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
  • G01N21/8806—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
  • G01N21/95—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
  • G01N21/956—Inspecting patterns on the surface of objects
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/0004—Microscopes specially adapted for specific applications
  • G02B21/002—Scanning microscopes
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/0004—Microscopes specially adapted for specific applications
  • G02B21/002—Scanning microscopes
  • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
  • G02B21/0052—Optical details of the image generation
  • G02B21/006—Optical details of the image generation focusing arrangements; selection of the plane to be imaged
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/06—Means for illuminating specimens
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/10—Scanning systems
  • G02B26/101—Scanning systems with both horizontal and vertical deflecting means, e.g. raster or XY scanners
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
  • G02B27/0905—Dividing and/or superposing multiple light beams
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
  • G02B27/0938—Using specific optical elements
  • G02B27/0944—Diffractive optical elements, e.g. gratings, holograms
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/10—Beam splitting or combining systems
  • G02B27/1086—Beam splitting or combining systems operating by diffraction only
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/10—Beam splitting or combining systems
  • G02B27/12—Beam splitting or combining systems operating by refraction only
  • G02B27/123—The splitting element being a lens or a system of lenses, including arrays and surfaces with refractive power
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
  • G02B27/4233—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive element [DOE] contributing to a non-imaging application
  • G02B27/425—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive element [DOE] contributing to a non-imaging application in illumination systems
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
  • G02F1/33—Acousto-optical deflection devices
• • 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
  • G01N2021/8848—Polarisation of light
• • 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
  • G01N21/956—Inspecting patterns on the surface of objects
  • G01N21/95607—Inspecting patterns on the surface of objects using a comparative method
• • 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
  • G01N2201/063—Illuminating optical parts
  • G01N2201/0635—Structured illumination, e.g. with grating
• • 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
  • G01N2201/10—Scanning
  • G01N2201/104—Mechano-optical scan, i.e. object and beam moving
• • 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
  • G01N2201/10—Scanning
  • G01N2201/105—Purely optical scan
• • 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
  • G01N2201/10—Scanning
  • G01N2201/106—Acousto-optical scan

Definitions

• the present disclosure relates generally to the field of oblique incidence spot scanning wafer inspection systems.
• Wafer inspection systems are often used to analyze wafers (or "dies") in order to determine the presence of potential defects.
• a typical wafer inspection system will generate an image of the die to be analyzed and compare this image to a reference image, which may be taken from a database or the image of another die in the series.
• Spot scanning architectures generate an image of a wafer pixel by pixel by scanning a focused beam of illumination across the sample and detecting light scattered and/or reflected from the sample. In this way, spot scanning systems are capable of detecting features on a wafer with high spatial resolution.
• oblique spot scanning wafer inspection systems are configured such that the illumination beam interacts with the wafer at an oblique angle rather than at a normal incidence angle.
• oblique angle incidence enables the detection of polarization-induced effects on the sample.
• many surface features such as integrated circuits approximate a diffraction grating; the use of an oblique sampling beam thus enables precise diffraction -based monitoring of wafer features.
• the use of an oblique angle sampling beam in traditional wafer inspection systems may reduce the throughput, or alternatively the efficiency, of a wafer inspection system. This is because only a single linear region may be sampled at a given time.
• This linear region is described by the intersection of the focal plane of the objective lens, which is typically normal to the optica! axis of the objective lens, and the plane of the wafer.
• a typical oblique angle scanning wafer inspection system will scan an illumination beam along this linear region and detect scattered and reflected light from the sample with one or more detectors.
• a two- dimensional image is generated through the acquisition of successive line scans in which the sample is moved via a translation stage between successive line scans. Therefore, there exists a critical need to develop systems and methods to increase the throughput of oblique scanning wafer inspection systems.
• the system includes a beam scanning device configured to scan a beam of illumination.
• the system includes an objective lens positioned to direct the beam to a surface of a sample such that the beam is scanned along a first direction, wherein an optical axis of the objective lens is oriented perpendicular to the first direction and is further oriented at an oblique incidence angle relative to a surface of the sample.
• the system includes one or more optical elements positioned between the objective lens and the beam scanning device, !n one illustrative embodiment, the one or more optica! elements are configured to split the beam into two or more offset beams, wherein the two or more offset beams are separated in at least a second direction, wherein the second direction is perpendicular to the first direction.
