Magnetically Opposed Iron-Core Linear Motor-Based Translation Stage for Semiconductor Wafer Positioning

Abstract

Presented herein are methods and systems for achieving a high-throughput wafer positioning system with high placement accuracy. The high-throughput, high-precision wafer positioning system is used to measure structural and material properties (e.g., material composition, structural and thin film dimensional properties, etc.) associated with different semiconductor fabrication processes. In one aspect, iron-core linear motor assemblies are arranged in a magnetically opposed configuration such that the magnetic attractive forces inherent in each opposed iron-core linear motor assembly nearly cancel each other. Reducing the force applied to the sensitive stage frame elements, in turn, reduces induced deformation and stage placement errors. In some embodiments, the wafer positioning system includes stacked, magnetically opposed long-stroke stages. In some of these embodiments, both magnetically opposed long-stroke stages use magnetic walkways mechanically coupled to the mid-frame of the stacked stage assembly.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This patent application claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application No. 63 / 413,250, entitled "Stacked XY Stage with moving magnets for high thermal stability," filed October 5, 2022, the subject matter of which is incorporated herein by reference in its entirety.

[0002] The described embodiments relate to systems and methods for wafer placement, and more particularly to methods and systems for improving high throughput placement of wafers in a manufacturing environment. [Background technology]

[0003] The various features and multiple structural levels of semiconductor devices, such as logic and memory devices, are typically fabricated by a series of processing steps applied to a specimen. For example, lithography is one semiconductor fabrication process that involves, among other things, creating patterns on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etching, deposition, and ion implantation. Multiple semiconductor devices may be fabricated on a single semiconductor wafer and then separated into individual semiconductor devices.

[0004] Metrology processes are used at various stages during the semiconductor fabrication process to detect defects on wafers and improve yield. Optical metrology techniques offer the potential for achieving 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.

[0005] As devices (e.g., logic and memory devices) move toward smaller nanometer-scale dimensions, characterization becomes more challenging. Devices incorporating complex three-dimensional shapes and materials with diverse physical properties contribute to the difficulty of characterization. In response, more complex optical tools have been developed. For example, tools with multiple illumination angles, shorter and broader ranges of illumination wavelengths, and more complete information acquisition from the reflected signal (e.g., measuring multiple Mueller matrix elements in addition to the more common reflectivity or ellipsometry signals) have been developed.

[0006] As devices move toward smaller nanometer-scale dimensions, commercially viable optical-based measurement tools are needed to position specimens faster and more accurately. Typically, wafer positioning systems are required to move semiconductor wafers over long distances in two dimensions, commonly referred to as the X and Y directions. Rapidly moving and precisely positioning a wafer under test over long distances requires large driving forces. These forces are typically generated by linear electric motors. However, linear motors capable of generating large forces generate significant amounts of heat. Existing wafer positioning systems are significantly limited in their achievable positioning accuracy due to thermal distortion induced by the heat generated by the linear motors.

[0007] Existing wafer positioning systems typically attempt to thermally isolate sensitive stage frame elements from the heat generated by the linear motors using materials with low thermal conductivity. Unfortunately, it is common to observe temperature increases of at least one degree Celsius throughout the sensitive stage frame elements. These temperature changes result in significant deformation throughout the sensitive stage frame elements, thereby degrading accuracy. Additionally, sensitive stage frame elements often comprise different materials with significantly different coefficients of thermal expansion (CTE). Along with temperature changes, mismatched CTEs further degrade stage positioning accuracy by creating significant internal strain and associated deformation within the sensitive stage frame elements.

[0008] 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 lower frame 11 and an intermediate frame 12. The coordinate system {X IF , Y IF , Z IF} are fixed to the intermediate frame 12. A set of mechanical linear bearings 13 limits the relative motion of the intermediate frame 12 with respect to the stage bottom frame 11 to one degree of freedom, namely Y IFFIG. 1 also shows an ironless U-channel linear motor, including a U-channel magnet passage 14 and an ironless motor assembly 15. As shown in FIG. 1, the ironless motor assembly 15 is mechanically fixed to the mid-frame 12, and the U-channel magnet passage 14 is mechanically fixed to the stage bottom frame 11. The ironless motor assembly 15 includes multiple conductive wire coils embedded in a non-magnetic package. In some examples, copper coils are embedded in an epoxy matrix material that fills an aluminum or copper housing. The U-channel magnet passage 14 includes multiple permanent magnets attached to magnetic backing plates on both sides of the U-shaped channel. This assembly generates a distinct magnetic field throughout the U-shaped channel. As shown in FIG. 1, magnetic field lines 17 are concentrated in the permanent magnets and iron backing plates of the U-shaped magnet passage. The portion of the magnetic field outside the U-shaped magnet passage is limited to a relatively small gap across the U-shaped channel.

[0009] As shown in Figure 1, an ironless motor assembly 15 is disposed within the U-shaped channel. A mechanical driving force is generated in the Y direction by passing a current through the coil windings 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 and the magnetic field produces a mechanical driving force in the Y direction.

[0010] The ironless U-channel linear motor is an inherently smooth-running motor due to the absence of iron within the ironless motor assembly 15. No significant magnetic attractive forces are generated between the ironless motor assembly 15 and the U-channel magnet passage 14. Therefore, the ironless motor assembly 15 can operate within the U-channel at any relative position to the permanent magnets of the magnet passage 14 without generating substantial off-axis forces. Additionally, the magnetic field generated throughout 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 magnet passage 14 is relatively smooth and predictable. Therefore, a relatively simple control algorithm can be used to distribute current through the coils of the ironless motor assembly 15, such that the driving force generated between the ironless motor assembly 15 and the U-channel magnet passage 14 is nearly position-independent.

[0011] Unfortunately, ironless U-channel linear motors also have some inherent limitations that adversely affect the achievable accuracy and throughput of wafer placement systems, such as the wafer placement system 10 shown in FIG. 1. Due to their ironless design, the magnitude of the drive force generated for a given amount of current is significantly smaller than that of iron-core designs. Despite optimization of the ironless motor winding design and magnetic field strength, ironless U-channel linear motors require significantly more current to generate the same linear drive force as comparable iron-core linear motors. Current flow through conductive materials generates heat, which must be dissipated somewhere, often at the expense of wafer placement accuracy. For example, as shown in FIG. 1, the ironless motor assembly 15 is mechanically secured to the intermediate frame 12. Heat generated in the coil windings of the ironless motor assembly 15 is conducted to the intermediate frame 12. As shown in FIG. 1, arrows 16 represent the flow of heat from the ironless motor assembly 15 into the intermediate frame 12. The temperature of the intermediate frame 12 increases as heat flow 16 is absorbed. The authors observed that under typical operating conditions inside a high-throughput optical metrology tool, the temperature of the intermediate frame increased by approximately 0.65°C. This temperature increase caused material expansion and deformation, which severely limited the repeatability of placement at the wafer.

[0012] 2 is a simplified diagram illustrating a typical prior art wafer positioning system 20 in another embodiment. The wafer positioning system 20 includes a stage lower frame 21 and an intermediate frame 22. The coordinate system {X IF , Y IF , Z IF} are fixed to the intermediate frame 22. A set of mechanical linear bearings 23 limits the relative motion of the intermediate frame 22 with respect to the stage bottom frame 21 to one degree of freedom, namely Y IFTo address the force-generation limitations of U-channel ironless linear motors, the wafer positioning system 20 uses an iron-core linear motor. Figure 2 shows an iron-core linear motor including a magnet passage 24 and an iron-core motor assembly 25. As shown in Figure 2, the iron-core motor assembly 25 is mechanically fixed to the mid-frame 22, and the magnet passage 24 is mechanically fixed to the stage underframe 21. The iron-core motor assemblies 25 each include multiple conductive wire coils wound around an iron post. Typically, each iron post is fabricated as part of a larger iron structure. In some examples, copper coils are embedded in an epoxy matrix material that fills the space around the conductive wire coils and the iron structure. The magnet passage 24 includes multiple permanent magnets 27 attached to a magnetic backing plate that is mechanically fixed to the stage underframe 21. This assembly generates a magnetic field in the space above the magnet passage 24. 2, the magnetic field lines 27 are concentrated at the permanent magnets and iron backing plate of the U-shaped magnet passage 24, but extend into the space above the magnet passage 24. The portion of the magnetic field outside the flat magnet passage 24 is wide compared to the relatively small gap across the U-shaped channel of a U-channel ironless linear motor.

