Moving object placing table based on magnetic opposed iron core linear motor and used for semiconductor wafer positioning

Abstract

Methods and systems for implementing high throughput wafer positioning systems with high positioning accuracy are presented herein. A high throughput, high accuracy wafer positioning system is used to measure structural and material characteristics (e.g., material composition, structural and membrane dimensional characteristics, etc.) associated with different semiconductor manufacturing processes. In one aspect, the core linear motor assemblies are arranged in a magnetically opposed configuration such that the inherent magnetic attraction forces of each opposed core linear motor assembly greatly cancel each other. Reducing forces applied to the sensitive shelving frame elements in turn reduce the induced deformations and shelving positioning errors. In some embodiments, a wafer positioning system includes a stacked magnetically opposed long stroke stage. In some of these embodiments, two magnetically opposed long stroke shelters employ tracks that are mechanically coupled to an intermediate frame of the stacked shelter assembly.

Description

[0001] CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application Serial No. 63 / 413,250, filed on October 5, 2022, entitled “Stacked XY Stage with moving magnets for high thermal stability,” the subject matter of which is incorporated herein by reference in its entirety. Technical Field

[0003] The described embodiments relate to wafer positioning systems and methods, and more particularly, the described embodiments relate to methods and systems for improving high-throughput positioning of wafers in a manufacturing environment. Background Art

[0004] The various features and multiple structural levels of semiconductor devices such as logic and memory devices are generally manufactured by a series of processing steps applied to a sample. For example, among others, photolithography is one semiconductor manufacturing process that involves creating patterns on a semiconductor wafer. Additional examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing, etching, deposition, and ion implantation. Multiple semiconductor devices can be manufactured on a single semiconductor wafer and then separated into individual semiconductor devices.

[0005] Metrology processes are used at various steps during the semiconductor manufacturing process to detect defects on the wafer to promote higher yields. Optical metrology techniques offer the potential for high throughput without the risk of sample destruction. Several optical metrology-based techniques, including scatterometry, reflectometry, and ellipsometry implementations and associated analysis algorithms, are commonly used to characterize critical dimensions, film thickness, composition, and other parameters of nanoscale structures.

[0006] As devices (such as logic and memory devices) move toward smaller nanoscale dimensions, characterization becomes more difficult. Devices incorporating complex three-dimensional geometries and materials with multiple physical properties create characterization difficulties. In response, more complex optical tools have been developed. For example, tools with multiple illumination angles, shorter and wider ranges of illumination wavelengths, and more complete information acquisition from the reflected signal (e.g., measuring multiple Mueller matrix elements in addition to more conventional reflectivity or ellipsometry signals) have been developed.

[0007] As devices move toward smaller nanoscale dimensions, commercially viable optical measurement tools must position samples faster and with greater accuracy. Generally, wafer positioning systems must move semiconductor wafers over long distances in two dimensions (generally referred to as X and Y directions). To quickly move long distances and accurately position the wafer being measured in a short period of time, a large amount of driving force is required. Generally, these forces are generated by linear electric motors. However, linear motors that are capable of generating large forces generate a large amount of heat. Available wafer positioning systems are subject to significant limitations in achievable positioning accuracy due to thermal deformation caused by the heat generated by the linear motors.

[0008] Generally, available wafer positioning systems employ low thermal conductivity materials in an attempt to thermally isolate the sensitive stage frame elements from the heat generated by the linear motors. Unfortunately, temperature increases of at least one degree Celsius are commonly observed across the sensitive stage frame elements. These temperature variations induce significant deformations across the sensitive stage frame elements, causing reduced accuracy. Additionally, the sensitive stage frame elements typically comprise different materials with significantly different coefficients of thermal expansion (CTE). The mismatched CTEs, along with temperature variations, induce significant internal strains and associated deformations within the sensitive stage frame elements, which further reduce stage positioning accuracy.

[0009] Figure 1 FIG. 1 is a simplified diagram illustrating a typical prior art wafer positioning system 10 in one embodiment. The wafer positioning system 10 includes a stage base frame 11 and an intermediate frame 12. The coordinate system {X IF ,Y IF ,Z IF A set of mechanical linear bearings 13 restricts the relative motion of the intermediate frame 12 with respect to the base frame 11 of the platform to one degree of freedom, namely, Y. IF direction. Figure 1 Also described is an ironless U-channel linear motor including a U-channel magnetic track 14 and an ironless motor assembly 15. Figure 1 As depicted in FIG. 1 , the ironless motor assembly 15 is mechanically fixed to the intermediate frame 12 and the U-channel magnetic track 14 is mechanically fixed to the storage table base frame 11. The ironless motor assembly 15 includes a plurality of conductive coils embedded in a non-magnetic package. In some examples, the copper coils are embedded in an epoxy matrix material that fills an aluminum or copper shell. The U-channel magnetic track 14 includes a plurality of permanent magnets attached to magnetic backing plates on both sides of the U-shaped channel. This assembly produces a well-defined magnetic field across the U-shaped channel. As shown in FIG. Figure 1 As depicted in FIG. 1 , the magnetic field lines 17 are concentrated in the permanent magnets and the iron backing plate of the U-shaped track. The portion of the magnetic field outside the U-shaped track is confined to a relatively small gap across the U-shaped channel.

[0010] like Figure 1, the ironless motor assembly 15 is disposed within a U-shaped channel. The mechanical driving force is generated in the Y direction by the flowing current through the windings of the coils of the ironless motor assembly 15. The orientation of the coil windings relative to the magnetic field across the U-shaped channel is such that the interaction of the current flow and the magnetic field generates the mechanical driving force in the Y direction.

[0011] Due to the lack of iron in the coreless motor assembly 15, the ironless U-channel linear motor is an inherently smooth operating motor. No significant magnetic attraction is generated between the ironless motor assembly 15 and the U-channel track 14. Thus, the ironless motor assembly 15 is able to operate within the U-channel at any relative position relative to the permanent magnets of the track 14 without generating significant off-axis forces. In addition, the magnetic field generated across the U-channel is relatively unperturbed by the ironless motor assembly 15. Therefore, the position dependence of the driving force generated between the ironless motor assembly 15 and the U-channel track 14 is relatively smooth and predictable. Thus, a relatively simple control algorithm can be used to distribute current through the coils of the ironless motor assembly 15 so that the driving force generated between the ironless motor assembly 15 and the U-channel track 14 is almost position independent.

[0012] Unfortunately, ironless U-channel linear motors also have the disadvantage of negatively impacting wafer positioning systems (e.g. Figure 1 10). Due to the ironless design of the ironless U-channel linear motor, the amount of driving force generated for a given amount of current is significantly less than an iron core design. Despite optimizing the design and magnetic field strength of the ironless motor windings, the ironless U-channel linear motor requires significantly more current to produce the same linear driving force as a comparable iron core linear motor. Current passing through conductive materials generates heat, and the generated heat must be dissipated somewhere, usually at the expense of wafer positioning accuracy. For example, as Figure 1 As depicted in FIG. 1 , the coreless motor assembly 15 is mechanically fixed to the intermediate frame 12. The heat generated in the coil windings of the coreless motor assembly 15 is conducted into the intermediate frame 12. Figure 1 As depicted in FIG. 1 , arrows 16 represent heat flow from the coreless motor assembly 15 into the intermediate frame 12. The temperature of the intermediate frame 12 increases as the heat flow 16 is absorbed. The authors have observed an intermediate frame temperature increase of approximately 0.65 degrees Celsius under normal operating conditions within a high throughput optical metrology tool. This temperature increase causes material expansion and deformation, severely limiting positioning repeatability at the wafer.

[0013] Figure 2 FIG. 2 is a simplified diagram of a typical prior art wafer positioning system 20 in another embodiment. The wafer positioning system 20 includes a stage base frame 21 and an intermediate frame 22. The coordinate system {X IF ,Y IF ,ZIF A set of mechanical linear bearings 23 restricts the relative motion of the intermediate frame 22 with respect to the base frame 21 of the platform to one degree of freedom, namely, Y. IF To address the limited force generation potential of U-channel ironless linear motors, the wafer positioning system 20 employs iron core linear motors. Figure 2 The iron core linear motor including the magnetic track 24 and the iron core motor assembly 25 is described. Figure 2 As depicted in , the iron core motor assembly 25 is mechanically fixed to the intermediate frame 22 and the magnetic track 24 is mechanically fixed to the base frame 21 of the storage table. The iron core motor assembly 25 includes a plurality of conductive coils each wrapped around an iron post. Generally, each iron post is manufactured as part of a larger iron structure. In some examples, the copper coils are embedded in an epoxy resin matrix material that fills the space around the conductive coils and the iron structure. The magnetic track 24 includes a plurality of permanent magnets 27 attached to a magnetic backing plate that is mechanically fixed to the base frame 21 of the storage table. This assembly generates a magnetic field in the space above the magnetic track 24. As shown in FIG. Figure 2 , the magnetic field lines 27 are concentrated in the permanent magnets and iron backing plate of the U-shaped track 24, but extend in the space above the track 24. The portion of the magnetic field outside the flat track 24 is expanded compared to the relatively small gap across the U-shaped channel of the U-channel ironless linear motor.

