GB2329517A

GB2329517A - Electromagnetic alignment and scanning apparatus

Info

Publication number: GB2329517A
Application number: GB9900926A
Authority: GB
Inventors: Akimitsu Ebihara; Thomas Novak
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 1994-06-27
Filing date: 1995-06-21
Publication date: 1999-03-24
Anticipated expiration: 2015-06-21
Also published as: GB2325565B; GB9825844D0; KR100281858B1; GB2329516B; GB9817493D0; GB2325565A; KR100281860B1; HK1035431A1; JPH0863231A; JP3804785B2; GB2329517B; JP2007242034A; GB2290658A; GB2325566A; HK1025840A1; GB2329520B; KR100281859B1; HK1025842A1; GB2329521A; GB2329518B

Abstract

A scanning type exposure apparatus which exposes a pattern onto an object while a stage 14 is moved in a scanning direction comprises apparatus capable of high accuracy position and motion control using one or more linear commutated motors to move a stage 14 in one long linear direction and a small yaw rotation in plane. A laser interferometry system LBX1, LBX2, LBY, 50X1, 50X2, 50Y detects the exact position and orientation of the stage. One element of the linear commutated motor is mounted upon a drive frame 22, called a balancing portion, which moves in the opposite direction to the stage by a reaction force to maintain the centre of gravity of the apparatus. A carrier/follower 60 holding a single voice coil motor 70 is controlled to follow the stage in the linear motion direction. The carrier/follower provides an electromagnetic force to move the stage small displacements in a direction perpendicular to the long linear direction, in order to ensure proper alignment.

Description

ELECTROMAGENTIC ALIGNMENT AND SCANNING APPARATUS The present invention relates to a movable stage apparatus capable of precise movement, and particularly relates to a stage apparatus moveable in one linear direction capable of high accuracy positioning and high speed movement, which can be especially favorably utilized n a microlithographic system.

In water steppers, the alignment of an exposure field to the reticle being imaged affects the success of the circuit or that field. In a scanning exposure system, the reticle and wafer are moved simultaneously and scanned across one another during the exposure sequence. This invention discloses an apparatus to achieve precise scanning motion or such a system.

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

Commutatorless electromagnetic alignement apparatuses such as the ones disclosed in U.S. Pat. os. 4, 506, 204, 4, 506, 205 and 4, 507, 597 are not easible 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 apparatuses was disclosed in U.S. pat. No. ,952,858, which employs a conventional XY mechanically guided sub-stage to province the large displacement motion in the 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. ven though current apparatus using commutated electromagnetic means is a significant improvement over prior commutatorless ones, 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 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 knorn. to move a movable retrer (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 o a linear guiding member and drive 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 guidless 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 to a long distance in one linear direction, a specially structured electromagnetic actuator as in the prior arts becomes necessary, causing the size of the apparatus to become larger, end as a result, generating a problem of consuming more electricity.

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

Furthermore, it is an object of the present invention to provide a guidless stage apparatus during commercially available regular liar motors as electromagnetic actuators or one linear direction motion.

Furthermore, it is an 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.

Furthermore, it is an object of the present invention to provide a completely non-contact stage apparatus bv providing a movable member (stage body) to move in one linear direction and the second movable member to move sequentially in the same direction, constantly keeping a certain space in between, anc providing the electromagnetic force (action and reaction force) in the direction orthogonal to the linear direct Ion between this second movable member and the stage body.

Furthermore, it is an 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 which moves as it supports an object.

Furthermore, it is an object of the present Invention to provide a non-contact apparatus which 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.

Furthermore, it is an object of the present invention to provide an apparatus which is structured so as not to change the location of the centre of the gravity of the entire apparatus even when the non-contact stage body moves in one linear direction.

According to one aspect of the present invention there is provided a stage apparatus having a movable stage which is movably supported on a base, comprising, a drive device for driving said movable stage, a balancing portion disposed outside said movable stage, and a non-contact bearing which opposes said balancing portion to said base without contact therebetween, whereby said balancing portion moves in response to a movement of said movable stage, with a movement component in the direction opposite to the direction of movement of said movable stage without any mechanical contact with said base.

As a specific feature of the invent ion linear commutated motors can be located on opposite slides of the stage and each 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 or 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 there is provided a stage driving method for driving a movable stage which is movably supported on a base, comprising, opposing a balancing portion disposed outside said movable stage to said base without contact therebetween by means of a non-contact bearing, and moving, in response to a movement of said movable stage, said balancing portion with a movement component in a direction opposite to the direction of movement of said movable stage without any mechanical contact with said base.

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 15 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 plane.

