Method and system for measuring semiconductor structures with active tilt correction

Abstract

Wafer tilt is measured and compensated for based on corrected tilt measurements derived from a set of height measurements across a wafer. A set of wafer orientation correction values is generated by a measurement system at a large number of wafer sites. At each site, a wafer orientation correction value is determined based on a difference between a local wafer tilt of a calibration wafer measured by an optical tilt sensor and a corresponding estimated value of a local slope of the calibration wafer derived from a Z measurement. The same measurement system performs Z measurements of a sample wafer and estimates the local slope at each site. The difference between the corresponding wafer orientation correction value and the local slope at each site accurately estimates the wafer orientation at each measurement site. The wafer orientation is adjusted based on the corrected wafer orientation value.

Description

[0001] CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority under 35 U.S.C. §119 from U.S. Provisional Patent Application Serial No. 63 / 424,468, filed on November 10, 2022, entitled “Metrology and Inspection based on active tilt correction,” the subject matter of which is incorporated herein by reference in its entirety. Technical Field

[0003] The described embodiments relate to metrology and verification systems and methods, and more particularly to methods and systems with improved measurement accuracy. Background Art

[0004] Semiconductor devices such as logic and memory devices are typically fabricated by a sequence of processing steps that are appropriate for a sample. Various features and multiple structural levels of the semiconductor device are formed by these processing steps. For example, photolithography, among other processing steps, is a semiconductor fabrication process that involves 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.

[0005] At various steps during the semiconductor manufacturing process, metrology and inspection processes are used to detect defects on the wafer to facilitate higher yields. Available semiconductor measurement systems include film and critical dimension (CD) metrology, overlay metrology, bare wafer and finished wafer inspection, etc. In many examples, X-ray and optical metrology techniques offer the potential for high throughput without the risk of sample destruction. Several X-ray and optical metrology-based techniques, including scatterometry, reflectometry, and ellipsometry implementations and associated analysis algorithms, are commonly used to characterize critical dimensions, film thickness, composition, overlay, and other parameters of nanoscale structures.

[0006] Typically, during measurement, the wafer is in the optical path of the metrology and inspection system. However, the wafer and the positioning system used to position the wafer are not completely planar. Therefore, the orientation of the wafer surface at the measurement spot varies depending on the lateral position (i.e., xy position) of the wafer relative to the measurement system. This is a problem for several reasons. In some examples, the metrology and inspection system has an extremely thin focal plane, and changes in the wafer tilt can cause the measurement to be out of focus. In some other examples, changes in the wafer tilt introduce changes in the illumination incident angle. This introduces undesirable changes in the measurement signal. A key challenge faced in the development of many metrology and inspection systems is to perform accurate measurements in the presence of local wafer tilt.

[0007] There are many reasons for the occurrence of local wafer tilt. In one example, the wafer positioning stage used to position the wafer in the optical path of the measurement system is constructed to have limited mechanical tolerances. Due to actual manufacturing limitations, the wafer positioning stage itself does not maintain the wafer in the same direction throughout its entire workspace, that is, the orientation of the axis normal to the top surface of the wafer positioning stage depends on the lateral position of the stage. Similarly, the wafer chuck used to fix the wafer to the wafer positioning stage is not completely planar. In another example, the thickness variation across the wafer, the presence of back particles, or both can cause flatness errors, and therefore, the orientation of the axis normal to the measured wafer surface depends on the location on the wafer surface.

[0008] Local wafer tilt shifts the point of incidence of the illumination beam spot on the wafer. This results in an induced shift in the measurement results (e.g., the measured spectrum), which leads to measurement inaccuracies. In addition, since local wafer tilt depends on individual tool characteristics, the induced local wafer tilt is different for each measurement tool. This increases tool-to-tool measurement variations and limits the achievable tool-to-tool matching.

[0009] In some examples, local wafer tilt is measured and corrected by adjusting system model calibration values. However, adjusting the values ​​of the system model does not physically change the incidence position of the illumination beam spot at each measurement position on the wafer. Therefore, this approach cannot compensate for all induced errors. The measurement accuracy and measurement sensitivity that can be achieved using existing measurement and calibration algorithms are still limited. In addition, it is not always practical or even impossible to determine appropriate changes to the system model calibration values ​​within reasonable constraints of computational workload and solution time.

[0010] Future metrology and inspection applications face challenges due to smaller and smaller resolution requirements and higher wafer area values. Therefore, methods and systems for improving measurements in the presence of wafer tilt are desired. Summary of the invention

[0011] Described herein are methods and systems for measuring local wafer tilt and compensating for the local wafer tilt based on a corrected tilt measurement derived from a set of height measurements across the wafer.

[0012] A set of wafer orientation correction values ​​(i.e., a wafer orientation correction map) is generated at a large number of sites on the wafer surface. At each site, a wafer orientation correction value is determined based on a difference between a local wafer tilt of the calibration wafer measured by an optical tilt sensor and a corresponding estimated value of the local slope of the calibration wafer derived from the Z measurement.

[0013] The optical tilt sensor accurately measures the actual local wafer tilt because the calibration wafer does not contain thick films or patterned structures that introduce undesirable measurement errors. The estimated value of the local slope derived from the Z measurement includes the actual local wafer tilt and also includes the wafer tilt error caused by the measured wafer height change. The difference value (i.e., the wafer orientation correction value) quantifies the wafer tilt error present in the estimated value of the local slope derived from the Z measurement.

[0014] When the same measurement system is used to make subsequent measurements of a sample wafer, the induced wafer tilt error present in the estimated value of the local slope derived from the Z measurement is the same as the wafer tilt error captured by the wafer orientation correction value. When the wafer orientation correction value is subtracted from the local slope derived from the Z measurement of the sample wafer, wafer orientation is accurately estimated at each measurement site.

[0015] In yet another aspect, the corrected wafer orientation value is communicated to a wafer stage. The wafer stage adjusts the orientation of the sample wafer based on the corrected wafer orientation value to orient the surface of the wafer at a measurement spot relative to the measurement subsystem in the desired in-plane orientation.

[0016] The foregoing is an inventive summary and therefore necessarily contains simplifications, summaries, and omissions of details; therefore, those skilled in the art will appreciate that the inventive summary is illustrative only and not limiting in any way. Other 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 DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a diagram illustrating a system for measuring values ​​of one or more parameters of interest characterizing a semiconductor structure after correction for wafer tilt error according to the exemplary methods presented herein.

[0018] Figure 2 It is a graphic description Figure 1 Another diagram of the metering system 100 is depicted in FIG.

[0019] Figure 3 is a diagram illustrating the top bare silicon wafer across the surface of the wafer Figure 2 Y W Axis orientation of the graph.

[0020] Figure 4 is a diagram illustrating the top bare silicon wafer along Z measured at several selected locations across the wafer surface. W Plot of the normal position of the axis.

