GB2329521A

GB2329521A - Electromagnetic alignment and scanning apparatus

Info

Publication number: GB2329521A
Application number: GB9900937A
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: HK1035431A1; KR100281860B1; JP3804787B2; GB9512659D0; HK1026767A1; HK1017824A1; GB9817493D0; GB2325564B; GB2325566B; GB9825844D0; GB2325564A; KR100281857B1; JP4687911B2; GB2329520A; GB2325563B; HK1035432A1; GB2325565B; JPH0863231A; GB2329519A; JP2007242034A

Abstract

A scanning type exposure apparatus which exposes a pattern of a mask 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 mask stage 14 in one long linear direction and a small yaw rotation in plane.One element of the linear commutated motor is mounts upon a drive frame 22, called a balancing portion, which moves in the opposite direction to the mask stage by a reaction force to maintain the centre of gravity of the apparatus, the balancing portion and mask stage may be freely suspended above the base by air bearings 32 and 48. A laser interferometry system LBX1, LBX2, LBY, 50X1, 50X2, 50Y detects the exact position and orientation of the mask stage.

Description

ELECTROMANGETIC ALIGNMENT AND SCANNING APPARATUS The presen invention relates to a movable stage apparatus capaoe of precise movement, and particularly relates to a stage apparatus movable in one linear direction cable e of high accuracy positioning and high steed movement, which can be especially favorably utilized in a microlighographic system.

In water 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 cross one another during the exposure sequence. This invention discloses an apparatus to achieve precise scanning motion or suc a system. o attain high accuracy, the stace 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 three from excessive heat generation wnicn might cause interferometer interference or mechanical changes that compromises alignment accuracy Commtatorless electromagnetic alignement apparatuses such as the ones disclosed in U.S. Pat. Nos. 4,506,204, 4,506, 205 and 4, 507, 597 are not feasible because ty recuire 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 or 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 provide the large displacement motion in the plane, thereby elimInating the ne for large magnet and coil assemblies. ihe 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 current apparatus using commutated electromagnetic means is a significant improvement over prior commutatorless ones, the problems of low control bandwidth and inteferometer interference persist. In such an apparatus, a sub-stage Is moved magnetically In one linear direction and the commutated electromacnetic 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. rcer, heat dissipation oin the stage compromises interferometer accuracy.

It is also well known to move a movable member (stage) in one long linear directicn (e.g more than 10 cm) by using two of the linear motors in parallel where coil and magnet are cornbin. In this case, the stage is guided b some sort o 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 guidless structure based on the combination of several electromagnetic actuators, as disclosed in the prior art mentioned befcre, 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, and as a result, generating a problem o consuming more electricity.

It is at 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 resent invention to provide a guidless stace apparatus using commercially available regular linear motors as electromagnetic actuators or one linear direction motion.

Furthermore, it is an object o 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 by providing a movable member (stage body) to move in one inear direction and the second movable member to move sequentially in the same direction, constantly keeping a certain space in between, and providing the electromagnetic orce (action ad reaction force) in the direction orthogonal to the linear direction 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 motes in one linear direction.

According to one aspect of the present invention there is provided a stage apparatus having a movable stage which is moveably 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 ar.y mechanical contact with said base.

As a specific feature of the invention linear commutated motors can be located on opposite sides 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 port ion 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 o 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 vaw rotation in the plane.

Other aspects and features and advantages of the present invention will become more apparent upon a perusal 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, and in which: Fic. 1 is a schematic perspective view of apparatus in accordance with 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 th.e arrows.

Fig. 4A is an enlarged perspective, partially exploded, view showing the carrier/follower structure o 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 43 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 4C in the direction of the arrow but with the voice coil motor removed.

Fig. 5 is an elevational sectional view o 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 plane view, similar to Fig. 2, illustrating the preferred embodiment of the present invention.

Fig. 8 is an elevational sectional view o- the structure shown in Fig. 7 taken alon line 8-8' in the direction o the arrows.