[0014] like Figure 2 As depicted in , the iron core motor assembly 25 is located above the flat track 24. In addition, the iron pillars and associated iron structures shape the magnetic field lines 27, that is, the magnetic field lines are concentrated in the iron pillars and associated structures. In this way, the iron pillars and structures define the shape of the magnetic field above the track 24 and are important components of the magnetic circuit. This is fundamentally different from the U-channel ironless linear motor. The mechanical drive force is generated in the Y direction by the flowing current through the windings of the coils of the iron core motor assembly 25. The concentration of magnetic lines of force in the iron pillars and associated iron structures enhances the magnetic field across the gap between the flat track 24 and the iron core motor assembly 25. Therefore, the amount of driving force generated for a given amount of current is significantly more than that of the ironless linear motor design. Therefore, compared with the U-channel ironless linear motor, the iron core linear motor is able to generate greater driving force and less heat.

[0015] Unfortunately, the presence of iron content in the iron core motor assembly 25 creates a large attractive force between the magnetic track 24 of the iron core linear motor and the iron core motor assembly 25. Figure 2 As described in the above, the large magnetic attraction F M In Z IF The linear bearing 23 acts on the iron core motor assembly 25 and the intermediate frame 21 by applying a restoring force F R1 and F R2 To balance the magnetic attraction F MAnd maintain the middle frame 22 at Z IF The intermediate frame 22 is supported in a position in the direction of rotation. Due to the large magnetic attraction force applied to the linear bearing, a relatively large capacity linear bearing must be used to avoid premature bearing damage. If a mechanical bearing is used, the relatively large bearing causes significant jitter in the position of the intermediate frame 22 during movement. This can excite high-frequency modes in the storage table and increase the settling time. In addition, the iron core motor assembly 25 is physically separated from the linear bearing 23 by a significant distance D. Therefore, the magnetic attraction force F M A considerable bending moment is induced on the intermediate frame 22. This bending moment induces a substantial deformation of the intermediate frame 22, which in turn results in reduced wafer positioning accuracy.

[0016] Finally, if Figure 2 As depicted in FIG. 2 , the iron core motor assembly 25 is mechanically fixed to the intermediate frame 22. The heat generated in the coil windings of the iron core motor assembly 25 is conducted to the intermediate frame 22. Figure 2 As depicted in FIG. 2 , arrows 26 represent heat flow from the iron core motor assembly 25 into the middle frame 22. The temperature of the middle frame 22 increases as the heat flow 26 is absorbed. Although the heat generated by the iron core motor assembly is less than that of the ironless motor assembly under the same driving force, the temperature increase of the middle frame is still large, and this temperature increase causes material expansion and deformation, severely limiting the positioning repeatability at the wafer.

[0017] Future metrology applications will challenge metrology due to the increasing measurement resolution and throughput requirements. Wafer positioning systems with higher accuracy and throughput capabilities are expected. Summary of the invention

[0018] Methods and systems for implementing a high-throughput wafer positioning system with high positioning accuracy are presented herein. High-throughput, high-accuracy wafer positioning systems are used to measure structural and material properties associated with various semiconductor manufacturing processes (e.g., material composition, dimensional properties of structures and films, etc.).

[0019] On the one hand, the iron core linear motor assemblies are arranged in a magnetically opposed configuration so that the inherent magnetic attraction forces of each opposed iron core linear motor assembly largely cancel each other. Therefore, the net force applied to the sensitive stage frame element due to the magnetic attraction force is negligible. The reduced force applied to the sensitive stage frame element in turn reduces the induced deformation and stage positioning error. In addition, the force applied to the bearing element required to constrain the position of the sensitive stage frame element can also be significantly reduced.

[0020] In another aspect, a wafer positioning system includes a second long-stroke stage stacked on top of a magnetically opposed long-stroke stage. In some embodiments, the two stacked long-stroke stages are configured as magnetically opposed stages. In some of these embodiments, the two magnetically opposed long-stroke stages employ magnetic tracks that are mechanically coupled to an intermediate frame of the stacked stage assembly. Thus, the intermediate frame is thermally isolated from heat generated by the core motor assemblies of the two long-stroke stages by a magnetic gap between the core motor assemblies and the corresponding magnetic tracks.

[0021] In another aspect, an iron core linear motor assembly includes one or more cooling channels within a housing of the assembly. A gas or liquid cooling fluid is pumped through the cooling channels to extract heat from the iron core linear motor assembly.

[0022] In another aspect, an iron core linear motor assembly arranged as a moving magnet motor includes multiple sets of electrical coils each wired in series and driven by separate current drivers operating at different phases to minimize thermal transients during operation.

[0023] In another aspect, measurements of one or more structures disposed on a semiconductor wafer are performed while the wafer is positioned with a magnetically opposed core wafer positioning system. In general, any suitable model-based or non-model-based metrology technique may be used to perform measurements of structures positioned by a magnetically opposed core wafer positioning system according to the methods and systems described herein.

[0024] The foregoing is an overview and therefore necessarily contains simplifications, generalizations, and omissions of detail; therefore, those skilled in the art will appreciate that the overview is illustrative only and not limiting in any way. Other aspects, inventive features, and advantages of the devices and / or processes described herein will be apparent in the non-limiting detailed description set forth herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a simplified diagram illustrating a typical prior art wafer positioning system 10 in one embodiment.

[0026] Figure 2 is a simplified diagram illustrating a typical prior art wafer positioning system 10 in another embodiment.

[0027] Figure 3 is a simplified diagram illustrating a wafer positioning system 120 in a magnetically opposed configuration in one embodiment.

[0028] Figure 4 is a diagram illustrating a perspective view of a wafer positioning system 150 including two stacked magnetically opposed long-stroke stages in one embodiment.

[0029] Figure 5is a diagram illustrating another perspective view of a wafer positioning system 150 including two stacked magnetically opposed long-stroke stages in one embodiment.

[0030] Figure 6 is a simplified diagram illustrating a cross section of an iron core linear motor assembly in one embodiment.

[0031] Fig. 7A is a graph depicting the temperature of a wafer frame of a wafer positioning system as the temperature increases from a starting temperature at the beginning of operation to a steady state temperature simulated under representative high throughput operating conditions.

[0032] Figure 7B is a graph depicting the temperature of the middle frame of a wafer positioning system as the temperature increases from a starting temperature at the beginning of operation to a steady state temperature simulated under representative high throughput operating conditions.

[0033] Figure 7C is a graph depicting the temperature of a stage base frame of a wafer positioning system as the temperature increases from a starting temperature at the beginning of operation to a steady state temperature simulated under representative high throughput operating conditions.

[0034] Figure 8 is a diagram illustrating a system 100 for performing spectroscopic ellipsometry of one or more structures disposed on a semiconductor wafer, the system 100 employing a magnetically opposed core wafer positioning system.

[0035] Fig. 9 is a diagram illustrating a system 200 for performing angle-resolved spectroscopic reflectance measurements of one or more structures disposed on a semiconductor wafer, the system 200 employing a magnetically opposed core wafer positioning system.

[0036] Fig.10 is a diagram illustrating a system 300 for performing spectroscopic reflectance measurements of one or more structures disposed on a semiconductor wafer, the system 300 employing a magnetically opposed core wafer positioning system.

[0037] Fig.11 is a flow chart of a method of positioning a wafer using a magnetically opposed core wafer positioning system as described herein. DETAILED DESCRIPTION

[0038] Reference will now be made in detail to background examples and some embodiments of the invention, examples of which are illustrated in the accompanying drawings.

[0039] Methods and systems for implementing a high-throughput wafer positioning system with high positioning accuracy are presented herein. High-throughput, high-accuracy wafer positioning systems are used to measure structural and material properties associated with various semiconductor manufacturing processes (e.g., material composition, dimensional properties of structures and films, etc.).

[0040] On the one hand, the iron core linear motor assemblies are arranged in a magnetically opposed configuration so that the inherent magnetic attraction forces of each opposed iron core linear motor assembly largely cancel each other out. Therefore, the net force applied to the sensitive stage frame element due to the magnetic attraction force is negligible. The reduced force applied to the sensitive stage frame element in turn reduces induced deformation and stage positioning errors. In addition, the force applied to the bearing element required to constrain the position of the sensitive stage frame element can also be significantly reduced. This extends the bearing life and enables the implementation of smaller bearing elements, which reduces induced friction and bearing-induced positioning jitter.

[0041] Figure 3 FIG. 1 is a simplified diagram of a wafer positioning system 120 in a magnetically opposed configuration according to one embodiment. The wafer positioning system 120 includes a stage base frame 121 and an intermediate frame 122. IF ,Y IF ,Z IF A set of mechanical linear bearings 123 restricts the relative motion of the intermediate frame 122 with respect to the base frame 121 of the platform to one degree of freedom, namely, Y. IF direction.

[0042] exist Figure 3 In the embodiment depicted in FIG. 1 , the wafer positioning system 120 employs a pair of iron core linear motors in a magnetically opposed configuration. Figure 3 A pair of iron core motor assemblies 124A to B and a pair of magnetic tracks 125A to B are illustrated. Figure 3 As depicted in FIG. 1 , the core motor assembly 124A-B is mechanically fixed to the platform base frame 121 and the track pair 125A-B is mechanically fixed to the platform middle frame 122. Figure 3 , the tracks 125A-B are positioned so that the faces of each track of the track pair face in opposite directions. Each track includes a plurality of permanent magnets 127 attached to a magnetic backing plate mechanically fixed to the middle frame 122. Each track generates a magnetic field in the space adjacent to the face of the track. The face of the track is defined by the side of the permanent magnet array that is exposed to the environment opposite the magnetic backing plate of the track.