[0021] Figure 5 Is a graphic description and cross reference Figure 4 A graph of the calculated local slope associated with each of the selected sites of the surface of a top-level bare silicon wafer is depicted.

[0022] Figure 6 Illustrated is a method for estimating a desired orientation correction of a semiconductor wafer based on measured corrected tilt values ​​as described herein. DETAILED DESCRIPTION

[0023] Reference will now be made in detail to background examples and some embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0024] Described herein are methods and systems for measuring local wafer tilt and compensating for the local wafer tilt based on a corrected tilt measurement derived from a set of height measurements across the wafer.

[0025] A large number of critical metrology and inspection applications involve measurement of wafers that include thick film structures, patterned structures (e.g., critical dimension (CD) structures), or both. Unfortunately, using optical tilt sensors to directly measure local wafer tilt is prone to errors when the measured wafer includes thick film structures, patterned structures, or both.

[0026] Accurate measurement of the position of a semiconductor wafer relative to a measurement subsystem in a direction normal to the surface of the semiconductor wafer (also referred to as a Z measurement) can be achieved using a variety of sensors, including Z focus sensors currently integrated with many metrology and inspection tools. In some examples, a Z measurement adjacent to a measurement site is used to estimate a local slope at the measurement site. Although the estimated local slope includes the actual wafer tilt, the local slope value derived from the Z measurement also includes a wafer tilt error caused by a measured wafer height change, rather than the actual wafer tilt. In one example, when the wafer stage changes the measurement site on the wafer surface (e.g., due to finite mechanical tolerances and alignment of the wafer stage components), the measured wafer height change is caused by movement of the wafer stage relative to the measurement subsystem in the Z direction.

[0027] To address these limitations, a set of wafer orientation correction values, i.e., a wafer orientation correction map, is generated at a large number of sites across the wafer surface. At each site, a wafer orientation correction value is determined based on the difference between the local wafer tilt of the calibration wafer measured by the optical tilt sensor and the corresponding estimated value of the local slope of the calibration wafer derived from the Z measurement. In a preferred embodiment, the calibration wafer is a bare semiconductor wafer or a bare semiconductor wafer coated with a thin film having a thickness of less than 5 nanometers.

[0028] The optical tilt sensor accurately measures the actual local wafer tilt because the calibration wafer does not include thick films or patterned structures that introduce undesirable measurement errors. The estimated value of the local slope derived from the Z measurement includes the actual local wafer tilt and also includes the wafer tilt error caused by the measured wafer height change. The difference value (i.e., the wafer orientation correction value) quantifies the wafer tilt error present in the estimated value of the local slope derived from the Z measurement.

[0029] When the same measurement system is used to make subsequent measurements on a sample wafer, the induced wafer tilt error present in the estimated value of the local slope derived from the Z measurement is the same as the wafer tilt error captured by the wafer orientation correction value. When the wafer orientation correction value is subtracted from the local slope derived from the Z measurement of the sample wafer, the wafer tilt can be accurately estimated at each measurement site. In a preferred embodiment, the sample wafer includes one or more thick film structures, one or more patterned structures, or both.

[0030] Figure 1 An exemplary metrology system 100 for performing structural feature measurements of semiconductor devices is depicted. Figure 1 , the metrology system 100 is configured as a broadband spectroscopic ellipsometer. However, in general, the metrology system 100 can be configured as a spectroscopic reflectometer, a scatterometer, a single wavelength ellipsometer, a beam profile reflectometer, or any combination thereof.

[0031] The metrology system 100 includes an illumination source 110 that generates an illumination beam 117 that is incident on a wafer 120. In some embodiments, the illumination source 110 is a broadband illumination source that emits illumination light in the ultraviolet spectrum, the visible spectrum, and the infrared spectrum. In one embodiment, the illumination source 110 is a laser sustained plasma (LSP) light source (also referred to as a laser driven plasma source). The pump laser of the LSP light source can be continuous wave or pulsed. Spanning the wavelength range from 150 nanometers to 2000 nanometers, the laser driven plasma source can generate significantly more photons than a xenon lamp. The illumination source 110 can be a single light source or a combination of multiple broadband or discrete wavelength light sources. The light generated by the illumination source 110 includes a continuous spectrum or a portion of a continuous spectrum from ultraviolet to infrared (e.g., vacuum ultraviolet to mid-infrared). In general, the illumination light source 110 can include a supercontinuum laser source, an infrared helium-neon laser source, an arc lamp, or any other suitable light source.

[0032] In yet another aspect, the amount of illumination light is broadband illumination light comprising a wavelength range spanning at least 500 nanometers. In one example, the broadband illumination light comprises wavelengths below 250 nanometers and wavelengths above 750 nanometers. Generally, the broadband illumination light comprises wavelengths between 120 nanometers and 3,000 nanometers. In some embodiments, broadband illumination light having wavelengths exceeding 3,000 nanometers may be employed.

[0033] like Figure 1 , metrology system 100 includes an illumination subsystem configured to direct illumination light 117 to one or more structures formed on a wafer 120 at an incident angle α, the incident angle being referenced to an axis normal to a surface of the wafer 120 (e.g., Figure 1 ) is defined by the Z axis depicted in . The illumination subsystem is shown to include a light source 110, one or more optical filters 111, a polarizing component 112, a field stop 113, an aperture stop 114, and an illumination optical device 115. One or more optical filters 111 are used to control the light level, spectral output, or both from the illumination subsystem. In some examples, one or more multi-zone filters are used as optical filters 111. The polarizing component 112 produces the desired polarization state emitted from the illumination subsystem. In some embodiments, the polarizing component is a polarimeter, a compensator, or both, and may include any suitable commercially available polarizing component. The polarizing component may be fixed, rotatable to different fixed positions, or continuously rotated. Although Figure 1The illumination subsystem depicted in FIG. 1 includes one polarizing component, but the illumination subsystem may include more than one polarizing component. Field stop 113 controls the field of view (FOV) of the illumination subsystem and may include any suitable commercially available field stop. Aperture stop 114 controls the numerical aperture (NA) of the illumination subsystem and may include any suitable commercially available aperture stop. Light from illumination source 110 is directed through illumination optics 115 to focus on one or more structures ( Figure 1 The illumination subsystem may include an optical filter 111, a polarizing element 112, a field stop 113, an aperture stop 114, and illumination optics 115 of any type and arrangement known in the art of spectroscopic ellipsometry, reflectometry, and scatterometry.

[0034] like Figure 1 , as the light beam propagates from illumination source 110 to wafer 120, illumination light beam 117 passes through optical filter 111, polarizing element 112, field stop 113, aperture stop 114, and illumination optics 115. Light beam 117 illuminates a portion of wafer 120 above measurement spot 116.

