Method and system for measurement of semiconductor structures based on differential measurement signals

Abstract

Presented herein are methods and systems for measuring structural parameters characterizing a measurement target based on changes in measurement signal values due to perturbations in an electrical property, an optical property, or both of the measurement target and estimated changes in the properties. The electrical and optical properties of a measurement target being measured are perturbed by inducing a change in the electric field within the measurement target. In a preferred embodiment, the change in the electric field is induced by directing a modulated illumination beam to the measurement target being measured. Both the change in the measurement signal value and the estimated change in both the electrical property, optical property, or both of the measurement target are quantified and provided as input to a measurement model. In this manner, the measurement is based on a differentiation of the measurement signal relative to an electrical property, an optical property, or both.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 63 / 420,087, filed on October 28, 2022, entitled "Apparatus and Method for Acquiring the Mueller Matrix Derivatives and Modulated Ellipsometry Spectra from a Semiconductor Specimen," and the subject matter of the patent application is incorporated herein by reference in its entirety. Technical Field

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

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

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

[0006] As devices (e.g., logic and memory devices) move toward smaller nanoscale dimensions, characterization becomes more difficult. Devices that incorporate complex three-dimensional geometries and materials with multiple physical properties create characterization difficulties. In some instances, the value of semiconductor devices is increasingly based on their energy efficiency, not just speed. For example, energy-efficient consumer products are more valuable because they operate at lower temperatures and last longer periods of time on fixed battery power. In another example, energy-efficient data servers are needed to reduce their operating costs. Therefore, there is a strong interest in reducing the energy consumption of semiconductor devices. Solutions include the use of high-K material layers and complex geometries, both of which create characterization difficulties.

[0007] Modern semiconductor processes are used to produce complex structures. Complex measurement models with multiple parameters are required to represent these structures and account for process and dimensional variations. Complex multi-parameter models contain modeling errors induced by parameter correlations and low measurement sensitivity for some parameters. In addition, regression of complex multi-parameter models with a relatively large number of floating parameter values ​​may not be computationally tractable.

[0008] In some examples, in model-based measurements, several parameters are often fixed to reduce the impact of these error sources and reduce computational effort. Although fixing the values ​​of several parameters can improve computational speed and reduce the impact of parameter dependencies, it also leads to errors in parameter value estimates.

[0009] In some other examples, the measurement is performed while the local environment around the measured metrology target is treated with a flushing gas flow containing a controlled amount of filler material. A portion of the filler material condenses onto the measured structure and fills openings in structural features, openings between structural features, etc. The presence of the filler material changes the optical properties of the measured structure compared to the measurement case where the flushing gas does not have any filler material. Model-based measurements are performed with a rich data set that includes measurement signals collected from a metrology target with geometric features filled with filler material. This reduces parameter correlations between floating measurement parameters and improves measurement accuracy. In this way, model-based measurement results can be obtained with reduced computational workload. Further details are described in U.S. Patent No. 10,145,674 assigned to KLA-Tencor Corporation, Milpitas, California, the entire contents of which are incorporated herein by reference. Unfortunately, applying fill material to the wafer introduces problems of contamination of the wafer itself, limited contrast induced by the fill material, lack of flexibility in selecting the fill material, increased system complexity, and increased risk due to contact with the wafer surface.

[0010] Other measurement examples include various forms of modulation spectroscopy, such as optical modulated reflectivity and electrical reflectivity spectroscopy, in which periodic changes are induced in the electric field of the sample being tested. The modulation of the electric field effectively results in a modulation of the dielectric function of the sample material at the same frequency. The measurement signal is typically expressed as a change in reflectivity ΔR divided by the nominal reflectivity R. The measurement signal ΔR / R exhibits features associated with various electronic transitions in the sample material. In one example, the measurement signal ΔR / R is highly sensitive to the band structure of the sample material.

[0011] In some existing systems, reflectance measurements are performed while modulating the intensity of a pump beam delivered to a measurement site. Measurements of light reflected or scattered from a sample in response to a probe beam are performed while the pump beam illuminates the measurement site. In some instances, the pump beam and the probe beam are the same beam. The modulated pump beam induces a change in the electric field in the sample, which in turn modulates the reflectance of the sample being measured. In some of these instances, the line shape of the measured change in reflectance (e.g., ΔR / R) is directly verified as a determined value of a parameter of interest (e.g., bandgap). In some other instances, a measurement model is employed to determine the value of a parameter of interest based on the measured change in reflectance (e.g., ΔR / R).

[0012] In existing systems, the induced changes in the internal optical properties of the measurement target due to the modulated pump beam are not quantified and provided as input to the measurement model. In fact, the measurement results are derived only from the observed changes in optical properties (e.g., reflectivity). This approach limits the range of parameters of interest that can be measured based on modulated reflectivity data.

[0013] Currently, solutions to complex multi-parameter measurement models often require unsatisfactory compromises. Current model reduction techniques sometimes fail to yield measurement models that are both computationally tractable and sufficiently accurate. Furthermore, complex multi-parameter models make it difficult or impossible to optimize system parameter selection for each parameter of interest (e.g., wavelength, angle of incidence, etc.).

[0014] Future metrology applications present challenges due to smaller and smaller resolution requirements, multi-parameter dependencies, increasingly complex geometries, and the increasing use of opaque materials. Therefore, it would be advantageous to develop high throughput systems and methods for characterizing complex semiconductor structures, such as structures incorporating high-k dielectric layers. In particular, it would be advantageous to develop robust, reliable, and stable methods for in-line metrology of gate stacks including high-k dielectrics. Therefore, methods and systems for improved measurement of semiconductor structures are desired. Summary of the invention

[0015] Methods and systems are proposed herein for measuring structural parameters characterizing a measurement target based on changes in measurement signal values ​​due to perturbations of electrical properties, optical properties, or both of the measurement target and estimated changes in said properties. The electrical and optical properties of the measurement target are perturbed by inducing changes in the electric field within the measurement target being measured.

[0016] In a preferred embodiment, the change in the electric field is induced by directing a modulated illumination beam to a measurement target being measured. The perturbation of the electrical and optical properties of the measurement target induces a change in the measurement signal value. Both the change in the measurement signal value and the estimated change in the electrical property, optical property, or both of the measurement target are quantified and provided as input to a measurement model. In this way, the measurement is based on the differential of the measurement signal with respect to the electrical property, optical property, or both. In some examples, measurements based on these differential quantities can increase sensitivity to film and CD parameters while reducing correlations between parameters characterizing different materials comprising the structure being measured.

[0017] The methods and systems described herein are applicable to a wide range of non-contact and non-destructive measurement systems, such as optical, electron-based, and x-ray-based measurement systems, operating in any number of signal modalities, such as reflectometry, ellipsometry, scatterometry, pupil imaging, field imaging, hyperspectral imaging, etc.

[0018] In a preferred embodiment, a tunable laser-based illumination source generates a modulated illumination beam with a selected beam energy directed to a measurement target. In one aspect, the beam energy of the modulated illumination beam is selected to destroy correlations between different materials comprising the structure being measured. In some examples, the different material layers have very low optical contrast but significant contrast in electrical properties (e.g., band gap). In these examples, the photon energy of the modulated illumination beam is selected to be between the band gaps of two different material layers of the multilayer stack.