[0013] As shown in FIG. 2, the iron-core motor assembly 25 is positioned above the flat magnet passage 24. Furthermore, the iron pillar and associated iron structure create magnetic field lines 27. That is, the magnetic field lines are concentrated at the iron pillar and associated structure. Thus, the iron pillar and iron structure define the shape of the magnetic field above the magnet passage 24 and are key components of the magnetic circuit. This is fundamentally different from a U-channel ironless linear motor. A mechanical driving force is generated in the Y direction by passing current through the windings of the coils of the iron-core motor assembly 25. The concentration of magnetic field lines within the iron pillar and associated iron structure intensifies the magnetic field across the gap between the flat magnet passage 24 and the iron-core motor assembly 25. As a result, the magnitude of the driving force generated for a given amount of current is substantially greater than that of an ironless linear motor design. Consequently, the iron-core linear motor can generate greater driving force with less heat compared to a U-channel ironless linear motor.

[0014] Unfortunately, the presence of iron in the iron-core motor assembly 25 creates a large attractive force between the magnet passage 24 of the iron-core linear motor and the iron-core motor assembly 25. As shown in FIG. M , Z with respect to the iron core motor assembly 25 and the intermediate frame 21 IF The linear bearing 23 acts in the direction of the restoring force F R1 and F R2 By supporting the intermediate frame 22 by applying a magnetic attraction force F M And balance it out with Z IF The linear bearings 23 maintain the position of the intermediate frame 22 in the axial direction. Due to the large magnetic attractive forces imposed on the linear bearings, relatively large linear bearings must be used to avoid premature bearing failure. If mechanical bearings are used, the relatively large bearings will cause significant deviations in the position of the intermediate frame 22 during operation. This can excite high frequency modes within the stage and increase settling time. In addition, the iron-core motor assembly 25 is physically separated from the linear bearings 23 by a significant distance D. Therefore, the magnetic attractive force F M This generates a significant bending moment in the intermediate frame 22. This bending moment causes a significant deformation of the intermediate frame 22, resulting in a decrease in wafer placement accuracy.

[0015] Finally, as shown in Figure 2, the iron-core motor assembly 25 is mechanically fixed to the intermediate frame 22. Heat generated in the coil windings of the iron-core motor assembly 25 is conducted into the intermediate frame 22. As shown in Figure 2, arrows 26 represent the heat flow from the iron-core motor assembly 25 into the intermediate frame 22. As the heat flow 26 is absorbed, the temperature of the intermediate frame 22 increases. Although the heat generated by the iron-core motor assembly is less than that of an ironless motor assembly for the same driving force, the temperature rise of the intermediate frame is still significant, and this temperature rise causes material expansion and deformation, which significantly limits placement repeatability at the wafer. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] U.S. Patent Application Publication No. 2008 / 0265688 [Patent Document 2] U.S. Patent Application Publication No. 2003 / 0007140 [Patent Document 3] U.S. Patent No. 5,996,437 [Patent Document 4] U.S. Patent Application Publication No. 2002 / 0015139 Summary of the Invention [Problem to be solved by the invention]

[0017] Future metrology applications pose metrology challenges due to ever-increasing measurement resolution and throughput requirements. Wafer positioning systems with higher accuracy and throughput capabilities are desirable. [Means for solving the problem]

[0018] A method and system for achieving a high throughput wafer placement system with high placement accuracy is presented herein. The high throughput and high accuracy wafer placement system is used to measure structural and material properties (e.g., material composition, structural and thin film dimensional properties, etc.) associated with different semiconductor fabrication processes.

[0019] In one aspect, by arranging the iron-core linear motor assemblies in a magnetically opposed configuration, the magnetic attractive forces inherent in each opposing iron-core linear motor assembly nearly cancel each other out. Therefore, the net force applied to the sensitive stage frame elements due to the magnetic attractive forces is negligible. The reduction in force applied to the sensitive stage frame elements in turn reduces induced deformation and stage placement errors. Furthermore, the force applied to the bearing elements required to constrain the position of the sensitive stage frame elements is also significantly reduced.

[0020] In a further aspect, the wafer positioning system includes a second long-stroke stage stacked on top of the magnetically opposed long-stroke stage. In some embodiments, both of the stacked long-stroke stages are configured as magnetically opposed stages. In some of these embodiments, the magnetically opposed long-stroke stages use magnet tracks that are mechanically coupled to the mid-frame of the stacked stage assembly. As a result, the mid-frame is thermally isolated from the heat generated by both iron-core motor assemblies of the long-stroke stages by a magnetic gap between the iron-core motor assemblies and the corresponding magnet tracks.

[0021] In a further aspect, the iron-core linear motor assembly includes one or more cooling channels within the housing of the assembly, through which a gaseous or liquid coolant is pumped to extract heat from the iron-core linear motor assembly.

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

[0023] In a further aspect, measurements are performed on one or more structures disposed on a semiconductor wafer while the wafer is positioned using a magnetically opposed iron-core wafer positioning system. Generally, any suitable model-based or modeless metrology technique may be used in accordance with the methods and systems described herein to perform measurements on structures positioned by the magnetically opposed iron-core wafer positioning system.

[0024] The foregoing is a summary and thus necessarily contains simplifications, generalizations, and omissions of detail; as a result, those skilled in the art will appreciate that the summary is merely illustrative and is not intended to be in any way limiting. Further aspects, inventive features, and advantages of the devices and / or processes described herein will become apparent in the non-limiting detailed description set forth herein. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a simplified diagram illustrating an exemplary conventional wafer positioning system 10 according to one embodiment. [Figure 2] 1 is a simplified diagram illustrating a typical prior art wafer positioning system 10 according to another embodiment. [Figure 3] FIG. 1 is a simplified diagram illustrating a wafer positioning system 120 in a magnetically opposed configuration according to one embodiment. [Figure 4] FIG. 1 is a perspective view of a wafer positioning system 150 including two stacked, magnetically opposed long-stroke stages according to one embodiment. [Figure 5] FIG. 1 is another perspective view of a wafer positioning system 150 including two stacked, magnetically opposed long-stroke stages according to one embodiment. [Figure 6] FIG. 1 is a simplified diagram illustrating a cross-sectional view of an iron-core linear motor assembly of one embodiment. [Figure 7A] 1 is a graph showing a simulation of the temperature of a wafer frame of a wafer positioning system as the temperature increases from a start-up temperature at the beginning of operation to a steady-state temperature under typical high throughput operating conditions. [Figure 7B] 10 is a graph showing a simulation of the temperature of the intermediate frame of a wafer positioning system as it ramps from a start-up temperature at the beginning of operation to a steady-state temperature under typical high throughput operating conditions. [Figure 7C] 10 is a graph showing a simulation of the temperature of the understage frame of a wafer positioning system as it ramps from a start-up temperature at the beginning of operation to a steady-state temperature under typical high throughput operating conditions. [Figure 8] FIG. 1 illustrates a system 100 for performing spectroscopic ellipsometry measurements on one or more structures disposed on a semiconductor wafer, the system 100 using a magnetically opposed iron-core wafer positioning system. [Figure 9] FIG. 2 illustrates a system 200 for performing angle-resolved spectroscopic reflectance measurements on one or more structures disposed on a semiconductor wafer, the system 200 using a magnetically opposed iron-core wafer positioning system. [Figure 10] FIG. 3 illustrates a system 300 for performing spectral reflectance measurements on one or more structures disposed on a semiconductor wafer, the system 300 using a magnetically opposed iron-core wafer positioning system. [Figure 11] 1 is a flowchart of a method for positioning a wafer using a magnetically opposed iron core wafer positioning system as described herein. DETAILED DESCRIPTION OF THE INVENTION

[0026] Reference will now be made in detail to certain background and embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0027] A method and system for realizing a high-throughput wafer placement system with high placement accuracy is presented herein. The high-throughput, high-accuracy wafer placement system is used to measure structural and material properties (e.g., material composition, dimensional properties, etc. of structures and thin films) associated with different semiconductor fabrication processes.

[0028] In one aspect, the iron-core linear motor assemblies are arranged in a magnetically opposed configuration such that the magnetic attractive forces inherent in each opposing iron-core linear motor assembly nearly cancel each other out. Therefore, the net force exerted by the magnetic attractive forces on the sensitive stage frame elements is negligible. Reducing the force exerted on the sensitive stage frame elements in turn reduces induced deformation and stage placement errors. Furthermore, the force exerted on the bearing elements required to constrain the position of the sensitive stage frame elements is also significantly reduced. This extends bearing life, allows for the implementation of smaller bearing elements, and reduces induced friction and bearing-induced placement jitter.

[0029] 3 is a simplified diagram illustrating the wafer positioning system 120 in a magnetically opposed configuration according to one embodiment. The wafer positioning system 120 includes a stage lower frame 121 and an intermediate frame 122. The coordinate system {X IF ,Y IF ,Z IF} are fixed to the intermediate frame 122. A set of mechanical linear bearings 123 limits the relative motion of the intermediate frame 122 with respect to the stage bottom frame 121 to one degree of freedom, namely, Y IF Constrain to direction.