[0035] The metrology system 100 also includes a collection optics subsystem configured to collect light generated by the interaction between the one or more structures and the incident illumination beam 117. The collected light beam 127 is collected from the measurement spot 116 by the collection optics 122. The collected light 127 passes through the collection aperture stop 123, the polarizing element 124, and the field stop 125 of the collection optics subsystem.

[0036] The collection optics 122 include any suitable optical elements for collecting light from one or more structures formed on the wafer 120. The collection aperture stop 123 controls the NA of the collection optics subsystem. The polarizing element 124 analyzes the desired polarization state. The polarizing element 124 is a polarimeter or compensator. The polarizing element 124 can be fixed, rotatable to different fixed positions, or continuously rotating. Although Figure 1 The collection subsystem depicted in FIG. 1 includes one polarizing element, but the collection subsystem may include more than one polarizing element. The collection field stop 125 controls the field of view of the collection subsystem. The collection subsystem acquires light from the wafer 120 and directs the light through the collection optics 122 and the polarizing element 124 to be focused on the collection field stop 125. In some embodiments, the collection field stop 125 is used as a spectrometer slit of a spectrometer of the detection subsystem. In other embodiments, the collection field stop 125 may be located at or near the spectrometer slit of the spectrometer of the detection subsystem.

[0037] The collection subsystem may include collection optics 122, aperture stop 123, polarizing element 124, and field stop 125 of any type and arrangement known in the art of spectroscopic ellipsometry, reflectometry, and scatterometry.

[0038] exist Figure 1 In the embodiment depicted in , the collection optics subsystem directs light to a spectrometer 126. The spectrometer 126 generates an output in response to light collected from one or more structures illuminated by the illumination subsystem. In one example, the detectors of the spectrometer 126 are charge coupled devices (CCDs) sensitive to ultraviolet and visible light (e.g., light with wavelengths between 190 nanometers and 860 nanometers). In other examples, one or more of the detectors of the spectrometer 126 are photodetector arrays (PDAs) sensitive to infrared light (e.g., light with wavelengths between 950 nanometers and 2500 nanometers). However, in general, other detector technologies (e.g., position sensitive detectors (PSDs), infrared detectors, photovoltaic detectors, etc.) are contemplated. Each detector converts incident light into an electrical signal indicative of the spectral intensity of the incident light. In general, the spectrometer 126 generates an output signal 128 indicative of the spectral response of the measured structure to the illumination light.

[0039] The metrology system 100 also includes a computing system 130 configured to receive a signal 128 indicative of a measured spectral response of a structure of interest and estimate a value 129 of one or more parameters of interest (e.g., film thickness, critical dimension, overlay, etc.) characterizing one or more measured structures based on the measured spectral response. As described herein, the signal 128 indicative of the measured spectral response of the structure of interest is collected after the orientation of the semiconductor wafer 120 is corrected by the wafer stage 140 to minimize local wafer tilt at the measurement site.

[0040] Wafer stage 140 positions wafer 120 relative to ellipsometer subsystem 101. In some embodiments, wafer stage 140 moves wafer 120 in the XY plane by combining two orthogonal translational movements (e.g., movements in the X direction and the Y direction) to position wafer 120 relative to the ellipsometer. In some embodiments, wafer stage 140 is configured to control the position of wafer 120 relative to illumination provided by the optical ellipsometer in six degrees of freedom. In one embodiment, wafer stage 140 is configured to control the azimuth angle AZ of wafer 120 relative to illumination provided by the optical ellipsometer by rotating about the z-axis. In general, sample positioning system 140 may include any suitable combination of mechanical elements for achieving desired linear and angular positioning performance, including but not limited to goniometer stages, magnetically levitated stages, hexapod stages, angle stages, and linear stages. Computing system 130 is communicatively coupled to wafer stage 140 and communicates motion command signals 141 to wafer stage 140. In response, wafer stage 140 positions wafer 120 relative to the ellipsometer according to the motion control commands.

[0041] Figure 2 It is a graphic description Figure 1 Another diagram of the metering system 100 is depicted in FIG. Figure 2 Elements of ellipsometer 101 are not included to enable a more visible illustration of wafer stage 140 .

[0042] like Figure 2 As depicted in the wafer coordinate system {X W ,Y W ,Z W} is attached to the wafer 120. Z W The axis is normal to the surface of the wafer 120 at the measurement spot 116. W Axis and Y W The axes are orthogonal to each other and are aligned with the surface of the wafer 120. The wafer 120 is removably attached to the wafer chuck 147, for example, using a vacuum chuck, an electrostatic chuck, an edge grip chuck, or the like.

[0043] like Figure 2 As depicted in FIG. 1 , wafer stage 140 includes base frame 142, X stage 143, Y stage 144, and a three-degree-of-freedom wafer stage supporting wafer chuck 147. In some embodiments, base frame 142 is mechanically coupled to a machine frame to which a measurement subsystem (e.g., ellipsometer 101) is also mechanically coupled. X stage 143 is mechanically constrained by a bearing assembly (e.g., mechanical bearings, magnetic bearings, or air bearings) to move in the X W The X-stage 143 is freely movable relative to the base frame 142 in the X direction. One or more actuators (e.g., linear motors (not shown)) are used to control the X-stage 143 to move freely in the X direction.W Similarly, the Y stage 144 is mechanically constrained by a bearing assembly (e.g., a mechanical bearing, a magnetic bearing, or an air bearing) to move in the Y direction relative to the base frame 142. W The Y stage 144 is freely movable in the Y direction relative to the X stage 143. One or more actuators (e.g., linear motors (not shown)) are used to control the Y stage 144 to move freely in the Y direction relative to the X stage 143. W The position relative to the X stage 143 in the direction. Figure 1 and 2 As depicted in FIG. 1 , the Y stage 144 is stacked on the X stage 143. The X stage 143 and the Y stage 144 together provide long travel capability, i.e., the X W Direction and X W The working space of at least 300 mm in the direction of the X stage 143 and the Y stage 144 is controlled to locate any position on the surface of the wafer 120 below the measurement spot 116 defined by the optical elements of the ellipsometer 101.

[0044] exist Figure 1 and 2 In the embodiment depicted in FIG. 1 , the three-degree-of-freedom wafer stage includes actuators 145A to 145C, such as voice coil motors, piezoelectric motors, etc. Each of the actuators 145A to 145C is mechanically coupled between the wafer chuck 147 and the Y stage 144. The extension direction of each of the actuators 145A to 145C is substantially parallel to the Z W The axis is the axis normal to the surface of the wafer 120, which is clamped to the wafer chuck 147. Figure 1 and 2 As depicted in FIG. 1 , actuators 145A to 145C are arranged at X W Direction and Y W In this configuration, the movement of actuators 145A to 145C is coordinated to independently control the position of wafer 120 in the Z direction, the position of wafer 120 with respect to the X direction, and the W The orientation of the Y axis and the wafer 120 with respect to W The orientation of the axis is determined by the actuators 145A to 145C and {X W ,Y W ,Z W} coordinate systems, represented by the geometric distance between the simple kinematic transformation, in {R x ,R x The movement of the wafer 120 specified in {R , Z} coordinates is mapped to the movement of the actuators 145A to 145C. In this way, the specified {R x ,R xThe control commands 141 for movement in the ,Z} coordinate are easily mapped to the movement of each actuator. The movement of each actuator is implemented at the actuator level by one or more motion controllers of the wafer stage 140.

