Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
  • G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/47—Scattering, i.e. diffuse reflection
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8806—Specially adapted optical and illumination features
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/9501—Semiconductor wafers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/9501—Semiconductor wafers
  • G01N21/9505—Wafer internal defects, e.g. microcracks
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T7/00—Image analysis
  • G06T7/0002—Inspection of images, e.g. flaw detection
  • G06T7/0004—Industrial image inspection
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P74/00—Testing or measuring during manufacture or treatment of wafers, substrates or devices
  • H10P74/20—Testing or measuring during manufacture or treatment of wafers, substrates or devices characterised by the properties tested or measured, e.g. structural or electrical properties
  • H10P74/203—Structural properties, e.g. testing or measuring thicknesses, line widths, warpage, bond strengths or physical defects
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8806—Specially adapted optical and illumination features
  • G01N2021/8822—Dark field detection
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
  • G01N2021/8854—Grading and classifying of flaws
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
  • G01N2021/8887—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges based on image processing techniques
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/06—Illumination; Optics
  • G01N2201/061—Sources
  • G01N2201/06113—Coherent sources; lasers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/06—Illumination; Optics
  • G01N2201/064—Stray light conditioning

Definitions

• the described embodiments relate to systems for surface inspection, and more particularly to semiconductor wafer inspection modalities.
• processing steps applied to a substrate or wafer The various features and multiple structural levels of the semiconductor devices are formed by these processing steps. For example, lithography among others is one semiconductor fabrication process that involves generating a pattern on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be
• inspection systems detect any type of defect on a sample at any point in a production process.
• inspection systems are commonly employed to locate defects on a substrate prior to processing to ensure the substrate is suitable for continued manufacture or to identify defect sites on wafers prior to production.
• One such inspection system is an optical surface inspection system that illuminates and inspects a wafer surface for undesired particles.
• Optical surface inspection systems are typically high-throughput systems that locate defects and generate a map of defects located on each inspected wafer .
• defects are located by an optical inspection tool. The inspected wafer and the map of defect locations are
• the defect review tool performs a detailed analysis of one or more of the defect locations identified by the optical inspection system to classify the defect at each location.
• Defects are often classified by material composition.
• knowledge of the defect material composition enables an operator to determine appropriate cleaning procedures to rid the wafer of defect particles.
• knowledge of the defect material composition indicates the source of wafer
• EDX Energy-Dispersive X-Ray Spectrometry
• EDX provides defect material analysis capability at high sensitivity for some materials, but not for other materials such as inorganic compounds or organic particles.
• EDX suffers from insufficient throughput for cost effective defect classification in a semiconductor fabrication facility.
• defect classification with an optical inspection tool is non destructive; the analysis is performed without destroying the sample, removing materials from the sample, etc.
• Zhao describes various optical inspection systems that detect arid classify defects with sufficient sensitivity to small particle sizes at high throughput, the contents of which are incorporated herein by reference in their entirety.
• Zhao describes optical inspection systems employing a phase shifting phase contrast imaging technique to classify defects.
• the phase shifting phase contrast technique requires spatial separation of specularly reflected light and scattered light at a collection pupil plane of the optical system to introduce a relative phase shift between the specularly reflected light and the scattered light.
• the distribution of the illumination beam is limited to selected location within the pupil plane of the objective lens. This limits the number of photons provided to the wafer by the illumination source, which in turn, limits the sensitivity of the optical inspection system.
• optical inspection and optical review tools are enhanced by incorporating the techniques described herein.
• a defect is classified based on the measured relative phase of scattered light collected from at least two spatially distinct locations in the collection pupil.
• the defect classification is based on the measured relative phase of scattered light for a given illumination angle.
• Scattered light is collected from at least two spatially distinct locations in the collection pupil, while the remaining light is blocked. Under these conditions, a well-defined interference pattern is formed at the image plane at the photosensitive surface of the detector.