[0019] In general, the illumination power of the illumination light incident at the measurement point can be varied between different illumination power levels in any periodic or non-periodic manner. In some examples, the illumination light varies in a binary manner, for example, on / off, according to a sine wave between different illumination power levels, according to a square wave between different illumination power levels, etc.

[0020] In some examples, changes in electrical properties, optical properties, or both of the measurement target are estimated based on separate measurements of the monolayer film samples. The electrical properties, optical properties, or both of each monolayer film sample are measured at a specified beam energy and beam power density level without and with pump illumination light. The difference in the measured properties is the induced change in the electrical property, optical property, or both associated with the specified beam energy and beam power density level. In some embodiments, the monolayer film samples are located on the same wafer as the measurement target. In some other embodiments, the monolayer film samples are located on other wafers.

[0021] The methods and systems described herein can improve the measurement of structural elements commonly found in semiconductor manufacturing, such as material composition, alloy fraction measurement of compound semiconductors, material bandgap, characterization of semiconductor surfaces and interfaces, film properties, critical dimensions, etc. Measurement applications include measurement of structural elements including complex semiconductor structures (e.g., 3D VNAND structures and gate-all-around (GAA) structures, including front-end-of-line (FEOL) layers from oxide definition layers to high-k metal gate (HKMG) stacks). Measurement applications include measurement of structural elements including semiconducting materials, insulating dielectric materials, and conductive materials (including organic materials, inorganic materials, or combinations thereof).

[0022] The foregoing is an inventive summary and therefore necessarily contains simplifications, generalizations, and omissions of detail; therefore, those skilled in the art will appreciate that the inventive summary is illustrative only and in no way limiting. 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

[0023] Figure 1 is a diagram illustrating a silicon nitride sample 10 illuminated by an illumination beam 11 having a photon energy greater than the bandgap of the silicon nitride material.

[0024] Figure 2 is a diagram illustrating a multilayer material stack disposed on a silicon substrate illuminated by an illumination beam having a photon energy greater than a bandgap of one of the stacked materials and less than a bandgap of another of the stacked materials.

[0025] Figure 3 is a diagram illustrating a spectroscopic ellipsometric measurement system configured to modulate electrical and optical properties of a measurement target and to measure structural parameters that characterize the measurement target based on changes in measurement signal values ​​and estimated changes in the optical properties of the measurement target.

[0026] Figure 4 is a diagram illustrating a differential-based measurement engine 160 in one embodiment.

[0027] Figure 5 is a diagram illustrating an illumination beam incident on a wafer at a particular orientation described by an incident angle θ and an azimuth angle φ.

[0028] Figure 6 is a flow chart illustrating a method 200 for measuring a structural parameter of a characterizing measurement target based on changes in measurement signal values ​​and estimated changes in optical properties of the measurement target as described herein. DETAILED DESCRIPTION

[0029] Reference will now be made in detail to background examples and some embodiments of the invention, examples of which are illustrated in the accompanying drawings.

[0030] Methods and systems are presented herein for modulating electrical and optical properties of a measurement target and measuring structural parameters characterizing the measurement target based on changes in measurement signal values ​​and estimated changes in electrical properties, optical properties, or both of the measurement target.

[0031] The electrical and optical properties of the measurement target are disturbed by inducing a change in the electric field within the measurement target being measured. In a preferred embodiment, the change in the electric field is induced by directing a modulated illumination beam to the measurement target being measured. The disturbance of the electrical and optical properties of the measurement target induces a change in the measurement signal value. Both the measurement signal value and the change in the electrical property, the optical property, or both are quantified and provided as input to a measurement model. In this way, the measurement is based on the differential of the measurement signal with respect to the electrical property (e.g., electron density) or the optical property (e.g., optical dispersion) or both. In some examples, measurements based on these differential quantities can increase the sensitivity to film and CD parameters while reducing the correlation between parameters characterizing different materials comprising the structure being measured.

[0032] The measurement model estimates the values ​​of one or more parameters of interest of one or more structural elements that characterize the measurement target based on both changes in the measurement signal value and changes in electrical properties, optical properties, or both. In this way, the measurement model operates on differential information (i.e., changes in the measurement signal that vary according to changes in electrical properties, optical properties, or both) to estimate the values ​​of one or more parameters of interest.

[0033] The methods and systems described herein are applicable to a wide range of non-contact and non-destructive measurement systems, e.g., optical, electron-based, and x-ray-based measurement systems operating in any number of signal modalities, e.g., reflectometry, ellipsometry, scatterometry, pupil imaging, field imaging, hyperspectral imaging, etc. Model-based measurements performed based on differential information as described herein destroy correlations and provide sensitivity to structural parameters that would otherwise be accessible by non-contact and non-destructive measurement systems.

[0034] In general, changes in both the electrical and optical properties of semiconductor materials are induced by illumination light incident on the material. When a semiconductor material is subjected to illumination light having a photon energy higher than the band gap of the material, the incident illumination light generates electron-hole pairs in the material. The electron-hole pairs induce plasma currents, thermal effects, or both, which in turn change the optical properties of the material, such as the refractive index n and the absorption coefficient k. The extent to which the illumination light changes the electrical and optical properties depends on the photon energy and power density of the incident illumination light and the material itself. In some embodiments, measurements are performed using different wavelengths, power densities, or both to further break up correlations and increase measurement sensitivity.

[0035] Figure 1 is a diagram illustrating a silicon nitride sample 10 illuminated by an illumination beam 11 having a photon energy greater than the band gap of the silicon nitride material. Figure 1 As depicted in FIG. 1 , illumination light 11 is absorbed by silicon nitride 10 and electron-hole pairs are generated in the material. The electron-hole pairs change the electrical properties of the material. In addition, the electron-hole pairs induce plasma currents and thermal effects, which in turn change the optical properties of the material, such as the refractive index n and the absorption coefficient k. Equations (1) and (2) describe the refractive index and absorption coefficient of silicon nitride material 10 under illumination light 11, where n0 is the nominal value of the refractive index when the illumination light 11 is not present, and Δn is the change in the value of the refractive index due to the illumination light 11. Similarly, k0 is the nominal value of the absorption coefficient when the illumination light 11 is not present, and Δk is the change in the value of the absorption coefficient due to the illumination light 11.

[0036] n(λ) = n0(λ) + Δn(λ) (1)

[0037] k(λ) = k0(λ) + Δk(λ) (2)

[0038] In some examples, the change in the value of the refractive index is significant, and measurements performed with and without illumination light 11 will result in two different measurement signals. In these examples, the difference between the two different measurement signals provides differential information, i.e., the change in the measurement signal that varies as a function of the change in the optical property.

[0039] The electrical and optical properties of the semiconductor material are modulated by modulating the power of the illumination light incident on the semiconductor material. The modulation of the illumination power may be binary, for example, on / off, sinusoidal, or any other suitable variation of the illumination power over time. In some embodiments, the modulation is achieved by electrically controlling the illumination power output of the illumination source. In some other embodiments, the modulation is achieved by mechanically blocking or otherwise diverting the illumination light to control the illumination power incident on the structure being measured, for example, using a chopper.

[0040] In some embodiments, a laser-based illumination source generates a modulated illumination beam directed to a measurement target to modulate electrical and optical properties of the structure being measured. In some embodiments, the illumination beam is a single wavelength beam. In other embodiments, the illumination beam is a broadband illumination beam.