[0043] Track 125A includes a plurality of permanent magnets attached to a magnetic backing plate that is mechanically fixed to the intermediate frame 122. This assembly generates a magnetic field in the space adjacent to track 125A. Figure 3 , magnetic field lines 128A are concentrated in the permanent magnets and iron backing plate of track 125A and extend in the space adjacent to track 125A. Similarly, track 125B includes a plurality of permanent magnets 127 attached to a magnetic backing plate mechanically fixed to the intermediate frame 122. This assembly generates a magnetic field in the space adjacent to track 125B. Figure 3As depicted in FIG. 1 , magnetic field lines 128B are concentrated in the permanent magnets and iron backing plate of track 125B and extend in the space adjacent to track 125B.

[0044] The iron core motor assembly 124A-B includes a plurality of conductive coils each wrapped around an iron post. Each iron post is manufactured as part of a larger iron structure. In some examples, the copper coils are embedded in an epoxy matrix material that fills the space around the conductive coils and the iron structure.

[0045] like Figure 3 As depicted in FIG. 1 , the iron core motor assemblies 124A-B are positioned adjacent to the faces of the magnetic tracks 125A-B, respectively. In addition, the iron pillars and associated iron structures shape the magnetic field lines 128A-B, respectively, i.e., the magnetic field lines are concentrated in the iron pillars and associated structures. The mechanical driving force is at Y IF The direction is created by the flowing current through the windings of the coils of the iron core motor assembly 124A-B.

[0046] As previously described herein, iron core linear motors are capable of generating greater drive force and less heat than U-channel ironless linear motors. However, the presence of iron content in the iron core motor assemblies 124A-B creates a large attraction force between the magnetic tracks 125A-B and the iron core motor assemblies 124A-B. Figure 3 As described in the above, the large magnetic attraction F M1 In the positive X IF The large magnetic attraction force F M2 In negative X IF The magnetic attraction force F M1 in the opposite direction.

[0047] In general, the magnetic attraction force of an iron core linear motor is substantially dependent on the magnetic flux density in the gap between the magnetic track and the iron core motor assembly, which in turn is greatly dependent on the size of the gap. In practice, the wafer positioning stage 120 is designed to maintain a constant gap between the magnetic track 125A and the iron core motor assembly 124A, which is similar to the constant gap between the magnetic track 125B and the iron core motor assembly 124B. The gap is determined by machine tolerances and is maintained by linear bearings above the working space of the wafer positioning stage 120. Assuming similar gaps are maintained, the magnetic attraction force F M1 and F M2 are roughly the same and cancel each other out. Therefore, due to the magnetic attraction F M1 and F M2 , the remaining force applied to the intermediate frame 122 is negligible along with any remaining bending moment applied to the intermediate frame 122. This significantly reduces any induced deformation of the intermediate frame 122, which in turn results in increased wafer positioning accuracy.

[0048] In addition, due to the magnetic attraction F M1 and F M2 The forces applied to the linear bearing 123 are substantially offset, so the forces applied to the linear bearing 123 are significantly reduced. Therefore, much smaller linear bearings can be used. For mechanical bearings, smaller bearing sizes can be used without sacrificing bearing life. Smaller size mechanical bearings operate with reduced friction and reduced positioning jitter. This improves the repeatability of the stage positioning and reduces settling time.

[0049] Finally, if Figure 3 As depicted in FIG. 1 , the iron core motor assembly 124A-B is mechanically fixed to the table base frame 101. The heat generated in the coil windings of the iron core motor assembly 124A-B is conducted into the table base frame 101. Figure 3 As depicted in FIG. 1 , arrows 126A to B respectively represent heat flow from the core motor assembly 124A to B to the stage base frame 101 instead of the intermediate frame 122. Therefore, the temperature of the intermediate frame 122 does not substantially change during the stage operation and the induced material expansion and deformation of the intermediate frame 122 are negligible. This significantly improves the positioning repeatability of the wafer-level stage.

[0050] In another aspect, the wafer positioning system includes a second long-stroke stage stacked on top of the magnetically opposed long-stroke stage, such as Figure 3 In some embodiments, the two stacked long-stroke tables are configured as magnetically opposed tables. In other embodiments, only the bottom long-stroke table (i.e., the table mounted to the table base frame) is configured as a magnetically opposed long-stroke table.

[0051] Figure 4 is a diagram illustrating a perspective view of a wafer positioning system 150 including two stacked magnetically opposed long-stroke stages in one embodiment.

[0052] Figure 5 is a diagram illustrating another perspective view of a wafer positioning system 150 including two stacked magnetically opposed long-stroke stages in one embodiment.

[0053] like Figure 4 and 5 As depicted in FIG. 1 , the wafer positioning system 150 includes a stage base frame 121, an intermediate frame 122, and a wafer frame 142. Coordinate system {X BF ,Y BF ,Z BF} is fixed to the base frame 121 of the storage table, and the coordinate system {X IF ,Y IF ,Z IF} is fixed to the middle frame 122, and the coordinate system {X WF,Y WF ,Z WF} is fixed to the wafer frame 142. A set of linear bearings 123 restricts the relative movement of the intermediate frame 122 relative to the stage base frame 121 to one degree of freedom, namely, Y IF A set of linear bearings 143 restricts the relative motion of the wafer frame 142 with respect to the intermediate frame 122 to one degree of freedom, namely, X. WF direction.

[0054] exist Figure 4 and 5 In the embodiment depicted in FIG. 1 , the wafer positioning system 150 employs a pair of iron core linear motors in a magnetically opposed configuration to provide a Y IF The driving force required to position the intermediate frame 122 relative to the base frame 121 of the storage table in the direction, and another pair of iron core linear motors in a magnetically opposed configuration to provide the ... WF The driving force required to position the wafer frame 142 relative to the intermediate frame 122 in the direction.

[0055] Figure 4 and 5 Also illustrated is a multi-DOF short-stroke positioning stage 146 mounted to the wafer frame 142. In some embodiments, the short-stroke positioning stage 146 is axially spaced relative to the wafer frame 142. WF The wafer chuck 141 is positioned in the Y direction relative to the wafer frame 142. WF Axis and X WF The short-stroke positioning stage 146 is generally referred to as a tip tilt Z stage in these embodiments. In some other embodiments, the short-stroke positioning stage 146 positions the wafer chuck 141 relative to the wafer frame 142 with additional degrees of freedom, such as about the Z axis. WF Axis orientation, in X WF and Y WF orientation, or any combination thereof.

[0056] Figure 4 and 5 Description as reference Figure 3 A pair of iron core motor assemblies 124A-B and a pair of magnetic tracks 125A-B are depicted in a magnetically opposed configuration. The mechanical driving force is at Y IF The direction is created by the flowing current through the windings of the coils of the iron core motor assembly 124A-B.

[0057] Figure 5 The core motor assembly 144A-B is mechanically fixed to the wafer frame 142 and a pair of magnetic tracks 145A-B is mechanically fixed to the intermediate frame 122. Figure 5As depicted in FIG. 1 , the tracks 145A-B are positioned so that the faces of each track of the track pair face in opposite directions. Each track includes a plurality of permanent magnets attached to a magnetic backing plate that is mechanically fixed to the middle frame 122. Each track generates a magnetic field in the space adjacent to the face of the track. The face of the track is defined by the side of the permanent magnet array that is exposed to the environment opposite the magnetic backing plate of the track.

[0058] The iron core motor assembly 144A-B includes a plurality of conductive coils each wrapped around an iron post. Each iron post is manufactured as part of a larger iron structure. In some examples, the copper coils are embedded in an epoxy matrix material that fills the space around the conductive coils and the iron structure.

[0059] like Figure 5 As depicted in FIG. 1 , the iron core motor assemblies 144A-B are positioned adjacent to the faces of the magnetic tracks 145A-B, respectively. In addition, the iron posts and associated iron structures of the iron core motor assembly 144A shape the magnetic field lines passing through the gap between the iron core motor assembly 144A and the magnetic tracks 145A. Similarly, the iron posts and associated iron structures of the iron core motor assembly 144B shape the magnetic field lines passing through the gap between the iron core motor assembly 144B and the magnetic tracks 145B. The mechanical driving force is at X WF The direction is created by the flowing current through the windings of the coils of the iron core motor assembly 144A-B.

[0060] The presence of iron content in the iron core motor assembly 144A-B creates a large attractive force between the magnetic tracks 145A-B and the iron core motor assembly 144A-B. Due to the magnetic interaction between the iron core motor assembly 144A and the magnetic track 145A, the magnetic attraction force is at the negative Y WF Similarly, due to the magnetic interaction between the core motor assembly 144B and the magnetic track 145B, the magnetic attraction force in the positive Y direction WF The magnetic attraction forces act on the core motor assembly 144B in the opposite direction. Since the magnetic attraction forces act on the core motor assemblies 144A-B respectively in opposite directions, and both of the core motor assemblies 144A-B are mechanically fixed to the wafer frame 142, the magnetic attraction forces cancel each other out. Assuming that similar gaps are maintained between the core motor assemblies 144A-B and the magnetic tracks 145A-B respectively, the residual force applied to the wafer frame 142 due to the magnetic attraction forces, together with the residual bending moment applied to the wafer frame 142, is negligible. This significantly reduces any induced deformation of the wafer frame 142, which in turn results in increased wafer positioning accuracy.

[0061] Additionally, because the magnetic forces substantially cancel each other out, the forces applied to the linear bearing 143 are significantly reduced. As a result, much smaller linear bearings can be used. For mechanical bearings, smaller sized bearings can be used without sacrificing bearing life. Smaller sized mechanical bearings operate with reduced friction and reduced positioning jitter. This results in improved stage positioning repeatability and reduced settling time.

