Power control technique for raman spectroscopy
The Raman spectroscopy system with real-time power control and beam splitting stabilizes incident illumination power, addressing nonlinear spectral responses in semiconductor nanostructures, ensuring accurate measurements in high-volume manufacturing environments.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- NOVA MEASURING INSTR LTD
- Filing Date
- 2026-01-16
- Publication Date
- 2026-07-23
AI Technical Summary
Conventional Raman spectroscopy methods struggle to maintain stable incident illumination power in high-volume manufacturing environments, particularly when semiconductor nanostructures exhibit nonlinear spectral responses due to sample heating and free charge carrier excitation, leading to distorted spectral measurements and interpretation challenges.
A Raman spectroscopy system with real-time power control, utilizing a beam splitter to split the illumination beam into two paths for concurrent power measurement and adjustment, maintaining power within one percent of a target value during sample measurement, and employing various power control mechanisms such as filter wheels, polarization-based units, and Opto-Acoustic Modulation devices to stabilize incident power.
This approach ensures accurate and stable Raman spectroscopy measurements by minimizing power fluctuations, thereby improving the interpretation of nonlinear spectral responses in high-volume manufacturing settings.
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Figure IB2026050378_23072026_PF_FP_ABST
Abstract
Description
POWER CONTROL TECHNIQUE FOR RAMAN SPECTROSCOPY CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Application No. 63 / 745,822, titled Power Control Technique For Raman Spectroscopy, filed 16 January 2025 which is hereby incorporated by reference in its entirety.FIELD OF INVENTION
[0002] The present disclosure relates to Raman spectroscopy systems for semiconductor metrology, and more particularly to power control techniques for maintaining stable incident illumination power during Raman spectroscopy measurements of samples exhibiting nonlinear spectral responses in high-volume manufacturing environments.BACKGROUND
[0003] Raman spectroscopy is a characterization technique that provides information about molecular vibrations and crystal structures by analyzing the inelastic scattering of monochromatic light, typically from a laser source. When light interacts with a sample, a small fraction of the scattered photons experiences a shift in energy corresponding to vibrational modes of the material, producing a characteristic spectrum that can reveal information about composition, stress, temperature, and other material properties.
[0004] In semiconductor manufacturing, Raman spectroscopy has emerged as a metrology tool for process control during fabrication of nanostructures. The technique offers non-destructive characterization capabilities that can provide insights into various properties of materials and structures at different stages of the manufacturing process. The Raman spectrum obtained from a sample depends on various measurement attributes, including excitation wavelength, polarization, and angle of incidence, which are typically controlled by the measurement platform.
[0005] Under many measurement conditions, the Raman signal line shape exhibits a linear relationship with incident light intensity. In such cases, variations in incident power result in proportional changes in the overall Raman spectrum intensity while preserving the spectral shape. This linear behavior enables straightforward calibration approaches in which the incident intensity is measured using a calibration target, and the Raman spectrum is normalized by dividing by the measured intensity value.
[0006] However, certain semiconductor nanostructures exhibit different behavior where the spectral response depends nonlinearly on the incident laser power. Physical processes such as sample heating and free charge carrier excitation can affect the spectral line shape in complex ways that vary with incident power. Under such nonlinear response conditions,conventional calibration approaches based on simple intensity normalization may not adequately address the relationship between incident power and spectral characteristics. Changes or instabilities in the incident power can cause changes in the measured line shape that may complicate interpretation of the Raman spectrum.
[0007] Approaches for addressing changes in illumination power have included direct calibration using separate measurements of characterized calibration targets. Alternative approaches have involved incorporating incident power as a parameter in measurement interpretation through algorithmic methods that attempt to account for line shape changes due to power variations. Such algorithmic approaches may be limited by the accuracy of the description of the nonlinear response, which can vary depending on the sample being measured.SUMMARY
[0008] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0009] According to an aspect of the present disclosure, a Raman spectroscopy system configured to operate in a high-volume manufacturing environment is provided. The Raman spectroscopy system includes an illumination module that is configured to generate an illumination beam. The Raman spectroscopy system includes a power control unit configured to receive, in real time, feedback on the illumination beam and to provide, in real time, a power-controlled illumination beam whose power is maintained within one percent of a target value during the sample measurement process" The Raman spectroscopy system includes a beam splitter that is configured to split the power-controlled illumination beam to a first beam and a second beam. The Raman spectroscopy system includes a Raman spectroscopy module that is configured to use the first beam, during the sample measurement process, to generate Raman spectra of multiple measurement sites of a sample that exhibits a nonlinear spectral response. The Raman spectroscopy system includes a power measurement module configured to measure, in real time, a power of the second beam and generate the feedback.