[0041] In one aspect, the beam energy (ie, wavelength) of the modulated illumination beam is selected to destroy correlations between different materials comprising the structure being measured. In a preferred embodiment, a tunable laser-based illumination source generates a modulated illumination beam with a selected beam energy directed to a measurement target.

[0042] In some examples, modulation-based measurements of a multilayer stack of different material layers are performed. In some of these examples, the different material layers have very low optical contrast, but have significant contrast in electrical properties (e.g., bandgaps). In these examples, the photon energy of the modulated illumination beam is selected to be between the bandgaps of two different material layers of the multilayer stack.

[0043] By modulating the pump beam with a photon energy above the bandgap of one material, the particular material absorbs the pump light, and the measurement signal includes a modulated signal component from the material layer. Furthermore, by modulating the pump beam with a photon energy below the bandgap of another material of the multilayer stack, the particular material does not absorb the pump light, and the measurement signal does not include a modulated component from the material layer. In these embodiments, the different materials may not provide significant optical contrast, but the contrast of electronic properties (e.g., bandgap) is exploited by selecting the photon energy of the pump beam to decouple the different materials in the measurement signal. More specifically, the difference between the measurement signal when the multilayer stack is illuminated by the pump light and the measurement signal when the multilayer stack is not illuminated by the pump light will result in a drop in the contribution of the non-absorbing material, leaving a difference signal that depends only on the absorbing layer. In this way, the difference signal effectively decouples the non-absorbing material layer from the measurement.

[0044] Figure 2 is a diagram illustrating a multilayer material stack disposed on a silicon substrate illuminated by an illumination beam having a photon energy greater than a bandgap of one of the stacked materials and less than a bandgap of another of the stacked materials.

[0045] like Figure 2, a multilayer material stack includes alternating layers 22 and 24 of silicon oxide (SiO2) and alternating layers 21 and 23 of silicon nitride (Si3N4) disposed on a silicon substrate 20. This type of thin film stack is often referred to as an oxide / nitride / oxide (ONO) thin film stack. In some embodiments, each of the silicon nitride and silicon oxide layers is very thin, for example, each layer has a thickness of about five nanometers. The optical properties of SiO2 and Si3N4 are very similar, and when optical-based measurement tools are employed, this results in a high correlation between the thickness, profile, and CD parameters of the stack structure fabricated using the two materials being characterized.

[0046] Although the optical contrast between the SiO2 and Si3N4 layers is very low, the electrical contrast between the two materials is significant, i.e., their electrical properties are very different. For example, the band gap of SiO2 is about 9 eV, and the band gap of Si3N4 is about 5 eV. The multilayer material stack is illuminated by an illumination beam 25 having a photon energy greater than the band gap of the silicon nitride material and less than the band gap of the silicon oxide material, for example, the photon energy is about 7 eV. In this example, the illumination light is absorbed only by the Si3N4 layer. This generates electron-hole pairs in the Si3N4 layer, but not in the SiO2 layer. The electron-hole pairs induce plasma currents and thermal effects, which in turn change the optical properties of the Si3N4 layer, but not the optical properties of the SiO2 layer. Therefore, the illumination beam 25 disturbs the optical properties of the Si3N4 layer, but not the optical properties of the SiO2 layer.

[0047] Furthermore, the difference between the optical measurements performed with and without the illumination light 11 will have virtually no contribution from the SiO2 material layer and a significant contribution from the Si3N4 material layer. In this example, the difference between the two different measurement signals provides differential information, i.e., the measurement signal changes as a function of the change in the optical property, where the differential is close to zero for the SiO2 material layer and non-zero for the Si3N4 material layer. In general, a large number of differential spectra can be generated by varying the pump beam wavelength.

[0048] Figure 3 is a diagram illustrating a spectroscopic ellipsometric measurement system configured to modulate electrical and optical properties of a measurement target and to measure structural parameters that characterize the measurement target based on changes in measurement signal values ​​and estimated changes in the optical properties of the measurement target.

[0049] Figure 3 An exemplary differential spectroscopic ellipsometer (SE) metrology system 100 for performing SE measurements of one or more metrology targets as described herein is depicted. Figure 3, the metrology system 100 includes a SE subsystem 105, which includes an illumination source 110 that generates a SE illumination beam 107 incident on the wafer 101. 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 called a laser driven plasma source). The pump laser of the LSP light source can be continuous wave or pulsed. 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, an incandescent rod source, or any other suitable light source.

[0050] In some embodiments, the SE illumination light quantity is a broadband illumination light comprising a wavelength range spanning at least 500 nanometers. In one example, the broadband SE illumination light comprises a wavelength below 250 nanometers and a wavelength above 750 nanometers. In general, the broadband SE illumination light comprises a wavelength between 120 nanometers and 4,200 nanometers. In some embodiments, a broadband illumination light comprising a wavelength exceeding 4,200 nanometers may be employed. In some embodiments, the illumination source 110 comprises a deuterium source emitting light having a wavelength spanning a range of 150 nanometers to 400 nanometers, an LSP source emitting light having a wavelength spanning a range of 180 nanometers to 2,500 nanometers, a supercontinuum light source emitting light having a wavelength spanning a range of 400 nanometers to 4,200 nanometers, and an incandescent rod source emitting light having a wavelength spanning a range of 2,000 nanometers to 20,000 nanometers.

[0051] like Figure 3 , SE subsystem 105 includes a SE illumination subsystem configured to direct SE illumination light 107 to one or more structures formed on wafer 101. The SE illumination subsystem is shown to include a light source 110, an illumination optics 111A, one or more optical filters 111B, a polarizing element 112, an illumination field stop 113, and an illumination pupil aperture stop 114. Figure 3 , as SE illumination beam 107 propagates from illumination source 110 to wafer 101, the beam travels through illumination optics 111A, optical filter(s) 111B, polarizing element 112, field stop 113, and aperture stop 114. SE illumination light 107 illuminates a portion of wafer 101 above measurement point 108.

[0052] Illumination optics 111A condition illumination light 107 and focus SE illumination light 107 onto measurement point 108. One or more optical filters 111B are used to control brightness, spectral output, or a combination thereof from the illumination subsystem. In some examples, one or more multi-zone filters are employed as optical filter 111B. Polarizing component 112 produces the desired polarization state exiting the illumination subsystem. In some embodiments, the polarizing component is a polarizer, 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 3 The SE illumination subsystem depicted in FIG. 1 includes one polarizing component, but the SE illumination subsystem may include more than one polarizing component. The field stop 113 controls the field of view (FOV) of the SE illumination subsystem and may include any suitable commercially available field stop. The aperture stop 114 controls the numerical aperture (NA) of the SE illumination subsystem and may include any suitable commercially available aperture stop. The SE illumination subsystem may include illumination optics 111A, optical filter(s) 111B, polarizing component 112, field stop 113, and aperture stop 114 of any type and arrangement known in the art of spectroscopic ellipsometric measurement.

[0053] The metrology system 100 also includes a collection optics subsystem configured to collect light generated by the interaction between one or more structures and the incident SE illumination light 107. A collection light beam 109 is collected from the measurement point 108 by the collection optics 115. The collected light 109 travels through a collection aperture stop 116, a polarizing element 117, and a field stop 118 of the collection optics subsystem.

