Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
1999-05-11
2001-09-04
Ponomarenko, Nicholas (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
C414S935000
Reexamination Certificate
active
06285097
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electric motors and more particularly to high precision electric motors having transverse magnets for use in lithography systems.
BACKGROUND OF THE INVENTION
Electric motors are used in a variety of electrical equipment. For example, wafer stages also utilize linear or planar electric motors to position a wafer during photolithography and other semiconductor processing.
A typical one-dimensional linear electric motor has a magnet track with pairs of opposing magnets facing each other. An armature is disposed in a space defined between the pairs of opposing magnets. The space extends along a direction along which the armature may move. The armature has windings of a conductor which, upon application of an electrical current, the electric current interacts with the magnetic fields of the magnet pairs to exert force on the armature, causing the armature to move. The armature moves along the length of the space. When the armature is attached to a wafer stage, the wafer stage experiences the same force as and moves in concert with the armature.
Two-dimensional planar electric motors are utilized in semiconductor manufacturing. For example, U.S. Pat. No. 4,654,571, entitled “Single Plane Orthogonally Moveable Drive System,” to Hinds and U.S. Pat. No. 4,535,278, entitled “Two-Dimensional Precise Positioning Device for Use in a Semiconductor Manufacturing Apparatus,” to Asakawa discuss two-dimensional electric motors and are incorporated herein by reference in their entireties. The two-dimensional motors have two-dimensional arrays of magnets and an armature or an array of coils movable relative to each other in two or more directions rather than magnet tracks having a space along which an armature moves along a single direction. The magnet array and the armature may move relative to each other in more than two dimensions depending upon the design. Conventional two-dimensional motors typically have an array of magnets and an armature having one or more coils disposed on one side of the array of magnets.
U.S. Pat. No. 5,623,853, entitled “Precision Motion Stage with Single Guide Beam and Follower Stage,” to Novak et al. and U.S. Pat. No. 5,528,118, entitled “Guideless Stage With Isolated Reaction Stage,” to Lee discuss examples of semiconductor fabrication equipment and are incorporated herein by reference in their entireties.
A platform may be attached to a two-dimensional motor and the platform can be moved in two or more dimensions by the motor. For example, a wafer stage in semiconductor processing equipment may be attached to an armature or a magnet array of a two-dimensional electric motor and the two-dimensional motor would control positioning of the wafer stage.
One problem with conventional magnet arrays is their relatively low magnetic flux to mass ratio. Without a backing by a magnetically permeable material, the magnetic flux is relatively low. A magnetically permeable backing facilitates the completion of magnetic flux paths between magnets having opposite polarities. The magnetic flux of the magnet array is greater when the flux paths are completed by the magnetically permeable backing. However, magnetically permeable backing, such as iron, are relatively heavy and decreases the magnetic flux to mass ratio of the magnet array. If the flux paths between the magnets of opposite polarities could still be completed without the use of a heavy magnetically permeable backing, the magnetic flux to mass ratio would be improved. For electric motors having a moving magnet array and a stationary coil array rather than a moving coil array and a stationary magnet array, this reduction in mass would improve the efficiency of the electric motor.
There is, therefore, a need for a compact motor which provides high speed and precision and energy efficient operation.
SUMMARY OF THE INVENTION
The present invention comprises a magnet array having a plurality of N and S magnets and transverse magnets disposed in a plane. The N and S magnets have opposing polarities substantially perpendicular to the plane and the transverse magnets have a polarity substantially parallel to the plane. The N and S magnets of the magnet array are arranged in a checkerboard pattern in the plane and the transverse magnets are disposed between immediate adjacent N and S magnets. The transverse magnets facilitate the forming of a continuous magnetic flux path through the transverse magnet and immediate adjacent N and S magnets.
The N and S magnets are periodically and alternately arranged along two orthogonal directions in the plane. In one embodiment, the N and S magnets are alternately disposed along two orthogonal edges of the magnet array. In another embodiment, the N and S magnets are alternately disposed along a diagonal of the array.
The magnet array preferably includes corner magnets at the corners of the array, non-corner edge magnets disposed along the edges of the array as well as interior magnets disposed interior of the corner and edge magnets. The interior magnets comprise N, S and transverse magnets. The edge magnets may comprise only N magnets, only S magnets or N, S and transverse magnets. The corner magnets comprises either N or S magnets. In one embodiment, the N and S edge magnets are alternately arranged in a periodic manner along the edges and corners of the magnet array and transverse edge magnets are disposed between immediate adjacent N and S edge magnets.
Each of the N and S interior magnets may have approximately equal magnetic flux. Each transverse interior magnet preferably has a magnetic flux less than the magnetic flux of the interior N and S magnets. For example, the magnetic flux of each transverse magnet may be approximately one-half of the magnetic flux of the interior N and S magnets.
Each edge magnet has a magnetic flux less than the magnetic flux of a corresponding N, S or transverse interior magnet. For example, an S edge magnet has less magnetic flux than an S interior magnet or a transverse edge magnet has less magnetic flux than a transverse interior magnet. In addition, each corner magnet has a magnetic flux less than the magnetic flux of a corresponding N or S interior magnet. In one embodiment, each edge magnet has approximately one-half the magnetic flux of the corresponding interior magnet and each corner magnet has one-quarter the magnetic flux of the corresponding interior magnet.
In another embodiment of the magnet array of the present invention, each N and S magnet may comprise two or more component magnets each having a polarity at an angle relative to the resultant N or S polarities. However, this increases the manufacturing complexity and thus increases the cost of the magnet array.
The magnet array of the present invention may be utilized in an electric motor or a positioning device comprising a coil array positioned adjacent to a magnet array. The coil array is operable by suitable application of current to interact with the magnetic fields of the magnet array to provide a force between the coil array and the magnet array. The force between the coil array and the magnet array causes the coil array and the magnet array to move relative to each other.
The magnet array may also be utilized in an exposure apparatus such as a photolithography system. The exposure apparatus comprises an optical system for imaging a pattern onto an article, and a stage device for positioning the article relative to the optical system. The stage device may include an electric motor and a stage movable relative to the optical system and having a surface for supporting the article. As described above, an electric motor comprises a magnet array and a coil array. Either the magnet array or the coil array is stationary and attached to a frame of the optical system and the other of the magnet array and the coil array is attached to a surface of the stage for positioning of the article.
The invention's electric motors and positioning devices are useful in environments requiring precise and wide ranges of positioning. In particular
Gery Jean-Marc
Hazelton Andrew J.
Jones Judson H.
Morrison & Foerster / LLP
Nikon Corporation
Ponomarenko Nicholas
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