Substrate processing apparatus and method

A substrate processing apparatus and method are disclosed.

FIELD OF THE INVENTION

This invention generally relates to substrate inspection and lithography and more particularly to movable stages used in substrate inspection and lithography.

BACKGROUND OF THE INVENTION

Historically wafer writing in lithography and scanning in metrology and inspection systems have used linear stepping or scanning motion to translate a substrate. Rectilinear motion has the advantages of simplicity in the rendering process, since the die on a semiconductor wafer are typically arranged in the direction of motion. In Cartesian (XY) reticle writing the data path follows the prevailing directionality in the geometry to be rendered. However, the factor limiting the throughput is the mechanical motion of the Cartesian stage. As the data path electronics get faster, this mechanical limitation of Cartesian systems becomes more limiting, and the data path rendering in polar coordinates becomes easier. The data path rendering speed is expected to continue to follow the Moore's law and improve with newer generations of semiconductors, while throughput of Cartesian stages is subject to relatively slow progress in precision engineering.

Reciprocating stages have a practical limit of turnaround time at the end of the swath of about 100 milliseconds. To shorten this time mechanics must allow higher bandwidths. The use of high performance materials allows only for moderate improvements of highest scanning speed. The increases in acceleration at the end of the motion also have their limitation in power of actuators, heat dissipation, reaction on the vibration isolation system and the machine base, settling after acceleration etc.

It is within this context that embodiments of the present invention arise.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

An example of a substrate processing apparatus100according to an embodiment of the present invention is depicted schematically inFIG. 1. The apparatus100generally includes a first stage102and a second stage104. The first stage102carries one or more substrate chucks103. Each substrate chuck103is adapted to support and retain a substrate101. Examples of suitable substrates include, but are not limited to, semiconductor wafers, or reticles for optical lithography. The first stage102moves with respect to the second stage104. By way of example, the first stage102may be a rotary stage102that rotates about a z axis. The second stage104may be a translating stage moves the rotary stage103linearly in a direction parallel to the plane of rotation of the rotary stage102. One or more bearings support the rotary stage102, facilitate smooth rotation of the rotary stage102and transfer translation forces between the rotary stage102and the translating stage104in such a way as to maintain the z axis of the rotating stage in a substantially fixed position and orientation relative to the translating stage104as the translating stage moves with respect to a support structure108. By way of example, the support structure108may be a vacuum chamber, the lid of the vacuum chamber, or a stage base structure.

By way of example, the rotary stage102and translating stage104may be disposed within a chamber, e.g., a vacuum chamber, to provide a controlled environment for processing the substrate101and serves as the support structure108. A substrate processing tool110may be used to probe selected portions of the substrate101with radiation, e.g., in the form of electromagnetic radiation, such as infrared, visible or ultraviolet light, or in the form of a beam of charged particles, such as electrons or ions. The processing tool,110, may be part of a lithographic system, e.g. an electron beam exposure column or an optical lithography lens system. Alternatively, the tool110may be part of a substrate metrology or inspection tool that exposes selected portions of the substrate101to radiation and collects scattered or secondary radiation from the substrate101. Examples of such tools include optical wafer inspection tools and scanning electron microscopes.

The combined rotary motion of the rotary stage102and linear motion of the translating stage104move the substrate101relative to the tool110in such a way that the optical column may probe the entire surface of the substrate101in a continuous fashion e.g., along a spiral path. Such motion is analogous to the movement of a phonograph needle relative to a record or a laser beam relative to a compact disc (CD). The principal difference being that in embodiments of the present invention, the tool110remains substantially fixed with respect to the chamber and the substrate101rotates and is moved linearly relative to the fixed tool110. By “substantially fixed” it is meant that the there may be some mechanism for adjustment of small scale variations in positioning. Preferably, such position variations are within an ability of a sensor to detect and within an ability of the adjustment mechanism to counteract while maintaining a desired resolution in relative positioning between the tool110(or a beam from the tool) and the substrate101. Mechanisms for such adjustment are described in detail below.

Unlike reciprocating motion or R-θ motion of conventional non-continuous R-θ positioning stages, continuous rotary motion, is inherently smooth. The inertial forces of the rotary stage102are inherently balanced, and gyroscopic effects tend to stabilize the orientation of the rotation axis z. Consequently, an apparatus of the type shown inFIG. 1may scan large substrates quickly without having to impart high acceleration to the substrate101. In alternative embodiments the tool may probe the surface of the substrate101with continuous rotary motion along a series of concentric circular paths having different radii. In such a case, the rotary motion may be kept continuous while the linear motion is discontinuous.

In multiple substrate configurations, multiple chucks may be arranged symmetrically on a rotating platter. The layout of the chucks103on the rotary stage102can be in a single radial arrangement, with all chucks103arranged at the same radial distance from the z axis. Alternatively, the chucks103may be arranged in multiple rows, a hexagonal pack, or another arrangement suitable for writing or probing of the substrates. Corresponding data path strategies would follow the substrate layout.

One or more of the chucks103may be equipped with sensors allowing for feedback of parameters important to accurate writing, for example thermal sensors, e-beam detectors, e-beam reflectors or position sensors.

Several configurations are possible for the bearings106, to meet the requirements of a very high throughput stage. For example, the rotary-translation stage may be implemented using magnetic levitation (maglev) in the bearings106to support the rotary stage102. Alternatively, the Rotary-Translation stage may use air bearings or conventional bearings as an alternative to magnetic levitation. In some embodiments a fixed rotary stage may be combined with one or more moving tools. For example a differentially pumped air bearing rotary stage may be combined with a differentially pumped air bearing tool slide. Alternatively, a conventional bearing rotary stage may be combined with a sliding seal moving tool.

