| 摘要 |
PURPOSE: An energy efficient lithography laser is provided to permit precise control of the fluorine concentration in a gas discharge laser chamber. CONSTITUTION: Laser chamber(1) comprises 20.3 liters of laser gas. Nominally, as described above for a KrF laser, the constituents are 1.0 percent krypton, 0.1 percent fluorine and the remainder neon. The 0.1 percent fluorine represents a volume of about 0.0020 liters or 2 ml of fluorine at 3 atm. In mass terms the nominal amount of fluorine in the laser chamber is about 8 grams (81 mg). The partial pressure of the fluorine is about 280 Pa, pure fluorine (corresponding to about 28 kPa of the 1% fluorine mixture). During normal operations with the laser operating at a duty factor of about 40 percent (which is typical for a lithography laser) fluorine is depleted at a rate of about 3.3 mg per hour (this corresponds to about 5% of the fluorine in the chamber per hour). In terms of partial pressure of pure fluorine, this normal depletion rate of fluorine is about 1.45 Pa per hour. To make up for this depletion using the 1% fluorine gas mixture, a volume of the mixture equivalent to about 1.15 kPa per hour is added to the chamber. |
