Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
  • H01L22/30—Structural arrangements specially adapted for testing or measuring during manufacture or treatment, or specially adapted for reliability measurements
• • 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
  • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
  • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
  • G01N21/65—Raman scattering
• • 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
  • G01N21/94—Investigating contamination, e.g. dust
• • 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
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
  • H01L22/10—Measuring as part of the manufacturing process
  • H01L22/12—Measuring as part of the manufacturing process for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
  • H01L22/20—Sequence of activities consisting of a plurality of measurements, corrections, marking or sorting steps
  • H01L22/24—Optical enhancement of defects or not directly visible states, e.g. selective electrolytic deposition, bubbles in liquids, light emission, colour change

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 processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield. As design rules and process windows continue to shrink in size, inspection systems are required to capture a wider range of physical defects on wafer surfaces while maintaining high
• One such inspection system illuminates and inspects an unpatterned wafer surface for undesired particles.
• the minimum particle size that must be detected by a surface inspection system continues to shrink in size.
• Integrated circuit yield loss due to particle contamination from wafer processing equipment must be remediated to realize a cost effective manufacturing process.
• particle contamination levels are monitored by an unpatterned wafer surface inspection system such as the Surfscan® family of products manufactured by KLA-Tencor Corporation, Milpitas, California (USA) .
• a typical contamination metric measured by the inspection tool is the number of particles-per- wafer-pass (PWP) .
• PWP particles-per- wafer-pass
• RAMAN spectroscopy is a potential analytical technique that may be employed to identify the composition of particle defects on a wafer surface.
• U.S. Patent Nos. 7,777,876 and 9,007,581 issued to Hitachi High-Technologies Corporation describe a surface inspection system that detects both elastic and inelastic scattered light (i.e., Rayleigh and Raman scattering, respectively) .
• Improvements to scanning surface inspection systems are desired to both detect the presence of defects on the wafer surface and identify the material composition of detected defect particles without transferring the wafer to a different review tool.
• spectroscopically active state and identifying a material composition of the activated particle by a spectroscopic technique are described herein.
• Particle defects are transformed by chemical treatment, thermal treatment, photochemical treatment, or a combination thereof, such that an activated particle exhibits atomic vibrational bands that can be observed spectroscopically.
• defect particles generated by semiconductor manufacturing equipment and processes are spectroscopically inactive.
• metallic nanoparticles having body centered cubic (bcc) or face centered cubic (fee) crystal symmetry have no observable Raman spectral lines.
• a scanning surface inspection system detects the presence of a particle defect on a wafer surface, activates observable Raman bands in one or more of the detected particles, and identifies the material
• composition of the activated particle by a spectroscopic technique.
• composition analysis on the same inspection tool it is not necessary to transfer a wafer to a different review tool, or combination of tools, to perform composition analysis of particle defects deposited on semiconductor wafers.
• a computing system is configured to receive
• the computing system matches the spectroscopic signature of the measured spectra (e.g., peak locations, peak
• the computing system matches the
• the computing system correlates the
• the library includes optical
• the library also includes other composition data (e.g., photoluminescence data, energy dispersive X-ray (EDX) spectrometer data, etc.).
• composition data e.g., photoluminescence data, energy dispersive X-ray (EDX) spectrometer data, etc.
• composition of a defect particle is determined based on the measurement of
• defect particles exhibit broadband photoluminescence (PL) spectra extending as far as the near IR.
• the collected light is cross-polarized with respect to the illumination light to improve the signal to noise ratio of the detected signals.
• a surface inspection system is employed to generate a map of defect locations on the wafer surface in a scanning mode to rapidly generate a defect mapping of the entire wafer surface or significant portions of the wafer surface. After mapping the wafer surface, the surface inspection system is employed to activate and analyze one or more of the defect particles previously detected by the defect particle detection subsystem. In some other embodiments, a defect particle is activated and analyzed immediately after detection.
• the activation of the particle is due to a chemical oxidation of a metallic particle.
• the transformation of the particle occurs in a chamber of controlled partial pressure of oxygen.
• the chamber includes additional partial pressures of substantially inert gases that do not
• the chamber includes additional partial pressures of gaseous compounds that catalyze the oxidative
• a metallic particle is treated with a surface-active material before oxidation to promote formation of the metallic oxide with oxidation state and crystalline polymorphic structure having an enhanced Raman scattering cross section.