It is noted that the placement of maglev bearings106proximate a periphery of the rotary stage102keeps stray magnetic fields from the bearings106at a safe distance from the tool110. This greatly reduces the effect of such magnetic fields on the operation of the tool, particularly when the tool110is a charged particle beam column, such as an electron beam column. It is further noted that this same concept may also apply to an X-Y translation stage, e.g., in which the first stage102moves linearly along an x axis that is fixed with respect to the second stage and the second stage104moves linearly along a y axis that is at an angle relative to the x axis.

In a preferred embodiment of a rotary-linear stage200shown inFIGS. 2A-2E, a rotary stage202is carried by a linear stage204using linear motors205. The rotary stage202supports multiple substrate chucks203. The rotary stage202includes a peripheral ferromagnetic ring206. Peripherally mounted rotary stage radial maglev units207X,207Y attached to the intermediate linear stage204apply magnetic forces to the ring206along the x and y axes, respectively along lines of force that intersect the rotation axis z. Peripherally mounted rotary stage vertical maglev units207X,207Y attached to the intermediate linear stage204apply magnetic forces to the ring206along the rotation axis z.

The linear stage204may suspended by electromagnet levitation units (Z maglevs)209from a support structure. By way of example, the support structure may be the underside of a lid of a vacuum chamber208. The chamber lid may also carry a substrate processing tool210. By way of example and without limitation, the tool210may include e.g., an e-beam column or multiple columns. To reduce the force path for reaction forces, the rotary stage vertical maglevs207Z and the X-stage vertical maglevs209may be arranged in close proximity, e.g., in a side-by-side or a back-to-back configuration such that the maglevs207Z,209apply forces along a common line of action.

The linear stage may be translated by one or more parallel linear motors205. In a preferred configuration two linear motors205are used, symmetrically placed in respect to the center of moving linear mass. For example, to guide the linear motion of the linear stage204, the linear motors205may include a set of lateral electromagnets212of alternating polarity that guide the linear stage204along parallel ferromagnetic guideways214. X-stage Y-maglevs216may be used to finely adjust the position of the x-stage204along the Y-direction relative to the guideways216. Preferably, the rotary stage202is suspended with respect to the X-stage204by at least 3, more preferably 4 rotary stage radial maglevs207X,207Y. These radial maglevs are preferably arranged in close proximity to corresponding Y-maglevs216that adjust the position of the linear stage204in the y direction. To shorten the path for reaction forces, the X-stage Y-maglevs216may be arranged back-to-back with the rotary stage radial maglevs207Y. Most preferably, 4 rotary stage radial maglevs207X,207Y may be assembled back to back with corresponding linear stage Y-maglevs216electromagnets. This way any forces controlling the imbalance of the rotary stage202are transmitted directly to the stationary chamber lid208, and do not excite structural vibration modes of the linear stage204.

The magnetic flux from the maglevs207X,207Y,207Z,209and216may be confined and shielded to prevent it from interfering with the tool210. In addition the peripheral placement of the maglevs207X,207Y,207Z,209and216and ferromagnetic ring206keep them and their flux far from the tool210so that these fluxes do not interfere with magnetic lens fields from the tool210that are used, e.g., to focus an electron beam. The rotary stage202may be made of a magnetically transparent material, e.g., a ceramic, aluminum, etc. to further reduce undesirable effects on the tool210. In addition, the rotary stage202may be made of a material having a high electrical resistivity reduce eddy currents that might affect the electron beam from an electron beam optical column, if one is included in the tool210. It is desirable for the electrical resistivity to be high enough to make eddy currents insignificant, while still allowing dissipation of electrical charge from the surface. By way of example, and without limitation, the electrical resistivity may range from about 1 ohm-cm to about 1000 ohm-cm. Examples of suitable high-resistivity materials include, but are not limited to silicon carbide, tungsten carbide. In addition insulating ceramics having electrical resistivities larger than about 1000 ohm-cm, with surface treatment for dissipating electric charge build-up may be used.

As shown inFIGS. 2C-2D, the rotary stage202may be spun by a central rotary motor220having a rotor222and a stator224. The rotor222is attached to the center of the rotary stage202and the stator224is attached to the linear stage204. InFIGS. 2C-2Dthe rotor222is depicted as being inside the stator224. It is also possible to configure the motor220so the stator224is in the center, attached to the linear stage204, and the rotor222is on the outside, attached to the rotary stage202. The stator224may exert magnetic forces on the rotor222along the z direction that partly counteract the weight of the rotary stage202or other z-directed forces acting on the rotary stage202.

In certain embodiments it may be desirable to support all or nearly all of the weight of the rotary stage202using the rotor222and stator224. This may be particularly useful where fine control of the rate of rotation of the rotary stage202is important in maintaining a high degree of resolution in the relative positioning of the substrates201and the tool210. In particular, the magnetic fields used by the rotary stage vertical maglevs207Z to levitate the rotary stage202may produce eddy currents in the ferromagnetic ring206. Such eddy currents can produce a magnetic drag torque that can slow down the rotation of the rotary stage202. Countering such drag forces with a torque from the motor220can produce an undesired torque ripple that leads to poor control of the rotation rate.

To reduce such eddy currents, the rotor222and stator224may be configured to bear the weight of the rotary stage202. This may be done using air bearings, mechanical bearings or magnetic levitation.FIG. 2Eshows close-up detail of an example of a magnetic levitation scheme. In this example, a pole piece225and one or more permanent magnets227are attached to the rotor at a point below the bottom of the stator224. A corresponding pole piece229is attached to the bottom of the stator224. The stator pole piece229may be laminated to reduce eddy currents. Attractive magnetic forces between the permanent magnet227and stator pole piece229are transferred in a vertical direction to the rotary stage202by the rotor222. In alternative embodiments, magnets may be attached to the stator224instead of the rotor222or to both the stator and rotor. Furthermore, the magnets and pole pieces on the rotor and stator may alternatively be configured to levitate the rotary stage202by magnetic repulsion.