• the phase difference, if any, between the light transmitted through the two spatially distinct locations at the pupil plane is determined from the positions of the interference fringes in the imaging plane .
• the measured phase difference is indicative of the material composition of the measured sample.
• a difference between the measured phase difference and a known value of phase difference associated with the specimen is determined by as a correction value.
• the material under measurement is a known material having known material properties and phase response.
• the difference between the phase difference measured by an inspection system and the known phase difference is
• the correction value is stored in memory. Subsequent measurements of phase difference performed by the system are corrected by the stored correction value to compensate for the systematic errors present in the measurement of phase difference.
• phase difference information is extracted from the interference patterns present in
• FFT Fast Fourier Transform
• the FFT algorithm provides excellent noise rejection and is computationally efficient.
• an iterative fit of a physical model of the measurement to a measured interference pattern is employed to determine the phase difference between the light
• an inspection system includes a programmable pupil aperture device configured to sample the pupil at different, programmable locations in the
• each sampling position in the pupil plane is controlled for each phaise difference measurement.
• FIG. 1 is a simplified diagram illustrative of one embodiment of an inspection system configured to measure phase difference between scattered light collected from a specimen at distinct locations in the collection pupil.
• FIG. 2 is a simplified diagram illustrative of a wafer 110 illuminated by an illumination beam.
• FIG. 3 is a diagram illustrative of a mask that blocks light at all collected NA, except light that is transmitted through an aperture.
• FIG. 4 depicts a plot of a simulation of an
• FIG. 5 depicts a plot of a simulation of an
• FIG. 6 depicts a plot of a simulation of an
• FIG. 7 depicts a diagram illustrative of pupil apertures located symmetrically about the center of the pupil in the x-direction in one embodiment.
• FIG. 8 depicts a diagram illustrative of pupil apertures located symmetrically about the center of the pupil in the x-direction in another embodiment.
• FIG. 9 depicts a diagram illustrative of pupil apertures located symmetrically about the center of the pupil in the y-direction in one embodiment.
• FIG. 10 depicts a diagram illustrative of pupil apertures located symmetrically about the center of the pupil in the y-direction in another embodiment.
• FIG. 11 is a simplified diagram illustrative of a programmable pupil mask device in one embodiment.
• FIG. 12 is a simplified diagram illustrative of a programmable pupil mask device in another embodiment.
• FIG. 13 illustrates a flowchart of an exemplary method 200 useful for measuring phase difference between scattered light collected from a specimen at distinct locations In the collection pupil.
• nanometer scale defect particles are detected and
• inspection tool a defect review tool, or an integrated- optical inspection/defect review tool.
• throughput is increased by detecting and classifying defects with the same optical system, i.e. , defect inspection and defect review performed by the same optical tool.
• optical inspection and optical review tools are enhanced by incorporating the techniques described herein.
• light scattering from a defect depends on many properties of the defect. For example, geometric properties such as defect shape and size affect light scattering, in addition to material properties such as the complex index of refraction described by the refractive index, n, and the extinction coefficient, k. Values of material parameters, such as n and k, indicate material composition. However, material parameters, such as n and k cannot be directly determined from a simple scattering light intensity measurement because they are not
• a defect is classified based on the measured relative phase of scattered light collected from at least two spatially distinct locations in the collection pupil.
• the defect classification is based on the measured relative phase of scattered light for a given illumination angle.
• a defect particle is classified either as a high-K metal or a low-K, transparent dielectric material based on the measured relative phase of scattered light at different locations in the pupil plane.
• values of material properties of a defect are determined based on the phase of light scattered from a defect.
• material properties are determined based on the measured phase difference of scattered light at different locations in the pupil plane.
• a defect is classified based on the determined material properties of the defect.
• FIG. 1 is a simplified schematic view of one embodiment of a surface inspection system 100 with
• Surface inspection system 100 is provided by way of non-limiting example. In general, any optical
• microscope or inspection system that images scattered light on a sensor to form an image of a defect as described herein is suitable for implementation of the inspection and classification functionality described herein.