[0054] The collection optics 115 include any suitable optical elements to collect light from one or more structures formed on the wafer 101. The collection aperture stop 116 controls the NA of the collection optics subsystem. The polarization element 117 analyzes the desired polarization state. The polarization element 117 is a polarizer or a compensator. The polarization element 117 can be fixed, rotatable to different fixed positions, or continuously rotated. Although Figure 3 The collecting subsystem depicted in includes one polarizing element, but the collecting subsystem may include more than one polarizing element. The collecting field of view aperture 118 controls the FOV of the collecting subsystem. The collecting subsystem acquires light from the wafer 101 and directs the light through the collecting optics 115, the aperture stop 116, and the polarizing element 117 to focus on the collecting field of view aperture 118. In some embodiments, the collecting field of view aperture 118 is used as a spectrometer slit of a spectrometer of the detector subsystem. However, the collecting field of view aperture 118 may be positioned at or near a separate spectrometer slit of a spectrometer of the detector subsystem. The collecting subsystem may include any type and arrangement of collecting optics 115, aperture stop 116, polarizing element 117, and field of view aperture 118 known in the art of spectroscopic ellipsometric measurement.

[0055] like Figure 3 , SE metrology system 100 includes a pump illumination source 150 that generates pump illumination light 151 that is directed to a measurement point 108 on a wafer 101. Pump illumination light 151 coincides with SE illumination light 107 that is projected onto the surface of the wafer being measured above measurement point 108. In this way, the optical properties of the structure measured by SE illumination light 107 are modulated by the incident pump illumination light 151 at the measurement point 108. Figure 3 As depicted, command signal 152 is transmitted to Figure 3 . The command signal 152 includes parameters required to characterize the desired pump illumination light 151. By way of non-limiting example, the command signal 152 includes a desired photon energy of the pump illumination light 151, a desired power density of the pump illumination light 151, a desired modulation frequency of the pump illumination light 151, a desired power waveform of the pump illumination light 151, etc. In response, the pump illumination light source 150 generates the pump illumination light 151 according to the desired characteristics specified by the command signal 152.

[0056] In general, the illumination power of the SE illumination light 151 incident on the measurement point 108 can be varied between different illumination power levels in any periodic or non-periodic manner. In some examples, the illumination light is varied in a binary manner, for example, on / off, according to a sine wave between different illumination power levels, according to a square wave between different illumination power levels, etc. In this manner, the reflectivity, transmittance, or polarization of the measured structure alternates between a signal value in the absence of an external perturbation of the optical property and a signal value in the presence of a perturbation of the optical property of the measured structure.

[0057] exist Figure 3 , the light collection optics subsystem directs light to a detector 119. The detector 119 generates an output in response to light collected from one or more structures illuminated at the measurement point 108 by the SE illumination subsystem. In one example, the detector 119 includes a charge coupled device (CCD) sensitive to ultraviolet and visible light (e.g., light having a wavelength between 190 nanometers and 860 nanometers). In other examples, the detector 119 includes a photodetector array (PDA) sensitive to infrared light (e.g., light having a wavelength between 950 nanometers and 2500 nanometers). However, in general, the detector 119 may include other detector technologies and arrangements (e.g., position sensitive detectors (PSDs), infrared detectors, photovoltaic detectors, orthogonal unit detectors, cameras, etc.). Each detector converts incident light into an electrical signal indicating the spectral intensity of the incident light. In general, the detector 119 generates a SE measurement signal 103 indicating the light detected on the detector 119.

[0058] Each orientation of SE illumination beam 107 relative to the surface normal of wafer 101, or vice versa, is described by any two angular rotations of semiconductor wafer 101 relative to illumination beam 107. In one example, the orientation can be described with respect to a coordinate system fixed to the wafer. Figure 5 Depicted is a SE illumination beam 107 incident on wafer 101 at a particular orientation described by an angle of incidence θ and an azimuth angle φ. Coordinate system XYZ is fixed to a SE metrology system (e.g., SE illumination beam 107), and coordinate system X'Y'Z' is fixed to wafer 101. The Y axis is aligned in a plane with the surface of wafer 101. X and Z are not aligned with the surface of wafer 101. Z' is aligned with an axis normal to the surface of wafer 101, and X' and Y' are in a plane aligned with the surface of wafer 101. As Figure 5 1, the SE illumination beam 107 is aligned with the Z axis and therefore lies in the XZ plane. The angle of incidence θ describes the orientation of the SE illumination beam 107 relative to the surface normal of the wafer in the XZ plane. In addition, the azimuth angle φ describes the orientation of the XZ plane relative to the X'Z' plane. θ and φ together uniquely define the orientation of the SE illumination beam 107 relative to the surface of the wafer 101. In this example, the orientation of the SE illumination beam relative to the surface of the wafer 101 is described by a rotation about an axis normal to the surface of the wafer 101 (i.e., the Z' axis) and a rotation about an axis aligned with the surface of the wafer 101 (i.e., the Y axis).

[0059] like Figure 3 , the SE metrology tool 100 includes a sample positioning system 190 that is configured to align and orient the sample 101 within a wide range of incident angles and azimuths relative to the illumination beam 107. In this manner, measurements of the sample 101 are collected by the metrology system 100 at any number of positions and orientations on the surface of the sample 101. In one example, the computing system 130 communicates a command signal (not shown) indicating a desired position of the sample 101 to the sample positioning system 190. In response, the sample positioning system 190 generates command signals to various actuators of the sample positioning system 190 to achieve the desired positioning of the sample 101.

[0060] In general, the sample positioning system 190 may include any suitable combination of mechanical elements to achieve the desired linear and angular positioning performance, including but not limited to a goniometer stage, a hexapod stage, an angular stage, and a linear stage.

[0061] In general, an optical scatterometer such as SE metrology system 100 is configured to deliver illumination light to a metrology target being measured at any desired angle of incidence and azimuth.

[0062] The optical properties of the structure illuminated by the pump illumination light 151 are modulated at the same frequency as the pump illumination light 151. In order to capture the induced changes in the SE measurement signal, the spectrum must be collected quickly (i.e., at a frequency at least twice the modulation frequency of the pump illumination light) to avoid losing signal information. In addition, the modulated SE measurement signal ΔSE is relatively small compared to the unmodulated SE measurement signal SE. Therefore, the SE measurement signal may be dominated by optical and electrical noise. Fortunately, the modulated SE signal exists at a known frequency and can be detected using any suitable lock-in detection scheme. Lock-in detection detects portions of the signal of a known modulation frequency or frequency group and distinguishes portions of the signal of other frequencies. Phase-sensitive detection and lock-in amplification are common signal extraction techniques that can be used to recover the modulated SE measurement signal from the detected measurement signal 103.

[0063] For example, extracting a modulated SE measurement signal using phase-sensitive lock-in amplification requires performing at least one measurement at each wavelength within a time interval, including instances when a pump laser beam is present and instances when the pump laser beam is not present. Serial detection at each wavelength with a lock-in amplifier results in long measurement times because the measurements within the desired wavelength range are performed sequentially over time.

[0064] In some embodiments, signal multiplexing is employed to simultaneously measure multiple wavelengths to reduce signal acquisition time. During each cycle of modulation, the detection system simultaneously measures each dispersed beam using a multiplexed readout of the signal from the detector. In addition, the detection system calculates the modulated SE signal from the signal at each wavelength.