[0045] Similarly, position measurement devices 146A to 146C (eg, linear encoders, linear variable differential transformers, inductance probes, capacitance probes, interferometers, etc.) are provided at X W Direction and Y W In this configuration, the position of the wafer 120 in the Z direction relative to the Y stage 144, the position of the wafer 120 in the X direction relative to the Y stage 144, W The orientation of the Y axis and the wafer 120 with respect to W The orientation of the axis is captured by the position measuring devices 146A to 146C. x ,R y , Z} coordinate systems, the displacements captured by the position measuring devices 146A to 146C are mapped to the coordinates represented by {R x ,R y , Z} coordinates. In this way, the displacements measured by the position measurement devices 146A to 146C can be easily mapped to {R x ,R y , Z} coordinates. The displacements are communicated to computing system 130 for tilt correction as described herein. In some embodiments, the displacements are communicated to one or more motion controllers of wafer stage 140 to implement a feedback positioning controller that positions wafer 120 in a desired position and orientation based on measurements made by position measurement devices 146A-146C.

[0046] In some embodiments, the position measurement devices 146A to 146C are co-located with the actuators 145A to 145C. Each of the position sensors is located in close proximity to the corresponding actuator and thus measures the displacement of each corresponding actuator in the extension direction. However, in general, the position measurement devices 146A to 146C may be located in a different location from the actuators 145A to 145C.

[0047] Figure 2 The wafer stage 140 illustrated in FIG. 1 includes a wafer stage 140 having three actuators to generate Z at three different positions. W The wafer stage of the wafer 120 is used to control the wafer 120 with three degrees of freedom by applying forces in the Z direction. However, in general, the wafer stage may include more than three actuators to generate Z and Z forces at more than three positions. WThe wafer 120 is controlled in three degrees of freedom by applying forces in the directions of the wafer 120. Although such a configuration is over-constrained, it may be desirable to include more than three actuators to limit the force requirements on any one actuator, stabilize bending modes in the wafer chuck 147, operate in conjunction as part of a magnetically suspended wafer chuck 147, and the like.

[0048] The metrology system 100 also includes a wafer orientation measurement subsystem 150 coupled to the same machine frame as the measurement subsystem (e.g., ellipsometer 101). Figure 1 and 2 1, the wafer orientation measurement subsystem includes an optical illumination source 151 configured to generate an optical illumination beam 154 directed to the surface of the wafer 120 at a measurement spot 116. Light 155 reflected from the surface of the wafer 120 in response to the optical illumination beam 154 is focused by focusing optics 153 onto an optical detector 152. The optical detector 152 generates a signal 156 indicating the orientation of the wafer 120 relative to the measurement subsystem (e.g., ellipsometer 101) at the measurement spot 116 on the surface of the wafer 120 based on the incident location of the light 155 on the optical detector 152. The measured orientation is the in-plane orientation of the wafer 120, for example, in degrees with respect to X. W Axis and Y W The angular position of the axis expresses the orientation, by definition, of the X W Axis and the Y W The axis lies in the same plane as the surface of the wafer. W The rotational displacement of the axis is not captured by the wafer orientation measurement subsystem 150 .

[0049] By moving the wafer 120 under the wafer orientation measurement subsystem 150 so that the measurement spot 116 is incident at selected locations across the surface of the wafer 120, the wafer orientation measurement subsystem 150 measures the in-plane orientation of the wafer 120 at each location and generates an in-plane orientation measurement map corresponding to the selected location, for example, about the in-plane axis X. W and Y W orientation.

[0050] In some embodiments, optical illumination source 151 is a light source based on a light emitting diode (LED). In other embodiments, optical illumination source 151 is a light source based on a laser. In some embodiments, optical illumination source is a light source based on a xenon arc lamp. In some of these embodiments, the optical illumination source is the same illumination source employed by the measurement subsystem, for example, illumination source 110 of ellipsometer 101. In some embodiments, optical detector 152 is a quadrant unit light receiver. However, in general, any suitable optical illumination source and optical detector may be employed to measure the in-plane orientation of wafer 120 relative to the measurement subsystem at measurement spot 116 on the surface of wafer 120.

[0051] As described above, using optical detectors, such as quadrant cell photoreceivers, to measure the in-plane orientation of the wafer 120 is sensitive to structures fabricated on the surface of the wafer 120 , particularly high aspect ratio structures and thick films.

[0052] The metrology system 100 also includes a wafer normal position sensor subsystem 160 coupled to the same machine frame as the measurement subsystem (e.g., ellipsometer 101). Figure 1 and 2 1, the wafer normal position sensor subsystem 160 includes an optical illumination source 161 configured to generate an optical illumination beam 164, which is directed to the surface of the wafer 120 at the measurement spot 116 via an optical element 163. Light 165 reflected from the surface of the wafer 120 in response to the optical illumination beam 164 is focused onto an optical detector 162. The optical detector 162 generates a signal 166 indicating the normal position of the wafer 120 relative to the measurement subsystem (e.g., the ellipsometer 101) based on the incident location of the light 165 on the optical detector 162 at the measurement spot 116 on the surface of the wafer 120. Each normal position value is a value of the normal position of the wafer 120 in a direction normal to the surface of the wafer 120 (i.e., along the Z direction). W axis) relative to the position of the measurement subsystem (e.g., ellipsometer 101).

[0053] By moving the wafer 120 under the wafer normal position sensor subsystem 160 so that the measurement spot 116 is incident at selected positions across the surface of the wafer 120, the wafer normal position sensor subsystem 160 measures the normal position of the wafer 120 at each point and generates a normal position measurement map corresponding to the selected position.

[0054] In some embodiments, the optical detector of the wafer normal position sensor subsystem is a dual-element photoreceiver. In some embodiments, the optical detector of the wafer normal position sensor subsystem 160 is a position sensitive detector comprising an array of photosensitive elements. In some embodiments, the optical detector of the wafer normal position sensor subsystem 160 is an interferometer. In some embodiments, the optical illumination source (e.g., illumination source 161) of the wafer normal position sensor subsystem is the same illumination source used to provide illumination to the measurement subsystem, e.g., illumination source 110 of the ellipsometer 101.