• Such an optical microscope or inspection subsystem may be
• an illumination source 101 generates a beam of illumination light 102 directed toward wafer 110.
• focusing optics 103 focus illumination light 102 onto wafer 110 over measurement spot 104.
• any suitable illumination optical elements may employed to provide illumination light 102 onto wafer 110 over a desired measurement spot size.
• one or more beam shaping elements are included in the illumination optical path (i.e., the optical path between illumination source 101 and wafer 110) to form a desired beam profile.
• Exemplary beam profiles include a Gaussian beam shape, a ring beam shape, a flat-top beam shape, etc.
• Typical measurement spot sizes include measurement spots
• one or more polarizer elements are located in the illumination optical path to polarize the illumination light in a desired manner.
• Exemplary polarizations include linear polarization, elliptical polarization, circular polarization, or no polarization.
• illumination 102 is provided to the surface of wafer 110 at an oblique angle by the illumination subsystem.
• the illumination subsystem in general, the
• illumination subsystem may be configured to direct the beam of light to the specimen at a normal angle of incidence. Typical incidence angles range from zero degrees (normal incidence) to eighty degrees from normal incidence.
• system 100 may be configured to direct multiple beams of light to the specimen at different angles of incidence, such as an oblique angle and a normal angle of incidence. The multiple beams of light may be directed to the specimen substantially simultaneously or
• Illumination source 101 may include, by way of example, : a laser, a diode laser, a helium neon laser, an argon laser, a solid state laser, a diode pumped solid state (DPSS) laser, a xenon arc lamp, a gas discharging lamp, and LED array, or an incandescent lamp.
• the light source may be configured to emit near monochromatic light or broadband light.
• the illumination subsystem is configured to direct light having a relatively narrow wavelength band to the specimen (e.g., nearly monochromatic light or light having a wavelength range of less than about 20 nm, less than about 10 nm, less than about 5 nm, or even less than about 2 nm) for an interval of time. Therefore, if the light source is a broadband light source, the illumination subsystem may also include one or more spectral filters that may limit the wavelength of the light directed to the specimen. The one or more spectral filters may be bandpass filters and/or edge filters and/or notch filters. In some examples, the wavelengths of light incident on wafer 110 include any subset of wavelengths ranging from infrared to extreme ultraviolet.
• illumination source 101 emits radiation at any desired wavelength or remge of wavelengths of light within the optical wavelength range.
• illumination source 101 is configured to control the optical power of the beam of illumination light 102 in accordance with command signal 134 received from computing system 140.
• illumination source 101 dynamically adjusts the illumination power during a surface inspection scan.
• Wafer positioning system 125 moves wafer 110 under measurement spot 104.
• Wafer positioning system 125 includes a wafer chuck 109, motion controller 123, a rotation stage 121 and a translation stage 122.
• Wafer 110 is supported on wafer chuck 109.
• wafer 110 is located with its geometric center 150 approximately aligned the axis of rotation of rotation stage 121.
• rotation stage 121 spins wafer 110 about its geometric center at a specified angular velocity, w, within an acceptable tolerance.
• translation stage 122 translates the wafer 110 in a direction approximately perpendicular to the axis of rotation of rotation stage 121 at a specified velocity, VT.
• inspection begins with measurement spot 104 located at the geometric center 150 of wafer 110 and then wafer 110 is rotated and translated until measurement spot 104 reach the outer perimeter of wafer 110 (i.e., when R equals the radius of wafer 110) . Due to the coordinated motion of rotation stage 121 and translation stage 122, the locus of points illuminated by measurement spot 104 traces a spiral path on the surface of wafer 110. The spiral path on the surface of wafer 110 is referred to as an inspection track 127 (not shown in its entirety) .
• inspection track 127 is illustrated in FIG. 2 as TRACKi. As illustrated in FIG. 2, measurement spot 104 is located a distance, R, from the geometric center of wafer 110, and defect particle 126 is approaching measurement spot 104.