[0065] The collected light is spatially dispersed across the detector array according to wavelength. Light from each narrowband wavelength is incident on a different pixel of the detector array. The detected light signal of each narrowband wavelength is measured simultaneously by a multiplexed readout of the pixels.

[0066] The detector's electronics subsystem reads the modulated SE signal as well as the unmodulated SE signal in rapid succession from each pixel of the detector array. Multiple measurements are made on the modulated signal within a single cycle of the modulation cycle. In this way, the detector is able to simultaneously measure SE measurement signals of all desired wavelengths in parallel.

[0067] In general, the detected SE measurement signal depends on the configuration of the SE subsystem. In some embodiments, the detected SE measurement signal is a SE harmonic signal, such as {α, β}, {ψ, Δ}, etc. In some embodiments, the detected SE measurement signal is one or more elements of a Mueller matrix representation of SE measurements. In general, any detected SE measurement signal that is sensitive to changes in optical properties due to modulated pump illumination light 151 may be considered within the scope of this patent document.

[0068] The metrology system 100 also includes a computing system 130 configured as a differential-based measurement engine 160 configured to estimate values ​​of one or more parameters of interest of a characterized structure based on changes in measurement signal values ​​induced by modulation of electrical and optical properties of the measured structure and estimated changes in optical properties of the structure.

[0069] Figure 4 is a diagram illustrating a differential-based measurement engine 160 in one embodiment. Figure 4 , the differential-based measurement engine 160 includes a modulation classifier module 161 and a differential-based measurement module 163. A signal 165 indicative of the properties of the pump illumination light 151 directed to the measurement point 108 is communicated to the modulation classifier 161. In one example, the signal 165 is communicated to Figure 3 1. The pump illumination light source 150 of FIG. 1 is a command signal 152 for the pump illumination light source 150 depicted in FIG. In this example, the signal 165 includes a desired photon energy of the pump illumination light 151 and a desired power density of the pump illumination light 151. In another example, the signal 165 is generated by one or more optical sensors (not shown) disposed in the optical path between the pump illumination light source 150 and the wafer 101. In this example, the signal 165 includes an indication of the photon energy of the pump illumination light 151 and the power density of the pump illumination light 151 measured by the optical sensors. In addition, a signal 164 indicating the material comprising the measured structure is communicated to the modulation classifier module 161.

[0070] In response to signals 164 and 165, modulation classifier module 161 generates signal 162 indicating induced changes in optical properties of the measured structure due to pump illumination light 151 incident on the measured structure, e.g., {Δn, Δk}. In some examples, modulation classifier module 161 includes a library database that characterizes changes in optical properties of various materials employed in semiconductor manufacturing induced by illumination of different photon energies and beam power density levels. In some other examples, modulation classifier module 161 includes a model that characterizes changes in optical properties of various materials employed in semiconductor manufacturing induced by illumination of different photon energies and beam power density levels.

[0071] The change in the optical properties of the semiconductor material depends on the photon energy and the beam power density, but is expected to be independent of the geometry. In some examples, single-layer film samples are prepared, each sample comprising a layer of each different material. When illuminated by pump illumination light of several different photon energy levels and beam power density levels, the optical properties, e.g., {n, k}, are measured using conventional SE measurements. In the absence of any pump illumination, the measured optical properties are compared to the measured values ​​of the optical properties. The difference between the optical properties measured at a specified pump illumination level and the optical properties measured in the absence of pump illumination is the induced change in the optical properties at each of the specified pump illumination levels, e.g., {Δn, Δk}. In some embodiments, these calibration values ​​are entered into a database and interpolated to specify the induced change in the optical properties for any specified pump illumination level. In these embodiments, the modulation classifier module 161 includes the database. In some other embodiments, the calibration values ​​are fit to a model that specifies the induced change in the optical properties for any specified pump illumination level. In these embodiments, the modulation classifier module 161 includes a trained model.

[0072] In some examples, one or more metrology targets are disposed at different locations on the same semiconductor wafer as the structure being measured. Each metrology target includes a single film layer corresponding to each of the different materials comprising the structure being measured. Changes in the values ​​of one or more electrical or optical properties of each metrology target induced by a power change of pump illumination light are measured. The power change of the pump illumination light used to measure each single film layer metrology target is the same as the power change of the pump illumination light used to measure the structure being measured. In this way, the measured changes in the values ​​of one or more electrical or optical properties of each metrology target are directly applicable to the model-based measurement of the structure being measured.

[0073] like Figure 4 As depicted in FIG. 1 , a signal 162 indicating the value of the induced change (e.g., {Δn, Δk}) of the optical property of the measured structure is communicated to a differential-based measurement module 162. In one example, the signal 162 includes two vectors. One vector expresses the induced change Δn of the refractive index as a function of wavelength, and the other vector expresses the induced change Δk of the absorption coefficient as a function of wavelength. In addition, the SE measurement signal 103 is communicated to the differential-based measurement module 163. The SE measurement signal changes due to the perturbation of the optical property of the measured structure induced by the modulated pump illumination light 151. In some examples, the SE measurement signal includes one or more elements of the Mueller matrix. In these examples, the change in the value of one or more elements of the Mueller matrix induced by the modulation is provided as an input to the measurement model. In some examples, the SE measurement signal is a harmonic signal generated by a spectrometer. In these examples, the change in the value of the harmonic signal induced by the modulation is provided as an input to the measurement model.

[0074] The derivative-based measurement module 163 includes a derivative-based model that estimates values ​​of one or more parameters of interest that characterize the measured structure based on changes in the SE measurement signal and the values ​​of the induced changes in the optical properties of the measured structure (eg, {Δn, Δk}).

[0075] In some embodiments, the differential-based measurement model is a trained, machine learning (ML)-based model. The ML-based model is trained using a design of experiments (DOE) data set associated with a DOE measurement target having known values ​​of the parameters of interest. The DOE data set includes changes in the SE measurement signal and values ​​(e.g., {Δn, Δk}) of the induced changes in the optical properties of the measured structure associated with the DOE measurements of the DOE measurement target. In some instances, the DOE measurements are actual SE measurements of the DOE measurement target having known values ​​of the parameters of interest. In some of these instances, the known values ​​of the parameters of interest are obtained by using measurements of a trusted reference metrology system. In some other instances, the DOE measurements are simulated SE measurements of a simulated DOE measurement target having programmed values ​​of the parameters of interest.

[0076] In some embodiments, the differential-based measurement model is a physics-based model that relates the value of the induced change in the optical property of the measured structure (e.g., {Δn, Δk}) and the assumed value of the parameter of interest to the predicted normalized change of the SE measurement signal (e.g., (ΔSE / SE)*). As part of the regression process, the assumed value of the parameter of interest is updated until a sufficiently good fit is obtained between the predicted normalized change of the SE measurement signal and the actual normalized change of the SE measurement signal (e.g., (ΔSE / SE)). When a sufficiently good fit is obtained, the estimated value of the parameter of interest is communicated to a memory, e.g., memory 180.

[0077] The normalized change in the SE measurement signal 103 defines the change in any ellipsometric measurement signal as described in equation (3), where SE ON is the SE measurement signal value when the power of the pump illumination light 151 is maximum, and SE OFF is the SE measurement signal value when the power of the pump illumination light 151 is minimum (for example, zero).