[0055] In some embodiments, the wafer normal position sensor subsystem is an element of an autofocus subsystem of a semiconductor measurement system, such as metrology system 100. The autofocus subsystem is configured to position a semiconductor wafer in a focal plane of a measurement subsystem (eg, ellipsometer 101).

[0056] In some other embodiments, the wafer normal position sensor subsystem includes a linear encoder subsystem or a grid encoder subsystem.

[0057] As described above, using an optical detector, such as a dual-unit photoreceiver, to measure the normal position of the wafer 120 is insensitive to structures fabricated on the surface of the wafer 120 , particularly aspect ratio structures and thick films.

[0058] In one aspect, a measurement of wafer tilt at a measurement spot based on a local slope derived from a neighboring Z measurement is corrected by a wafer orientation correction map. The corrected wafer tilt measurement accurately estimates the orientation change of the wafer required to orient the surface of the wafer at the measurement spot to be oriented in a desired plane relative to the measurement subsystem. In one example, the measurement subsystem is represented by an illumination source and a detector of the measurement subsystem.

[0059] In yet another aspect, a wafer orientation correction value at each wafer position is determined based on the difference between the orientation of the calibration wafer relative to the measurement subsystem as measured by the wafer orientation measurement subsystem at each site and the corresponding estimated value of the local slope derived from the Z measurement at each site and adjacent sites.

[0060] In one example, the wafer orientation measurement subsystem 150 is used to measure the in-plane orientation of the calibration wafer relative to the ellipsometer 101 at selected locations on the surface of the calibration wafer to generate an in-plane orientation measurement map corresponding to the selected locations.

[0061] Figure 3 is a diagram illustrating the top bare silicon wafer over the entire surface of the wafer Figure 2 Y W170. This corresponds to a rotational displacement in and out of the plane of incidence of the ellipsometer 101. Figure 3 As described in W The axis orientation varies by 30 arc seconds or more. These variations indicate non-planarity of the wafer stage and wafer chuck.

[0062] In yet another aspect, wafer normal position sensor subsystem 160 is used to measure the normal position of the calibration wafer at selected locations on the surface of the calibration wafer relative to ellipsometer 101. In this manner, wafer normal position sensor subsystem 160 generates a map corresponding to normal position measurements for the selected locations.

[0063] Figure 4 is a diagram illustrating the top bare silicon wafer measured at a large number of sites across the wafer surface along Z W A graph of the normal position of the axis 171. Figure 4 As depicted, along Z W The normal position of the axis can vary by as much as 80 microns. These variations indicate non-planarity of the wafer stage, wafer chuck, and wafer.

[0064] In yet another aspect, a value characterizing a local slope associated with each of the selected sites across the surface of the calibration semiconductor wafer is estimated based on the normal position value. More specifically, at each selected site, gradient values ​​in the X and Y directions are calculated based on the normal position value of the selected site and the normal position values ​​adjacent to the selected site. The gradient value expresses the change in normal position (along the Z direction) divided by the change in lateral position (along the X and Y directions).

[0065] Figure 5 Is a graphic description and cross reference Figure 4 A graph 172 of the calculated local slopes associated with each of the selected sites of the surface of the top bare silicon wafer is depicted.

[0066] In yet another aspect, a wafer orientation correction map is generated based on a difference between an estimated orientation of the calibration semiconductor wafer relative to the measurement subsystem and an estimated value characterizing a local slope at each of selected locations across a surface of the calibration semiconductor wafer.

[0067] At each selected location, the difference between the estimated orientation of the calibration semiconductor wafer as measured by the wafer orientation measurement subsystem 150 and the value of the local slope derived from the normal position measurement is calculated. In this manner, the map of the wafer orientation measurement subsystem 150 produces a map of wafer orientation correction values ​​corresponding to the selected locations.

[0068] As illustrated by equation (1), WAxis and Y W A set of wafer orientation correction values ​​{R XW ,R YW} CORR is calculated as the Z measurement of the calibration wafer with respect to X W Axis and Y W Local slope of the axis CAL {R XW ,R YW} Z with respect to X as measured by the optical tilt sensor W Axis and Y W Axis calibration and wafer orientation CAL {R XW ,R YW} TILT The difference between.

[0069] {R Xw , R Yw )} CORR = CAL {R Xw , R Yw} Z - CAL {R Xw , R Yw} TITL (1)

[0070] R XW and R XY are vectors of the same length. Each pair of wafer orientation correction values ​​corresponds to a different selected location on the wafer. Therefore, {R XW ,R YW} CORR is a graph of wafer orientation correction values ​​corresponding to selected sites.

[0071] In yet another aspect, the wafer normal position sensor subsystem 160 is used to measure the normal position of the sample wafer at selected locations on the surface of the sample wafer relative to the ellipsometer 101. In this manner, the wafer normal position sensor subsystem 160 generates a map corresponding to the normal position measurements for the selected locations.

[0072] In yet another aspect, a value characterizing a local slope associated with each of the selected sites across the surface of the sample semiconductor wafer is estimated based on the normal position value.

[0073] In yet another aspect, for each selected location across the surface of the sample wafer, a corrected value for wafer orientation is determined by subtracting the wafer orientation correction value corresponding to the selected location from the local slope calculated at the selected location. In this manner, measurement errors induced by height variations are removed from the local slope values ​​calculated at each selected location.

[0074] As illustrated by equation (2), the X associated with the sample wafer is W Axis and Y W A set of corrected orientation values ​​for the axis S {R XW ,R YW} is calculated as the X-dependent Z-measurement derived from the sample wafer. W Axis and Y W The local slope of the axis and the wafer orientation correction value {R XW ,R YW} CORR The difference between.

[0075] S {R Xw , R Yw}= S {R Xw , R Yw} Z -{R Xw , R Yw ) CORR (2)

[0076] If the wafer orientation correction value directly corresponds to the selected site, then the wafer orientation correction value is used directly. However, if there is no wafer orientation correction value directly corresponding to the selected site, then interpolation among the wafer orientation correction values ​​corresponding to wafer sites adjacent to the selected site is used to calculate the wafer orientation correction value.

[0077] like Figure 1 and 2 As depicted in FIG. 1 , wafer stage 140 is configured to correct for a desired orientation in multiple degrees of freedom (including with respect to X). W The rotational freedom of the axis and about Y W The wafer 120 is positioned on the axis of rotational freedom (rotational freedom about the axis) to minimize wafer tilt at the measurement spot 116.

[0078] In yet another aspect, the corrected wafer orientation value is communicated to wafer stage 140, and wafer stage 140 adjusts the orientation of the sample wafer based on the corrected wafer orientation value to orient the surface of the wafer at the measurement spot in a desired in-plane orientation relative to the measurement subsystem.

