Multi-wavelength interferometry for defect classification

Abstract

Embodiments of the present application relate to multi-wavelength interferometry for defect classification. An inspection system may include a controller coupled to a differential interference contrast imaging tool, the differential interference contrast imaging tool being used to generate an image of a sample based on illumination by two sheared illumination beams. The controller may determine a first defect-induced phase shift based on a first image set of a defect on the sample, the first image set having a first selected illumination spectrum and two or more selected induced phase differences between the two sheared illumination beams; determine a second defect-induced phase shift based on a second image set of the defect, the second image set having a second selected illumination spectrum and two or more selected induced phase differences between the two sheared illumination beams; and classify the defect as metal or non-metal based on a comparison of the first phase shift and the second phase shift.

Description

[0001] Information about divisional applications

[0002] This application is a divisional application of the invention patent application with the application date of August 29, 2019, application number "201980057650.0", and invention name "Multi-wavelength interferometry for defect classification".

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This application claims the benefit of U.S. Provisional Application No. 62 / 726,782, filed on September 4, 2018, entitled “COMPOSITION ANALYSIS OF METAL AND MONMETAL DEFECTS BY USING PHASE CONTRAST IMAGING INTERFEROMETER,” under 35 U.S.C. §119(e), the entire contents of which are incorporated herein by reference. Technical Field

[0005] The present invention relates generally to defect classification in semiconductor manufacturing, and more particularly to multi-wavelength interferometry for defect classification. Background Art

[0006] Defect detection is a critical step in the semiconductor manufacturing process and may be performed at various stages of manufacturing to control yield. In addition, it may be desirable to identify the composition of an identified defect to facilitate determining the root cause of the defect. For example, identifying whether an identified particle on a sample is metal or non-metal (e.g., dielectric) may provide insight into the source of contamination.

[0007] However, typical defect inspection systems are not suitable for classifying identified defects based on composition. Instead, compositional analysis can often be performed using separate tools, such as energy dispersive X-ray (EDX) tools, which can suffer from relatively long measurement times, which negatively impacts throughput. Additionally, transferring samples between tools can potentially expose samples to further contaminants and further reduce throughput. Therefore, there is a need to develop systems and methods to address the above-mentioned drawbacks. Summary of the invention

[0008] An inspection system according to one or more illustrative embodiments of the present invention is disclosed. In one illustrative embodiment, the system includes a controller communicatively coupled to a differential interference contrast imaging tool, the differential interference contrast imaging tool being configured to generate one or more images of a sample based on illumination of two clipped illumination beams, wherein illumination spectra of the two clipped illumination beams and induced phase differences between the two clipped illumination beams are selectable for any particular image of the sample. In another illustrative embodiment, the controller receives a first set of images of a defect on the sample, the first set of images having a first selected illumination spectrum and two or more selected induced phase differences between the two clipped illumination beams. In another illustrative embodiment, the controller determines a first defect-inducing phase shift based on the first selected illumination spectrum. In another illustrative embodiment, the controller receives a second set of images of the defect on the sample, the second set of images having a second selected illumination spectrum different from the first illumination spectrum and two or more selected induced phase differences between the two clipped illumination beams. In another illustrative embodiment, the controller determines a second defect-inducing phase shift based on the second selected illumination spectrum. In another illustrative embodiment, the controller classifies the defect as metal or non-metal based on a comparison of the first phase shift and the second phase shift.

[0009] An inspection system according to one or more illustrative embodiments of the present invention is disclosed. In one illustrative embodiment, the system includes a differential interference contrast imaging tool, the differential interference contrast imaging tool being used to generate one or more images of a sample based on illumination of two clipped illumination beams, wherein the illumination spectra of the two clipped illumination beams and the phase difference between the two clipped illumination beams can be selected for any particular image of the sample. In another illustrative embodiment, the system includes a controller communicatively coupled to the imaging tool. In another illustrative embodiment, the controller receives a first set of images of a defect on the sample, the first set of images having a first selected illumination spectrum and two or more selected induced phase differences between the two clipped illumination beams. In another illustrative embodiment, the controller determines a first phase shift associated with the defect based on the first selected illumination spectrum. In another illustrative embodiment, the controller receives a second set of images of the defect on the sample, the second set of images having a second selected illumination spectrum different from the first illumination spectrum and two or more selected induced phase differences between the two clipped illumination beams. In another illustrative embodiment, the controller determines a second phase shift associated with the defect based on the second selected illumination spectrum. In another illustrative embodiment, the controller classifies the defect as metal or non-metal based on a comparison of the first phase shift and the second phase shift.

