Electric discharge laser with active wavelength chirp correction

US6621846B1 · kind B1 · utility

Assignee

• Cymer, LLC · US

Inventors

• Richard L. Sandstrom · Encinitas, US
• Palash P. Das · Vista, US
• George J. Everage · San Diego, US
• Frederick Erie · Oceanside, US
• William N. Partlo · Poway, US
• Igor V. Fomenkov · San Diego, US

Key dates

• Filing date: Feb 9, 2000
• Grant date: Sep 16, 2003
• Expiry date: Feb 9, 2020

Classification

• Technology area (CPC H): Electricity
• CPC primary: H01S3/225
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

Electric discharge laser with active chirp correction. This application discloses techniques for moderating and dispensing these pressure waves. In some lasers small predictable patterns remain which can be substantially corrected with active wavelength control using relatively slow wavelength control instruments of the prior art. In a preferred embodiment a simple learning algorithm is described to allow advance tuning mirror adjustment in anticipation of the learned chirp pattern. Embodiments include stepper motors having very fine adjustments so that size of tuning steps are substantially reduced for more precise tuning. However, complete elimination of wavelength chirp is normally not feasible with structural changes in the laser chamber and advance tuning; therefore, Applicants have developed equipment and techniques for very fast active chirp correction. Improved techniques include a combination of a relatively slow stepper motor and a very fast piezoelectric driver. In another preferred embodiment chirp correction is made on a pulse-to-pulse basis where the wavelength of one pulse is measured and the wavelength of the next pulse is corrected based on the measurement. This co…