Figs. 9 and 10 are much simplified schematic views similar to Figs. 7 and 8 and illustrating still another embodiment of the preset invention.

While the present invention has applicability generally to electromagnetic alignment systems, the preferred embodiment involves a scanning apparatus or 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 an moved as desired, a reticle stage position tracking laser nterferometer system 15, a position sensor 13 and 2 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 or driving the reticle stage 14 in the X direction and small yaw rotation.

The driving frame includes a pair o 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 o the base structure 12 such as by air bearings 32 so that te 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 corwarc or back in the X direction along a lie 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. support bracket 18 is mounted on each end of te 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 173 of the rear side of the guiding member 17. The air bearing 20' is fixed inside the free end of the support brackets 18 ann against the rear guiding surface 173. Therefore, each of the support brackets 18 is constrained in its displacement n the Y direction by the guiding member 17 and bearings 20 and 20' and is able to move only in te X direction.

Now, according to this first embodiment of the present invention, the air bearings 32, which are f 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 m) between the pad surface and the surface 12A of the base structure 12. The driving frame is s buoyed up from the surface 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 te upper part of the elongate arm 24 is positioned laterally in the Y direction by air bearings 66A ad 663 supported by a bracket 62 against opposite surfaces 17A and 173 of guiding member 17 and vertically in the Z direction by air bearings 66 above the surface 12A of the base structure i2. 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 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 42A and 423 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 or operation with the laser interferometer position sensing system 15 (see Fig. 6) for determining the exact position or the reticle stage which is fed to the position control system 16 in order to direct the appropriate drive signals or moving the reticle stace 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 52A and 523 on each of the opposed sides 42A and 42B, respectively The drive assemblies 52A and 523 include drive coils 54A ana 543 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, c 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. ere, 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 tat it is free to move in the Y direction in the rectangular space insice the driving frame 22. The air bearing 48 fixed under each of the four corners o the stage body 42 makes an extremely small gap between the pad surface and the base surface 12, and buoys up and supports the entire stage 14 from the surface 12A. These air bearings 48 should preferably be pre-loaded types wltn a recess or 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 or the projected Image via the ectangle opening 46 to pass through the projection optical system PD (See Fig. 5) which is installed below the rectangle opening, there is another opening 123 provicec at the center part of the base structure 12. The reticle 44 is loaded on the top surface cf 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 5CY, which is fixed near the side 42B o the stage body 42 near the arm 26, has vertical elongate reflecting surface in the X direct Ion which length is somehwat longer than the movable stroke of the stage 14 in the X direction, and the laser beam L3Y from the Y-axis interferometer is incidnet perpendicularly on the reflecting surface. In Fig. 2, the laser beam LBY is bent at a right angle by the mirror 12D which is fixed on the side of 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 BY 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 2C. Furthermore, in rig. 3, the air bearing 20 o the end side of the support brackets i8 against the guiding surface 173 of the guiding member 17 is also shown, Referring once again to Figs. 1 and 2, the laser beam LBX1 from the Xl-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 50X1 and 50X2 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 witi 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 tart of the base structure 12. The corresponding block for the L3y laser beam is not shown.

In Fig. 2, the distance BL in the Y direction between each o the center lines of the two laser beams L3X1 and L3X2 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 #X1 in the X direction o the X1-axis interferometer and the measured value X2 in the X direction or the X2-axis interferometer divided by the base line length sL is the approximate amount o yaw rotation in an extremely small range. A so, half the value of the sum of the #X1 and AX2 represents the X coordinate position of the entire stage 14. These calculations are done on the high speed digital processor n the position control system 15 shown in Fig. 6.

Furthermore, the center lines of each of the laser teams LBX1 and LBX2 are set on the same surface ere te pattern is formed on the reticle 44. The extension of the line CX, which is shown in Fig. 2 ano 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 ormed. And furthermore, the optical axis AX (See Figs. 1 and 5) also crosses at this intersection as shown in Fig. 1. In rig.

