WO2010006197A1 - Système d'inspection d'échantillon à bas coût, sensible à une détection de petits défauts - Google Patents

Système d'inspection d'échantillon à bas coût, sensible à une détection de petits défauts Download PDF

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Publication number
WO2010006197A1
WO2010006197A1 PCT/US2009/050151 US2009050151W WO2010006197A1 WO 2010006197 A1 WO2010006197 A1 WO 2010006197A1 US 2009050151 W US2009050151 W US 2009050151W WO 2010006197 A1 WO2010006197 A1 WO 2010006197A1
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WO
WIPO (PCT)
Prior art keywords
light
unpatterned surface
illuminating
defects
unpatterned
Prior art date
Application number
PCT/US2009/050151
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English (en)
Inventor
Michael E. Fossey
Original Assignee
Motion Optics Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motion Optics Corporation filed Critical Motion Optics Corporation
Publication of WO2010006197A1 publication Critical patent/WO2010006197A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
    • 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
    • G01N21/8806—Specially adapted optical and illumination features
    • G01N2021/8822—Dark field detection

Definitions

  • This disclosure relates to inspection of unpattemed specimen surfaces and, in particular, to a low cost specimen inspection system that is implemented with spatially selective imaging optics to reduce the effect of background light on detection of small defects.
  • Unpattemed silicon wafers both with and without deposited metal or dielectric films, have historically been inspected by systems that are constructed with a laser for illumination; optics to focus the laser to a relatively small spot (about 50 ⁇ m diameter) on the wafer surface; some combination of mechanical, electo-mechanical, or electo- optic devices to scan the laser spot across the wafer; wide angle light collection optics (or multiple light collection optics); and a photomultiplier tube or tubes to detect light scattered from particles or other defects on the surface.
  • the model numbers of inspection systems produced by Tencor and KLA- Tencor include the 6200, SP1 , SP1-TBI, and SP2.
  • Inspection systems produced by Aeronca, Estek, and ADE Optical Systems include the WIS-100, WIS600, WIS-800, WIS-900, WIS-CR80, WIS-CR81 , and AWIS.
  • Different laser wavelengths, incident angles, and collection geometries were all incorporated at various times in an effort to reduce the amount of detected light that was scattered by the surface and thereby increase the amount of detected light that was scattered by particles or other defects. Defect detection sensitivity limits characteristic of the early systems were on the order of one micron.
  • a highly sensitive defect detecting, low cost wafer inspection system achieves, with use of relatively modest power density in the illumination beam, sufficiently small defect detection sensitivity to comply with the roadmap for semiconductors.
  • a high intensity light emitting diode (LED) or a laser source illuminates a larger area of an unpatterned wafer specimen than the relatively small area illuminated in the systems described above.
  • An advantageous consequence of the larger illuminated area is that the preferred wafer inspection system disclosed is not bound by a fundamental limitation of power in the illumination beam.
  • a method of detecting defects in or on an unpatterned surface of a specimen is practiced with use of a specimen inspection system that scans a light beam across the unpatterned surface and collects with a light sensor light scattered by defects in or on the unpatterned surface.
  • defects include particles, pits, scratches, surface contamination, or surface imperfections.
  • the method entails directing the light beam to illuminate the unpatterned surface of the specimen. Defects in or on the unpatterned surface produce scattered light propagating from the unpatterned surface in response to the illuminating light beam.
  • a camera functioning as the light sensor cooperates with imaging optics and includes an array of light sensitive sensor elements, each of which has a sensor element area. The imaging optics define imaged sensor element areas on the unpatterned surface.
  • the array of light sensitive sensor elements is a component of an electron multiplying charge-coupled device (EMCCD).
  • ECCD electron multiplying charge-coupled device
  • the light beam illuminating the unpatterned surface has a beam spot area that is substantially larger than any one of the imaged sensor element areas but is substantially smaller than the unpatterned surface area.
  • the beam spot area is established by a 2 mm - 20 mm diameter beam
  • the imaged sensor element area is established by a 3 ⁇ m - 30 ⁇ m square imaged sensor element of a 1.974 mm x 1.488 mm - 19.74 mm x 14.88 mm imaged sensor array
  • the unpattemed surface area is established by a 150 mm - 450 mm diameter wafer.
