Optical: systems and elements – Optical frequency converter
Reexamination Certificate
1999-03-09
2001-06-19
Lee, John D. (Department: 2874)
Optical: systems and elements
Optical frequency converter
C359S328000, C372S022000
Reexamination Certificate
active
06249371
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wavelength converter for converting the wavelength of an incident laser beam and generating a laser beam with a specific wavelength.
2. Description of the Related Art
Generally, a laser beam has characteristics that as the frequency is higher than that of an electric wave, it is excellent in information storage capacity, as the wavelength is equal and a laser beam is in phase, a laser beam is excellent in monochromaticity and directivity, has coherence which is not seen for a normal beam and further, as a laser beam can be extremely thinly focused, energy is focused on a minute area and high temperature and high voltage can be locally and instantaneously realized, and a laser beam is applied to many fields such as communication, information, instrumentation, processing technique and medical science.
For example, it is considered that in a stepper used for manufacturing a semiconductor device, an argon fluoride laser which oscillates by a pulse 193 nm in wavelength will be used in the future. However, for the argon fluoride laser, it is difficult to increase a repetition frequency so that it is a few kHz or more with reduced peak power. Efforts toward widening pulse length are made, however, currently it is not achieved.
Therefore, light intensity and light energy density on synthetic fused silica used in a stepper are required to be a fixed value or less so as to prevent the deterioration of transmissivity and the thermal gradient due to polarization and absorption, and to prevent compaction and aberration due to the occurrence of local optical path differences. Therefore, a demand for the performance of a laser such as the stabilization of pulse energy becomes extremely severe and the sensitivity of a photoresist is required to be enhanced. As a fixed number of pulses are required to be radiated to equalize optical density, it is difficult to enhance throughput.
As toxic gas required to be frequently replaced is used in an argon fluoride laser and the life of each high-priced unit constituting the laser is short, the maintenance cost is high.
In the meantime, a technique for generating an ultraviolet ray 194 nm in wavelength which is a continuous wave for a laser trap for confining a mercury ion is described on p. 4159 in Vol. 36 of Applied Optics written by D. J. Berkeland et al. and published in 1997. That is, this document describes a case that a sum frequency 194 nm in wavelength is generated by approximately 2 mW by radiating a second harmonic 257 nm in wavelength from an argon ion laser 515 nm in wavelength and an amplified laser beam 792 nm in wavelength from a semiconductor laser on a crystal of &bgr;-barium borate (BBO) (&bgr;-BaB
2
O
4
). In this case, the BBO crystal is arranged in a position shared by both an external resonator which resonates with light 257 nm in wavelength and an external resonator which resonates with light 792 nm in wavelength and the optical paths of the two external resonators are spatially separated utilizing a difference in an angle of refraction by dispersion of the BBO crystal cut at Brewster's angle.
However, the above defects cannot be avoided by the above well-known technique when an argon fluoride laser is used, the apparatus is large-sized because an external resonator is used, reflectance and transmissivity are deteriorated because of adhesion of impurities to the surface of a mirror and others and output readily becomes unstable because of the misalignment of a mechanism. In addition, circuits for simultaneously locking external resonators with two wavelengths and actuators are required to be provided in only a step for generating a sum frequency and facilities for strictly matching the optical path length of the resonator are essential to lead light into the resonator.
If a higher harmonic from a solid state laser which can generate a high repetition frequency in place of an argon fluoride laser is used, the problems of the damage of synthetic fused silica and others and the cost are reduced. However, as an acquired wavelength is generally different from a wavelength generated by the argon fluoride laser, there is a defect that the above solid state laser is incompatible with the preceding argon fluoride laser.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a wavelength converter (particularly a laser beam generator) wherein the above defects are solved, a laser beam the repetition frequency of which is high and which has a wavelength 200 nm or less is acquired and damage applied to mineral material such as synthetic fused silica is reduced, the life of a device such as a stepper is extended, the life of laser parts is extended without using toxic gas, the throughput of a stepper and others is enhanced with a high repetition frequency and the stability of a pulse compatible, an ultraviolet radiation source the whole of which is composed of a solid is realized, the problems of reliability, size, maintenance and plumbing and others can be solved and can be sufficiently enhanced. Another object is to provide a laser beam source with the same wavelength to evaluate a system in which such devices are utilized.
That is, the present invention relates to a wavelength converter provided with a first laser for generating a laser beam with a first wavelength (particularly between 1 and 1.1 &mgr;m), a wavelength converting section for converting the wavelength of the laser beam with the first wavelength from the first laser and generating a laser beam with a second wavelength (particularly between 500 and 550 nm) which is shorter than the first wavelength, a wavelength converting section for converting the wavelength of the laser beam with the second wavelength and generating a laser beam with a third wavelength (particularly between 250 and 275 nm) which is shorter than the second wavelength, a second laser which receives the laser beam with a wavelength between 500 and 550 nm and oscillates at a fourth wavelength (particularly between 650 and 785 nm) which is shorter than the first wavelength and is longer than the second wavelength and a wavelength converting part for generating a laser beam with a fifth wavelength (particularly between 190 and 200 nm) which is shorter than the third wavelength by mixing the laser beam with the third wavelength and the laser beam with the fourth wavelength in the second laser.
According to the wavelength converter according to the present invention, as a laser beam (a second higher harmonic) with the second wavelength is acquired by converting the wavelength of a laser beam with the first wavelength from the first laser, a laser beam with the third wavelength (a fourth higher harmonic) is acquired by further converting the wavelength of the laser beam, the second laser is oscillated using the laser beam with the second wavelength for example, a laser beam with the fourth wavelength is acquired and a laser beam with the fifth wavelength is acquired by mixing the laser beam with the fourth wavelength and the laser beam with the third wavelength in the second laser, the following remarkable effects (1) to (4) can be produced. Another light source can be also utilized for exciting the second laser.
(1) A laser beam with the fifth wavelength (particularly 200 nm or less) the repetition frequency of which is high can be acquired, and hereby, damage applied to mineral material such as synthetic fused silica is reduced and the life of a device such as a stepper can be extended.
(2) As an infrared solid state laser can be used for the first laser, such toxic gas as used in an argon fluoride laser is not required to be used and the life of laser parts can be extended.
(3) As a laser beam with the third wavelength and a laser beam with the fourth wavelength are mixed in the second laser (that is, in its internal resonator), a high repetition frequency and the stability of a pulse or average power are readily compatible and the throughput of a stepper and others can be enhanced.
(4) A locking and
Kubota Shigeo
Masuda Hisashi
Lee John D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sony Corporation
LandOfFree
Wavelength converter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wavelength converter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wavelength converter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2464573