Coherent light generators – Particular active media – Gas
Reexamination Certificate
2003-06-10
2004-07-27
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
Gas
C372S055000, C372S058000, C372S068000, C372S087000, C372S090000, C372S023000, C372S101000, C372S103000, C372S108000
Reexamination Certificate
active
06768762
ABSTRACT:
FIELD OF THE INVENTION
The subject invention is directed generally to an High Repetition Rate UV Excimer Laser.
BACKGROUND OF THE INVENTION
Throughout this application various publications are referenced. The disclosures of each of these publications in their entireties are hereby incorporated by reference in this application.
Excimer lasers have been conventionally developed for commercial use as a light source of a reducing projection and exposure device for a semiconductor manufacturing apparatus, because an excimer laser enables extremely precise work.
Light oscillating from the excimer laser has various wavelength components and the central wavelength varies. As a result, if the light is in the as-is status, an aberration will occur when the light passes through an external optical element, such as a lens, thereby reducing the accuracy of the work. For this reason, there is a widely used art of making a narrow band, in which an excimer laser is equipped with a wavelength selecting element, such as a grating, to narrow the spectral width of the laser oscillation wavelength and to stabilize the central wavelength as a central value of the oscillation wavelength.
U.S. Pat. No. 6,181,724 discloses an excimer laser. Laser gas is sealed in a laser chamber and energy is supplied as a result of an electrical discharge in a discharge electrode, causing the laser beam to oscillate. The oscillating laser beam exits through a rear window, the beam size is widened while passing through a first prism and a second prism, and then the laser beam enters a grating. In the grating, an angle relative to the light path of the laser beam is controlled by an actuator and by oscillating the laser beam at a predetermined wavelength, a narrow band is achieved. A group of optical components, which are the first prism, the second prism, and the grating, is collectively called the narrow-band optics. The laser beam, with the wavelength being controlled by the narrow-band optics, passes through a front window and a front mirror, which is a partial reflecting mirror, and part of the laser beam exits the laser chamber.
Typically, synthetic fused silica or calcium fluoride is used as the material of the optical components for the excimer lasers, however, there are significant disadvantages in using these materials; for example, laser included absorption as a result of the use high fluence radiation. In order to manufacture semiconductors efficiently in large quantities, there has been a demand to increase the power of a laser by increasing the laser oscillation pulse numbers per unit time (also called the repetition frequency or repetition rate). However, the energy density is high in the resonator of the laser, and moreover, a laser beam reciprocates in the resonator and passes through the optical components many times. For this reason, as the power of a laser becomes higher, the optical components are deteriorated as a result of even minor distortion or unevenness inside the material. Even minor deterioration of the optical components exerts a great influence on the quality of the oscillating laser beam. Thus, the optical components of synthetic fused silica or calcium fluoride are insufficient in durability when the power of an excimer laser is increased, and a highly accurate control of the wavelength of an High Repetition Rate UV Excimer Laser is difficult when these optical components are used. It is one of the objects of this invention to overcome these laser induced problems, for example in calcium fluoride, by the use of an in situ annealing process using a secondary laser beam.
SUMMARY OF THE INVENTION
The present invention relates to an High Repetition Rate (≧4 kilohertz) UV Excimer Laser which includes a source of a laser beam and one or more windows which include magnesium fluoride.
Another aspect of the present invention includes an High Repetition Rate UV Excimer Laser which includes a source for a laser beam, one or more windows which include magnesium fluoride, and a source for annealing the one or more windows, such annealing reducing laser induced absorption problems.
Yet another aspect of the present invention includes an High Repetition Rate UV Excimer Laser window which includes magnesium fluoride.
Yet another aspect of the present invention includes a method of producing a predetermined narrow width laser beam. The method includes oscillating a laser beam whereby the laser beam exits a first window of a chamber, widening the laser beam through one or more prisms, controlling the laser beam to a predetermined narrow width, and passing the predetermined narrow width laser beam through a second window of the chamber, where the first and second windows of the chamber include magnesium fluoride.
REFERENCES:
patent: 2001/0043331 (2001-11-01), Rebhan
patent: 2002/0044586 (2002-04-01), Myers et al.
patent: 2041298 (1995-08-01), None
Douglas Walter M
Rodriguez Armando
Wong Don
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