• the one or more optical elements are configured to modify the phase characteristics of the two or more offset beams such that the two or more offset beams are simultaneously in focus on the sample during a scan.
• the apparatus includes one or more optical elements positionabie in a beam scanning system prior to an objective lens oriented at an oblique angle relative to a surface, and wherein an optical axis of the lens is perpendicular to a first direction on a plane defined by the surface.
• the one or more optical elements are configured to split a beam into two or more offset beams, wherein the two or more offset beams are separated in at least a second direction, wherein the second direction is perpendicular to the first direction.
• the one or more optical elements are configured to modify the phase characteristics of the two or more offset beams such that the two or more offset beams are simultaneously in focus on the surface during a scan.
• the method includes generating a beam of illumination, !n another illustrative embodiment, the method includes directing the beam to a surface at an oblique angle, wherein the beam is substantially perpendicular to a first direction on a plane defined by the surface. In another illustrative embodiment, the method includes prior to directing the beam, splitting the beam into two or more offset beams, wherein the two or more offset beams are separated in at least a second direction, and wherein the second direction is perpendicular to the first direction. In another illustrative embodiment, the method includes prior to directing the beam, modifying the phase characteristics of the two or more offset beams such that the two or more offset beams are simultaneously in focus on the surface.
• FIG. 1 is a schematic view of an oblique incidence multi-beam spot scanning wafer inspection system, in accordance with one embodiment of the present disclosure.
• FIG. 2 is a schematic view of a portion of an oblique incidence multi-beam spot scanning wafer inspection system illustrating the use of acousto-optic deflectors to linearly scan a beam and an optical element to modify the focal characteristics of the beam, in accordance with one embodiment of the present disclosure.
• FIG. 3A is a simplified schematic of a diffraction grating generating three beams formed from the -1 , 0, and +1 diffraction orders that are not properly focused on a wafer, in accordance with one embodiment of the present disclosure.
• FIG. 3B is a schematic diagram of a diffraction grating with defocus generating three beams formed from the -1 , 0, and +1 diffraction orders that are properly focused on a wafer, in accordance with one embodiment of the present disclosure.
• FIG. 3C is a schematic diagram of a diffraction grating with defocus generating two beams formed from the 0 and +1 diffraction orders that are properly focused on a wafer, in accordance with one embodiment of the present disclosure.
• FIG. 3D is a schematic diagram of a diffraction grating with defocus generating two beams formed from the -1 and +1 diffraction orders that are properly focused on a wafer, in accordance with one embodiment of the present disclosure.
• FIG. 4A is a simplified schematic of a scan pattern with two sets of four beams oriented along two scan lines simultaneously in focus on a wafer, in accordance with one embodiment of the present disclosure.
• FIG. 4B is a simplified schematic of a scan pattern with three sets of three beams oriented along three scan lines simultaneously in focus on a wafer, in accordance with one embodiment of the present disclosure.
• FIG. 5 is a flow diagram illustrating a method for generating multiple beams in an oblique multi-beam spot scanning wafer inspection system, in accordance with one embodiment of the present disclosure.
• one or more optical elements 109 e.g. one or more diffractive optical elements (DOEs)
• DOEs diffractive optical elements
• the one or more optical elements 109 are further arranged so as to modify the phase of the two or more offset beams 1 1 1 such that the two or more offset beams 1 1 1 located along two or more scan lines 122 are simultaneously in focus on the wafer after being focused by an objective lens 1 10.
• the one or more optical elements 109 rotate the focal plane 306 of the two or more offset beams 109 to match the sample orientation.
• a spot scanning wafer inspection system is generally described in U.S. Patent No. 6,755,051 B2 filed on May 3, 2002; and U.S. Patent No. 8,995,746 B2 filed on May 21 , 2013; which are incorporated herein by reference in their entirety.
• Multi-spot scanning wafer inspections are generally described in U.S. Patent No. 6,236,454 B1 filed on December 15, 1997; and U.S. Patent No. 8, 194,301 B2 filed on March 4, 2008; which are incorporated herein by reference in their entirety.
• a given wafer inspection system may detect defects on a wafer through the acquisition of an image of the wafer and the comparison of this image to a reference image.
