Patent Number: 
Section: description

The invention is described below in the context of representative embodiments, which are not intended to be limiting in any way. It will be understood that any of the various stage apparatus according to the invention are not limited to use in a charged-particle-beam (CPB) microlithography system (in which exposure occurs in a vacuum). The stage apparatus can be used in any of various applications, including environments that are not evacuated. Electron-Beam Microlithography Apparatus An electron-beam (as a representative charged particle beam) microlithography system 100 is shown in FIG. 7. The system of FIG. 7 comprises an electron-optical lens barrel 101 that is evacuated using a vacuum pump 102. The vacuum pump 102 maintains a desired vacuum level inside the lens barrel 101. Inside the lens barrel 101 is an electron gun 103 that emits an electron beam propagating in a downstream direction (vertically downward in the figure). The electron gun 103 is mounted at the xe2x80x9ctopxe2x80x9d (in the figure) of the lens barrel 101. Disposed below the electron gun 103 along an optical axis Ax are a condenser lens 104, an electron-beam deflector 105, and a reticle M. The electron beam emitted from the electron gun 103 is converged by the condenser lens 104 to illuminate the reticle M. During illumination of the reticle M, respective exposure units (e.g., xe2x80x9csubfieldsxe2x80x9d) of the reticle M that are within the field of the condenser lens 104 are sequentially scanned (in the horizontal direction in the figure) by action of the deflector 105 deflecting the electron beam. Thus, the subfields are sequentially illuminated for exposure. The reticle M is fastened by electrostatic adhesion or the like to a chuck 110 that is mounted on an xe2x80x9cupperxe2x80x9d portion of a reticle stage 111. The reticle stage 111 is mounted on a base 116. A stage drive 112 is connected to the reticle stage 111 and functions, when actuated, to move the reticle stage 111. The stage drive 112, in turn, is connected to a controller 115 via a drive control 114. The drive control 114 receives stage-drive commands from the controller 115 and converts those commands (e.g., digital-to-analog conversion) for use by the stage drive 112. Feedback control is achieved by a laser interferometer (IF) 113 that also is connected to the controller 115. The laser interferometer 113 produces highly accurate position data concerning the reticle stage 111, and the position data are input to the controller 115. Based on this data, stage-actuation commands are sent as required from the controller 115 to the drive control 114, which actuates the stage drive 112 to move the reticle stage 111 accordingly. Thus, the position of the reticle stage 111 is accurately controlled in real time. A substrate chamber 121 is situated xe2x80x9cbelowxe2x80x9d the base 116. The substrate chamber 121 is evacuated to a suitable vacuum level by a vacuum pump 122. The substrate chamber 121 contains a condenser lens 124, a deflector 125, and a wafer W (as a suitable substrate). In the substrate chamber 121 the electron beam, having passed through the reticle M, is converged by the condenser lens 124 and deflected by the deflector 125 as required to form an image of the illuminated portion of the reticle at a desired location on the wafer W. The wafer W is fastened by electrostatic adhesion to a chuck 130 disposed on the upstream-facing surface of the wafer stage 131. The wafer stage 131 is mounted on a base 136 and is connected to a respective stage drive 132. The stage drive 132 is connected to the controller 115 via a drive control 134. The stage drive 132 and drive control 134 function in a manner similar to the stage drive 112 and drive control 114, respectively. The position of the wafer stage 131 is accurately determined by a laser interferometer 133 that also is connected to the controller 115. Precise positioning information about the wafer stage 131, as measured by the laser interferometer 133, is input to the controller 115. The laser interferometer 133 provides feedback control of the position of the wafer stage 131 by routing data to the controller 115. Respective commands from the controller 115 are routed to the drive control 134 based on this information, which converts the commands as appropriate to actuate the stage drive 132. Thus, the position of