[0010] According to another aspect of the present disclosure, a method for performing Raman spectroscopy in a high-volume manufacturing environment is provided. The method includes generating an illumination beam. The method includes receiving, in real time, feedback indicative of a power of the illumination beam. The method includes controlling, inreal time, a power of the illumination beam based on the feedback to provide a power-controlled illumination beam having a power maintained within a deviation of up to one percent of a target value during a sample measurement process. The method includes splitting the power-controlled illumination beam into a first beam and a second beam. The method includes measuring, in real time, a power of the second beam to generate the feedback. The method includes using the first beam to generate Raman spectra of multiple measurement sites of a sample that exhibits a nonlinear spectral response.
[0011] The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.BRIEF DESCRIPTION OF FIGURES
[0012] Non-limiting and non-exhaustive examples are described with reference to the following figures.
[0013] FIG. 1A illustrates a diagram of a linear spectral response to incident power, according to aspects of the present disclosure.
[0014] FIG. IB illustrates a diagram of a nonlinear spectral response to incident power, according to aspects of the present disclosure.
[0015] FIG. 1C illustrates a diagram of a calibration process for Raman spectroscopy, according to aspects of the present disclosure.
[0016] FIG. 2A illustrates a schematic optical layout of a Raman spectroscopy system with real-time power control, according to aspects of the present disclosure.
[0017] FIG. 2B illustrates a schematic optical layout of an alternative Raman spectroscopy system with a power monitor module positioned below an objective, according to aspects of the present disclosure.
[0018] FIG. 3 illustrates a schematic view of a multiple-filter implementation for power control, according to aspects of the present disclosure.
[0019] FIG. 4 illustrates a schematic view of a polarization based attenuating unit, according to aspects of the present disclosure.
[0020] FIG. 5 illustrates a method 100 for performing Raman spectroscopy in a high-volume manufacturing environment.DETAILED DESCRIPTION
[0021] The following description sets forth exemplary aspects of the present disclosure. It should be recognized, however, that such description is not intended as a limitation on thescope of the present disclosure. Rather, the description also encompasses combinations and modifications to those exemplary aspects described herein.
[0022] Referring to Figs. 1A, IB, and 1C, diagrams illustrating linear and nonlinear spectral responses to incident power in Raman spectroscopy are shown. In Raman spectroscopy, the spectral response of a sample to incident laser power may exhibit either linear or nonlinear behavior depending on the characteristics of the sample under measurement.
[0023] Fig. 1A illustrates a linear spectral response to incident power. In the linear response condition, the spectral line shape is preserved when incident power varies. As shown in Fig. 1A, a high incidence power spectral response 1 and a low incidence power spectral response 2 are depicted along a vertical axis labeled b and a horizontal axis labeled k. The high incidence power spectral response 1 and the low incidence power spectral response 2 maintain the same spectral line shape, with the curves differing in overall intensity. Under linear response conditions, variation of the incident power results in an equal change in the overall Raman spectrum intensity, but with no change in the spectral shape.
[0024] With continued reference to Figs. 1A, IB, and 1C, Fig. IB illustrates a nonlinear spectral response to incident power. In the nonlinear response condition, the spectral line shape is not preserved when incident power varies. As shown in Fig. IB, a high incidence power nonlinear spectral response 3 and a low incidence power nonlinear spectral response 4 are depicted along a vertical axis labeled b and a horizontal axis labeled k. The high incidence power nonlinear spectral response 3 and the low incidence power nonlinear spectral response 4 exhibit different spectral line shapes, demonstrating that the spectral shape changes under varying incident power conditions. In some cases, the sample may include a semiconductor nanostructure, and the nonlinear spectral response may result from at least one of sample heating and free charge carrier excitation. These physical processes may affect the line shape in nontrivial ways when the sample is illuminated with varying power levels.
[0025] Fig. 1C illustrates a calibration process that is applicable under linear spectral response conditions. The calibration process includes a calibration target measurement step 5 that leads to an incident power extraction step 6. The incident power extraction step 6 provides incident power information that is used in conjunction with an application measurement step 7. Following the application measurement step 7, a spectrum division step 8 is performed where the measured spectrum is divided by the incident power obtained from the incident power extraction step 6. The spectrum division step 8 results in a calibratedspectrum 9. This direct calibration approach is effective when samples exhibit linear spectral response because the spectral line shape is preserved regardless of incident power variations.