• inspection system 100 is able to locate a defect particle as small as 50 nanometers along a dimension of maximum extent of the particle. In some embodiments, inspection system 100 is able to locate a defect particle as small as 10 nanometers along a dimension of maximum extent of the particle.
• inspection system 100 includes an imaging collection objective 112 employed to image the light 111 scattered and/or reflected from wafer 110 over a range of collection angles at measurement spot 104 onto one or more wafer image planes of the collection optics subsystem (e.g., image plane 119).
• Objective 112 is configured to collect dark field scattering light.
• objective 112 captures scattered light with a Numerical Aperture (NA) of 0.1 to 0.99.
• NA Numerical Aperture
• the collection optical path (i.e., the optical path between wafer 110 and detector 120) includes one or more polarizer optical elements 113 to select light having desired polarization.
• the collection optical path includes one or more polarizer optical elements 113 to select light having desired polarization.
• the one or more polarizer elements 113 include a simple polarizer. In some other embodiments, the one or more polarizer elements 113 include a phase plate combined with a polarizer. In some of these embodiments, the phase plate is designed to alter the polarization of scattering light .
• the collection optical path includes one or more pupil relay optics (e.g., pupil relay optics 115) to form one or more relayed pupil planes (e.g., pupil plane 106) .
• This may be desirable to permit easier access to a collection pupil plane for one or more light modification elements (e.g., mask elements) to control the amount of light collected from specific regions of the pupil as described herein.
• it may be desirable to locate all light modification elements (e.g., mask elements) that control the amount of light collected from specific regions of the pupil as described herein at or near one pupil plane.
• the collection optical path includes two pupil planes (e.g., pupil planes 105 and 106) , and pupil masks 114 and 116 are located at pupil planes 105 and 106, respectively.
• optical elements 117 focus the collected light 111 onto the image plane 119, where the image is detected by detector 120.
• Imaging detector 120 generally functions to convert the detected light into electrical signals indicative of the detected image of the wafer 110 within the detected field of view.
• imaging detector 120 may include substantially any photodetector known in the art. However, a particular detector may be selected for use within one or more embodiments of the invention based on desired performance characteristics of the detector, the type of specimen to be inspected, and the configuration of the illumination.
• detector 120 acquires image information in a frame mode or a scanning mode. In a scanning mode, the image is collected while wafer 110 is moving. If the amount of light available for inspection is relatively low, an efficiency enhancing detector such as a time delay integration (TDI) camera may employed to
• signal integration is employed to achieve sufficient SNR for phase measurement.
• the integration time may be selected from a few nanoseconds to a second.
• CCD charge- coupled device
• PMTs photomultiplier tubes
• individual PMT/photodiode with a scannable aperture in front of the detector may be used, depending on the amount of light available for inspection and the type of
• Imaging detector 120 may be implemented in various imaging modes, such as bright field, dark field, and confocal .
• imaging modes such as bright field, dark field, and phase contrast can be implemented by using different apertures or Fourier filters.
• detector 120 generates dark field images by imaging scattered light collected at larger field angles.
• a pinhole that matches the incident spot 104 can be placed in front of a detector (e.g., detector 120) to generate a confocal image.
• U.S. Pat. No. 6,208,411 which is incorporated by reference herein, describes these imaging modes in further detail.
• computing system 140 is configured to determine the location of a defect in the scan path based on changes in the detected signals 131. In addition, computing system 140 is configured to classify the defect based on its material characteristics as
• scattered light is collected from at least two spatially distinct locations in the collection pupil, while the remaining light is blocked.
• a well-defined interference pattern is formed at the image plane at the photosensitive surface of the detector.
• the phase difference, if any, between the light transmitted through the two spatially distinct locations at the pupil plane is determined from the positions of the interference fringes in the imaging plane.
• the measured phase difference is indicative of the material composition of the measured sample.
• a difference between the measured phase difference and a known value of phase difference associated with the specimen is determined by computing system 140 as a correction value.