[0010] An inspection method according to one or more illustrative embodiments of the present invention is disclosed. In one illustrative embodiment, the method includes receiving a first set of images of a defect on a sample from a differential interference contrast imaging tool, the first set of images having a first selected illumination spectrum and two or more selected induced phase differences between two sheared illumination beams. In another illustrative embodiment, the method includes determining a first defect-inducing phase shift based on the first selected illumination spectrum. In another illustrative embodiment, the method includes receiving a second set of images of a defect on the sample from the differential interference contrast imaging tool, the second set of images having a second selected illumination spectrum different from the first illumination spectrum and two or more selected induced phase differences between the two sheared illumination beams. In another illustrative embodiment, the method includes determining a second defect-inducing phase shift based on the second selected illumination spectrum. In another illustrative embodiment, the method includes classifying the defect as a metal or a non-metal based on a comparison of the first defect-inducing phase shift and the second defect-inducing phase shift.

[0011] It should be understood that both the foregoing summary and the following detailed description are exemplary and explanatory only and do not necessarily limit the claimed invention. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the summary serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Numerous advantages of the present invention may be better appreciated by those skilled in the art by referring to the accompanying drawings.

[0013] Figure 1 is a conceptual diagram of a DIC inspection system according to one or more embodiments of the present invention.

[0014] Figure 2 is a simulated graph of the RPC of tungsten (W) and copper (Cu) on a silicon substrate as a function of thickness at a wavelength of 365 nm according to one or more embodiments of the present invention.

[0015] Figure 3 is a simulated graph of the RPC of SiO2 on a silicon substrate as a function of thickness at a wavelength of 365 nm according to one or more embodiments of the present invention.

[0016] Figure 4 is a graph of copper (Cu) on a silicon substrate as a function of thickness in accordance with one or more embodiments of the present invention.

[0017] Figure 5 is a graph of copper SiO2 on a silicon substrate as a function of thickness in accordance with one or more embodiments of the present invention.

[0018] Figure 6Contains simulated graphs of the intensity of defects generated using multiple sequential scans with four different selected system-induced phase shifts in accordance with one or more embodiments of the present invention.

[0019] Figure 7 According to one or more embodiments of the present invention, Figure 6 Graphs of defect contours and graphs of simulated and reconstructed defect-induced phase shifts in FIG.

[0020] Figure 8 Included are three measured images of a sample having no defects in accordance with one or more embodiments of the present invention.

[0021] Fig. 9 According to one or more embodiments of the present invention Figure 8 Plot of the reconstructed phase shift of the sample imaged in .

[0022] Fig.10 is a flow chart illustrating steps performed in a method for classifying defects according to one or more embodiments of the present invention. DETAILED DESCRIPTION

[0023] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. The present invention has been particularly shown and described with respect to specific embodiments and specific features thereof. The embodiments described herein are to be considered illustrative and not restrictive. It should be readily apparent to one of ordinary skill in the art that various changes and modifications may be made in form and detail without departing from the spirit and scope of the present invention.

[0024] Embodiments of the present invention are directed to multi-wavelength interferometry-based microscopy systems and methods for providing both defect identification (eg, detecting the presence of a defect) and classification of the composition of a defect based on a reflective phase change (RPC) of an identified defect.

[0025] It is recognized herein that light reflected by a material exhibits amplitude variations based on the material's reflectivity and phase changes, e.g., reflective phase changes (RPCs). The amount of RPC induced by a given material may vary based on several factors, including, but not limited to, the composition of the material and the wavelength of the incident light. For example, metals may exhibit a nearly constant RPC over a wide range of wavelengths. As another example, dielectrics may exhibit an RPC that varies as a function of wavelength.

[0026] In one embodiment of the present invention, multi-wavelength differential interference contrast (DIC) microscopy may be used to identify (e.g., detect) and classify defects. A DIC inspection system may generate an image of a sample or portion thereof by shearing an illumination beam into two sheared beams; illuminating a sample with the sheared beams; and recombining the sheared beams to form an image captured by a detector. The contrast in the corresponding image (e.g., variation in light intensity and thus detected signal intensity) is related to the interference of the combined sheared beams at the detector based on the optical phase of the combined light on the detector. This optical phase may be affected by a number of factors, including but not limited to the optical path difference (OPD) between the optical paths of the two sheared beams as they propagate through the system and reflect off the sample, the difference between the RPC introduced to the two sheared beams upon reflection. In the context of the inspection system, the presence of a defect on the sample may induce a phase shift associated with both the OPD based on the defect height and the RPC difference between the defect and the surrounding material. It may also be the case that the DIC inspection system may further introduce a phase shift based on the specific configuration of components in the optical path of the sheared beams. For example, the optical path of the sheared beams may be different based on the position and / or orientation of the shearing prism.

