Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
2001-09-05
2004-03-30
Ponomarenko, Nicholas (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
C318S135000, C355S053000, C355S072000
Reexamination Certificate
active
06713900
ABSTRACT:
FIELD
This disclosure pertains to stages and the like as used in charged-particle-beam (CPB) lithographic-exposure systems such as “direct-drawing” and “projection” exposure systems. CPB direct-drawing systems are used mainly for, e.g., manufacturing masks and reticles as used in optical and CPB microlithography apparatus and methods. CPB projection exposure systems are any of various CPB microlithography apparatus used principally in the manufacture of microelectronic devices such as integrated circuits, displays, thin-film magnetic heads, and micromachines.
BACKGROUND
Charged-particle-beam (CPB) direct-drawing lithography systems literally draw a pattern using a charged particle beam such as an electron beam. These systems, and their associated methods, are used mainly for drawing a pattern to be defined on a mask or reticle (generally termed a “reticle” herein). CPB projection-lithography systems project an image of a pattern, defined on a reticle, onto a substrate (e.g., semiconductor wafer) that has been “sensitized” so as to be imprintable with the image. In both general types of lithography systems, one or more stages are used to hold and controllably move the substrate and, if one is used, the reticle. Specifically (e.g., in a CPB projection-lithography system), a “reticle stage” supports and moves a reticle, and a “wafer stage” supports and moves a substrate. Each such stage is generally termed a “stage.”
Various approaches have been considered for driving a stage. In a conventional CPB direct-drawing system, a common approach involves driving the stage using a motor connected to the stage using a mechanical power-transfer mechanism such as a ball screw for transforming rotational motion of the motor into linear motion of the stage. Unfortunately, power-transfer mechanisms such as ball screws capable of achieving finely controlled motion of the stage actually are quite complex and disadvantageously generate fine dust particles that contaminate the reticle or substrate held by the stage.
To counter the problem posed by motors and ball screws, the use of gas-based actuators, such as air cylinders, has been proposed. Modern CPB lithographic-exposure systems, however, must be capable of accurately transferring pattern elements that are only 100 nm wide or less, with satisfactorily high throughput, operating speed, and accuracy of establishing and maintaining stage position. Gas-based actuators simply are incapable of meeting these requirements.
In response to the need for better stage actuators, actuators based on linear motors have come recently into use. Linear motors that contain permanent magnets, however, have a problem in that the charged particle beam is adversely affected by the magnetic field generated by the permanent magnets. If the lithography system is to be used for forming a 100-nm linewidth pattern on a wafer or other substrate at high throughput, the effects of the magnetic field generated by the permanent magnets in the linear motor cannot be ignored.
Two types of linear motors are in current use. In a moving-coil (MC) linear motor, the permanent magnet is provided on the “stator” side, and a coil is provided on the “armature” or “moving member” side. In a moving-magnet (MM) linear motor, the permanent magnet is provided on the moving member side, and a coil is provided on the stator side.
Of these two types of linear motors, in the MC type, the magnetic field created by the permanent magnet remains constant. During an actual lithographic exposure, no current flows in the coil. The coil either does not generate a magnetic field, or generates a magnetic field that is exceedingly small compared with the magnetic field generated by the permanent magnet. Hence, it is relatively simple to compensate for the effects on a CPB optical system of the magnetic field generated by the linear motor. Nevertheless, to facilitate compensation, it is desirable to reduce the magnetic field generated by the linear motor, especially in the vicinity of the optical axis of the CPB optical system.
MC-type linear motors also are disadvantageous because the coils (which generate heat during operation and require cooling) are difficult to cool. I.e., a coil located on a moving component requires that the coolant be supplied to the coil via a flexible conduit. The necessary flexibility of the conduit results in unstable positional control of the linear motor. For these reasons, it more desirable to use an MM-type linear motor for stage movement.
MM-type linear motors have a drawback in that the magnetic field generated by the permanent magnet, as experienced at the optical axis, changes with movement of the stage. This change in the magnetic field can cause problems with controlling the charged particle beam propagating through the CPB optical system. Correcting this problem at the CPB optical system requires a changing magnitude of correction, depending upon stage position, which is essentially impossible to accomplish.
SUMMARY
In view of the shortcomings of conventional apparatus and methods as summarized above, an object of the present claims is to provide a stage for a charged-particle-beam CPB exposure system, wherein any impact of the magnetic field generated by a stage-driving linear motor on the CPB optical system is minimized.
To such end, stage assemblies are provided for CPB lithographic-exposure systems. An embodiment of such an assembly comprises a stage configured for holding a reticle or substrate. The stage extends in an X-Y plane perpendicular to an optical axis that is parallel to a Z axis. The assembly also includes a linear motor operatively coupled to the stage and configured for moving the stage in the X-Y plane. The linear motor comprises a permanent magnet split into multiple permanent-magnet subunits arranged symmetrically with respect to a plane that is perpendicular to the X-Y plane. The linear motor can be a moving-coil type or moving-magnet type of linear motor. Also, the first and a second permanent-magnet subunits produce respective first and second magnetic fields that desirably cancel at least a portion of each other at the optical axis.
By splitting the permanent magnet into two or more subunits, each subunit can be disposed farther from the optical axis (i.e., laterally farther from the CPB optical system) than the permanent magnet in a conventional linear motor in a stage assembly. Such a configuration minimizes the impact of the magnetic field generated by the subunits CPB optical system.
A stage assembly according to another embodiment comprises a stage as summarized above. The stage assembly also includes a moving-coil type of linear motor operatively coupled to the stage. The linear motor comprises first and second linear-motor portions that are disposed in respective positions that are symmetric with respect to a plane including the optical axis and extending perpendicularly to the X-Y plane and parallel to the movement direction of the stage. Each linear-motor portion comprises a respective permanent magnet split into multiple respective magnet subunits, wherein the magnet subunits of the first linear-motor portion are disposed relative to the magnet subunits of the second linear-motor portion in a point-symmetrical manner with respect to a point at which the X-Y plane intersects the optical axis.
I.e., in a 3-dimensional rectangular coordinate system in which the optical axis is designated as the Z-axis, if the central axis for a linear motor is on the X-Y plane and the linear motor drives the stage in the Y-direction, then the linear-motor portions are disposed in positions that are plane-symmetrical with respect to the Y-Z plane that passes through the optical axis. Because the respective permanent magnets of each linear-motor portion are each split into two or more respective magnet subunits, the magnet subunits of a first linear-motor portion are disposed with respect to the magnet subunits of a second linear-motor portion so as to be point-symmetrical relative to the point (i.e., the origin) at which the X-Y plane containing the resp
Jones Judson H.
Klarquist & Sparkman, LLP
Nikon Corporation
Ponomarenko Nicholas
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