CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation-in-Part of application Ser. No. 08/698,827 filed Aug. 16, 1996, abandoned, which in turn is a Divisional of Application Ser. No. 09/260,544, filed Mar. 2, 1999, which is a Continuation of application Ser. No. 08/266,999 filed Jun. 27, 1994, abandoned.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a movable stage apparatus capable of precise movement, and particularly relates to a stage apparatus movable in one linear direction capable of high accuracy positioning and high speed movement, which can be especially favorably utilized in a microlithographic system. This invention also relates to an exposure apparatus that is used for the transfer of a mask pattern onto a photosensitive substrate during a lithographic process to manufacture, for example, a semiconductor element, a liquid crystal display element, a thin film magnetic head, or the like.

2. Description of Related Art

When a semiconductor element or the like is manufactured, a projection exposure apparatus is used that transfers an image of a pattern of a reticle, used as a mask, onto each shooting area on a wafer (or a glass plate or the like) on which a resist is coated, used as a substrate, through a projection optical system. Conventionally, as a projection exposure apparatus, a step-and-repeat type (batch exposure type) projection exposure apparatus (stepper) has been widely used. However, a scanning exposure type projection exposure apparatus (a scanning type exposure apparatus), such as a step-and-scan type, which performs an exposure as a reticle and a wafer are synchronously scanned with respect to a projection optical system, has attracted attention.

In a conventional exposure apparatus, a reticle stage, which supports and carries the reticle, which is the original pattern, and the wafer to which the pattern is to be transferred, and the driving part of the wafer stage are fixed to a structural body that supports a projection optical system. The vicinity of the center of gravity of the projection optical system is also fixed to the structural body. Additionally, in order to position a wafer stage with high accuracy, the position of the wafer stage is measured by a laser interferometer, and a moving mirror for the laser interferometer is fixed to the wafer stage.

Furthermore, in order to carry a wafer to a wafer holder on the wafer stage, a wafer carrier arm that takes out a wafer from a wafer cassette and carries it to the wafer holder, and a wafer carrier arm that carries the wafer from the wafer holder to the wafer cassette, are independently provided. When the wafer is carried in, the wafer that has been carried by the wafer carrier arm is temporarily fixed to and supported by a special support member that can be freely raised and lowered and that is provided on the wafer holder. Thereafter, the carrier arm is withdrawn, the support member is lowered, and the wafer is disposed on the wafer holder. After this, the wafer is vacuum absorbed to the top of the wafer holder. When the wafer is carried out from the exposure device, the opposite operation is performed.

As described above, in the conventional exposure apparatus, the driving part of the wafer stage or the like and the projection optical system are fixed to the same structural body. Thus, the vibration generated by the driving reaction of the stage is transmitted to the structural body, and the vibration is also transmitted to the projection optical system. Furthermore, all the mechanical structures were mechanically resonate to a vibration of a predetermined frequency, so there are disadvantages such that deformation of the structural body and the resonance phenomenon occurred, and position shifting of a transfer pattern image and deterioration of contrast occurred when this type of vibration is transmitted to the structural body.

Furthermore, because the wafer stage moves over a long distance from the carrier arm for carrying in and out of the wafer to the exposure position, it is necessary to provide an extremely long moving mirror for the laser interferometer. Because of this, the weight of the wafer stage becomes relatively heavy and the driving reaction becomes large because a heavy motor with a large driving force is needed. Furthermore, in order to improve throughput, when the moving speed and acceleration of the stage needs to be increased, the driving reaction becomes even larger. In addition, as the weight and acceleration of the stage increase, the heating amount of the motor increases, and there is a disadvantage such that measurement stability or the like of the laser interferometer deteriorates.

Furthermore, in the case of carrying the wafer into and out of the exposure apparatus, the wafer is temporarily fixed and supported on the top of a special support member, so carrying in and out of the wafer consumes time. This causes deterioration of throughput. Additionally, as one example, because giving and receiving of the wafer is performed between the carrier arms, the probability of the wafer being contaminated is high, and the probability of having an operation error when the wafer was given and received is high. Furthermore, the number of carrier arms is a major point governing the size of the carrier unit, so the carrier path becomes long when giving and receiving of the wafer is performed between the carrier arms on the carrier path. Additionally, a floor area (foot print) that is needed for the exposure apparatus also becomes large.

In wafer steppers, the alignment of an exposure field to the reticle being imaged affects the success of the circuit of that field. In a scanning exposure system, the reticle and wafer are moved simultaneously and scanned across one another during the exposure sequence.

To attain high accuracy, the stage should be isolated from mechanical disturbances. This is achieved by employing electromagnetic forces to position and move the stage. It should also have high control bandwidth, which requires that the stage be a light structure with no moving parts. Furthermore, the stage should be free from excessive heat generation which might cause interferometer interference or mechanical changes that compromise alignment accuracy.

Commutatorless electromagnetic alignment apparatus such as the ones disclosed in U.S. Pat. Nos. 4,506,204, 4,506,205 and 4,507,597 are not feasible because they require the manufacture of large magnet and coil assemblies that are not commercially available. The weight of the stage and the heat generated also render these designs inappropriate for high accuracy applications.