• a spot scanning imaging system generates an image of a wafer pixel- by-pixel by scanning illumination from an illumination source (e.g. a laser) across the wafer and collecting illumination from the wafer from discrete locations on the wafer. It is noted herein that illumination may be collected from the wafer using one or more detectors. It is further noted that the physical location of the sampled points defines a grid of sampled points (i.e. a sampling grid) and further defines the pixels of the image. The combination of point-by-point detection and the use of one or more detectors to gather information from each sampled point enables the generation of highly resolved and highly sensitive images.
• FIGS. 1 -3 illustrate a wafer inspection system 100 in which two or more offset beams 1 1 1 are scanned along two or more scan lines 122 on a wafer 1 12 oriented at an oblique angle relative to an objective lens 1 10, in accordance with one or more embodiments of the present disclosure. It is noted that the speed or throughput of an oblique angle scanning inspection system with multiple parallel scan lines 122 is increased relative to a system in which ail beams lie on a single scan line.
• an illumination source 101 generates a beam of illumination 102.
• a beam scanner 108 transforms the beam 102 into a scanning beam 108.
• an objective lens 1 10 collects the scanning beam 108.
• one or more optical elements 109 are positioned prior to the objective lens 1 10.
• the one or more optical elements 109 split the scanned beam 108 into two or more offset beams 1 1 1 separated in at least the x-direction.
• the one or more optical elements 109 may rotate the focal plane 306 of the two or more offset beams 1 1 1 focused by the objective lens 1 10 to match the surface of the wafer 1 12. It is noted herein that the rotation of the focal plane 306 of the two or more offset beams 1 1 1 focused by the objective lens 1 10 enables the two or more offset beams 1 1 1 located on two or more scan lines 122 to be in focus at all points during a scan.
• one or more beam conditioning elements 104 are positioned prior to the beam deflector 106,
• the one or more beam conditioning elements 104 may include any optical element known in the art suitable for conditioning the beam 102.
• the one or more beam conditioning elements 104 may include, but are not limited to, one or more lenses, one or more polarizers, one or more filters, one or more wavepiates, or one or more beam shapers.
• the one or more beam conditioning elements 104 expand the beam 102 to fill an input aperture of a beam scanner 106. In another embodiment, the one or more beam conditioning elements 104 adjust the polarization of the beam 102. In another embodiment, the one or more beam conditioning elements 104 modify the spatial profile of the beam 102. For example, the one or more beam conditioning elements 104 may be configured such that the spot size of each of the two or more offset beams 1 1 1 is constant and independent of the location on the wafer 1 12.
• the system 100 includes a relay lens 107 positioned after the beam deflector 106 to collect the beam 108.
• a relay lens 107 may coilimate a focused scanning beam 108 directed from a beam scanner 106 and direct the collimated scanning beam 108 to the one or more optical elements 109.
• one or more beam conditioning elements 105 are positioned prior to the objective lens 1 10.
• the one or more beam conditioning elements 105 may include any optical element known in the art suitable for conditioning the beam 108.
• the one or more beam conditioning elements 105 may include, but are not limited to, one or more lenses, one or more magnification controllers, one or more polarizers, one or more filters, one or more wavepiates, or one or more beam shapers.
• the one or more beam conditioning elements 105 includes a magnification controller suitable for adjusting the focused size of the two or more offset beams 1 1 1 on the wafer 1 12. It is noted herein that the one or more beam conditioning elements 105 may be positioned either prior to or subsequent to the one or more optical elements 109. It is further noted that the one or more optical elements 109 may be positioned between two beam conditioning elements 105.
• the system 100 includes a stage assembly 120 suitable for securing and positioning a wafer 1 12.
• the stage assembly 120 may include any sample stage architecture known in the art.
• the stage assembly 120 may include a linear stage.
• the stage assembly 120 may include a rotational stage.
• the wafer 1 12 may include a wafer, such as, but not limited to, an unpatterned semiconductor wafer, !t is noted herein that a two- dimensional image of a wafer 1 12 may be generated by translating the wafer 1 12 between successive scans along the two or more scan lines 122.