[0030] In the embodiment shown in FIG. 3, the wafer positioning system 120 uses a pair of iron-core linear motors in a magnetically opposed configuration. FIG. 3 shows a pair of iron-core motor assemblies 124A-B and a corresponding pair of magnet passages 125A-B. As shown in FIG. 3, the iron-core motor assemblies 124A-B are mechanically fixed to the stage bottom frame 121, and the pair of magnet passages 125A-B are mechanically fixed to the stage mid-frame 122. As shown in FIG. 3, the magnet passages 125A-B are arranged so that the faces of each magnet passage of a pair face in opposite directions. Each magnet passage includes a plurality of permanent magnets 127 attached to a magnetic backing plate mechanically fixed to the mid-frame 122. Each magnet passage generates a magnetic field in the space adjacent to the face of the magnet passage. The face of the magnetic passage is defined by the side of the permanent magnet array exposed to the environment opposite the magnetic backing plate of the magnetic passage.

[0031] Magnet passage 125A includes a plurality of permanent magnets attached to a magnetic backing plate that is mechanically secured to intermediate frame 122. This assembly generates a magnetic field in the space adjacent to magnet passage 125A. As shown in FIG. 3, magnetic field lines 128A are concentrated in the permanent magnets and iron backing plate of magnet passage 125A and extend into the space adjacent to magnet passage 125A. Similarly, magnet passage 125B includes a plurality of permanent magnets 127 attached to a magnetic backing plate that is mechanically secured to intermediate frame 122. This assembly generates a magnetic field in the space adjacent to magnet passage 125B. As shown in FIG. 3, magnetic field lines 128B are concentrated in the permanent magnets and iron backing plate of magnet passage 125B and extend into the space adjacent to magnet passage 125B.

[0032] Each iron-core motor assembly 124A-B includes multiple conductive wire coils wound around a steel pole. Each steel pole is fabricated as part of a larger steel structure. In some examples, the copper coils are embedded in an epoxy matrix material that fills the space around the conductive wire coils and the steel structure.

[0033] As shown in Figure 3, iron core motor assemblies 124A-B are positioned adjacent to the faces of magnet passages 125A-B, respectively. Additionally, the iron pillars and associated iron structures create magnetic field lines 128A-B, i.e., the magnetic field lines are concentrated at the iron pillars and associated structures. A mechanical driving force is generated by passing a current through the windings of the coils of iron core motor assemblies 124A-B, Y IF It is generated in the direction.

[0034] As previously mentioned, iron-core linear motors generate less heat and are capable of generating greater driving forces than U-channel ironless linear motors. However, the inclusion of iron within the iron-core motor assemblies 124A-B creates a large attractive force between the magnet passages 125A-B and the iron-core motor assemblies 124A-B. As shown in FIG. 3, the large magnetic attractive force F M1 is positive X with respect to the magnet passage 125A and the intermediate frame 122. IF Similarly, the large magnetic attractive force F M2 is applied to the magnet passage 125B and the intermediate frame 122 by a magnetic attractive force F M1 Negative X in the opposite direction IF It acts in a direction.

[0035] In general, the magnetic attractive force of an iron-core linear motor is highly dependent on the magnetic flux density in the gap between the magnet passageway and the iron-core motor assembly, which in turn is highly dependent on the size of the gap. In practice, wafer placement stage 120 is designed to maintain a constant gap between magnet passageway 125A and iron-core motor assembly 124A, similar to the constant gap between magnet passageway 125B and iron-core motor assembly 124B. The gap is determined by mechanical tolerances and maintained by linear bearings 123 above the workspace of wafer placement stage 120. Assuming a similar gap is maintained, the magnetic attractive force F M1 and F M2 are nearly equal and therefore cancel each other out. As a result, the magnetic attractive force F M1 and F M2The residual force exerted on the intermediate frame 122 by the axial force is negligible, along with any residual bending moment exerted on the intermediate frame 122. This significantly reduces the induced deformation of the intermediate frame 122, which in turn results in improved wafer placement accuracy.

[0036] In addition, the magnetic attraction force F M1 and F M2 and nearly cancel each other out, greatly reducing the forces applied to the linear bearing 123. As a result, much smaller linear bearings can be used. For mechanical bearings, smaller bearings can be used without sacrificing bearing life. Smaller mechanical bearings operate with reduced friction and reduced placement jitter. This can improve the placement repeatability of the stage and reduce settling time.

[0037] Finally, as shown in FIG. 3, the iron-core motor assemblies 124A-B are mechanically fixed to the stage underframe 101. Heat generated in the coil windings of the iron-core motor assemblies 124A-B is conducted to the stage underframe 101. As shown in FIG. 3, arrows 126A-B respectively represent the heat flow from the iron-core motor assemblies 124A-B into the stage underframe 101 rather than into the intermediate frame 122. As a result, the temperature of the intermediate frame 122 does not substantially change during stage operation, and induced material expansion and deformation of the intermediate frame 122 are negligible. This allows for significantly improved stage placement repeatability at the wafer level.

[0038] In a further aspect, the wafer positioning system includes a second long stroke stage stacked on top of a magnetically opposed long stroke stage, such as the magnetically opposed long stroke stage shown in Figure 3. In some embodiments, both of the stacked long stroke stages are configured as magnetically opposed stages. In other embodiments, only the bottom long stroke stage, i.e., the stage attached to the stage underframe, is configured as a magnetically opposed long stroke stage.

[0039] FIG. 4 is a perspective view of a wafer positioning system 150 including two stacked, magnetically opposed long-stroke stages in one embodiment.

[0040] FIG. 5 illustrates another perspective view of a wafer positioning system 150 including two stacked, magnetically opposed long-stroke stages according to one embodiment.

[0041] 4 and 5, the wafer positioning system 150 includes a stage lower frame 121, an intermediate frame 122, and a wafer frame 142. The coordinate system {X BF ,Y BF ,Z BF} is fixed to the stage lower frame 121 and is defined by the coordinate system {X IF ,Y IF ,Z IF} is fixed to the intermediate frame 122 and is in the coordinate system {X WF ,Y WF ,Z WF} is fixed to the wafer frame 142. A set of linear bearings 123 limits the relative motion of the intermediate frame 122 with respect to the stage lower frame 121 to one degree of freedom, namely, Y IF A set of linear bearings 143 limits the relative motion of the wafer frame 142 with respect to the intermediate frame 122 to one degree of freedom, namely, X WF Constrain to direction.

[0042] In the embodiment shown in FIGS. 4 and 5, the wafer positioning system 150 uses a pair of iron-core linear motors in a magnetically opposed configuration to rotate the intermediate frame 122 in Y with respect to the stage bottom frame 121. IF and another pair of iron-core linear motors in a magnetically opposed configuration are used to rotate the wafer frame 142 relative to the intermediate frame 122 in the X direction. WF It provides the driving force necessary to position it in the desired direction.

[0043] 4 and 5 also show a multi-degree-of-freedom short-stroke positioning stage 146 attached to the wafer frame 142. In some embodiments, the short-stroke positioning stage 146 rotates the wafer gripper 141 in Z-axis relative to the wafer frame 142. WF and the wafer gripper 141 is arranged in the Y direction with respect to the wafer frame 142. WF axis and X WF In these embodiments, the short stroke positioning stage 146 is commonly referred to as a Z-up stage. In some other embodiments, the short stroke positioning stage 146 adjusts the position of the wafer gripper 141 relative to the wafer frame 142, for example, by adjusting the Z-up position. WF Direction around the axis, X WF and Y WF Control with additional degrees of freedom of orientation, position, or any combination thereof.

[0044] 4 and 5 show a pair of iron-core motor assemblies 124A-B and a corresponding pair of magnet passages 125A-B in a magnetically opposed configuration, as described with reference to FIG. 3. A mechanical driving force is applied by passing current through the windings of the coils of the iron-core motor assemblies 124A-B, thereby generating a Y IF It is generated in the direction.

[0045] FIG. 5 illustrates iron-core motor assemblies 144A-B mechanically secured to wafer frame 142 and a corresponding pair of magnet passages 145A-B mechanically secured to intermediate frame 122. As shown in FIG. 5, magnet passages 145A-B are arranged such that the faces of each magnet passage of a pair face in opposite directions. Each magnet passage includes a plurality of permanent magnets attached to a magnetic backing plate mechanically secured to intermediate frame 122. Each magnet passage generates a magnetic field in the space adjacent the face of the magnet passage. The face of the magnet passage is defined by the side of the array of permanent magnets exposed to the environment opposite the magnet passage's magnetic backing plate.

[0046] The iron-core motor assemblies 144A-B each include multiple conductive wire coils wrapped around a steel pole. Each steel pole is fabricated as part of a larger steel structure. In some examples, the copper coils are embedded in an epoxy matrix material that fills the space around the conductive wire coils and the steel structure.

