Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2001-05-30
2002-10-29
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S055000, C355S072000, C355S075000, C355S076000, C355S073000, C355S077000, C430S022000, C430S311000, C356S329000, C356S365000, C356S399000
Reexamination Certificate
active
06473161
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a lithographic projection apparatus and more specifically to a lithographic projection apparatus supporting assembly.
2. Background of the 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 projection system may also include elements operating according to any of these principles for directing, shaping or controlling the projection beam, 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.
In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation or particle flux, including, but not limited to, ultraviolet radiation (e.g. at a wavelength of 365 nm, 248 nm, 193 nm, 157 nm or 126 nm), extreme ultraviolet radiation (EUV), X-rays, electrons and ions. Also herein, the invention is described using a reference system of orthogonal X, Y and Z directions and rotation about an axis parallel to the I-direction is denoted Ri. Furthermore, unless the context otherwise requires, the term “vertical” (Z) used herein is intended to refer to the direction normal to the substrate or mask surface, rather than implying any particular orientation of the apparatus. Similarly, the term “horizontal” refers to a direction parallel to the substrate or mask surface, and thus normal to the “vertical” direction.
Lithographic projection apparatus 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 an exposure 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 at once; 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 WO97/33205, for example.
Until very recently, lithographic apparatus contained a single mask table and a single substrate table. However, machines are now becoming available in which there are at least two independently moveable substrate tables; see, for example, the multi-stage apparatus described in International Patent Applications WO98/28665 and WO98/40791. The basic operating principle behind such multi-stage apparatus is that, while a first substrate table is at the exposure position underneath the projection system for exposure of a first substrate located on that table, a second substrate table can run to a loading position, discharge a previously exposed substrate, pick up a new substrate, perform some initial measurements on the new substrate and then stand ready to transfer the new substrate to the exposure position underneath the projection system as soon as exposure of the first substrate is completed; the cycle then repeats. In this manner it is possible to increase substantially the machine throughput, which in turn improves the cost of ownership of the machine. It should be understood that the same principle could be used with just one substrate table which is moved between exposure and measurement positions.
EP-0,973,067-A discloses a supporting assembly for supporting a structure, such as the first or second object table or a reference, or metrology, frame, against gravity. The assembly comprises a piston associated with the supported structure and further comprises a cylindrical housing in which the piston is journalled. Gas bearings are provided in between the housing and the piston for providing a frictionless movement of the piston in its housing. The housing comprises a gas-filled pressure chamber and the gas in the chamber acts on the piston so as to counteract the weight of the supported structure. Gas from the pressure chamber is supplied to the gas bearing and may escape from the pressure chamber through a gap between the piston and its housing.
In the device described in EP-0,973,067-A it may be difficult to keep the pressure in the pressure chamber entirely constant. In practice, the pressure maintained in the pressure chamber will have a time varying component. This time varying, or dynamic component is due largely to the fact that gas is flowing from the pressure chamber to the various gas bearings. This flow induces pressure variations in the pressure chamber superimposed over the nominal static force which the pressure chamber must exert in order to counteract the forces of gravity due to the weight of the supported structure. The variations in chamber pressure due to the fact that gas must be supplied to the gas bearings lead to a dynamic pressure variation which can be seen as noise on the static force. This adversely affects the positioning accuracy of the positioning device.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a lithographic projection apparatus in which the supporting assembly is constructed and arranged such that substantially no gas flows through the pressure chamber when said moveable member is substantially stationary.
The apparatus of the present invention is constructed so that substantially no vibration forces are transmitted between the moveable member and its housing. This may be achieved by making them physically unconnected. However, in this case, there is necessarily a gap between the moveable member and its housing through which gas from the pressure chamber can escape. This is reduced in the present invention by ensuring that substantially no gas flows through the pressure chamber when the moveable member is stationary. This can be achieved in practice by providing a further gas supply to a further pressure chamber adjacent to the pressure chamber and at least partially surrounding the moveable member, in which the pressure is maintained so as to be substantially identical to that in the pressure chamber.
In one embodiment, the pressure chamber is supplied via a pneumatic resistor, which may include a small gap between the moveable member and a wall connecting the pressure chamber with the further pressure chamber. In this embodiment, the gas supply to the pressure chamber is provided from the further pressure chamber and passes through the pneumatic resistor gap.
Preferably, one or more gas bearings are located between the moveable member and its housing or between the moveable member and the supported structure. These gas bearings conveniently may be supplied via the further pressure chamber.
A gas cylinder as here referred to is sometimes also referred to as a (frictionless) pneumatic cylinder. By using the gas cylinder in the manner described above, the moveable member is supported by a constant pneumatic supporting force that is determined by gas pressure present in the pressure chamber. This gas pressure is not adversely influenced by flow
Auer Frank
Cuijpers Martinus Agnes Willem
van Ballegoij Robertus Nicodemus Jacobus
Adams Russell
ASML Netherlands B.V.
Brown Khaled
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