[0027] Further embodiments of the invention relate to performing phase retrieval analysis to extract or otherwise isolate defect contributions to the DIC signal.For example, a DIC inspection system may utilize phase shifting techniques to isolate defect-induced phase shifts based on multiple images of a sample with different induced phase deviations between sheared illumination beams.

[0028] Further embodiments of the present invention relate to classifying defects based on comparing defect-inducing phase shifts associated with two or more wavelengths. For example, a DIC inspection system may image a sample or portion thereof with two or more wavelengths and classify identified defects based on a comparison of the defect-inducing phase shift at each wavelength. In addition, the DIC inspection system may perform phase retrieval analysis based on multiple images at each wavelength to extract the defect-inducing OPD at each wavelength.

[0029] As described above, the RPC of metals may remain substantially constant as a function of wavelength, while the RPC of many non-metals (such as, but not limited to, dielectrics) may vary as a function of wavelength. Therefore, comparing the defect-induced phase shifts produced with different wavelengths (or the RPC difference between the defect and the surrounding material, if determined directly) can provide insight into the composition of the defect. For example, an identified defect can be classified by determining the ratio of the defect-induced phase shifts produced with two different wavelengths. In one case, when the ratio is within a selected tolerance of 1, the defect can be classified as a metal, otherwise the defect can be classified as a non-metal (e.g., a dielectric).

[0030] In some embodiments, the RPC is extracted or otherwise isolated from the defect-induced OPD. In this regard, contributions to defect height that do not vary with imaging wavelength may be removed. For example, defects may be classified based on a comparison of the RPC at two or more wavelengths. In some cases, the RPC for a particular material (e.g., a particular metal or dielectric material) at a particular wavelength may be known based on theoretical and / or experimental data. Accordingly, the composition of the defect may be identified based on a comparison of the measured value of the RPC with these known values.

[0031] Reference Figures 1 to 9 , describing systems and methods for defect identification and classification based on multi-wavelength differential interference contrast (DIC) inspection according to one or more embodiments of the present invention.

[0032] Figure 1 is a conceptual diagram of a DIC inspection system 100 according to one or more embodiments of the present invention.

[0033] In one embodiment, the DIC inspection system 100 includes an illumination source 102 for generating an illumination beam 104; a shearing prism 106 for splitting the illumination beam 104 into two sheared beams 108 separated along a shearing direction 110; an objective lens 112 for directing the two sheared beams 108 to a sample 114 at spatially separated locations; and a detector 116 for capturing an image of the sample 114 based on interference between the two sheared beams 108. Figure 1 , sample 114 is illustrated as substrate 118 and defect 120. In addition, sample 114 may be mounted on a translation stage 122 to control the position of sample 114 within the field of view of DIC inspection system 100. For example, translation stage 122 may include, but is not limited to, any combination of linear, rotational, or tilt / tilt actuators.

[0034] In another embodiment, objective lens 112 further collects a portion of sheared light beam 108 (e.g., reflected light 124) reflected from sample 114 so that reflected light 124 associated with two sheared light beams 108 are recombined along a common optical path by shearing prism 106. Figure 1 , the DIC inspection system 100 may include a beam splitter 126 used to separate the illumination beam 104 and the combined reflected light 124 along a common optical path toward the detector 116.

[0035] The shearing prism 106 may be any type of optical element known in the art suitable for shearing the illumination beam 104 into two sheared beams 108. For example, the shearing prism 106 may include a polarizing prism that separates the illumination beam 104 into the sheared beams 108 based on polarization. For example, the sheared beams 108 may include a Nomarski prism, a Wollaston prism, a Rochon prism, or the like, where the two sheared beams 108 correspond to ordinary rays and extraordinary rays.

[0036] In another embodiment, the DIC inspection system 100 includes a phase adjustment subsystem 128 configured to introduce, adjust, or otherwise control a relative optical path difference (OPD) between the optical paths of the two sheared beams 108 through the system, including reflections from the sample 114. For example, Figure 1 , the phase adjustment subsystem 128 may include an actuator (e.g., a translation stage or the like) coupled to a base that holds the shear prism 106. In this regard, the phase adjustment subsystem 128 may control the OPD between the shear beams 108 by adjusting the position of the shear prism 106. As another example, although not shown, the phase adjustment subsystem 128 may include a de Sénarmont compensator.