• the one or more beam deflectors 106 can include any type of beam deflectors known in the art including, but not limited to, acousto-optic beam deflectors, electro-optic beam deflectors, a polygonal scanner, a resonant scanner, or a galvanometer scanner.
• the illumination source 101 may include any illumination source known in the art.
• the illumination source 101 may include, but is not limited to, any laser system, including one or more laser sources, configured to generate a set of wavelengths or a wavelength range.
• the laser system may be configured to produce any type of laser radiation such as, but not limited to infrared radiation, visible radiation and/or ultraviolet (UV) radiation.
• the illumination source 101 is a laser system configured to emit continuous wave (CW) laser radiation.
• the illumination source 101 is a pulsed laser source.
• the illumination source 101 is configured to produce a modulated output.
• the illumination source 101 may be modulated with an acousto-optic or an electro-optic modulator to produce temporally shaped illumination,
• the illumination source 101 includes one or more excimer laser systems.
• the illumination source may include, but is not limited to, an excimer laser with molecular fluorine as an active gas, which provides emission of 157 nm laser light.
• the illumination source 101 includes one or more diode laser systems (e.g., one or more diodes for emitting light at 445 nm).
• the illumination source includes one or more diode lasers.
• the illumination source includes one or more diode-pumped solid state lasers.
• the illumination source may include a diode-pumped solid state laser with a wavelength including, but not limited to 266 nm.
• the illumination source 101 includes one or more frequency converted laser systems.
• the illumination source 101 may include, but is not limited to, a frequency converted laser suitable for emitting light having a nominal central illumination wavelength of 532 nm coupled with a frequency-doubling system that produces illumination with a 266 nm central wavelength.
• one or more multi-channel detectors are positioned to simultaneously collect reflected and/or scattered light from two or more scan lines 122 on the wafer 1 12.
• a detector 1 18 is positioned to receive laser light reflected from the wafer.
• the detector 1 18 may operate as a "reflectivity sensor” or a "brightfield sensor".
• the detector 1 18 may be used to generate a reflectivity map of the sample.
• the detector 1 18 may be used to monitor wafer characteristics including, but not limited to, structure height, film thickness, or dielectric constant.
• a detector 1 16 is positioned normal to the surface of the wafer to detect light scattered in a direction normal to the wafer surface.
• a detector 1 16 may detect light directly reflected from structures on the wafer surface.
• detectors 1 14a and 1 14b detect light scattered from two or more scan lines 122.
• one or more detectors 1 14 may collect forward scattered light, laterally scattered light, or backward scattered light according the detector position relative to the sampled point.
• the one or more detectors 1 14a, 1 14b, 1 16 or 1 18 may include any detector known in the art.
• detectors 1 14a, 1 14b, 1 16 or 1 18 may include, but are not limited to, a CCD detectors, photodiodes, avalanche photodiodes (APDs) and/or or photomultiplier tubes (PMTs).
• the one or more detectors 1 14a, 1 14b, 1 16 or 1 18 may be multi-channel detectors configured to simultaneously detect signals from multiple detection regions on the wafer 1 12 (e.g. one or more regions of one or more scan lines 122). It is contemplated herein that cross-talk between channels of a detector (e.g. 1 14a, 1 14b, 1 16 or 1 18) may be minimized by separating the detection regions on a wafer 1 12 such that illumination (e.g.
• the system 100 includes a controller 130 configured to transmit driving signals to the stage assembly 120, the one or more beam deflectors 108, and defectors 1 14a, 1 14b, 1 16, and 1 18 in order to initiate the linear sweep of the beam 108 across the wafer 1 12, the sampling of illumination scattered and/or reflected from the wafer 1 12, and the movement of the wafer 1 12 by the stage assembly 120.
• An image of a linear region of the wafer 1 12 is generated by triggering the one or more detectors 1 14a, 1 14b, 1 18, and/or 1 18 at one or more locations on the sample as the two or more offset beams 1 1 1 are swept across the wafer 1 12.
• a two-dimensional image of the wafer 1 12 may be generated by translating by the stage assembly 120 in a direction orthogonal to the beam scan direction such that each linear scan may be performed on a new location of the wafer 1 12.
• the sampling grid of the wafer may be defined by both the sampling rate of the detectors as well as the translation of the stage assembly 120.