[0078]

[0079] As described above, the SE signal includes any suitable SE signal generated by a spectrometer of the SE measurement system, such as a harmonic signal, one or more Mueller matrix elements, and the like.

[0080] The dielectric function ε of a material is characterized by a complex function with real coefficient ε1 and imaginary coefficient ε2, as described by equation (4).

[0081] ε=ε1+iε2 (4)

[0082] The predicted normalized change in the SE signal is related to the perturbation of the dielectric function induced by the pump illumination light, as described by equation (5), where a(ε1,ε2) and b(ε1,ε2) are two coefficients related to the dielectric function.

[0083]

[0084] The coefficients a(ε1,ε2) and b(ε1,ε2) depend on both the material and the geometry of the structure under optical modulation. However, the perturbations of the dielectric function coefficients Δε1 and Δε2 are related by the Kramers-Kronig relationship and are independent of the geometry of the measured structure. For this reason, these perturbations can be determined based on the known material and known properties of the pump illumination light 151 using the modulation classifier module 161 as described above.

[0085] For the case where the optical properties of a single material are perturbed by pump illumination light 151, equation (5) relates the predicted normalized change in the SE signal to the perturbation in the dielectric function. For the case where the optical properties of d different materials are perturbed by pump illumination light 151, equation (6) describes the relationship between the predicted normalized change in the SE signal and the perturbation in the dielectric function.

[0086]

[0087] In the example illustrated in equation (6), the measured structure includes d different material layers having optical properties that are modulated by the pump illumination light 151. In one example, a Lorentz model of the dielectric function of a grating structure including d material layers is assumed. In this example, equation (6) can be rewritten as illustrated by equation (7), where d is the number of different modulating materials having a bandgap energy below the modulating photon energy, Aj is a dimensionless amplitude that varies depending on the photon energy of the pump illumination light and the material geometry (e.g., CD and HT), Γj is a broadening parameter expressed in electron volts, θj is a linear phase parameter expressed in radians, Ej is a transition energy expressed in electron volts, and m is a parameter related to the dimensionality of the transition. In the case of silicon, the value of m is 3.

[0088]

[0089] Equation [7] is an approximate form of the differential of the SE measurement signal under the assumption of the Lorentz model of the dielectric function.

[0090] Perturbations in the dielectric function can be expressed in terms of perturbations in the refractive index and the extinction coefficient, as illustrated by equation (8), where Δn is the change in the refractive index, Δk is the change in the extinction coefficient, and I is the strength of the oscillator.

[0091]

[0092] Equation (8) can be rewritten as illustrated by equations (9) to (12).

[0093] Δε i = [(A En f E i + A Γn f Γ i + A In f I i )Δn + (A Ek f E i + A Γk f Γ i + A Ik f I i )Δk](1 / Γ), i = 1,2 (9)

[0094] in

[0095]

[0096]

[0097]

[0098] For many semiconductor materials, the values ​​of the elements of equations (10) to (12) are known. The unperturbed dielectric function can be expressed in many different forms depending on the material, thickness, confinement effects, crystallinity, temperature, etc. The most common assumptions are Lorentz or Gaussian. The Lorentz dielectric function is described by equation (13).

[0099]

[0100] Under the assumed form described by equation (13), the modulation term of equation (12) can be expressed as described by equations (14) to (15), where y = (EE g ) / Γ.

[0101]

[0102]

[0103] Assuming that the intensity modulation is negligible, then using equations (10) to (15) in (8), we obtain the general form of the measured differential spectrum.

[0104] In general, there are multiple models that describe the dielectric function. Although the Lorentz model is described above, in general, any suitable model of the dielectric function is considered within the scope of this patent document.

[0105] Generally speaking, reference Figure 3 The SE metrology system described may be any form of spectroscopic ellipsometer, including but not limited to a rotating compensator SE system, a rotating polarizer SE system, a rotating polarizer, a rotating compensator SE system, a rotating compensator, a rotating compensator SE system, etc. In addition, the differential-based measurement technique may be applied to other ellipsometric measurement systems that employ non-rotating solid-state devices (e.g., photoelastic modulators) to measure all or a portion of a sample Mueller matrix.

[0106] In general, the electrical properties of the measurement target are disturbed by inducing a change in the electric field within the measurement target being measured, which in turn changes the optical properties of the measurement target. As described above, the change in the electric field is induced by directing a modulated illumination beam to the measurement target being measured. However, in general, any suitable technology for changing the electric field is considered within the scope of this patent document. In some embodiments, the wafer is positioned between two electrodes, and a time-varying bias voltage is applied across the electrodes. The time-varying bias voltage induces modulation of the electric field within the wafer containing the measurement target. This electrical modulation induces modulation of the electrical and optical properties of the measurement target being measured, which is used for the measurement purpose as described above.

[0107] The methods and systems described herein can improve the measurement of structural elements commonly found in semiconductor manufacturing, such as material composition, alloy fraction measurement of compound semiconductors, material bandgap, characterization of semiconductor surfaces and interfaces, film properties, critical dimensions, etc. Measurement applications include measurement of structural elements including complex semiconductor structures (e.g., 3D VNAND structures and gate-all-around (GAA) structures, including front-end-of-line (FEOL) layers from oxide definition layers to high-k metal gate (HKMG) stacks). Measurement applications include measurement of structural elements including semiconductor materials, insulating dielectric materials, and conductive materials (including organic materials, inorganic materials, or combinations thereof).

[0108] In general, the modulation wavelength and power density of the pump illumination light are selected for each measurement application to improve sensitivity and reduce correlation.

[0109] As described above, the measurement of ONO thin film stacks is improved by using an illumination pump light having a photon energy greater than 4.5 electron volts. In some embodiments, a 244 nm solid-state continuous laser is used as a pump illumination source to enhance the measurement of ONO thin film stacks.

[0110] In some examples, a pump illumination source that produces pump illumination light having a photon energy below the bandgap of silicon (ie, 1.12 electron volts) is employed to measure silicon / silicon germanium superlattice structures.

[0111] In other examples, a pump illumination source that generates pump illumination light having a photon energy between the band gaps of hafnium oxide (HfO 2 ) and silicon oxide (SiO 2 ) is employed to measure a high-k / interface layer (HK / IL) gate stack.

[0112] In general, the techniques described herein for destroying correlations between various contributors to the measured optical response can be combined to improve measurement accuracy of complex semiconductor structures. For example, differential-based measurements of the structure at various wavelengths, incident angles, azimuth angles, or any combination thereof can be analyzed sequentially or in parallel to accurately decorrelate structural features associated with a complex multilayer structure.

