Coherent light generators – Particular beam control device – Nonlinear device
Reexamination Certificate
1999-07-19
2002-11-05
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular beam control device
Nonlinear device
Reexamination Certificate
active
06477188
ABSTRACT:
TECHNICAL FIELD
1. Field of the Invention
The invention relates to a light source device which is used for a semiconductor lithography device, surface activating, precision machining (perforation, cutting to size, grooving), perforation of a printed board, installation of nozzles in an inkjet printer, marking and the like. The invention relates especially to a light source device consisting of a solid state laser device which can be used as a replacement light source for an excimer laser.
2. Description of the Related Art
There has recently been a demand for an increase of image definition according to refinement of an integrated semiconductor circuit or the like. The wavelengths of the exposure source are therefore becoming shorter and shorter. An ArF excimer laser with a wavelength of 193 nm is regarded as definitive as a light source for semiconductor lithography for the coming generation.
It is therefore well known that a light source using the above described excimer laser has the following disadvantages:
(1) Since corrosive gas is used as a laser medium, the electrodes which form the main part of the laser, and the main parts such as a capacitor and the like, are often corroded and degraded. Therefore the cost for their maintenance is high.
(2) The laser gas is also soon degraded. Therefore the gas must be replaced upon each recording by 10°.
(3) There is a problem with respect to safety precautions since the corrosive gas leaks.
(4) The gas pipelines consist of stainless steel in order to preserve the laser power. The accessories therefore become expensive.
The inventors therefore have already proposed the above described light source device in which using a solid state laser device light with a wavelength of 193 nm is generated (JP-HEI 9-112346).
(a) Quintuple waves of the laser light which is emitted from a Nd—YLF laser light source are produced by means of a nonlinear optical crystal LBO, CLBO (the first coherent light beam has a wavelength of 209.4 nm).
Furthermore double waves of the laser light which is emitted by a Nd—YLF laser light source are produced by means of a nonlinear optical crystal LBO and a difference frequency between these double waves and the laser light which is emitted by a semiconductor laser light source is produced by means of a photoparametric oscillator (the second coherent light beam has a wavelength of 2532.814 nm). Light with a frequency (193.4 nm) formed by the sum of the first and the second coherent light beams is produced by means of the nonlinear optical crystal CLBO (first embodiment in JP-HEI 9-112346).
(b) Quintuple waves of the laser light which is emitted by a Nd—YAG laser light source are produced by means of a nonlinear optical crystal LBO, CLBO (the first coherent light beam has a wavelength of 212.824 nm).
Furthermore, double waves of the laser light which is emitted by a Nd—YAG laser light source are produced by means of a nonlinear optical crystal LBO and a difference frequency between these double waves and the laser light which is emitted by a semiconductor laser light source is produced by means of a photoparametric oscillator (the second coherent light beam has a wavelength of 2185.8206 nm). Light with a frequency (193.9 nm) formed by the sum of the first and the second coherent light beams is produced by means of the nonlinear optical crystal CLBO (second embodiment in JP-HEI 9-112346).
The light source device described above in (a) and (b) had the following defects:
(1) The disadvantage of phase mismatch of the nonlinear optical crystal CLBO (hereinafter called “CLBO crystal”) in the generation of the frequency formed by the sum of the first and the second coherent light beams.
The CLBO crystal has the property of often producing hydrates. Here, as shown in
FIG. 26
, there is an absorption band in the wavelength range of greater than 1800 nm, i.e. in the vicinity of 2 microns.
In the above described (a) and (b) therefore absorption of the second coherent light beam becomes large (in (a) the light with a wavelength of 2532.814 nm and in (b) the light with a wavelength of 2185.8206 nm).
Therefore it is regarded as a disadvantage that heat is generated within the CLBO crystal, that due to the heat formed the phase matching angle deviates in the process of generation of the summed frequency, that therefore a phase mismatch state arises and that the efficiency of wavelength conversion into the light with the summed frequency decreases. The phase mismatch and phase matching can be taken for example from the Japanese patent application HEI 8-312478 already proposed by the inventors.
Furthermore, there is the disadvantage that absorption of the resulting light with a wavelength of 193 nm causes heating of the CLBO crystal, that therefore a phase mismatch state in the above described manner arises, and that the efficiency of wavelength conversion into the light with the summed frequency decreases.
(2) Disadvantage of phase mismatch of the CLBO crystal when the first coherent light beam is produced
In the second coherent light beam the basic waves from a Nd—YLF laser light source and a Nd—YAG laser light source are converted by a first nonlinear optical crystal into double waves, by a second nonlinear optical crystal into quadruple waves and by a third nonlinear optical crystal into quintuple waves.
Here the crystals which can be used in practice as the third nonlinear optical crystal which is used as the last stage for generating the quintuple waves are a CLBO crystal and a BBO crystal.
But for the two crystals it is considered a disadvantage that due to phase mismatch as a result of absorption (linear absorption or two-photon absorption) of the resulting quintuple waves essentially the efficiency of wavelength conversion into quintuple waves decreases.
As was described above, in the above described light source device it was considered disadvantageous that the nonlinear optical crystal in the generation of quintuple waves and of light with the summed frequency absorbs light and furthermore also fundamentally light with the summed frequency, that therefore the state of phase matching of the crystal changes, and that the efficiency of wavelength conversion drops (hereinafter the above described change of the state of phase matching of the crystal into the state of phase mismatch is called “heat induced phase mismatch”).
The invention was devised to eliminate the defects of the above described conventional light source device. Therefore the object of the invention is to devise a replacement light source with a simple arrangement for an ArF excimer laser in which light with a wavelength of roughly 193 nm can be produced with high efficiency without reducing the efficiency of wavelength conversion, and in which thus the degradation of beam quality is only little.
DISCLOSURE OF THE INVENTION
The above described object is achieved as claimed in the invention as follows:
(1) A light source device which comprises:
a solid state laser light source which produces basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm;
a means for producing a harmonic which produces a harmonic of the above described basic laser light;
a coherent light source which is excited by the above described harmonic; and
a means for producing a summed frequency which produces laser light with a summed frequency with a wavelength of roughly 193 nm from the basic laser light which is emitted from the above described solid state laser light source, and from the coherent light which is emitted from the above described coherent light source.
(2) A light source device which comprises:
a first solid state laser light source which produces first basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm;
a second solid state laser light source which produces second basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm;
a means for producing a harmonic which produces a harmonic of
Deki Kyoichi
Horiguchi Masahiro
Takaoka Eiko
Jr. Leon Scott
Kabushiki Kaisya Ushiosougougizyutsukenkyusyo
Nixon & Peabody LLP
Safran David S.
LandOfFree
Light source does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light source, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light source will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2935806