With all or most of the weight of the rotary stage202supported by the forces between the rotor222and stator224, and the rotary stage properly balanced, torque from the motor220may be primarily used to “spin up” the rotary stage202to a desired rotational speed. After that, the torque exerted by the motor220on the rotary stage202may be greatly reduced as the rotary stage spins under its own inertia. In addition, the rotary stage vertical maglevs207Z can finely adjust the vertical position of the rotary stage202with relatively small magnetic forces, and therefore, much smaller eddy currents. This allows the use of a non-laminated ferromagnetic ring206, which may simplify fabrication and reduce cost.

It is also possible to drive the rotary motion of the rotary stage202using a conductive ring, such as the outside ring ferromagnetic ring206of the rotary stage202, and having the rotary motion stator224built into the linear stage204, proximate the periphery of the ring206. In one such configuration the resulting rotary motor may be an induction AC motor, using eddy currents induced in a conductive ring mounted at the periphery of the rotary stage202. It is noted that this latter configuration keeps stray magnetic fields from the motor away from the beam column210even if the rotary stage202supports a single substrate chuck that is concentric with the z axis.

In the example shown inFIGS. 2A-2E, the rotary stage202has six chucks203for supporting substrates201. Note that the placement of the chucks203shown inFIGS. 2A-2Dand2F keeps the substrates at a distance from stray magnetic fields from the motor220. This particular example is for purposes of illustration, and is not to be considered a limitation on any embodiment of the invention. The rotary stage202is carried by a linear X stage204. The rotary stage202and its coordinate system defined by axes xs, ysrotates with rotary speed ω in the direction shown. Patterned spokes211may be used as part of a reference system for tracking the position of the substrates201relative to the rotary stage coordinate system with optical sensors that sense a pattern on the spokes211. By way of example, the spokes211may be visible to both the tool210and a separate substrate metrology system.

Substrates201, e.g., semiconductor wafers are exposed to radiation from the beam column210in a spiral from an outer radius Roto an inner radius Ri. Substrates201, e.g., semiconductor wafers, are placed on the chucks203at radius Rwi(i=1, 2 . . . N) and angle θwifrom the center of the rotary stage, which defines the axis z. In this example, the substrates are rotated by an angle φwi=45° relative to the substrate placement radius. Each substrate offset and rotation from the stage coordinate system is slightly different and is individually tracked

FIG. 2Gillustrates an example of a maglev unit230that may be used in the apparatus ofFIGS. 2A-2F, e.g., as a radial maglev207X,207Y, X-stage Y-maglev216or Z-maglev209. The maglev unit230includes a permanent magnet232an electromagnetic having a magnetically permeable core234and a winding coil236. The core234conducts magnetic flux from both the permanent magnet232and the electromagnet. In the vertical configuration shown inFIG. 2G, the permanent magnet232produces enough flux to fully suspend the weight of the maglev and the attached payload (e.g., a portion of the combined weight of the rotary stage202, linear stage204and motor220. The coil236produces additional flux, which controls a gap g between the maglev230and a ferromagnetic guideway238. In certain embodiments it may be desirable to contain the leakage flux shown on the sides of core, e.g., by a properly designed mu-metal shield and/or by shaping of the ferromagnetic material around the gap.

A gap sensor240may be coupled to a sensor amplifier242and a controller244that regulates current to the coil236, e.g., by applying a signal to a power amplifier246. If, for example, dynamic forces tend to move the maglev230downwards, e.g., as determined by an increase in the gap g measured by the gap sensor240, the controller244may signal the power amplifier246increase current to the coil236to add additional flux to the flux due to the permanent magnet232, thereby increasing the attractive force. If the gap g decreases, as measured by the gap sensor240, the controller244may signal the power amplifier246to adjust the current to the coil236to produce flux in the direction opposite to that of the permanent magnet232. The controller244may be commanded to maintain a constant gap g, or to exert a prescribed force across the gap to cause deliberate motion of the maglev, as in stage focusing action.

The rotary stage202spins about its axis of symmetry z and translates along the x axis. The linear stage204maintains the rotary stage202on a straight path. A following metrology system may close the loop on the position of the rotary stage202and the position of the electron beam relative to the substrates on the chucks203. Feedback of the stage position may be derived from a number of different sensors. As shown inFIG. 2B, these sensors may include interferometers250Y,250Z mounted to the translation stage204to sense horizontal and vertical movement of the rotary stage202and/or translation stage204relative to the chamber lid208. By way of example, an interferometer250Y may track y-axis movement of the rotary stage202using a Y-reference mirror254mounted to the chamber lid208and a cylindrical surface of a ring mirror256attached to a periphery of the rotary stage202. The cylindrical (side) surface of the ring mirror256is concentric with the rotation axis z. In addition, rotary encoders252may sense the rotation of the rotary stage202. Another interferometer may track z-axis movement of the rotary stage using a reference mirror258(seen inFIG. 2C) mounted to the chamber lid208and a flat (top) reflecting surface of the ring mirror256. The top reflecting surface of the ring mirror256and the Z-reference mirror256.

The heavy and rigid chamber lid208forms the inertial frame of reference for the stage metrology. A set of interferometer mirrors is kinematically attached to the lid and forms the metrology frame. This configuration reduces the effect of stage forces on the metrology.