[0113] In a further aspect, the wavelengths emitted by the measurement illumination source (e.g., illumination source 110), the pump illumination source (e.g., illumination source 150) are selectable. In some embodiments, illumination source 110 or illumination source 150 is an LSP light source that is controlled by computing system 130 to maximize the throughput in one or more selected spectral regions. The laser peak intensity of the target material controls the plasma temperature and thus the spectral region of the emitted radiation. The laser peak intensity is varied by adjusting the pulse energy, pulse width, or both. Figure 3 , computing system 130 communicates command signal 140 to illumination source 110 to cause illumination source 110 to adjust the spectral range of wavelengths emitted from illumination source 110. Similarly, computing system 130 communicates command signal 152 to illumination source 150 to cause illumination source 150 to adjust the spectral range of wavelengths emitted from illumination source 150. In one example, illumination source 110 is an LSP light source, and the LSP light source adjusts any of pulse duration, pulse frequency, and target material composition to achieve a desired spectral range of wavelengths emitted from the LSP light source. In another example, illumination source 150 is a tunable laser-based light source, such as a tunable supercontinuum laser light source, and the laser light source adjusts one or more operating parameters of the laser light source to achieve a desired spectral range of wavelengths emitted from the laser-based light source.

[0114] In some examples, the differential-based measurement engine 160 reads a file containing equations describing the shape and composition of the structure being measured. In some examples, this file is generated by a lithography simulator, such as PROLITH software available from KLA-Tencor, Inc., Milpitas, California, USA. Based on this application information, the differential-based measurement engine automatically sets the parameterization and constraints of the structure model.

[0115] Although the methods discussed herein are described with reference to system 100, any optical or x-ray based metrology system configured to illuminate and detect light scattered from a sample may be employed to implement the exemplary methods described herein. Furthermore, any electronic based metrology system configured to illuminate and detect scattered electrons from a sample may be employed to implement the exemplary methods described herein. Exemplary systems include angle resolved reflectometers (i.e., beam profile reflectometers), angle resolved ellipsometers (i.e., beam profile ellipsometers), scatterometers, spectroscopic reflectometers or ellipsometers, spectroscopic reflectometers or ellipsometers with multiple illumination angles, Mueller matrix spectroscopic ellipsometers (e.g., rotating compensator spectroscopic ellipsometers), single wavelength ellipsometers, single wavelength reflectometers, Raman scatterometers, transmission small angle x-ray scatterometers, reflection small angle x-ray scatterometers, grazing incidence small angle x-ray scatterometers, transmission electron microscopes, scanning electron microscopes, and the like.

[0116] By way of non-limiting example, an ellipsometer may include a single rotating compensator, multiple rotating compensators, a rotating polarizer, a rotating analyzer, a modulating element, multiple modulating elements, or no modulating element.

[0117] It should be noted that the output from the source and / or target measurement systems can be configured so that the measurement systems use more than one technique.In fact, the application can be configured to employ any combination of available metrology subsystems within a single tool or across several different tools.

[0118] Systems implementing the methods described herein can also be configured in a number of different ways. For example, a wide range of wavelengths (including visible, ultraviolet, and infrared), angles of incidence, polarization states, and coherence states can be considered. In another example, the system can include any of a number of different light sources (e.g., a direct coupled light source, a laser continuous plasma light source, etc.). In another example, the system can include elements to condition the light directed to or collected from the sample (e.g., an apodizer, a filter, etc.).

[0119] In general, the optical dispersion properties of the measured semiconductor structure can be approximated as isotropic. Under this assumption, the material parameters are scalar values. Alternatively, the optical dispersion properties of the measured semiconductor structure can be more accurately modeled as anisotropic. Under this assumption, the material parameters will be a matrix of different values, rather than scalar values. Additional details on the processing of anisotropic structures being measured are described in U.S. Patent Publication No. 2018 / 0059019, the entire contents of which are incorporated herein by reference.

[0120] Figure 6 A method 200 suitable for implementation by the metrology system 100 of the present invention is described. In one aspect, it should be recognized that the data processing blocks of the method 200 may be carried out via a pre-programmed algorithm executed by one or more processors of the computing system 130. Although the following description is presented in the context of the metrology system 100, it should be recognized herein that specific structural aspects of the metrology system 100 are not meant to be limiting and should be interpreted merely as illustrative.

[0121] In block 201, a structure fabricated on a semiconductor wafer is illuminated with an amount of measurement illumination light and an amount of pump illumination light during a measurement time interval. The power of the pump illumination light incident on the structure varies over time during the measurement time interval.

[0122] In block 202 , a measurement signal associated with a measurement of a structure is detected in response to the amount of measurement illumination light and the amount of pump illumination light.

[0123] In block 203, a change in value of one or more electrical or optical properties of one or more materials comprising the structure is estimated. The change in value is induced by a change in the power of the pump illumination light.

[0124] In block 204 , changes in the value of the detected measurement signal induced by changes in the power of the pump illumination light are estimated.

[0125] In block 205 , a value of a parameter of interest characterizing the structure is estimated based on changes in values ​​of one or more electrical or optical properties of one or more materials comprising the structure being measured and changes in values ​​of the detected measurement signal.

[0126] It should be recognized that the various steps described throughout the present invention may be performed by a single computer system or (alternatively) multiple computer systems. In addition, different subsystems such as the spectroscopic ellipsometer 105 may include computer systems suitable for performing at least part of the steps described herein. Therefore, the foregoing description should not be interpreted as limiting the present invention, but is merely illustrative. In addition, the one or more computing systems 130 may be configured to perform any (several) other steps of any of the method embodiments described herein.

[0127] The computing system 130 may include, but is not limited to, a personal computer system, a mainframe computer system, a workstation, an image computer, a parallel processor, or any other computing 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. In general, the computing system 130 may be integrated with a measurement system such as the measurement system 100, or alternatively, may be separate from any measurement system. In this sense, the computing system 130 may be remotely located and receive measurement data and user input from any measurement source and user input source, respectively.

[0128] Program instructions 134 implementing a method, such as the method described herein, may be transmitted via or stored on a carrier medium. The carrier medium may be a transmission medium such as a wire, cable, or wireless transmission link. The carrier medium may also include a computer-readable medium such as a read-only memory, a random access memory, a magnetic or optical disk, or a tape. For example, Figure 3 1, program instructions 134 stored in memory 132 are transmitted to processor 131 via bus 133. Program instructions 134 are stored in a computer readable medium (e.g., memory 132). Exemplary computer readable media include read-only memory, random access memory, magnetic or optical disks, or tapes.

[0129] 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, trench depth, etc.), a critical dimension between any two or more structures (e.g., a distance between two structures), a displacement between two or more structures (e.g., an overlay displacement between overlay grating structures, etc.), and a dispersion property value of a material used in a structure or portion of a structure. The structure may include a three-dimensional structure, a patterned structure, an overlay structure, etc.

[0130] As described herein, the term "critical dimension application" or "critical dimension measurement application" includes any critical dimension measurement.

[0131] As described herein, the term "metrology system" includes any system used at least in part to characterize a sample in any aspect. However, such technical terms do not limit the scope of the term "metrology system" as described herein. The metrology system can be configured as an LED inspection tool, an edge inspection tool, a backside inspection tool, a macro inspection tool, or a multi-mode inspection tool (involving data from one or more platforms simultaneously), and any other metrology or inspection tool.

[0132] Various embodiments are described herein for a semiconductor processing system (e.g., an inspection system or a lithography system) that can be used to process a sample. The term "sample" is used herein to refer to one or more sites on a wafer, a mask, or any other sample that can be processed (e.g., printed or inspected for defects) by methods known in the art. In some instances, a sample includes a single site with one or more measurement targets, and the simultaneous combined measurement of the one or more measurement targets is considered a single sample measurement or reference measurement. In some other instances, a sample is a collection of sites, where the measurement data associated with the collection measurement site is a statistical collection of data associated with each of a plurality of sites. In addition, each of these multiple sites may include one or more measurement targets associated with a sample or reference measurement.