[0037] In another embodiment, the DIC inspection system 100 includes one or more polarization control optics used to modify the polarization of light at any location. For example, the DIC inspection system 100 may include a polarizer 130 used to provide a linearly polarized illumination beam 104 on the shearing prism 106. As another example, the DIC inspection system 100 may include an analyzer 132 used to isolate the reflected light 124 associated with the reflection of the sheared light beam 108 and promote high contrast interference at the detector 116. As another example, the DIC inspection system 100 may include a half-wave plate 134 used to adjust the orientation of the linearly polarized illumination beam 104 so that the sheared light beams 108 have equal intensity. For example, in the case of a polarizing shearing prism 106, when the polarization of the illumination beam 104 is oriented at 45 degrees relative to the optical axis of the one or more birefringent materials forming the shearing prism 106, the sheared light beams 108 may have equal intensity. Accordingly, the half-wave plate 134 may allow for precise adjustment of the polarization of the illumination beam 104 at the shearing prism 106 , regardless of the orientation or initial polarization of the illumination source 102 .

[0038] In another embodiment, although not shown, the DIC inspection system 100 may include beam conditioning optics used to control, shape, or otherwise adjust the properties of light at any point in the DIC inspection system 100. For example, the beam conditioning optics may include, but are not limited to, one or more spectral filters, one or more neutral density filters, one or more apertures, or one or more homogenizers.

[0039] The illumination source 102 may include any type of light source known in the art suitable for generating the illumination beam 104, including but not limited to a laser source, a light emitting diode (LED) source, a lamp source, or a laser sustained plasma (LSP) source. Furthermore, the illumination source 102 may generate the illumination beam 104 having any selected spectrum. For example, the illumination beam 104 may include any combination of ultraviolet (UV) light, visible light, or infrared (IR) light. As another example, the illumination beam 104 may include short wavelength light, such as but not limited to extreme ultraviolet (EUV) light, deep ultraviolet (DUV) light, or vacuum ultraviolet (VUV) light.

[0040] In another embodiment, the illumination source 102 is a tunable light source, wherein the spectrum (eg, center wavelength, broadband, or the like) of the illumination beam 104 can be selectively tuned. In this regard, the DIC inspection system 100 can operate as a multi-wavelength inspection system.

[0041] The illumination source 102 may include any type of tunable light source known in the art. In one embodiment, the illumination source 102 includes a light emitter having a tunable emission spectrum, such as, but not limited to, a tunable laser source. In another embodiment, the illumination source 102 includes a broadband light source coupled to one or more spectral filters to provide a selected spectrum to the illumination beam 104. For example, the spectral filter may include one or more selectively rotatable angle tunable filters, wherein the spectral filtering properties can be tuned by adjusting the incident angle of the light. As another example, the spectral filter may include one or more fixed spectral filters that can be selectively placed in the optical path of the broadband light from the broadband light source (e.g., using a filter wheel, one or more independent actuators, or the like) to provide a selected spectrum to the illumination beam 104.

[0042] In another embodiment, the detector 116 is a multi-pixel detector, such that the DIC inspection system 100 can be operated as a multi-pixel imaging system. For example, the sheared beam 108 can illuminate an extended portion of the sample 114, which is then imaged onto the detector 116 (e.g., using the objective lens 112 and any additional lenses suitable for imaging the sample 114). It should be recognized herein that the multi-pixel DIC inspection system 100 can provide relatively higher resolution and / or detection sensitivity than a single-pixel inspection system (e.g., a scanning DIC system). For example, the DIC inspection system 100 can combine a high-resolution objective lens 112, a low-noise detector 116, and a low-noise illumination source 102 to achieve highly sensitive defect detection and classification at a resolution of approximately nanometers or less in the longitudinal (e.g., height) direction and a few microns or less in the lateral direction.

[0043] In addition, the detector 116 may generate an image of the stationary or moving sample 114. For example, a detector 116 suitable for capturing an image of a stationary sample may include, but is not limited to, a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device. In another embodiment, the detector 116 is a frame mode detector configured to generate an image of the sample 114 when the sample 114 is stationary. As another example, the detector 116 suitable for capturing an image of a moving sample may include, but is not limited to, a line scan sensor or a time delay integration (TDI) sensor. In another embodiment, the detector 116 is a scan mode detector configured to generate an image of the sample 114 when the sample 114 moves along a scan direction, wherein the shear direction is oriented along the scan direction.

[0044] In another embodiment, the DIC inspection system 100 includes a controller 136. In another embodiment, the controller 136 includes one or more processors 138 configured to execute a set of program instructions maintained in a memory medium 140 or a memory. In addition, the controller 136 may include one or more modules containing one or more program instructions stored in the memory medium 140 that can be executed by the processor 138. The processor 138 of the controller 136 may include any processing element known in the art. In this sense, the processor 138 may include any microprocessor-type device configured to execute algorithms and / or instructions. In one embodiment, the processor 138 may be composed of a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or any other computer system (e.g., a network computer) configured to execute a program configured to operate the DIC inspection system 100, as described throughout the present invention. It should be further recognized that the term "processor" can be broadly defined to cover any device having one or more processing elements that execute program instructions from a non-transitory memory medium 140.

