Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
2000-11-21
2003-09-30
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
Optical output stabilization
C372S057000
Reexamination Certificate
active
06628682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a wavelength detection device for a line-narrowed laser apparatus and to a line-narrowed laser apparatus. More specifically, the present invention relates to a wavelength detection device that is ideal for detecting wavelengths in line-narrowed laser light spectrums. The present invention also relates to an ultra line-narrowed fluorine laser apparatus that narrows the line of the laser light of a fluorine laser and provides it as an exposure light source for an exposure apparatus.
2. Description of the Related Art
In cases where laser light is used as the light source in a stepper (reduction projection exposure device), it is necessary to narrow the line of the laser light spectrum by a line narrowing element such as an etalon or grating.
It is also necessary that the center wavelength in the spectrum of this line-narrowed oscillation line be stabilized and controlled with high precision so that there is no divergence during exposure.
In
FIG. 27
is diagrammed a common laser wavelength stabilizing control device.
The line narrowing and wavelength selecting are performed by driving an etalon
3
that is a line narrowing element by a wavelength controller
11
through a driver
10
(regulating the installation angle of the etalon
3
), and driving a fully reflective mirror
8
by the wavelength controller
11
through a driver
9
a
(regulating the installation angle of the fully reflective mirror
8
).
The wavelength is controlled so that the center wavelength of the narrowed oscillation line L
0
does not fluctuate during the exposure.
That is, during the exposure, the absolute wavelength of the line-narrowed oscillation line L
0
is detected by detecting the relative wavelength of the line-narrowed oscillation line L
0
relative to a constant reference beam Lx.
In other words, the laser beam output from a reference light source
32
is input as the reference light Lx to a spectroscope
12
. The narrowed oscillation line L
0
for which it is desired to detect the wavelength is simultaneously input, as the light to be detected L
0
, via beam splitters
13
and
14
, to the same spectroscope
12
. In the spectroscope
12
, the reference light Lx and the light to be detected L
0
are subjected to spectral diffraction, and an image of the diffracted light is formed on a line sensor
20
. The detection position on the line sensor
20
corresponds to the detected wavelength.
Then, using a dispersion value, from the difference in the positions detected on the line sensor
20
, the relative wavelength of the light to be detected L
0
relative to the reference light Lx is found, whereupon, based on that found relative wavelength and the known wavelength of the reference light Lx, the absolute wavelength of the light to be detected L
0
is calculated.
These calculation results are next fed back to the wavelength controller
11
, and, thereby, the etalon
3
is driven by the driver
9
e.
The center wavelength of the narrowed oscillation line. L
0
that is made to oscillate between the fully reflecting mirror
8
and the output mirror
4
through the laser chamber
1
and etalon
3
is then fixed as the targeted wavelength.
In this manner, stabilizing control is effected with high precision so that the center wavelength in the narrowed oscillation line L
0
does not diverge during exposure.
With the conventional laser wavelength stabilizing control device, however, a problem is incurred in that the structure becomes complex due to the necessity of the reference light source
32
for outputting the reference light Lx, as described above. When the wavelength of the narrowed oscillation line L
0
is detected with high precision, furthermore, a problem is incurred in that the light intensity of the laser beam output by the lamp used for the reference light source is low.
Thereupon, in Japanese Patent Application Laid-Open No. 5-95154, as published, for example, an invention is described wherewith, when the narrowed oscillation line L
0
is a molecule fluorine F
2
laser beam, an atom fluorine laser beam is used having a wavelength in the visible region.
Based on the invention described in this publication, it is possible not to provide a reference light source in the wavelength stabilizing control device.
With the invention described in the publication noted above, the wavelength of the fluorine atom laser oscillation line used as the reference light Lx is in the visible light region. That is, the wavelength of an atom fluorine laser beam is in a region that is removed from the vacuum ultraviolet region that contains the wavelength of a molecule fluorine laser.
For this reason, when the narrowed oscillation line L
0
is a molecule fluorine laser beam, the precision wherewith the wavelength of the narrowed oscillation line L
0
is detected will decline when detected on the basis of the wavelength of the molecule fluorine laser beam.
In other words, with the invention described in the publication noted above, a problem is incurred in that it is very difficult to effect stabilizing control with high precision on the center wavelength of the spectrum of the narrowed oscillation line L
0
.
With the invention described in the publication noted above, moreover, a dielectric multilayer film mirror is employed for causing fluorine atom laser light and molecule fluorine laser light to oscillate simultaneously, providing a resonator for causing the fluorine atom laser light to oscillate inside the resonator for causing the molecule fluorine laser light to oscillate, for example.
With such a mirror, the number of layers becomes large, and a film material must be used which exhibits high absorbency for light having a wavelength of 157 nm, wherefore problems are incurred in that the molecule fluorine laser light oscillation efficiency becomes poor, and the output of the narrowed oscillation line L
0
from the molecule fluorine laser light declines.
A first object of the present invention, which was devised with the situation described in the foregoing in view, is to improve the precision wherewith the wavelength of a narrowed oscillation line is detected, without using a reference light source, and without causing a decline in the narrowed oscillation line output.
Now, in terms of the performance demanded in an exposure tool used in lithography, there are many different factors, such as resolution, alignment precision, processing power, and equipment reliability. Among these factors, the resolution R that directly impacts pattern fineness is expressed by the formula R=k·&lgr;\NA (where k is a constant, &lgr; is the exposure light wavelength, and NA is the numerical aperture of the projection lens). Accordingly, the shorter the exposure light wavelength &lgr; the better in the interest of obtaining good resolution.
Thereupon, in a conventional exposure tool, a mercury lamp i line (wavelength=365 nm) or a krypton-fluoride (KrF) excimer laser having a wavelength of 248 nm is used as the exposure tool light source. These are called an i-line exposure tool and KrF exposure tool, respectively. For the projection optical system employed in such an i-line exposure tool or KrF exposure tool, a reduction projection lens unit wherein a larger number of quartz glass lenses are assembled together is widely used.
As a next-generation exposure tool for performing ultra-fine processing, moreover, use is beginning to be made of exposure tools which employ an argon-fluoride (ArF) excimer laser having a wavelength of 193 nm for the exposure light source. These are called ArF exposure tools. In the ArF exposure tool, an ArF excimer laser is used which has its line-narrowed down to a wavelength width of approximately 0.6 pm, and an achromatic lens made of two types of material is used in the reduction projection optical system.
For the next generation of lithographic exposure tools for the ArF exposure tools described above, furthermore, research is being done on fluorine exposure tools wherein a fluorine laser having a wavele
Iwata Yasuaki
Nagai Shinji
Shio Kouji
Takehisa Kiwamu
Wakabayashi Osamu
Ip Paul
Komatsu Ltd.
Nguyen Dung
Varndell & Varndell PLLC
LandOfFree
Wavelength detection device for line-narrowed laser... 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 detection device for line-narrowed laser..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wavelength detection device for line-narrowed laser... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3015968