  • the method also entails scanning the illuminating light beam across the unpattemed surface and directing for incidence on the light sensitive sensor elements of the camera measurement light corresponding to the scattered light from the imaged sensor element areas. Portions of the measurement light propagating from the imaging optics and impinging on the light sensitive sensor elements correspond to the imaged sensor element areas of different light scattering regions of the unpattemed surface in or on which are present the defects producing the scattered light. The portions of measurement light are substantially free from contributions of background light scattered by the imaged sensor element areas of neighboring ones of the light scattering regions encompassed within the beam spot area at any instant as the light beam is scanned across the unpattemed surface.
  • the result is a higher degree of defect detection sensitivity than that achievable by a light sensor having a sensor area that is about the same as the beam spot area.
  • the method further entails correlating intensities of measurement light impinging on the light sensitive sensor elements to sizes of defects present in the corresponding different light scattering regions of the unpattemed surface.
  • An inspection system implemented with wide area illumination, spatially selective imaging optics, and an image array light sensor greatly reduces the effect of background light on detection of small defects in the practice of the disclosed method.
  • Conventional CCD light sensors exhibit noise properties that would dominate small particle signals.
  • FIGS. 1 and 2 are respective top plan and side elevation diagramatic views of a specimen inspection system for use in practicing the disclosed defect detection method.
  • FIGS. 3A and 3B show the amounts of background light detected from an illuminated surface of a specimen undergoing inspection by, respectively, a typical prior art specimen inspection system and the specimen inspection system of FIGS. 1 and 2.
  • FIGS. 1 and 2 A preferred highly sensitive defect detecting, low cost wafer inspection system 10 is illustrated in FIGS. 1 and 2.
  • a high power LED or laser diode light source 12 emits a light beam 14 that propagates through a beam-forming lens or lens assembly 18.
  • Lens assembly 18 collimates light beam 14 to form an incident beam 20 that illuminates a region of, and thereafter propagates as a reflected beam 24 from, an unpatterned major surface 26 of a semiconductor wafer specimen 28 under inspection.
  • Wafer 28 is secured to a rotary stage 34, which is mounted on a linear stage 36 that positions wafer 28 selectively to locations in an X-Y plane.
  • Imaging optics 40 preferably implemented as a video lens, and an electron- multiplying charge-coupled device (EMCCD) camera 42 are positioned over unpatterned surface 26 of wafer 28.
  • Video lens 40 images onto light sensitive sensor elements in camera 42 the illuminated region of unpatterned surface 26.
  • a beam trap 44 is positioned to prevent reflected beam 24 from scattering into camera 42.
  • Measurement light corresponding to scattered light from the imaged light sensor element areas of different light scattering regions of unpatterned surface 26 propagates from video lens 40 and carries to camera 42 information about sizes of defects in the illuminated regions.
  • a processor 50 correlates intensities of measurement light impinging on the light sensitive sensor elements of camera 42 to sizes of defects present in corresponding different light scattering illuminated regions of unpatterned surface 26.
  • Processor 50 includes stored information relating defect sizes to corresponding scattered light intensities.
  • Table 1 lists examples of basic EMCCD sensor devices at the integrated circuit level that are suitable for use in camera 42.
  • Table 2 lists examples of complete video cameras 42 that incorporate the sensor devices of the types listed in Table 1.
  • EMCCD electronic multi-dimensional digital camera
  • CCD charge-coupled device
  • These CCD elements operate at a higher voltage than that at which the usual CCD elements operate and through an electron multiplying effect that provides nearly noise-free gain.
  • the result is a video camera that can simultaneously detect light at nearly single photon levels and operate at full video frame rates on the order of 30 Hz.
  • a preferred embodiment of wafer inspection system 10 is implemented with the Andor luca DL-658M camera because of its low cost, high video frame rate, and relatively high light detection sensitivity in the 400 nm to 500 nm range.
  • Table 3 lists examples of candidate high intensity LED sources 12 of single LED and multiple LED array types, for use in wafer system 10.
  • a candidate laser diode system available from RgBLase LLC is the FB-445 series laser diode system, which exhibits an 800 mW output at 445 nm.
  • a preferred embodiment of wafer inspection system 10 is implemented with the OD-405-99-110 LED device. Since light scatters from small particles in proportion to the inverse fourth power of the wavelength, the shorter wavelength of 405 nm gives an overall advantage, even against the higher power of the OD-470-99-110 470 nm-LED device. For an ultimate low cost system, the LXL-LR5C LED device may be optimal.