• the oxidative transformation is driven by elevated temperature.
• the elevated temperature may be generated by radiative heating, illumination with electromagnetic radiation, or a
• the oxidative transformation of a particle is driven by a photochemical pathway stimulated by exposure to photons emitted from an electromagnetic
• the transformation is a chemical reaction, other than an oxidative reaction, with gaseous, liquid, or solution-borne reagents and a photothermal or photochemical driving force.
• multiple, different illumination sources may be employed to provide illumination for activation, spectral measurement, or both.
• one or more illumination sources employed to map the locations of defect particles on the wafer surface may also be employed to provide illumination for activation, spectral
• wavelengths are employed and the wavelengths are selected because they are known to interact with surface asperities of the substrate wafer (e.g., thin films, high aspect ratio protrusions of highly non-spherical defect particles, etc.).
• the surface asperities produce enhanced
• FIG. 1 is a simplified diagram illustrative of one embodiment of an inspection system configured to detect, activate, and identify the material composition of a defect particle on a specimen under inspection.
• FIG. 2 is a diagram illustrative of a top view of wafer positioned on a rotary scanning stage.
• FIG. 3 is a diagram illustrative of a simulation of the absorption cross-section of a copper particle as a function of sphere diameter.
• FIG. 4 is a diagram illustrative of a simulation of the thermal heating of a copper particle deposited on the surface of a silicon wafer as a function of incident irradiance and various values of effective thermal
• FIG. 5 is a diagram illustrative of spectral measurements of a defect particle activated at a low illumination power level.
• FIG. 6 is a diagram illustrative of spectral measurements of a defect particle activated at a high illumination power level.
• FIG. 7 is a diagram illustrative of spectral measurements of a defect particle activated at different illumination power levels.
• FIG. 8 is a diagram illustrative of spectral measurements of a titanium dioxide particle collected by a surface inspection system at low illumination power.
• FIG. 9 is a simplified diagram illustrative of a reference Raman spectrum associated with titanium dioxide (Ti0 2 ) .
• FIG. 10 illustrates a flowchart of an exemplary method 100 useful for identifying the material composition of activated defect particles on a wafer surface.
• inventive concepts described herein are based on the observation that many defect particles generated by semiconductor manufacturing equipment and processes are spectroscopically inactive (e.g., particles do not have atomic vibrational bands that can be observed with Raman spectroscopy) .
• particle defects are transformed such that an activated particle exhibits atomic vibrational bands that can be observed spectroscopically (e.g., via Raman
• a scanning surface inspection system detects the presence of a particle defect on a wafer surface, activates observable Raman bands in one or more of the detected particles, and identifies the material
• composition of the activated particle by a spectroscopic technique.
• FIG. 1 is a simplified schematic view of one embodiment of a surface inspection system 100 that may be used to perform the inspection methods described herein. For simplification, some optical components of the system have been omitted. By way of example, folding mirrors, polarizers, beam forming optics, additional light sources, additional collectors, and additional detectors may also be included. All such variations are within the scope of the invention described herein.
• the inspection system
• surface inspection system 100 includes a defect particle detection subsystem
• surface inspection system 100 includes a defect particle activation and analysis subsystem including illumination source 111, optical elements 112-115, 130-132, and detector 116.
• Illumination source 101 of the defect particle detection subsystem generates a beam of illumination light 102 that is directed toward wafer 110. As depicted in FIG. 1, illumination is provided to the surface of wafer 110 at an oblique angle by the defect particle detection
• the defect particle detection subsystem may be configured to direct the beam of light to the specimen at a normal angle of incidence.
• the defect particle detection subsystem 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.
• 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 defect particle detection subsystem is configured to direct light having a relatively narrow wavelength band to the specimen
• the defect particle detection 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.
• the defect particle detection subsystem is configured to direct light to the specimen having a very narrow wavelength band suitable for Raman spectroscopy.
• the linewidth of the illumination has a linewidth on the order of 30 gigahertz (1 cm -1 ), or less.
• a laser illumination source is configured to emit light at 405 nanometers with a linewidth of less than 0.016 nanometers.
• a constant power laser beam is generated by illumination source 101, and an illumination power control element 103 is employed to regulate beam power to prevent damage to the wafer surface.
• beam power is regulated based on the size and material composition of the particles being scanned.