Other aspects and reatures and advantages of the present invention will become more apparent upon a perusal of the ollowing specification taken in conjunction wit the accompanying drawings whereIn sImilar characters of reference indicate sImilar elements in each of the several views, and in which: @ Fig. 1 is a schematic perspective view of apparatus in accordance with the present invent ion.

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 3-32 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 4B in the direction of the arrow.

Fig. oC is an enlarged elevational sectional view of a portion of the structure shown in Fig. 2 taken along line 4C 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 sown 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 plane view, similar to Fig. 2, illustrating the 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 t arrows. rigs 9 and nO are much simplified schematic views similar to Figs. 7 and 8 and illustrating still another embodiment o the present invention While the present invention has applicability generally to electromagnetic alignment systems, the preferred embodiment involves a scanning apparatus for a reticle stage as illustrated in Figs. 1-6.

Referring now to the drawings, the positioning apparatus 10 of the preset 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 corm of a magnetic track assembly or driving'frame fcr 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 torm 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 tree to move on the base structure in a direction aligned with the longitudinal axis ot the guice 17, the principal direction in which the scanning motion ot the reticle stage is desired. As used herein one dIrection' or a "first direction" applies to movement o tne frame 22 or the reticle stage 14 either toward o back in the X direction along a line aligned with the longitudinal axis o the guide 17.

Referring now to Figs. 1 and 5 to explain further in detail, the elongate guiding member 17 in the X direction has front and rear guiding surfaces 17A and 173 which are almost perpendicular to the surface 12A of the base structure 12. The front guiding surface 17A 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 per surface o 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 173 of the rear side of the guiding member 17. The air bearing 20' is fixed inside the zree end of the support brackets 18 and against the rear guiding surface 173. Therefore, each o the support brackets 18 is constrained in its displacement in the Y direction by the guiding merger 17 and air bearings 20 and 20' and is able to me only in the X direction.

Now, according to this 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 gap (1 several Hm) between the pad surface and the surface 12A of the base structure 12. The driving frame is buoyed up from te surace 12A and supported perpendicularly (in 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 per part of the elongate arm 24 is positioned laterally in the Y direction by air bearings 565 and 66B sported 5 a bracket 52 against opposite surfaces 17A and 173 o guiding member 17 and vertically in the Z direction by air bearings 66 above the surface 12A 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 12A and laterally by the guiding member 17.

Referring now to both Fig. 1 and rig. 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 6. The reticle body 42 includes a pair of opposed si-des 42A and 42B 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 2 of the reticle stage 14 for operation with the laser interferometer position sensing system 15 (see Fig. 6) or determining the exact position of the reticle stage which is fed to the position control system 16 in orcer to direct the appropriate drive signals or moving the reticle stage 14 as desired.

Primary movement of the reticle stage 14 5 accomplished with first electromagnetic drive assembly or means in the form o separate drive assemblies 52A and 523 on each of the opposed sides 42A and 423, respectively The drive assemblies 52A and 52B include drive coils 54A and 54B fixedly mounted on the reticle stage 14 at the sides 42A and 42B, respectively, for cooperating with magnet tracks 56A and 563 on the magnet track arms 24 and 25, respectively, of the drive frame 22. Tile in the preferred embodiment o the invention the magnet coils are mounte on the reticle stage and the magnets are mounted o 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 12A, and buoys up and supports the entire stage 14 from the surface 12A. These air bearings 48 should preferably be pre-loaded types witn a recess for vacuum attraction to the surface 12A.

As shown in Fig. 2, a rectangle 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 go through. In order for the projected image via the rectangle opening 46 to pass through the projection optical system PL (See Fig. 5) which is installed below the rectangle opening, there is another opening 123 proviced at the center part of the base structure 12. The reticle 4 is loaded on the top surface of the stage body by clamping members 42C which are protrusively placed at four points around the rectangle opening 46, and clamped by the vacuum. pressure.

Now, the interferometer mirror 50Y, which is fixed near the side 42B of the stage body 42 near the arm 2', has a vertical elongate reflecting surface in the X direction which length is somehwat longer than te movable stroke o the stage 14 In the X direction, and the laser beam LBY rom the Y-axis interferometer is incident perpendicularly on the reflecting surface. In Fig. 2, the laser beam m3Y is bent at a right angle by the mirro 12D which is fixed on the sice o the base structure 12.

Referring now to Fig. 3 as a partial cross-sectional drawing of the 3-3' view in Fig. 2, the laser beam L3Y which is incident on the reflecting surface of the interferometer mirror 50Y 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 420. Furthermore, in Fig. 3, the air bearing 20 on the end side of the support brackets 18 against the guiding surface 17B of the guiding member 17 is also shown.