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 into the photo-sensitive substrate via the projectio optical system PL.

Furthermore, there are two rectangular blocks 90A and 90B fixed on the side 42A of the stage body 42 in Figs. 1 and 2. These blocks 90A and 903 are to receive the driving orce 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 driving coils 54A and 54B which are fixed on the botn 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 c tne magnetic track 56A and 56B without any contact. The assembly of the driving coil 54 and the magnetic track 55 used in the present emoodiment is a commercially easily accessible linear motor for general purposes, and it could be either with or without a commutator.

Her, 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 o scanningfor exposure and the amount of movement needed at the time o removal o the reticle from the olluminatioin optical system to change the reticle). In the case of the present embodiment, when a 6-inch (15.24 cm) reticle is se, the moving stroke is about 30 Cm.

As mentioned before, te driving frame 22 and the stage 14 are independently buoyed up and supported on the base.sur=ace 12A, and at the same time, magnetic action and reaction force is applied to one another in the X direction onlv bv the linear motor 52. Because of that, the law cf the conservation of momentum is seen between the driving frame 22 and the stage 14. o, 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 i3, 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. is means that the location o the center or the gravity of the apparatus on the Dase structure 12 is essentially fixed In the X direction. in the Y direction, there is no movement c any heavy object. Therefore, change in the location of the center or the gravity in the Y direction is also relatively fixeci.

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 the 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 is. 1, 2, 3, and 5, the structures of them will be explained here.

As shown In Fig. 1, the carrier/follower 50 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 ab 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 C3 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 o the gravity above te base structure 12 is substantial.

Furthermore referring now to Fig. 4A, the structure o the carrier/follower 6C will be explained. In Fig. 4A, the carrier/follower 60 is disassembled into two parts, 60A and 60B, for the sake of facilitating ones understanding.

As evident rrom 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 60 of the carrier/follower 60.

Furthermore, th air bearing 65C is placed against the base structure 12 on the bottom surface of the eno 60E and helps to buoy up the carrier/follower 60.

Hence the carrier/follower 60 is supported in the Z direction with the following three points, the two air bearings 66 and one air bearing 65C, and is constrained in the Y direction for movement in the X direction by air bearings 66A and 663. What is important in tis structure is that the second electromagnetic actuator 70 is arranged back to back wi th the support bracket 52 so tnat when tie actuator generates the driving force in the Y direction, reaction forces in the Y direction between the stage 14 and tie carrier/follower 70 actively act upon te air bearings 66A and 66B which are fixed inside the support bracket 62.

In other words, arranging the actuator 70 and the air bearings 66A, 56B on the line parallel to the y-axis in the 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, the magnetic track 56A in the arm 24 of the driving frame 22 provides magnetic flux for the driving coil 54A 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 66A, 663 and 66C, a vacuum pre-loaded type is preferable, since the carrier/follower 60 is light.

3esides the vacuum pre-loaded type, a magnetic pre-loaded type is also acceptable.

Next with reference to FIgs. 3, 4B and 5, 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 and a .agnat 72 attached to the carrier/follower 60 to move the stage 14 for small displacements in the Y direction in the plane of the travel of the stage 14 orthogonal to the X direction long liner 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. 43. Shown in Fig. 4B is a cross-sectional view o the VCM 70 sectioned at the norizontal plane shown with an arrow 43 in Fig. 5. in Fig.

4B, the magnets 72 of the VCM 70 are fixed onto the carrier/follower 60 sice. And the coil or the VCM 70 comprises the coil body 74A and its supporting part 743, and the sorting 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 90B A center line KX of the VCM 70 shows the direction o the driving force of the coil 74, 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, 2 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 Hig. 6) as shown in Fig. 4B, In Fig. 43, electrodes for capacitance sensors are placed so as to detect tne change in the gap In the X direction between the side surface o te rectangular blocks 90A and 903 facing witn 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 o a non-contact type such as photoelectric, inductive, ultrasonic, or air-micro system.

