Exposure apparatus

Details Exposure apparatus Exposure apparatus

2000-12-26

2003-04-22

Nguyen, Hung Henry (Department: 2851)

Photocopying

Projection printing and copying cameras

Step and repeat

C355S067000

Reexamination Certificate

active

06552774

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an exposure apparatus and method and a device manufacturing method and, more particularly, to an exposure apparatus and method for transferring a pattern onto an object such as a substrate, and a device manufacturing method.
BACKGROUND OF THE INVENTION
An increase in the integration degree of semiconductor devices such as ICs and LSIs has progressed rapidly, and micropatterning techniques for semiconductor wafers have also been developed remarkably. In the projection exposure technique, as the central issue of micropatterning techniques, an improvement in resolution is indispensable and is realized by decreasing the wavelength of exposure light. A laser beam is utilized as short-wavelength exposure light. Because the laser beam has a high coherence, while it passes through an illumination optical system, interference occurs to form interference fringes called a speckle pattern, leading to nonuniform exposure.
For this reason, in order to decrease the contrast of the interference fringes, a projection optical system utilizing a laser beam has an optical member within its illumination optical system to deflect a beam. Exposure is performed while changing the phase of the interference fringes in units of pulses of the laser beam by moving this optical member during exposure. This levels off the influence of the interference fringes, so that the illumination distribution within the shot region is made uniform to decrease nonuniform exposure. Above all, a method of rotating a wedge prism about an optical axis as the center is effective, and has thus been put into practical use.
As the exposure light, light from an i-line (&lgr;=365 nm), a KrF excimer laser (&lgr;−248 nm), and the like has been put into practical use, and a projection exposure apparatus using an ArF excimer laser (&lgr;=193 nm) as the light source has also been developed. Such short-wavelength exposure light is obtained in, e.g., an exposure apparatus utilizing an i-line, by using a filter for transmitting only a beam with a desired wavelength from beams within a wide wavelength band emitted from a mercury lamp as a light source, or a wavelength-selective thin film (an optical thin film deposited on the surface of a lens or mirror to transmit or reflect only a beam with a desire wavelength). These days, as the throughput increases and the pattern line width decreases, exposure light with a higher power is required, and a decrease in band of the exposure light is required.
In the exposure apparatus utilizing an i-line (wavelength &lgr;=365 nm) and an exposure apparatus utilizing exposure light with a wavelength shorter than that of the i-line, due to a decrease in wavelength, exposure light is known to cause impurities in air to photochemically react with oxygen. The reaction product (fogging material) produced by this reaction attaches to a glass member to make it opaque or fogged.
A typical example of materials that cause fogging is ammonium sulfate (NH
4
)
2
SO
4
. For example, ammonium sulfate (NH
4
)
2
SO
4
is generated when sulfur dioxide SO
2
, excited upon absorption of light energy, reacts (is oxidized) with oxygen in air. Ammonium sulfate is whitish, and fogs an optical member such as a lens or mirror upon attaching to its surface.
Exposure light is scattered and absorbed by ammonium sulfate, so the transmittance of the optical member decreases. In particular, when exposure light, such as a KrF excimer laser, in a short wavelength range of 248 nm shorter than that of the i-line, or less is utilized, the exposure light causes a stronger photochemical reaction. This not only fogs the optical member but also generates ozone out of oxygen in air. Ozone has a nature of absorbing exposure light together with the remaining oxygen. For this reason, the exposure light decreases its light amount before it reaches a photosensitive substrate. In order to compensate for this, the exposure time must be prolonged, resulting in a small throughput.
In one technique proposed in view of the foregoing, a lens barrel, in which a glass member such as a lens is placed, is arranged in a housing with a sealed structure, and the housing and lens barrel are filled with an inert gas. This maintains the oxygen concentration low to prevent generation of ozone (Japanese Patent Application No. 6-216000). According to this technique, a flow path for flowing the inert gas into the housing and lens barrel is provided, so the oxygen concentration in the space where the glass member is arranged remains low. Accordingly, an oxidizing reaction in the photochemical reaction process is prevented, generation of a material that causes fogging is suppressed, and fogging of the optical member is prevented. Also, generation of ozone from oxygen by the exposure light is prevented effectively.
However, even in the illumination optical system with the structure as described above, optical elements in its house and lens barrel can be contaminated by organic molecules. These molecules are probably generated when chemicals and the like used during manufacture and machining remain in the components that make up the illumination optical system on the component, or an adhesive used in the housing or lens barrel is partly evaporated.
Depending on the situation in the manufacture, for example, the ambient air is contaminated by organic molecules generated from an adhesive layer between the substrate and photoresist, and these molecules may enter the housing or lens barrel. If the organic molecules are present in the housing or lens barrel even only in a low concentration, they can destructively affect the projection lens system. More specifically, the organic molecule particles can be decomposed by the exposure light and then be deposited on the optical element to form a carbon film or a carbon-containing film on their surfaces, to eventually decrease the effective transmittance of the optical elements to a non-allowable degree.
Therefore, dust and unwanted gas sources must be eliminated from the interiors of the housing and lens barrel. Regarding glass components and mechanical parts, cutting oil and the like used for machining them must be eliminated or washed off completely.
As a mechanism for rotating the wedge prism which decreases the adverse influence of the interference fringes, ball bearings, a stepping motor, a DC motor, an AC motor, and the like have conventionally been used. With these ball bearings and motors, the structural members produce friction and therefore require lubricant oil or the like. When the bearing and the motors are arranged in the lens barrel of the illumination system, it generates dust by friction, or unwanted gas from the lubricant oil or the like in the housing. Also, since the motor and a driving power transmitting mechanism projects outside the housing, the entire apparatus cannot be downsized and the housing cannot be hermetically sealed.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above situation, and has as its main object to decrease the adverse influence of interference fringes formed by exposure light while suppressing dust and unwanted gases.
It is a subsidiary object of the present invention to suppress an increase in the size of an exposure apparatus when a mechanism for decreasing the adverse influence of the interference fringes is provided.
According to the first aspect of the present invention, there is provided an exposure apparatus for transferring a pattern onto an object, comprising an optical member constituting part of an optical system arranged between a light source and the object, a moving body which moves while supporting the optical member, a non-contact bearing for supporting the moving body, and a driving mechanism for moving the moving body together with the optical member.
According to a preferable embodiment of the present invention, the optical member includes an optical element for changing a phase of interference fringes formed on the object with exposure light.
According to a pre

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