Referring once again to Figs. 1 and 2, the laser beam L2X1 from the X1-axis interferometer is incident and reflected on the interferometer mirror 50X1, and the laser beam LBX2 from the X2-axis interferometer is incident and reflected on the interferometer mirror 50X2. These two mirrors 50Xi and 50X2 are structured as corner tube type mirrors, and even when tne 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 12C in Fig. 2 is an optical block such as a prism to orient the laser beams LBX1 and LBX2 to each of the mirrors 50X1 and 50X2, and is fixed to a part of the base structure 12. The corresponding block for the L3y laser beam is not shown.

In Fig. 2, the distance 3L in the. Y direction between each of the center lines of the two laser beams 3X1 and LBX2 is the lent of the base line used to calculate the amount of yaw rotation. Accordingly, the val of the difference between the measured value #X1 in the X direction o the Xl-axis interferometer and the measuran value #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 the #X1 and #X2 represents the X coordinate position of the entire stage 14. These calculations are done on the high speed digital processor in the position control system 16 shown in Fig. 6.

Furthermore1 the center lines of each of the laser beams L3X1 and LBX2 are set on the same surface where the pattern is formed on the reticle 44. The extension of the line CX, which is shown in rig. 2 and divides in half the space between each of the center lines of laser beams L3X1 and L3X2, and the extension of te laser beam LBY Intersect within the same surface where the pattern is formed. And furthermore, the optical axis AX (See FIgs. 1 and 5) also crosses at this intersection as shown in Fis. 1. In Fig.

1, a slit shape 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 photo-sensitive substrate via the projection optical system Pb.

Furthermore, there are two rectangular blocks 90A and 903 fixed on the side 42A of tne stage body 42 in Figs. 1 and 2. These blocks 90A and 903 are to receive the driving force in the Y direction from the second electro-magnetic actuator 70 which is mounted on the carrier/follower 60.

Details will be explained later.

The ariving coils 54A and 54B 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 track 56A and 563 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 w,th. or without a commutator. ere, considering the actual design, the moving stroke of the reticle stage 14 is mostly determined by the size o the reticle to (the amount of movement required at the time of scanningfor exposure and the amount of movement needed 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 (15.24 cm) 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 12t, and at the same time, magnetic action and reaction force is applied to one another in the X direction only by the linear motor 52. Because of that, the law of the conservation or momentum is see between the driving rame 22 and the stage 14 Now, suppose the weight o the entIre reticle stage 14 is about one fifth o the entire weigh o the frame 22 which Includes the support brackets 28, then the forward movement o 30 cm of the stace 14 in the X direction makes the driving frame 22 move by 5 cm backwarcs in the X direction. This means that the location or the center or the gravity of the apparatus on the base structure 12 is essentially fixed in the X direction. in the t direction, here is no movement of any heavy object. therefore, the change in the location oc the center of the 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 (54A, 54B) and the stators (56A, 56B) 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 .ne second electromagnetic actuator 70, which are the characteristic components of the present Invention, are provided to control the stage 14 in the Y direction.

Referring now to Figs. 1, 2, 3, and 5, the structures of them will be explained here.

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 t2) and to the arm 24, respectively. One end 60E of the carrier/follower 60, is substantially protruding inward (toward the stage body 42) over the arm 24. InsIde this end part 60 is fixed a driving coil 68 (same shape as the coil 54) which enters a slot space of the magnetic track 56A.

Furthermore, the bracket 62 supported air bearing 66A (See Figs. 2, 3, 4A and S) against te guiding surface 17A o 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 to buoy up and support tne carrier/follower 60 on the base surface 12A is also shown in Fig. 3.

The air bearing 663 against the guiding surface 173 of the guiding member 17 is also fixed to the free end o support bracket 62 on the other side of the hock from bearing 66A with guiding member 17 therebetween.

Now, as evident from Fig. 5, the carrIer/ PL. Such an arrangement is typical for a projection aligner, and unnecessary shift of the center of the 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 Pb, and thus result in a deflection of the image on the photosensitive substrate at the time o exposure. Hence, the merit o the device as in the present embodiment where the motion of tne stage 14 does not shift the center of the 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. oA, the carrier/follower 60 is disassembled into two arts, 60A and 603 for the sake o cacilitating onets understanding.

As evident crom Fig. 4A, the driving coil 68 to move the carrier/follower 60 itself in the X direction is fixed at the lower part of the end 60E of the carrier/follower 60.

Furthermore, the air bearing 66C is placed against the base structure 12A on the bottom surface of the end 60E and helps to buoy up the carrier/follower 60.

