Electricity: motive power systems – Plural – diverse or diversely controlled electric motors – Motors with diverse motions
Reexamination Certificate
1997-11-18
2001-08-28
Martin, David S. (Department: 2837)
Electricity: motive power systems
Plural, diverse or diversely controlled electric motors
Motors with diverse motions
C318S051000, C318S135000, C318S649000, C318S685000, C318S687000
Reexamination Certificate
active
06281643
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a stage apparatus, and more particularly to a stage apparatus suitably applied for a precision positioning apparatus for a table on which a work of a semiconductor producing equipment or a precision working machine or a specimen to be measured by a precision measuring instrument is carried.
2. Description of the Prior Art
Operation in a progressively high efficiency and high precision is required in recent years for a stage apparatus employed for semiconductor producing equipments including light exposing apparatus, precision measuring instruments employing a laser beam or precision working machines, that is, for an apparatus for moving a table on which a work or a specimen (hereinafter referred to only as work) such as a semiconductor wafer is carried to position and stop the table at a predetermined position. A stage apparatus of the type mentioned generally forms a peculiar vibration system including a work supporting and guiding mechanism including a table and a driving mechanism for the table. Thus, such stage apparatus has a serious problem in that vibrations produced upon stopping of the table (upon deceleration) deteriorate the positioning efficiency (that is, shortness of a period of time required before a stopped condition is reached) and the accuracy (positioning accuracy with respect to an aimed stopping position). Therefore, improvement in dynamic characteristic of the vibration system is demanded.
Referring to
FIG. 7
which schematically shows an exemplary one of conventional stage apparatus, a table
20
for receiving a work thereon is supported and guided for linear movement in a leftward or rightward direction (hereinafter referred to as X direction) in
FIG. 7
by a guide mechanism
21
composed of an arrangement of a plurality of needle bearings, and is driven to move by a motor
24
by way of a feed screw
23
which extends in parallel to the passage provided by the guide mechanism
21
. A coordinate axis x for driving the table
20
is formed on a base
22
, and a current position x of the table
20
on the coordinate axis x is measured precisely by a laser interferometer
25
on the base
22
and a reflector (flat mirror)
26
provided at an end portion of the table
20
. A controller
27
controls operation of the motor
24
so that the table
20
is fed to an aimed stopping position x
0
for the table
20
prescribed on the coordinate x in accordance with a result of measurement by the laser interferometer
25
such that it is first accelerated and then moved at a uniform speed whereafter it is decelerated until the current position x measured by the interferometer
25
coincides with the position x
0
. The table
20
is positioned with respect to the base
22
in this manner.
Here, however, the table
20
forms a vibration system which is supported by a resilient force of the feed screw
23
and an attenuating force of the guide mechanism
21
, and attenuating vibrations are produced on the table
20
by a force of inertia produced upon deceleration and stopping of the table
20
. Accordingly, a next operation (for example, a working operation) cannot be started until after such vibrations are attenuated until the table
20
is stopped completely after stopping of the motor
24
, and the waiting time for such attenuation deteriorates the efficiency in positioning operation.
Thus, in such conventional apparatus as described above, the mass of a movable part (table
20
) is designed small so as to reduce the vibration energy of the vibration system while a lubricant having a high viscosity is employed for the guide mechanism
21
in order to achieve a possible most quick attenuation of vibrations.
Meanwhile, as for an accuracy required here, the feed screw
23
cannot be regarded as a rigid body and a play exists at every joining portion or contacting portion, and consequently, also an attenuating force of lubricating oil and an unnecessary frictional force act. Therefore, a stopping time of the motor
24
does not coincide with a stopping time of the table
20
. Consequently, the actual stopping position x
1
of the table
20
does not coincide with the aimed position x
0
, and the positioning accuracy is deteriorated by the presence of a difference &Dgr;x between them.
Thus, conventionally the rigidity of the feed screw
23
and so forth is generally designed high and the play and the viscous force and frictional force at every joining portion or contacting portion are selected small so as to improve the responsibility of the table
20
to the motor
24
.
By the way, if the responsibility of the table
20
to the motor
24
is raised in order to reduce the difference &Dgr;x as described above, then the attenuating force for vibrations produced upon stopping of the table
20
becomes short, and consequently, another problem takes place that the attenuation waiting time is extended. Or on the contrary if precedence is taken to attenuation of vibrations, then the responsibility of the table
20
to the motor
24
is deteriorated, and consequently, the position difference &Dgr;x upon stopping of the table
20
is increased. Accordingly, when it is intended to cope, only by any of such means as described above, with a progressively increasing demand for improvement in both of the efficiency and accuracy in positioning, there is a certain limitation, which is a serious problem.
Thus, such an attempt has been made to minimize vibrations upon stopping of the table
20
by controlling the motor
24
in accordance with an optimum deceleration curve of the table obtained taking the attenuating force of the guide mechanism
21
into consideration. However, since the needle bearings employed for the guide mechanism
21
include differences in working error or lubricating condition among individual products or over the overall length, the attenuating forces of them present such a large dispersion that precise numeric conversion or normalization cannot be achieved and also actual effects lack in reproducibility.
Thus, also such an apparatus has been proposed wherein an unstable member which provides an acting force lacking in reproducibility such as a needle bearing or a drive shaft is not employed but a table is supported in a non-contacting relationship by means of an air bearing and the table is driven to move by a linear motor provided between a base and the table. With such stage apparatus wherein a table is floating in the air, an actual behavior of the table coincides with a high degree of accuracy with a table deceleration curve obtained in accordance with an expression. However, it does not provide a sufficient thrust. Besides, since a mechanical vibration attenuating force including a frictional force does not act at all, it is unstable and lacks in fixed position holding faculty such that fine vibrations continue for a long period of time.
On the other hand, as for a difference &Dgr;x remaining upon stopping of a table, it has been attempted to construct, for example, the table from two parts including a bolt part held in meshing engagement with a feed screw and main part constituting the table and to provide a fine feeding device such as a piezo-electric element between the two parts such that the table part is finely fed after stopping of movement thereof by the feed screw in order to correct the difference &Dgr;x. With the arrangement, however, the entire table is complicated in structure and increased in weight. Accordingly, the arrangement has such drawbacks that the vibration energy is increased, that the attenuating time is elongated and the controlling procedure is complicated.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to solve such contradictory problems as described above, or in other words, to provide a stage apparatus wherein vibrations of a table upon stopping are minimized without deteriorating the responsibility of the table to a driving shaft for the table for a period of time until the table is stopped to improve bot
Martin David S.
Nikon Corporation
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