[0079] In some embodiments, active local tilt correction in a spectroscopic ellipsometry, a single wavelength spectroscopic ellipsometry, or a beam profile reflectometer is accomplished by manipulating the orientation of the wafer being measured based on active local tilt measurements. In some of these embodiments, the local tilt is measured and the wafer stage adjusts the orientation of the wafer so that the wafer is aligned with respect to X. W Axis and Y W The tilt of the X axis is eliminated. In some other embodiments, the wafer stage adjusts the orientation of the wafer based on a local wafer orientation correction map. The local wafer orientation correction map specifies the desired change in the orientation of the wafer so that the tilt of the X axis is eliminated based on the location of the measurement spot on the wafer. W Axis and Y W The wafer stage adjusts the orientation of the wafer based on the local wafer orientation correction values ​​corresponding to the measurement locations on the wafer.

[0080] Figure 6 The diagram illustrates a method suitable for use by a metering system such as the present invention. Figure 1 and 2 1. In one aspect, it should be appreciated that the data processing blocks of method 200 may be implemented via pre-programmed algorithms that are executed by one or more processors of computing system 130 or any other general purpose computing system. It should be appreciated herein that specific structural aspects of metrology system 100 are not meant to be limiting and should be interpreted merely as illustrative.

[0081] In block 201, normal position values ​​are measured at a first plurality of locations across a surface of a semiconductor wafer. Each normal position value is a position of the semiconductor wafer relative to an illumination source and a detector of a semiconductor measurement system in a direction normal to the surface of the semiconductor wafer.

[0082] In block 202 , a value characterizing a local slope associated with each of a first plurality of sites across a surface of a semiconductor wafer is estimated based on normal position values ​​at the first plurality of sites.

[0083] In block 203 , a desired orientation correction of the semiconductor wafer at a measurement site of the semiconductor wafer is estimated based on the value characterizing the local slope and the value of the wafer orientation correction map.

[0084] Exemplary measurement techniques that may benefit from wafer tilt correction as described herein include, but are not limited to, optical spectroscopic tools such as Miller ellipsometers, spectroscopic ellipsometers, single wavelength ellipsometers, spectroscopic reflectometers, beam profile reflectometers, imaging reflectometers, imaging spectroscopic reflectometers, polarized spectroscopic imaging reflectometers, scanning reflectometer systems, systems with two or more reflectometers capable of parallel data acquisition, systems with two or more spectroscopic reflectometers capable of parallel data acquisition, systems with two or more polarized spectroscopic reflectometers capable of parallel data acquisition, systems with two or more polarized spectroscopic reflectometers capable of serial data acquisition without moving the wafer stage or without moving any optical elements or the reflector stage. Systems, imaging spectrometers, imaging systems with wavelength filters, imaging systems with long pass wavelength filters, imaging systems with short pass wavelength filters, imaging systems without wavelength filters, interferometer imaging systems, imaging ellipsometers, imaging spectroscopic ellipsometers, scanning ellipsometer systems, systems with two or more ellipsometers capable of parallel data acquisition, systems with two or more ellipsometers capable of serial data acquisition without moving the wafer stage or without moving any optical elements or ellipsometer stages, Michelson interferometers, Mach-Zehnder interferometers, Sagnac interferometers, scanning incidence angle systems, scanning azimuth angle systems, wafer inspection systems, x-ray based metrology systems, and electron beam metrology tools, etc. In addition, in general, measurement data collected by different measurement techniques and analyzed according to the methods described herein can be collected from multiple tools rather than from one tool integrating multiple techniques.

[0085] In yet another embodiment, system 100 may include one or more computing systems 130 used to perform measurements according to the methods described herein. One or more computing systems 130 may be communicatively coupled to detectors 126, 152, and 162. In one aspect, one or more computing systems 130 are configured to receive measurement data 128 associated with measurements of a metrology target disposed on sample 120.

[0086] It should be appreciated that the various steps described throughout this disclosure may be performed by a single computer system 130 or (alternatively) multiple computer systems 130. In addition, different subsystems of the system 100 (e.g., detectors 126, 152, and 162, wafer stage 140, etc.) may include computer systems suitable for performing at least a portion of the steps described herein. Therefore, the foregoing description should not be construed as limiting the present invention but is merely illustrative. In addition, one or more computing systems 130 may be configured to perform any (any) other steps of any of the method embodiments described herein.

[0087] Additionally, computer system 130 may be communicatively coupled to detectors 126, 152, and 162 in any manner known in the art. For example, one or more computing systems 130 may be coupled to computing systems associated with detectors 126, 152, and 162. In another example, detectors 126, 152, and 162 may be directly controlled by a single computer system coupled to computer system 130.

[0088] The computer system 130 of the metrology system 100 may be configured to receive and / or collect data or information from the subsystems of the system (e.g., detectors 126, 152, and 162, etc.) via a transmission medium that may include wired and / or wireless portions. In this manner, the transmission medium may serve as a data link between the computer system 130 and the other subsystems of the system 100.

[0089] The computer system 130 of the metrology system 100 may be configured to receive and / or collect data or information (e.g., measurements, modeling inputs, modeling results, etc.) from other systems via a transmission medium that may include wired and / or wireless portions. In this manner, the transmission medium may be used as a data link between the computer system 130 and other systems (e.g., memory onboard the metrology system 100, external memory, reference measurement sources, or other external systems). For example, the computing system 130 may be configured to receive measurement data from a storage medium (i.e., memory 132 or external memory) via a data link. For example, measurements obtained using the detectors 126, 152, and 162 may be stored in a permanent or semi-permanent memory device (e.g., memory 132 or external memory). In this regard, the measurements may be imported from the onboard memory or from an external memory system. In addition, the computer system 130 may send data to other systems via a transmission medium. For example, a measurement model determined by the computer system 130 or an estimated value of one or more parameters of interest 129 may be communicated and stored in an external memory. In this regard, the measurement results may be exported to another system.

[0090] The computing system 130 may include, but is not limited to, a personal computer system, a cloud-based computer system, a mainframe computer system, a workstation, an image computer, a parallel processor, or any other device known in the art. In general, the term "computing system" may be broadly defined to encompass any device having one or more processors that execute instructions from a memory medium.

[0091] Program instructions 134 implementing methods such as those described herein may be transmitted via a transmission medium such as a wire, cable, or wireless transmission link. Figure 1 and 2As illustrated in FIG, program instructions 134 stored in memory 132 are transferred to processor 131 via bus 133. Program instructions 134 are stored in a computer readable medium, such as memory 132. Exemplary computer readable media include read-only memory, random access memory, magnetic or optical disks, or tape.

[0092] In yet another aspect, a metrology system for performing measurements as described herein (e.g., metrology system 100) includes an infrared optical measurement system. In these embodiments, metrology system 100 includes an infrared light source (e.g., an arc lamp, an electrodeless lamp, a laser sustained plasma (LSP) source, or a supercontinuum source). Infrared supercontinuum laser sources are superior to conventional lamp sources due to the higher available power and brightness in the infrared region of the spectrum. In some examples, the power provided by the continuum laser enables measurement of stacked structures having opaque thin film layers.

