A very narrow band excimer laser. The very narrow bandwidth is achieved by using an etalon (44) as an output coupler in combination with a line narrowing element (18) located at the rear of the laser. Preferred embodiments are capable of producing 10 mJ laser pulses at 1000 Hz with a 95% integral bandwidth of less than 1.5 pm.

Very narrow band laser

A line narrowed laser having a grating based line narrowing module, etalon-based line narrowing output coupler (64) and a technique for tuning the laser. The etalon-based output coupler (64) is adjusted to preferentially reflect light at or near the spectral maximum produced by the grating (16). Substantial improvement in line narrowing results from amplification in the laser resonance chamber of light at or near the grating spectral maximum which is preferentially reflected by the etalon-based output coupler (64). Several preferred methods are disclosed for tuning the etalon-based output coupler (64) to match the wavelength selected by the grating based line narrowing module.

Narrow band laser with etalon based output coupler

A bidirectional bandwidth controlled grating assembly. A spring housing is connected to one of two end plates extending away from the lined surface of the grating. An adjustment rod threaded through the other end plate extends into the spring housing. Inside the spring housing in a preferred embodiment are two compression springs mounted between pressure surfaces in the housing and a piston which is fixed on the adjustment rod. The lined surface of the grating can be made more concave (or less convex) by screwing the rod in a direction into the spring housing compressing one of the springs to push the end plates apart and the surface can be made more convex (or less concave) by screwing the rod in a direction out of the spring housing compressing the other spring to pull the end plates toward each other.

Grating assembly with bi-directional bandwidth control

A laser beam machining apparatus including a laser beam irradiation unit, the laser beam irradiation unit including: a laser beam oscillator for oscillating a laser beam; a beam splitter by which the laser beam oscillated by the laser beam oscillator is split into a first laser beam and a second laser beam; a rotary half-wave plate disposed between the laser beam oscillator and the beam splitter; a condenser lens disposed in a first optical path for guiding the first laser beam split by the beam splitter; a first reflecting mirror disposed in a second optical path for guiding the second laser beam split by the beam splitter; a first quarter-wave plate disposed between the beam splitter and the first reflecting mirror; a second reflecting mirror disposed in a third optical path for splitting thereinto the second laser beam returned to the beam splitter through the second optical path; a second quarter-wave plate disposed between the beam splitter and the second reflecting mirror; and a cylindrical lens disposed between the beam splitter and the second quarter-wave plate.

Laser beam machining apparatus

A narrow-band laser apparatus comprises an optical resonator including first and second reflectors for reflecting radiation, a laser medium for amplifying radiation in said resonator and an etalon for selecting a given wavelength component from said radiation. A polarizing beam splitter is provided for linearly polarizing said radiation and also for acting as an output coupler. In order to obtain very narrow bandwidth radiation of high intensity, a Faraday rotator is provided for rotating the plane of polarization while maintaining the linear polarization thereby allowing a second wavelength selection element (such as a grating) to be efficiently employed to further narrow the output of the laser.

Narrow-band laser apparatus

A laser apparatus comprises an optical resonator including first and second mirrors, and laser medium. An wavelength selection element is provided in the resonator for narrowing band-width. A polarizing conversion element for changing ratio of S to P components and polarizing beam splitter are provided for amplifying laser beam to output after wavelength selection and for reducing light load of the wavelength selection element. The polarizing conversion element is provided in the resonator light path. In another embodiment, the polarizing conversion element is provided in a branch light path formed by a second polarizing conversion element and a third mirror, where the second polarizing conversion element reflects and transmits P component at a given ratio and reflects S component. The wavelength selection element comprises a Fabry-Perot etalon, grating, or prism. The polarizing conversion element comprises a quarter-wave plate or a phase retarder mirror. The polarizing beam splitting element comprises a polarizing beam splitter or polarizing beam splitting prism. Such laser apparatus is suited for an exposure light source for photolithography.

A gas laser apparatus includes an insulating material layer covering the outside of a pair of metal electrodes disposed on the outer peripheral surface of a dielectric discharge tube. The insulating material layer thus provided electrically separates the metal electrodes and prevents a dielectric tube which would otherwise occur through an air gap between adjacent portions of the metal electrodes when a high-frequency voltage is applied across the metal electrodes.

Gas laser apparatus

A discharge-pumped gas laser (10) has a pressure container (11) filled with a laser gas under pressure and a pair of elongate main discharge electrodes (14,15). The main discharge electrodes (14,15) are disposed in the pressure container (11) in confronting relationship to each other for producing an electric discharge in the laser gas in a main discharge region (16) defined therebetween to excite the laser gas for laser emission. The laser gas is circulated to flow through the main discharge region (16) in a direction perpendicular to the main discharge electrodes (14,15). The laser gas in the main discharge region (16) is preionized by an UV preionizer (17,18) disposed either upstream or downstream of the main discharge region (16) with respect to the direction of flow of the laser beam. The pressure container (11) houses a baffle partition (33) for controlling the laser gas to flow past one of the main discharge electrodes (14,15) and the preionizer (17) while blocking the laser gas from directly flowing to the other of the main discharge electrodes (14,15) and the preionizer (18).

Discharge-pumped gas laser with baffle partition for controlled laser gas flow at preionizers

As a light source for deep submicron lithography the authors have developed a long life and high power KrF narrow band excimer laser by installing a polarization coupled resonator into the conventional narrow band excimer laser with intra-cavity etalons. A maximum output power of 1O. 5Yi with a low etalon-load of L5W arid a narrow spectral band-width of 24pm at 200Hz is obtained. The central wavelength is stabilized to within only 5pm and drift is not observed when increasing the repetition rate from 4Hz to 200Hz without a wavelength feedback loop system. Furthermore the etalon-life is expected to be drastically prolonged to over a billion pulses resulting from the reduction of the etalonload to only about 10 of that in a conventional laser. 2.

High-power and narrow-band excimer laser with a polarization-coupled resonator

A laser apparatus with preionization comprises: a laser medium; main electrodes (3,3a) for produce a glow discharge therebetween; an optical resonator; a first capacitor (1) for storing a first charge used for production of the glow discharge; a preionizing circuit including a spark gap (2) and a second capacitor (13) connected to the spark gap in series for illuminating the laser medium around the electrodes with sparks developed between the spark gap in response to charging of the second capacitor through the spark gap with a second charge, the preionizing circuit being connected to the first capacitor in parallel; and a charging circuit responsive to a control signal for charging the first and second capacitors with the first and second charges received from a high voltage source. The second capacitor is provided only for discharging, thus the current flows in the spark gap is reduced, so that wear of the spark gap is reduced. Inductance associated with glow discharge is reduced because the spark gap is removed from the discharge circuit including the first capacitor, so that the discharge glow starts rapidly. A coil may be inserted in the preionizing circuit in series to control a current flowing therein.

Naoya Horiuchi

Papers

Narrow-band laser apparatus

Gas laser apparatus

Discharge-pumped gas laser with baffle partition for controlled laser gas flow at preionizers

High-power and narrow-band excimer laser with a polarization-coupled resonator

Laser apparatus with preionization