• illumination optics 104 that focus the beam of illumination light 102 onto the wafer surface.
• the light that reaches the surface of the wafer may be altered in one or more ways, including polarization, intensity, size and shape, etc.
• wafer positioning system 125 moves wafer 110 under illumination beam 102 to adjust the location of the measurement spot 106 on the wafer surface. Wafer positioning system 125
• Wafer 110 is supported on wafer chuck 126. As illustrated in FIG. 2, wafer 110 is located with its geometric center 150
• rotation stage 121 spins wafer 110 about its geometric center at a specified angular velocity, ⁇ , within an acceptable tolerance.
• translation stage 122 translates the wafer 110 in a
• Motion controller 123 coordinates the spinning of wafer 110 by rotation stage 121 and the translation of wafer 110 by translation stage 122 to achieve the desired scanning motion of wafer 110 within inspection system 100.
• inspection begins with measurement spot 106 located at the geometric center 150 of wafer 110 and then wafer 110 is rotated and translated until measurement spot 106 reaches 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 106 trace 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 .
• measurement spot 106 is located a distance, R, from the geometric center of wafer 150.
• Collection optics 107 collect light scattered and/or reflected from measurement spot 106. Although a
• orientation of the collection optics with respect to the wafer surface may be arranged appropriately depending upon, for example, the angle of incidence and/or topographical characteristics of the wafer.
• Detector 109 generally functions to convert the detected light into electrical signals indicative of the detected light collected from wafer 110 within the detected field of view.
• detector 109 may include substantially any photodetector known in the art.
• 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. For example, 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 increase the signal-to-noise ratio and throughput of the system.
• TDI time delay integration
• detectors such as a photodiode, a phototube, a photomultiplier tube (PMT) , a charge-coupled device (CCD) camera, arrays of photodiodes, phototubes and photomultiplier tubes (PMTs) , may be used, depending on the amount of light available for inspection and the type of inspection being performed.
• PMT photomultiplier tube
• CCD charge-coupled device
• detector 109 is a non-imaging detector configured to generate a single output signal indicative of the amount of light scattered from the measurement spot 106.
• a single output signal allows for efficient detection of large particles with high
• detector 109 is an imaging detector that 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.
• a detector generates dark field images by imaging scattered light collected at larger field angles.
• a pinhole that matches the incident spot 106 can be placed in front of a detector (e.g., detector 109) to generate a confocal image.
• multiple detectors are provided.
• one or more flip-in mirrors or beam splitters may be employed to selectably direct collected light 108 toward different detectors
• a single detector e.g., an individual
• photomultiplier tube (PMT) is employed as detector 109 to detect light scattered from the measurement spot 106.
• the output signal 134 of detector 109 is communicated to a computing system 140 for processing to determine the presence of a defect particle.
• the defect particle detection subsystem of surface inspection system 100 is employed to generate a map of defect locations on the wafer surface. In these embodiments, the defect particle detection
• subsystem is operated in a scanning mode to rapidly
• the defect particle activation and analysis subsystem is employed to activate and analyze one or more of the defect particles previously detected by the defect particle detection subsystem. However, in some other embodiments, the defect particle activation and analysis subsystem is employed to activate and analyze a defect particle immediately after detection by the defect particle detection subsystem.
• Illumination source 111 of the defect particle activation and analysis subsystem generates a beam of illumination light 117 that is directed toward wafer 110. As depicted in FIG. 1, illumination is provided to the surface of wafer 110 at multiple angles of incidence by the defect particle activation and analysis subsystem.
• the defect particle activation and analysis subsystem may be configured to direct the beam of light to the specimen at any single angle of incidence or set of multiple angles of incidence, including a normal angle of incidence.
• Illumination source 111 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 defect particle activation and analysis 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 defect particle activation and analysis subsystem may also include one or more spectral filters 112 that may limit the
• the one or more spectral filters may be bandpass filters and/or edge filters and/or notch filters.
• the defect particle detection subsystem is configured to direct light to the specimen having a very narrow
• the linewidth of the illumination has a linewidth on the order of 30 gigahertz (1 cm -1 ), or less.
• a laser illumination source is configured to emit light at 405 nanometers with a linewidth of less than 0.016 nanometers .
• illumination beam 117 is directed to illumination power control element 130.