• one or more linear scans may be performed on a single location of the wafer 1 12 before translation to a new location. Multiple beam scans may be desirable, for example, to reduce system noise.
• the accuracy of a spot scanning wafer inspection system may be further improved by run-time alignment of the sample grid of a wafer 1 12 to the sample grid of a reference image or with respect to previous scan data.
• run-time alignment of the sample grid of a wafer 1 12 based on data associated with the previous scans may improve scan accuracy.
• the sample grid of the wafer 1 12 may become misaligned relative to the sample grid of a reference image as a result of multiple factors, including, but not limited to, original alignment errors when positioning a wafer 1 12 with a stage assembly 120, mechanical vibrations, air wiggle, air currents, and/or drift of the two or more offset beams 1 1 1 .
• a beam scanner 108 includes a beam deflector 202 and an accousto-optic deflector 210, in accordance with one or more embodiments of the present disclosure. It is noted herein that for the purposes of the present disclosure, the terms “beam scanner” and “beam deflector” are used interchangeably.
• a beam 102 is generated by the illumination source 101 and is incident on a beam deflector 202 communicatively coupled to the controller 130.
• the beam deflector 202 sweeps the beam 204 directed from the beam deflector 202 across a range of angles that define an angular spread.
• the beam deflector 202 deflects a beam in a first position 204a to a second position 204b.
• the beam deflector 202 may include any beam deflector known in the art.
• the beam deflector 202 may be formed from, but is not limited to, an acousto-optic deflector, an electro- optic deflector, a polygonal deflector, a resonant deflector, or a galvanometer deflector.
• the beam deflector 202 is an acousto-optic deflector consisting of a solid medium 202b coupled with a transducer 202a configured to generate ultrasonic waves that propagate through the solid medium 202b.
• Properties of the solid medium 202b such as, but not limited to, the refractive index are modified by the propagating ultrasonic waves such that the beam 102 is deflected upon interaction with the solid medium 202b according to the wavelength of the ultrasonic waves. Furthermore, the ultrasonic waves propagate through the solid medium 202b at the velocity of sound in the medium and have a wavelength related to the frequency of the drive signal as well as the velocity of sound in the solid medium 202b. In one embodiment, the transducer 202a generates ultrasonic waves in response to a drive signal generated by a controller 130.
• a lens assembly 206 translates the angular sweep of the beam 204 to a linear sweep of the beam 208 directed from the lens assembly 206.
• a lens 206 collimates the beam.
• the one or more lenses 206 modify the spatial profile of the beam 204,
• the lens assembly 206 expands the diameter of the beam 204.
• the beam 204 is directed to an acousto-optic deflector 210 configured as a traveling lens.
• a transducer 210a communicatively coupled to the controller 130 generates a chirp packet 212 of ultrasonic waves with linearly varying frequency that propagates through a solid medium 210b along a linear path 214.
• the chirp packet 212 operates as a traveling cylindrical lens such that a beam 208 incident on the chirp packet 212 is focused to a position on a line 216; portions of a light beam 208 incident on relatively low frequency portions of the chirp packet 212 are deflected less than portions of a light beam 208 incident on relatively high frequency portions of the chirp packet 212.
• a cylindrical lens 209 focuses the scanning beam 108 in a plane orthogonal to the direction of focus induced by the chirp packet 212.
• the axis of the cylindrical lens 209 is oriented parallel to the scan direction 214).
• a cylindrical lens 209 may be placed either before the acousto-optic deflector 210 (e.g. as shown in FIG. 2) or directly after the acousto-optic deflector 210.
• the position and rate of the linear sweep of beam 208 are synchronized with the propagation of a chirp packet 212.
• a beam 208a may be incident on a travelling chirp packet 212a; as the chirp packet 212 propagates from position 212a to 212b, the beam 208a correspondingly propagates from position 208a to position 208b.
• a scanning beam 108 directed from a chirp packed 212 is focused on and linearly scanned along a line 218. It is noted herein that the width of a chirp packet 212 may be less than the length of the solid medium 210b. It is further noted that multiple chirp packets 212 may propagate through the solid medium 210b at the same time in sequence.
• the beam scanner 106 is formed from a lens and a single accousto-optical deflector 210 operating in "flood mode".
• the lens 208 expands the beam 102 and illuminates the full length of the accousto-optical deflector 1 10 with a stationary beam 208.