The case 70' in Fig. 3 is formed wit t carrier/follower 60 In one, and placed (spatially) so as not to contact any member on the reticle stage 14 side. As tor the gap between the case 70' and the rectangular blocks 90A and 90B in the X direction (scanning direction), when the gap on the sensor 13A side becomes wiper, 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 13B is obtained by either digital operation or analoq operation, and a direct servo (feedback) control system which controls te driving current of the driving coil 68 for the carrier/follower 60 is deslgne 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. 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 42 would be acceptable at around +.5 - 1 mm. This accuracy depends on now mucn of the yaw rotation o the stage body is allowed, and also depends on the length of tne line in the KX direction (energizing direction) of the coil body 74A 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 t2 using an interferometer (e.g., -0.03 pm supposing tne resolution of the interferometer is 0,01 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 s sat so as to go through the center of the gravity o the entire stage 14 on 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 t is also positioned on the line KX in the XY plane.

Shown in Fig. cC 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 4C in Fig. 2. The arm 24 storing 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 supported 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 driving coil 54A on the stage body 42 side keeping z 2 - 3 mm gap in Z direction in the slot space of the magnetic track 56A.

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 12A. rurthermore, even it there is a difference in the height in the Z direction between the tart on the base surrace 12A where the air bearing 32 the bottom surface of the drivIng frame 22 (arm 24) is guided and the part on the base surface 12A where thhe air bearing 48 at the bottom surface c te 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 SEA 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 o 2 - 3 mm above and below in the slot space of the magnetic track 56A. And the driving coil 68 hardly shifts In the t direction with respect to the magnetic track SEA.

Cables 82 (see Fig. 2) are provided for directing the signals to the arrive coils 54A and 54B on stage 14, the voice coil motor coil 74 and the carrier/follower drive coil 68, and these cables 82 are mounted on the carrier/follower 60 and guide 17 thereby eliminating 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 on, the cable issues will be described further in detail. As shown in Fig. 2, a connector 80 which connects wires or 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 urtnar connected to the end Dart 6C of the carrier/follower 60, and electric system wires and the air pressure and the vacuum system tubes 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 appears 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 o 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/follower 60, is not problematic, but the one which shifts the stage bod in X, Y, or e direction (yaw rotation direction) could affect the alignment or overlay accuracy. As for in X and e 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 1 by VCM 70 in the Y direction and the response by the linear motor in X and 8 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. mach of the driving signals to the driving coil 54A, 54B for the stage body 42 and the driving coil 74 of the VCM 70 and the detection signal from the position sensor 13 (the gap sensors 13A, 133) go through the electric system wire 82A from the connector 80. The pressure gas and the vacuum to each of the air sear ass 48 and 66 go through the pneumatic system tube 82B from the connector 80. On the other hand, te driving signal to the driving coil 54A and 543 goes trough the electric system wire 83A which is connected to the stage body 42, and the pressurized gas or 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 shown In rig. 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 that case, the moment can be canceled only by the VCM 70 with the highest response.

Referring now to Figs. 1, 2 and 6, the 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 543 for driving the stage 14 in 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 o the reticle stage 14. An appropriate drive signal to the voice coil 72 c voice coil motor 70 produces small displacements of the reticle stage 14 In the direction. As the position of the reticle stag 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 the applied drive forces will move the magnetic track assembly or drive frame 22 in a direction opposite to the movement o 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 i0 are placedin the reticle stage 14, and the driving coil 68 is placed in the carrier/follower 60. Each o these driving coils is driven in response to the driving signals SX1, SX2, SYl, and S#X, respectively, from the position control system 16. The laser interferometer system which measures the coordinates position of the stage i4 comprises the Y axis interferometer which wends/receives the beam L3Y, 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, IFY, IFX1, IFX2 to the position control system 15. The position control system 15 sends two driving signals SXI and 5X2 to the driving coils 54A and 543 so that the difference between the position information IFX1 and IX2 in the x direction will become a preset value, or in other words, the yaw rotation of the reticle stace 14 is maintained a the specified amount. Thus, the yaw rotation (in 6 direction) positioning by the beams LBX1 and L3X2, 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 5 and 543, 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 54B to give the same or slightly different forces as needed.