[0026] However, the direct calibration approach illustrated in Fig. 1C is not effective when samples exhibit nonlinear spectral response. Under nonlinear response conditions, a change or instability in the incident power causes a change in the measured line shape, and simple division by the incident power does not correct for the line shape distortion. In a Raman spectroscopy system configured to operate in a high-volume manufacturing environment, when the sample includes a semiconductor nanostructure and the nonlinear spectral response results from at least one of sample heating and free charge carrier excitation, the direct calibration method fails to provide accurate spectral measurements. Similarly, in a method for performing Raman spectroscopy in a high-volume manufacturing environment, when the sample includes a semiconductor nanostructure and the nonlinear spectral response results from at least one of sample heating and free charge carrier excitation, power fluctuations may result in erroneous interpretation of the Raman spectrum when using direct calibration approaches.
[0027] Furthermore, in high-volume manufacturing environments, where throughput is important - using a separate calibration target that required to move the stage to enable a calibration based on the separate calibration target - may be too slow and may negatively impact the throughput.
[0028] Referring to FIG. 2A, a schematic optical layout of a Raman spectroscopy system configured to operate in a high-volume manufacturing environment is shown. The Raman spectroscopy system includes an illumination module 22 that is configured to generate an illumination beam 11. Illumination beam 11 is directed toward a power control 26 that is configured to receive, in real time, feedback 31 and the illumination beam 11. The power control 26 is further configured to provide, in real time, a power-controlled illumination beam 12 having a power that is maintained within a deviation of up to one percent of a target value during a sample measurement process. This aggressive power control scheme reduces the impact of the nonlinear response to not exceed a tolerable amount.
[0029] According to an embodiment, the illumination beam is generated during the entire sample measurement process (even when moving from one site to the other, even when obtaining the sample and releasing the sample) and / or even between one sample measurement process to another - to reduce the power fluctuations of the illumination beam.
[0030] With continued reference to FIG. 2A, the power control 26 may account for short term power variations due to changes in laser output intensity and / or transmission of opticalelement. The power control 26 may also account for long term power variations due to changes in laser output intensity, transmission of optical elements, and collection efficiency. By maintaining the power of the power-controlled illumination beam 12 within the deviation of up to one percent of the target value, the Raman spectroscopy system addresses the challenges associated with samples that exhibit nonlinear spectral response.
[0031] The Raman spectroscopy system further includes a beam splitter 28 that is configured to split the power-controlled illumination beam 12 into a first beam 13 and a second beam 17. The beam splitter 28 may be a partially transmitting mirror or any existing beam-splitter in the optical path. As shown in FIG. 2A, the beam splitter 28 is located upstream to an objective 32 of the Raman spectroscopy system. The first beam 13 is directed toward the objective 32, while the second beam 17 is directed toward a power meter 30.
[0032] The Raman spectroscopy system includes a power measurement module that includes the power meter 30. The power meter 30 is configured to measure, in real time, a power of the second beam 17 and generate the feedback 31. The feedback 31 is transmitted from the power meter 30 to the power control 26 to enable real-time adjustment of the power-controlled illumination beam 12. The measurement to adjusting process may last for one or few seconds. The power meter 30 may be placed along the illumination path as close as possible to the measured sample so that the measured power accounts for variations in transmission of optical elements along the illumination but does not depend on changes along the collection path.
[0033] As further shown in FIG. 2A, the first beam 13 passes through the objective 32, which focuses the first beam 13 to produce a focused illumination beam 15. The focused illumination beam 15 is directed toward a wafer 99 positioned on a stage 34. The wafer 99 represents a sample under measurement that may exhibit a nonlinear spectral response. Light returning from the wafer 99 forms a returned beam 16, which passes back through the objective 32 to produce a collimated returning beam 14. The collimated returning beam 14 reaches the beam splitter 28, where the collimated returning beam 14 is directed toward a detection module 24.
