Radiant energy – Irradiation of objects or material
Reexamination Certificate
2000-04-17
2003-08-05
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
C250S492200, C250S492210, C250S492220, C250S492300, C250S440110, C250S441110, C250S442110, C355S053000, C355S072000, C355S076000
Reexamination Certificate
active
06603130
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to bearings for use in vacuum chambers. More particularly, the invention relates to the application of such a device in lithographic projection apparatuses.
2. Discussion of Related Art
For the sake of simplicity, the projection system may hereinafter be referred to as the “lens”; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, catadioptric systems, and charged particle optics, for example. The radiation system may also include elements operating according to any of these principles for directing, shaping or controlling the projection beam of radiation, and such elements may also be referred to below, collectively or singularly, as a “lens”. In addition, the first and second object tables may be referred to as the “mask table” and the “substrate table”, respectively. Further, the lithographic apparatus may be of a type having two or more mask tables and/or two or more substrate tables. In such “multiple stage” devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more stages while one or more other stages are being used for exposures. Twin stage lithographic apparatuses are described in International Patent Applications WO 98/28665 and WO 98/40791, for example.
Lithographic projection apparatuses can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the mask (reticle) may contain a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target area (die) on a substrate (silicon wafer) which has been coated with a layer of photosensitive material (resist). In general, a single wafer will contain a whole network of adjacent dies which are successively irradiated via the reticle, one at a time. In one type of lithographic projection apparatus, each die is irradiated by exposing the entire reticle pattern onto the die in one go; such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus—which is commonly referred to as a step-and-scan apparatus—each die is irradiated by progressively scanning the reticle pattern under the projection beam in a given reference direction (the “scanning” direction) while synchronously scanning the wafer table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally <1), the speed v at which the wafer table is scanned will be a factor M times that at which the reticle table is scanned. More information with regard to lithographic devices as here described can be gleaned from International Patent Application WO 97/33205.
In a lithographic apparatus, the size of features that can be imaged onto the wafer is limited by the wavelength of the projection radiation. To produce integrated circuits with a higher density of devices and hence higher operating speeds, it is desirable to be able to image smaller features. Whilst most current lithographic projection apparatuses employ ultraviolet light generated by mercury lamps or excimer lasers, it has been proposed to use shorter wavelength radiation of around 13 nm. Such radiation is termed extreme ultraviolet (EUV) or soft x-ray, and possible sources include laser plasma sources or synchrotron radiation from electron storage rings. An outline design of a lithographic projection apparatus using synchrotron radiation is described in “Synchrotron radiation sources and condensers for projection x-ray lithography”, J B Murphy et al, Applied Optics Vol. 32 No. 24 pp 6920-6929 (1993).
Other proposed radiation types include electron beams and ion beams. These types of beam share with EUV the requirement that the beam path, including the mask, substrate and optical components, be kept in a high vacuum. This is to prevent absorption and/or scattering of the beam, whereby a total pressure of less than about 10
−6
millibar is typically necessary for such charged particle beams. Wafers can be contaminated, and optical elements for EUV radiation can be spoiled, by the deposition of carbon layers on their surface, which imposes the additional requirement that hydrocarbon partial pressures should generally be kept below 10
−8
or 10
−9
millibar. Otherwise, for apparatuses using EUV radiation, the total vacuum need pressure only be 10
−3
or 10
−4
mbar, which would typically be considered a rough vacuum.
Further information with regard to the use of electron beams in lithography can be gleaned, for example, from U.S. Pat. No. 5,079,122 and U.S. Pat. No. 5,260,151, as well as from EP-A-0 965 888.
Working in such a high vacuum imposes quite onerous conditions on the components that must be put into the vacuum and on the vacuum chamber seals, especially those around any part of the apparatus where a motion must be fed-through to components inside the chamber from the exterior. For components inside the chamber, materials that minimise or eliminate contaminant and total outgassing, i.e. both outgassing from the materials themselves and from gases adsorbed on their surfaces, should be used. It would be very desirable to be able to reduce or circumvent such restrictions.
Bearings in vacuum are a particular problem. Most lubricants are unsuitable for use in high vacuum conditions, particularly when low hydrocarbon partial pressures are required. Unlubricated bearings are known, but are subject to wear and cannot meet the speed of operation and lifetime requirements of lithography apparatuses. It is also difficult with conventional bearings to reduce the bearing gap below about 30 &mgr;m. Such a gap around a motion feed-through into the vacuum chamber would present an unacceptable leak.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved bearing that can be used in a vacuum chamber of a lithographic projection apparatus, e.g. to support a slidable plate sealing an aperture in the vacuum chamber, a member passing through an aperture in the vacuum chamber or a moveable object within the vacuum chamber, and can operate at high speed for a very great number of cycles.
According to the present invention, these and other objects are achieved in a lithographic projection apparatus that has:
a radiation system for supplying a projection beam of radiation;
a first object table provided with a mask holder for holding a mask;
a second object table provided with a substrate holder for holding a substrate; and
a projection system for imaging an irradiated portion of the mask onto a target portion of the substrate, the lithographic projection apparatus has
a vacuum chamber having a wall enclosing at least one of the first and second object tables, the vacuum chamber wall having an aperture therein;
a moveable sealing member for sealing the aperture;
a bearing for bearing the sealing member and maintaining a gap, between the sealing member and the vacuum chamber wall, the bearing including
a gas bearing for providing pressurised gas into the gap thereby to generate forces tending to hold the sealing member away from said vacuum chamber wall; and
an evacuation component spaced apart from the gas bearing for removing the gas from the gap.
Another aspect of the invention provides a lithographic projection apparatus that is:
a radiation system for supplying a projection beam of radiation;
a first object table provided with a mask holder for holding a mask;
a second object table provided with a substrate holder for holding a substrate; and
a projection system for imaging an irradiated portion of the mask onto a target portion of the substrate. The lithographic projection apparatus also has
a vacuum chamber having a wall enclosing at least one of the first and second object tables, the one object table being movable;
a bearing for displaceably bearing the one object table against a bearing surface within the vacuum chamber and maintaining a gap therebetween, the bear
Bisschops Theodorus H. J.
Bouwer Adrianus G.
Driessen Johannes C.
Renkens Michael J. M.
Soemers Hermanus M. J. R.
ASML Netherlands B.V.
Lee John R.
Pillsbury & Winthrop LLP
Vanore David A.
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