[0062] Finally, if Figure 5 As depicted in FIG. 1 , the core motor assemblies 144A-B are mechanically fixed to the wafer frame 142. The heat generated in the coil windings of the core motor assemblies 144A-B is conducted to the wafer frame 142 rather than the intermediate frame. Therefore, the temperature of the intermediate frame 122 does not substantially change during the stage operation and the induced material expansion and deformation of the intermediate frame 122 is negligible. This improves the positioning repeatability of the wafer level stage.

[0063] like Figure 4 and 5 As depicted in FIG, two magnetically opposed long-stroke stages of wafer positioning system 150 employ magnetic tracks that are mechanically coupled to intermediate frame 122. Thus, intermediate frame 122 is thermally isolated from the heat generated by core motor assemblies 124A-B and 144A-B by the physical magnetic gaps between the core motor assemblies and the corresponding magnetic tracks. A small amount of heat transfer occurs through linear bearings 123 and 143, but the mechanical contact area of ​​the linear bearings is quite small, and thus the total amount of heat transfer is negligible. In some embodiments, air bearings, porous or orifice-type air bearings, may be employed in place of mechanical bearings, such as roller bearings or ball bearings. In these embodiments, heat transfer through the air gaps of the air bearings is negligible.

[0064] The coefficient of thermal expansion (CTE) of the steel structure of the linear bearing 143 does not match the CTE of the aluminum intermediate plate 122. Figure 4 and 5 In the embodiment depicted in FIG, the linear bearing 143 is mounted near the neutral axis of the middle plate 122. The neutral axis of the middle plate 122 is the axis in the cross section of the middle plate 122 along which no longitudinal stress or strain exists, i.e., when temperature changes occur, no longitudinal strain is induced due to the CTE mismatch of the linear bearing and the middle frame 122. Therefore, a small temperature change of the middle frame 122 and the linear bearing 143 does not induce a significant deformation of the middle frame 122.

[0065] The wafer positioning system 150 includes two stacked magnetically opposed long-stroke stages. Each magnetically opposed long-stroke stage is capable of moving a wafer over a distance of at least 300 mm in the long-stroke direction (i.e., the X and Y directions). The wafer positioning system 150 is capable of positioning the wafer at any position in the workspace with a repeatability of less than 300 nanometers. To meet the high throughput requirements of semiconductor manufacturing plants, the wafer positioning system is capable of generating high accelerations in both the X and Y directions. In some embodiments, the wafer positioning system 150 is capable of generating high accelerations in both the X and Y directions at a speed of at least 30 meters per second. 2 In some embodiments, the wafer positioning system 150 accelerates the wafer at an acceleration of at least 50 m / s. 2 The moving mass of the Y stage (i.e., the total mass of the intermediate frame 122 and all components carried by the intermediate frame 122) is relatively large, for example, more than 40 kg. 2 To accelerate this mass at an acceleration of , the iron-core linear motor assemblies 124A and 124B each continuously generate a force of at least 600 Newtons. To generate such large forces, the iron-core linear motor assemblies 124A and 124B each generate a large amount of heat.

[0066] In another aspect, an iron core linear motor assembly includes one or more cooling channels within a housing of the assembly. A gas or liquid cooling fluid is pumped through the cooling channels to extract heat from the iron core linear motor assembly.

[0067] Figure 6 1 is a diagram illustrating a cross section of an iron core linear motor assembly in one embodiment. The iron core linear motor assembly 160 includes an iron structure 161, coil assemblies 162-165, and cooling channels 166 integrated into a housing 167. In some embodiments, the space between the iron structure 161, coil assemblies 162-165, and cooling channels 166 is filled with a solidifying material 168 (e.g., epoxy). In some other embodiments, the housing is manufactured with a gap to match the iron structure 161, coil assemblies 162-165, and cooling channels 166, and optionally, any remaining space is filled with a solidifying material 168. Figure 6 In the embodiment depicted in , a cooling fluid 169 is pumped through the channels 166 to extract heat from the iron core linear motor assembly 160 .

[0068] As described above, due to the high acceleration requirements and high payload of the long stroke Y stage, the iron core linear motor assemblies 124A-B of the wafer positioning system 150 generate most of the heat. Thus, a large amount of cooling fluid (gas or fluid) is circulated through the cooling channels of the iron core linear motor assemblies 124A-B. The cooling channels of the iron core linear motor assemblies 124A-B are directly coupled to a cooling fluid source, such as a heat exchanger, a housing supplied cooling source, etc. The direct connection is possible because the iron core linear motor assemblies 124A-B are mechanically coupled to the stage base frame 121 (which does not substantially move relative to the measurement system frame sitting in the wafer fabrication plant).

[0069] In some other embodiments, the iron core linear motor assemblies 124A-B of the wafer positioning system 150 are mounted to the middle plate 122. In these embodiments, a flex tube is required to supply cooling fluid to the iron core linear motor assemblies 124 as the middle plate 122 moves relative to the stage base frame 121. This embodiment is not preferred because the reliability of the flex tube is low and the large mass and hysteresis of the flex tube negatively affect the positioning accuracy and settling time of the wafer positioning system.

[0070] In some embodiments, a flex tube is required to supply cooling fluid to the iron core linear motor assemblies 144A-B of the wafer positioning system 150. Although it is not preferred to provide cooling to the X stage, the amount of moving mass of the X stage is much smaller than that of the Y stage. Therefore, the amount of cooling required, along with the size of the flex tube that must be routed from the stage base frame 101 to the wafer frame 142 via the intermediate frame 122, is much smaller. Therefore, the force perturbation from the flex tube to the wafer frame 142 is limited and does not substantially affect the positioning accuracy and settling time of the wafer positioning system.

[0071] On the other hand, an iron core linear motor assembly arranged as a moving magnet motor includes multiple sets of electrical coils each wired in series and driven by separate current drivers operating at different phases to minimize thermal transients during operation of the wafer positioning system 150 .

[0072] like Figure 6 As depicted in FIG. 1 , the iron structure 161 includes a number of pole pieces. In some embodiments, the iron structure 161 is made of laminated electrical steel sheets to minimize power losses due to induced eddy currents. A coil of conductive wire (e.g., copper wire) is wrapped around each pole piece. Figure 6 In the embodiment depicted in , the electrical coils are divided into groups 162 to 165. Each group includes three adjacent coils, each operating in a different electrical phase to cause the moving portion of the linear motor to travel through its full stroke.

[0073] like Figure 6, the first coil of each coil group (e.g., coils 162A-165A) is electrically coupled in series with a first controlled current source. Similarly, the second coil of each coil group (e.g., coils 162B-165B) is electrically coupled in series to a second current source, and the third coil or each coil group (e.g., coils 162C-165C) is electrically coupled in series to a third current source. Current 170A is provided by electrical coils 162A-165A, current 170B is provided by electrical coils 162B-165B, and current 170C is provided by electrical coils 162C-165C. Currents 170A-C are operated out of phase with each other to smoothly drive the linear motor independently of the relative position of the iron core linear motor assembly 160 with respect to the corresponding track. By operating all coils with the same phase together, the entire coil assembly of the iron core linear motor assembly 160 is heated uniformly, thereby eliminating possible moving hot spots.

[0074] In some other embodiments, each adjacent coil is independently operated in a different electrical phase to cause the moving portion of the linear motor to travel within its full stroke. In this way, the current through each electrical coil is independently controlled based on the position of the mover relative to the stator assembly of the linear motor. This control method is generally referred to as coil switching. In these embodiments, current is only supplied to the electrical coils that are located opposite the track and are therefore able to generate significant driving force. This method results in less overall heat generation, but the heating along the entire length of the iron core linear motor assembly is uneven. Generally speaking, the impact of uneven heating on overall positioning accuracy exceeds the impact of total heating on overall positioning accuracy.

[0075] The iron core linear motor assembly 160 is a three phase motor, ie, three different sets of coils are wired in series and driven by separate current drivers that operate one hundred twenty degrees out of phase with the other sets of coils. However, in general, the iron core linear motor assembly can be configured to operate in any number of different phases.

[0076] Fig. 7A 1 is a graph 180 depicting the temperature of the wafer frame 142 of the wafer positioning system 150 as the temperature of the wafer frame 142 increases from a starting temperature at the beginning of operation to a steady state temperature simulated under representative high throughput operating conditions. Fig. 7A As depicted in FIG. 1 , the temperature of the wafer frame 142 increases by approximately 0.23 degrees Celsius. This is similar to conventional stacking station designs that employ U-channel ironless linear motors.

[0077] Figure 7B 1 is a graph 181 depicting the temperature of the intermediate frame 122 of the wafer positioning system 150 as the temperature of the intermediate frame 122 increases from a starting temperature at the beginning of operation to a steady-state temperature simulated under representative high-throughput operating conditions. Figure 7B, the temperature of the intermediate frame 122 rises by about 0.023 degrees Celsius. The comparable temperature rise of a conventional stacking stage design employing a U-channel ironless linear motor is more than 30X. The temperature stability of the intermediate frame 122 achieved using a magnetically opposed iron core linear motor as described herein achieves significantly improved wafer positioning performance. By limiting heat transfer to the intermediate frame 122, thermally induced Abbe errors at the wafer are significantly reduced. In addition, the thermal stability of the intermediate frame 122 enables high wafer positioning accuracy after error mapping.

[0078] Figure 7C 1 is a graph 182 depicting the temperature of the stage base frame 121 of the wafer positioning system 150 as the temperature of the stage base frame 121 increases from a starting temperature at the beginning of operation to a steady state temperature under simulated representative high throughput operating conditions. Figure 7C , the temperature of the table base frame 121 increases by approximately 0.027 degrees Celsius. The large thermal mass of the table base frame allows for a large amount of heat absorption generated by the iron core linear motor assemblies 124A-B without inducing significant temperature changes in the table base frame 121.

