Gas bearing, and lithographic apparatus provided with such a bearing

A gas bearing has a first bearing part defining a first bearing surface and a second bearing part defining a second bearing surface. Between the first bearing surface and the second bearing surface there is a gap. A gas supply device supplies a gas to the gap. The first bearing part is at least partly ferromagnetic, and the second bearing part has at least one permanent magnet interacting with the first bearing part for pre-tensioning the gas bearing. The gas bearing may be part of a lithographic apparatus.

BACKGROUND

1. Field of the Invention

The present invention relates to a gas bearing, and to a lithographic apparatus provided with such a bearing.

2. Description of the Related Art

A lithographic apparatus contains a large number of moving parts, where a relatively large mass is moved at high speed and at a high accuracy to a specific position, possibly with a predetermined setpoint profile of the movement. The moving part is to be moved relative to a frame part, which frame part may be movable in turn relative to another frame part. As an example, reference is made to a substrate stage having a substrate support which carries a substrate. The dimensions of a substrate may be considerable, and hence the dimensions and weight of the substrate support are considerable.

In order to ensure a smooth movement of the moving part with a required change in position over time, and with a required accuracy, the moving part is supported by gas bearings relative its associated frame part. A gas bearing includes two surfaces which are highly complementary to each other. The surfaces usually are flat and straight, but they may also be curved, or e.g. V-shaped when viewed in cross-section. Between the surfaces, a gas film is maintained allowing a virtually frictionless movement of the moving part relative to the associated frame part.

In the prior art, a gas bearing assembly composed of one or more gas bearing parts connected to each other and to a magnet plate to be movable relative to a ferromagnetic frame part has been used. The magnet plate includes permanent magnets, drawing the gas bearing parts towards the frame part. Thus, a pre-tensioned or pre-loaded gas bearing is obtained. However, the surface area on the frame part needed for such a gas bearing assembly is relatively large, since it includes the combined surface area of the gas bearing parts and the magnet plate. A further drawback is the stiffness needed for the gas bearing assembly, resulting in a relatively bulky structure, adding mass to the moving part.

SUMMARY

It is desirable to provide a pre-tensioned or pre-loaded gas bearing of small dimensions.

According to an embodiment of the present invention, there is provided a gas bearing, including: a first bearing part defining a first bearing surface; a second bearing part defining a second bearing surface; a gap between the first bearing surface and the second bearing surface; and a gas supply device to supply a gas to the gap, wherein the first bearing part includes a ferromagnetic material, and the second bearing part includes at least one permanent magnet interacting with the ferromagnetic material of the first bearing part.

According to another embodiment of the present invention, there is provided a lithographic apparatus arranged to transfer a pattern from a patterning device onto a substrate, the apparatus having at least one gas bearing, the gas bearing including: a first bearing part defining a first bearing surface; a second bearing part defining a second bearing surface; a gap between the first bearing surface and the second bearing surface; and a gas supply device to supply a gas to the gap, wherein the first bearing part includes a ferromagnetic material, and the second bearing part includes at least one permanent magnet interacting with the ferromagnetic material of the first bearing part.

According to another embodiment of the present invention, there is provided a lithographic apparatus including: an illumination system configured to condition a radiation beam; a patterning support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate support constructed to support a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, wherein at least one of the patterning support and the substrate support includes a gas bearing, the gas bearing including: a first bearing part defining a first bearing surface; a second bearing part defining a second bearing surface; a gap between the first bearing surface and the second bearing surface; and a gas supply device to supply a gas to the gap, wherein the first bearing part includes a ferromagnetic material, and the second bearing part includes at least one permanent magnet interacting with the ferromagnetic material of the first bearing part.

In an embodiment of the invention, there is provided a gas bearing including a first bearing part defining a first bearing surface, the first bearing part including a ferromagnetic material, a second bearing part defining a second bearing surface, the second bearing part including a frame that is adapted to receive at least one permanent magnet; and a gas supply device configured to supply gas to a gap that extends between the first bearing surface and the second bearing surface, wherein the at least one permanent magnet of the second bearing part interacts with the ferromagnetic material of the first bearing part through a portion of the frame to reduce the gap.

In another embodiment of the invention, there is provided a method of moving a first part relative to a second part, the first part defining a first bearing surface and including a ferromagnetic material, and the second bearing part including a frame that is adapted to receive at least one permanent magnet, the method including providing a flow of gas in a gap between the first bearing surface and the second bearing surface; and creating a magnetic interaction between the at least one permanent magnet of the first bearing part and the ferromagnetic material of the second bearing part through a portion of the frame so as to reduce the gap.

In an embodiment, there is provided a gas bearing, including a first bearing part defining a first bearing surface, the first bearing part including a ferromagnetic material; a second bearing part defining a second bearing surface, the second bearing part including a frame that is adapted to receive at least one permanent magnet; and a gas supply device configured to supply gas to a gap that extends between the first bearing surface and the second bearing surface, wherein the at least one permanent magnet of the second bearing part interacts with the ferromagnetic material of the first bearing part through a portion of the frame to reduce said gap.

In another embodiment, there is provided a method of moving a first part relative to a second part, the first part defining a first bearing surface and including a ferromagnetic material, and the second part defining a second bearing surface and including a frame that is adapted to receive at least one permanent magnet, the method including supplying gas between the first bearing surface and the second bearing surface so as to create a gap between the first bearing surface and the second bearing surface; and creating a magnetic interaction between the at least one permanent magnet of the first part and the ferromagnetic material of the second part through a portion of the frame so as to reduce the gap.