• Illumination power control element 130 is configured to control the optical power of the beam of illumination light 117 in accordance with command signal 133 received from computing system 140.
• illumination power control element 130 is located in the illumination beam path between illumination source 111 and beam
• splitting element 113 to dynamically adjust the
• the illumination power control element 130 is a high efficiency, low cost
• AOM acousto-optic modulator
• illumination power control element 130 may be implemented with a selectively transmissive optical component, which may be adapted to transmit a portion of the incident light based on a polarization of the incident light.
• illumination power control element 130 includes a wave plate (such as a quarter wave plate) and a polarizing beam splitter. In this
• the wave plate may be used to change the polarization of the incoming light, while the beam splitter functions to transmit one or more select polarizations (e.g., linearly polarized light) and reflect all others (e.g., randomly, circularly or elliptically polarized light) .
• the wave plate and beam splitter function to reduce the intensity or power level of the transmitted light.
• illumination power control element 130 includes an electro-optical material that is switchable between an "on” condition and an "off"
• the electro-optical material When “on,” the electro-optical material changes the polarization of the incoming light into a predetermined polarization orientation. This so-called “re-polarized light” may then be supplied to a polarizing beam splitter, which may transmit only a portion of the re-polarized light, depending on the particular polarization output from the electro-optical switch. Remaining portions of the re- polarized light may be reflected and discarded (e.g., absorbed by a beam dump material) . In some cases, the electro-optical material may switch between “on” and “off” conditions within a time span of a few nanoseconds to a few microseconds .
• illumination power control element 130 includes a high-speed electrically-controlled optical shutter, known as a Pockels Cell.
• a Pockels Cell may be set in an "on" condition to allow the light
• the Pockels Cell may be switched to an "off" condition to change the polarization of the generated light to a different
• an electrical voltage provided by a variable power supply may be supplied to the Pockels Cell to change the polarization of the light passed through the electro-optical material (typically, an electro-optical crystal) .
• the voltage supplied to the Pockels Cell may be determined by control signal 133 communicated from
• An AOM can be driven at any suitable frequency, and thus modulate illumination power over a broad range.
• a Pockels Cell can be driven to produce substantially any phase shift, and thus, may be combined with a polarizing beam splitter to create substantially any output power level.
• circuitry and/or software may be included with illumination power control element 130 to provide a continuous power level adjustment (e.g., in the form of a closed feedback loop) .
• illumination power control element 130 includes a combination of discrete optical density filters that are selectively inserted into the beam path based on control commands 133 received from computing system 140.
• the present invention may encompass any appropriate technique for dynamically altering the power level of an illumination source provided that the power control element provides a relatively fast response and sufficient dynamic range.
• beam power is modulated at sub-second timescales to illuminate a metal particle with high power to initiate oxidation, then immediately lowering power to continue absorption by the oxide at the illumination wavelength without damaging the oxidized particle.
• illumination light 117 is also polarized by polarizing element 131.
• illumination sources such as lasers, intrinsically emit polarized light.
• the illumination light is polarized at different orientation angles with respect to one or more crystal axes of the defect particle.
• the incident polarization and analyzer directions may be changed and spectra collected for each for a set of orientation angles.
• the spectral responses are analyzed to confirm whether a particle defect is crystalline, aid the identification of its composition, or identify defect class membership. It is noted that gathering a set of
• the illumination beam 117 After passing through illumination power control element 130, the illumination beam 117 is directed to a beam splitting element 113 that directs a portion of the illumination beam 119 toward objective 114.
• beam splitting element 113 is a dichroic beam splitter.
• any suitable beam splitter may be contemplated within this patent document.
• Objective 114 focuses the illumination beam 119 onto wafer 110 at measurement spot 106. As described
• wafer positioning system 125 moves wafer 110 the projection of illumination beam 119 onto the wafer surface over measurement spot 106.
• Motion controller 123 coordinates the rotation of wafer 110 by rotation stage 121 and the translation of wafer 110 by translation stage 122 to achieve the desired positioning of wafer 110 within the field of view of the defect particle activation and
• objective 114 collects light scattered and/or reflected from wafer 110 in response to illumination beam 119 over a range of
• the collected light 120 passes through beam splitting element 113.
• the defect particle activation and analysis subsystem is configured to perform a Raman analysis of the collected light.
• the one or more spectral filters may be bandpass filters and/or edge filters and/or notch filters.