An improvement over these commutatorless apparatus was disclosed in U.S. Pat. No. 4,592,858, which employs a conventional XY mechanically guided sub-stage to provide the large displacement motion in a plane, thereby eliminating the need for large magnet and coil assemblies. The electromagnetic means mounted on the sub-stage isolates the stage from mechanical disturbances. Nevertheless, the combined weight of the sub-stage and stage still results in low control bandwidth, and the heat generated by the electromagnetic elements supporting the stage is still substantial.

Even though the current apparatus using commutated electromagnetic means is a significant improvement over prior commutatorless apparatus, the problems of low control bandwidth and interferometer interference persist. In such an apparatus, a sub-stage is moved magnetically in one linear direction and the commutated electromagnetic means mounted on the sub-stage in turn moves the stage in the normal direction. The sub-stage is heavy because it carries the magnet tracks to move the stage. Moreover, heat dissipation on the stage compromises interferometer accuracy.

It is also well known to move a movable member (stage) in one long linear direction (e.g. more than 10 cm) by using two of the linear motors in parallel where coil and magnet are combined. In this case, the stage is guided by some sort of a linear guiding member and driven in one linear direction by a linear motor installed parallel to the guiding member. When driving the stage only to the extent of extremely small stroke, the guideless structure based on the combination of several electromagnetic actuators, as disclosed in the prior art mentioned before, can be adopted. However, in order to move the guideless stage by a long distance in one linear direction, a specially structured electromagnetic actuator as in the prior art becomes necessary, causing the size of the apparatus to become larger, and as a result, generating a problem of consuming more electricity.

SUMMARY OF THE INVENTION

It is an object of the present invention to make it possible for a guideless stage to move with a long linear motion using electromagnetic force, and to provide a light weight apparatus in which low inertia and high response are achieved.

It is another object of the present invention to provide a guideless stage apparatus using commercially available regular linear motors as electromagnetic actuators for one linear direction motion.

It is another object of the present invention to provide a guideless stage apparatus capable of active and precise position control for small displacements without any contact in the direction orthogonal to the long linear motion direction.

It is another object of the present invention to provide a completely non-contact stage apparatus by providing a movable member (stage body) that moves in one linear direction and a second movable member that moves sequentially in the same direction, constantly keeping a certain space therebetween, and providing the electromagnetic force (action and reaction forces) in the direction orthogonal to the linear direction between this second movable member and the stage body.

It is another object of the present invention to provide a non-contact stage apparatus capable of preventing the positioning and running accuracy from deteriorating by changing tension of various cables and tubes to be connected to the non-contact stage body that moves as it supports an object.

It is another object of the present invention to provide a non-contact apparatus that is short in its height, by arranging the first movable member and the second movable member in parallel, which move in the opposite linear direction to one another.

It is another object of the present invention to provide an apparatus that is structured so as not to change the location of the center of gravity of the entire apparatus even when the non-contact stage body moves in one linear direction.

Another object of this invention is to provide an exposure apparatus that can perform an exposure with high accuracy by reducing the effects of vibration on a projection optical system or the like that occurs when the wafer stage or the like is driven.

Another object of this invention is to provide an exposure apparatus that suppresses the amount of heat generated by the driving part of the wafer stage, to perform positioning of the driving part of the wafer stage with high accuracy, and to maintain the measurement stability of a position measurement device or the like.

Another object of this invention is to provide an exposure apparatus with high throughput that can carry a wafer to an exposure apparatus without temporarily fixing the wafer, and without giving and receiving of the wafer between wafer carrier arms.

In order to achieve the above and other objects, embodiments of the present invention may be constructed as follows.

An apparatus that is capable of high accuracy position and motion control utilizes linear commutated motors to move a guideless stage in one long linear direction and to create small yaw rotation in a plane. A carrier/follower holding a single voice coil motor (VCM) is controlled to approximately follow the stage in the direction of the long linear motion. The VCM provides an electromagnetic force to move the stage for small displacements in the plane in a linear direction perpendicular to the direction of the long linear motion to ensure proper alignment. This follower design eliminates the problem of cable drag for the stage since the cables connected to the stage follow the stage via the carrier/follower. Cables connecting the carrier/follower to external devices will have a certain amount of drag, but the stage is free from such disturbances because the VCM on the carrier/follower acts as a buffer by preventing the transmission of mechanical disturbances to the stage.

According to one aspect of the invention, the linear commutated motors are located on opposite sides of the stage and are mounted on a driving frame. Each linear commutated motor includes a coil member and a magnetic member, one of which is mounted on one of the opposed sides of the stage, and the other of which is mounted on the driving frame. Both motors drive in the same direction. By driving the motors slightly different amounts, small yaw rotation of the stage is produced.

In accordance with another aspect of the present invention, a moving counter-weight is provided to preserve the location of the center of gravity of the stage system during any stage motion by using the conservation of momentum principle. In an embodiment of the present invention, the drive frame carrying one member of each of the linear motors is suspended above the base structure, and when the drive assembly applies an action force to the stage to move the stage in one direction over the base structure, the driving frame moves in the opposite direction in response to the reaction force to substantially maintain the center of gravity of the apparatus. This apparatus essentially eliminates any reaction forces between the stage system and the base structure on which the stage system is mounted, thereby facilitating high acceleration while minimizing vibrational effects on the system.