• the material under measurement i.e., within the measurement spot 104 is a known material having known material properties and phase response.
• the difference between the phase difference measured by an inspection system (e.g., inspection system 100) and the known phase difference is indicative of systematic errors in the measurement system, e.g., optical aberration, measurement electronics errors, etc.
• the correction value is stored in memory (e.g., memory 142). Subsequent measurements of phase difference performed by the system are corrected by the stored correction value to compensate for the systematic errors present in the
• the correction value is valid for measurements performed by the inspection system using the mask arrangement employed to perform the
• mask 114 is located at pupil plane 106.
• mask 114 may be located at pupil plane 105. Whether a mask is located a one pupil plane or another is a matter of design preference, and all
• FIG. 3 depicts an illustration of mask 114.
• mask 114 blocks light at all collected NA, except light that is transmitted through apertures 151 and 152.
• the center of aperture 151 is located at 0.358NA X and 0.0NAy (corresponds to an angle of incidence of 21 degrees at the wafer) .
• the radius of aperture 151 is 1/12 of the radius of the pupil 153.
• the center of aperture 152 is located at 0.788NA X and 0.0NA y ( corresponds to an angle of incidence of 52 degrees at the wafer) .
• the radius of aperture 152 is 1/12 of the radius of the pupil 153.
• FIG. 4 depicts a plot 160 of a simulation of the interference pattern at the image plane at the
• detector 120 generated by the interference of light transmitted through apertures 151 and 152.
• detector 120 includes a 973x973 array of 70 micrometer square pixels, and the illumination light has a wavelength of 266 nanometers.
• FIG. 4
• the scattered light collected from the sample material and transmitted through aperture 151 has the same phase as the scattered light collected from the sample material and transmitted through aperture 152, i.e., zero phase
• FIG, 5 depicts a plot 161 of another simulation of the interference pattern at the image plane at the
• FIG. 5 A photosensitive surface of detector 120 generated by the interference of light transmitted through apertures 151 and 152 from a different material than FIG. 4, FIG. 5
• FIG. 5 illustrates a zoomed view of the image plane at the center of the measurement spot. As illustrated in FIG. 5, the interference fringes are not centered at the center
• the scattered light collected from the sample material and transmitted through aperture 151 has different phase than the scattered light collected from the sample material and transmitted through aperture 152,
• the phase difference is characterized by the angle, F A .
• FIG. 6 depicts a plot 162 of another simulation of the interference pattern at the image plane at the
• FIG. 6 illustrates a zoomed view of the image plane at the center of the measurement spot. As illustrated in FIG. 6, the interference fringes are not centered at the center
• the scattered light collected from the sample material and transmitted through aperture 151 has different phase than the scattered light collected from the sample material and transmitted through aperture 152.
• the phase difference is characterized by the angle, fr,.
• phase difference between the scattered light collected from the sample material and transmitted through aperture 151 and the scattered light collected from the sample material and transmitted through aperture 152.
• the phase difference associated with each material is dramatically different. For example, as depicted in FIGS. 5 and 6, the difference in phase
• phase difference characterized by the difference between F A a F B is approximately 0.6 multiplied by the spatial period of the interference fringes (i.e., approximately 200 degrees).
• optical properties e.g., n and k values
• apertures 151 and 152 are provided by way of non-limiting example. In general, many different aperture sizes and locations may be contemplated within the scope of this patent document. For example, each aperture in the pupil plane may be sized in range from 0.01NA to 0.3NA.
• the value of phase difference measured using a particular mask geometry does not uniquely identify the material composition of the measured sample, although it may in some cases.
• the value of phase difference may be measured using a number of different mask geometries, i.e. , measure the phase differences associated with multiple sets of different locations in the pupil plane. If the number of different mask geometries is sufficiently large, a map of phase in the pupil plane may be derived from the measured interference fringes associated with each of the difference mask geometries. This phase map is then used to uniquely identify the material properties of the measured sample, e.g., n and k.