• the defect particle activation and analysis subsystem is configured to cross-polarize the illumination and collected light to improve the signal to noise ratio of the detected signals.
• collected light 120 is polarized by analyzer 132 with a polarization that is orthogonal to the polarization of the illumination light 118 provided by polarizing element 131.
• any suitable polarizing optical element may be contemplated within the scope of this patent document.
• collected light 120 is projected onto a detecting surface of spectrometer 116.
• Spectrometer 116 generally functions to measure the detected light in a wavelength or energy resolved manner.
• Spectrometer 116 communicates electrical signals 135 indicative of the measured spectra to computing system 140 for further analysis of the material composition of the defect particle under measurement.
• spectrometer 116 may include substantially any
• a particular detector may be selected for use within one or more
• an efficiency enhancing detector such as a time delay integration (TDI) camera may employed to improve the performance characteristics of the detector. For example, 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 improve the performance characteristics of the detector.
• TDI time delay integration
• CCD charge-coupled device
• PMTs photomultiplier tubes
• a defect particle activation and analysis subsystem of a surface inspection tool is
• metallic nanoparticles have no observable Raman spectral lines because of their body centered cubic (bcc) or face centered cubic (fee) crystal symmetry.
• metallic copper (Cu) has a fee crystal structure .
• FIG. 5 depicts spectral measurements collected by the defect particle activation and analysis subsystem of surface inspection system 100 at low illumination power.
• illumination source 111 supplied
• Plotline 160 depicts the measured spectrum of the wafer surface without a particle in the laser illumination spot.
• Plotline 161 depicts the measured spectrum of the wafer surface with a copper particle of 945 nanometers diameter in the laser illumination spot.
• weak Raman bands indicative of graphitic carbon are visible, but there is no evidence of any Raman bands despite integrating for 100 seconds. Thus, the amount of oxidized copper, if any, is too small to yield an identifiable Raman spectrum.
• FIG. 6 depicts spectral measurements collected by the defect particle activation and analysis subsystem of surface inspection system 100 at high illumination power.
• illumination source 111 supplied
• Plotline 163 depicts the measured spectrum of the wafer surface with a copper particle of 945 nanometers diameter in the laser
• Plotline 162 depicts a reference spectrum of CuO .
• the measured spectra depicted in FIG. 6 were measured by cross-polarizing the collected light with the illumination light as described hereinbefore.
• the first order phonon peak and the second order phonon peak associated with the silicon substrate are suppressed.
• background signals associated with multiphonon scattering are also suppressed, resulting in enhanced CuO peaks in the measured spectra.
• cross-polarization as described herein enhances the signal to noise ratio (SNR) of the detected Raman bands in a range of waveirumhers between 200cm "1 and 1000 cm "1 .
• FIG. 7 depicts spectral measurements collected by the defect particle activation and analysis subsystem of surface inspection system 100 at different illumination power levels.
• illumination source 111 supplied different levels of illumination power at 405 nanometer wavelength onto the surface of wafer 111 over a measurement spot size of approximately one micrometer diameter.
• One hundred scans, each with one second of exposure time, are averaged to realize the depicted
• Plotline 164 depicts exposure power of 0.1 milliwatts.
• Plotline 165 depicts exposure power of 0.5 milliwatts.
• Plotline 166 depicts exposure power of 1 milliwatt.
• Plotline 167 depicts exposure power of 5 milliwatts.
• Plotline 168 depicts exposure power of 10 milliwatts.
• the Raman response associated with CuO increases in magnitude. In general, the response is practically undetectable at 0.1 milliwatt exposure, but begins to become detectable at 1.0 milliwatt exposure.
• cupric oxide unit cell has a 74% larger volume than metallic copper.
• a micrograph image of the particle after activation with 10 milliwatts illumination showed a 56% increase in diameter, which represents an increase in volume of approximately 45%.
• micrometer can heat a small copper particle to 150-1500 C, driving oxidation in ambient atmosphere.
• ⁇ is the Stefan-Boltzmann constant (5.67 x 10-8 W/m 2 *K 4 ) .
• FIG. 3 depicts the absorption cross-section of the copper particle as a function of sphere diameter, calculated in accordance with Mie theory.
• the absorption cross-section, C a bs is 3.91xl0 "10 cm 2 .