the wafer stage 131 is accurately controlled in real time by feedback. First Representative Embodiment of Stage Apparatus Referring first to FIG. 2, a stage apparatus 1 according to this embodiment is mounted on a base 3. This stage apparatus 1 corresponds to, e.g., the wafer stage 131 of the microlithography system shown in FIG. 7. In FIG. 2 a stage assembly 10 is disposed at the center of the stage apparatus 1. The stage assembly 10 comprises a first stage 11 (shown as a xe2x80x9clowerxe2x80x9d stage) that is driven in the Y-axis direction by respective linear motors 79a, 79b, and a second stage 17 (shown as an xe2x80x9cupperxe2x80x9d stage) that is driven in the X-axis direction by respective linear motors 79axe2x80x2, 79bxe2x80x2.  The first stage 11 is provided with an air bearing (described below, referring to FIG. 5) that moves on a movable X-axis guide 5 that extends in the X-axis direction. Each end of the X-axis guide 5 includes a respective Y-axis slider 7 configured to slide in the Y-axis direction on a respective stationary Y-axis guide 8. To facilitate such sliding, each Y-axis slider 7 includes a respective air bearing (described below, referring to FIG. 5) that moves on the respective Y-axis guide 8. The Y-axis guides 8 are mounted to the base 3 by respective guide anchors 9 disposed at each end of the respective guide. The second stage 17 is provided with an air bearing (described below, referring to FIG. 5) that moves on a movable Y-axis guide 5xe2x80x2 that extends in the Y-axis direction. Each end of the Y-axis guide 5xe2x80x2 includes a respective X-axis slider 7xe2x80x2 configured to slide in the X-axis direction on a respective stationary X-axis guide 8xe2x80x2. To facilitate such sliding, each X-axis slider 7xe2x80x2 includes a respective air bearing (described below, referring to FIG. 5) that moves on the respective X-axis guide 8xe2x80x2. The X-axis guides 8xe2x80x2 are mounted to the base 3 by respective guide anchors 9xe2x80x2 disposed at each end of the respective guide. The linear motors 79a, 79b, 79axe2x80x2, 79bxe2x80x2 are disposed, as described below, in the respective Y-axis sliders 7 and X-axis sliders 7xe2x80x2. Actuating the linear motors 79a, 79b causes movement of the Y-axis sliders 7 (with first stage 11) in the Y-axis direction relative to the Y-axis guides 8. Similarly, actuating the linear motors 79axe2x80x2, 79bxe2x80x2 causes movement of the X-axis sliders 7xe2x80x2 (with second stage) in the X-axis direction relative to the Y-axis guides 8xe2x80x2. Reference now is made to FIG. 1, which provides an exploded oblique view of the construction of the stage assembly 10. In the depicted embodiment, and along the Z-axis, the stage assembly 10 comprises the first (xe2x80x9clowerxe2x80x9d) stage 11 that is movable in the Y-axis direction and the second (xe2x80x9cupperxe2x80x9d) stage 17 that is movable in the X-axis direction. The stage assembly 10 also comprises a frame 13, desirably having a rectilinear configuration and that is rotatable in the xcex8Z direction by piezo actuators 15. The stage assembly 10 also includes a table 23, desirably having an open triangular configuration, that is driven in the xcex8X, xcex8Y, and Z directions by piezo actuators 25a, 25b, 25c. A wafer table 27 is attached to the upstream-facing surface of the table 23, and a wafer W or other suitable substrate is mounted to the wafer table 27. The configuration shown in FIG. 1 is drivable with six degrees of freedom. The first (xe2x80x9clowerxe2x80x9d) stage 11 has an open-box configuration that facilitates sliding of the first stage 11 on the movable X-axis guide 5 in the X-axis direction (see FIG. 2). The frame 13 is mounted on the upstream-facing surface of the first stage 11. One piezo actuator 15 is disposed at each end, in the X-axis direction, of the frame 13. With respect to each piezo actuator 15, one end 15a is attached to the frame 13, and the other end is linked to the first stage 11 by a pin or the like to allow rotation of the piezo actuator relative to the first stage. The frame 13 thus can be rotated in the xcex8Z direction by extending and contracting the piezo actuators 15 in a coordinated manner. The second (xe2x80x9cupperxe2x80x9d) stage 17 has an open-box configuration that facilitates sliding of the second stage 17 on the movable Y-axis guide 5xe2x80x2 in the Y-axis direction. Two relatively short