[0034] The detection module 24 forms part of a Raman spectroscopy module that is configured to use the first beam 13, during the sample measurement process, to generate Raman spectra of multiple measurement sites of the wafer 99 that exhibits a nonlinear spectral response. In some cases, the multiple measurement sites may be between ten and ninety per sample. In some cases, an overall duration of the sample measurement process, aP0340preliminary step that includes obtaining the sample, and a final step of outputting the sample may be about a few tens of seconds. Few - for example - between one and ten.
[0035] This configuration enables the Raman spectra to be generated concurrently with the generation of the feedback 31. Because the beam splitter 28 directs the second beam 17 to the power meter 30 while simultaneously allowing the first beam 13 to proceed toward the wafer 99, power monitoring and sample measurement may occur at the same time. This concurrent operation allows the power control 26 to compensate for fast power variations with no delay between the power measurement and the power control.
[0036] In a method for performing Raman spectroscopy in a high-volume manufacturing environment, the method includes generating an illumination beam 11 using the illumination module 22. The method further includes receiving, in real time, feedback 31 indicative of a power of the illumination beam 11. The method includes controlling, in real time, a power of the illumination beam 11 based on the feedback 31 to provide the power-controlled illumination beam 12 having a power maintained within a deviation of up to one percent of a target value during a sample measurement process.
[0037] The method further includes splitting the power-controlled illumination beam 12 into the first beam 13 and the second beam 17 using the beam splitter 28. Splitting the power-controlled illumination beam 12 is performed upstream of focusing the first beam 13 through the objective 32 onto the sample. The method includes measuring, in real time, a power of the second beam 17 to generate the feedback 31 using the power meter 30. The method includes using the first beam 13 to generate Raman spectra of multiple measurement sites of a sample that exhibits a nonlinear spectral response.
[0038] In some cases, generating the Raman spectra is performed concurrently with generating the feedback 31. In some cases, the multiple measurement sites may be between ten and ninety per sample, and an overall duration of the sample measurement process, a preliminary step that includes obtaining the sample, and a final step of outputting the sample may be about a few tens of seconds.
[0039] Referring to FIG. 2B, a schematic optical layout of an alternative embodiment of the Raman spectroscopy system is shown in which a power monitor module 38 is positioned below the objective 32. The Raman spectroscopy system includes the illumination module 22 that generates the illumination beam directed toward the power control 26. The power control 26 regulates the intensity of the illumination beam before the illumination beam passes to the beam splitter 28. The beam splitter 28 directs a portion of the light upward toward theP0340detection module 24 and another portion downward toward the objective 32. The objective 32 focuses the illumination beam onto a wafer 99 supported by the stage 34.
[0040] In the embodiment shown in FIG. 2B, the power monitor module 38 includes a collimating lens 36 designed to collimate the beam emerging from the objective 32 and a mirror 35 that redirects the collimated beam toward the power meter 30. The collimating lens 36 and the mirror 35 are mechanically mounted onto the stage 34. When a power measurement is desired, the stage 34 is moved to position the collimating lens 36 and the mirror 35 below the objective 32, directing the light beam toward the power meter 30. The power meter 30 is separate from the stage 34.
[0041] With continued reference to FIG. 2B, this configuration provides accurate measurement of the power reaching the measured sample by accounting for all elements in the illumination path including the objective 32. However, power measurement is not performed concurrently with sample measurement when using the power monitor module 38, as movement of the stage 34 between the measurement location and the power monitoring site is required. The frequency of power monitoring and calibration when using this configuration may depend on the power fluctuation temporal properties and the required power stabilization as derived from the spectral sensitivity to incident power for the sample under study.
[0042] In some cases, an internal calibration target may be used for power monitoring. The internal calibration target may include a stable, characterized target such as polished crystalline Silicon placed inside the measurement unit. By measuring the internal calibration target using the detection module 24, variations in the illumination intensity may be obtained. This approach does not require the addition of a dedicated power monitoring element.However, the internal calibration target approach may not be implemented concurrently with the measurement, as the internal calibration target approach is based on a separate measurement sequence. In addition, the internal calibration target approach measures changes in the entire optical path, and any transmission change in the collection path or the detector may affect the calibration measurement without affecting the incident power on the sample.
[0043] In some cases, an external calibration wafer may be used for power monitoring. The external calibration wafer includes a dedicated sample that may be measured at selected times for power monitoring without requiring added components inside the measurement unit. However, the external calibration wafer approach incurs time delays between the power monitoring and power control sequences, which may not allow compensation of rapid powerP0340changes. In addition, the external calibration wafer approach is sensitive to changes in the collection path.