[0047] As shown in Figure 5, iron-core motor assemblies 144A-B are positioned adjacent to the faces of magnet passages 145A-B, respectively. Additionally, the iron columns and associated iron structures of iron-core motor assembly 144A create magnetic field lines that pass through the gap between iron-core motor assembly 144A and magnet passage 145A. Similarly, the iron columns and associated iron structures of iron-core motor assembly 144B create magnetic field lines that pass through the gap between iron-core motor assembly 144B and magnet passage 145B. A mechanical driving force is generated by passing a current through the windings of the coils of iron-core motor assemblies 144A-B, thereby generating X WF It is generated in the direction.

[0048] The inclusion of iron within the iron-core motor assemblies 144A-B creates a large attractive force between the magnet passages 145A-B and the iron-core motor assemblies 144A-B. The magnetic attractive force creates a negative Y with respect to the iron-core motor assembly 144A based on the magnetic interaction between the iron-core motor assembly 144A and the magnet passage 145A. WF Similarly, a magnetic attractive force acts in a positive Y direction relative to the iron core motor assembly 144B based on the magnetic interaction between the iron core motor assembly 144B and the magnet passage 145B. WFThe magnetic attractive forces act in opposite directions on the iron core motor assemblies 144A-B, respectively, and because both iron core motor assemblies 144A-B are mechanically fixed to the wafer frame 142, the magnetic attractive forces cancel each other out. Assuming a similar gap is maintained between the iron core motor assemblies 144A-B and the magnet passages 145A-B, respectively, the residual force applied to the wafer frame 142 due to the magnetic attractive forces, along with the residual bending moment applied to the wafer frame 142, is negligible. This significantly reduces the induced deformation of the wafer frame 142, which in turn results in improved wafer placement accuracy.

[0049] Additionally, the forces applied to the linear bearings 143 are significantly reduced because the magnetic attractive forces nearly cancel each other out. As a result, much smaller linear bearings can be used. In the case of mechanical bearings, smaller bearings can be used without sacrificing bearing life. Smaller mechanical bearings operate with reduced friction and reduced placement jitter. This improves stage placement repeatability and allows for shorter settling times.

[0050] 5, the iron-core motor assemblies 144A-B are mechanically fixed to the wafer frame 142. Heat generated in the coil windings of the iron-core motor assemblies 144A-B is conducted into the wafer frame 142, not the intermediate frame 122. As a result, the temperature of the intermediate frame 122 does not substantially change during stage operation, and induced material expansion and deformation of the intermediate frame 122 is negligible. This allows for improved stage placement repeatability at the wafer level.

[0051] As shown in FIGS. 4 and 5, both magnetically opposed long-stroke stages of wafer positioning system 150 use magnetic tracks mechanically coupled to intermediate frame 122. As a result, intermediate frame 122 is thermally isolated from the heat generated by iron-core motor assemblies 124A-B and 144A-B by the physical gap between the iron-core motor assemblies and the corresponding magnetic tracks. Although a small amount of heat transfer occurs through linear bearings 123 and 143, the total amount of heat transfer is negligible due to the very small mechanical contact area of ​​the linear bearings. In some embodiments, air bearings, porous or orifice-type air bearings, may be used in place of mechanical bearings, such as roller or ball bearings. In these embodiments, heat transfer through the air gap of the air bearings is negligible.

[0052] The coefficient of thermal expansion (CTE) of the steel structure of the linear bearings 143 is mismatched to the coefficient of thermal expansion of the aluminum intermediate plate 122. However, in the embodiment shown in FIGS. 4 and 5 , the linear bearings 143 are mounted near the neutral axis of the intermediate plate 122. The neutral axis of the intermediate plate 122 is an axis within the cross section of the intermediate plate 122 along which there is no longitudinal stress or strain, i.e., temperature changes do not induce longitudinal strain based on the CTE mismatch between the linear bearings and the intermediate frame 122. Therefore, small temperature changes in the intermediate frame 122 and linear bearings 143 do not induce large deformations in the intermediate frame 122.

[0053] The wafer positioning system 150 includes two stacked, magnetically opposed, long-stroke stages. Each magnetically opposed long-stroke stage can move a wafer over a distance of at least 300 millimeters in the long-stroke directions, i.e., the X and Y directions. The wafer positioning system 150 can position a wafer anywhere within the workspace with a repeatability of less than 300 nanometers. To meet the high throughput requirements of semiconductor fabrication facilities, the wafer positioning system can generate high acceleration in both the X and Y directions. In some embodiments, the wafer positioning system 150 can move a wafer 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 50 meters / sec. 2 The moving mass of the Y stage, i.e., the intermediate frame 122 plus the mass of all parts carried by the intermediate frame 122, is large, e.g., greater than 40 kilograms. Such a mass is accelerated at an acceleration rate of at least 30 meters per second. 2 To accelerate at an acceleration of 1 / 2, iron-core linear motor assemblies 124A and 124B each continuously generate a force of at least 600 Newtons. To generate such a large force, iron-core linear motor assemblies 124A and 124B each generate a significant amount of heat.

[0054] In a further aspect, the iron-core linear motor assembly includes one or more cooling channels within the housing of the assembly, and a gaseous or liquid cooling fluid is pumped through the cooling channels to extract heat from the iron-core linear motor assembly.

[0055] FIG. 6 is a cross-sectional view of an iron-core linear motor assembly in one embodiment. Iron-core linear motor assembly 160 includes iron structure 161, coil sets 162-165, and cooling channels 166 integrated within housing 167. In some embodiments, the spaces between iron structure 161, coil sets 162-165, and cooling channels 166 are filled with a hardening material 168, such as epoxy. In some other embodiments, the housing is fabricated with voids that correspond to iron structure 161, coil sets 162-165, and cooling channels 166, and optionally, any remaining space is filled with hardening material 168. In the embodiment shown in FIG. 6, cooling fluid 169 is pumped through channels 166 to extract heat from iron-core linear motor assembly 160.

[0056] As previously mentioned, the iron-core linear motor assemblies 124A-B of the wafer positioning system 150 generate the most heat due to the high acceleration requirements and high net weight of the long-stroke Y-stage. Therefore, a large amount of cooling fluid, either gas or liquid, 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 source of cooling fluid, such as a heat exchanger, a self-supplied cooling source, or the like. Direct connection is possible because the iron-core linear motor assemblies 124A-B are mechanically coupled to the stage underframe 121, which does not move substantially relative to the measurement system frame that occupies the wafer fabrication facility.

[0057] In some alternative embodiments, the iron-core linear motor assemblies 124A-B of the wafer positioning system 150 are mounted to the mid-plate 122. In these embodiments, flexible tubing is required to supply cooling fluid to the iron-core linear motor assemblies 124 as the mid-plate 122 moves relative to the stage lower frame 121. This embodiment is not preferred because the flexible tubing is unreliable and the substantial mass and hysteresis characteristics of the flexible tubing adversely affect the positioning accuracy and settling time of the wafer positioning system.

[0058] In some embodiments, flexible tubing is required to supply cooling fluid to the iron-core linear motor assemblies 144A-B of the wafer positioning system 150. Although it is preferable not 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. As a result, the amount of cooling required is much smaller, along with the size of the flexible tubing that must be routed from the stage underframe 101, through the intermediate frame 122, to the wafer frame 142. As a result, force disturbances from the flexible tubing to the wafer frame 142 are limited and do not substantially affect the positioning accuracy and settling time of the wafer positioning system.

[0059] In a further 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, thereby minimizing thermal transients during operation of the wafer positioning system 150.

[0060] As shown in FIG. 6, an iron structure 161 includes several magnetic pole pieces. In some embodiments, iron structure 161 is fabricated from laminated sheets of electrical steel to minimize power losses due to induced eddy currents. A coil of conductive wire, such as copper wire, is wound around each pole piece. In the embodiment shown in FIG. 6, the electrical coils are grouped into sets 162-165. Each set includes three adjacent coils, each operating at a different electrical phase, allowing the moving part of the linear motor to move through its entire stroke.

[0061] As shown in Figure 6, a first coil in each coil set, e.g., coils 162A-165A, is electrically coupled in series with a first controllable current source. Similarly, a second coil in each coil set, e.g., coils 162B-165B, is electrically coupled in series with a second current source, and a third coil in each coil set, e.g., coils 162C-165C, is electrically coupled in series with a third current source. Current 170A is supplied through electrical coils 162A-165A, current 170B is supplied through electrical coils 162B-165B, and current 170C is supplied through electrical coils 162C-165C. Currents 170A-C operate out of phase with each other to smoothly drive the linear motor regardless of the relative position of the iron-core linear motor assembly 160 with respect to the corresponding magnet path. By operating all coils of the same phase together, the entire coil assembly of the iron-core linear motor assembly 160 is heated uniformly, thereby eliminating the possibility of moving hot spots.

