Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
2001-11-02
2004-09-07
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
C355S075000, C355S030000
Reexamination Certificate
active
06788392
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for substituting an inert gas for a gas (e.g., air including impurities) in a pellicle space surrounding a mask and a pellicle, which is provided to prevent foreign matter such as particles from adhering to a pattern surface. The method is suitably applied to an exposure apparatus in which a mask pattern is irradiated to a photosensitive substrate through a projection optical system by using ultraviolet light as exposure light while gas in the exposure apparatus is replaced with an inert gas. Also, the present invention relates to an exposure apparatus provided with an inert gas substituting apparatus for substituting an inert gas for a gas in the pellicle space.
2. Description of the Related Art
Hitherto, a scale-down (reduction) projection exposure apparatus for projecting and printing a circuit pattern drawn in the form of a mask as a scaled-down image on a substrate, over which a photoresist is coated, has been employed in a process for manufacturing semiconductor devices formed of very fine patterns, such as LSIs and ultra LSIs. Even finer patterns have been demanded with an increase in packing density of semiconductor devices, and exposure apparatuses have been improved to be adaptable for such a demand in step with development of the resist process.
The resolution provided by an exposure apparatus can be improved by setting the wavelength of exposure light to be shorter, or by setting the numerical aperture (NA) of a projection optical system to be greater.
The wavelength of exposure light has become shorter with the development of KrF excimer lasers having oscillation wavelengths ranging from 365 nm of the i-line to about 248 nm in a recent version, and of ArF excimer lasers having oscillation wavelengths of about 193 nm. A fluorine (F
2
) excimer laser having an oscillation wavelength of about 157 nm has also been developed.
In connection with an ArF excimer laser having an oscillation wavelength of about 193 nm and a fluorine (F
2
) excimer laser having an oscillation wavelength of about 157 nm, it is known that a plurality of oxygen (O
2
) absorption bands exist in the far ultraviolet range, particularly, in the ranges near those oscillation wavelengths.
Applications of a fluorine excimer laser, for example, to an exposure apparatus have progressed because it has a short oscillation wavelength of about 157 nm. The wavelength of 157 nm resides in a wavelength range that is generally called a vacuum ultraviolet range. The reason is that since, in such a wavelength range, oxygen molecules greatly absorb light and the atmosphere (air) is hardly transmissive to light, applications of a fluorine excimer laser are feasible only under an environment in which the air pressure is reduced to a level close to a vacuum and the oxygen concentration is reduced to a sufficiently low level. According to a reference “Photochemistry of Small Molecules” (by Hideo Okabe, A Wiley-Interscience Publication, 1978, p.178), the absorption coefficient of oxygen to light having a wavelength of 157 nm is about 190 atm
−1
cm
−1
. This means that when the light having a wavelength of 157 nm passes air at 1 atm with an oxygen concentration of 1%, the transmittance per 1 cm is that as given below:
T
=exp(−190×1 cm×0.01 atm)=0.150
Further, ozone (O
3
) is generated upon oxygen absorbing the above light. Various materials produced from ozone adhere to the surfaces of optical devices and hence lower the efficiency of an optical system.
In an optical path of an exposure optical system of a projection exposure apparatus which employs, as a light source, a far ultraviolet ray emitted from an ArF excimer laser, a fluorine (F
2
) excimer or the like, therefore, the concentration of oxygen present in the optical path is reduced to a level lower than an order of several ppm by a method purging out the oxygen with an inert gas such as nitrogen.
Thus, in exposure apparatuses utilizing far ultraviolet rays, particularly, an ArF excimer laser beam having a wavelength of about 193 nm and a fluorine (F
2
) excimer laser beam having a wavelength of about 157 nm, oxygen in an optical path must be purged out to a level lower than an order of several ppm because the ArF excimer laser beam and the fluorine (F
2
) excimer laser beam are very easily absorbed by components of the exposure apparatus.
The above description is similarly applicable to moisture. That is, moisture (H
2
O) must also be removed to a level lower than an order of several ppm. For that reason, it has been conventional that air containing oxygen and moisture in the interior of an exposure apparatus, especially in a path of an ultraviolet ray, is purged out with an inert gas. Also, a load lock mechanism is provided in a section communicating the interior and the exterior of an exposure apparatus with each other. When a reticle or a wafer is carried into the interior of the exposure apparatus from the exterior, it is first placed in the load lock mechanism for being cut-off from the open atmosphere and for purging-out of impurities with an inert gas. Thereafter, the reticle or the wafer is carried into the interior of the exposure apparatus.
FIG. 14
is a schematic sectional view showing one example of a semiconductor exposure apparatus which employs a fluorine (F
2
) excimer laser as a light source and includes load lock mechanisms.
Referring to
FIG. 14
, reference numeral
1
denotes a reticle stage on which a reticle having a pattern drawn thereon is mounted, and
2
denotes a projection optical system for projecting the pattern on the reticle to a wafer. Numeral
3
denotes a wafer stage which mounts the wafer on it and is driven to rotate in directions of X, Y, Z, &thgr; and tilt. Numeral
4
denotes an illumination optical system for irradiating illumination light to the reticle, and
5
denotes a guiding optical system for introducing light from a light source to the illumination optical system
4
. Numeral
6
denotes a fluorine (F
2
) excimer laser unit as the light source, and
7
denotes a masking blade for blocking off the exposure light so that only a pattern area on the reticle is illuminated. Numerals
8
and
9
denote housings provided respectively around the reticle stage
1
and the wafer stage
3
to enclose an axis of the exposure light. Numeral
10
denotes a He gas conditioner for adjusting atmospheres in the projection optical system
2
and the illumination optical system
4
to a predetermined He atmosphere. Numerals
11
and
12
denote N
2
gas conditioners for adjusting atmospheres in the housings
8
and
9
, respectively, to predetermined N
2
atmospheres. Numerals
13
and
14
respectively denote a reticle load lock and a wafer load lock used when carrying the reticle and the wafer into the housings
8
and
9
. Numerals
15
and
16
respectively denote a reticle hand and a wafer hand for carrying the reticle and the wafer. Numeral
17
denotes a reticle alignment mark used for adjusting the reticle position,
18
denotes a reticle storage device for storing a plurality of reticles in the housing
8
, and
19
denotes a pre-alignment unit for making pre-alignment of the wafer. Further, if necessary, the entirety of the exposure apparatus is placed in an environment chamber (not shown), and the temperature in the environment chamber is controlled to be kept constant by circulating air controlled at a predetermined temperature in the environment chamber.
FIG. 15
is a schematic sectional view showing another example of a semiconductor exposure apparatus which employs a fluorine (F
2
) excimer laser as a light source and includes load lock mechanisms.
In the example of
FIG. 15
, a housing
20
covers the entirety of the exposure apparatus, and O
2
and H
2
O present in the housing
20
are purged out with an N
2
gas. Numeral
21
denotes an N
2
gas conditioner for establishing an N
2
gas atmosphere in the entire inner space of the housing
20
. In this exposure apparatus, inner s
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Henry Hung
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