[0045] The memory medium 140 may include any storage medium known in the art suitable for storing program instructions that can be executed by the associated processor 138. For example, the memory medium 140 may include a non-transitory memory medium. As additional examples, the memory medium 140 may include, but is not limited to, a read-only memory, a random access memory, a magnetic or optical storage device (e.g., a disk), a tape, a solid-state drive, and the like. It should be further noted that the memory medium 140 may be housed in a common controller housing with the processor 138. In one embodiment, the memory medium 140 may be remotely located relative to the physical location of the processor 138 and the controller 136. For example, the processor 138 of the controller 136 may access a remote memory (e.g., a server) that is accessible via a network (e.g., the Internet, an intranet, and the like). Therefore, the above description should not be construed as limiting the present invention, but merely illustrating the present invention.

[0046] The controller 136 may be communicatively coupled with any component of the DIC inspection system 100. In one embodiment, the controller 136 receives data from one or more components of the DIC inspection system 100. For example, the controller 136 may receive an image or portion thereof from the detector 116. In another embodiment, the controller 136 performs one or more processing steps of the present invention. For example, the controller 136 may receive images of the sample 114 generated with different induced phases (e.g., based on different configurations of the phase adjustment subsystem 128) and perform one or more analysis steps (e.g., phase retrieval analysis) to isolate defect-inducing phase shifts. As another example, the controller 136 may receive images of the sample 114 or portions thereof generated using different wavelengths of the illumination beam 104 and classify one or more defects based on the defect-inducing phase shift of each wavelength.

[0047] In another embodiment, controller 136 may generate one or more control signals to direct or otherwise control components of DIC inspection system 100. Controller 136 may generate control signals for any component of DIC inspection system 100, including but not limited to detector 116, translation stage 122, or illumination source 102.

[0048] Reference Figures 2 to 9 , describes in more detail defect detection and classification based on multi-wavelength DIC interferometry according to one or more embodiments of the present invention.

[0049] The contrast in the image produced by the DIC inspection system 100 (e.g., Figure 1 ) can generally be associated with interference between reflected light 124 associated with reflecting the sheared light beam 108 from a spatially offset portion of the sample. In particular, Figure 1 As illustrated in FIG. 1 , it may be the case that one of the sheared beams 108 may be incident on a beam having a height (hd ) and the other may not be incident on a defect with height (h d ) defect. In this case, the light intensity can usually be characterized as:

[0050]

[0051] and

[0052]

[0053] Where I1 and I2 are the intensities of the two sheared beams 108, R d is the reflectivity of the defect, R s is the reflectivity of the sample 114 surrounding the defect, Δφ d is the defect-induced phase difference, and Δφ s is the phase difference induced by the system. For example, Δφ s The value of may be related to a particular position and / or orientation of the shear prism 106 .

[0054] As described above, the defect-induced phase difference (Δφ d ) can be based on the defect height relative to the surrounding material (h d ) and the difference between the RPC of the defect and the surrounding material. Specifically, the defect-induced phase difference (Δφ d ) can be written differently as:

[0055]

[0056] Where n is the refractive index, Δφ r is the phase difference associated with the RPC difference between the defect and the surrounding portion of the sample 114, and h TOT Based on the actual height h d and additional contribution RPC The apparent height of the defect (e.g., the apparent OPD of the defect) of both, the additional contribution h RPC is the RPC difference between the sample 114 based on the defect and surrounding the defect. The factor 2 in equation (3) accounts for the round trip path of the reflected light in the DIC inspection system 100.

[0057] It is recognized herein that RPC generally depends on various factors, such as, but not limited to, material composition, material size, and wavelength of incident light. Accordingly, the defect-induced phase (Δφ) associated with multiple wavelengths is compared. d ) and / or RPC difference (Δφ r ) itself can facilitate the classification of defects based on these factors.

[0058] Figure 2 and 3Shows the RPC of metals and non-metals as a function of defect thickness (size) at a common wavelength. Figure 2 is a simulated graph 202 of the RPC of two metals, tungsten (W) and copper (Cu), on a silicon substrate as a function of thickness at a wavelength of 365 nm in accordance with one or more embodiments of the present invention. Figure 3 is a simulated graph 302 of the RPC of SiO 2 on a silicon substrate as a function of thickness at a wavelength of 365 nm in accordance with one or more embodiments of the present invention.