[0062] In some alternative embodiments, adjacent coils operate independently with different electrical phases, allowing the linear motor's working portion to move throughout its entire stroke. In this approach, the current through each electrical coil is independently controlled based on the position of the mover relative to the linear motor's stator elements. This control approach is commonly referred to as coil switching. In these embodiments, current is supplied only to electrical coils located on opposite sides of the magnet path and therefore capable of generating a large driving force. While this approach results in less overall heat generation, the heating is not uniform along the entire length of the iron-core linear motor assembly. Generally, the impact of uneven heating on overall placement accuracy outweighs the impact of overall heating on overall placement accuracy.

[0063] The iron-core linear motor assembly 160 is a three-phase motor, i.e., three different sets of coils are wired in series and driven by separate current drivers that operate 120 degrees out of phase from another set of coils. In general, however, the iron-core linear motor assembly may be configured to operate with any number of different phases.

[0064] 7A is a graph 180 illustrating a simulation of the temperature of the wafer frame 142 of the wafer positioning system 150 as the temperature of the wafer frame 142 increases from a start-up temperature at the beginning of operation to a steady-state temperature under typical high-throughput operating conditions. As shown in FIG. 7A, the temperature of the wafer frame 142 increases by approximately 0.23° C., which is similar to a conventional stacked stage design using a U-channel ironless linear motor.

[0065] FIG. 7B is a graph 181 illustrating a simulation of the temperature of the intermediate frame 122 of the wafer positioning system 150 as it increases from a startup temperature at the beginning of operation to a steady-state temperature under typical high-throughput operating conditions. As shown in FIG. 7B, the temperature of the intermediate frame 122 increases by approximately 0.023°C. The equivalent temperature increase for a conventional stacked stage design using a U-channel ironless linear motor is more than 30 times greater. The thermal stability of the intermediate frame 122 achieved using magnetically opposed iron-core linear motors as described herein enables significantly improved wafer positioning performance. By limiting heat transfer to the intermediate frame 122, thermally induced Abbe errors in the wafer are dramatically reduced. Furthermore, the thermal stability of the intermediate frame 122 enables high wafer positioning accuracy after error mapping.

[0066] 7C is a graph 182 illustrating a simulation of the temperature of the stage under frame 121 of the wafer positioning system 150 as the temperature of the stage under frame 121 increases from a startup temperature at the beginning of operation to a steady-state temperature under typical high-throughput operating conditions. As shown in FIG. 7C, the temperature of the stage under frame 121 increases by approximately 0.027°C. The large thermal mass of the stage under frame allows it to absorb a large amount of heat generated by the iron-core linear motor assemblies 124A-B without causing a significant change in the temperature of the stage under frame 121.

[0067] Typically, the under-stage frame of the magnetically opposed iron-core wafer positioning system is attached to the mechanical frame of the measurement system, and in this manner, the magnetically opposed iron-core wafer positioning system is configured to accurately position the wafer to be measured relative to the optical subsystem of the measurement system.

[0068] Figure 8 illustrates a system 100 for measuring properties of a semiconductor wafer. As shown in Figure 8, the system 100 performs spectroscopic ellipsometry measurements on one or more structures 112 disposed on a semiconductor wafer 114 that is positioned relative to a spectroscopic ellipsometer 101 by a magnetically opposed iron-core wafer positioning system.

[0069] In this embodiment, system 100 includes a spectroscopic ellipsometer 101 with an illumination device 102 and a spectrometer 104. The illumination device 102 of system 100 is configured to generate and direct illumination in a selected wavelength range (e.g., 100 nanometers to 20 micrometers) toward one or more structures 112 disposed on the surface of a semiconductor wafer 114. The spectrometer 104 is then configured to receive light from the surface of the semiconductor wafer 114. Note further that light emitted from the illumination device 102 is polarized using a polarization state generator 107 to produce a polarized illumination beam 106. Radiation reflected by the structures 114 disposed on the wafer 112 is passed to the spectrometer 104 through a polarization state analyzer 109. The radiation received by the spectrometer 104 in a collected beam 108 is analyzed with respect to polarization state, thereby enabling spectral analysis of the radiation passed by the analyzer. The detected spectrum 111 is passed to a computing system 130 for analysis of one or more structures 112 .

[0070] 8, metrology system 100 includes a magnetically opposed iron-core wafer positioning system 150 configured to position wafer 114 relative to spectrometer 101 during measurement. Magnetically opposed iron-core wafer positioning system 150 receives command signals (not shown) from computing system 130. The command signals include an indication of a desired position of wafer 114 relative to spectrometer 101. In response to the command signals, magnetically opposed iron-core wafer positioning system 150 moves wafer 114 to the desired position relative to spectrometer 101.

[0071] In one aspect, the spectroscopic ellipsometry measurements are performed while the wafer 114 is positioned at a desired position relative to the spectrometer 101. Measurement data 111 collected from the measurements is communicated to the computing system 130, and an estimate of one or more structure parameters of interest 115 is made based on the collected measurement data. The computing system 130 is configured to receive the measurement data 111 associated with measurements (e.g., critical dimensions, film thickness, concentration, composition, process, etc.) for one or more structures 112 disposed on the wafer 114. In one example, the measurement data 111 includes an indication of the spectral response of the 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 use real-time critical dimensioning (RTCD) to access model parameters in real time or may access a library of pre-computed models to determine values ​​of at least one parameter of interest associated with the target structures 112. In some embodiments, the estimates of the one or more parameters of interest are stored in a memory (e.g., memory 132). In the embodiment shown in Figure 8, the estimates 115 of the one or more parameters of interest are communicated to an external system (not shown).

[0072] 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 parameterizing the structure (e.g., film thickness, critical dimensions, material properties, etc.) and the machine (e.g., wavelength, angle of incidence, polarization angle, etc.). The measured values ​​(e.g., α meas and β measA measurement model is created that attempts to predict the machine's associated parameters (P machine ) and sample-related parameters (P specimen ) is included.

number

[0073] Machine parameters are parameters used to characterize a metrology tool (e.g., the ellipsometer 101). Examples of machine parameters include the angle of incidence (AOI), analyzer angle (AO), polarizer angle (PO), illumination wavelength, numerical aperture (NA), compensator or waveplate (if present), etc. Sample parameters are parameters used to characterize a sample (e.g., the wafer 114 containing the structure 112). For thin film samples, examples of sample parameters include refractive index, dielectric function tensor, nominal layer thickness of all layers, layer order, etc. For CD samples, examples of sample parameters include geometric parameter values ​​associated with different layers, refractive indices associated with different layers, etc. For measurement purposes, the machine parameters are treated as known, fixed parameters, and one or more of the sample parameters are treated as unknown, floating parameters.

[0074] In some instances, the floating parameters are analyzed by an iterative process (e.g., regression) that produces a best fit between theoretical predictions and experimental data. specimen is varied, and the model output values ​​(e.g., α model and β model ) is the correlation between the model output values ​​and experimentally measured values ​​(e.g., α meas and β meas) until a set of sample parameter values ​​is determined that results in a close fit between the model output and the experimentally measured values. In model-based measurement applications such as spectroscopic ellipsometry on CD samples, a regression process (e.g., ordinary least squares regression) is utilized to identify sample parameter values ​​that minimize the difference between the model output and the experimentally measured values ​​for a fixed set of machine parameter values.

[0075] In some instances, the floating parameters are determined by searching a library of pre-calculated solutions to find the closest match. In model-based measurement applications such as spectroscopic ellipsometry on CD samples, a library search process is used to identify sample parameter values ​​that minimize the difference between pre-calculated output values ​​and experimentally measured values ​​for a fixed set of machine parameter values.

[0076] In model-based measurement applications, simplifying assumptions are often required to maintain sufficient throughput. In some examples, the truncation order of rigorous coupled wave analysis (RCWA) needs to be reduced to minimize computation time. In another example, the number or complexity of library functions is reduced to minimize search time. In another example, the number of floating parameters is reduced by fixing certain parameter values. In some examples, these simplifying assumptions result in unacceptable errors in estimating the values ​​of one or more parameters of interest (e.g., critical dimension parameters, overlay parameters, etc.). As described herein, by performing measurements on structures undergoing gas adsorption, a model-based measurement model can be determined by reducing parameter correlations to increase measurement accuracy.

[0077] In general, spectroscopic ellipsometer 101 may utilize any architecture suitable for measuring modulation of optical properties, such as dielectric function, bandgap, etc. As a non-limiting example, spectroscopic ellipsometer 101 may be configured with a rotating polarizer, a rotating compensator, or any combination thereof.

[0078] 8 may be further configured as described herein. In addition, system 100 may be configured to perform any other block(s) of any of the method embodiment(s) described herein.