flexures 19 extend laterally from each end (in the X-axis direction) of the second stage 17. The xe2x80x9cbottomxe2x80x9d of the second stage 17 fits into a corresponding opening defined in the frame 13, wherein the flexures 19 are attached to the frame 13 in corresponding slots. The second stage 17 is sufficiently smaller than the opening in the frame 13 so that no mechanical interference occurs when the frame 13 is rotated in the xcex8Z direction relative to the second stage 17. The flexures 19 deform only in the Y-axis direction. Consequently, the flexures 19 restrict movement of the frame 13 in the X-axis and Z-axis directions, but allow movement of the frame 13 in the xcex8Z direction. Relatively long flexures 21a, 21b are attached to each end (in the X-axis direction) of the second stage 17 xe2x80x9cabovexe2x80x9d the short flexures 19. The flexure 21a extending in the positive X-axis direction is branched. The flexures 21a, 21b attach the second stage 17 to the first stage 11. By the flexures 21a, 21b, some tolerance is provided in the orthogonality of the second stage 17 relative to the first stage 11 (serving as a reference). In addition, the frame 13 provides some freedom of rotation relative to the first stage 11. The table 23, desirably having a triangular configuration and having a defined thickness, is situated xe2x80x9cabovexe2x80x9d the second stage 17. The table 23 defines three holes 23a that reduce the mass of the table 23. The table 23 is supported on piezo actuators 25a, 25b, 25c that extend from respective corners of the table 23 to respective locations on the frame 13. The piezo actuator 25a (disposed in the positive X-axis direction) passes between the branches of the flexure 21a and is attached at a location 13a as shown to the upstream-facing surface of the frame 13. The piezo actuators 25b, 25c (disposed in the negative X-axis direction) extend so as to flank both edges of the flexure 21b and are attached at respective locations 13b, 13c as shown to the upstream-facing surface of the frame 13. The table 23 can be driven in the Z-axis direction by extending or contracting all the piezo actuators 25a, 25b, 25c equally in the Z-axis direction. The table 23 also can be driven in the xcex8Y direction by extending or contracting the piezo actuator 25a and the piezo actuators 25b and 25c relative to each other. For instance, the table 23 can be driven in the positive xcex8Y direction by extending the piezo actuators 25b and 25c while leaving the piezo actuator 25a fixed or in a contracted state. The table 23 can be driven in the xcex8X direction by extending or contracting the piezo actuators 25b and 25c relative to one another. For instance, by extending the piezo actuator 25c while leaving the piezo actuator 25b fixed or in a contracted state, the table 23 can be driven in the negative xcex8X direction. Thus, the three piezo actuators 25a, 25b, 25c are independently controllable, allowing a variety of controlled motions to be imparted to the table 23. In this embodiment, the table 23 is triangular. However, it will be understood that the table 23 can have any of various other suitable configurations. In addition, although the table 23 is described as being movable with three degrees of freedom (as achieved using the three piezo actuators 25a, 25b, 25c), it will be understood that the table 23 can be configured as movable with fewer or more degrees of freedom of motion (e.g., six degrees of freedom) using fewer or more (e.g., six) piezo actuators, respectively. The wafer table 27, on which the wafer W is mounted, is situated upstream of the table 23. The wafer table 27 normally includes a substrate-holding device such as an electrostatic chuck or the like (not shown, but see FIG. 7) situated on the upstream-facing surface of the wafer table 27. The wafer W is attached to the substrate-holding device. The wafer table 27 includes a mark plate 28 that defines marks used for determining the position of the wafer table 27 along the X-axis and Y-axis directions. The mark plate 28 desirably is situated to the side of the wafer W on the wafer table 27. Movable mirrors 29a, 29b are disposed at respective locations along respective edges of the wafer table 27. The outward-facing surfaces of the movable mirrors 29a, 29b are precision-polished and serve as corresponding reflective surfaces for the laser interferometer 133 shown