By restricting the stage motion to the three specified degrees of freedom, the apparatus is simple. By using electromagnetic components that are commercially available, the apparatus design is easily adaptable to changes in the size of the stage. This high accuracy positioning apparatus is ideally suited for use as a reticle scanner in a scanning exposure system by providing smooth and precise scanning motion in one linear direction and ensuring accurate alignment by controlling small displacement motion perpendicular to the scanning direction and small yaw rotation in the scanning plane.

An exposure apparatus according to another aspect of this invention includes a projection optical system support member that supports a projection optical system, so that the projection optical system rotates within a specified area, taking a reference point as a center. Therefore, even if vibration from a substrate stage and a mask stage is transmitted to the projection optical system, the position relationship between the object plane (mask) and the image plane (substrate) is not shifted. Thus, it is possible to prevent position shifting of the pattern to be transferred, and highly accurate exposure can be performed.

Furthermore, a mask stage that moves a mask, a structural body that supports this mask stage and the projection optical system, and a substrate stage that moves a substrate are provided. The projection optical system support part (the structural body) has at least three flexible support members extending from the structural body, and the extending lines of each support member cross at the reference point. In this case, even if vibration is transmitted to the projection optical system, the projection optical system is minutely rotated taking the reference point as a center. Therefore, it is possible to prevent position shifting of the pattern to be transferred to the substrate. Furthermore, the support members are flexible, so the minute vibration can be reduced and the deterioration of contrast of a pattern to be formed can be prevented.

An exposure apparatus according to another aspect of this invention controls the mask base so that the mask base moves at a specified speed in a direction opposite to the moving direction of the mask stage. This reduces the effects to the structural body of the driving reaction of the mask stage. Additionally, the excitation of mechanical resonance is controlled, and the vibration transmitted to the structural body and the projection optical system can be reduced. Therefore, exposure with a high accuracy can be performed.

In an exposure apparatus according to another aspect of this invention, by having an elastic member at both ends of a guide axis, when the substrate table performs constant velocity reciprocation on the guide axis, the kinetic energy of the substrate table is converted to potential energy and is stored in the elastic members. Therefore, the energy to be consumed when the substrate table is reciprocated at constant velocity is mainly only the energy to be consumed in the viscosity resistance of the substrate table with respect to air. The only heat generated is the heat from when the elastic members are deformed. Therefore, it is possible to control the heating amount of the driving part when the substrate table moves at constant velocity.

Furthermore, when the elastic member has first magnetic members disposed at both ends of the guide axis and second magnetic members disposed corresponding to the first magnetic members, by the attraction of the first and second magnetic members, when the substrate table is still-positioned at an end of the guide axis, it is possible to reduce the thrust of the driving part of the substrate table required to oppose the resistance of the elastic member. Thus, the heating amount of the driving part can be controlled when the substrate table is still-positioned.

In an exposure apparatus according to another aspect of this invention, by controlling the length of the support legs that can be freely extended and retracted in the support direction, the tilt angle of the substrate table and its position in the height direction can be controlled, and highly accurate exposure can be performed as the surface of the substrate is aligned within the image plane.

Furthermore, when the mask and the substrate are synchronously and moved during exposure, the tilt angle of the scanning surface of the substrate stage of the structural body in the scanning direction, the tilt angle in the non-scanning direction, and the height are detected. When the support legs that can be freely extended and retracted are controlled based upon the detection result, highly accurate scanning exposure can be performed as the surface of the substrate is aligned within the image plane.

Furthermore, when the rotation angle of the substrate stage about the optical axis of the projection optical system and the position shifting amount are detected, and the position of the mask stage or the substrate stage is controlled based upon this detection result, the positioning between the surface of the substrate and the image plane can be performed with high accuracy.

In an exposure apparatus according to another aspect of this invention, a visco-elastic body exists between the support member and the structural body, so it is possible to reduce the vibration from the floor on which the exposure device is disposed. Therefore, exposure can be performed with high accuracy.

In an exposure apparatus according to another aspect of this invention, at least one groove is provided in the substrate table, and a substrate can be disposed on the substrate table without the substrate carrier arms contacting the substrate table. That is, there is an advantage such that the substrate can be carried into and out from the exposure device, without temporarily fixing and supporting the substrate on the substrate table, and throughput can be improved.

Furthermore, when the substrate carrier mechanism has at least two substrate carrier arms and substrate storage case support members, the substrate carrier arms can be freely moved in the three directions such as a rotational direction about the optical axis of the projection optical system, the horizontal direction, and the vertical direction, and the substrate storage case support member can be freely moved in the vertical direction, there are advantages such that the substrate stage can be moved below the substrate carrying-out arms or the substrate carrying-in arms, the substrate can be carried to the exposure device without transferring the substrate between the substrate carrier arms, and the probability of problems occurring during the carrying and the probability of foreign objects attaching to the wafer can be reduced.

Other aspects and features and advantages of the present invention will become more apparent upon a review of the following specification taken in conjunction with the accompanying drawings wherein similar characters of reference indicate similar elements in each of the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic perspective view of an apparatus in accordance with an embodiment of the present invention.

FIG. 2

is a top plan view of the apparatus shown in FIG.