[0079] Generally, the stage base frame of the magnetically opposed core wafer positioning system is attached to the machine frame of the measurement system. In this manner, the magnetically opposed core wafer positioning system is configured to accurately position the wafer being measured relative to the optical subsystem of the measurement system.

[0080] Figure 8 A system 100 for measuring characteristics of a semiconductor wafer is described. Figure 8 As shown in , system 100 performs spectroscopic ellipsometer measurements of one or more structures 112 disposed on a semiconductor wafer 114 that is positioned relative to a spectroscopic ellipsometer 101 by a magnetically opposed core wafer positioning system.

[0081] In this aspect, system 100 includes a spectroscopic ellipsometer 101 equipped with an illuminator 102 and a spectrometer 104. Illuminator 102 of system 100 is configured to generate illumination of a selected wavelength range (e.g., 100 nanometers to 20 micrometers) and direct the illumination to one or more structures 112 disposed on a surface of a semiconductor wafer 114. Spectrometer 104 is in turn configured to receive light from the surface of semiconductor wafer 114. Further note that light exiting illuminator 102 is polarized using polarization state generator 107 to produce polarized illumination beam 106. Radiation reflected by structures 114 disposed on wafer 112 passes through polarization state analyzer 109 and to spectrometer 104. Radiation received by spectrometer 104 to collect beam 108 is analyzed for polarization state, allowing spectral analysis of the radiation delivered by the analyzer. Detected spectrum 111 is delivered to computing system 130 for analysis of one or more structures 112.

[0082] like Figure 8 , the metrology system 100 includes a magnetically opposed core wafer positioning system 150 configured to position the wafer 114 relative to the spectrometer 101 during measurement. The magnetically opposed core wafer positioning system 150 receives a command signal (not shown) from the computing system 130. The command signal includes an indication of a desired position of the wafer 114 relative to the spectrometer 101. In response to the command signal, the magnetically opposed core wafer positioning system 150 moves the wafer 114 to the desired position relative to the spectrometer 101.

[0083] In one aspect, a spectroscopic ellipsometry measurement is performed while the wafer 114 is located at a desired position relative to the spectrometer 101. Measurement data 111 collected from the measurement is transmitted to a computing system 130 and an estimation of one or more structural parameters of interest 115 is made based on the collected measurement data. The computing system 130 is configured to receive measurement data 111 associated with measurements (e.g., critical dimensions, film thicknesses, concentrations, compositions, processes, etc.) of one or more structures 112 disposed on the wafer 114. In one example, the measurement data 111 includes an indication of a spectral response of a sample measured by the measurement system 100 based on one or more sampling processes from the spectrometer 104. In some embodiments, the computing system 130 is further configured to determine sample parameter values ​​115 of the structures 112 from the measurement data 111. In one example, the computing system 130 is configured to access model parameters in real time using real-time critical dimensions (RTCD), or it may access a library of pre-computed models to determine a value of at least one parameter of interest associated with the target structure 112. In some embodiments, estimates of one or more parameters of interest are stored in a memory (e.g., memory 132). Figure 8 In the embodiment depicted in , estimates 115 of one or more parameter values ​​of interest are communicated to an external system (not shown).

[0084] In general, ellipsometry is an indirect method for measuring the physical properties of the sample under examination. In most cases, the raw measurement signal (e.g. α meas and β meas ) cannot be used to directly determine the physical properties of the sample. The nominal measurement process consists of parameterization of the structure (e.g., film thickness, critical dimensions, material properties, etc.) and parameterization of the machine (e.g., wavelength, angle of incidence, polarization angle, etc.). Creating a process that attempts to predict the measured value (e.g., α meas and β meas ) measurement model. As described in equations (1) and (2), the model includes parameters (P machine ) and parameters associated with the sample (P specimen ).

[0085] α model =f(P machine ,P specimen ) (1)

[0086] β model =g(P machine ,P specimen ) (2)

[0087] Machine parameters are parameters used to characterize a metrology tool, such as the ellipsometer 101. Exemplary machine parameters include angle of incidence (AOI), analyzer angle (A0), polarizer angle (P0), illumination wavelength, numerical aperture (NA), compensator or wave plate (if any), etc. Sample parameters are parameters used to characterize a sample, such as a wafer 114 including the structure 112. For thin film samples, exemplary sample parameters include refractive index, dielectric function tensor, nominal layer thickness of all layers, layer sequence, etc. For CD samples, exemplary sample parameters include geometric parameter values ​​associated with different layers, refractive index associated with different layers, etc. For measurement purposes, the machine parameters are considered as known fixed parameters, and one or more of the sample parameters are considered as unknown floating parameters.

[0088] In some examples, the floating parameters are resolved by an iterative process (e.g., regression) that produces the best fit between theoretical predictions and experimental data. specimen And calculate the model output value (such as α model and β model ) until a value that leads to a difference between the model output and the experimental measurement (e.g. α meas and β meas). In model-based measurement applications such as spectroscopic ellipsometers on CD samples, a regression process (e.g., least squares regression) is used to identify sample parameter values ​​that minimize the difference between model output values ​​and experimentally measured values ​​for a set of fixed machine parameter values.

[0089] In some examples, floating parameters are resolved by searching a library of pre-computed solutions to find the closest match. In model-based measurement applications such as spectroscopic ellipsometers on CD samples, a library search process is used to identify sample parameter values ​​that minimize the difference between pre-computed output values ​​and experimentally measured values ​​for a set of fixed machine parameter values.

[0090] In model-based measurement applications, simplifying assumptions are often required to maintain adequate throughput. In some instances, the truncation order of rigorous coupled wave analysis (RCWA) must be reduced to minimize computational time. In another instance, the number or complexity of library functions is reduced to minimize search time. In another instance, the number of floating parameters is reduced by fixing certain parameter values. In some instances, these simplifying assumptions lead to unacceptable errors in estimating the value of one or more parameters of interest (e.g., critical dimension parameters, superposition parameters, etc.). By performing measurements of structures subjected to gas absorption as described herein, model-based measurement models can be solved with reduced parameter dependencies and increased measurement accuracy.

[0091] In general, the spectroscopic ellipsometer 101 may employ any architecture suitable for measuring modulation of an optical property, such as dielectric function, bandgap, etc. By way of non-limiting example, the spectroscopic ellipsometer 101 may be configured with a rotating polarizer, a rotating compensator, or any combination thereof.

[0092] also, Figure 8 The embodiments of the system 100 illustrated in may be further configured as described herein. Additionally, the system 100 may be configured to perform any other blocks of any of the method embodiments described herein.

[0093] Fig. 9 An angularly resolved spectroscopic reflectometer system configured to measure reflectivity over a wide range of angles to estimate values ​​of one or more characteristics of a semiconductor wafer in at least one novel aspect is described. Fig. 9 Like numbered elements described in the reference Figure 8 The components described. Fig. 9, system 200 performs spectroscopic ellipsometry of one or more structures 112 disposed on a semiconductor wafer 114 that is positioned relative to an angle-resolved spectroscopic reflectometer by a magnetically opposed core wafer positioning system. In one embodiment, system 200 is an angle-resolved spectroscopic reflectometer that includes one or more measurement channels across a wide wavelength range, such as infrared wavelengths between 750 nanometers and 2600 nanometers.

[0094] The angle-resolved spectroscopic reflectometer 200 includes a polarizer 204, an objective lens 201, an analyzer 210, and a spectrometer 212. Fig. 9 2, an illumination beam is generated by illumination source 202 in response to command signal 229 received from computing system 130. Light from illumination source 202 is conditioned by optional beam shaping optics 203 to generate illumination beam 220. Illumination beam 220 is directed to polarizer 204. Although as depicted, the illumination light directed to polarizer 204 is from illumination source 202, in general, light from any number of illumination sources of system 200 may be combined to generate the illumination beam directed to polarizer 204. In this manner, the spectral components of the illumination light may be configured as a combination of light emitted from multiple illumination sources.

[0095] In some embodiments, polarizer 204 is configured to rotate the polarizing element around the optical axis of illumination beam 220. In general, polarizer 204 may include any polarizing element and system for rotating a polarizing element known in the art. For example, polarizer 204 may include a polarizing element mechanically coupled to a rotational actuator. In one example, the polarizing element may be a Rochon prism. In another example, the polarizing element may include a beam displacer. Polarizer 204 is configured to operate in a rotationally active or rotationally inactive state within system 200. In one example, the rotational actuator of polarizer 204 may be inactive so that the polarizing element remains rotationally fixed around the optical axis of illumination light 220. In another example, the rotational actuator may be rotated at a selected angular frequency ω. p Rotate the polarizing element around the optical axis of the illumination light.

[0096] In some other embodiments, polarizer 204 is configured with a fixed polarization angle around the optical axis of illumination beam 220 .

[0097] like Fig. 9 As depicted, the illumination beam 220 passes through the polarizer 204 while the rotary actuator rotates at a selected angular frequency ω p The polarizing element is rotated. In this way, the polarizer 204 generates a polarized light beam 221 which is directed toward the beam splitter 206. The beam splitter 206 directs the polarized light beam 221 toward the objective lens 201.

[0098] exist Fig. 9In the embodiment depicted in FIG. 1 , objective lens 201 focuses polarized light beam 221 onto the surface of wafer 114 within a range of incident angles. In some examples, polarized light beam 221 is focused onto the surface of wafer 114 within a range of incident angles between 0 degrees and 40 degrees. In some examples, focusing polarized light beam 221 onto the surface of wafer 114 at a small incident angle results in a small illumination spot, such as less than 100 microns in diameter.