Hence the carrier/follower 60 is supported in te Z direction with the following three points, the two air bearings 66 and one air bearing 66C, and is constrained in the Y direction for movement in the X direction by air bearings 66A and 66B, 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 arc the carrier/follower 70 actively act upon the air bearings 66A and 663 which are fixed inside the support bracket 62.

In other words, arranging the actuator 70 and tne air bearings 66A, 663 on the line parallel to the y-axis in tne XY plane helps prevent generating 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, 4A and 4C described above, te magnetic track 56A in the arm 24 of tne driving frame 22 provides magnetic flux for the driving coil 54A on the stage body 42 side, and concurrently provides magnetic flux òr the driving coil 68 for the carrier/follower 60. As for the air bearings 66A, 663 and 66C, 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, 43 and S, the second actuator mounted on the carrier/follower 60 will be explained. A second electromagnetic drive assembly in the .orm 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 ana a nagnet 72 attached to the carrier/follower 60 to move the stage 14 cor small displacements in the Y direction in the plane of the 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. t3. Shown in Fig. 43 is a cross-sectional view of the VCM 70 sectioned at the horizontal plane shown with an arrow t3 in Fig. s. in Fig.

43, the magnets 72 c the VCM 70 are fixed onto the carrier/follower 60 sice. And the coil c the VCM 70 comprises the coil body 74A and its supporting part 743 and the support inc part 743 is fixed to a connecting plate 92 (a plate vertical to the XY plane) which is rigidly laid across the two rectangular blocks 90A and 903. A center line KX of the VCM 70 shows the direction of the driving force of the coil 7, and when an electric current flows through the coil body 74A, 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 correspondent 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 13A and 133 are provided as a positioning sensor 13 (see Fig. 6) as shown in Fig. 4B. 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.t and 903 acing with 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 bod 42) . Furthermore, the type of the sensor can be any of a non-contact type such as 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 or tne gap between the case 70' and the rectangular blocks 9 and 903 in the X direction (scanning direction) , when the gap on the sensor 13A side becomes wider, the gap on the sensor 13 B side becomes smaller. Therefore, if the difference between the measured gap value by the sensor 13A and the measured gap value by the sensor r33 is obtained by either dIgital operation or analog operation, and a direct servo (feedback) control system which controls the drivlno current of the driving coil 68 for the Carrier/follower 60 is designed musing a servo driving circuit which makes the gap difference zero, then the carrie-/.ollower 60 will automatically perform a follower movement in the X direction always keeping a certain space to the stage body 42. Or, 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 13A and 133 differentially.

In. the VCM 70 as described in Fig. 43, the gap between the coil body 74A 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 t2 would be acceptable at around #.5 - 1 mm. This accuracy depenos on how much of the yaw rotation of the stage body is allowed, and also depends on the length o the line i in the KX direction (energizing direction) of the coil body 74A of the VCM 70. Furthermore, the decree 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 m supposing the resolution of the interferometer is 0.01 jim.) This means net tne 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. 43 is set so as to go through the center of the gravity of the entire stage 14 cn the XY plane, and each of centers of the pair of the air bearing 66A and 663 provided inside the support brackets 62 shown in Fig. 4 is also positioned on the line XX In the XY plane.

Shown In Fig. oC is a cross-sectional drawing of the part which includes the guiding member 17, the carrier/follower 60, and the magnetic track 56A sectioned from the direction of the arrow zC in Fig. 2. The arm 24 stroing the magnetic track 56A is buoyed up and supported on the base surface 12A by the air bearing 32, and the carrier/follower 60 is buoyed up and sported on the base surface 12A 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 driven coil 54A on the stage body t2 side keeping 2 - 3 mm gap in Z direction in the slot space of the magnetic track 56A. ach of the spaces between the carrier/follower 60 and te 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 12A. Furthermore, even if there is a difference in the height in the Z direction between the cart on the base surface 12A where the air bearing 32 at the bottom surface of the driving frame 22 (arm 24) is rice: and the part on the base surface 12A 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 tne Z direction between the magnetic track 56A and the driving coil 54A is also preserved 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 56A. And the driving coil 53 hardly sits in the w direction with respect to the magnetic track 55.

Cables 82 (see Fig. 2) are provided for directing the signals to the drive coils 54A and 543 on stage 14, the voice coil motor coil 74 and the carrier/follower drive coil 68, and these cables 82 are mounted on the carrierfollower 60 and guide 17 thereby elirninating drag on the reticle stage 14. The voice coil motor 70 acts as a buffer by denying transmission of external mechanical disturbances to the stage 14.