1

.

FIG. 3

is an end elevational view of the structure shown in

FIG. 2

taken along line

3

—

3

′ in the direction of the arrows.

FIG. 4A

is an enlarged perspective, partially exploded view showing the carrier/follower structure of FIG.

1

and exploded from the positioning guide.

FIG. 4B

is an enlarged horizontal sectional view of a portion of the structure shown in

FIG. 5

taken along line

4

B in the direction of the arrow.

FIG. 4C

is an enlarged elevational sectional view of a portion of the structure shown in

FIG. 2

taken along line

4

C in the direction of the arrow but with the voice coil motor removed.

FIG. 5

is an elevational sectional view of a portion of the structure shown in

FIG. 2

taken along line

5

—

5

′ in the direction of the arrows.

FIG. 6

is a block diagram schematically illustrating the sensing and control systems for controlling the position of the stage.

FIG. 7

is a plan view, similar to

FIG. 2

, illustrating a preferred embodiment of the present invention.

FIG. 8

is an elevational sectional view of the structure shown in

FIG. 7

taken along line

8

—

8

′ in the direction of the arrows.

FIGS. 9 and 10

are simplified schematic views similar to

FIGS. 7 and 8

and illustrating still another embodiment of the present invention.

FIG. 11

is a perspective view showing a schematic structure of a projection exposure apparatus according to an embodiment of this invention.

FIG. 12

is a cross-sectional view taken through a part showing a method of supporting the projection optical system of FIG.

11

.

FIG. 13A

is a plan view showing the wafer stage of FIG.

11

.

FIG. 13B

is a cross-sectional view of

FIG. 13A

along line B—B.

FIG. 13C

is a front view omitting part of FIG.

13

A.

FIG. 13D

is across-sectional view of

FIG. 13A

along line D—D.

FIG. 14

is a block diagram showing a structure of a controller that controls a wafer table and a carrier.

FIGS. 15A-C

are schematic diagrams that accompany an operation explanation of a guide shaft and a guide member of the wafer table of

FIGS. 13A-C

.

FIG. 16A

is a diagram showing the speed of the wafer table when the moving speed of the wafer table is shifted to a constant speed on a guide axis without an elastic body.

FIG. 16B

is a diagram showing thrust of linear motors.

FIG. 17A

is a diagram showing a speed curve of a wafer table that is calculated assuming the case where an ideal wafer table without vibration is accelerated to a constant speed on a guide axis with springs.

FIG. 17B

is a diagram showing thrust of linear motors which is calculated assuming the case where a wafer table with vibration is controlled taking the speed curve of

FIG. 17A

as a speed governing value.

FIG. 18A

is a diagram showing the speed when a wafer table is accelerated to a constant speed using a guide axis with springs, taking the speed curve of

FIG. 17A

as a speed governing value.

FIG. 18B

is a diagram showing thrust of a wafer table at that time and the thrust generated by linear motors.

FIG. 19A

is a diagram showing a speed curve when a wafer table is accelerated to a constant speed when a guide axis with springs in which a spring constant is the optimum value is used.

FIG. 19B

is a diagram showing thrust of the wafer table.

FIG. 20

is a diagram showing the resistance of the springs at the ends of a guide axis with springs.

FIGS. 21A-C

are schematic diagrams that accompany the explanation of the operation of the guide member and the guide shaft when a magnetic member is further provided.

FIG. 22A

is a diagram showing speed that is calculated assuming the case where an ideal wafer table without vibration is accelerated to a constant speed on a guide axis provided with springs, steel plates, and magnets.

FIG. 22B

is a diagram showing thrust of linear motors calculated assuming the case where a wafer table with vibration is controlled taking the speed curve of

FIG. 22A

as a speed governing value.

FIG. 23A

is a diagram showing the speed curve when a wafer table on a guide axis with steel plates and magnets is accelerated to a constant speed, taking the speed curve of

FIG. 22A

as a speed governing value.

FIG. 23B

is a diagram showing thrust of the wafer table at that time, and the thrust of linear motors.

FIG. 24

is a diagram showing the resultant force between the resistance of the spring and the attraction between the magnet and the steel plate at an end of the guide axis to which the steel plate and the magnet are fixed.

FIG. 25A

is a schematic diagram showing a support leg that supports a wafer table, and the vicinity thereof, by enlargement.

FIG. 25B

is a side view of FIG.

25

A.

FIG. 26

is a block diagram showing a structure of a controller that controls a reticle stage, a wafer stage, and a wafer base.

FIGS. 27A-B

are diagrams explaining the operation of the wafer stage when a wafer is carried into or out from an exposure device.

FIGS. 28A-B

are diagrams explaining the operation of a wafer carrier arm when an already-exposed wafer is carried out from an exposure device.

FIGS. 29A-B

are diagrams explaining the operation of a wafer carrier arm when a non-exposed wafer is carried into an exposure device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While the present invention has applicability generally to electromagnetic alignment system, the preferred embodiments involve a scanning apparatus for a reticle stage as illustrated in

FIGS. 1-6

.

Referring now to the drawings, the positioning apparatus

10

of the present invention includes a base structure

12

above which a reticle stage

14

is suspended and moved as desired, a reticle stage position tracking laser interferometer system

15

, a position sensor

13

and a position control system

16

operating from a CPU

16

′ (see FIG.