[0079] FIG. 9 illustrates an angle-resolved spectroscopic reflectometer system configured to estimate values ​​for one or more properties of a semiconductor wafer in at least one novel manner by measuring reflectivity over a wide angular range. Like-numbered elements shown in FIG. 9 are similar to those described with reference to FIG. 8. As shown in FIG. 9, system 200 performs angle-resolved spectroscopic reflectometry measurements on one or more structures 112 disposed on a semiconductor wafer 114, which are positioned relative to the angle-resolved spectroscopic reflectometer by a magnetically opposed iron-core wafer positioning system. In one embodiment, system 200 is an angle-resolved spectroscopic reflectometer including one or more measurement channels spanning a wide wavelength range, e.g., infrared wavelengths between 750 nanometers and 2600 nanometers.

[0080] The angle-resolved spectroscopic reflectometer 200 includes a polarizer 204, an objective lens 201, an analyzer 210, and a spectrometer 212. As shown in FIG. 9 , an illumination beam is generated by an illumination source 202 in response to a command signal 229 received from the computing system 130. Light from the illumination source 202 is conditioned by optional beam-forming optics 203 to generate an illumination light beam 220. The illumination light beam 220 is directed to a polarizer 204. As shown, the illumination light directed to the polarizer 204 comes from the illumination source 202; however, in general, light from any number of illumination sources in the system 200 may be combined to generate the illumination light beam directed to the polarizer 204. In this manner, the spectral content of the illumination light may be configured as a combination of light emitted from multiple illumination sources.

[0081] In some embodiments, the polarizer 204 is configured to selectively rotate the polarizing element about the optical axis of the illumination light beam 220. In general, the polarizer 204 may include any polarizing element and system for rotating a polarizing element known in the art. For example, the 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. The polarizer 204 is configured to operate within the system 200 in either a rotationally active state or a rotationally inactive state. In one example, the rotational actuator of the polarizer 204 may be in an inactive state such that the polarizing element remains fixed for rotation about the optical axis of the illumination light 220. In another example, the rotational actuator rotates the polarizing element about the optical axis of the illumination light at a selected angular frequency ω. p You can also rotate it with .

[0082] In some other embodiments, the polarizer 204 is configured with a fixed polarization angle about the optical axis of the illumination light beam 220 .

[0083] As shown in FIG. 9, the illumination light beam 220 is rotated by the rotary actuator to rotate the polarization element at a selected angular frequency ω p While rotating the light at 1000 Hz, the light passes through polarizer 204. Polarizer 204 thus generates a polarized beam 221 that is directed towards beam splitter 206. Beam splitter 206 directs polarized beam 221 towards objective lens 201.

[0084] 9, objective lens 201 focuses polarized beam 221 onto the surface of wafer 114 over a range of angles of incidence. In some examples, polarized beam 221 is focused onto the surface of wafer 114 within a range of angles of incidence between 0 and 40 degrees. In some examples, polarized beam 221 is focused onto the surface of wafer 114 at small angles of incidence, resulting in a small illumination spot, for example, less than 100 micrometers in diameter.

[0085] Interaction of the focused polarized beam 221 with the wafer 114 modifies the polarization of the radiation by either reflection, scattering, diffraction, transmission, or another type of process. 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. In the embodiment shown in FIG. 9, the analyzer 210 includes a polarizer element that remains fixed for rotation about the optical axis of the modified light beam 222 as it passes through the analyzer 210 and optional beam-focusing optics 211 to reach 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 measuring radiation within a different wavelength range. The radiation received by the spectrometer 212 is analyzed with respect to polarization state, allowing the spectrometer to perform a spectral analysis of the radiation passed by the polarizer 212. The measured spectrum 228 is communicated to the computing system 130. The computing system 130 is configured to receive the signal 228 indicative of the measured spectral response of the structure of interest and to estimate a value of the parameter of interest based on the measured spectral response.

[0086] 9, metrology system 200 includes a magnetically opposed iron-core wafer positioning system 150 configured to position wafer 114 relative to the angle-resolved spectroscopic reflectometer during measurements. Magnetically opposed iron-core wafer positioning system 150 receives command signals (not shown) from computing system 130. The command signals include an indication of a desired position of wafer 114 relative to the angle-resolved spectroscopic reflectometer. In response to the command signals, magnetically opposed iron-core wafer positioning system 150 moves wafer 114 to the desired position relative to the angle-resolved spectroscopic reflectometer, as described above with respect to spectroscopic ellipsometer system 100.

[0087] Figure 10 illustrates a spectroscopic reflectometer system configured, in at least one novel aspect, to estimate values ​​of one or more properties of a semiconductor wafer by measuring reflectance at normal incidence. Like-numbered elements shown in Figure 10 are similar to those described with reference to Figure 8. As shown in Figure 10, the system 300 performs spectroscopic reflectance measurements of one or more structures 112 disposed on a semiconductor wafer 114 that is positioned relative to the spectroscopic reflectometer by a magnetically opposed iron-core wafer positioning system.

[0088] 10 , an illumination beam is generated by an illumination source 302 in response to a command signal 329 received from the computing system 130. An illumination light beam 320 from the illumination source 302 is directed to the polarizer 304. As shown, the illumination light directed to the polarizer 304 comes from the illumination source 302; however, in general, light from any number of illumination sources in the system 300 may be combined to generate the illumination light beam directed to the polarizer 304. In this manner, the spectral content of the illumination light may be composed of a combination of light emitted from multiple illumination sources.

[0089] In some embodiments, the polarizer 304 is configured to selectively rotate a polarizing element about the optical axis of the illumination light beam 320. In general, the polarizer 304 may include any polarizing element and system for rotating a polarizing element known in the art. For example, the polarizer 304 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. The polarizer 304 is configured to operate within the system 300 in either a rotationally active state or a rotationally inactive state. In one example, the rotational actuator of the polarizer 304 may be inactive such that the polarizing element remains fixed for rotation about the optical axis of the illumination light 320. In another example, the rotational actuator may rotate the polarizing element at a selected angular frequency ω about the optical axis of the illumination light.p The polarizing element may be rotated by

[0090] In some alternative embodiments, the polarizer 304 is configured with a fixed polarization angle about the optical axis of the illumination light beam 320 .

[0091] As shown in FIG. 10, the illumination light beam 320 is rotated by the rotary actuator to rotate the polarization element at a selected angular frequency ω p The light passes through polarizer 304 while being rotated at a constant speed. Polarizer 304 thus generates polarized beam 321 that is directed towards beam splitter 306. Beam splitter 306 directs polarized beam 321 at normal incidence onto wafer 114. Polarized beam 321 is incident on the surface of wafer 114 over a small illumination spot, e.g., less than 100 micrometers in diameter.

[0092] Interaction of polarized beam 221 with wafer 114 modifies the polarization of the radiation by either reflection, scattering, diffraction, transmission, or another type of process. After interaction with wafer 114, modified light 322 is directed to beam splitter 306. Beam splitter 306 is configured to transmit modified light 322 toward analyzer 310. In the embodiment shown in FIG. 10 , analyzer 310 includes a polarizer element that remains fixed for rotation about the optical axis of modified light beam 322 while it passes through analyzer 310 and reaches spectrometer 312. In spectrometer 312, beam components with 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 is a linear array of photodiodes, each measuring radiation within a different wavelength range. The radiation received by the spectrometer 312 is analyzed with respect to polarization state to enable the spectrometer to perform spectral analysis of the radiation passed by the polarizer 312. The measured spectrum 328 is communicated to the computing system 130. The computing system 130 is configured to receive the signal 328 indicative of the measured spectral response of the structure of interest and to estimate a value of the parameter of interest based on the measured spectral response.

[0093] 10 , metrology system 300 includes a magnetically opposed iron-core wafer positioning system 150 configured to position wafer 114 relative to the spectroscopic reflectometer during measurements. Magnetically opposed iron-core wafer positioning system 150 receives command signals (not shown) from computing system 130. The command signals include an indication of a desired position of wafer 114 relative to the spectroscopic reflectometer. In response to the command signals, magnetically opposed iron-core wafer positioning system 150 moves wafer 114 to the desired position relative to the spectroscopic reflectometer, as described above with respect to spectroscopic ellipsometer system 100.

[0094] Although reflectometer systems 200 and 300 include polarization optics, in general, reflectometer systems 200 and 300 may not include polarization optics.

[0095] In general, the measurement system may include any combination of spectroscopic ellipsometry, spectral reflectance, and angle-resolved spectral reflectance measurements using a magnetically opposed iron-core wafer positioning system. The measurements may be performed sequentially or simultaneously.

[0096] 8-10, measurements are taken on one or more structures while the wafer is positioned by the magnetically opposed iron-core wafer positioning system. In general, any suitable model-based or modeless metrology technique may be used to perform measurements on structures positioned by the magnetically opposed iron-core wafer positioning system in accordance with the methods and systems described herein.