• One or more propagating chirp packets 212 may then be continually illuminated by a portion of the stationary beam 208; portions of the beam 208 not incident on the one or more propagating chirp packets 212 remain unfocused by the accousto-optical deflector 210.
• a lens 107 coliimafes the scanning beam 108 and an objective lens 1 10 focuses the scanning beam 108 onto the wafer 1 12.
• the relay lens 107 and the objective lens 1 10 are positioned in a telecentric configuration.
• the relay lens 107 and the objective lens 1 10 share a common optical axis.
• the optical axis 222 of the objective lens 1 10 is shifted from, but parallel to, the optical axis 220 of the relay lens 107. In this way, the optical axis 222 of the objective lens 210 may be centered on the scan line 122 of the focused scanning beam 108 on the wafer 1 12. It is noted that all optical rays in FIG.
• one or more optical elements 109 positioned prior to the objective lens 1 10 may split the scanning beam 108 into two or more offset beams 1 1 1 separated along the x-direction in order to generate additional scan lines 122 not on the y-z plane.
• the one or more optical elements 109 may be formed from any type in the art suitable for splitting the beam 108 and rotating the focal plane 306.
• the one or more optical elements 109 may include, but are not limited to, one or more diffractive optical elements, one or more refractive optical elements, or one or more beam splitters.
• the one or more optical elements 109 may operate in either transmission or reflection mode.
• the one or more optical elements 109 include one or more holographic DOEs.
• the one or more optical elements 109 include one or more micro-lens assemblies.
• an optical element 109 is formed from a DOE configured as a diffraction grating with focus correction (e.g. defocus) such that one or more diffracted orders are generated along the x direction and the focal plane 306 of the diffracted orders are simultaneously in focus on the wafer 1 12.
• focus correction e.g. defocus
• an optical element 109 consisting of a diffraction grating without focus correction 302 will generate three offset beams 1 1 1 a, 1 1 1 1 b, and 1 1 1 c (i.e. diffracted orders) separated in the x-direction that are focused through the objective lens 1 10 to a focal plane 306 oriented perpendicular to an optical axis 222 rather than the plane of the wafer 1 12.
• an optical element 109 consisting of a diffraction grating with focus correction 304 will effectively tilt the focal plane 306 of the three offset beams 1 1 1 a, 1 1 1 b, and 1 1 1 c through the objective lens 1 10 such that the focal plane 306 overlaps the surface plane of the wafer 1 12.
• each of the three offset beams 1 1 1 a, 1 1 1 b, and 1 1 1 c may be scanned along separate scan lines 122 in the y-direction and remain in focus during the scan.
• defocus is a second order aberration and is described by a wavefront aberration function of Woaor 2 , or alternatively W 0 2o(x 2 + y 2 )-
• an optical element 109 is configured as a diffraction grating with defocus such that the optical phase delay of an incident beam 108 is modified according to the equation:
• the DOE operates as a phase mask to simultaneously split the scanning beam 108 into two or more offset beams 1 1 1 and modify the phase characteristics of the two or more offset beams 1 1 1 such that all offset beams 1 1 1 are simultaneously in focus on the wafer 1 12 through the objective lens 1 10. Further, the value of A may be chosen to adjust the rotation of the focal plane 306 to overlap the surface plane of the wafer 1 12.
• the two or more offset beams 1 1 1 may include any number of beams. It is further noted that offset beams 1 1 1 may be generated from any combination of diffracted orders from an optical element 109.
• FIG. 3C illustrates the formation of a first offset beam 1 1 1 b formed from the 0 (undiffracted) order of an optical element 109 and a second offset beam 1 1 1 c formed from the +1 diffraction order of an optical element 109, in accordance with one or more embodiments of the present disclosure.
• FIG. 3C illustrates the formation of a first offset beam 1 1 1 b formed from the 0 (undiffracted) order of an optical element 109 and a second offset beam 1 1 1 c formed from the +1 diffraction order of an optical element 109, in accordance with one or more embodiments of the present disclosure.