6

).

An elongate positioning guide

17

is mounted on the base

12

, and support brackets

18

(two brackets in the illustrated embodiment) are movably supported on the guide

17

such as by air bearings

20

. The support brackets

18

are connected to a driving assembly

22

in the form of a magnetic track assembly or driving frame for driving the reticle stage

14

in the X direction and small yaw rotation. The driving frame includes a pair of parallel spaced apart magnetic track arms

24

and

26

which are connected together to form an open rectangle by cross arms

28

and

30

. In the preferred embodiment, the driving frame

22

is movably supported on the base structure

12

such as by air bearings

32

so that the frame is free to move on the base structure in a direction aligned with the longitudinal axis of the guide

17

, the principal direction in which the scanning motion of the reticle stage is desired. As used herein “one direction” or a “first direction” applies to movement of the frame

22

or the reticle stage

14

either forward or backward in the X direction along a line aligned with the longitudinal axis of the guide

17

.

Referring now to

FIGS. 1 and 3

to explain further in detail, the elongate guiding member

17

in the X direction has front and rear guiding surfaces

17

A and

17

B, which are almost perpendicular to the surface

12

A of the base structure

12

. The front guiding surface

17

A is against the rectangular driving frame

22

and guides the air bearing

20

which is fixed to the inner side of the support bracket

18

. A support bracket

18

is mounted on each end of the upper surface of the arm

24

, which is parallel to the guiding member

17

of the driving frame

22

. Furthermore, each support bracket

18

is formed in a hook shape so as to straddle the guiding member

17

in the Y direction, and with the free end against the rear guiding surface

177

B of the rear side of the guiding member

17

. The air bearing

20

′ is fixed inside the free end of the support brackets

18

and against the rear guiding surface

17

B. Therefore, each of the support brackets

18

is constrained in its displacement in the Y direction by the guiding member

17

and air bearings

20

and

20

′ and is able to move only in the X direction.

Now according to the first embodiment of the present invention, the air bearings

32

, which are fixed to the bottom surfaces of the four rectangular parts of the driving frame

22

, make an air layer leaving a constant (several &mgr;m) between the pad surface and the surface

12

A of the base structure

12

. The driving frame is buoyed up from the surface

12

A and supported perpendicularly (in the Z direction) by the air layer. It will be explained in detail later, but in

FIG. 1

, the carrier/follower

60

shown positioned above the upper part of the elongate arm

24

is positioned laterally in the Y direction by air bearings

66

A and

66

B supported by a bracket

62

against opposite surfaces

17

A and

17

B of guiding member

17

and vertically in the Z direction by air bearings

66

above the surface

12

A of the base structure

12

. Thus, the carrier/follower

60

is positioned so as not to contact any part of the driving frame

22

. Accordingly, the driving frame

22

moves only in one linear X direction, guided above the base surface

12

A and laterally by the guiding member

17

.

Referring now to both FIG.

1

and

FIG. 2

, the structure of the reticle stage

14

and the driving frame

22

will be explained. The reticle stage

14

includes a main body

42

on which the reticle

44

is positioned above an opening

46

. The reticle body

42

includes a pair of opposed sides

42

A and

42

b

and is positioned or suspended above the base structure

12

such as by air bearings

48

. A plurality of interferometer mirrors

50

are provided on the main body

42

of the reticle stage

14

for operation with the laser interferometer position sensing system

15

(see

FIG. 6

) for determining the exact position of the reticle stage which is fed to the position control system

16

in order to direct the appropriate drive signals for moving the reticle stage

14

as desired.

Primary movement of the reticle stage

14

is accomplished with first electromagnetic drive assembly or means in the form of separate drive assemblies

52

A and

52

B (

FIG. 2

) on each of the opposed sides

42

A and

42

B, respectively. The drive assemblies

52

A and

52

B include drive coils

54

A and

54

B fixedly mounted on the reticle stage

14

at the sides

42

A and

42

B, respectively, for cooperating with magnet tracks

56

A and

56

B on the magnet track arms

24

and

26

, respectively, of the drive frame

22

. While in the preferred embodiment of the invention the magnet coils are mounted on the reticle stage and the magnets are mounted on the drive frame

22

, the positions of these elements of the electromagnetic drive assembly

52

could be reversed.

Here, the structure of the reticle stage

14

will be explained further in detail. As shown in

FIG. 1

, the stage body

42

is installed so that it is free to move in the Y direction in the rectangular space inside the driving frame

22

. The air bearing

48

fixed under each of the four corners of the stage body

42

makes an extremely small air gap between the pad surface and the base surface

12

A, and buoys up and supports the entire stage

14

from the surface

12

A. These air bearings

48

should preferably be pre-loaded types with a recess for vacuum attraction to the surface

12

A.

As shown in

FIG. 2

, a rectangular opening

46

in the center of the stage body

42

is provided so that the projected image of the pattern formed on the reticle

44

can pass therethrough. In order for the projected image via the rectangular opening

46

to pass through the projection optical system PL (see

FIG. 5

) which is installed below the rectangular opening, there is another opening

12

B provided at the center part of the base structure

12

. The reticle

44

is loaded on the top surface of the stage body by clamping members

42

C, which are protrusively placed at four points around the rectangular opening

46

, and clamped by vacuum pressure.