Therefore, referring now to Figs. 2 and 4A, the cable issues will be described further in detail. As shown in ig. 2, a connector 80 which connects wires o the electric system and tuSes of the air pressure and the vacuum system (hereinafter called "cables") is mounted on the base structure 12 on one end of the guiding member 17. The connector 80 connects a cable 81 from the external control system (including the control system of air pressure and vacuum system besides the electric system control system shown in Fig. 6) to a flexible cable 82. The cable 82 is further connected to the end part 60 of the carrier/follower 60, and electric system wires and te air pressure and the vacuum system tuSes necessary for the stage body 42 are distributed as the cable 83.

As mentioned before, the VCM 70 works to cancel a cables drag or an influence by tension, but sometimes its influence apt ears as moment in unexpected direction between the carrier/follower 60 and the stage body 42. In other words, the tension of the cable 82 gives the carrier/follower 60 a force to rotate the guiding surface of the guiding member 17 or the base surface 12A, and the tension of the cable 83 gives a force to the carrier/follower 60 and the stage body to rotate relatively.

One of these moments, the constituent which shifts the carrier/=ollower 60, is not problematic, but the one which shifts the stage body in X, Y, or 6 direction (yaw rotation direction) could affect the alignment or overlay accuracy. As for in X and 6 directions, shifts can be corrected by a consecutive drive by the two linear motors (54A, 56A, 54B, 56B), and as for in the Y direction, the shift can be corrected by the VCM 70. In the present embodiment, since the weight of the entire stage 14 can be reduced substantially, the response of the motion of the stage 14 by VCM 70 in the Y direction and the response by the linear motor in X and 6 directions will be extremely high In cooperation with the completely non-contact guidless structure. Furthermore, even when a micro vibration (micron order) is generated in the carrier/follower 60 and it is transferred to the stage 14 via the cable 83, the vibration (from several Hz to tens of Hz) can be sufficiently canceled by the above mentioned high response.

Now, Fig. 4A shows how each of the cables is distributed at the carrier/follower 60. Sach of the driving signals to the driving coil 54A, 54B for the stage body 42 and the driving coil 74 of the VCY. 70 and the detection signal from the position sensor 13 (the gap sensors 13A, 133) so through the electric system wire 82A from the connector 80. The pressure gas and the vacuum to each o the air bearings 48 and 66 go through the pneumatic system tube 823 from the connector 80. On the other hand, the driving signal to the driving coil 54A and 543 goes through the electric system wire 83A which is connected to the stage body 42, and the pressurized gas for the air bearing 48 and the vacuum for the clamping member 42C so through the pneumatic system hoses 833.

Furthermore, it is preferable to have a separate line for the pneumatic system for the air bearings 20, 20' and 32 of the driving frame 22, independent of the one shov, in Fig. 2. Also, as shown in Fig. 4A, in case the tension or vibration of the cable 83 cannot be prevented, it is advisable to arrange the cable 83 so as to limit the moment by the tension or vibration the stage body 42 receives only to Y direction as much as possible. In tat case, the moment can be canceled only by the VCM 70 with the highest response.

Referring now to Figs. 1, 2 and 6, te positioning o the reticle stage 14 is accomplished first knowing its existing position utilizing the laser interferometer system 15. Drive signals are sent to the reticle stage drive coils 54A and 54B for driving the stage 14 n the X direction. A difference in the resulting drive to the opposite sides 42A and 423 of the reticle stage 14 will produce small yaw rotation of the reticle stage 14. An appropriate drive signal to the voice coil 72 o voice coil motor 70 produces small displacements o the reticle stage 1 in the Y direction. As the position o the reticle stage 14 changes, a drive signal is sent to the carrier/follower coil 68 causing the carrier/follower 60 to follow the reticle stage 14. Resulting reaction forces to te applied drive forces will move the magnetic track assembly or drive crame 22 in a direction opposite to the movement of the reticle stage 14 to substantially maintain the center of gravity of the apparatus. It will be appreciated that the counter-weight or reaction movement of the magnetic track assembly 22 need not be included in the apparatus in which case the magnetic track assembly 22 could be fixedly mounted on the base 12.

As described above, in order to control the stage system according to the present embodiment, a control system as shown in Fig. 6 is installed. This control system in Fig. 6 will be further explained in detail here.