[0044] Referring to FIG. 3, a schematic view of a multiple-filter implementation for power control in the Raman spectroscopy system is shown. In some cases, the power control 26 may include a plurality of filter wheels arranged in series along the illumination path, each filter wheel including a plurality of transmission filters having different transmission values. As shown in FIG. 3, the configuration includes a first filter wheel 26A and a second filter wheel 26B arranged in series along an optical path through which the illumination beam 11 passes to produce the power-controlled illumination beam 12.
[0045] The first filter wheel 26A provides coarse power adjustment and includes a plurality of transmission filters arranged around a circumference of the first filter wheel 26A. The transmission filters of the first filter wheel 26A include a ten percent transmission filter 10, a twenty percent transmission filter 20, a forty percent transmission filter 40, a fifty percent transmission filter 50, a sixty percent transmission filter 60, a seventy percent transmission filter 70, an eighty percent transmission filter 80, a ninety percent transmission filter 90, and a full transmission filter 100. The transmission values represent the amount of light transmitted through each filter position of the first filter wheel 26 A.
[0046] With continued reference to FIG. 3, the second filter wheel 26B provides fine power adjustment and includes transmission filters with finer increments than the first filter wheel 26A. The transmission filters of the second filter wheel 26B include a ninety-one percent transmission filter 91, a ninety-two percent transmission filter 92, a ninety-three percent transmission filter 93, a ninety-four percent transmission filter 94, a ninety-five percent transmission filter 95, a ninety-six percent transmission filter 96, a ninety-seven percent transmission filter 97, a ninety-eight percent transmission filter 98, a ninety-nine percent transmission filter 99, and the full transmission filter 100.
[0047] The illumination beam 11 enters the first filter wheel 26A and passes through a selected filter position of the first filter wheel 26A. The illumination beam 11 then continues through the second filter wheel 26B and a corresponding selected filter position of the second filter wheel 26B to produce the power-controlled illumination beam 12. By selecting appropriate combinations of filters from the first filter wheel 26A and the second filter wheel 26B, fine-tuned overall transmission may be achieved, enabling precise control of the incident power on a sample during Raman spectroscopy measurements.
[0048] In a method for performing Raman spectroscopy in a high-volume manufacturing environment, controlling the power of the illumination beam 11 may include rotating aP0340plurality of filter wheels arranged in series along an illumination path, each filter wheel including a plurality of transmission filters having different transmission values. In some cases, the first filter wheel 26A of the plurality of filter wheels provides coarse power adjustment and the second filter wheel 26B of the plurality of filter wheels provides fine power adjustment.
[0049] In some cases, the power control 26 may include a continuously varying transmission attenuation filter (not shown) mounted on a motorized stage. The continuously varying transmission attenuation filter (for example a continuous neutral density filter). A continuously varying transmission attenuation filter may have gradually varying absorption properties across a surface of the continuously varying transmission attenuation filter. The motorized stage may be a rotational motorized stage or a linear motorized stage. A one-time calibration sequence may be used to find the transmission versus motor position for the continuously varying transmission attenuation filter, following which accurate transmission control is possible. Following each power measurement using the power meter 30, the continuously varying transmission attenuation filter may be moved to compensate for any change compared to a desired power.
[0050] In a method for performing Raman spectroscopy in a high-volume manufacturing environment, controlling the power of the illumination beam 11 may include adjusting a continuously varying transmission attenuation filter mounted on a motorized stage. The adjustment may be based on the feedback 31 received from the power meter 30 to maintain the power of the power-controlled illumination beam 12 within the deviation of up to one percent of the target value during the sample measurement process.
[0051] Referring to FIG. 4, a schematic view of a polarization based attenuating unit is shown. In some cases, the power control 26 may include a polarization based attenuating unit. The polarization based attenuating unit includes a sequence of optical elements arranged along an optical axis, which corresponds to the path of the illumination beam 11.
[0052] A first polarizer 51 is positioned at an input side of the polarization based attenuating unit to receive the illumination beam 11. The first polarizer 51 serves to eliminate residual polarization from the laser beam and to fix the polarization axis in reference to subsequent optical elements. The first polarizer 51 fixes the polarization axis in reference to a half-wave plate 53 and a second polarizer 52. The function of fixing the polarization axis carries significance because the laser beam polarization direction may change over time. Without the first polarizer 51, the direction to turn the half- wave plate 53 with a given powerP0340reading would not be known a-priori, which may make the power attenuation correction process slower and more error-prone.