There are a number of different possible configurations for the interferometers and sensors described above. For example, as shown inFIG. 2Hbetween 1 and 4 radial sensors r1, r2, r3, r4may measure the radial displacement of the rotary stage202relative to the X-stage204while 1 to 4 rotary encoders Θ1, Θ2, Θ3, Θ4, measure the tangential displacement of the rotary stage periphery. Using redundant sensors allows dynamic measurement of both the deviation of the cylindrical surface of the rotary stage202from a perfect cylinder, and direct measurement of the motion of the center of the cylinder relative to the X carriage reference frame. It is noted that the radial sensors r1, r2, r3and r4ofFIG. 2Hmay also be implemented as differential interferometers or as other types of sensors, such as capacitance sensors. The bandwidth of these sensors may be up to about 200 MS/s. Rotary velocity measurements from these sensors may be coupled in a feedback loop with position update from the optical sensors in a reference based on the spokes210. If the redundancy is excessive, some of the sensors may be dropped.

Differential interferometers x, y, z1, z2, z3track changes in the relative position of the rotary stage202with respect to a mechanically stable fixed reference, e.g., the chamber lid208. The interferometers may be characterized by a bandwidth between about 100 kHz and about 1 MHz. The interferometers are used in a feedback loop with corresponding maglevs to stabilize the rotary axis z in relation to the tool210with a mechanical servo bandwidth of about 100 to 300 Hz. Such a system may be characterized by a following error within 100 nm in the x, y, and z directions.

Embodiments of the present invention may use differential interferometers to monitor the relative movement of the rotary stage so that a beam from the tool210follows a predetermined path P across the substrates201retained by the chucks203. For example, as shown inFIG. 2Han interferometer Ysmay measure the position of the stage relative to a stationary reference system (e.g., with respect to the chamber lid208) along the y axis. Another differential interferometer Xc,smay measure the position of the cylindrical perimeter of the rotary stage202relative to the tool210, which may be an electron beam column. The Ycinterferometer differentially measures the location of the tool210relative to stationary reference mirror254along the y axis using a mirror266mounted to the beam column. The Xc,sinterferometer may similarly track variation in the location of the tool210with respect to the x axis using a stationary reference mirror mounted to the chamber lid208parallel to the y-z plane and a mirror268mounted to the tool210. The YS differential interferometer measures the position of the rotary stage202relative to a reference mirror254. The above-mentioned interferometers may alternatively be implemented in non-differential configurations.

In addition to the above-described interferometers, the following sensors may be used to track the remaining degrees of freedom of the rotary stage: interferometers z1, z2, z3may be kinematically mounted to the chamber lid208to measure position of the top or the bottom of the stage relative to a stationary plane mirror in a z-direction perpendicular to the x and y axes. The use of three interferometers allows tracking of the tilt of the cylinder about the x and y axes. Alternatively, using 4 interferometers for z sensing may have advantages over the 3 interferometer configuration. Signals from the interferometers and sensors shown inFIGS. 2G-2Hmay be fed back to the various maglevs used to position the rotary stage202relative to the x-stage204, the x-stage relative to the guideways214and the linear motors205that move the x-stage along the guideways214.

Several metrology configurations exist for an apparatus of the type described above with respect toFIGS. 2A-2I. By way of exampleFIG. 2J, illustrates metrology for direct column and Substrate metrology system (SMS)260using the chamber lid208as a metrology reference frame In this example an optical based SMS260covers a die-size wide 30 mm swath upstream of an electron beam (e-beam) from the tool210. A much narrower (e.g., 200-μm) field of view of the e-beam may be used to capture sparse die alignment marks on the substrates201on every pass.

The SMS260may include one or more optical sensors262adapted to sense reference features located on the substrates201. Reference mirrors264may be used in conjunction with interferometers (not shown) to track the location of the SMS260relative to the chamber lid208. The optical sensors measure the x and y positions of substrate marks with respect to a substrate coordinate system. Such reference marks may be located, e.g., on the spokes211. The sensors may also measure Z (focus). A process coupled to the SMS260interpolates signals from the optical sensors and creates a grid of wafer surface distortion values. The coordinate system for the SMS260may be a moving coordinate system, having as its origin a corner of a reference die on the substrate201. The processor may designate one wafer as a master wafer and calculate the origin shift of the other wafers relative to the master wafer. The processor may also updates the optical sensor position relative to null position of the electron beam using interferometric measurements of the sensor position relative to the chamber lid208.

If the locations of the tool210and SMS260are not stable, they may be tracked using differential measurements and reference mirrors. The SMS cluster may be tracked in x and y directions and yaw angle about the z axis as it focuses on a substrate201. E-beam to column shifts may also be tracked dynamically. The stage to substrate coordinates may be updated several times on every turn of the rotary stage202, e.g., using the SMS260and e-beam tracking.

Differential interferometers Ys, Yxand Yc, which are referenced to a y-reference mirror262attached to the chamber lid208, track the position of the rotary stage202, X-stage204and e-beam column210, respectively along the y axis. Differential interferometers Z1, Z2, Z3, which are referenced to a mirror mounted to chamber lid,208track vertical position, tip and tilt of the rotary stage202. Interferometers X1, X2, which are referenced to x-reference mirror264attached to the chamber lid208, track the position of the X-stage204along the x axis and yaw of the X-stage204about the z axis.