• the values of material parameters, e.g., n and k are floated in physical model of the material and an iterative fitting procedure is employed to estimate values of the material parameters that best fit the measured phase map.
• phase difference measurements of a defect particle with two different mask geometries sire sufficient to classify the measured particle as a metal (very large k value) or a non- metal (a very small or zero k value) with accuracy greater than 90%.
• computing system 140 is
• FFT Fast Fourier Transform
• the FFT algorithm provides
• an iterative fit of a physical model of the measurement to a measured interference pattern is employed to determine the phase difference between the light scattered from two different locations in the pupil plane.
• one or more parameters indicative of the phase difference are floated in the physical model, and the values are estimated in an iterative manner.
• the location of apertures located in the pupil plane is optimized to enhance the contrast between phase differences measured for different materials. For example, if the spacing between apertures in the pupil plane is too large, the measured phase
• the spacing between apertures in the pupil plane is too small, the value of measured phase difference will suffer from low signal to noise ratio.
• the spacing between apertures is informed by knowledge of the phase map associated with each material of interest. For example, if it is known that a large
• the spacing of the apertures is selected to just span the range of NA where the transition is known to occur.
• a spatial separation between the apertures in the pupil plane spans a range of NA from 0.1 to 0.9.
• the aperture locations are selected to minimize measurement errors induced by focus offset ⁇ i.e., focus errors) of the inspection tool.
• focus offset ⁇ i.e., focus errors
• FIGS. 7 and 8 depict
• FIGS. 9 and 10 depict different locations of apertures 151 and 152 that are symmetric about the center of the pupil in the y-direction.
• the size of apertures located in the pupil plane is optimized to both enhance the
• the aperture size is in a range from 0.01NA to 0.3NA.
• phase difference may be calculated among more than two locations (e.g., three or more locations). Estimating phase difference among more than two locations shortens acquisition time, but requires a more computationally complex determination of phase.
• the characterization of material properties based- on measured phase differences associated with different locations in the pupil plane relies on the non-uniformity of phase of scattered light in the pupil plane.
• the intensity of light scattering in the pupil plane may also be very non-uniform. If intensity
• FIG. 1 depicts a neutral density filter 118 at pupil plane 106 that spans aperture 152, but not aperture 151. In this manner, the intensity of light transmitted through aperture 152 that reaches detector 120 is attenuated relative to the intensity of light transmitted through aperture 151 that reaches detector 120.
• two or more different locations of sampling positions in the pupil are required to classify a defect.
• optimal sampling locations in the pupil vary depending on the material under consideration.
• an inspection system includes a programmable pupil aperture device configured to sample the pupil at different locations under control of computing system 140. In this manner, computing system 140 controls the location of each sampling position in the pupil plane for each phase difference measurement.
• FIG. 11 depicts a programmable pupil mask device
• programmable pupil mask device 170 includes mask element
• Mask element 171 includes optical elements 171A and 171B that block collected light in the pupil.
• Optical elements 171A and 171B are fixed with respect to one another and are fixed in their position within the pupil.
• Optical elements 171A and 171B are spatially separated; revealing a linear, optically
• Mask element 172 includes V-shaped optical elements 172A and 172B that block collected light in the pupil. Optical elements 172A and 172B are fixed with respect to one another and are spatially separated revealing a V-shaped optically transparent slit 172C. Mask element 172 is movable in the x-direction across the pupil. In addition, mask element 172 is coupled to actuator 174. Actuator 174 is communicatively coupled to a computing system, e.g., computing system 140. In one example, computing system 140 communicates control commands 175 to actuator 174 indicating a desired position of mask element 172 in the pupil. In response actuator 174 translates mask element 172 to the desired position in the pupil.
• a computing system e.g., computing system 140. In one example, computing system 140 communicates control commands 175 to actuator 174 indicating a desired position of mask element 172 in the pupil. In response actuator 174 translates mask element 172 to the desired position in the pupil.
