Grant date | Feb 13, 2001 |
| Priority date | — |
| Expiry date | Jul 27, 2019 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH01S3/2256
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
The present invention provides a very narrow band pulse excimer laser capable of producing pulses at a rate in the range of about 500 to 2000 Hz with enhanced energy dose control and reproducibility. Very small quantities of a stablizing additive consisting of oxygen or a heavy noble gas (xenon or radon for KrF lasers, or krypton, xenon or radon for ArF lasers), are added to the gas mixture. Tests performed show substantial improvements in energy stability with the addition of about 30 ppm of xenon to a KrF laser. Tests show improved performance for the ArF lasers with the addition of about 6-10 ppm of Xe or 40 ppm of Kr. In a preferred embodiment very narrow bandwidth is achieved on a KrF laser by reducing fluorine partial pressure to less than 0.10 percent and by increasing the reflectance of the output coupler to greater than 25 percent. In a preferred embodiment, prior art fused silica beam expansion prisms used in the prior art line-narrowing module were replaced with calcium fluoride prisms.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.