[0059] Figure 2 and 3 A thin film simulation using a thin film model that provides a first approximation of the RPC associated with the defects is included. Figure 2 As described in , when the defect size is greater than about 100 nm, the RPC of the metal is constant. In addition, the amount of RPC varies substantially based on the composition of the metal. In contrast, Figure 3 As explained in , the RPC of SiO2 depends strongly on the thickness. In addition, it should be noted that Figure 3 A wrapped phase having a modulus of 360 degrees (2π radians) is illustrated.

[0060] Figure 4 and 5 The RPC of metals and non-metals is shown as a function of defect thickness (size) at multiple wavelengths (365 nm and 405 nm) according to one or more embodiments of the present invention. Figure 4 and 5 It is shown how the variation of RPC as a function of wavelength can be used for defect classification. Figure 4 is a graph 402 of copper (Cu) on a silicon substrate as a function of thickness in accordance with one or more embodiments of the present invention. Figure 5 is a graph 502 of copper SiO2 on a silicon substrate as a function of thickness in accordance with one or more embodiments of the present invention.

[0061] like Figure 4 As shown in , the RPC of metals exhibits relatively small dependence (e.g., less than 5 degrees) on wavelength for almost all sizes greater than 200 nm. Figure 5 As illustrated in , the RPC of SiO 2 exhibits a relatively large dependence (eg, greater than 90 degrees) on wavelength for sizes greater than approximately 200 nm.

[0062] Referring now to Table 1 below, RPC values ​​for various materials and sizes are summarized to further highlight the dependence of RPC on material composition, size, and wavelength.

[0063] Table 1:

[0064]

[0065]

[0066] consider Figures 2 to 5 1, the RPC of metals varies based on the specific composition of the metal, but is relatively constant as a function of illumination wavelength and size, regardless of composition. In contrast, the RPC of non-metals (as exemplified by but not limited to SiO2) exhibits a relatively large dependence on defect size greater than approximately 200 nm. In one embodiment, based on the measured variation of the RPC as a function of wavelength, defects can be classified as metal or non-metal, where variations exceeding a selected threshold indicate non-metal defects.

[0067] Reference Figures 6 to 9 , describes in more detail the classification of defects based on measured DIC signals according to one or more embodiments of the present invention.

[0068] As shown in equations (1) to (3) above, the light intensity I at a particular location on the detector 116 depends in part on the optical phase (φ) at the detector 116 associated with the reflected light 124 recombined by the shearing prism 106. In addition, this optical phase (φ) may include a system-induced phase shift (Δφ) s ) and defect-induced phase shift (Δφ d ).

[0069] In one embodiment, a phase retrieval analysis (eg, by controller 136) is used to induce a phase shift (Δφ) from the system. s ) to extract or otherwise separate the defect-induced phase shift (Δφ d ) to isolate the effect of RPC on the intensity I. A phase shift (Δφ) may be induced from the system using any technique or combination of techniques known in the art s ) to extract or otherwise separate the defect-induced phase shift (Δφ d In one embodiment, the defect-induced phase shift (Δφ) can be extracted using phase shift analysis. d ). For example, the system may be induced to phase shift (Δφ) based on having different (eg, selected) system induced phase shifts (Δφ) at each wavelength. s ) to determine the defect-induced phase shift (Δφ) associated with the defect d ). For example, as previously described herein, the system-induced phase shift (Δφ) may be adjusted using the phase adjustment subsystem 128. s ), the phase adjustment subsystem 128 may include, but is not limited to, an actuator for translating the shear prism 106 along the shear direction 110. In this regard, in response to a selected system induced phase shift (Δφ s ) can be used to isolate the phase shift (Δφ) induced by the selected system. s) contribution, so that the defect-induced phase shift (Δφ d ). In addition, phase retrieval analysis can be applied to multiple images at each of the two or more wavelengths in order to extract the defect-induced phase shift (Δφ) associated with each of the two or more wavelengths. d In another embodiment, a low-pass filter (such as but not limited to a movable median filter) may be used to separate the defect-induced phase shift (Δφ d ) and the system-induced phase shift (Δφ s ). It should be recognized in this article that the system induced phase shift (Δφ s ) may originate from sources such as, but not limited to, non-uniform differences between the sheared beams 108 (e.g., the extraordinary beam and the ordinary beam from the shearing prism 106) or local slopes associated with natural or sample holder induced variations in the surface of the sample 114. In addition, these system induced phase shifts (Δφ s ) can have a relatively slow varying frequency, so that the low-pass filter can separate the defect-induced phase shift (Δφ d ) and the system-induced phase shift (Δφ s ).

[0070] Additionally, any imaging technique known in the art may be used to generate images with different selected system-induced phase shifts (Δφ s ). For example, where the DIC inspection system 100 is configured to image a stationary sample 114, different selected system-induced phase shifts (Δφ) may be used. s ) sequentially acquires multiple images while the sample 114 remains stationary. As another example, where the DIC inspection system 100 is configured to image a moving sample 114, the phase shift (Δφ) may be induced using different selected system s ) are scanned sequentially multiple times to obtain multiple images.