X1 driving coil and X2 driving coil composed as the driving coils 54A and 543 of two linear motors respectively, and Y driving coil composed as the driving coil 72 of the VCM 70 are placedin the reticle stage 14, and the driving coil 68 is placed in the carrier/follower 60. Each of these driving coils is driven in response to the driving signals SX1, SX2, SY1, and SAX, respectively, from the position control system 16. The laser interferometer system which measures the coordinates position of the stage 14 comprises the Y axis interferometer which sends/receives the beam LBY, the Xl axis interferometer which sends/receives the beam L3X1, and the X2 axis interferometer which sends/receives the beam LBX2, and they send position information for each of the directions of the axes, IFf, IFX1, IFX2 to the position control system 16. The position control system 15 sends two driving signals SXI and SX2 to tne driving coils 54A and 543 so that the difference between the position information IFX1 and IFX2 in the X direction will become a preset value, or in other words, the yaw rotation of the reticle stage 14 is maintained at tne specified amount. Thus, the yaw rotation (in 6 direction) positioning byy the beams LBX1 and LBX2, X1 axis and X2 axis interferometers, the position control system 16, and the driving signals SX1 and SX2 is constantly being conducted, once the reticle 44 is aligned on the stage body 42, needless to mention the time of the exposure.

Furthermore, the control system 16, which obtained the current coordinates position of the stage 14 in the X direction from the average of the sum of position information IFX1 and IFX2 in the X direction, sends the driving signals SX1, SX2 to the driving coils 54A ano 5, respectively, based on the various commands from the Host CPU 16' and the information CD for the parameters.

Especially when scanning exposure is in motion, it is necessary to move the stage 14 straight in the X direction while correcting the yaw rotation, and the control system 16 controls the two driving coils 54A and 543 to give the same or slightly different forces as needed.

Furthermore, the position information IFY from the Y axis interferometer is also sent to the control system 16, and the control system 16 sends an optimum driving signal SeX to the driving coil 68 of the carrier/follower 6C. At that time, the control system 15 receives the motion signal S pd from the position sensor 13 which measures the space between the reticle stage 14 and the carrier/follower 60 in the X direction, and sends a necessary signal S#X to make the signal S pd into the preset value As mentioned before, the follow-up accuracy for the carrier/follower 60 is not so strict that the detection signal S pd of te control system 16 does not have to be evaluated strictly either. For example, when controlling the motion by reading the position information IFY, IFX1, IFX2 every second from each of the interferometers, the high speed processor in the control system 15 samples the current cc the detection signal S pd each time, determines whether tne value is large or small compared to the reference value (acknowledge the direction), and if the deviation surpasses a certain point, the signal S#X in proportion to the deviation can be sent to the driving coil 68. Furthermore as mentioned before, it is also acceptable to install a control system 95 which directly servo controls the driving coil 68, and directly controls the follow-up motion of the carrier/follower 60 without going through the position control system 16.

Since the moving stage system as shove has no attachment to constrain it in the X direction, small influences may cause the system to drift toward the positive or negative X direction. This would cause certain parts to collide after this imbalance became excessive.

The influences include cable forces, imprecise leveling of the base reference surface 12A or friction between components. One simple method is to use weak bumpers (not shown) to prevent excessive travel of the drive assembly 22. Another simple method is to turn off the air to one or more o the air bearings (32,20) used to guide the drive assembly 22 when the drive assembly reaches close to the end of the stroke. The air bearings can be turned on when the drive begins to move back in tte opposite direction.

More precise methods require monitoring the position of the drive assembly by a measuring means (not shown) and applying a driving force te restore and maintain the correct position. The accuracy c the measuring means need not be precise, but on the order of 0.1 to 1.0 mm. The driving force can be obtained by using another linear motor (not shown) attached to the drive assembly 22, or another motor that is coupled to the drive assembly.

Finally, the one or more air bearings (56,66A.,663) of the carrier/follower 60 can be turned of to act as a brake during idle periods of the stage t2. If the coil 68 of the carrier/.oNlower 60 is energized with the carrier/follower 60 in the braked condition the drive assembly will be driven and accelerated. Thus, the position control system 16 monitors the location of the drive assembly 22. When the drive assembly drifts out of position, the drive assembly is repositioned with sufficient accuracy by intermittently using the coil 68 of the carrier/follower 22.

In the first embodiment of the present invention, the driving frame 22 which functions as a counter weight is installed in order to prevent the center of the gravity of the entire system from shifting, and was made to move in the opposite direction from the stage body 42. However, when the structures in Figs. 1 - 5 are applied to a system where the shift of the center of the gravity is not a major problem, it is also acceptable to fix the driving frame 22 on the base structure 12 together. In that case, except for the problem regarding the center of the gravity, some of the effects and function can b applied without making any changes.

This invention provides a stage whIch can be used for high accuracy position and motion control in three degrees of freedom in one plane: (1) long linear motion; (2) short linear motion perpendicular to the long linear motion; and (3) small yaw rotation. The stage is isolated from mechanical disturbances of surrounaina structures by utilizing electro-magnetic forces as the stage driver. By further using a structure for this guideless stage, a hl control bandwidth is attained. These two factors contribute to achieve the smooth and accurate operation o the stage.