[0053] With continued reference to FIG. 4, the half-wave plate 53 is positioned downstream from the first polarizer 51. The half-wave plate 53 is rotatable about the optical axis, as indicated by a rotation arrow 54. Rotation of the half-wave plate 53 changes the polarization direction of the light passing through the half-wave plate 53.
[0054] The second polarizer 52 is positioned downstream from the half-wave plate 53. The second polarizer 52 receives light from the half-wave plate 53 and transmits light according to Malus's law based on the relative angle between the polarization direction established by the half-wave plate 53 and the transmission axis of the second polarizer 52. The attenuation of the illumination beam 11 is determined by the angular position of the rotatable half-wave plate 53. By rotating the half-wave plate 53, the polarization direction relative to the second polarizer 52 is changed, thereby controlling the power transmission through the polarization based attenuating unit to produce the power-controlled illumination beam 12.
[0055] In some cases, the polarization based attenuating unit may include a sequence of the first polarizer 51, the rotatable half-wave plate 53, and the second polarizer 52 arranged along the optical axis. This configuration provides accurate power control while addressing laser polarization instabilities through the inclusion of the first polarizer 51.
[0056] In some cases, the polarization based attenuating unit may include an alternative configuration with the rotatable half-wave plate 53 and the second polarizer 52 without the first polarizer 51. In this alternative configuration, power is attenuated by rotating the halfwave plate 53 to change the polarization direction relative to the second polarizer 52 according to Malus's law. The rotation of the half-wave plate 53 changes the polarization direction relative to the second polarizer 52 and then the power changes according to Malus's law. However, this alternative configuration may be sensitive to laser polarization instabilities because when the nominal polarization is not set in the same orientation as the second polarizer 52, variations in the laser output polarization may incur a more significant impact on the overall transmission.
[0057] In a method for performing Raman spectroscopy in a high-volume manufacturing environment, controlling the power of the illumination beam 11 may include adjusting a polarization based attenuating unit including a sequence of the first polarizer 51, the rotatable half-wave plate 53, and the second polarizer 52 arranged along an optical axis. The adjustment may include rotating the half-wave plate 53 to change the polarization directionP0340relative to the second polarizer 52, thereby controlling the power of the power-controlled illumination beam 12 based on the feedback 31 received from the power meter 30.
[0058] In some cases, the power control may include an Opto-Acoustic Modulation device acting in transmission mode. Opto-Acoustic Modulation devices are suitable for power control when the incident light is monochromatic, such as light originating from an excitation laser used in Raman spectroscopy. Opto-Acoustic Modulation devices operating in transmission mode receive the illumination beam and modulate the transmission of the illumination beam based on acoustic waves propagating through an acousto-optic medium. The Opto-Acoustic Modulation device in transmission mode provides fast response times for power control, enabling compensation for rapid power fluctuations during the sample measurement process.
[0059] In some cases, the power control may include an Opto-Acoustic Modulation device acting in reflection mode. Opto-Acoustic Modulation devices operating in reflection mode are also suitable for power control when the incident light is monochromatic originating from the excitation laser. The Opto-Acoustic Modulation device in reflection mode modulates the power of the illumination beam by controlling the diffraction efficiency of the acoustic grating within the acousto-optic medium. Opto-Acoustic Modulation devices, whether operating in transmission mode or reflection mode, provide fast response times for power control. However, Opto-Acoustic Modulation devices may have deficiencies related to complexity, cost, and dynamic range compared to other power control implementations.
[0060] In some cases, the sample nonlinear response may depend on power density rather than total incident power. When the sample nonlinear response depends on power density, changes in an illuminated spot size on the sample may cause errors and instabilities in the Raman spectroscopy measurements. The power control may compensate for changes in the illuminated spot size by making a corresponding change of the illuminated power. By adjusting the illuminated power in response to changes in the illuminated spot size, the power density on the sample may be maintained at a target value, thereby resolving errors and instabilities that would otherwise result from spot size variations.