DETAILED DESCRIPTION

The first positioning device PM and the second positioning device PW may include one or more gas bearings according to an embodiment of the invention, as described below in detail with reference, for example, toFIGS. 2,3and/or4. Also other moving components of the lithographic apparatus or other similar apparatus may include one or more gas bearings according to an embodiment the invention.

The lithographic apparatus may be of a type having two (dual stage) or more substrate tables or “substrate supports” (and/or two or more mask tables or “mask supports”). In such “multiple stage” machines the additional tables or supports may be used in parallel, or preparatory steps may be carried out on one or more tables or supports while one or more other tables or supports are being used for exposure.

FIG. 2shows a gas bearing according to an embodiment of the present invention, including a schematically indicated first bearing part2, and a second bearing part4depicted in more detail. The first bearing part2and the second bearing part4are movable relative to each other in any of the directions indicated by the double arrow6, and in other directions if the bearing construction so provides, such as at an angle to the arrow6, or in a rotational sense. When considered relative to a specific frame of reference, the first bearing part2may be stationary while the second bearing part4is movable relative to the first bearing part2. However, when a different frame of reference is considered, the second bearing4part may be stationary while the first bearing part2is movable relative to the second bearing part4. Moreover, when a still different frame of reference is considered, both the first bearing part2and the second bearing part4may be movable relative to the latter frame of reference.

The first bearing part2includes a ferromagnetic material, i.e. is at least partially made from a ferromagnetic material. By way of example, the ferromagnetic material may have been applied as a layer on the first bearing part2, or may have been fixed (i.e. glued, welded, screwed and the like) as a strip or plate on the first bearing part2, in particular at the side of the first bearing part2facing the second bearing part4. The first bearing part2may also be made entirely from a ferromagnetic material.

As shown in FIGS.2,3,4and5, the second bearing part4includes a bottom wall8having a first side10facing away from the first bearing part2, and a second side12facing the first bearing part2. A side14of the first bearing part2facing the second bearing part4forms a first bearing surface, while the second side12of the bottom wall8forms a second bearing surface of the gas bearing.

The second bearing part4is provided with a plurality of permanent magnets20which are each fixed to the bottom wall8through a plurality of bonding areas22. InFIGS. 2 and 4, as an example, three rectangular bonding areas are shown. However, also one, two, or more than three bonding areas, having possibly different shapes, may be used. The bonding area22may include a glue layer.

A permanent magnet20may include a plurality of sub-magnets24, as shown inFIG. 2.FIG. 2shows an embodiment having four sub-magnets24which have alternating directions of magnetization, or magnetic polarization, which may be directed essentially at right angles (i.e. substantially perpendicular) to the sides10,12of the bottom wall8of the second bearing part4, or the plane of the side14of the first bearing part2. Alternatively, as shown by solid arrows inFIG. 4, the direction of magnetization of the sub-magnets24may be inclined to the sides10,12of the bottom wall8of the second bearing part4, or the plane of the side14of the first bearing part2, thus having a non-zero component in a direction substantially parallel to the first or second bearing surface, and having a non-zero component in a direction substantially at right angles (i.e. substantially perpendicular) to the first or second bearing surface. At a side of the permanent magnet20facing away from the first side10of the bottom wall8, the permanent magnet20is provided with a yoke part26made at least partially from a ferromagnetic material.

The permanent magnets20interact with the first bearing part2through magnetic attraction, thus exerting a force acting to reduce a gap between the first bearing surface and the second bearing surface.

The bonding areas22may compensate for any irregularities in the surface of the permanent magnet20(or, the combined surfaces of the sub-magnets24) and the first side10of the bottom wall8facing each other. In this way, any temperature effects due to differences in coefficients of expansion of the bottom wall8and the permanent magnet20may be decreased. Further, by using a plurality of bonding areas22per permanent magnet20, any forces exerted by the permanent magnet20interacting with the first bearing part2are spread evenly over the surface of the bottom wall8.

The second bearing part4includes ribs28of different configurations and partly intersecting each other, supporting the bottom wall8.

A gas is supplied to the gap between the first bearing surface and the second bearing surface from a gas supply device29(known per se, and shown only schematically) through a gas input30and ducts32in the ribs28leading to the second bearing surface, i.e. the second side12of the bottom wall8of the second bearing part4. Instead or additionally, gas may also be supplied to the gap between the first bearing surface and the second bearing surface through ducts provided in the first bearing part2(details not shown in the Figures).

Integration of the permanent magnets20in the gas bearing including the first bearing part2and the second bearing part4provides a pre-tensioned gas bearing with a low surface area and relatively low mass.

The gas bearing includes two surfaces that are highly complementary to each other. Although the surfaces usually are flat and straight as illustrated in the embodiment above, they may also be curved, or e.g. V-shaped when viewed in cross-section.

The gas bearing may be used in a lithographic apparatus as described above with reference toFIG. 1, or any other type of lithographic apparatus. The gas bearing also finds an application in other types of apparatus using a gas bearing.

In the gas bearing according to an embodiment of the invention, any suitable gas, such as air or nitrogen gas, but not limited thereto, may be used.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as including (i.e., open language).

The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope and spirit of the claims set out below.