Furthermore, the position information IFY from theY axis interferometer is also sent to the control system 16, and the control system 16 sends an optimum driving signal S#X to the driving coil 68 of the carrier/follower 60. t that time, the control system 16 receives the detection 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 SAX 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 the 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 16 samples the current o the detection signal S pd each time, determiners whether the 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 63, 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 shown 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. Thus would cause certain parts to collide after this imbalance became excessive.

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

More precise methods recuire monitoring the position of the drive assembly by a measuring means (not shown) and applying a driving force to restore and maintain the correct position. The accuracy of the measuring means need not be precise, but on the orer 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 (66, 66A, 66B) o the carrier/follower 60 can be turned off to at as a brake during idle periods of the stage 42. If the coil 68 of the carrier/follower 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 o 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 or the problem regarding the center of the gravity, some of the effects and function can be applied without making any chages.

This invention provides a stage which can be used or 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; ano (3) small yaw rotation. The stage is isolated from mechanical disturbances of surrounding structures by utilizing electro-magnetic forces as the stage driver. 3y further using a structure for this guideless stage, a high control bandwidth is attained. These two factors contribute to achieve the smooth and accurate operation - the stage.

Descriptio Beraing in mind the description o the embodiment illustrated in Figs. 1-6, the preferred embodiment o 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 numbe-ed elements in Figs. 1-5.

In Figs. 7 and 8, differing from the previous first embodiment, the driving frame which functions as a counter weight is removed, and each of the magnet tracks 156A and 1563 of the two linear motors is rigidly mounted onto the base structure 112. The stage bod 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 o the stage body 142 in the Y direction, and they buoy up and support the stage body 142 against the base surface 112A.

Furthermore, according to the present embodiment, the reticle 144 is clamped and supported on the reticle chuck slate 143 which is separately placed on the stage body 142.

The straight mirror i50Y for the Y axis laser interferometer and two corner mirrors 150X1, 150X2 for the X axis laser interferometer are mounted on tne reticle chuck plate 143. The driving coils 154A and 154B are horizontally fixed at the both ends o the stage body 142 in the Y direction with respect to the magnetic tracks 156A ad 156B, and due to the control subsystem previously described, make the stage body 142 run straight in the X direction and yaw only to an extremely small amount.

As evident from Fig. 8, the magnetic track 1563 of the right side of the linear motor and the magnetic track 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 o 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 elevated 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 lower. Furthermore, two pre-loaded air bearings 165 against the vertical guiding surface 117A o the straight guiding member 117, which is mounted onto the base structure 112, are fixed on the side surface of the carrier/follower 160. This carrier/follower 160 is different from the one in Fig. 4A according to the previous embodiment, and the driving coil 168 (Fig. 7) for the carrier/follower 160 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 an tart o the magnetic track 156A within the range of te moving stroke, and has the VCM 170 which positons the stage body 142 precisely in the Y direction Furthermore, In wig. 7, the air bearing 165 which buoys up and supports the carrier/follower 160 is provided uncer the VCM 170. The follow-up motion to the stage body t2 of the carrier/follower 160 is also do based on the detection signal from the position sensor 13 as in the 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 shit 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 VCM 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 cit the vectors of the force moment generated by each of the linear motors can be minimized at the center of the gravity o 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. t3) Of the VCM 170 is arranged so as to pass through the center o the gravity of the entire structure o 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 carrier/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.