[0093] A potential problem in overlay measurements is that light is not able to penetrate enough to the bottom grating. In many examples, there is a non-transparent (i.e., opaque) film layer between the top and bottom gratings. Examples of these opaque film layers include amorphous carbon, tungsten silicide (WSI x ), tungsten, titanium nitride, amorphous silicon, and other metal and non-metal layers. Typically, illumination light with wavelengths limited to the visible range and below (e.g., between 250nm and 700nm) does not penetrate to the bottom grating. However, illumination light in the infrared spectrum and above (e.g., greater than 700nm) typically penetrates the opaque layer more efficiently.

[0094] In yet another aspect, the measurements described herein can be used to provide active feedback to process tools (e.g., lithography tools, etching tools, deposition tools, etc.). For example, film thickness values, critical dimensions, overlays, etc. determined using the methods described herein can be communicated to the lithography tool to adjust the lithography system to achieve the desired output. In a similar manner, etching parameters (e.g., etching time, diffusion rate, etc.) or deposition parameters (e.g., time, concentration, etc.) can be included in the measurement model to provide active feedback to the etching tool or deposition tool, respectively.

[0095] In general, the systems and methods described herein may be implemented as part of an off-line or on-tool measurement process.

[0096] 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.), a critical dimension between any two or more structures (e.g., a distance between two structures), and a displacement between two or more structures (e.g., an overlay displacement between overlaid grating structures, etc.). The structure may include a three-dimensional structure, a patterned structure, an overlaid structure, etc.

[0097] As described herein, the term "critical dimension application" or "critical dimension measurement application" includes any critical dimension measurement.

[0098] As described herein, the term "metrology system" includes any system used, at least in part, to characterize a sample in any aspect, including measurement applications such as critical dimension metrology, overlay metrology, focus / dose metrology, and composition metrology. However, such terms of art do not limit the scope of the term "metrology system" as described herein. Additionally, the metrology system 100 may be configured to perform measurements on patterned wafers and / or unpatterned wafers. The metrology system may be configured as an LED inspection tool, an edge inspection tool, a backside inspection tool, a macro inspection tool, or a multi-mode inspection tool (involving data from one or more platforms simultaneously), as well as any other metrology or inspection tool that benefits from correction of wafer tilt.

[0099] Various embodiments of semiconductor processing systems (e.g., inspection systems or lithography systems) that can be used to process samples are described herein. The term "sample" is used herein to refer to a wafer, a mask, or any other sample that can be processed (e.g., printed or inspected for defects) by means known in the art.

[0100] As used herein, the term "wafer" generally refers to a substrate formed of semiconductor or non-semiconductor materials. Examples include, but are not limited to, single crystal silicon, gallium arsenide, and indium phosphide. Such substrates are commonly found and / or processed in semiconductor fabrication 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 die having repeatable pattern features.

[0101] A "reticle" may be a reticle at any stage of a 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 having substantially formed thereon opaque areas configured in a pattern. For example, the substrate may comprise a glass material such as amorphous SiO2. The reticle may be deposited on top of a photoresist-covered wafer during the exposure step of a photolithography process so that the pattern on the reticle may be transferred to the photoresist.

[0102] The one or more layers formed on a wafer may be patterned or unpatterned. For example, a wafer may include multiple dies, each having repeatable pattern features. The formation and processing of such material layers may ultimately produce a finished device. Many different types of devices may be formed on a wafer, and the term wafer as used herein is intended to encompass a wafer having any type of device known in the art fabricated thereon.

[0103] In one or more exemplary embodiments, the functions described can be implemented by hardware, software, firmware or any combination thereof. If implemented in software, the functions can be stored on a computer-readable medium or transmitted via a computer-readable medium as one or more instructions or codes. Computer-readable media include both computer storage media and communication media that facilitate the transfer of a computer program from one place to another. Storage media can be any available media that can be accessed by a general or special-purpose computer. By way of example and not limitation, such computer-readable media may include: RAM, ROM, EEPROM, CD-ROM or other optical disk storage devices, magnetic disk storage devices or other magnetic storage devices, or any other media that can be used to carry or store desired program code components in the form of instructions or data structures and can be accessed by a general or special-purpose computer or a general or special-purpose processor. And, any connection can be properly referred to as a computer-readable medium. For example, if the software is transmitted from a website, server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then 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 disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with the aid of lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0104] Although some specific embodiments are described above for instructional purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. Therefore, 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 semiconductor measurement system, comprising: an illumination source configured to generate an amount of illuminating radiation incident on a semiconductor wafer having one or more structures fabricated on a surface of the semiconductor wafer; a detector configured to detect an amount of radiation collected from the semiconductor wafer in response to the incident amount of illuminating radiation; a wafer normal position sensor subsystem configured to measure normal position values ​​at a first plurality of locations across the surface of the semiconductor wafer, wherein each normal position value is a position of the semiconductor wafer relative to the illumination source and the detector in a direction normal to the surface of the semiconductor wafer; A computing system configured to: estimating a value characterizing a local slope associated with each of the first plurality of sites across the surface of the semiconductor wafer based on the normal position values ​​at the first plurality of sites; and A desired orientation correction of the semiconductor wafer at a measurement site of the semiconductor wafer is estimated based on the value characterizing the local slope and the value of a wafer orientation correction map.

2. The semiconductor measurement system according to claim 1, further comprising: A sample positioning system is configured to orient the semiconductor wafer about a first axis and a second axis at the measurement site based on the desired orientation correction, wherein the first axis and the second axis are aligned with the surface of the semiconductor wafer and the second axis is orthogonal to the first axis.

3. The semiconductor measurement system of claim 2, wherein the computing system is further configured to: After orienting the semiconductor wafer about the first axis and the second axis based on the desired orientation correction, a value of a parameter of interest characterizing the one or more structures is estimated based on a collected amount of radiation detected at a measurement spot.

4. The semiconductor measurement system according to claim 1, further comprising: Wafer orientation measurement subsystem, comprising: a first optical illumination source configured to generate an optical illumination beam directed onto a surface of a calibration semiconductor wafer; and a first optical detector configured to detect light reflected from the calibration semiconductor wafer in response to the incident optical illumination beam, wherein the computing system is further configured to: An orientation of the calibration semiconductor wafer relative to the illumination source and the detector at each of a second plurality of locations across the surface of the calibration semiconductor wafer is estimated based on an incidence location of the light reflected from the calibration semiconductor wafer on the first optical detector at each of a second plurality of locations across the surface of the calibration semiconductor wafer.