• 3D illustrates the formation of a first offset beam 1 1 1 b formed from the -1 order of an optical element 109 and a second offset beam 1 1 1 c formed from the +1 diffraction order of an optical element 109, in accordance with one or more embodiments of the present disclosure. It is further noted that increased separation between scan lines may reduce cross-talk between adjacent channels in a multichannel detector (e.g. 1 14a, 1 14b, 1 18, or 1 18). !n another embodiment, the two or more offset beams 1 1 1 associated with diffracted orders generated by an optical element 109 are selected with one or more irises in the system 100.
• the one or more optical elements 109 may further split the beam 108 into multiple offset beams separated along the y-direction. In this way, a two- dimensional array of offset beams 1 1 1 may be in focus on the wafer 1 12 during a scan.
• one or more optical elements 109 split the beam 108 into a two- dimensional array of offset beams 1 1 1 with two or more staggered rows, wherein the rows are oriented along the y-direction (e.g. the scan direction). It is noted herein that a staggered row configuration enables increased separation between beams in adjacent rows in order to reduce cross-talk between adjacent channels in a multi-channel detector (e.g. 1 14a, 1 14b, 1 16, or 1 18).
• FIGS. 4A and 4B illustrate two non-limiting examples of scan patterns on the surface of a wafer 1 12, in accordance with two or more embodiments of the present disclosure.
• FIG. 4A illustrates a scan pattern on a wafer 1 12 in which offset beams 1 1 1 are arranged in a 2x4 array with staggered rows, in accordance with one or more embodiments of the present disclosure.
• a first row of offset beams 1 1 1 d includes a set of four beams 1 1 1 d ⁇ 1 , 1 1 1 d ⁇ 2, 1 1 1 d-3, and 1 1 1 d ⁇ 4; and a second row of offset beams 1 1 1 e includes a set of four beams 1 1 1 e-1 , 1 1 1 e-2, 1 1 1 e-3, and 1 1 1 e-4.
• the arrows represent the scan lines 122 (e.g. 122d and 122e) of the offset beams 1 1 1 .
• each of the offset beams 1 1 1 are separated in the y-direction as well as the direction perpendicular to the y-direction on the sample in order to minimize cross-talk. It is further noted that ail offset beams 1 1 1 are simultaneously in focus on the surface of the wafer 1 12 during the length of each scan path.
• the offset beams 1 1 d located on scan line 122d are formed from a 0 (undiffracted) order of an optical element 109
• the offset beams 1 1 1 e located on scan line 122e are formed from a +1 diffraction order of an optical element 109.
• the offset beams 1 1 1 1 d located on scan line 122d are formed from a -1 diffraction order of an optical element 109
• the offset beams 1 1 1 e located on scan line 122e are formed from a +1 diffraction order of an optical element 109.
• FIG. 4B illustrates a scan pattern on a wafer 1 12 in which offset beams 1 1 1 are arranged in a 3x3 array with staggered rows, in accordance with one or more embodiments of the present disclosure.
• a first row of offset beams 1 1 1f includes a set of three beams 1 1 1 f-1 , 1 1 1f-2, and 1 1 1 d-3;
• a second row of offset beams 1 1 1 1 g includes a set of three beams 1 1 1 1 g-1 , 1 1 1 g-2, and 1 1 1 g-3;
• a third row of offset beams 1 1 1 h includes a set of three beams 1 1 1 h ⁇ 1 , 1 1 1 h-2, and 1 1 1 h-3.
• the arrows represent the scan lines 122 (e.g. 122f, 122g, and 122h) of the offset beams
• each of the offset beams 1 1 1 are separated in the y ⁇ direction as well as the direction perpendicular to the y-direction on the sample in order to minimize cross-talk. It is further noted that all offset beams 1 1 1 are simultaneously in focus on the surface of the wafer 1 12 during the length of each scan path.
• the offset beams 1 1 1 1 f located on scan line 122f are formed from a -1 diffraction order of an optical element 109
• the offset beams 1 1 g located on scan line 122g are formed from a 0 (undiffracted) order of an optical element 109
• the offset beams 1 1 1 h located on scan line 122h are formed from a +1 diffraction order of an optical element 109.
• scan patterns may include any number of beams arranged in any orientation such that the scan beams are simultaneously in focus on the sample.
• offset beams may be generated by any method known in the art such as, but not limited to, any diffraction order of an optical element.