• a movement of mask element 172 in the x-direction changes the separation distance between aperture openings 173A and 173B in the pupil through which light is transmitted to detector 120.
• aperture openings 173A and 173B are symmetrical about the x-axis and the distance between them in the y-direction is determined by the x- position of mask element 172.
• mask element 171 is located at pupil plane 105 and mask element 172 is located at pupil plane 106 of inspection system 100 depicted in FIG. 1.
• FIG. 12 depicts a programmable pupil mask device
• programmable pupil mask device 180 includes mask element
• Optical elements 181A-D are fixed with respect to one another, and optical elements 182A-D are fixed with respect to one another.
• Optical elements 181A-D are spatially separated; revealing linear, optically transparent slits aligned with the x-direction and y-direction, respectively.
• optical elements 182A-D are spatially separated; revealing linear, optically transparent slits aligned with the x-direction and y-direction, respectively.
• Mask element 181 is movable in the x-direction across the pupil.
• mask element 181 is coupled to actuator 181B.
• Actuator 184B is communicatively coupled to a computing system, e.g., computing system 140.
• computing system 140 communicates control commands 185B to actuator 184B indicating a desired position of mask element 181 in the pupil.
• actuator 184B translates mask element 181 to the desired position in the pupil.
• mask element 182 is movable in the y- direction across the pupil.
• mask element 182 is coupled to actuator 184A. Actuator 184A is
• computing system 140 communicatively coupled to a computing system, e.g., computing system 140.
• computing system 140 communicates control commands 185A to actuator 184A
• mask element 181 in the x-direction changes the location of aperture opening 183B in the x-direction without moving the location of aperture opening 183A.
• a movement of mask element 182 in the y-direction changes the location of aperture opening 183B in the y-direction without moving the location of aperture opening 183A.
• phase difference measurements between a number of different locations in the pupil and a fixed point in the pupil are made by adjusting the position of mask elements 181, 182, or both, between each measurement.
• mask element 181 is located at pupil plane 105 and mask element
• a programmable pupil mask device includes a number of different mask elements each having a fixed aperture pattern.
• the programmable pupil mask device includes an actuator subsystem (e.g. a linear translation stage, a rotational stage, etc.) to selectively locate a desired mask element in a desired location in a pupil plane.
• actuator subsystem e.g. a linear translation stage, a rotational stage, etc.
• the actuator subsystem locates a desired mask element in a desired location in a collection pupil plane of the optical system in accordance with the control command signal.
• computing system 140 is configured to detect features, defects, or light scattering properties of the wafer using electrical signals obtained from each detector.
• the computing system 140 may include any combination
• the computing system 140 may be configured to use any appropriate defect detection algorithm or method known in the art.
• the computing system 140 may use a die-to-database comparison or a thresholding algorithm to detect defects on the specimen.
• inspection system 100 may include peripheral devices useful to accept inputs from an operator (e.g., keyboard, mouse, touchscreen, etc.) and display outputs to the operator ⁇ e.g., display monitor). Input commands from an operator may be used by computing system 140 to adjust the sampling locations within the collection pupil. The resulting sampling locations may be graphically presented to an operator on a display monitor.
• peripheral devices useful to accept inputs from an operator (e.g., keyboard, mouse, touchscreen, etc.) and display outputs to the operator ⁇ e.g., display monitor).
• Input commands from an operator may be used by computing system 140 to adjust the sampling locations within the collection pupil. The resulting sampling locations may be graphically presented to an operator on a display monitor.
• Inspection system 100 includes a processor 141 and an amount of computer readable memory 142, Processor 141 and memory 142 may communicate over bus 143.
• Memory 142 includes an amount of memory 144 that stores a program code that, when executed by processor 141, causes processor 141 to execute the defect detection and classification
• FIG. 13 illustrates a flowchart of an exemplary method 200 useful for classifying defects.
• inspection system 100 described with reference to FIG. 1 is configured to implement method 200.