[0133] 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. These substrates are typically found and / or processed in semiconductor manufacturing 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.

[0134] A "reticle" may be a reticle at any stage of the reticle manufacturing process, or a finished reticle that may or may not be released for use in a semiconductor manufacturing facility. A reticle or "mask" is generally defined as a substantially transparent substrate having substantially opaque regions formed thereon and configured as a pattern. The substrate may include, for example, a glass material such as amorphous SiO2. The reticle may be placed over a wafer covered with photoresist during the exposure step of a photolithography process so that the pattern on the reticle may be transferred to the photoresist.

[0135] 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 these material layers may ultimately result in a finished device. Many different types of devices may be formed on a wafer, and the term wafer as used herein is intended to encompass a wafer on which any type of device known in the art is manufactured.

[0136] In one or more exemplary embodiments, the described functions may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted by computer-readable media as one or more instructions or codes. Computer-readable media include both computer storage media and communication media, including any media that facilitates the transfer of computer processes from one location to another. Storage media may be any available media that can be accessed by a general or special-purpose computer. By way of example and not limitation, this computer-readable medium may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage device or any other media that can be used to carry or store the desired 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. Moreover, any connection is appropriately referred to as a computer-readable medium. For example, if software is transmitted from a website, server or other remote source using coaxial cable, optical cable, twisted pair, digital subscriber line (DSL), or wireless technology (such as infrared, radio, and microwave), coaxial cable, optical cable, twisted pair, DSL, or wireless technology (such as infrared, radio, and microwave) are included in the definition of media. 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 lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0137] Although 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 present invention as set forth in the claims.

Claims

1. A metering system comprising: an illumination subsystem configured to illuminate structures fabricated on a semiconductor wafer with an amount of measurement illumination light during a measurement time interval; a pump illumination subsystem configured to illuminate the structure with an amount of pump illumination light during the measurement time interval, wherein a power of the pump illumination light incident on the structure varies over time during the measurement time interval; a detector configured to detect a measurement signal associated with a measurement of the structure in response to the amount of measurement illumination light and the amount of pump illumination light; and A computing system configured to: estimating a change in a value of one or more electrical or optical properties of one or more materials comprising the structure induced by the change in the power of the pump illumination light; estimating a change in the value of the detected measurement signal induced by the change in the power of the pump illumination light; and A value of a parameter of interest characterizing the structure is estimated based on the changes in values ​​of one or more electrical or optical properties of the one or more materials comprising the measured structure and the changes in values ​​of the detected measurement signal. 2 . The metrology system of claim 1 , wherein the estimation of the value of the parameter of interest involves a trained differential-based measurement model. 3 . The metrology system of claim 2 , wherein the trained differential-based measurement model is a machine learning-based model or a physics-based model.

4. The metrology system of claim 2, wherein the parameter of interest is any of a critical dimension, a film thickness, or a material property.

5. The metrology system of claim 1, wherein the detected measurement signals are associated with measurements of the structure at multiple wavelengths, multiple angles of incidence, multiple azimuth angles, or any combination thereof.

6. The metrology system of claim 1, wherein a pump illumination source of the pump illumination subsystem is a laser-based illumination source having a selectable wavelength output.

7. The metrology system of claim 1, wherein the structure to be measured comprises a plurality of different materials, and wherein photon energy of the pump illumination light is between a band gap energy of a first one of the plurality of materials and a band gap energy of a second one of the plurality of materials.

8. The metrology system of claim 1, wherein the metrology system is an optical-based metrology system, an electronic-based metrology system, or an x-ray-based metrology system.

9. The metrology system of claim 1 , wherein the estimation of the change in the value of one or more electrical or optical properties of a material including the one or more materials of the structure involves measuring a change in the value of one or more electrical or optical properties of a metrology target induced by the change in the power of the pump illumination light, wherein the metrology target is disposed at a location on the semiconductor wafer different from a location of the structure being measured, and wherein the metrology target comprises a single film layer of the material.

10. The metering system according to claim 1, wherein the power of the pump illumination light is varied by mechanical modulation or electronic modulation.

11. The metering system according to claim 10, wherein the modulation is a sinusoidal modulation or a square wave modulation.

12. The metrology system of claim 1, wherein the detected measurement signals are values ​​of one or more Mueller matrix elements, values ​​of one or more harmonic signals, or values ​​of one or more detected image signals.

13. The metrology system of claim 1, wherein the structure being measured is an array of partially fabricated transistor devices.

14. The metrology system of claim 1, wherein the variation in the power of the pump illumination light is periodic or aperiodic.

15. A method comprising: illuminating a structure fabricated on a semiconductor wafer with an amount of measurement illumination light and an amount of pump illumination light during a measurement time interval, wherein the power of the pump illumination light incident on the structure varies over time during the measurement time interval; detecting a measurement signal associated with a measurement of the structure in response to the amount of measurement illumination light and the amount of pump illumination light; estimating a change in a value of one or more electrical or optical properties of one or more materials comprising the structure induced by the change in the power of the pump illumination light; estimating a change in the value of the detected measurement signal induced by the change in the power of the pump illumination light; and A value of a parameter of interest characterizing the structure is estimated based on the changes in values ​​of one or more electrical or optical properties of the one or more materials comprising the measured structure and the changes in values ​​of the detected measurement signal.

16. The method of claim 15, wherein the detected measurement signals are associated with measurements of the structure at multiple wavelengths, multiple angles of incidence, multiple azimuth angles, or any combination thereof. 17 . The method of claim 15 , wherein the measured structure comprises a plurality of different materials, and wherein photon energy of the pump illumination light is between a band gap energy of a first one of the plurality of materials and a band gap energy of a second one of the plurality of materials.

18. The method of claim 15, wherein the estimating of the change in the value of one or more electrical or optical properties of a material including the one or more materials of the structure involves measuring a change in the value of one or more electrical or optical properties of a metrology target induced by the change in the power of the pump illumination light, wherein the metrology target is disposed at a location on the semiconductor wafer different from a location of the measured structure, and wherein the metrology target comprises a single film layer of the material.

19. The method according to claim 15, wherein the variation of the power of the pump illumination light is periodic or non-periodic.

20. A metering system comprising: an illumination subsystem configured to illuminate structures fabricated on a semiconductor wafer with an amount of measurement illumination light during a measurement time interval; a pump illumination subsystem configured to illuminate the structure with an amount of pump illumination light during the measurement time interval, wherein a power of the pump illumination light incident on the structure varies over time during the measurement time interval; a detector configured to detect a measurement signal associated with a measurement of the structure in response to the amount of measurement illumination light and the amount of pump illumination light; and A non-transitory computer-readable medium storing instructions that, when executed by one or more processors, cause the one or more processors to: estimating a change in a value of one or more electrical or optical properties of one or more materials comprising the structure induced by the change in the power of the pump illumination light; estimating a change in the value of the detected measurement signal induced by the change in the power of the pump illumination light; and A value of a parameter of interest characterizing the structure is estimated based on the changes in values ​​of one or more electrical or optical properties of the one or more materials comprising the measured structure and the changes in values ​​of the detected measurement signal.

Images