in FIG. 7. Configurational details of a Y-axis slider 7 and respective Y-axis guide 8 are shown in FIGS. 3-5. It will be understood that each slider 7 and guide 8 and each slider 7xe2x80x2 and guide 8xe2x80x2 have similar structures to the illustrated structure. Note the axes shown in FIG. 3 relative to the axes shown in FIG. 2; FIG. 3 is a view in the negative X-axis direction of FIG. 2. Referring first to FIG. 3, the Y-axis guide 8 comprises a tubular member 61. As shown in FIG. 4, the tubular member 61 has a square or rectangular transverse section. Each end of the tubular member 61 is attached to a respective guide anchor 9 via a bearing 67. A respective air pad (air bearing) 51 is disposed in each of the xe2x80x9ctopxe2x80x9d- and xe2x80x9cbottomxe2x80x9d-contact surfaces between the respective guide anchor 9 and respective end of the tubular member 61. Around each air pad 51 in the guide anchor 9 is defined a groove and xe2x80x9cguard ringxe2x80x9d (not shown). The air pads 51 effectively sandwich the tubular member 61 from xe2x80x9cabovexe2x80x9d and xe2x80x9cbelowxe2x80x9d (i.e., in the Z-axis direction) and thus serve to maintain alignment of the tubular member 61 and guide anchors 9 along the respective longitudinal axis A1 of the tubular member 61. In the Z-axis direction, magnets 63, 65 are disposed xe2x80x9cabovexe2x80x9d and xe2x80x9cbelowxe2x80x9d the tubular member 61. As shown in FIG. 4, each of the magnets 63, 65 has a squared-U-shaped configuration and extends longitudinally in the Y-axis direction, with the opening in the xe2x80x9cUxe2x80x9d facing away from the optical axis Ax. The Y-axis slider 7 comprises a tubular member 71 having a square or rectangular transverse section (FIG. 4). The tubular member 61 of the Y-axis guide 8 extends coaxially through the tubular member 71 of the slider 7. Mounted to the tubular member 71 is a slider plate 73 having a specified thickness. T-shaped coil mounts 75a, 75b are mounted to the slider plate 73 and extend away from the slider plate 73 (leftward in the figure). Mounted to each coil mount 75a, 75b is a respective rectangular, flat-plate motor coil 77a, 77b. Each motor coil 77a, 77b extends into the respective U-shaped trough of the respective magnet 63, 65 to form a respective linear motor 79a, 79b, which (in the figure) achieve motion of the slider 7 in the Y-direction relative to the guide 8. Thus, the respective points of engagement of the driving force of the linear motors 79a, 79b are nearly aligned with the center of gravity of the Y-axis slider 7. By exerting the driving force on the center of gravity of the slider 7, high-precision and high-speed positional control of the Y-axis sliders 7 can be achieved. Although not shown, it will be understood that electrical wiring is mounted as required to the slider 7 for delivering electrical power to the motor coils 77a, 77b. Also, tubing is mounted to the slider 7 for circulating coolant as required. The Y-axis slider 7 does not actually contact the Y-axis guide 8; rather, air bearings are situated between the slider 7 and the guide 8. The construction of an exemplary air bearing is shown in FIG. 5, which depicts a tubular member 71 through which the tubular member 61 coaxially extends. In the figure, the xe2x80x9cupperxe2x80x9d wall 71a of the tubular member 71 is depicted pivoted upward to show underlying detail of the respective air bearing on a respective xe2x80x9cbearing surfacexe2x80x9d 71s.  As noted above, the air bearing shown in FIG. 5 is exemplary of the various air bearings in a stage apparatus according to the invention. However, the structure of the air bearing is not limited to the specific configuration shown. The depicted air bearing comprises two air pads 51, each comprising a respective unit of gas-porous material. The air pads 51 are situated at opposite ends of the bearing surface 71s of the upper wall 71a. An air-supply groove 51c is defined in the bearing surface 71s and extends linearly along the longitudinal median of the bearing surface 71s from one air pad 51 to the other. Surrounding the air-supply groove 51c and air pads 51 is an atmospheric-pressure guard xe2x80x9cringxe2x80x9d (groove) 52 defined in the bearing surface 71s. The atmospheric-pressure guard ring 52 is connected to the external atmosphere to allow release of air from the atmospheric-pressure guard ring 52 to the atmosphere. Surrounding