[0099] The interaction of the focused polarized light beam 221 with the wafer 114 modifies the polarization of the radiation by any of reflection, scattering, diffraction, transmission, or other types of processes. After interaction with the wafer 114, the modified light 222 is collected by the objective lens 201 and directed to the beam splitter 206. The beam splitter 206 is configured to transmit the modified light 222 toward the analyzer 210. Fig. 9 , the analyzer 210 includes a polarizer element that remains rotationally fixed about the optical axis of the modified beam 222 as the modified beam 222 passes through the analyzer 210 and optional beam focusing optics 211 to the spectrometer 212. In the spectrometer 212, beam components having different wavelengths are refracted (e.g., in a prism spectrometer) or diffracted (e.g., in a grating spectrometer) in different directions to different detectors. The detector may be a linear array of photodiodes, each of which measures radiation in a different wavelength range. The radiation received by the spectrometer 212 is analyzed for polarization state, allowing spectral analysis of the radiation passed by the polarizer 212 by the spectrometer. The measured spectrum 228 is transmitted to the computing system 130. The computing system 130 is configured to receive a signal 228 indicative of a measured spectral response of the structure of interest and estimate a value of a parameter of interest based on the measured spectral response.

[0100] like Fig. 9 , the metrology system 200 includes a magnetically opposed core wafer positioning system 150 configured to position the wafer 114 relative to the angle-resolved spectroscopic reflectometer during measurement. The magnetically opposed core wafer positioning system 150 receives a command signal (not shown) from the computing system 130. The command signal includes an indication of a desired position of the wafer 114 relative to the angle-resolved spectroscopic reflectometer. In response to the command signal, the magnetically opposed core wafer positioning system 150 moves the wafer 114 to the desired position relative to the angle-resolved spectroscopic reflectometer, as described above with respect to the spectroscopic ellipsometer system 100.

[0101] Fig.10 A spectroscopic reflectometer system configured to measure reflectivity at normal incidence to estimate values ​​of one or more properties of a semiconductor wafer in at least one novel aspect is described. Fig.10 Like numbered elements described in the reference Figure 8 The components described. Fig.10As shown in FIG. 3 , system 300 performs spectral reflectance measurements of one or more structures 112 disposed on a semiconductor wafer 114 that is positioned relative to a spectral reflectometer by a magnetically opposed core wafer positioning system.

[0102] The spectroscopic reflectometer 300 includes a polarizer 304, an analyzer 310, and a spectrometer 312. Fig.10 , an illumination beam is generated by illumination source 302 in response to command signal 329 received from computing system 130. Illumination beam 320 from illumination source 302 is directed to polarizer 304. Although as depicted, the illumination light directed to polarizer 304 is from illumination source 302, in general, light from any number of illumination sources of system 300 may be combined to generate the illumination beam directed to polarizer 304. In this manner, the spectral components of the illumination light may be configured as a combination of light emitted from multiple illumination sources.

[0103] In some embodiments, polarizer 304 is configured to rotate the polarizing element around the optical axis of illumination beam 320. In general, polarizer 304 may include any polarizing element and system for rotating a polarizing element known in the art. For example, polarizer 304 may include a polarizing element mechanically coupled to a rotational actuator. In one example, the polarizing element may be a prism. In another example, the polarizing element may include a beam displacer. Polarizer 304 is configured to operate in a rotationally active or rotationally inactive state within system 300. In one example, the rotational actuator of polarizer 304 may be inactive so that the polarizing element remains rotationally fixed around the optical axis of illumination light 320. In another example, the rotational actuator may rotate the polarizing element at a selected angular frequency ω. p Rotate the polarizing element around the optical axis of the illumination light.

[0104] In some other embodiments, polarizer 304 is configured with a fixed polarization angle around the optical axis of illumination beam 320 .

[0105] like Fig.10 As depicted, the illumination beam 320 passes through the polarizer 304 while the rotary actuator rotates at a selected angular frequency ω p The polarizing element is rotated. In this manner, the polarizer 304 generates a polarized light beam 321 that is directed toward the beam splitter 306. The beam splitter 306 directs the polarized light beam 321 toward the wafer 114 according to the directional incidence. The polarized light beam 221 is incident on the surface of the wafer 114 through a small illumination spot (e.g., less than 100 microns in diameter).

[0106] The interaction of the polarized light beam 221 with the wafer 114 modifies the polarization of the radiation by any of reflection, scattering, diffraction, transmission, or other types of processes. After interaction with the wafer 114, the modified light 322 is directed to the beam splitter 306. The beam splitter 306 is configured to transmit the modified light 322 toward the analyzer 310. Fig.10 , the analyzer 310 includes a polarizer element that remains rotationally fixed about the optical axis of the modified beam 322 as the modified beam 322 passes through the analyzer 310 to the spectrometer 312. In the spectrometer 312, beam components having different wavelengths are refracted (e.g., in a prism spectrometer) or diffracted (e.g., in a grating spectrometer) in different directions to different detectors. The detector may be a linear array of photodiodes, each of which measures radiation within a different wavelength range. The radiation received by the spectrometer 312 is analyzed for polarization state, allowing spectral analysis of the radiation passed by the polarizer 312 by the spectrometer. A measured spectrum 328 is transmitted to the computing system 130. The computing system 130 is configured to receive a signal 328 indicative of a measured spectral response of the structure of interest and to estimate a value of a parameter of interest based on the measured spectral response.

[0107] like Fig.10 , the metrology system 300 includes a magnetically opposed core wafer positioning system 150 configured to position the wafer 114 relative to the spectroscopic reflectometer during measurement. The magnetically opposed core wafer positioning system 150 receives a command signal (not shown) from the computing system 130. The command signal includes an indication of a desired position of the wafer 114 relative to the spectroscopic reflectometer. In response to the command signal, the magnetically opposed core wafer positioning system 150 moves the wafer 114 to the desired position relative to the spectroscopic reflectometer, as described above with respect to the spectroscopic ellipsometer system 100.

[0108] Although reflectometer systems 200 and 300 include polarizing optics, in general, reflectometer systems 200 and 300 may not include polarizing optics.

[0109] In general, the measurement system may include any combination of spectroscopic ellipsometry, spectroscopic reflectometry, and angularly resolved spectroscopic reflectometry using a magnetically opposed core wafer positioning system. The measurements may be performed sequentially or simultaneously.

[0110] exist Figures 8 to 10 In the embodiment depicted in , measurements of one or more structures are performed while a wafer is positioned using a magnetically opposed core wafer positioning system. In general, any suitable model-based or non-model metrology technique may be used to perform measurements of structures positioned by a magnetically opposed core wafer positioning system according to the methods and systems described herein.

[0111] Suitable metrology techniques may be contemplated individually or in any combination, including but not limited to spectroscopic ellipsometry and spectral reflectometry (including single wavelength, multi-wavelength, and angle-resolved implementations), spectral scatterometry, scatterometry superposition, beam profile reflectometry, and beam profile ellipsometry (including angle-resolved and polarization-resolved implementations).

[0112] Fig.11 A method 400 suitable for implementation by the metrology systems 100, 200, and 300 of the present invention is described. In one aspect, it should be recognized that any data processing elements of the method 400 may implement the method via pre-processed algorithms executed by one or more processors of the computing system 130. Although the following description is presented in the context of the metrology systems 100, 200, and 300, it should be recognized herein that specific structural aspects of the metrology systems 100, 200, and 300 do not represent limitations and should be interpreted merely as illustrative.

[0113] In frame 301, a first moving frame is positioned relative to a base frame along a first axis. A first magnet assembly and a second magnet assembly are mechanically coupled to the first moving frame. A first iron-core linear motor assembly and a second iron-core linear motor assembly are mechanically coupled to the base frame. The first iron-core linear motor assembly is disposed adjacent to the first magnet assembly. The first iron-core linear motor assembly and the first magnet assembly are physically separated by a first magnetic gap. A first magnetic attraction force is induced across the first magnetic gap. The first magnetic attraction force acts along a second axis. The second iron-core linear motor assembly is disposed adjacent to the second magnet assembly. The second iron-core linear motor assembly and the second magnet assembly are physically separated by a second magnetic gap. A second magnetic attraction force is induced across the second magnetic gap. The second magnetic attraction force acts along the second axis in a direction opposite to the first magnetic attraction force.

[0114] In frame 302, the second moving frame is positioned along a third axis relative to the first moving frame. The third axis is orthogonal to the first axis. The third magnet assembly and the fourth magnet assembly are mechanically coupled to the first moving frame. The third core linear motor assembly and the fourth core linear motor assembly are mechanically coupled to the second moving frame. The third core linear motor assembly is disposed adjacent to the third magnet assembly. The third core linear motor assembly and the third magnet assembly are physically separated by a third magnetic gap. A third magnetic attraction force is induced across the third magnetic gap. The third magnetic attraction force acts along a fourth axis. The fourth core linear motor assembly is disposed adjacent to the fourth magnet assembly. The fourth core linear motor assembly and the fourth magnet assembly are physically separated by a fourth magnetic gap. A fourth magnetic attraction force is induced across the fourth magnetic gap. The fourth magnetic attraction force acts along the fourth axis in a direction opposite to the third magnetic attraction force.

