Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Reexamination Certificate
1999-07-15
2002-01-08
Anderson, Bruce (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
C250S492200, C250S453110, C355S053000, C355S072000, C355S075000
Reexamination Certificate
active
06337484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a positioning device, and more particularly to such a device included in a lithographic projection apparatus.
2. Description 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 projection system may 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 that 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.
Lithographic apparatuses may employ various types of projection radiation, such as ultra-violet light (UV), extreme UV, X-rays, ion beams or electron beams, for example. Depending on the type of radiation used and the particular design requirements of the apparatus, the projection system may be refractive, reflective or catadioptric, for example, and may comprise vitreous components, grazing-incidence mirrors, selective multi-layer coatings, magnetic and/or electrostatic field lenses, etc. The apparatus may comprise components that are operated in vacuum, and are correspondingly vacuum-compatible. As mentioned above, the apparatus may have more than one substrate table and/or mask table.
A positioning device using Lorentz-motors is known from EP-B-0 342 639. The first part of the known positioning device comprises a slide that, by means of a system of servomotors, can be displaced with relatively low accuracy over relatively large distances in the X- and Y-directions. The second part comprises a substrate holder that, by means of a system of Lorentz-force motors, can be displaced relative to the first part with relatively high accuracy over relatively small distances with six mutually independent degrees of freedom. By using the system of Lorentz-force motors, mechanical contacts between the first part and the second part, and transmission of mechanical vibrations from the first part to the second part, are limited. This results in a high positioning accuracy of the known positioning device. An embodiment of the known positioning device comprises a further system of permanent magnets which exerts a supporting force on the second part in a direction parallel to the vertical Z-direction. This avoids the need to support the second part in the vertical Z-direction by Lorentz forces generated by the system of Lorentz-force motors, which would lead to a high energy dissipation in the coils of the Lorentz-force motors. Consequently, the Lorentz-force motors are used only to generate displacements of the second part, so that the energy dissipation of the electric coils of the Lorentz-force motors is considerably reduced.
A drawback of the known positioning device is that the magnitude of the supporting force of the further system of permanent magnets changes substantially if the distance between the first part and the second part changes in the Z-direction, so that the further system of permanent magnets has a substantial magnetic stiffness in the Z-direction. As a result of this stiffness, a mass spring system formed by the further system of permanent magnets and the displaceable mass of the second part exhibits a rather high natural frequency in the Z-direction, resulting in a substantial transmission of mechanical vibrations from the first part to the second part. This adversely affects the positioning accuracy of the known positioning device.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a positioning device in which the above-described drawback of the known positioning device is alleviated.
The present invention relates to a positioning device comprising a first part and a second part that is displaceable relative to the first part by means of a system of Lorentz-force motors. More particularly, the invention relates to such a device comprised in a lithographic projection apparatus comprising a radiation system for supplying a projection beam of radiation; a first movable object table provided with a mask holder for holding a mask; a second movable 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.
According to the present invention, there is provided: a positioning device comprising a first part and a second part which is displaceable relative to the first part by means of a system of Lorentz-force motors, characterized in that, relative to the first part, the second part is supported in a Z-direction by means of at least one gas cylinder, said gas cylinder comprising a housing having a pressure chamber, which housing is coupled to the first part; and a piston which is coupled to the second part and which can be displaced in the pressure chamber in the Z-direction, said piston being journaled relative to said housing at right angles to the Z-direction.
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 second part is supported relative to the first part by a pneumatic supporting force that is determined by gas pressure present in the pressure chamber. By a suitable choice of supply pressure and area of the piston, it is achieved that the pneumatic supporting force of the gas cylinder remains substantially constant when the piston is moved in the Z-direction. Since the piston is journaled perpendicularly to the Z-direction relative to the housing of the gas cylinder, e.g. by means of a static gas bearing, the piston can be displaced in the Z-direction substantially without friction, so that the relatively constant supporting force of the gas cylinder is substantially uninfluenced by the frictional forces of the static gas bearing exerted on the piston.
In the invention, the gas cylinder, acting as a gravi
Bouwer Adrianus Gerardus
Janssen Henricus W. A.
Loopstra Erik Roelof
Van Der Schoot Harmen Klaas
Anderson Bruce
ASM Lithography B.V.
Pillsbury & Winthrop LLP
Wells Nikita
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