The interferometer mirror

50

Y, which is fixed near the side

42

B of the stage body

42

near the arm

26

, has a vertical elongate reflecting surface in the X direction which length is somewhat longer than the movable stroke of the stage

14

in the X direction, and the laser beam LBY from the Y-axis interferometer is incident perpendicularly on the reflecting surface. In

FIG. 2

, the laser beam LBY is bent at a right angle by the mirror

12

D, which is fixed on the side of the base structure

12

.

Referring now to

FIG. 3

as a partial cross-sectional drawing of the view along line

3

—

3

′ in

FIG. 2

, the laser beam LBY which is incident on the reflecting surface of the interferometer mirror

50

Y is placed so as to be on the same plane as the bottom surface (the surface where the pattern is formed) of the reticle

44

which is mounted on the clamping member

42

C. Furthermore, in

FIG. 3

, the air bearing

20

on the end side of the support brackets

18

against the guiding surface

17

B of the guiding member

17

is also shown.

Referring once again to

FIGS. 1 and 2

, the laser beam LBX1 from the X1-axis interferometer is incident and reflected on the interferometer mirror

50

X1, and the laser beam LBX2 from the X2-axis interferometer is incident and reflected on the interferometer mirror

50

X2. These two mirrors

50

X1 and

50

X2 are structured as corner tube type mirrors, and even when the stage

14

is in yaw rotation, they always maintain the incident axis and reflecting axis of the laser beams parallel within the XY plane. Furthermore, the block

12

C in

FIG. 2

is an optical block, such as a prism, to orient the laser beams LBX1 and LBX2 to each of the mirrors

50

X1 and

50

X2, and is fixed to a part of the base structure

12

. The corresponding block for the laser beam LBY is not shown.

In

FIG. 2

, the distance BL in the Y direction between each of the center lines of the two laser beams LBX1 and LBX2 is the length of the base line used to calculate the amount of yaw rotation. Accordingly, the value of the difference between the measured value &Dgr;X1 in the X direction of the X1-axis interferometer and the measured value &Dgr;X2 in the X direction of the X2-axis interferometer divided by the base line length BL is the approximate amount of yaw rotation in an extremely small range. Also, half the value of the sum of &Dgr;X1 and &Dgr;X2 represents the X coordinate position of the entire stage

14

. These calculations are performed by a high speed digital processor in the position control system

16

shown in FIG.

6

.

Furthermore, the center lines of each of the laser beams LBX1 and LBX2 are set on the same surface where the pattern is formed on the reticle

44

. The extension of the line GX, which is shown in FIG.

2

and divides in half the space between each of the center lines of laser beams LBX1 and LBX2, and the extension of the laser beam LBY intersect within the same surface where the pattern is formed. Additionally, the optical axis AX (see

FIGS. 1 and 5

) also crosses at this intersection as shown in FIG.

1

. In

FIG. 1

, a slit shaped illumination field ILS which includes the optical axis AX is shown over the reticle

44

, and the pattern image of the reticle

44

is scanned and exposed onto the photosensitive substrate via the projection optical system PL.

Furthermore, there are two rectangular blocks

90

A and

90

B fixed on the side

42

A of the stage body

42

in

FIGS. 1 and 2

. These blocks

90

A and

90

B are to receive the driving force in the Y direction from the second electromagnetic actuator

70

which is mounted on the carrier/follower

60

. Details will be explained below.

The driving coils

54

A and

54

B which are fixed on the both sides of the stage body

42

are formed flat parallel to the XY plane, and pass through the magnetic flux space in the slot which extends in the X direction of the magnetic tracks

56

A and

56

B without any contact. The assembly of the driving coil

54

and the magnetic track

56

used in the present embodiment is a commercially easily accessible linear motor for general purposes, and it could be either with or without a commutator.

Here, considering the actual design, the moving stroke of the reticle stage

14

is mostly determined by the size of the reticle

44

(the amount of movement required at the time of scanning for exposure and the amount of movement required at the time of removal of the reticle from the illumination optical system to change the reticle). In the case of the present embodiment, when a 6-inch reticle is used, the moving stroke is about 30 cm.

As mentioned before, the driving frame

22

and the stage

14

are independently buoyed up and supported on the base surface

12

A, and at the same time, magnetic action and reaction forces are applied to one another in the X direction only by the linear motor

52

. Because of that, the law of the conservation of momentum is seen between the driving frame

22

and the stage

14

.

Now, suppose the weight of the entire reticle stage

14

is about one fifth of the entire weight of the frame

22

which includes the support brackets

18

. Then, the forward movement of 30 cm of the stage

14

in the X direction makes the driving frame

22

move by 6 cm backwards in the X direction. This means that the location of the center of gravity of the apparatus on the base structure

12

is essentially fixed in the X direction. In the Y direction, there is no movement of any heavy object. Therefore, the change in the location of the center of gravity in the Y direction is also relatively fixed.

