Electricity: measuring and testing – Magnetic – Combined
Reexamination Certificate
1999-04-01
2002-11-12
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Combined
C324S262000, C355S053000
Reexamination Certificate
active
06479991
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates generally to a stage system for precisely positioning an article carried thereon. In another aspect, the invention is concerned with an exposure apparatus having such a stage system for positioning a wafer on a reticle, and also with a device manufacturing method using such an exposure apparatus.
FIG. 14
shows an example of a conventional stage system. A guide
52
is fixed on a base, not shown. A stage
51
which is slidably movable along a driving direction is supported by the guide. A workpiece
60
is placed on the stage. There are linear motors disposed on the opposite sides of the stage
51
, for moving the stage in the driving direction. Linear motor stators
53
each comprise six flat coils
56
fixed to a stator frame
57
, and they are fixed to the base, not shown, through fixing members, not shown.
A movable element
54
of the linear motor comprises an integral structure of four-pole magnets
58
, being magnetized in the vertical direction, and yoke plates
55
which are disposed above and below the stator unit and fixed to the stage
51
without contact to the stator element
53
. The six coils
56
are disposed along the driving direction at a pitch 1.5 times the pitch of the magnetic poles. The coil pitch corresponds to a 0.75 period of the basic wave of the magnetic density and, in terms of electric angle, to 270 deg. or −90 deg.
While the relative position of the coils
56
and the magnets
58
is detected by means of a sensor, not shown, coils
56
at positions spaced by 270 deg. or −90 deg. are selected sequentially and electric currents are supplied to them in an appropriate direction, whereby the magnets are driven In the same direction. Although the coil means has six phases in the sense that the coils
56
are interchanged sequentially, the motor comprises a two-phase motor.
In the stage system of the structure described above, an integral structure of yokes and magnets is moved. Therefore, the weight of movable components is large and stage acceleration is slow. Also, there occurs thrust ripple due to the coil interchanging during the driving. This is an external disturbance, disturbing high-precision positioning control.
FIG. 15
shows another example of a conventional stage system. A guide
52
is fixed on a base, not show. A stage
51
which is slidably movable along a driving direction is supported by the guide
52
. A workpiece, not show, is placed on the stage, There are movable magnets
58
disposed on the opposite sides of the stage
51
, and they are held by holding frames
59
. Stators
53
to be associated with these movable magnets
58
each comprise single-phase colis
56
extending throughout the whole stroke of the stage
51
. Each coil
56
is wounded coaxially around an upper yoke
55
a
or a lower yoke
55
b
, extending through the whole stroke.
In order to prevent eddy current resistance to be produced during relative motion of the magnets
58
and yokes
55
, each yoke
55
comprises laminated steel plates as shown in the drawing.
In the structure described above, in response to supply of electric current to the single-phase coil
56
, forces in the same direction and corresponding to the electric current are produced at every location within the stroke. Thus, only application of electric current in a desired direction is necessary. No coil interchanging is necessary throughout the stroke.
Since, however, in the stage system described above, high-speed relative motion between the magnets and yokes causes an eddy current in the yokes which applies a resistive force to the relative motion of the magnets and yokes. If the eddy current resistance is large, a large driving force is necessary for the stage. The yoke may be provided by laminated steel plates to solve this problem. However, assembling such long steel plages is not easy, and also supporting the yoke after assemblage is not easy. It is, therefore, practically difficult to produce a yoke of a complicated shape by use of laminated steel plates. Consequently, the yoke has a large weight.
Further, there is an attraction force caused between the yoke and magnet. If the stoke, that is, the length of the yoke, is large, flexure of the yoke as the magnet comes to the central portion of the stroke becomes large. Also, the flexure changes largely between the moment where the magnet is at the central portion and the moment where it is at an end portion. This excites vibration of the yoke. For these reasons, the yoke should be formed with a sectional area larger than that as required only for passage of the magnetic flux, to thereby reduce the absolute value of flexure. This means a large increase in dimension of the required sectional area. The increase in size of the yoke necessarily leads to an increase of mass of the yoke and, in contrast to reduction in weight of movable components, the stator becomes very heavy. Finally, when an X-Y stage mechanism is provided by a simple two-level structure, the movable stage must include a portion, having such a very heavy yoke, and a large acceleration is difficult to accomplish to such portion. Further, what is contributable to production of thrust is only the portion of the coil structure which is opposed to the magnet, and most of the apparatus is unnecessary with respect to the thrust production. Also, there is no large or unnecessary heat generation.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved high-speed and high-precision stage system, by which at least one of the problems described above can be solved.
In accordance with an aspect of the present invention, there is provided a stage system, comprising: a movable stage; a first driving mechanism having a magnet and a coil, for moving said stage along a predetermined direction; and a second driving mechanism for moving said first driving mechanism along the predetermined direction; wherein one of said magnet and said coil of said first driving mechanism is connected to the stage side, while the other is connected, together with a yoke, to the second driving mechanism side: and wherein, while a position or a speed of said stage is controlled as said stage is driven through said first driving mechanism, one of said magnet and said coil of said first driving mechanism connected to said second driving mechanism is moved substantially in synchronism with said stage.
In one preferred form of this aspect of the present invention, said magnet is provided at the stage side while said coil is provided at the second driving mechanism side. Said second driving mechanism may include a feed screw. Said second driving mechanism may include a linear motor. Said magnet and said coil may have substantially the same size with respect to the movement direction. Said yoke may comprise a ferromagnetic material of flat plate shape. Said coil may be wound around said yoke. Said coil may comprise a flat coil. Said first driving mechanism may include a plurality of coils. Said first driving mechanism may be operable to move the movable member two-dimensionally. Said coil may comprise a first coil for producing a driving force in a first direction with respect to said magnet, and a second coil for producing a driving force in a second direction with respect to said magnet. Said second driving mechanism may be operable to move, two-dimensionally, one of said magnet and said coil of said first driving mechanism as connected to said second driving mechanism. Said yoke may have a recess formed in a peripheral portion thereof.
In accordance with another aspect of the present invention, there is provided an exposure apparatus, comprising: a stage being movable while holding one of a wafer and a reticle thereon; a first driving mechanism having a magnet and a coil, for moving said stage along a predetermined direction; and a second driving mechanism for moving said first driving mechanism along the predetermined direction; wherein one of said magnet and said coil of said first driving mechanism is connected
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Snow Walter E.
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