• the one or more optical elements 109 may be placed in any number of suitable arrangements to simultaneously split the beam 108 into two or more offset beams 1 1 1 and rotate the focal plane 306 to overlap the plane of the wafer
• the one or more optical elements 109 include a single DOE to split the beam 108 into two or more offset beams 1 1 1 , rotate the focal plane 306 to overlap the plane of the wafer 1 12, and further split each of the two or more offset beams into a set of two or more beams.
• the one or more optical elements 109 include a first DOE to split the beam 108 into two or more offset beams 1 1 1 and rotate the focal plane 306 to overlap the plane of the wafer 1 12; and a second DOE to further split each of the two or more offset beams into a set of two or more beams.
• the one or more optical elements 109 includes a micro-lens assembly to split the beam 108 into two or more offset beams 1 1 1 and a DOE to rotate the focal plane 306 to overlap the plane of the wafer 1 12 and further split each of the two or more offset beams into a set of two or more beams. It is noted herein that the one or more optical elements 109 may be arranged in any order. For example, the one or more optical elements 109 may include a first DOE to rotate the focal plane 306 to overlap the plane of the wafer 1 12 and a second DOE to split the beam 108 into two or more offset beams 1 1 1 . It is further noted that the above descriptions of the one or more optical elements 109 are provided merely for illustration and should not be interpreted as limiting.
• the one or more optical elements 109 are configurable such that a tradeoff between the number of offset beams 1 1 1 and the power in each of the offset beams 1 1 1 may be adjusted. In this way, a tradeoff between the sensitivity and the throughput of the system 100 may be adjusted.
• a system 100 may include two configurable optical elements 109 including a first 1x2 DOE to split the beam 108 into two offset beams 1 1 1 separated in at least the x-direction and rotate the focal plane 306, and a second 7x1 DOE to split each of the two offset beams 1 1 1 into seven offset beams 1 1 1 separated along the y-direction.
• the power in each offset beam may be doubled by removing the first DOE such that a 7x1 array of offset beams 1 1 1 is simultaneously in focus on the sample 1 12,
• the power of each beam may be increased by a ratio of 7/3 by replacing the second 7x1 DOE with a 3x1 DOE such that a 3x2 array of offset beams 1 1 1 is simultaneously in focus on the sample.
• the number of offset beams 1 1 1 may be increased.
• the set of optics of system 100 as described above and illustrated in FIGS. 1 through 3 are provided merely for illustration and should not be interpreted as limiting. It is anticipated that a number of equivalent or additional optical configurations may be utilized within the scope of the present disclosure. It is anticipated that one or more optical elements including, but not limited to circularly symmetric lenses, cylindrical lenses, beam shapers, mirrors, waveplates, polarizers or filters may be placed in the system 100. For example, a cylindrical lens may be placed prior to the beam deflector 108, or alternatively, after the beam deflector in order to modify the spatial profile of the beam 108 on the wafer 1 12,
• any of the elements in the system 100 may be configured to include one or more coatings, including, but not limited to, anti-reflective coatings or spectrally selective coatings.
• a spectrally selective coating may be placed on the faces of acousto-optic deflectors 202 and/or 210, one or more lenses included in the lens assembly 206, and/or one or more lenses throughout the system 100 in order to further the spectral content of the beam 102 and/or 108.
• anti-reflective coatings may be placed on non-optical elements of the system 100 including an enclosing chamber for the purposes of reducing stray light throughout the system 100.
• FIG. 5 describes a flow diagram illustrating a method 500 for generating multiple beams in an oblique multi-beam spot scanning wafer inspection system in accordance with one or more embodiments of the present disclosure.
• a beam of illumination is generated.
• the beam is directed to a surface at an oblique angle, wherein the beam is substantially perpendicular to a first direction on a plane defined by the surface.
• step 506 prior to directing the beam, the beam is split into two or more offset beams separated in at least a second direction, wherein the second direction is perpendicular to the first direction, !n step 508, prior to directing the beam, the phase characteristics of the two or more offset beams are modified such that the two or more offset beams are simultaneously in focus on the surface.
• any two components so associated can also be viewed as being “connected”, or “coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “coupiable”, to each other to achieve the desired functionality.
• Specific examples of coupiable include but are not limited to physically interactable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interactable and/or logically interacting components.

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