Method for controlling the position of a movable object, a positioning system, and a lithographic apparatus

#The present invention relates to a method for controlling the position of a movable object and a positioning system for a lithographic apparatus. More particularly, the present invention relates to a method and a positioning system for controlling a short stroke module of a substrate stage or reticle stage of a lithographic apparatus.

#A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”—direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

#The known lithographic apparatus includes a number of movable objects, which have to be actuated with relatively large accelerations and high accuracy. An example of such moveable object is a wafer stage, which supports a wafer during the projection process. Such wafer stage may include a long stroke module and a short stroke module. The long stroke module supports the short stroke module, while the short stroke module is configured to carry the wafer. The long stroke module is used for coarse positioning of the wafer stage, while the short stroke module is used for fine positioning of the wafer with respect to the projection system. In the known lithographic apparatus, a Lorentz motor is used for the actuation of the short stroke module. Such Lorentz motor is known to be a very accurate motor with which the short stroke module can be placed with high accuracy in the correct position. However, Lorentz motors are not highly efficient and a relatively large amount of heat is dissipated during the use of the motor. Such dissipation of heat is in generally undesirable, in particular when large forces have to be produced by the motor during acceleration of the short stroke module. The generated heat may have a negative influence on the control accuracy of the Lorentz motor and on the performance of other systems in the lithographic apparatus.

#Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

#FIG. 1 depicts a lithographic apparatus according to an embodiment of the invention;

#FIG. 2 depicts schematically a wafer stage including a positioning system according to an embodiment of the invention; and

#FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or other radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W.

#The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

#The support structure supports, i.e. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”