Description o the Preferred Smbodirrent Bearing in mind the description of the embodiment illustrated in Figs. 1-6, the preferred embodiment of the present invention is illustrated in Figs. 7 and 8 wherein the last two digits of the numbered elements are similar to the corresponding two digit numbered elements in Figs. 1-5. in Figs. 7 and 8, differing from the previous first emoociment, the driving frame which functions as a counter weight is removed, and each of the magnet tracks 156A and 1565 of the two linear motors is rigidly mounted onto the base structure 112. The stage body 143 which moves straight in the X direction is placed between the two magnetic tracks 156A and 156B. As shown in Fig. 8, an opening 112B is formed in the base structure 112, and the stage body 142 is arranged so as to straddle the opening part 1123 in the Y direction. There are four pre-loaded air bearings 148 fixed on the bottom surface at both ends -r te stage body 142 in the Y direction, 156A of the left side of the linear motor are arranged so as to have a difference in level in z direction between them. In other words, the bottom surface of the both ends in the direction of the long axis of the magnetic track 156 on the left side is, as shown in Fig. 7, elevated by a certain amount with a block member 155 against the base surface 112A. And the carrier/follower 160 where the VCM is fixed is arranged in the space below the elevate magnetic track 156A.

The carrier/follower 160 is buoyed up and supported by the pre-loaded air bearings 166 (at 2 points) on the base surface 112A' o the base structure 112 which is one level lbwer. Furthermore, two pre-loaded air bearings 164 against the vertical guiding surface 117A of the straight guiding member 117, which is mounted onto the base structure 112, are fixed on the side surface o the carrier/follower 160, This carrier/follower 160 is different from the one in Fig. MA according to the previous embodiment, and the driving coil 168 (Fig. 7) for the carrier/follower 150 is fixed horizontally to the part which extends vertically from the bottom of the carrier/follower 160, and positioned in the magnetic flux slot of the magnetic track 156A without any contact. The carrier/follower 160 is arranged so as not to contact any part of the magnetic track 156A within the range of the moving stroke, and has the VCM 170 which positions the stage body 142 precisely in the Y direction.

Furthermore, in Fig 7, the air bearing 166 which buoys up and supports the carrier/follower 160 is provided under the vCM 170. The follower motion to the stage body 142 of the carrier/follower 160 is also done based on the detection signal from the position sensor 13 as in t previous embodiment.

In the second embodiment structured as above, there is an inconvenience where the center of the gravity of the entire system shifts in accordance with the shift of the stage body 142 in the X direction, since there is substantially no member which functions as a counter weight. It is, however, possible to position the stage body 142 precisely in the Y direction with non-contact electro-magnetic force by the VOM 170 by way of following the stage body 142 without any contact using the carrier/follower 160. Furthermore, since the two linear motors are arranged with a difference in the level in the Z direction between them, there is a merit where the sum of the vectors of the force noment generated by each of the linear motors can be minimized at the center of the gravity of the entire reticle stage because the force moment of each of the linear motors substantially cancels with the other.

Furthermore, since an elongated axis of action (the line KX in Fig. 3) of the VCM 170 is arranged se as to pass through the center o the gravity of the entire structure of the stage not only on the XY plane but also in the Z direction, it is more difficult for the driving force of the VCM 170 to give unnecessary moment to the stage body 142. Furthermore, since the method of connecting the cables 82, 83 via the carrer/follower 160 can be applied in the same manner as in the first embodiment, the problem regarding the cables in the completely non-contact guideless stage is also improved. he same guideless principle can be employed In another e.bodiment. For example, in schematic Figs. 9 and 10, the stage 22, supported on a bases 212, is driven in the long X direction by c single moving coil 254 moving within z single magnetic track 256. The magnetic track is rigidly attached to the base 212. The center of the coil is located close to the center of gravity of the stage 242.

To move the stage in the Y direction, a pair of VCM's (274A,274B,272A,272B) are energized to provide an acceleration force in the Y direction. To control yaw, the coils 274L. and 2743 are energized differentially under control of the electronics subsystem. The VCM magnets (272A,2723) are attached to a carrier/follower stage 250.

The carrier/follower stage is guided and driven like the first embodiment previously described.

This alternative embodiment can be utilized for a wafer stage. Where it is utilized for a reticle stage the reticle can be positioned to one side of the coil 254 and track 256, and if desired to maintain the center of gravity of the stage 242 passing through the coil 25 and track 256, a compensating opening in the stage 242 can be provided on the opposite side of the coil 25t and track 255 from the reticle.

