Photocopying – Projection printing and copying cameras – With temperature or foreign particle control
Reexamination Certificate
2002-06-12
2004-07-13
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
With temperature or foreign particle control
C355S072000, C355S075000
Reexamination Certificate
active
06762821
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a gas purge method which is preferably applied to an exposure apparatus that uses ultraviolet rays as exposure light, purges the interior of the apparatus with gas, and projects the pattern of a master such as a mask onto a photosensitive substrate via a projection optical system, and which purges with gas a pellicle space defined by a master and a pellicle used to prevent deposition of a foreign matter on a pattern surface. The present invention also relates to an exposure apparatus having a gas purge apparatus for purging the pellicle space with gas.
BACKGROUND OF THE INVENTION
A conventional manufacturing process for a semiconductor element such as an LSI or a VLSI formed from a micropattern uses a reduction type projection exposure apparatus for printing and forming by reduction projection a circuit pattern drawn on a master such as a mask onto a substrate coated with a photosensitive agent. With an increase in the packaging density of semiconductor elements, demands have arisen for further micropatterning. Exposure apparatuses are coping with micropatterning along with the developing of a resist process.
A means for increasing the resolving power of the exposure apparatus includes a method of changing the exposure wavelength to a shorter one, and a method of increasing the numerical aperture (NA) of the projection optical system.
As for the exposure wavelength, a KrF excimer laser with an oscillation wavelength of 365-nm i-line to recently 248 nm, and an ArF excimer laser with an oscillation wavelength around 193 nm have been developed. A fluorine (F
2
) excimer laser with an oscillation wavelength around 157 nm is also under development.
An ArF excimer laser with a wavelength around ultraviolet rays, particularly, 193 nm, and a fluorine (F
2
) excimer laser with an oscillation wavelength around 157 nm are known to have an oxygen (O
2
) absorption band around their wavelength band.
For example, a fluorine excimer laser has been applied to an exposure apparatus because of a short wavelength of 157 nm. The 157-nm wavelength falls within a wavelength region called a vacuum ultraviolet region. In this wavelength region, light is greatly absorbed by oxygen molecules, and hardly passes through the air. The fluorine excimer laser can only be applied in an environment in which the atmospheric pressure is decreased to almost vacuum and the oxygen concentration is fully decreased. According to the reference “Photochemistry of Small Molecules” (Hideo Okabe, A Wiley-Interscience Publication, 1978, page 178), the absorption coefficient of oxygen to 157-nm light is about 190 atm
−1
cm
−1
. This means when 157-nm light passes through gas at an oxygen concentration of 1% at one atmospheric pressure, the transmittance T per cm is only T=exp(−190×1 cm×0.01 atm)=0.150.
Oxygen absorbs light to generate ozone (O
3
), and the ozone promotes absorption of light, greatly decreasing the transmittance. In addition, various products generated by ozone are deposited on the surface of an optical element, decreasing the efficiency of the optical system.
To prevent this, the oxygen concentration in the optical path is suppressed to a low level on the order of several ppm order or less by a purge means using inert gas such as nitrogen in the optical path of the exposure optical system of a projection exposure apparatus using a far ultraviolet laser such as an ArF excimer laser or a fluorine (F
2
) excimer laser as a light source.
In such an exposure apparatus using an ArF excimer laser with a wavelength around ultraviolet rays, particularly, 193 nm, or a fluorine (F
2
) excimer laser with a wavelength around 157 nm, an ArF excimer laser beam or a fluorine (F
2
) excimer laser beam is readily absorbed by a substance. A light absorption substance in the optical path must be purged to several ppm order or less. This also applies to moisture, which must be removed to a ppm order or less.
For this reason, the interior of the exposure apparatus, particularly, the optical path of ultraviolet rays is purged with inert gas. A load-lock mechanism is arranged at a coupling portion between the inside and outside of the exposure apparatus. When a reticle or wafer is to be externally loaded, the interior of the exposure apparatus is temporarily shielded from outside air. After the impurity in the load-lock mechanism is purged with inert gas, the reticle or wafer is loaded into the exposure apparatus.
FIG. 1
is a schematic sectional view showing an example of a semiconductor exposure apparatus having a fluorine (F
2
) excimer laser as a light source and a load-lock mechanism.
In
FIG. 1
, reference numeral
1
denotes a reticle stage for setting a reticle bearing a pattern;
2
, a projection optical system for projecting the pattern on the reticle onto a wafer serving as a photosensitive substrate;
3
, a wafer stage which supports the wafer and is driven in the X, Y, Z, &thgr;, and tilt directions;
4
, an illumination optical system for illuminating the reticle with illumination light; and
5
, a guide optical system for guiding light from the light source to the illumination optical system
4
.
Reference numeral
6
denotes a fluorine (F
2
) laser serving as a light source;
7
, a masking blade for shielding exposure light so as not to illuminate the reticle except for the pattern region;
8
and
9
, housings which cover the exposure optical path around the reticle stage
1
and wafer stage
3
, respectively; and
10
, an He air-conditioner for adjusting the interiors of the projection optical system
2
and illumination optical system
4
to a predetermined He atmosphere.
Reference numerals
11
and
12
denote N
2
air-conditioners for adjusting the interiors of the housings
8
and
9
to a predetermined N
2
atmosphere;
13
and
14
, reticle load-lock chambers and wafer load-lock chambers used to load a reticle and wafer into the housings
8
and
9
, respectively; and
15
and
16
, a reticle hand and wafer hand for transferring the reticle and wafer, respectively.
Reference numeral
17
denotes a reticle alignment mark used to adjust the reticle position;
18
, a reticle stocker for stocking a plurality of reticles in the housing
8
; and
19
, a pre-alignment unit for pre-aligning the wafer.
If necessary, the overall apparatus is stored in an environment chamber (not shown). Air controlled to a predetermined temperature is circulated within the environment chamber to keep the internal temperature of the chamber constant.
FIG. 2
is a schematic sectional view showing another example of the semiconductor exposure apparatus having a fluorine (F
2
) excimer laser as a light source and a load-lock mechanism. In
FIG. 2
, the same reference numerals as in
FIG. 1
denote the same parts.
The whole exposure apparatus shown in
FIG. 2
is covered with a housing
20
, and O
2
and H
2
O in the housing
20
are purged with N
2
gas. Reference numeral
21
denotes an air-conditioner for setting the entire housing
20
in an N
2
atmosphere. In this exposure apparatus, the lens barrel of a projection optical system
2
and the internal space of an illumination optical system
4
are partitioned from the internal space (driving system space) of the housing
20
, and independently adjusted to an He atmosphere. Reference numerals
13
and
14
denote a reticle load-lock chamber and wafer load-lock chamber used to load a reticle and wafer into the housing
20
, respectively.
In general, a reticle is equipped with a pattern protection device called a pellicle. The pellicle prevents deposition of a foreign matter onto a reticle pattern surface, and suppresses the occurrence of defects caused by transfer of a foreign matter onto a wafer.
FIG. 3
is a schematic view showing the structure of a pellicle.
A pellicle
24
is adhered to the pattern surface of a reticle
23
with an adhesive agent or the like. The pellicle
24
is made up of a support frame
25
large enough to surround the reticle pattern, and a pellicle film
26
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