Examples of preferred differential interferometer configurations for use in motion tracking are shown inFIGS. 3A-3E. Specifically, as shown inFIGS. 3A-3B, in a rotary-linear stage of the type shown inFIGS. 2A-2E, optical motion tracking may be implemented with a differential interferometer310disposed between a reference mirror254and a stage ring mirror256having a cylindrical surface257that is concentric with the z axis. The interferometer310is mounted to the linearly translatable X-stage204. The reference mirror254is mounted in a fixed in position relative to the X-stage204. By way of example, in preferred embodiments, the reference mirror may be mounted the lid of the chamber208that contains the X-stage204and rotary stage202. In the example shown inFIG. 3A, the stage ring mirror256is peripherally mounted to the rotary stage202, which rotates about a rotation axis z that is in a substantially fixed position and orientation with respect to the X-stage202. The stage ring mirror256provides a cylindrical reflecting surface that is symmetric about the rotation axis z. The interferometer310includes a folding mirror312, a polarization beamsplitter314disposed between first and second quarter waveplates316A,316B a corner cube mirror318and wavefront compensation optics320. Interferometers having this design are described in detail in International Patent Application Publication WO 2005/078526 A1, published 25 Aug. 2005 and entitled “A SYSTEM FOR POSITIONING A PRODUCT”.

Light from a source, such as a laser306is deflected by the folding mirror312towards the polarization beamsplitter314. The light from the source306contains first and second polarizations. Light having the first polarization of the light passes through the beamsplitter and is reflected by the corner cube318back through the polarization beamsplitter to the folding mirror312, which deflects the light to a detector308. This light serves as a reference beam305indicated by the dashed optical path.

Light having the second polarization is reflected at a diagonal interface315of the polarization beamsplitter314through the first quarter waveplate316A, off the reference mirror254and back through the first quarter waveplate316A. The two trips through the first quarter waveplate316A convert the light from the second polarization to the first polarization. As a result, the light can pass through the interface315, the second quarter waveplate316B and the wavefront compensation optics320to the curved surface of a cylindrical stage ring mirror256having an axis concentric with the z axis. After reflection by the stage ring mirror256the light passes back through the wavefront compensation optics320and the second quarter waveplate316B. The two trips through the second quarter waveplate convert the light from the first polarization back to the second polarization. As a result, the light is deflected by the interface315towards the corner cube318, which bends the light back to the folding mirror312. The folding mirror312deflects the light to the detector308. Light following this path serves as a measurement beam307indicated by the solid optical path. Light from the reference path305and measurement beam307interfere at the detector producing a signal that depends on relative changes in the lengths of the two beam paths due to motion of the rotary stage202with respect to the reference mirror254.

In an alternative embodiment depicted inFIG. 3B, a small cylindrical mirror324having a cylindrical surface326concentric with the z axis may be used in place of the peripheral ring mirror256. In either configuration, the wavefront compensation optics320are configured so that wavefronts traveling from the interferometer310and the cylindrical reflecting surface257,326are compensated for reflection from the cylindrical mirror256,324so that light reflected from the cylindrical reflecting surface257,326follows the proper path back through the interferometer310. By way of example, the wavefront compensation optics320may include cylindrical optical components or spherical optical components.

A number of different configurations for the wavefront compensation optics320may be used to couple light between the interferometer310and cylindrical reflecting surface257or326. By way of example and without limitation, two possible configurations of the wavefront compensation optics are shown inFIG. 3CandFIG. 3D. InFIG. 3C, the wavefront compensation optics320focuses parallel light from the interferometer310at the axis of curvature of the wavefront compensation optics, e.g., on the rotation axis z. In this way, light reflected from the cylindrical surface257,326of mirror256,324follows essentially the same path as the light incident on the cylindrical mirror from the interferometer310. In an alternative configuration depicted inFIG. 3D, the wavefront compensation optics is configured to focus parallel light from the interferometer310onto the surface257or326of the cylindrical mirror256or324. In this way, light beams incident on and reflected from the cylindrical mirror256,324follow parallel paths through the interferometer310.

It is noted that tracking the rotary stage motion using reflection from the curved reflecting surface257or326using the wavefront compensation optics320as described above is suitable for measuring small amplitude vibrations relative to the X-stage204or the lid208. As used herein small amplitude refers to motions that are no larger than the depth of focus of the wavefront compensation optics320.

The differential interferometer310is carried by the motion of the X-stage301, so that the interferometer310is always pointed at the center of rotation of the rotary stage303and remains in alignment with the rotary stage303. Although a stage ring mirror256at the periphery of the rotary stage is shown inFIG. 3A, alternatively, a small cylindrical hub324at the center of the rotary stage303may provide a cylindrical reflecting surface, e.g., as shown inFIG. 3B. It is noted that in bothFIG. 3AandFIG. 3B, the reference mirror254, laser306and detector308remain fixed with respect to the X-stage204and rotary stage202as indicated by the dashed line surrounding these components. Preferably, these components are mounted to a lid of a chamber that contains the X-stage204, rotary stage202and interferometer310, which move in the x-direction, as indicated by the dashed line surrounding these components.

The interferometer310is carried by the X stage204, and is aligned to the center of the X Stage204. A servo system based on this interferometer system maintains the prescribed linear motion of the X stage204and the rotary stage202moving together, and following each other as closely as possible. The rotary stage axis z remains fixed relative to the X stage204. Therefore, the alignment does not change as a result of this motion.

The interferometer310moves with the X stage towards the laser306and detector308, however, to first order, this motion does not affect the reading of the detector308. The detector308only senses an optical path difference between the cylindrical mirror256and the stationary reference mirror254.

As shown inFIG. 3E, the Z interferometers may also be configured differentially. Once again, an interferometer330is attached to the X-stage204along an optical path between a stationary reference mirror258and the stage ring mirror256. The reference mirror258may be mounted to the lid of the chamber208, e.g., as shown inFIGS. 2C-2D. The interferometer includes a polarization beamsplitter334, quaffer waveplates336A,336B, and corner cube338. Light from a laser346is divided into a reference path335and a measurement path337through the interferometer330to a detector348. Operation of the interferometer330is similar to operation of the interferometer310described above with respect toFIG. 3A. Since the measurement beam337reflects from a flat upper surface259of the stage ring mirror256wavefront compensation optics between the interferometer330and the stage ring mirror256are not necessary.