• the irradiance, Io is lMW/cm 2 . Under these conditions the thermal absorption of the copper sphere is illustrated in equation (2 ) .
• the absorbed energy is converted to heat, and the particle temperature rises.
• FIG. 4 depicts a plot 155 representative the solution of Equation (4) for T as a function of incident irradiance, Io, for various values of k e ff.
• the value of k e ff associated with each plotline is illustrated in FIG. 4.
• Each plotline represents the steady state temperature of an irradiated, copper sphere of 180 nanometer diameter.
• k e ff is zero valued.
• k e ff is approximately 0.024.
• k e ff must be larger because the
• system 100 may include amplifier circuitry to receive signals from the detectors and to amplify the signals by a predetermined amount.
• ADC analog-to- digital converter
• the processor 141 may be coupled directly to an ADC by a transmission medium.
• the processor 141 may receive signals from other electronic components coupled to the ADC. In this manner, the processor may be indirectly coupled to the ADC by a transmission medium and any
• 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
• Input commands from an operator may be used by computing system 140 to adjust threshold values used to control illumination power.
• the resulting power levels 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 activation and composition analysis functionality described herein.
• computing system 140 is configured to receive spectroscopic measurement results collected from an activated particle and estimate a
• computing system 140 matches the
• spectroscopic signature of the measured spectra e.g., peak locations, peak magnitudes, etc.
• computing system 140 matches the spectroscopic signature of the measured spectra with the signature of analytically derived spectra.
• computing system 140 correlates the spectroscopic signature of the measured spectra with a library database of previously analyzed defect particles.
• the library includes optical
• the library also includes other composition data (e.g., photoluminescence data, energy dispersive X-ray (EDX) spectrometer data, etc.).
• computing system 140 assigns a classification code to the particle that best matches a classification code associated with the closest spectral match in the library. In this manner, the composition of the measured defect particle is identified with a defect classification code that most closely matches the measured spectra.
• the optical spectroscopic signatures of a transformed particle can be observed with one of more of a plurality of optical spectroscopic methods including, but not limited to: spontaneous Raman spectroscopy; stimulated Raman spectroscopy; coherent anti-Stokes Raman
• composition of a defect particle is determined based on the measurement of
• photoluminescence (PL) spectra e.g., PL spectra measured by surface inspection system 100
• defect particles exhibit broad-band photoluminescence (PL) spectra extending as far as the near IR.
• PL spectra are unstable and tend to bleach out over time if excessive illumination power is employed.
• the PL spectra are unstable and tend to bleach out over time if excessive illumination power is employed.
• irradiance provided by the illumination source is initially set to a low level to acquire PL spectra to minimize bleaching that would occur if relatively high power were employed.
• the irradiance is increased to spectroscopically activate the particle and acquire Raman spectral measurements.
• both PL and Raman spectra are available to identify the composition of the defect particle.
• defect particles exhibit Raman spectra without significant activation.
• FIG. 8 depicts spectral measurements collected by the defect particle activation and analysis subsystem of surface inspection system 100 at low illumination power.
• illumination source 111 supplied approximately 0.1
• Plotline 170 depicts the measured spectrum of the wafer surface without a particle in the laser illumination spot.
• Plotline 171 depicts the measured spectrum of the wafer surface with a particle of approximately 117 nanometers diameter in the laser
• FIG. 9 depicts a plotline 172 of a reference Raman spectrum associated with titanium dioxide (T1O2) .
• T1O2 titanium dioxide
• FIG. 9 Comparing the measured Raman spectrum of the defect particle depicted in FIG. 8 with the reference Raman spectrum associated with T1O2 in FIG. 9, it is clear that the measured defect particle is T1O2.
• inspection system 100 is configured to measure many different types of particles, including, but not limited to particles having organic, inorganic, or metallic chemical composition with crystalline, poly-crystalline, or
• the particle under inspection is a metallic particle with a bcc or fee crystalline structure that lacks intrinsic vibrational Raman spectroscopic signatures .
• the particle under inspection is a metallic particle with a hexagonal close packed (hep) structure that has a very weak intrinsic vibrational Raman spectroscopic signature.
• particle activation is employed to transform the particle and improve the detectability of vibrational Raman
• the transformation of the particle is a chemical oxidation of a metallic particle in the ambient terrestrial atmosphere at an elevation between 0 and 10,000 feet above mean sea level.