[0115] In general, the aforementioned measurement techniques can be applied to the measurement of process parameters, structural parameters, layout parameters, dispersion parameters, or any combination thereof. By way of non-limiting example, overlay, profile geometry parameters (e.g., critical dimension, height, sidewall angle), process parameters (e.g., lithography focus and lithography dose), dispersion parameters, layout parameters (e.g., pitch walk, edge placement error), film thickness, composition parameters, or any combination of parameters can be measured using the aforementioned techniques.

[0116] By way of non-limiting example, structures measured with shape filling include all-around gate structures, line-space grating structures, FinFet structures, SRAM device structures, flash memory structures, and DRAM memory structures.

[0117] In another aspect, the structure being measured can be a design rule target. In other words, the metrology target follows the design rules applicable to the underlying semiconductor manufacturing process. In some instances, the metrology target is preferably located within the active die area. In some instances, the metrology target has a size of 15 microns by 15 microns or less. In some other instances, the metrology target is located in a scribe line or otherwise outside the active die area.

[0118] In some examples, the measurement of a parameter of interest performed at a particular measurement site relies on data collected only from the particular measurement site, even though data may be collected from multiple sites on the wafer. In some other examples, measurement data collected from multiple sites across the wafer or a subset of the wafer is used for measurement analysis. This may be desirable to capture parameter variations across the wafer.

[0119] In some examples, the measurement of the parameter of interest is performed based on the metrology target using multiple different measurement techniques, including single target techniques, multi-target techniques, and spectral feedforward techniques. The accuracy of the measured parameter can be improved by any combination of feed-back analysis, feed-forward analysis, and parallel analysis. Feed-back analysis refers to obtaining multiple data sets on different regions of the same sample and transferring the common parameters determined from the first data set to the second data set for analysis. Feed-forward analysis refers to obtaining data sets on different samples and forwarding the common parameters to subsequent analysis using a step-by-step replication accurate parameter feed-forward method. Parallel analysis refers to applying a nonlinear fitting method to multiple data sets in parallel or simultaneously, wherein at least one common parameter is coupled during fitting.

[0120] Multiple tool and structural analysis refers to feed-forward, feed-side, or parallel analysis based on regression, lookup tables (i.e., "library" matching), or another fitting process of multiple data sets. Exemplary methods and systems for multiple tool and structural analysis are described in U.S. Pat. No. 7,478,019, issued to KLA-Tencor Corporation on Jan. 13, 2009, which is incorporated herein by reference in its entirety.

[0121] In another aspect, the measurements obtained as described herein can be used to provide active feedback to a process tool (e.g., a lithography tool, an etching tool, a deposition tool, etc.). For example, the value of a critical dimension determined using the methods and systems described herein can be communicated to a lithography tool to adjust the lithography system to achieve a desired output. In a similar manner, etching parameters (e.g., etching time, diffusion rate, etc.) or deposition parameters (e.g., time, concentration, etc.) can be included in the measurement tool to provide active feedback to the etching tool or deposition tool, respectively. In some examples, corrections to process parameters determined based on measured device parameter values ​​can be communicated to the lithography tool, etching tool, or deposition tool.

[0122] It should be recognized that the various steps described in the present disclosure may be performed by a computer system 130, multiple computer systems 130, or multiple different computer systems 130. Furthermore, different subsystems of the systems 100, 200, and 300 (e.g., magnetically opposed core wafer positioning systems) may include computer systems suitable for performing at least a portion of the steps described herein. Therefore, the foregoing description should not be construed as limiting the present invention, but is merely illustrative. Furthermore, the computing system 130 may be configured to perform any other steps of any of the method embodiments described herein.

[0123] The computing system 130 may include, but is not limited to, a personal computer system, a mainframe computer system, a cloud-based computing system, a workstation, an image computer, a parallel processor, or any other device known in the art. In general, the term "computing system" may be broadly defined to encompass any device or combination of devices having one or more processors that execute instructions from a memory medium. In general, the computing system 130 may be integrated with a measurement system, such as measurement systems 100, 200, and 300, or alternatively, may be completely or partially separate from any measurement system. In this sense, the computing system 130 may be remotely located and receive measurement data from any measurement source and transmit command signals to any element of the metrology systems 100, 200, and 300.

[0124] Program instructions 134 implementing methods such as those described herein may be transmitted via a transmission medium such as a wire, cable, or wireless transmission link. The memory 132 storing program instructions 134 may include a computer-readable medium such as a read-only memory, random access memory, a magnetic or optical disk, or a tape.

[0125] Additionally, computing system 130 may be communicatively coupled to elements of measurement systems 100 , 200 , and 300 in any manner known in the art.

[0126] The computing system 130 may be configured to receive and / or obtain data or information from subsystems of the measurement system (e.g., spectrometer 104, illuminator 102, magnetically opposed core wafer positioning system, etc.) through a transmission medium that may include wired and / or wireless portions. In this manner, the transmission medium may serve as a data link between the computer system 130 and other subsystems of the systems 100, 200, and 300. In addition, the computing system 130 may be configured to receive measurement data via a storage medium (i.e., memory). For example, spectral results obtained using the spectrometer of the ellipsometer 101 may be stored in a permanent or semi-permanent memory device (not shown). In this regard, the spectral results may be input from an external system. Furthermore, the computer system 130 may receive data from an external system via a transmission medium.

[0127] The computing system 130 may be configured to transmit data or information to a subsystem of the system (e.g., spectrometer 104, illuminator 102, magnetically opposed core wafer positioning system, etc.) via a transmission medium that may include wired and / or wireless portions. In this manner, the transmission medium may serve as a data link between the computer system 130 and other subsystems of the systems 100, 200, and 300. In addition, the computing system 130 may be configured to transmit command signals and measurement results via a storage medium (i.e., memory). For example, the measurement results 115 obtained by analyzing the spectral data may be stored in a permanent or semi-permanent memory device (not shown). In this regard, the spectral results may be output to an external system. Furthermore, the computer system 130 may send data to an external system via a transmission medium. In addition, the determined values ​​of the parameters of interest are stored in the memory. For example, the values ​​may be stored on-board on the measurement systems 100, 200, and 300 (e.g., in the memory 132) or may be transmitted to an external memory device (e.g., via the output signal 115).

[0128] As described herein, the term "critical dimension" includes any critical dimension of a structure (e.g., bottom critical dimension, middle critical dimension, top critical dimension, sidewall angle, grating height, etc.), any critical dimension between two or more structures (e.g., distance between two structures), and displacement between two or more structures (e.g., overlay displacement between overlay grating structures, etc.). The structure may include a three-dimensional structure, a patterned structure, a stacked structure, etc.

[0129] As described herein, the term "critical dimension application" or "critical dimension measurement application" includes any critical dimension measurement.

[0130] As described herein, the term "metrology system" includes any system used at least in part to characterize a sample in any aspect, including critical dimension applications and overlay metrology applications. However, such technical terms do not limit the scope of the term "metrology system" as described herein. In addition, the metrology systems described herein may be configured to measure patterned wafers and / or unpatterned wafers. The metrology system may be configured as an LED inspection tool, an edge inspection tool, a backside inspection tool, a macro inspection tool, or a multi-mode inspection tool (involving data from one or more platforms simultaneously), and any other metrology or inspection tool that benefits from the measurement techniques described herein.

[0131] Various embodiments are described herein for a semiconductor processing system (e.g., an inspection system or a lithography system) that can be used to process a sample. The term "sample" is used herein to refer to a wafer, a retracted mask, or any other sample that can be processed (e.g., printed or inspected for defects) by means known in the art.

[0132] As used herein, the term "wafer" generally refers to a substrate formed of semiconductor or non-semiconductor materials. Examples include, but are not limited to: single crystal silicon, gallium arsenide, and indium phosphide. Such substrates are commonly found and / or processed in semiconductor fabrication plants. In some cases, a wafer may include only a substrate (i.e., a bare wafer). Alternatively, a wafer may include one or more layers of different materials formed on a substrate. The one or more layers formed on a wafer may be "patterned" or "unpatterned." For example, a wafer may include multiple die having repeatable pattern features.

[0133] A "shrink mask" may be a shrink mask in any stage of a shrink mask manufacturing process or a finished shrink mask that may or may not be released for use in a semiconductor manufacturing facility. A shrink mask or "mask" is generally defined as a substantially transmissive substrate having substantially opaque areas formed thereon and configured in a pattern. The substrate may include, for example, a glass material such as amorphous SiO2. The shrink mask may be placed over a wafer covered with resist during the exposure step of a photolithography process so that the pattern on the shrink mask can be transferred to the resist.

[0134] The one or more layers formed on a wafer may be patterned or unpatterned. For example, a wafer may include multiple dies, each having repeatable pattern features. The formation and processing of such material layers may ultimately result in a finished device. Many different types of devices may be formed on a wafer, and the term wafer as used herein is intended to encompass a wafer on which any type of device known in the art is fabricated.

[0135] In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium or transmitted through a computer-readable medium as one or more instructions or codes. Computer-readable media include both computer storage media and communication media, including any media that facilitates the transmission of a computer process from one location to another. The storage medium may be any available media that can be accessed by a general-purpose computer or a special-purpose computer. By way of example and without limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage devices, magnetic disk storage devices or other magnetic storage devices, or any other media that can be used to implement or store desired process code components in the form of instructions or data structures and can be accessed by a general-purpose or special-purpose computer or a general-purpose or special-purpose processor. In addition, any connection may be appropriately referred to as a computer-readable medium. For example, if the software is transmitted from a website, server or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technology (such as infrared, radio and microwave), then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technology (such as infrared, radio and microwave) is included in the definition of medium. As used herein, disk and disc include compact disc (CD), laser disc, XRF disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically and discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0136] Although certain specific embodiments are described above for guidance purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. Accordingly, various modifications, adaptations, and combinations of the various features of the described embodiments may be practiced without departing from the scope of the invention as set forth in the claims.