the atmospheric-pressure guard ring 52 is a xe2x80x9clow-vacuumxe2x80x9d guard ring (groove) 53 defined in the bearing surface 71s. The low-vacuum guard ring 53 is evacuated to a suitable xe2x80x9clow-vacuumxe2x80x9d level during operation of the air bearing. Surrounding the low-vacuum guard ring 53 is a xe2x80x9chigh-vacuumxe2x80x9d guard ring (groove) 55 defined in the bearing surface 71s. The high-vacuum guard ring 55 is evacuated to a suitable xe2x80x9chigh-vacuumxe2x80x9d level during operation of the air bearing. In the depicted desired configuration, the respective ends of the guard rings 52, 53, 55 have semicircular profiles, with linear portions extending parallel to the axis A1 and connecting together the respective semicircular ends. Respective conduits for supplying and circulating air to the air-supply groove 51c, atmospheric-pressure guard ring 52, and air pads 51, and for evacuating the vacuum guard rings 53, 55 extend along the inner surfaces of the tubular member 61. In a desired configuration as shown, high-vacuum exhaust conduits 55a extend lengthwise at the upper-left and lower-right of the section of the tubular member 61 shown in FIG. 5. Flanking the high-vacuum exhaust conduits 55a are respective low-vacuum exhaust conduits 53a. Thus, each of the low-vacuum exhaust conduits 53a has a semi-circular transverse profile. Flanking the low-vacuum exhaust conduits 53a are respective air-venting conduits 52a. Thus, each of the air-venting conduits 52a has a semi-circular transverse profile. The remaining space inside the tubular member 61 defines an air-supply conduit 51a that supplies air (or other suitable gas) to the air pads 51 via the air-supply groove 51c.  For making connections between the respective conduits 55a, 53a, 52a, 51a and the respective grooves 55, 53, 52, 51c, respective holes 55b, 53b, 52b, 51b are defined in the middle area in the sides of the cylinder guide 61 corresponding with the respective conduits 55a, 53a, 52a, 51a. As shown, each hole 55b, 53b, 52b, 51b is aligned with the respective groove 55, 53, 52, 51c to supply, circulate, and exhaust air. Since the longitudinal portions of each guard ring 52, 53, 55 and air-supply groove 51c are straight and extend parallel to the axis A1, as the tubular member 71 moves relative to the tubular member 61 in the Y-axis direction, the holes 55b, 53b, 52b, 51b remain aligned and thus connected with their respective grooves 55, 53, 52, 51c. Thus, the grooves 55, 53, 52, 51c are constantly supplied with air, vented, or evacuated as appropriate. Air is supplied from the air-supply conduit 51a to the air-supply groove 51c and discharged through the porous material of the air pads 51 into the air bearing. This discharged air is collected in the atmospheric-pressure guard ring 52, conducted from the guard ring 52 to the air-venting conduit 52a, and discharged to the atmosphere. Air leaking from the atmospheric-pressure guard ring 52 is collected in the low-vacuum guard ring 53 and evacuated through the low-vacuum exhaust conduit 53a. Any remaining air is collected in the high-vacuum guard ring 55 and evacuated through the high-vacuum conduit 55a. As a result of this coordinated functioning of the guard rings, virtually no air leaks from the air pads into the substrate chamber 121, which is maintained at a high vacuum. As noted above, each movable guide 5, 5xe2x80x2 has associated therewith a respective slider 7, 7xe2x80x2 on each end. With respect to each movable guide 5, 5xe2x80x2, one slider 7, 7xe2x80x2 has a respective air bearing situated on each of the xe2x80x9ctop,xe2x80x9d xe2x80x9cbottom,xe2x80x9d and sides of the slider. The other slider 7, 7xe2x80x2 has a respective air bearing situated only on the xe2x80x9ctopxe2x80x9d and xe2x80x9cbottomxe2x80x9d surfaces of the slider. Thus, the movable guides 5, 5xe2x80x2 and stages 11, 17 are movable in the X-axis, Y-axis, and Z-axis directions while employing a minimal number of air pads. In this and other embodiments, it is desirable that the first and second stages and as many of the other components as possible be made of non-magnetic and electrically non-conductive materials, especially if the stage apparatus is to be used in a charged-particle-beam system. These types of materials substantially reduce the probability of generating unwanted magnetic fields in the vicinity of the charged particle