Some of the design concepts described above with respect to rotary-linear stages may be advantageously applied to more conventional X-Y stages. For example, it is noted that one of the advantages of the apparatus200described above is that the various maglevs and magnetic motors are located near the edges of the rotary stage and X-stage. This places the magnetic fields generated by these devices at a considerable distance with respect to the tool210. Such a configuration can be particularly advantageous if the tool is sensitive to stray magnetic fields. For example, where the tool210includes an electron beam column stray magnetic fields from the maglevs may deflect the electron beam, resulting in an error in its position. Although the deflection of the beam may be tracked and compensated, it is more desirable to avoid, or at least significantly reduce, such magnetic deflection. The placement of the maglevs at the edges of the rotary stage202and X-stage204and away from the optical column210may significantly reduce errors associated with stray magnetic fields from the maglevs. The rotary stage202may be made of a magnetically transparent material, e.g., a ceramic, so that magnetic fields from a magnetic lens of the tool210are not distorted.

This same concept of supporting the stages with edge-mounted maglevs may be applied to an X-Y stage according to an embodiment of the present invention. For example,FIGS. 4A-4Bdepict a substrate processing apparatus400according to an alternative embodiment of the present invention. The apparatus400includes an X-stage402and a Y-stage404. The X-stage402includes a chuck403adapted to retain a substrate401. The X-stage402is suspended from the Y-stage404by vertical maglevs406A mounted at the corners of the X-stage402. Controlled movement of the X-stage402along an X-axis relative to the Y-stage404may be imparted, e.g., by linear motors405. The Y-stage404is suspended from a chamber lid408by vertical maglevs406B mounted at corners of the Y-stage404. The Y-stage404may be adapted to move in a Y direction relative to the chamber lid408, e.g., using linear motors (not shown). The position of the X-stage402relative to the Y-stage404along the Y axis may be regulated using edge-mounted horizontal maglevs406C coupled in feedback loops with appropriate sensors. The X-stage402may move in the X and Y directions relative to a substrate processing tool410, which may include, e.g., an electron beam column. By placing the linear motors405, vertical maglevs406A,406B and horizontal maglevs406C away from the substrate401, undesired magnetic deflection of the electron beam from the column410may be avoided. The X-stage402may be made of a magnetically transparent material, e.g., a ceramic, so that magnetic fields from a magnetic lens of the tool410are not distorted.

Metrology for directing the tool410and a substrate metrology system (SMS)411may use the chamber lid408as a metrology reference frame. The SMS410may be tracked in the x and y directions and yaw about the z axis as it focuses on the substrate401. The SMS411may use reference pattern412similar to those seen on the spokes211inFIG. 2FandFIG. 2J. By way of example, the SMS411may cover a swath approximately as wide as a (e.g., about 30 mm) upstream of the e-beam column410and a much narrower field of view (e.g., about 200 μm) to capture sparse die alignment marks on every pass. Since the stage402reverses direction, the SMS411may include two optical sensors. One sensor may be located on either side of column410arranged in an X-scanning direction. If the column and SMS locations are not differential measurements, reference mirrors may be used to determine these positions. In addition, shifts in the e-beam position relative to the tool410may be tracked dynamically to precisely position the electron beam from the column410on the substrate401. Stage to substrate coordinates may be updated on turnarounds of the X-stage402on a calibration chip, using SMS and e-beam location information.

The apparatus400may use one or more interferometers to track the position of various components with respect to the chamber lid408. These may include an interferometer X1that measures movement along the x axis of the X-Stage402relative to the tool410and chamber lid408. A second interferometer X2measures movement of the X-stage402relative to the chamber lid408, thereby facilitating measurement of yaw of the X-stage402. A third interferometer Y measures movement along the y axis of the X-Stage402relative to the chamber lid and the tool410. Vertical differential interferometers Z1, Z2, Z3, may be configured, e.g., as shown inFIG. 3Eto measure changes in position of the top of the X-stage402relative to the chamber lid408. X Stage top to lid, differential. Although additional interferometers may be used to track the motion of the carriage in the Y-stage404, this may alternatively be accomplished with the maglevs and/or linear motors used to support and/or move the Y-stage404along the y direction. Although in this example, the x and y axes are perpendicular to one another, they may alternatively be oriented at some oblique angle.

The advantage of the configuration shown inFIGS. 4A-4Bmay be illustrated by comparison with a prior art X-Y stage500, e.g., as depicted inFIG. 5. In the prior art X-Y stage500an X-stage502is levitated by maglev units506. Mounts504attached to the X-stage502support a chuck503that retains a substrate501. The X-stage and Y-stage are adapted to move along x and y axes respectively, e.g., using linear motors505. An example of such a prior art X-Y stage is described in detail, e.g., in International Patent Application Publication WO 2005/078526 A1, published 25 Aug. 2005 and entitled “A SYSTEM FOR POSITIONING A PRODUCT”.

Downward looking differential interferometers Z1, Z2, track variations of the vertical z position of the X-stage502relative to a base509of a chamber508. A mirror512is positioned on the underside of the X-stage502for this purpose. It is noted that in this design, the maglev units506are directly beneath the substrate. This is done to keep the maglev system from interfering with the downward-looking interferometers Z1, Z2. Stray magnetic fields from the maglev units506can deflect the path of an electron beam. Furthermore, the configuration of the maglevs506requires a relatively tall central support504and correspondingly long mechanical paths507for reaction forces from the maglevs506to the chamber lid508, which is used as a reference mass. For example, the moment arm between the top of the X-stage502and the point of application of horizontal forces by the maglevs506may be as much as 200 mm. This configuration also requires a relatively large chamber to support the X-Y stage500. In embodiments of the present invention, by contrast, the upward-looking interferometers use the chamber lid as a reference. This allows the maglev units to be placed at or near the edges of the X-stage or rotary stage. Consequently the mechanical path for reaction forces can be made much shorter, the apparatus made more stable and the chamber may be smaller.