Merits gained from each of the embodiments can be roughly listed as follows. To preserve accuracy, the carrier/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 nave a certain amount of drag, but the stage is free from such disturbances since there is no direct connection to the carrier/follower which acts as a buffer by dening the transmission of mechanical disturbances to the stage.

Furthermore, the counter-weight design preserves the location o t center oc gravity of the stage system during any stage motion in the long stroke direction by using the conservation of momentum principle. This apparatus essentially eliminates any reaction forces between the stage system and the base structure on which the stage system is mounted1 thereby facilitating high acceleration while minimizing vibrational effects on the system.

In addition, because the stage is designed for limited motion in the three degrees of freedom as described, the stage is substantially simper than those which are designed for full range motions in all three degrees of freedom. Moreover, unlike a commutatorless apparatus, the instant invention uses electromagnetic components that are commercially available. Because this invention does not require custom-made electromagnetic components which become increasingly difficult to manufacture as the size and stroke owt the stage increases, this invention is easily adaptable to changes in the size or stroke of the stage.

The embodiment with the single linear motor eliminates the second linear motor and achieves yaw correction using two VCM's.

While the present invention has been described in terms of the preferred embodiment, the invention can take many different forms and is only limited by the scope of the following claims.

Claims

CLAIMS 1. A scanning type exposure apparatus arranged to expose a pattern onto an object while a stage is moved in a scanning direction, comprising: an exposure device which exposes said pattern onto said object; a first drive device which moves said stage in the scanning direction; a position detection device comprising an interferometer system to detect a position of said stage; and a balancing portion which moves in the scanning direction responsive to the movement of said stage such that the centre of gravity of said scanning type exposure apparatus does not shift substantially.
2. An exposure apparatus according to Claim 1, wherein said first drive device has a first portion to be connected to said stage and a second portion to be connected to said balancing portion.
3. An exposure apparatus according to Claim 2, wherein said first portion and said second portion are not in contact with each other.
4. An exposure apparatus according to Claim 2 or 7, wherein said first portion comprises a coil member and said second portion comprises a magnet member.
5. An exposure apparatus according to Claim 2, 3 or 4, wherein the movements of said stage and said balancing portion follow the law of conservation of momentum.
6. An exposure apparatus according to Claim 1, 2, 3, 4 or 5, wherein said first drive device comprises a linear motor.
7. An exposure apparatus according to any one of the preceding claims, wherein said stage is movably supported by a base structure.
8. An exposure apparatus according to Claim 7, wherein said balancing portion is movably supported by the base structure.
9. An exposure apparatus according to Claim 7 or 8, wherein said stage is movable over a surface of said base structure via a bearing.
10. An exposure apparatus according to Claim 9, wherein said bearing is a non-contact bearing which opposes said stage to said base structure without any contact therebetween.
11. An exposure apparatus according to Claim 10, wherein said non-contact bearing is an air bearing.
12. An exposure apparatus according to any one of the preceding claims, wherein said position detection device comprises a reflective surface fixed to said stage.
13. An exposure apparatus according to Claim 12, wherein said reflective surface is a corner-cube type mirror.
14. An exposure apparatus according to any one of the preceding claims, wherein said position detection device detects a position of said stage with regard to said scanning direction during the movement of said stage.
15. An exposure apparatus according to any one of the preceding claims, wherein said position detection device detects a position of said stage with regard to a direction which is different from said scanning direction during the movement of said stage.
16. An exposure apparatus according to any one of the preceding claims, further comprising a control system which corrects yaw rotation of said stage based on a detection result by said position detection device.
17. An exposure apparatus according to Claim 16, wherein said control system is connected to said first drive device.
18. An exposure apparatus according to any one of the preceding claims, further comprising a second drive device which moves said stage in a direction which is different from said scanning direction.
19. An exposure apparatus according to any one of the preceding claims, wherein said exposure device includes a projection system which projects said pattern onto said object.
20. An exposure apparatus according to Claim 19, wherein said stage is located above said projection system.
21. An exposure apparatus according to Claim 19 or 20, wherein said projection system projects the pattern optically.
22. An exposure apparatus according to any one of the preceding claims, wherein said exposure device includes a mask which defines said pattern.
23. An exposure apparatus according to Claim 22, wherein said stage holds said mask.
24. An exposure apparatus according to any one of the preceding claims, wherein said balancing portion operates without a drive source.
25. An exposure apparatus according to any one of the preceding claims7 wherein said mask stage comprises an opening through which said exposure device exposes said pattern onto said object.
26. An exposure apparatus according to any one of the preceding claims, wherein said balancing portion is of a rectangular shape.