5. The semiconductor measurement system according to claim 4, wherein the wafer normal position sensor subsystem is further configured to measure normal position values ​​at the second plurality of locations across the surface of the calibration semiconductor wafer, wherein each normal position value is a position of an unpatterned semiconductor wafer relative to the illumination source and the detector in a direction normal to the surface of the calibration semiconductor wafer, and The computing system is further configured to: estimating a value characterizing a local slope associated with each of the second plurality of sites across the surface of the calibration semiconductor wafer based on the normal position values ​​at the second plurality of sites; and The wafer orientation correction map is generated based on a difference between the estimated values ​​characterizing the local slope at each of the second plurality of locations across the surface of the calibration semiconductor wafer and the estimated orientation of the calibration semiconductor wafer relative to the illumination source and the detector.

6. The semiconductor measurement system of claim 1, wherein the wafer normal position sensor subsystem is an element of an autofocus subsystem of the semiconductor measurement system, the element configured to position the semiconductor wafer in a focal plane of the illumination source and the detector.

7. The semiconductor measurement system of claim 1, wherein the illumination source and the detector are elements of any of a single wavelength ellipsometer, a spectroscopic ellipsometer, a beam profile reflectometer, an x-ray based scatterometer, and a spectroscopic reflectometer.

8. The semiconductor measurement system of claim 1, wherein the one or more structures fabricated on the surface of the semiconductor wafer comprises one or more film structures, one or more critical dimension structures, or a combination thereof.

9. The semiconductor measurement system of claim 4, wherein the optical illumination source is a light emitting diode (LED) based light source, a laser based light source, or a xenon based light source.

10. The semiconductor measurement system of claim 4, wherein the optical detector is a quadrant unit photoreceiver.

11. The semiconductor measurement system of claim 1 , wherein the wafer normal position sensor subsystem comprises: an optical illumination source configured to generate an amount of optical illumination directed toward the surface of the semiconductor wafer; and an optical detector configured to detect light reflected from the semiconductor wafer in response to the incident optical illumination, wherein the computing system is further configured to estimate the normal position values ​​at the first plurality of locations across the surface of the semiconductor wafer based on an incidence location on the optical detector of the light reflected from the semiconductor wafer at each of the first plurality of locations across the surface of the semiconductor wafer.

12. The semiconductor measurement system according to claim 11, wherein the optical detector is a dual-element light receiver, a position sensitive detector including an array of photosensitive elements, or an interferometer.

13. The semiconductor measurement system of claim 11, wherein the illumination source and the optical illumination source are the same illumination source.

14. The semiconductor measurement system of claim 2, wherein the sample positioning system comprises: a dual-axis wafer stage configured to position the semiconductor wafer relative to the illumination source and the detector at any location on the surface of the semiconductor wafer; a wafer chuck configured to removably couple the semiconductor wafer to the sample positioning system; and At least three actuators are spaced apart from each other, wherein each of the at least three actuators is mechanically coupled between the wafer chuck and the dual-axis wafer stage, wherein when coupled to the wafer chuck, each of the at least three actuators extends in a direction substantially parallel to a direction normal to the surface of the semiconductor wafer.

15. The semiconductor measurement system of claim 14, the sample positioning system further comprising: At least three position sensors, each of the at least three position sensors being located in close proximity to a corresponding actuator of the at least three actuators, wherein each of the at least three position sensors is configured to measure a displacement of each corresponding actuator in the extension direction.

16. A method comprising: measuring normal position values ​​at a first plurality of locations across a surface of a semiconductor wafer, wherein each normal position value is a position of the semiconductor wafer relative to an illumination source and a detector of a semiconductor measurement system in a direction normal to the surface of the semiconductor wafer; estimating a value characterizing a local slope associated with each of the first plurality of sites across the surface of the semiconductor wafer based on the normal position values ​​at the first plurality of sites; and A desired orientation correction of the semiconductor wafer at a measurement site of the semiconductor wafer is estimated based on the value characterizing the local slope and the value of a wafer orientation correction map.

17. The method according to claim 16, further comprising: The semiconductor wafer is oriented at the measurement site about a first axis and a second axis based on the desired orientation correction, wherein the first axis and the second axis are aligned with the surface of the semiconductor wafer, and the second axis is orthogonal to the first axis.

18. The method according to claim 17, further comprising: generating an amount of illumination radiation incident on the semiconductor wafer at the measurement site, wherein one or more structures are fabricated on the surface of the semiconductor wafer; detecting an amount of radiation collected from the semiconductor wafer in response to the incident amount of illuminating radiation; and After orienting the semiconductor wafer about the first axis and the second axis based on the desired orientation correction, a value of a parameter of interest characterizing the one or more structures is estimated based on the collected amount of radiation detected at a measurement spot.

19. The method of claim 16, further comprising: measuring normal position values ​​at a second plurality of locations across a surface of a calibration semiconductor wafer, wherein each normal position value is a position of the semiconductor wafer relative to the illumination source and the detector of the semiconductor measurement system in a direction normal to the surface of the calibration semiconductor wafer; estimating a value characterizing a local slope associated with each of the second plurality of sites across the surface of the calibration semiconductor wafer based on the normal position values ​​at the second plurality of sites; and The wafer orientation correction map is generated based on a difference between the estimated value characterizing the local slope at each of the second plurality of locations across the surface of the calibration semiconductor wafer and a measured orientation of the calibration semiconductor wafer relative to the illumination source and the detector.

20. The method of claim 19, further comprising: generating an optical illumination beam directed onto the surface of the calibration semiconductor wafer; detecting light reflected from the calibration semiconductor wafer in response to the incident optical illumination beam; and The measured orientation of the calibration semiconductor wafer relative to the illumination source and the detector at each of a second plurality of locations across the surface of the calibration semiconductor wafer is determined based on an incident location of the detected light reflected from the calibration semiconductor wafer at each of a second plurality of locations across the surface of the calibration semiconductor wafer.

21. A semiconductor measurement system, comprising: an illumination source configured to generate an amount of illumination radiation incident on a semiconductor wafer at a measurement spot, wherein one or more critical dimension structures are fabricated on a surface of the semiconductor wafer at the measurement spot; a detector configured to detect an amount of radiation collected from the semiconductor wafer in response to the incident amount of illuminating radiation; a sample positioning system configured to position the semiconductor wafer in a desired orientation relative to the illumination source and the detector about a first axis and a second axis, wherein the first axis and the second axis are aligned with the surface of the semiconductor wafer and the second axis is orthogonal to the first axis; and A computing system configured to: estimating the desired orientation of the semiconductor wafer relative to the illumination source and the detector based on the location of the measurement spot on the semiconductor wafer and a local wafer orientation correction map; and After positioning the semiconductor wafer in the desired orientation about the first axis and the second axis, a value of a parameter of interest characterizing the one or more structures is estimated based on the collected amount of radiation detected at the measurement spot.

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