• the implementation of method 200 is not limited by the specific embodiments described herein.
• a first amount of illumination light is generated by and illumination source and directed to a measurement spot on a surface of a specimen.
• a first amount of collected light is collected from the measurement spot on the surface of the specimen in response to the first amount of illumination light.
• the first amount of collected light includes dark field scattering light within a collection pupil of a collection objective.
• a second portion of the first amount of collected light is transmitted.
• the second portion of the first amount of collected light is selected by one or more mask elements in a first configuration.
• the first amount of collected light is selected from at least two spatially distinct locations in the collection pupil.
• a first interference pattern formed by the second portion of the first amount of collected light is detected at or near a field plane conjugate to the surface of the specimen.
• a first phase difference between the transmitted light selected by the one or more mask elements in the first configuration from ai first location of the ait least two spatially distinct locations and the transmitted light selected by the one or more mask elements in the first configuration from a second location of the at least two spatially distinct locations is determined from the first interference pattern.
• specimen is used herein to refer to a wafer, a reticle, or any other sample that may be inspected for defects, features, or other information ⁇ e.g., an amount of haze or film properties) known in the art.
• wafer generally refers to substrates formed of a semiconductor or non-semiconductor material. Examples include, but are not limited to,
• a wafer may include only the substrate (i.e., bare wafer) .
• a wafer may include one or more layers of different materials formed upon si substrate.
• One or more layers formed on a wafer may be "patterned" or “unpatterned. "
• a wafer may include a plurality of dies having repeatable pattern features.
• a "reticle” may be a reticle at any stage of a reticle fabrication process, or a completed reticle that may or may not be released for use in a semiconductor fabrication facility.
• a reticle, or a "mask,” is generally defined as a substantially transparent substrate having substantially opaque regions formed thereon and configured in a pattern.
• the substrate may include, for example, a glass material such as quartz.
• a reticle may be disposed above a resist-covered -wafer during sin exposure step of si lithography process such that the pattern on the reticle may be transferred to the resist.
• the functions described may be implemented in hardware, software, firmware, or any combination thereof.
• Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another
• a storage media may be any available media that can be accessed by a general purpose or special purpose computer.
• such computer-readable media can comprise RAM, ROM, ESPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special- purpose processor.
• any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) , or wireless
• Disk and disc includes compact disc (CD) , laser disc, optical disc, digital versatile disc (DVD) , floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media,
• detector 120 can be replaced by a fiber array.
• inspection system 100 may include more than one light source (not shown) .
• the light sources may be configured differently or the same.
• the light sources may be configured to generate light having
• the light sources may be configured according to any of the embodiments described herein. In addition one of the light sources may be configured according to any of the embodiments described herein, and another light source may be any other light source known in the art.
• an inspection system may illuminate the wafer over more than one illumination area simultaneously.
• the multiple illumination areas may spatially overlap.
• the multiple illumination areas may be spatially distinct.
• an inspection system may illuminate the wafer over more than one illumination area at different times.
• the different illumination areas may temporally overlap (i.e. , simultaneously illuminated over some period of time) .
• the different illumination areas may be
• illumination areas may be arbitrary, and each illumination area maty be of equal or different size, orientation, and single of incidence.
• inspection system 100 may be a scanning spot system with one or more illumination areas that scan independently from any motion of wafer 110.
• an illumination area is made to scan in a repeated pattern along a scan line. The scan line may or may not align with the scan motion of wafer 110.
• wafer positioning system 125 generates motion of wafer 110 by coordinated rotational and translational movements
• wafer positioning system 100 may generate motion of wafer 110 by coordinating two translational movements. For example motion wafer positioning system 125 may
• an inspection system includes an illumination source and a wafer
• the illumination source supplies an amount of radiation to a surface of a wafer over an
• the wafer positioning system moves the wafer in a scanning motion characterized by a scan pitch (e.g., scanning back and forth in one direction and

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• 2020
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