[0097] Suitable metrology techniques include, but are not limited to, spectroscopic ellipsometry and spectroscopic reflectometry (including single wavelength, multi-wavelength, and angle-resolved implementations), and spectroscopic scatterometry, scatterometry overlay, beam profile reflectometry, and beam profile ellipsometry (including angle-resolved and polarization-resolved implementations) may be considered individually or in any combination.

[0098] 11 illustrates a method 400 suitable for implementation by metrology systems 100, 200, and 300 of the present invention. It is recognized that, in one aspect, any data processing elements of method 400 may be performed via pre-programmed algorithms executed by one or more processors of computing system 130. While the following description is presented in the context of metrology systems 100, 200, and 300, it is recognized herein that the particular structural aspects of metrology systems 100, 200, and 300 should be construed as illustrative only, and not limiting.

[0099] In block 301, a first moving frame is positioned relative to the lower 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 lower 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 attractive force is induced across the first magnetic gap. The first magnetic attractive force acts along a second axis. A 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 attractive force is induced across the second magnetic gap. The second magnetic attractive force acts along the second axis in a direction opposite to the first magnetic attractive force.

[0100] In block 302, a second moving frame is positioned relative to the first moving frame along a third axis. 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. 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. The third iron-core linear motor assembly and the third magnet assembly are physically separated by a third magnetic gap. A third magnetic attractive force is induced across the third magnetic gap. The third magnetic attractive force acts along a fourth axis. The fourth iron-core linear motor assembly is disposed adjacent to the fourth magnet assembly. The fourth iron-core linear motor assembly and the fourth magnet assembly are physically separated by a fourth magnetic gap. A fourth magnetic attractive force is induced across the fourth magnetic gap. The fourth magnetic attractive force acts along a fourth axis in a direction opposite to the third magnetic attractive force.

[0101] In general, the aforementioned measurement techniques may be applied to measurements of process parameters, structural parameters, layout parameters, dispersion parameters, or any combination thereof. As non-limiting examples, overlay, profile shape parameters (e.g., critical dimensions, height, sidewall angle), process parameters (e.g., lithography focus and lithography dose), dispersion parameters, layout parameters (e.g., pitch walk, edge placement error), thin film thickness, composition parameters, or any combination of parameters may be measured using the aforementioned techniques.

[0102] By way of non-limiting example, structures measured by shape filling include gate-all-around structures, line-space-lattice structures, FinFet structures, SRAM device structures, flash memory structures, and DRAM memory structures.

[0103] In yet another aspect, the structure to be measured may be a design rule target. In other words, the metrology target conforms to the design rules applicable to the underlying semiconductor manufacturing process. In some examples, the metrology target is preferably positioned within the active die area. In some examples, the metrology target has dimensions of 15 micrometers by 15 micrometers or less. In some other examples, the metrology target is positioned within a scribe line or outside the active die area.

[0104] In some instances, measurements of a parameter of interest performed at a particular measurement site rely on data collected only from that particular measurement site, even though data may be collected from multiple sites on the wafer. In other instances, measurement data collected from multiple sites across a wafer or a subset of a wafer is used in the measurement analysis. This may be desirable to capture parameter variations across the wafer.

[0105] In some examples, measurements of the parameter of interest are performed based on the measurement target using multiple different measurement techniques, including single-target, multiple-target, and spectral feedforward techniques. The accuracy of the measured parameter may be improved by any combination of feed-sideways analysis, feedforward analysis, and parallel analysis. Feed-sideways analysis refers to acquiring multiple data sets in different regions of the same sample and passing common parameters determined from the first data set to the second data set for analysis. Feedforward analysis refers to acquiring data sets in different samples and passing common parameters to subsequent analysis using a stepwise copy exact parameter feedforward approach. Parallel analysis refers to applying a nonlinear fitting method to multiple data sets in parallel or simultaneously, where at least one common parameter is combined during the fitting.

[0106] Analysis of multiple tools and structures refers to feed-forward, feed-sideway, or parallel analysis based on regression, look-up tables (i.e., "library" matching), or another fitting procedure of multiple data sets. An example of a method and system for analysis of multiple tools and structures is described in U.S. Patent No. 7,478,019, issued January 13, 2009, to KLA-Tencor Corp., which is incorporated herein by reference in its entirety.

[0107] In yet another aspect, measurements obtained as described herein may be used to provide active feedback to a process tool (e.g., a lithography tool, an etch tool, a deposition tool, etc.). For example, critical dimension values ​​determined using the methods and systems described herein may be communicated to a lithography tool to adjust the lithography system to achieve a desired output. Similarly, etch parameters (e.g., etch time, diffusivity, etc.) or deposition parameters (e.g., time, concentration, etc.) may be included in a metrology model to provide active feedback to an etch tool or a deposition tool, respectively. In some examples, corrections to process parameters determined based on measured device parameter values ​​may be communicated to a lithography tool, an etch tool, or a deposition tool.

[0108] It should be appreciated that the various steps described throughout this disclosure may be performed by a single computer system 130, multiple computer systems 130, or multiple different computer systems 130. Additionally, different subsystems of systems 100, 200, and 300, such as the magnetically opposed iron-core wafer positioning system, may include computer systems suitable for performing at least some of the steps described herein. As such, the foregoing description should not be construed as limiting the present invention, but merely as illustrative. Additionally, computing system 130 may be configured to perform other step(s) of any of the method embodiments described herein.

[0109] 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 include any device or combination of devices having one or more processors that execute instructions from a memory medium. In general, computing system 130 may be integrated with a measurement system, such as measurement systems 100, 200, and 300, or alternatively, may be wholly or partially separate from any measurement system. In this sense, computing system 130 may be remotely positioned and may receive measurement data from any measurement source and transmit command signals to any element of measurement systems 100, 200, and 300.

[0110] The program instructions 134 for performing the methods as described herein may be transmitted over a transmission medium such as a wire, cable, or wireless transmission link. The memory 132 for storing the program instructions 134 may include a computer-readable medium such as a read-only memory, a random-access memory, a magnetic or optical disk, or a magnetic tape.

[0111] Additionally, computing system 130 may be communicatively coupled to elements of measurement systems 100, 200, and 300 in any manner known in the art.

[0112] The computing system 130 may be configured to receive and / or acquire data or information from subsystems of the measurement system (e.g., spectrometer 104, illumination device 102, magnetically opposed iron-core wafer positioning system, etc.) via a transmission medium, which 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. Additionally, 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, spectral results may be imported from an external system. Additionally, the computer system 130 may receive data from an external system via the transmission medium.

[0113] The computing system 130 may be configured to transmit data or information to subsystems of the system (e.g., the spectrometer 104, the illumination device 102, the magnetically opposed iron-core wafer positioning system, etc.) via a transmission medium, which 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. Furthermore, 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 exported to an external system. Furthermore, the computer system 130 may send data to the external system via the transmission medium. Additionally, the determined values ​​for the parameters of interest are stored in the memory. For example, the values ​​may be stored on-board measurement systems 100, 200, and 300, for example, in memory 132, or may be communicated (eg, via output signal 115) to an external memory device.

[0114] 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.), the critical dimension between any two or more structures (e.g., the distance between two structures), and the displacement between two or more structures (e.g., the overlay displacement between overlay grating structures, etc.). The structures may include three-dimensional structures, patterned structures, overlay structures, etc.

[0115] As described herein, the terms "critical dimension application" or "critical dimension measurement application" include any critical dimension measurement.

[0116] As described herein, the term "metrology system" includes any system used at least in part to characterize a specimen in any manner, including critical dimension and overlay metrology applications. However, such terminology does not limit the scope of the term "metrology system" as described herein. In addition, the metrology systems described herein may be configured for measurements of patterned 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 (including data from one or more platforms simultaneously), as well as any other metrology or inspection tool that would benefit from the measurement techniques described herein.

[0117] Described herein are various embodiments for semiconductor processing systems (e.g., inspection systems or lithography systems) that may be used to process specimens. The term "specimen" is used herein to refer to a wafer, reticle, or any other specimen that may be processed (e.g., printed or inspected for defects) by means known in the art.

[0118] As used herein, the term "wafer" generally refers to a substrate formed from a semiconductor or non-semiconductor material. Examples include, but are not limited to, monocrystalline silicon, gallium arsenide, and indium phosphide. Such substrates may be commonly found and / or processed in semiconductor fabrication facilities. 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 dies having repeating pattern features.

[0119] A "reticle" may be a reticle at any stage in the reticle fabrication process, or a finished reticle that may or may not be released for use in a semiconductor fabrication facility. A reticle or "mask" is generally defined as a substantially transparent substrate on which substantially opaque regions are formed and arranged in a pattern. The substrate may comprise, for example, a glass material such as amorphous SiO2. The reticle may be disposed over a resist-coated wafer during the exposure step of a lithography process, thereby transferring the pattern on the reticle into the resist.