[0061] The measurement sequence of the Raman spectroscopy system may be adapted to include power monitoring and control. The frequency of power monitoring and calibration may depend on the power fluctuation temporal properties of the illumination source and optical elements. The frequency of power monitoring and calibration may also depend on the required power stabilization as derived from the spectral sensitivity to incident power for the sample under study. When the power monitoring implementation does not support concurrentP0340power measurement with the sample measurement, the frequency of power monitoring and calibration may be selected based on the temporal characteristics of power fluctuations and the tolerance of the sample to power variations. Samples with higher spectral sensitivity to incident power may require more frequent power monitoring and calibration to maintain the power of the power-controlled illumination beam within the deviation of up to one percent of the target value during the sample measurement process.
[0062] Referring to FIG. 5, and with continued reference to FIGS. 2A, 2B, and 4, a method 100 for performing Raman spectroscopy in a high-volume manufacturing environment is shown. The method 100 includes a sequence of operations that enable stable power control during measurement of samples exhibiting nonlinear spectral responses.
[0063] The method 100 begins at step 102 of generating an illumination beam by illumination module 22. The illumination beam 11 may originate from a laser source configured to provide monochromatic light suitable for Raman spectroscopy measurements.
[0064] The method 100 proceeds to step 104 of receiving feedback of a power of the illumination beam in real time. The feedback 31 may be generated by the power meter 30 based on measurements of the second beam 17 as shown in FIG. 2A or based on measurements obtained through the power monitor module 38 as shown in FIG. 2B.
[0065] The method 100 continues to step 106 of controlling power of the illumination beam 11 in real time based on the feedback 31 to provide the power-controlled illumination beam 12 having a power maintained within a deviation of up to one percent of a target value during a sample measurement process. Step 106 may be performed using the power control 26. In some cases, step 106 may include adjusting a polarization based attenuating unit as shown in FIG. 4, wherein the half- wave plate 53 is rotated to change the polarization direction relative to the second polarizer 52.
[0066] The method 100 proceeds to step 108 of splitting the power-controlled illumination beam 12 into the first beam 13 and the second beam 17 using the beam splitter 28. As shown in FIG. 2A, the split beam operation 108 may be performed upstream of focusing the first beam 13 through the objective 32 onto the sample.
[0067] The method 100 continues to step 110 of measuring a power of the second beam 17 in real time to generate the feedback 31. Step 110 may be performed using the power meter 30. In some cases, as shown in FIG. 2A, step 110 may be performed concurrently with sample measurement or at a certain time shift. In some cases, as shown in FIG. 2B, step 110 may be performed using the power monitor module 38 positioned below the objective 32.P0340
[0068] The method 100 also includes step 112 of generating Raman spectra of the first beam 13 of multiple measurement sites of a sample that exhibits a nonlinear spectral response. Step 112 may be performed using the detection module 24 to collect and analyze light returned from the wafer 99.
[0069] According to an embodiment the nonlinear response of nanostructures of a sample can be measured or otherwise estimated or evaluated - and the power control scheme may be adapted to the amount of power deviation that will result in a response that its nonlinearity is below an allowable threshold (which can be defined by the manufacturer of the sample, by a measurement entity and the like).
[0070] According to an embodiment the power-controlled illumination beam may have a power that is maintained within a deviation of up to a fraction of one percent of a target value.
[0071] The target value is a desired value of the power - which can be defined by the manufacturer of the sample, by a measurement entity and the like. According to an embodiment the target power provides a tradeoff between the measurement parameter - for example signal to noise versus the risk of triggering a significant non-linear response.
[0072] Several implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.
[0073] Any reference to the term "comprising" or "having" should be applied, mutatis mutandis to "consisting of or "essentially consisting of".
[0074] Any reference to a system should be applied, mutatis mutandis to a method executable by the system and / or should be applied, mutatis mutandis to a non-transitory computer readable medium that stores instructions executable by the system.
[0075] Any reference to a method system should be applied, mutatis mutandis to a system configured to execute the method and / or should be applied, mutatis mutandis to a non-transitory computer readable medium that stores instructions executable by the system.
[0076] Any reference to a computer readable medium should be applied, mutatis mutandis to a method executed based on instructions stored in the computer readable medium and / or should be applied, mutatis mutandis to a system configured to execute the instructions.
[0077] In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that variousP0340modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims.
[0078] Moreover, the terms "front, " "back, " "top, " "bottom, " "over, " "under " and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
[0079] Any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with " each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected, " or "operably coupled, " to each other to achieve the desired functionality.
[0080] Furthermore, those skilled in the art will recognize that boundaries between the above-described operations are merely illustrative. The multiple operations may be combined into a single operation; a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.