The stage

14

can be moved in the X direction as described above, but the moving coils (

54

A,

54

B) and the stators (

56

A,

56

B) of the linear motors

52

will interfere with each other (collide) in the Y direction without an X direction actuator. Therefore, the carrier/follower

60

and the second electromagnetic actuator

70

are provided to control the stage

14

in the Y direction. Their structures will be explained with reference to

FIGS. 1

,

2

,

3

and

5

.

As shown in

FIG. 1

, the carrier/follower

60

is movably installed in the Y direction via the hook-like support bracket

62

which straddles over the guiding member

17

. Furthermore as evident from

FIG. 2

, the carrier/follower

60

is placed above the arm

24

, so as to maintain a certain space between the stage

14

(the body

42

) and the arm

24

, respectively. One end

60

E of the carrier/follower

60

, is substantially protruding inward (toward the stage body

42

) over the arm

24

. Inside this end part

60

E is fixed a driving coil

68

(

FIGS. 4A and 6

) (having the same shape as the coil

54

) which enters a slot space of the magnetic track

56

A.

Furthermore, the bracket

62

supported by air bearing

66

A (see

FIGS. 2

,

3

,

4

A and

5

) against the guiding surface

17

A of the guiding member

17

is fixed in the space between the guiding member

17

of the carrier/follower

60

and the arm

24

. The air bearing

66

that buoys up and supports the carrier/follower

60

on the base surface

12

A is also shown in FIG.

3

.

The air bearing

66

B against the guiding surface

17

B of the guiding member

17

is also fixed to the free end of support bracket

62

on the other side of the hook from air bearing

66

A with guiding member

17

therebetween.

Now, as evident from

FIG. 5

, the carrier/follower

60

is arranged so as to keep certain spaces with respect to both the magnetic track

56

A and the stage body

42

in the Y and Z directions, respectively. Shown in

FIG. 5

are the projection optical system PL and column rod CB to support the base structure

12

above the projection optical system PL. Such an arrangement is typical for a projection aligner, and unnecessary shift of the center of gravity of the structures above the base structure

12

would cause a lateral shift (mechanical distortion) between the column rod CB and the projection optical system PL, and thus result in a deflection of the image on the photosensitive substrate at the time of exposure. Hence, the merit of the device as in the present embodiment where the motion of the stage

14

does not shift the center of gravity above the base structure

12

is substantial.

Furthermore referring now to

FIG. 4A

, the structure of the carrier/follower

60

will be explained. In

FIG. 4A

, the carrier/follower

60

is disassembled into two parts,

60

A and

60

B, for the sake of facilitating one's understanding. As evident from

FIG. 4A

, the driving coil

68

that moves the carrier/follower

60

itself in the X direction is fixed at the lower part of the end

60

E of the carrier/follower

60

. Furthermore, the air bearing

66

C is placed against the base structure

12

A on the bottom surface of the end

60

E and helps to buoy up the carrier/follower

60

.

Hence the carrier/follower

60

is supported in the Z direction with three points—the two air bearings

66

and one air bearing

66

C—and is constrained in the Y direction for movement in the X direction by air bearings

66

A and

66

B. What is important in this structure is that the second electromagnetic actuator

70

is arranged back to back with the support bracket

62

so that when the actuator generates the driving force in the Y direction, reaction forces in the Y direction between the stage

14

and the carrier/follower

60

actively act upon the air bearings

66

A and

66

B which are fixed inside the support bracket

62

. In other words, arranging the actuator

70

and the air bearings

66

A,

66

B on the line parallel to the Y-axis in the XY plane helps prevent the generation of unwanted stress, which might deform the carrier/follower

60

mechanically when the actuator

70

is in operation. Conversely, it means that it is possible to reduce the weight of the carrier/follower

60

.

As evident from

FIGS. 2

,

4

A and

4

C described above, the magnetic track

56

A in the arm

24

of the driving frame

22

provides magnetic flux for the driving coil

54

A on the stage body

42

side, and concurrently provides magnetic flux for the driving coil

68

for the carrier/follower

60

. As for the air bearings

66

A,

66

B and

66

C, a vacuum pre-loaded type is preferable, since the carrier/follower

60

is light. Besides the vacuum pre-loaded type, a magnetic pre-loaded type is also acceptable.

Next with reference to

FIGS. 3

,

4

B and

5

, the second actuator mounted on the carrier/follower

60

will be explained. A second electromagnetic drive assembly in the form of a voice coil motor

70

is made up of a voice coil

74

attached to the main body

42

of the reticle stage

14

and a magnet

72

attached to the carrier/follower

60

to move the stage

14

for small displacements in the Y direction in the plane of travel of the stage

14

orthogonal to the X direction long linear motion produced by the driving assembly

22

. The positions of the coil

74

and magnet

72

could be reversed. A schematic structure of the voice coil motor (VCM)

70

is as shown in

FIGS. 3 and 5

, and the detailed structure is shown in FIG.

4

B.

FIG. 4B

is a cross-sectional view of the VCM

70

sectioned at the horizontal plane shown with an arrow

4

B in FIG.