beam. Exemplary materials include any of various ceramics, aluminum alloys, and titanium alloys. It also is desirable that the actuators in this and other embodiments be non-magnetic and have minimal electrical conductivity, especially if the stage apparatus is to be used in a charged-particle-beam system. In this embodiment, the actuators 15 and 25a-25c are described as being piezo actuators (electrostrictive actuators), which are the preferred type of actuators if the stage apparatus is to be used with a charged-particle-beam system. Alternatively, any of various other types of actuators can be used such as ultrasonic, mechanical, and hydraulic/pneumatic actuators. Also, if the generation of stray magnetic fields is not of serious concern, the actuators can be electromagnetic (e.g., Lorentz-type, EI core, etc.) or magnetostrictive. As noted above, in a charged-particle-beam system that must operate under conditions of substantially no stray magnetic fields, high vacuum (low-emission), high controllability (linearity), and extreme accuracy and precision (servo characteristics), electrostrictive (piezo) actuators are especially desired. Second Representative Embodiment of Stage Apparatus A second representative embodiment of a stage assembly 10xe2x80x2 is shown in FIG. 6. The stage assembly 10xe2x80x2 comprises a first (xe2x80x9clowerxe2x80x9d) stage 11 and a second (xe2x80x9cupperxe2x80x9d) stage 17. Attached to each of two opposing ends (in the X-axis direction) of the second stage 17 are relatively long respective flexures 21a, 21b. The long flexure 21a attached to the surface of the second stage 17 facing in the positive X-axis direction is branched as shown. The second stage 17 is attached to the first stage 11 by the relatively long flexures 21a, 21b.  A xe2x80x9clowerxe2x80x9d plate 81 (desirably rectangular in shape and having a specified thickness) is disposed xe2x80x9cabovexe2x80x9d the second stage 17. Three piezo actuators 25a, 25b, 25c are disposed extending from the xe2x80x9clowerxe2x80x9d surface of the xe2x80x9clowerxe2x80x9d plate 81 to the first stage 11. The piezo actuator 25a extends between the branches of the flexure 21a from the xe2x80x9clowerxe2x80x9d plate 81 to the xe2x80x9cupperxe2x80x9d surface of the first stage 11. The piezo actuators 25b, 25c extend on respective sides of the flexure 21b from the xe2x80x9clowerxe2x80x9d plate 81 to the xe2x80x9cupperxe2x80x9d surface of the first stage 11. The xe2x80x9clowerxe2x80x9d plate 81 can be driven in the Z direction by extending or contracting the piezo actuators 25a, 25b, 25c equally. The xe2x80x9clowerxe2x80x9d plate 81 can be driven in the xcex8Y direction by extending or contracting the piezo actuator 25a relative to the piezo actuators 25b, 25c. The xe2x80x9clowerxe2x80x9d plate 81 can be driven in the xcex8X direction by extending or contracting the piezo actuators 25b and 25c relative to each other. An xe2x80x9cupperxe2x80x9d plate 83 (desirably having a rectangular profile and a specified thickness) is disposed xe2x80x9cabovexe2x80x9d the xe2x80x9clowerxe2x80x9d plate 81. A respective piezo actuator 15 is disposed at each end (in the X-axis direction) of the xe2x80x9cupperxe2x80x9d plate 83. One end 15a of each piezo actuator 15 is attached to the xe2x80x9cupperxe2x80x9d plate 83. The other end of each piezo actuator 15 is linked to the xe2x80x9clowerxe2x80x9d plate 81 by a pin or the like allowing rotation of the piezo actuator relative to the plate 81. The xe2x80x9cupperxe2x80x9d plate 83 thus can be rotated in the xcex8Z direction by extending and contracting the piezo actuators 15. A wafer table or the like is mounted on the xe2x80x9cupperxe2x80x9d plate 83. As is understood from the foregoing description, stage apparatus are provided that comprise a table that can be driven with multiple degrees of freedom of motion without disturbing neighboring magnetic fields, thereby improving the accuracy and precision of a charged-particle-beam process being conducted on a substrate held by the table. Whereas the invention has been described in connection with representative embodiments, it will be understood that the invention is not limited to those embodiments. On the contrary, the invention is intended to encompass all modifications, alternatives, and equivalents as may be included within the spirit and scope of the invention, as defined by the appended claims.