Embodiments of the invention allow for more compact and stable rotary-translation stages and X-Y stages. Embodiments relating to rotary stages provide for high substrate throughput with lower linear acceleration that would be required for an X-Y stage, with short path lengths for reaction forces, stable configuration of the bearings and compact design. Embodiments of the invention relating to X-Y stages provide for shorter path lengths for reaction forces, greater stability and more compact design than in prior art X-Y stages.

It is noted that some embodiments of the present invention may utilize something other than magnetic levitation, e.g., mechanical bearings or air bearings, to provide bearings for the X-stage and rotary stage and/or Y-stage. For example,FIGS. 6A-6Bdepict an alternative substrate processing apparatus600according to an alternative embodiment.

The apparatus600includes a rotary stage602and translation stage604disposed in a chamber608. The rotary stage602carries a plurality of substrate chucks, which may be configured as described above. The rotary stage602may be spun by a central rotary motor620mounted to the linear stage604. The motor620includes a spindle bearing622attached to the center of the rotary stage602. The rotary stage602spins about a z axis and the X-stage604moves the rotary stage along an x axis. A substrate processing tool610remains more or less fixed with respect to the chamber lid608as described above. Note that the placement of the chucks603shown inFIGS. 6A-6Bkeeps substrates mounted to the chucks at a distance from stray magnetic fields from the motor620. Linear motors605mounted at edges of the X-stage604move the linear stage604along parallel ferromagnetic guideways614mounted to the chamber608. The linear motors605may include a set of lateral electromagnets612of alternating polarity. In this example, bearings618between the X-stage604and chamber608may keep the motion of the X-stage604aligned with the x axis. By way of example, the bearings618may be mechanical cross-bearings. Mechanical bearings may be used if stage positioning noise from the bearings does not exceed the ability of the metrology systems to track motion of the substrates mounted to the chucks603. In alternative embodiments, the bearings618may be air bearings. It is noted that if the bearings are in vacuum, differential pumping may be used for air bearings. It is further noted that the motor620may include an air bearing.

Positioning of the rotary stage602and X-stage604may be monitored as described above, e.g., using interferometers650Z and peripherally mounted ring mirror656on the rotary stage602and reference mirrors658mounted to the chamber lid608.

In embodiments of the present invention it is often desirable for a rotary-linear stage to control a position of the substrates relative to the tool to within 10 nanometers of a desired position. There are a number of different ways to accomplish this. For example, as described above, the position of the substrates and the tool may be very tightly controlled with respect to a reference frame, such as the chamber lid. Generally, it is desirable to have very high resolution (e.g., less than 1 nm) in sensing the stage position and in positioning the beam from the tool with respect to the substrates. Embodiments of the invention may use precise control of the rotary-linear stage in conjunction with precise control of a position of the beam from the tool to achieve the desired resolution in beam positioning. For example, in the case of an electron beam tool, beam positioning may be adjusted through the use of electrostatic and/or electromagnetic lenses in conjunction with electrostatic and/or electromagnetic beam deflection mechanisms (e.g., raster plates or deflection coils). If the range of focus and/or X-Y beam deflection is both sufficiently large and sufficiently accurate it may be possible to tolerate a somewhat greater degree of variation in the position of the substrates relative to the optical column. For example, if the positioning accuracy of the beam deflection and focusing is less than about 1 nm and the range of beam positioning is about 1 micron, the system can tolerate stage position variations of roughly 1 micron, provided the metrology system can track these variations and the beam deflection mechanism can respond quickly enough.

In the particular example of an electron beam tool, there are a number of different ways of controlling stage and/or beam position in order to achieve the desired positioning accuracy for the optical column. Control of the beam and/or stage position may be understood with respect to the block diagram shown inFIG. 7. By way of example, control of a rotary-linear stage of the types described above may be implemented using three sets of inner multiple input multiple output (MIMO) control loops: a) the stage loops, b) the lid and optical sensor loops and c) optical column-beam position and focus control loops. An overall outer control loop may estimate the relative position between the optical column and the substrate using a spoke-reference system (SRS) and substrate metrology system (SMS) as described above. Servo mechanisms may be used to bring this error to zero using a slower stage loop and a faster beam loop.

InFIG. 7a stage Setpoint Generator702generates nominal trajectories in x and θ that are used to perform probing of the substrates with the optical column. In addition this stage setpoint generator702may be used to position the stage for loading, to perform substrate alignment, map the substrate distortions prior to writing, and create a focus map for the optical column and the SMS. In some embodiments, data regarding known topographic features of the substrates may be stored in a database, which may include information regarding the relative orientation of the substrates and their thickness variations. These may be measured as a part of a spin up process and used to generate a correction table to compensate for any misalignments.

The stage setpoint generator702may also utilize calibration data that captures thermal and elastic deformation of the rotary stage and/or substrates. For example, the temperature of various components in the system and the resulting distortion due to CTE differences may be monitored. The distortion values may be pre-computed and stored as a part of the calibration data in the setpoint generator702. The stage setpoint generator702may also include corrections for measured non-uniformities in a given rotary stage. Furthermore, models of the distortion of the rotary stage due to centrifugal forces during spin-up may be stored as a part of calibration data in the setpoint generator702.