5

. In

FIG. 4B

, the magnets

72

of the VCM

70

are fixed onto the carrier/follower

60

side. The coil of the VCM

70

comprises the coil body

74

A and its supporting part

74

B. The supporting part

74

B is fixed to a connecting plate

92

(a plate vertical to the XY plane) which is rigidly laid across the two rectangular blocks

90

A and

90

B. A center line KX of the VCM

70

shows the direction of the driving force of the coil

74

, and when an electric current flows through the coil body

74

A, the coil

74

displaces into either positive or negative movement in the Y direction in accordance with the direction of the current, and generates a force corresponding to the amount of the current. Normally, in a commonly used VCM, a ring-like damper or bellows are provided between the coil and magnet so as to keep the gap between the coil and magnet, but according to the present embodiment, that gap is kept by a follow-up motion of the carrier/follower

60

, and therefore, such supporting elements as a damper or bellows are not necessary.

In the present embodiment, capacitance gap sensors

13

A and

13

B are provided as a positioning sensor

13

(see

FIG. 6

) as shown in FIG.

4

B. In

FIG. 4B

, electrodes for capacitance sensors are placed so as to detect the change in the gap in the X direction between the side surface of the rectangular blocks

90

A and

90

B facing each other in the X direction and the side surface of a case

70

′ of the VCM

70

. Such a positioning sensor

13

can be placed anywhere as far as it can detect the gap change in the Y direction between the carrier/follower

60

and the stage

14

(or the body

42

). Furthermore, the type of the sensor can be any of a non-contact type such as, for example, photoelectric, inductive, ultrasonic, or air-micro system.

The case

70

′ in

FIG. 4B

is formed with the carrier/follower

60

in one, and placed (spatially) so as not to contact any member on the reticle stage

14

side. As for the gap between the case

70

′ and the rectangular blocks

90

A and

90

B in the X direction (scanning direction), when the gap on the sensor

13

A side becomes wider, the gap on the sensor

133

B side becomes smaller. Therefore, if the difference between the measured gap value by the sensor

13

A and the measured gap value by the sensor

13

B is obtained by either digital operation or analog operation, and a direct servo (feedback) control system which controls the driving current of the driving coil

68

for the carrier/follower

60

is designed using a servo driving circuit which makes the gap difference zero, then the carrier/follower

60

will automatically perform a follow-up movement in the X direction always keeping a certain space to the stage body

42

. Alternatively, it is also possible to design an indirect servo control system which controls an electric current flow to the driving coil

68

, with the operation of position control system

16

in

FIG. 6

using the measured gap value obtained only from one of the sensors and the X coordinate position of the stage

14

measured from the X axis interferometer, without using the two gap sensors

13

A and

13

B differentially.

In the VCM

70

as described in

FIG. 4B

, the gap between the coil body

74

A and the magnet

72

in the X direction (non-energizing direction) is in actuality about 2-3 mm. Therefore, a follow-up accuracy of the carrier/follower

60

with respect to the stage body

42

would be acceptable at around ±0.5-1 mm. This accuracy depends on how much of the yaw rotation of the stage body is allowed, and also depends on the length of the line in the KX direction (energizing direction) of the coil body

74

A of the VCM

70

. Furthermore, the degree of the accuracy for this can be substantially lower than the precise positioning accuracy for the stage body

42

using an interferometer (e.g., ±0.03 &mgr;m supposing the resolution of the interferometer is 0.01 &mgr;m). This means that the servo system for a follower can be designed fairly simply, and the amount of cost to install the follower control system would be small. Furthermore, the line KX in

FIG. 4B

is set so as to go through the center of gravity of the entire stage

14

on the XY plane, and each of centers of the pair of the air bearings

66

A and

66

B provided inside the support brackets

62

shown in

FIG. 4

is also positioned on the line KX in the XY plane.

FIG. 4C

is a cross-sectional drawing of the part which includes the guiding member

17

, the carrier/follower

60

, and the magnetic track

56

A sectioned from the direction of the arrow

4

C in FIG.

2

. The arm

24

storing the magnetic track

56

A is buoyed up and supported on the base surface

12

A by the air bearing

32

, and the carrier/follower

60

is buoyed up and supported on the base surface

12

A by the air bearing

66

. At this time, the height of the air bearing

48

at the bottom surface of the stage body

42

(see

FIGS. 3

or

5

) and the height of the air bearing

32

are determined so as to place the driving coil

54

A on the stage body

42

side keeping a 2-3 mm gap in the Z direction in the slot space of the magnetic track

56

A.

Each of the spaces between the carrier/follower

60

and the arm

24

in the Z and Y directions hardly changes because they are both guided by the common guiding member

17

and the base surface

12

A. Furthermore, even if there is a difference in the height in the Z direction between the part on the base surface

12

A where the air bearing

32

at the bottom surface of the driving frame

22

(arm

24

) is guided and the part on the base surface

12

A where the air bearing

48

at the bottom surface of the stage body is guided, as long as the difference is precisely constant within the moving stroke, the gap in the Z direction between the magnetic track

56

A and the driving coil

54

A is also maintained constant.

Furthermore, since the driving coil

68

for the carrier/follower

60

is originally fixed to the carrier/follower

60

, it is arranged, maintaining a certain gap of 2-3 mm above and below in the slot space of the magnetic track

56

A. The driving coil

68

hardly shifts in the Y direction with respect to the magnetic track

56

A.

Cables

82

(see

FIG. 2

) are provided for directing the signals to the drive coils