[0081] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Claims
CLAIMSWe Claim1. A Raman spectroscopy system configured to operate in a high-volume manufacturing environment, Raman spectroscopy system comprising:an illumination module that is configured to generate an illumination beam;a power control unit that is configured to (i) receive in real time, feedback and the illumination beam and (ii) provide in real time, a power-controlled illumination beam having a power that is maintained within a deviation of up to one percent of a target value, during a sample measurement process;a beam splitter that is configured to split the power-controlled illumination beam to a first beam and a second beam;a Raman spectroscopy module that is configured to use the first beam, during the sample measurement process, to generate Raman spectra of multiple measurement sites of a sample that exhibits a nonlinear spectral response; anda power measurement module configured to measure, in real time, a power of the second beam and generate the feedback.
2. The Raman spectroscopy system according to claim 1, wherein the Raman spectra are generated concurrently with the generation of the feedback.
3. The Raman spectroscopy system according to claim 1, wherein the beam splitter is located upstream to an objective lens of the Raman spectroscopy module.
4. The Raman spectroscopy system according to claim 1, wherein the power control unit comprises a continuously varying transmission attenuation filter mounted on a motorized stage.
5. The Raman spectroscopy system according to claim 1, wherein the power control unit comprises a plurality of filter wheels arranged in series along the illumination path, each filter wheel comprising a plurality of transmission filters having different transmission values.
6. The Raman spectroscopy system according of claim 5, wherein a first filter wheel of the plurality of filter wheels provides coarse power adjustment and a second filter wheel of the plurality of filter wheels provides fine power adjustment.
7. The Raman spectroscopy system according claim 1, wherein the power control unit comprises a continuously varying transmission attenuation filter mounted on a motorized stage8. The Raman spectroscopy system according claim 1, wherein the power control unit comprises a polarization based attenuating unit.P03409. The Raman spectroscopy system according claim 8, wherein the polarization based attenuating unit comprises a sequence of a first polarizer, a rotatable half-wave plate and a second polarizer arranged along an optical axis.
10. The Raman spectroscopy system according claim 1, wherein the sample comprises a semiconductor nanostructure and the nonlinear spectral response results from at least one of sample heating and free charge carrier excitation.
11. The Raman spectroscopy system according to claim 1, wherein the multiple measurement sites are between ten and ninety per sample, and wherein an overall duration of the sample measurement process, a preliminary step that comprises obtaining the sample, and a final step of outputting the sample is about a few tens of seconds.
12. A method for performing Raman spectroscopy in a high-volume manufacturing environment, the method comprising: generating an illumination beam; receiving, in real time, feedback indicative of a power of the illumination beam; controlling, in real time, a power of the illumination beam based on the feedback to provide a power-controlled illumination beam having a power maintained within a deviation of up to one percent of a target value during a sample measurement process; splitting the power-controlled illumination beam into a first beam and a second beam; measuring, in real time, a power of the second beam to generate the feedback; and using the first beam to generate Raman spectra of multiple measurement sites of a sample that exhibits a nonlinear spectral response.
13. The method according to claim 12, wherein generating the Raman spectra is performed concurrently with generating the feedback.
14. The method according to claim 12, wherein splitting the power-controlled illumination beam is performed upstream of focusing the first beam through an objective lens onto the sample.
15. The method according to claim 12, wherein controlling the power of the illumination beam comprises adjusting a continuously varying transmission attenuation filter mounted on a motorized stage.
16. The method according to claim 12, wherein controlling the power of the illumination beam comprises rotating a plurality of filter wheels arranged in series along an illumination path, each filter wheel comprising a plurality of transmission filters having different transmission values.
17. The method according to claim 16, wherein a first filter wheel of the plurality of filter wheels provides coarse power adjustment and a second filter wheel of the plurality of filter wheels provides fine power adjustment.
18. The method according to claim 12, wherein controlling the power of the illumination beam comprises adjusting a polarization based attenuating unit comprising a sequence of a first polarizer, a rotatable half-wave plate and a second polarizer arranged along an optical axis.
19. The method according to claim 12, wherein the sample comprises a semiconductor nanostructure and the nonlinear spectral response results from at least one of sample heating and free charge carrier excitation.
20. The method according to claim 12, wherein the multiple measurement sites are between ten and ninety per sample, and wherein an overall duration of the sample measurement process, a preliminary step that comprises obtaining the sample, and a final step of outputting the sample is about a few tens of seconds.