A stage metrology system704may perform the r, θ measurements of the rotary stage in addition to the x, y and z interferometer measurements, as described above. The stage metrology system704may include multiple redundant sensors and one of the functions represented in this block may include a set of sensor fusion algorithms that provide estimates of the various coordinates of the stage position. The stage metrology system704may also contain calibration tables for each of the sensors to compensate for errors that are systematic. For example, harmonic errors in the θ measurements may be measured during a calibration process and stored. These known errors may then be removed from actual measurements before generating estimates of the position of the rotary stage. Similar calibration data is generated and used for the other sensors that are a part of the stage metrology system704.

An optional Substrate Metrology System (SMS)706may provide a measurement between the optical sensors held by the lid and the substrate. If the optical sensors are referenced to the column, the SMS706may provide an estimate of the position of a substrate relative to the beam from the optical column. The SMS706may optionally utilize reference marks707on the substrates to obtain input, e.g., regarding the relative orientation and thickness variations of the substrates.

The SMS706may receive input from a spoke reference system (SRS)708that uses spokes of the type described above. The SRS708may allow a sensor, e.g., an optical sensor, in the SMS706to provide a measurement of the relative position between spokes on the stage and the substrates. The spokes may be features on the rotary stage such as those shown inFIGS. 2F and 2J. Initial positions of the spokes relative to the substrate position may be stored as a part of the calibration data after loading the substrates.

Measurements obtained from the Stage Metrology system704, SMS706, and SRS708may be used to control the position of the rotary-linear stage710using MIMO control referenced to the chamber lid for minimal length, force and metrology paths. By way of example, the electron beam may be “visible” to the spokes in the spoke reference system708. For example, the spokes may be electrically conducting and configured so that it is possible to determine where the beam strikes a particular spoke. This information may be used to by the SMS706. For example, the WMS706may also use the information from the spoke reference system708to produce an adjusted substrate position signal, which may be filtered by the low pass filter712. The output of the low pass filter712may then be combined with inputs from the stage setpoint generator702and stage metrology system704to produce an error signal that is fed to a stage controller714. By way of example, the stage controller714may be a MIMO controller that issues a simultaneous command to all actuators that control the positioning of the rotary stage and linear stage in the stage710. In the case of the system200ofFIGS. 2A-2J, the controller714may adjust the actuation of rotary-stage positioning maglevs, the x-translation and θ-rotation actuators to drive the error signal to zero.

The command to this stage control loop may have two components. The first component is the reference trajectory command from the stage setpoint generator702. The second component is a low-pass filtered beam to substrate position error estimate from the low pass filter712. The stage controller714may be used to stabilize the rotary stage and reject imbalance, precession and nutation motion of the rotary stage. In addition, the stage controller714may make corrective actions to rectify the low frequency portion of the beam to substrate position error. These corrections may be fed back to the stage metrology system704in the form of a stage state vector716. By way of example, the Stage Metrology System704may measure displacements at the interferometer points of incidence, e.g., as described above. Knowing the laser beam configuration relative to the point of reference on the stage, the stage vector716may be calculated. The stage state vector716may contain displacements, velocities, accelerations and possibly jerks (derivatives of accelerations with respect to time), in all stage degrees of freedom: e.g., XYZ, pitch, roll, and yaw.

Measurements from the Stage Metrology system704SMS706and SRS708may also be used to estimate a Beam to substrate position error. The beam position error may be used to drive a beam controller718in such a way as to drive the beam to substrate position error to zero. The beam controller718may operate on an error between the commanded beam position and the actual measured beam position and aims to minimize the error. The beam controller718receives an input from the stage metrology system704that is filtered with a high-pass filter720. The beam controller718also receives an input from the substrate metrology system706. The combination of these inputs provides a high pass filtered value of a beam-substrate position error estimate.

By way of example the beam controller718may produce signals that control a beam deflection mechanism722and the actual beam dynamics. The beam deflection mechanism722may include electrostatic deflectors or electromagnetic deflectors. The beam deflection control signals may be used to derive a beam-in-substrate state vector724, which may be combined with measurements of the beam position from the spoke referencing system708to produce a measured beam-in-substrate state vector. The measured beam-in-substrate state vector may be used as an input to the beam controller718.

The beam controller718may also obtain input from a Beam In-Lens Position detector726that senses the position of the beam relative to the optical column. The beam-in-lens position detector726may sense a position of an optical or electron beam from the optical column relative to an optical axis. The beam-in-lens position detector may also receive input from the beam deflection mechanism722. In some embodiments, the beam-in-lens position detector726may also include a focus sensing scheme.

It may be seen from the preceding discussion that the stage controller714and stage710provide correction for a low-frequency component of the beam-substrate position error and the beam controller718and beam deflection720provide correction for a high-frequency component of the beam-substrate position error. The stage controller714and beam controller718may receive additional input from adaptive Filter Logic728which may be implemented in hardware or in software, e.g., in the form of adaptive control algorithms. By way of example, the adaptive filter logic728may use Kalman filtering. The adaptive filter logic728may receive input from the Stage Metrology System704. There are a number of different possible implementations of the adaptive filter logic728. For example an imbalance between actuators used to translate the rotary stage in the x direction may cause a variation in the angular speed of the rotary stage. The sensors used in the stage metrology system704may sense this imbalance and a differential command may be applied by the stage controller to the x actuators to compensate for the imbalance between the two actuators. Alternatively, reaction forces from controlling the rotary stage may cause motion in the chamber lid. These reaction forces may be adaptively cancelled, e.g., using electrodynamic actuators. In addition, the adaptive filter logic728may adaptively correct for effects of thermal and elastic deformation of the rotary stage and/or substrates based on measurements from the substrate metrology system706and the spoke referencing system708during operation.

It is noted that if the rotation of the rotary stage is relatively slow and/or the substrates are not subject to significant deformation due to heat loads and/or high acceleration, embodiments of the invention may be able to achieve resolution of 10 nm or better in tool-substrate positioning without the substrate metrology system706.