[0071] Figure 6 Including using a system with four different selected system induced phase shifts (Δφ) according to one or more embodiments of the present invention s ) (0 degrees, 90 degrees, 180 degrees and 270 degrees, respectively). Figure 7 According to one or more embodiments of the present invention, Figure 6 The defect profile (e.g., height (h d )) and the simulated and reconstructed defect-induced phase shift (Δφ d ) of the diagram 704. Figure 7 As described in the s ) can accurately extract the defect-induced phase shift (Δφd ). Accordingly, the DIC inspection system 100 may be configured to detect defect-induced phase shifts (Δφ) associated with two or more wavelengths. d ) to classify the defects.

[0072] Reference Figure 8 and 9 , showing the induced phase shift (Δφ) based on eleven selected systems s ) of the non-defective sample 114 of multiple still images of the still sample. Figure 8 Three of the eleven measured images 802 - 806 of a non-defective sample 114 in accordance with one or more embodiments of the present invention are included. Fig. 9 According to one or more embodiments of the present invention Figure 8 902 of the reconstructed phase shift of the sample 114 imaged in FIG. Figure 8 and 9 The associated shear direction 110 is 45 degrees in the corresponding diagram. Figure 8 and Fig. 9 The ability to extract (e.g., reconstruct) phase shifts using the phase extraction techniques disclosed herein may be demonstrated even in the presence of optical inhomogeneities in the illumination beam 104. It is recognized herein that the phase extraction techniques disclosed herein may be used to characterize phase shifts induced by inherent variations in the surface of the sample 114 and phase shifts induced by one or more defects.

[0073] Referring again to equations (1) to (3) above, the RPC difference between the defect and the surrounding portion of the sample 114 can be expressed as the defect-induced phase shift (Δφ d ) changes, causing the defect-induced phase shift (Δφ) of different wavelengths d ) can facilitate the classification of defects. Table 2 below provides defect-induced phase shifts (Δφ) associated with multiple wavelengths for defect sizes in the range of 200 nm to 350 nm according to one or more embodiments of the present invention. d ) associated simulation data. Specifically, Table 2 contains h RPC and h TOT The simulated value of

[0074] Table 2:

[0075]

[0076]

[0077] In one embodiment, based on the defect-induced phase shift (Δφ) associated with the two wavelengths d ) (which is equivalent to the ratio of h shown in Table 2 based on the above equation (3) TOTFor example, if the defect induces a phase shift (Δφ d ) is below a selected threshold, then the defect can be classified as a non-metal. The threshold can be any selected value and can be adjusted based on the specific material of interest and / or wavelength used. For example, a threshold of 0.9 would enable a Cu defect to be classified as a metal and would enable a SiO2 defect to be classified as a non-metal.

[0078] Fig.10 1 is a flow chart illustrating steps performed in a method 1000 for classifying defects according to one or more embodiments of the present invention. Applicants should note that the embodiments and enabling techniques previously described herein in the context of a DIC inspection system 100 should be interpreted as extending to the method 1000. However, it should be further noted that the method 1000 is not limited to the architecture of the DIC inspection system 100.

[0079] In one embodiment, method 1000 includes step 1002: receiving a first image set of defects on a sample from a differential interference contrast imaging tool, the first image set having a first selected illumination spectrum and two or more selected induced phase differences between two sheared illumination beams. In another embodiment, the differential interference contrast imaging tool includes a bright field differential interference contrast imaging tool. In another embodiment, method 1000 includes step 1004: determining a first defect-inducing phase shift based on the first selected illumination spectrum. In another embodiment, method 1000 includes step 1006: receiving a second image set of defects on a sample from a differential interference contrast imaging tool, the second image set having a second selected illumination spectrum different from the first illumination spectrum and two or more selected induced phase differences between two sheared illumination beams. In another embodiment, method 1000 includes step 1008: determining a second defect-inducing phase shift based on the second selected illumination spectrum. For example, steps 1004 and 1008 may include applying a phase retrieval algorithm that incorporates a phase shifting technique using the first image set. In another embodiment, method 1000 includes step 1010: classifying the defect as metal or non-metal based on a comparison of the first defect-induced phase shift and the second defect-induced phase shift. For example, step 1010 may include, but is not limited to, classifying the defect as metal or non-metal based on a ratio of the first defect-induced phase shift relative to the second defect-induced phase shift. In one case, step 1010 includes classifying the defect as non-metal if the absolute value of the ratio of the first defect-induced phase shift relative to the second defect-induced phase shift is below a selected threshold.