[0120] 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 completed 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 having any type of device fabricated thereon known in the art.

[0121] 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 or transmitted as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media, including any medium that facilitates transfer of a computer program from one place to another. A storage medium may be any available medium that can be accessed by a general-purpose or special-purpose computer. By way of example, and not limitation, such computer-readable media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if software is transmitted from a website, server, or another remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included within the definition of medium. As used herein, disk and disc include compact discs (CDs), laser discs, XRF discs, digital versatile discs (DVDs), floppy disks, and Blu-ray discs, where disks typically reproduce data magnetically, while discs reproduce data optically using lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0122] Although certain specific embodiments are described above for educational 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 first iron-core linear motor assembly disposed adjacent to a first magnet assembly, the first iron-core linear motor assembly and the first magnet assembly being physically separated by a first magnetic gap, a first magnetic attractive force being induced across the first magnetic gap, the first magnetic attractive force acting along a first axis; a second iron-core linear motor assembly disposed adjacent to a second magnet assembly, the second iron-core linear motor assembly and the second magnet assembly being physically separated by a second magnetic gap, a second magnetic attractive force being induced across the second magnetic gap, the second magnetic attractive force acting along the first axis in a direction opposite to the first magnetic attractive force, the first magnet assembly being mechanically coupled to the second magnet assembly, and the first iron-core linear motor assembly being mechanically coupled to the second iron-core linear motor assembly; A placement system comprising:

2. The lower frame and a first moving frame movable relative to the lower frame along a second axis perpendicular to the first axis, the first magnet assembly and the second magnet assembly being mechanically coupled to the first moving frame, and the first iron-core linear motor assembly and the second iron-core linear motor assembly being mechanically coupled to the lower frame; The placement system of claim 1 further comprising:

3. a second moving frame movable relative to the first moving frame along a third axis perpendicular to the second axis; a third iron-core linear motor assembly disposed adjacent to a third magnet assembly, the third iron-core linear motor assembly and the third magnet assembly being physically separated by a third magnetic gap, a third magnetic attractive force being induced across the third magnetic gap, the third magnetic attractive force acting along a fourth axis orthogonal to the third axis; a fourth iron-core linear motor assembly disposed adjacent to a fourth magnet assembly, the fourth iron-core linear motor assembly and the fourth magnet assembly being physically separated by a fourth magnetic gap, a fourth magnetic attractive force being induced across the fourth magnetic gap, the fourth magnetic attractive force acting along the fourth axis in a direction opposite to the third magnetic attractive force, the third magnet assembly being mechanically coupled to the fourth magnet assembly, and the third iron-core linear motor assembly being mechanically coupled to the third linear motor assembly; The placement system of claim 2 further comprising:

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

5. 3. The arrangement system of claim 2, wherein the first iron-core linear motor assembly includes a plurality of iron-core linear motor units disposed adjacent to one another along an entire length of the first iron-core linear motor assembly, each iron-core linear motor unit including a plurality of conductive coils, a first one of the plurality of conductive coils of each of the plurality of iron-core linear motor units being electrically connected in series, and a second one of the plurality of conductive coils of each of the plurality of iron-core linear motor units being electrically connected in series.

6. a first cooling channel within a housing of the first iron-core linear motor assembly; a second cooling channel within the housing of the second iron-core linear motor assembly; The placement system of claim 1 further comprising:

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

8. The positioning system of claim 1 , wherein the first movement frame is constrained to move relative to the lower frame along the second axis by a mechanical bearing, an air bearing, or a magnetic bearing.

9. 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; 1. A wafer placement system comprising: a first iron-core linear motor assembly disposed adjacent to a first magnet assembly, the first iron-core linear motor assembly and the first magnet assembly being physically separated by a first magnetic gap, a first magnetic attractive force being induced across the first magnetic gap, the first magnetic attractive force acting along a first axis; and a second iron-core linear motor assembly disposed adjacent to a second magnet assembly, the second iron-core linear motor assembly and the second magnet assembly being physically separated by a second magnetic gap, a second magnetic attractive force being induced across the second magnetic gap, the second magnetic attractive force acting along the first axis in an opposite direction to the first magnetic attractive force, the first magnet assembly being mechanically coupled to the second magnet assembly, and the first iron-core linear motor assembly being mechanically coupled to the second iron-core linear motor assembly. a wafer placement system comprising: a computing system configured to determine a value of at least one parameter of interest characterizing the one or more structures of the object of measurement based on the amount of detected light; A measurement system comprising:

10. the wafer placement system a lower frame mechanically coupled to the illumination source and the detector; a first moving frame movable relative to the lower frame along a second axis perpendicular to the first axis, the first magnet assembly and the second magnet assembly being mechanically coupled to the first moving frame, and the first iron-core linear motor assembly and the second iron-core linear motor assembly being mechanically coupled to the lower frame; The measurement system of claim 9 further comprising:

11. the wafer placement system a second moving frame movable relative to the first moving frame along a third axis perpendicular to the second axis; a third iron-core linear motor assembly disposed adjacent to a third magnet assembly, the third iron-core linear motor assembly and the third magnet assembly being physically separated by a third magnetic gap, a third magnetic attractive force being induced across the third magnetic gap, the third magnetic attractive force acting along a fourth axis orthogonal to the third axis; a fourth iron-core linear motor assembly disposed adjacent to a fourth magnet assembly, the fourth iron-core linear motor assembly and the fourth magnet assembly being physically separated by a fourth magnetic gap, a fourth magnetic attractive force being induced across the fourth magnetic gap, the fourth magnetic attractive force acting along the fourth axis in an opposite direction to the third magnetic attractive force, the third magnet assembly being mechanically coupled to the fourth magnet assembly, and the third iron-core linear motor assembly being mechanically coupled to the third linear motor assembly; The measurement system of claim 10 further comprising:

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

13. 11. The measurement system of claim 10, wherein the first iron-core linear motor assembly includes a plurality of iron-core linear motor units disposed adjacent to one another along an entire length of the first iron-core linear motor assembly, each iron-core linear motor unit including a plurality of conductive coils, a first one of the plurality of conductive coils of each of the plurality of iron-core linear motor units being electrically connected in series, and a second one of the plurality of conductive coils of each of the plurality of iron-core linear motor units being electrically connected in series.

14. the wafer placement system a first cooling channel within a housing of the first iron-core linear motor assembly; a second cooling channel within the housing of the second iron-core linear motor assembly; The measurement system of claim 9 further comprising:

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

16. 10. The measurement system of claim 9, wherein the first moving frame is constrained to move relative to the lower frame along the second axis by a mechanical bearing, an air bearing, or a magnetic bearing.

17. disposing a first motion frame movable relative to a lower frame along a first axis, wherein a first magnet assembly and a second magnet assembly are mechanically coupled to the first motion frame, a first iron-core linear motor assembly and a second iron-core linear motor assembly are mechanically coupled to the lower frame, the first iron-core linear motor assembly being disposed adjacent to the first magnet assembly, the first iron-core linear motor assembly and the first magnet assembly being physically separated by a first magnetic gap, a first magnetic attractive force being induced across the first magnetic gap, the first magnetic attractive force acting along a second axis, the second iron-core linear motor assembly being disposed adjacent to the second magnet assembly, the second iron-core linear motor assembly and the second magnet assembly being physically separated by a second magnetic gap, a second magnetic attractive force being induced across the second magnetic gap, the second magnetic attractive force acting along the second axis in a direction opposite to the first magnetic attractive force; disposing a second motion frame movable relative to the first motion frame along a third axis, the third axis being orthogonal to the first axis, a third magnet assembly and a fourth magnet assembly being mechanically coupled to the first motion frame, a third iron-core linear motor assembly and a fourth iron-core linear motor assembly being mechanically coupled to the second motion frame, the third iron-core linear motor assembly being disposed adjacent to the third magnet assembly, the third iron-core linear motor assembly and the third magnet assembly being physically separated by a third magnetic gap, a third magnetic attractive force being induced across the third magnetic gap, the third magnetic attractive force acting along a fourth axis, the fourth iron-core linear motor assembly being disposed adjacent to the fourth magnet assembly, the fourth iron-core linear motor assembly and the fourth magnet assembly being physically separated by a fourth magnetic gap, a fourth magnetic attractive force being induced across the fourth magnetic gap, the fourth magnetic attractive force acting along the fourth axis in a direction opposite to the third magnetic attractive force; A method comprising:

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

19. flowing a first amount of cooling fluid or gas through a first cooling channel within a housing of the first iron-core linear motor assembly; flowing a second amount of cooling fluid or gas through a second cooling channel within a housing of the second iron-core linear motor assembly; 20. The method of claim 17, further comprising:

20. 18. The method of claim 17, further comprising constraining the first movement frame to move relative to the lower frame along the first axis with a mechanical bearing, an air bearing, or a magnetic bearing.

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