• the particle occurs in a chamber of controlled partial pressure of oxygen greater or less than 0.2 atmospheres.
• the chamber includes additional partial pressures of substantially inert gases that do not participate in the oxidation process.
• gases include, but not limited to, nitrogen, helium, neon, argon, xenon, carbon dioxide, halogenated hydrocarbons, fluorinated metals, and non- metals such as uranium hexafluoride and sulfur
• the oxidative transformation of a metallic particle is carried out with additional partial pressures of gaseous compounds that catalyze the oxidative transformation .
• the oxidative transformation of a metallic particle is carried out in a chamber with
• the metallic particle is treated with a surface-active material before oxidation to promote formation of the metallic oxide with oxidation state and crystalline polymorphic structure having an enhanced Raman scattering cross section, relative to other possible oxidation states or polymorphs said metallic particle that form absent the treatment.
• a surface-active material include, but are not limited to an organic amine in gas phase or dissolved in a liquid solution, or a liquid that is itself surface active and coats the metallic particle .
• the oxidative transformation is driven by elevated temperature.
• the elevated temperature may be generated by radiative heating, illumination with electromagnetic radiation, or a
• the temperature-driven oxidative transformation is driven by the same source of
• the oxidative transformation of a particle is driven by a photochemical pathway stimulated by exposure to photons emitted from an electromagnetic
• the photon-driven oxidative transformation is driven by the same source of electromagnetic radiation that stimulates the transformed particle to emit a spectroscopic signature that is measured and employed to identify the composition of the particle.
• the transformation is a chemical reaction, other than an oxidative reaction, with gaseous, liquid, or solution-borne reagents and a photothermal or photochemical driving force.
• the driving force provided by a source of electromagnetic radiation that may be different from or the same as the source that stimulates the
• surface inspection system 100 includes an illumination source 111 that provides illumination for both particle activation and spectral measurement
• multiple, different illumination sources may be employed to provide illumination for activation, spectral measurement, or both.
• one or more illumination sources employed to map the locations of defect particles on the wafer surface e.g., illumination source 101 depicted in FIG. 1 may also be employed to provide illumination for activation, spectral measurement, or both.
• surface inspection system 100 includes a spectrometer 116 that performs spectral measurements of a defect particle, in general, multiple, different
• spectrometer subsystems may be employed to provide spectral measurements of a defect particle.
• one or more beam splitting elements are included in the
• a movable mirror or movable turret is employed in the
• illumination light at 405 nanometers were described with reference to FIGS. 5-9, in general, one or more different wavelengths of illumination light may be employed to improve the signal to noise ratio of the spectral
• wavelengths are employed and the wavelengths are selected because they are known to interact with surface asperities of the substrate wafer (e.g., thin films, high aspect ratio protrusions of highly non-spherical defect particles, etc.).
• the surface asperities produce enhanced
• a surface inspection system (e.g., surface inspection system 100) includes a source of visible light
• electromagnetic radiation having a wavelength between 600 and 700 nm.
• Light in this range of wavelengths is known to excite local surface plasmon resonances in high aspect ratio protrusions and features of non-spherical copper nanoparticles .
• the enhanced electromagnetic fields associated with the excited plasmons enhance the Raman scattering signature from a thin layer of cuprous oxide, cupric oxide, or both, on the surface of the copper
• the oxide layer is present in sufficient quantity on the surface of the defect
• FIG. 10 illustrates a flowchart of an exemplary method 200 useful for identifying the material composition of activated defect particles as described herein.
• 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 measurement spot on a surface of a specimen is illuminated with a beam of illumination light.
• the beam of illumination light chemically alters a defect particle such that the defect particle becomes
• an output signal indicative of a material composition of the activated defect particle is generated based on an amount of light scattered from the activated defect particle.
• a material composition of the activated defect particle is determined based on the output signal .
• 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, monocrystalline silicon, gallium arsenide, and indium phosphide. Such substrates may be commonly found and/or processed in semiconductor fabrication facilities. In some cases, a wafer may include only the substrate
• a wafer may include one or more layers of different materials formed upon a
• 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 an exposure step of a lithography process such that the pattern on the reticle may be transferred to the resist.
• Computer-readable media includes both computer storage media and commu ic tion 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, EEPROM, 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 as used herein, inciud.es compact d.isc (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.

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