[0080] The target described herein sometimes illustrates different components contained in other components or connected with other components.It should be understood that these depicted architectures are only exemplary, and in fact many other architectures that realize the same function can be implemented.In a conceptual sense, any component arrangement that realizes the same function is effectively "associated" so that the desired function is realized.Therefore, any two components combined to realize a specific function in this article can be regarded as "associated" with each other so that the desired function is realized, regardless of the architecture or intermediate components.Similarly, any two components so associated can also be regarded as "connected" or "coupled" to realize the desired function, and any two components that can be so associated can also be regarded as "coupleable" to realize the desired function.Specific examples that can be coupled include but are not limited to physically interactive and / or physically interactive components and / or wirelessly interactive and / or wirelessly interactive components and / or logically interactive and / or logically interactive components.

[0081] It is believed that the present invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of components without departing from the disclosed object or without sacrificing all of its material advantages. The described form is illustrative only, and the appended claims are intended to cover and encompass such changes. Furthermore, it is understood that the present invention is defined by the appended claims.

Claims

1. A testing system, comprising: a differential interference contrast imaging tool configured to generate one or more images of a sample based on illumination by two clipped illumination beams, wherein the illumination spectra of the two clipped illumination beams and the phase difference between the two clipped illumination beams can be selected for any particular image of the sample; and a controller communicatively coupled to the imaging tool, the controller configured to perform a phase retrieval analysis to extract or isolate a defect-inducing phase shift based on the one or more images of the sample having different induced phase deviations between the two sheared illumination beams, wherein the controller includes one or more processors configured to execute program instructions that cause the one or more processors to: receiving a first set of images of defects on the sample, the first set of images having a first selected illumination spectrum and two or more selected induced phase differences between the two clipped illumination beams; determining a first defect-induced phase shift associated with the defect based on the first selected illumination spectrum; receiving a second set of images of defects on the sample, the second set of images having a second selected illumination spectrum different from the first selected illumination spectrum and two or more selected induced phase differences between the two sheared illumination beams; determining a second defect-induced phase shift associated with the defect based on the second selected illumination spectrum; and classifying the defect as a metal or a non-metal based on a selected threshold of a ratio of the first defect-induced phase shift to the second defect-induced phase shift, wherein the selected threshold is adjusted based on at least one of: a material of interest including the defect, the first selected illumination spectrum, or the second selected illumination spectrum, wherein classifying the defect as a metal or a non-metal comprises: classifying the defect as metal if the magnitude of the ratio is equal to or above the selected threshold; or If the magnitude of the ratio is below the selected threshold, then the defect is classified as non-metallic.

2. The inspection system of claim 1, wherein the magnitude of the ratio is an absolute value of the ratio, wherein classifying the defect as metal or non-metal comprises: An absolute value of the ratio of the first defect-induced phase shift to the second defect-induced phase shift is determined.

3. The inspection system of claim 1, wherein the imaging tool comprises: an illumination light source configured to generate an illumination light beam; a shearing prism configured to split illumination from the illumination source into the two sheared illumination beams spatially separated along a shearing direction; an objective lens configured to direct the two clipped illumination beams to the sample, wherein the objective lens is further configured to collect sample light including light emitted from the sample in response to illumination by the two clipped illumination beams, wherein the shearing prism is further configured to combine portions of the sample light associated with the two clipped illumination beams into a common light beam; and A multi-pixel detector is configured to generate one or more images of the sample based on the common light beam.

4. The inspection system of claim 3, wherein the shear prism comprises: Wollaston prism.

5. The inspection system of claim 3, wherein the shear prism comprises: Nomarski prism.

6. The inspection system of claim 3, wherein the multi-pixel detector comprises: A frame mode detector is configured to generate an image of the sample while the sample is stationary.

7. The inspection system of claim 6, wherein the frame pattern detector comprises: At least one of a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) sensor.

8. The inspection system of claim 3, wherein the multi-pixel detector comprises: A scanning mode detector is configured to generate an image of the sample as the sample moves along a scanning direction.

9. The inspection system of claim 8, wherein the scanning mode detector comprises: At least one of a line scan sensor or a time delay integration sensor.

10. The inspection system of claim 8, wherein the shear direction is oriented along the scanning direction.

11. An inspection system according to claim 3, wherein the two or more selected induced phase differences between the two sheared illumination beams of at least one of the first image set or the second image set are selected by translating the shearing prism to two or more selected positions along a lateral direction relative to the optical axis of the imaging tool.

12. The inspection system of claim 1, wherein the differential interference contrast imaging tool comprises: Brightfield differential interference contrast imaging tool.

Images