Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2002-08-20
2004-08-24
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000
Reexamination Certificate
active
06781672
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus used when producing a semiconductor integrated circuit, a liquid crystal display element, a thin film magnetic head, or another microdevice using lithography and to an illumination apparatus which may be applied for such an exposure apparatus.
2. Description of the Related Art
In the lithographic process for producing a microdevice, use is made of an exposure apparatus to transfer a circuit pattern to be formed on a photomask (including reticle) on to a semiconductor wafer, glass plate, or other photosensitive substrate. Further improvement of the resolution is being demanded for improving the integration degree of such microdevices. To meet these demands, exposure apparatuses are being designed which use illumination light of shorter wavelengths such as from the g-rays (wavelength 436 nm) or i-rays (wavelength 365 nm) of mercury lamps to KrF excimer laser light (wavelength 248 nm) or Arf excimer laser light (wavelength 193 nm).
An excimer laser emits pulse light by discharge in a laser medium (gas). The wavelength spectral width &Dgr;&lgr; of general excimer lasers is about 500 pm (5×10
−10
m) as shown by the broken line in FIG.
14
. When used as the light source of an exposure apparatus, however, it is necessary to narrow the spectral width &Dgr;&lgr; to less than about 1 pm as shown by the solid line in
FIG. 14
so as to suppress chromatic aberration etc. of the optical lenses mounted in the exposure apparatus.
The wavelength spectral width is narrowed by an optical prism, Fabry-Perot etalon, grating, or other wavelength selection element alone or in combination. The variation in the thus narrowed center wavelength of the laser has to be controlled to as low as ±0.1 pm with respect to the reference wavelength.
In this way, the excimer laser light source used for exposure apparatuses inevitably becomes complicated in structure due to the need for control etc. Further, the discharge electrode has to be made longer to make up for the loss of laser output resulting from the narrowing. Accordingly, the excimer laser light source becomes complicated and large in size. The components are also high in price and the running costs high as well.
In general, however, plants manufacturing microdevices install several exposure apparatuses in a clean room. The usual practice is to provide such an excimer laser light source for each exposure apparatus. Each excimer laser light source, as explained above, is complicated and large in size in hardware configuration and is high in initial cost and running costs, so overall a large space is required for the installation of the light sources. This becomes a cause for higher costs as well.
To deal with this problem, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 60-154527, it has been proposed to use a single laser light source and selectively supply laser light for exposure to a plurality of exposure units (exposure stages).
This configuration will be explained in brief with reference to FIG.
16
. In
FIG. 16
, the laser light emitted from a laser light source
51
is selectively sent to a plurality of exposure units
54
A to
54
D through a light path switch comprised of a light path switching controller
52
and a plurality of mirrors
53
A to
53
D. That is, the mirrors
53
A to
53
C are movable mirrors able to be changed in position. The positions of the mirrors
53
A to
53
C are changed under the control of the light path switching controller
52
, whereby the laser light from the light source
51
is guided selectively to one of the exposure units
54
A to
54
D and used for exposure by the corresponding exposure unit (one of
54
A to
54
D).
In this configuration, since it is sufficient to provide just a single laser light source
51
for four exposure units
54
A to
54
D, the configuration becomes simpler, the hardware becomes more compact, and the initial cost becomes cheaper compared with providing a laser light source for each of the exposure units
54
A to
54
D.
According to this technique, however, since light is supplied from a single light source to a plurality of exposure units, the distance of transmission of the light inevitably becomes longer, it is difficult to maintain the precision of alignment of the optical elements in the light path, and, due in part to this, there is a large loss of light. This problem becomes particularly notable in the case of short wavelength light like KrF excimer laser light of a wavelength of 248 nm or ArF excimer laser light of a wavelength of 193 nm. Therefore, to compensate for this loss, it is necessary to increase the output of the light source. The light source becomes larger in size or shorter in service life and the initial cost and running costs rise.
Further, in a laser light source, even before the end of the service life of the light source as a whole is reached, maintenance such as exchange of the gas or exchange of worn out parts has to be performed periodically or upon need. In the above art, however, since it is necessary for a single light source to provide the pulses used for the plurality of exposure units, the frequently of maintenance becomes high and the time until reaching the end of the service life becomes shorter. Not that great a reduction in the running costs can therefore be hoped for.
Further, since light from a single light source is selectively sent to the exposure units, more than one exposure units cannot simultaneously perform exposure work. Therefore, the throughput (amount of production per unit time) is liable to fall.
In addition, when increasing the number of exposure units so as to increase the production capacity in the above art, the light source itself has to be changed to a higher output one etc. It is structurally difficult to flexibly deal with such changes.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an exposure apparatus and illumination apparatus enabling a reduction of size and reduction of costs.
Another object of the present invention is to provide an exposure apparatus able to improve the throughput.
Still another object of the present invention is to provide an exposure apparatus able to flexibly handle changes in the production capacity.
To achieve the above objects, according to a first aspect of the present invention, there is provided an exposure apparatus comprising a single light source for emitting light, a plurality of exposure units for performing exposure using illumination light derived from the light from the light source, a light transmitter having a plurality of light paths for optically connecting the light source and the exposure units, and a plurality of amplifiers, provided in the light paths corresponding to the exposure units, for amplifying the light from the light source.
According to the exposure apparatus of the present invention, since a single light source is provided for a plurality of exposure units and each exposure unit is just provided with an amplifier, but no light source, the overall apparatus is smaller in size and lower in cost. In addition to this, since an amplifier for amplifying the light from the light source is provided corresponding to each of the exposure units, a light source which is low in output, that is, small in size and inexpensive in price, can be used and can be extended in service life.
Therefore, the initial cost required for the light source itself and the running costs can be greatly reduced. Further, since the energy of the light transmitted over the light paths from the light source to the exposure units is small, the optical components (for example, lenses, mirrors, optical fibers, etc.) constituting the light transmitter optically connecting these may be ones of relatively low price and may be extended in service life. The cost can be further reduced by this as well.
Note that some cost is of course required along with the provision of the amplifiers, but amplifiers, unlike light sources, do not need
Nguyen Henry Hung
Nikon Corporation
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