Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
2002-12-03
2004-04-27
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S030000, C355S067000
Reexamination Certificate
active
06727981
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illuminating optical apparatus and the making method thereof, an exposure apparatus and the making method thereof, and device manufacturing method. More specifically, the invention relates to an illuminating optical apparatus suitable for application to an exposure apparatus used in a lithographic process for manufacturing semiconductor devices or liquid crystal display devices (liquid crystal devices) and the making method of the optical apparatus, an exposure apparatus comprising this illuminating optical apparatus and a making method of the exposure apparatus, and a manufacturing method of devices using this exposure apparatus in the lithographic process. The illuminating optical apparatus of the invention is suitable for illuminating an object by the use of an energy beam having a short wavelength, for example, not longer than 300 nm.
2. Description of the Related Art
When forming fine patterns on electronic devices such as semiconductor devices (such as integrated circuits) and liquid crystal displays, conventionally, the patterns to be formed were proportionally enlarged four to five times on a photomask or a reticle (hereinafter collectively referred to as a “reticle”), and then transferred onto a substrate to be exposed such as a wafer. The exposure was performed, in reduced magnification, with a reduction projection exposure apparatus such as a stepper.
With the projection exposure apparatus used for transferring such a pattern, the exposure wavelength has shifted to a smaller wavelength to cope with the tendency toward finer semiconductor integrated circuits. Currently, a wavelength of 248 nm in a KrF excimer laser is widely used, and the use of a shorter wavelength of 193 nm in an ArF excimer laser is becoming practical. Projection exposure apparatus employing a shorter wavelength of 157 nm in a F
2
laser and 126 nm in an Ar
2
laser are now being proposed.
Light with the wavelength from 120 to 200 nm is a vacuum ultraviolet light beam. Since a light flux within this wavelength band is poor in transmittance through an optical glass, materials for lenses and reticles capable of being used in a VUV exposure apparatus using vacuum ultraviolet (VUV) light for exposure are limited to crystals of fluorite, magnesium fluoride and lithium fluoride. Also, energy absorption by oxygen, water vapor or hydrocarbon gas (hereinafter from time to time referred to as “absorptive gases”) is extremely large. Therefore, it becomes necessary to alter the gas in the optical path portion with a gas which energy absorption of the exposure light is smaller (low-absorptive gas) in order to exclude oxygen from the optical path.
The amount of vacuum ultraviolet light beams absorbed by oxygen gas is very large. In order to avoid absorption by oxygen, therefore, it is necessary to limit the concentration of oxygen gas in the optical path so that it does not exceed 1 ppm of the average concentration of oxygen gas in the optical path. Particularly, in the illuminating optical system where the light illuminated from the light source proceeds to the reticle through the optical system, the total distance of the optical path is long, so the concentration of oxygen is required to be limited to a smaller value than described above.
FIG. 10
schematically illustrates an example of the illuminating optical system (illuminating optical unit) which configures a conventional exposure apparatus using an excimer laser beam.
This illuminating optical system shown in
FIG. 10
comprises a first fly-eye lens system
202
, a folded mirror
204
, a second fly-eye lens system
206
, an illuminating system diaphragm plate (diaphragm revolver)
208
, a first relay lens system
210
, a reticle blind
212
, a second relay lens system
214
, a folded mirror
216
, and a condenser lens
218
, sequentially arranged along the optical path of the exposure light in a predetermined positional relationship. The first fly-eye lens system
202
and the illuminating system diaphragm plate
208
are rotatably-driven by actuators
220
and
222
. Movable blinds configuring the first relay lens system
210
and the reticle blind
212
are driven by actuators
224
and
226
, respectively in predetermined directions. Sensors S
1
, S
2
, S
3
and S
4
for detecting the position or displacement are respectively provided on these movable portions. In this illuminating optical system, the above-mentioned optical members, the actuators and the sensors are in general, covered with a cover
230
, and the interiors were purged with nitrogen (N
2
) gas, one of low-absorptive gases.
In this conventional illuminating optical system, the optical members configuring the illuminating optical system, the actuators, and the sensors are covered with a cover, therefore, the actuators and the sensors are located in the same space as the lenses and the mirrors. Consequently, adhesives, sealers and paints used for the actuators and the sensors, and gases emitted from these component members themselves have become the cause of chemical pollution sources of the optical devices such as lenses and mirrors.
In the above-mentioned conventional illuminating optical system, the shape of the cover has caused difficulty to completely cut off the air in the cover interior from open air outside the cover, and has allowed the chemically polluted open air containing oxygen to be mixed with the cover interior. This causes the problem of absorption of the illuminating light by the ozone generated from oxygen or photochemical reactions between oxygen and the illuminating light. Also, chemical pollution decreases the transmittance of the lenses and reflectivity of the mirrors, due to clouding substances adhered and deposited on the surfaces of the optical elements.
With an exposure apparatus, all these cases have caused a decrease in exposure accuracy resulting from a shortage in the amount of exposure light irradiated onto the wafer.
In the lithographic process for manufacturing semiconductor devices, conventionally, a stationary type exposure apparatus such as a reduction projection exposure apparatus (known as a stepper) employing a step-and-repeat method has been mainstream. However, along with the recent tendency toward a higher degree of integration of semiconductor devices and a larger wafer size, the scanning exposure apparatus employing a so-called slit scanning method and the step-and-scan method are becoming more popular. With these apparatus, a rectangular or arcuated illuminating areas on a reticle having a pattern formed are illuminated with an illuminating light, and the reticle and substrate such as a wafer are synchronously moved in a linear direction, thereby sequentially transferring the pattern onto the substrate.
With this apparatus, a movable blade (also called a “movable blind”) is arranged for limiting the illuminating area on the reticle so as to avoid unnecessary exposure of a portion outside the pattern area on the reticle during exposure. This blind is a movable member, which moves during exposure. It has been arranged in the illuminating optical system, which illuminates the reticle R by an illuminating light from a light source, and is driven synchronously with the reticle during exposure (refer to Japan Patent Laid Open No. 04-196513 and the corresponding U.S. Pat. No. 5,473,410).
Semiconductor devices are formed, by depositing multiple layers of circuit patterns with respect to one another in a predetermined positional relationship onto a wafer. For this reason, in an exposure apparatus used for manufacturing semiconductor devices or the like, it is necessary to accurately overlay the patterns formed on the reticle and conduct transferring.
In the conventional scanning type exposure apparatus, however, as described above, in the illuminating optical system the movable member is arranged and moves during exposure, causing vibration in the illuminating optical system. This, in turn, causes an adverse effect on the main portion of the exposure apparatus
Nakamura Kyoji
Ohya Eizo
Taniuchi Taichi
Yoshimoto Hiromitsu
Adams Russell
Esplin D. Ben
Nikon Corporation
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