Claims

1. A positioning system, comprising: a first iron-core linear motor assembly disposed adjacent to a first magnet assembly, wherein the first iron-core linear motor assembly and the first magnet assembly are physically separated by a first magnetic gap, wherein a first magnetic attraction force is induced across the first magnetic gap, the first magnetic attraction force acting along a first axis; and A second iron-core linear motor assembly is disposed adjacent to a second magnet assembly, wherein the second iron-core linear motor assembly and the second magnet assembly are physically separated by a second magnetic gap, wherein a second magnetic attraction force is induced across the second magnetic gap, the second magnetic attraction force acting along the first axis in a direction opposite to the first magnetic attraction force, wherein the first magnet assembly is mechanically coupled to the second magnet assembly and the first iron-core linear motor assembly is mechanically coupled to the second iron-core linear motor assembly.

2. The positioning system according to claim 1, further comprising: Base frame; A first moving frame is movable relative to the base frame along a second axis orthogonal to the first axis, wherein the first and second magnet assemblies are mechanically coupled to the first moving frame and the first and second iron-core linear motor assemblies are mechanically coupled to the base frame.

3. The positioning system according to claim 2, further comprising: a second mobile frame movable relative to the first mobile frame along a third axis orthogonal to the second axis; a third iron-core linear motor assembly disposed adjacent to a third magnet assembly, wherein the third iron-core linear motor assembly and the third magnet assembly are physically separated by a third magnetic gap, wherein a third magnetic attraction force is induced across the third magnetic gap, the third magnetic attraction force acting along a fourth axis orthogonal to the third axis; and a fourth iron-core linear motor assembly disposed adjacent to a fourth magnet assembly, wherein the fourth iron-core linear motor assembly and the fourth magnet assembly are physically separated by a fourth magnetic gap, wherein a fourth magnetic attraction force is induced across the fourth magnetic gap, the fourth magnetic attraction force acting along the fourth axis in a direction opposite to the third magnetic attraction force, wherein the third magnet assembly is mechanically coupled to the fourth magnet assembly and the third iron-core linear motor assembly is mechanically coupled to the third linear motor assembly.

4. The positioning system of claim 3, wherein the third and fourth magnet assemblies are mechanically coupled to the first moving frame and the third and fourth iron-core linear motor assemblies are mechanically coupled to the second moving frame.

5. The positioning system of claim 2, wherein the first iron-core linear motor assembly comprises a plurality of iron-core linear motor units, the plurality of iron-core linear motor units being disposed adjacent to each other along a length of the first iron-core linear motor assembly, each iron-core linear motor unit comprising a plurality of conductive coils, wherein a first of the plurality of conductive coils of each of the plurality of iron-core linear motor units are electrically coupled in series, and wherein a second of the plurality of conductive coils of each of the plurality of iron-core linear motor units are electrically coupled in series.

6. The positioning system according to claim 1, further comprising: a first cooling channel located within a housing of the first iron-core linear motor assembly; and A second cooling channel is located in the housing of the second iron core linear motor assembly.

7. The positioning system of claim 6, wherein a cooling fluid or a cooling gas passes through the first and second cooling channels.

8. The positioning system of claim 1, wherein the first moving frame is constrained to move relative to the base frame along the second axis by mechanical bearings, air bearings, or magnetic bearings.

9. A measurement system comprising: an illumination source configured to generate an amount of illumination light directed toward one or more structures fabricated on the semiconductor wafer; a detector configured to detect an amount of light from the one or more structures in response to the amount of illumination light; A wafer positioning system comprising: a first iron-core linear motor assembly disposed adjacent to a first magnet assembly, wherein the first iron-core linear motor assembly and the first magnet assembly are physically separated by a first magnetic gap, wherein a first magnetic attraction force is induced across the first magnetic gap, the first magnetic attraction force acting along a first axis; and a second iron-core linear motor assembly disposed adjacent to a second magnet assembly, wherein the second iron-core linear motor assembly and the second magnet assembly are physically separated by a second magnetic gap, wherein a second magnetic attraction force is induced across the second magnetic gap, the second magnetic attraction force acting along the first axis in a direction opposite to the first magnetic attraction force, wherein the first magnet assembly is mechanically coupled to the second magnet assembly and the first iron-core linear motor assembly is mechanically coupled to the second iron-core linear motor assembly; and A computing system is configured to determine, based on the amount of detected light, a value of at least one parameter of interest that characterizes the one or more structures being measured.

10. The measurement system of claim 9, wherein the wafer positioning system further comprises: a base frame mechanically coupled to the illumination source and the detector; A first moving frame is movable relative to the base frame along a second axis orthogonal to the first axis, wherein the first and second magnet assemblies are mechanically coupled to the first moving frame and the first and second iron-core linear motor assemblies are mechanically coupled to the base frame.

11. The measurement system of claim 10, wherein the wafer positioning system further comprises: a second mobile frame movable relative to the first mobile frame along a third axis orthogonal to the second axis; a third iron-core linear motor assembly disposed adjacent to a third magnet assembly, wherein the third iron-core linear motor assembly and the third magnet assembly are physically separated by a third magnetic gap, wherein a third magnetic attraction force is induced across the third magnetic gap, the third magnetic attraction force acting along a fourth axis orthogonal to the third axis; and a fourth iron-core linear motor assembly disposed adjacent to a fourth magnet assembly, wherein the fourth iron-core linear motor assembly and the fourth magnet assembly are physically separated by a fourth magnetic gap, wherein a fourth magnetic attraction force is induced across the fourth magnetic gap, the fourth magnetic attraction force acting along the fourth axis in a direction opposite to the third magnetic attraction force, wherein the third magnet assembly is mechanically coupled to the fourth magnet assembly and the third iron-core linear motor assembly is mechanically coupled to the third linear motor assembly.

12. The measurement system of claim 11, wherein the third and fourth magnet assemblies are mechanically coupled to the first moving frame and the third and fourth iron-core linear motor assemblies are mechanically coupled to the second moving frame.

13. The measurement system of claim 10, wherein the first iron-core linear motor assembly comprises a plurality of iron-core linear motor units disposed adjacent to each other along a length of the first iron-core linear motor assembly, each iron-core linear motor unit comprising a plurality of conductive coils, wherein a first one of the plurality of conductive coils of each of the plurality of iron-core linear motor units is electrically coupled in series, and wherein a second one of the plurality of conductive coils of each of the plurality of iron-core linear motor units is electrically coupled in series.

14. The measurement system of claim 9, wherein the wafer positioning system further comprises: a first cooling channel located within a housing of the first iron-core linear motor assembly; and A second cooling channel is located in the housing of the second iron core linear motor assembly.

15. The measurement system of claim 14, wherein a cooling fluid or a cooling gas passes through the first and second cooling channels.

16. The measurement system of claim 9, wherein the first moving frame is constrained to move relative to the base frame along the second axis by mechanical bearings, air bearings, or magnetic bearings.

17. A method comprising: Positioning a first moving frame movable along a first axis relative to a base frame, a first magnet assembly and a second magnet assembly mechanically coupled to the first moving frame and a first iron-core linear motor assembly and a second iron-core linear motor assembly mechanically coupled to the base frame, the first iron-core linear motor assembly disposed adjacent to the first magnet assembly, wherein the first iron-core linear motor assembly and the first magnet assembly are physically separated by a first magnetic gap, wherein a first magnetic attraction force is induced across the first magnetic gap, the first magnetic attraction force acting along a second axis, the second iron-core linear motor assembly disposed adjacent to the second magnet assembly, wherein the second iron-core linear motor assembly and the second magnet assembly are physically separated by a second magnetic gap, wherein a second magnetic attraction force is induced across the second magnetic gap, the second magnetic attraction force acting along the second axis in a direction opposite to the first magnetic attraction force; and A second moving frame is positioned that is movable relative to the first moving frame along a third axis, wherein the third axis is orthogonal to the first axis, a third magnet assembly and a fourth magnet assembly are mechanically coupled to the first moving frame and a third iron-core linear motor assembly and a fourth iron-core linear motor assembly are mechanically coupled to the second moving frame, the third iron-core linear motor assembly is disposed adjacent to the third magnet assembly, wherein the third iron-core linear motor assembly and the third magnet assembly are physically separated by a third magnetic gap, wherein a third magnetic attraction force is induced across the third magnetic gap, the third magnetic attraction force acting along a fourth axis, the fourth iron-core linear motor assembly is disposed adjacent to the fourth magnet assembly, wherein the fourth iron-core linear motor assembly and the fourth magnet assembly are physically separated by a fourth magnetic gap, wherein a fourth magnetic attraction force is induced across the fourth magnetic gap, the fourth magnetic attraction force acting along the fourth axis in a direction opposite to the third magnetic attraction force.

18. The method of claim 17, wherein a semiconductor wafer chuck is disposed above the second moving frame, and wherein an illumination source and a detector of a semiconductor measurement system are mechanically coupled to the base frame.

19. The method of claim 17, further comprising: flowing a first quantity of cooling fluid or cooling gas through a first cooling passage within a housing of the first iron-core linear motor assembly; and A second quantity of cooling fluid or cooling gas is flowed through a second cooling passage within the housing of the second iron-core linear motor assembly.

20. The method of claim 17, further comprising: The first moving frame is constrained to move relative to the base frame along the first axis by mechanical bearings, air bearings, or magnetic bearings.

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