The same guideless principle can be employed in another embodiment. For example, in schematic Figs. 9 and 10, the stage 242, supported on a bases 212, Is drive in the long X direction by a single moving coil 25 moving within a 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 stag 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 274A and 2743 are energized differentially under control of the electronics subsystem. The VCM magnets (272A, 272B) are attached to a carrier/follower stage 260.

The carrier/follower stage is guided and drive 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 25t and track 256, a compensating opening in the stage 242 can be provided on the opposite sid of the coil 254 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 or the stage since the cables connected to the stage follow the stage via the carrier/follower. Cables connecting the carrier/follower to external devices ill have a certain amount ci 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 denying the transmission of mechanica' disturbances to the stage.

Furthermore, the counter-weight design preserves the locaticn o the center of gravity o the stage system during any stage motion in the long stroke direction Dy 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 mounted, 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 simpler 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 of 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 microlithographic system for exposing a pattern of a mask onto an object, comprising: an exposure device which exposes said pattern onto said object; a mask stage which moves holding said mask; a first drive device which moves said mask stage in a first direction; and a balancing portion which moves in a direction opposite to the direction of movement of said mask stage without holding either said mask nor said object, said balancing portion being heavier than said mask Stage.
2. A system according to Claim 1, wherein said first drive device has a first portion to be connected to said mask stage and a second portion to be connected to said balancing portion.
3. A system according to Claim 2, wherein said first portion and said second portion are not in contact with each other.
4. A system according to Claim 2 or 3, wherein said first portion comprises a coil member and said second portion comprises a magnet member.
5. A system according to Claim 2, 3 or 4, wherein movements of said mask stage and said balancing portion follow the law of conservation of momentum.
6. A system according to Claim 1, 2, 3, 4 or 5, wherein said first drive device comprises a linear motor.
7. A system according to any one of the preceding claims, wherein said mask stage is movably supported by a base structure.
8. A system according to Claim 7, wherein said balancing portion is movably supported by the base structure.
9. A system according to Claim 7 or 8, wherein said mask stage- is movable over a surface of said base structure via a bearing.
10. A system according to Claim 9, wherein said bearing is a non-contact bearing which opposes said mask stage to said base structure without any contact therebetween.
11. A system according to any one of the preceding claims, further comprising a position detection device which detects a position of said mask stage.
12. A system according to Claim 11, wherein said position detection device comprises a reflective surface fixed to said mask stage.
13. A system according to Claim 12, wherein said reflective surface is a corner-cube type mirror.
14. A system according to Claim 11, 12 or 13, wherein said position detection device detects a position of said mask stage with regard to said first direction during the movement of said mask stage.
15. A system according to Claim 11, 12 or 13, wherein said position detection device detects a position of said mask stage with regard to a direction which is different from said first direction during the movement of said mask stage.
16. A system according to Claim 11, 12, 13, 14 or 15, further comprising a control system which corrects yaw rotation of said mask stage based on a detection result by said position detection device.
17. A system according to Claim 16, wherein said control system is connected to said first drive device.
18. A system according to any one of the preceding claims, further comprising a second drive device which moves said mask stage in a second direction which is different from said first direction.
19. A system according to any one of the preceding claims, wherein said projection system projects the pattern optically.
20. A system according to any one of the preceding claims, wherein said balancing portion moves in such a way as to cancel a shift of the centre of gravity of said exposure apparatus.
21. A system according to any one of the preceding claims, wherein said exposure device exposes said pattern while said stage is moved in the first direction.
22. A system according to any one of the preceding claims, wherein said balancing portion operates without a drive source.
23. A system according to Claim 10, wherein said noncontact bearing is an air bearing.
24. A system according to any one of the preceding claims, wherein said mask stage comprises an opening through which said exposure device exposes said pattern onto said object.
25. A system according to any one of the preceding claims, wherein said balancing portion is of a rectangular shape.
26. A system according to Claim 1, 12, 13, 14, 15, 16 or 17, wherein said position detection device comprises an interferometer system.