  • a typical laser-based system may be constructed with a 2000 mW, 532 nm laser source or an 800 mW, 445 nm laser diode module. Light source 12 can be easily collimated using lens assembly 18 composed of standard off-the-shelf lenses to illuminate the imaging region of unpatterned surface 26 of wafer 28.
  • a tradeoff in the design of an inspection system of this type is between defect detection sensitivity and throughput. For highest defect detection sensitivity, a smaller illuminated region with corresponding small imaging area would be chosen. For highest throughput, a larger illuminated region and corresponding large imaging area would be chosen.
  • a reasonable tradeoff entails use of an illuminated imaging area of 4.4 mm x 3.3 mm. Since the luca DL-658M camera has an array size of 6.58 mm x 4.96 mm, the selected imaging area represents a video lens magnification of 1.5.
  • video lens 40 located approximately 40 mm from the imaging array of camera 42 and 26.67 mm from wafer surface 26, and then adjusting for focus.
  • the effective pixel size at wafer surface 26 is about 6.67 ⁇ m square.
  • imaging area dictates that 2160 images be captured to cover the entire surface of a 200 mm wafer. With the 37 frames per second capability of the luca DL-658M camera, throughput of 40 wafers per hour can be achieved with commercially available linear and rotary stages capable of conventional performance. [0024] To make the system more flexible, it may be advantageous to replace the beam-forming lens assembly 18 with a variable beam expander and implement imaging optics 40 as a zoom lens. With this combination, system 10 can then be adjusted for higher specimen throughput (larger imaged area) or better surface contamination or imperfection detection sensitivity (smaller imaged area and higher intensity illumination) to better suit the application.
  • Rotary stage 34 is the higher performance stage because it moves much more often than does linear stage 36, assuming wafer 28 is scanned in a sequence of circles, rotating wafer 28 one complete rotation before moving linear stage 36.
  • a preferred embodiment of wafer inspection system 10 is implemented with a Model No. RTH-6 rotary stage available from Intellidrives, Inc. This rotary stage is implemented with direct drive and integral air bearings, which provide for very rapid move and settle times when operated with a high performance servo controller.
  • the linear stage performance requirements are more modest and can be met using the ILS200CC linear stage available from Newport Corporation.
  • inspection system 10 Much of the semiconductor industry has adopted standard front opening universal pod (FOUP)-based wafer handling systems.
  • the described preferred embodiment of inspection system 10 is designed for initial implementation on an industry standard box opener/loader-to-tool standard interface (BOLTS) configuration platform, which allows easy integration with most present day wafer handling platforms.
  • BOLTS box opener/loader-to-tool standard interface
  • a more detailed analysis that takes into account the much narrower noise bandwidth and smaller amount of scattered light of inspection system 10 makes apparent its performance advantage. Since a system has no a priori knowledge of the actual location of a defect to be detected, the collection optics of video lens 40 collects light from the entire illuminated region of water surface 26.
  • FIGS. 3A and 3B show a comparative relationship between amounts of scattered background light propagating from illuminated surface 26 of wafer 28 and detected by, respectively, a typical prior art inspection system and inspection system 10.
  • a 50 ⁇ m diameter laser spot illuminates a region 58 of wafer surface 26 in which a particle 60 resides and produces a scattered light signal.
  • the scattered light detected includes the signal light scattered by particle 60 and background light scattered by the entire 50 ⁇ m diameter illuminated region 58 of wafer surface 26.
  • scattered light detection performed by inspection 10 as shown in FIG.
  • FIG. 3B a portion 62 of an illuminated imaging area of 4.4 mm x 3.3 mm on wafer surface 26 contains a particle 60 that produces a scattered light signal.
  • FIG. 3B shows fifteen of imaged array pixels or elements 64 neighboring the imaged array element 64 in which particle 60 resides. Because inspection system 10 images the illuminated region onto a detector array of camera 42, each imaged array element 64 of about 6.67 ⁇ m square detects light scattered by and received from only a small portion of wafer surface 26. Since the imaged pixel in inspection system 10 is only 6.67 ⁇ m square, the amount of surface scatter is 44 times smaller than that from a 50 ⁇ m diameter spot detected by prior art systems. This difference in detected scattered light is illustrated in FIGS. 3A and 3B. This advantage in surface scatter tips the balance well in favor of inspection system 10.
  • the detected current due to surface scatter is:
  • I n V(2e * I surf * B) .
  • a 2 represents a wavelength at which the power of scattered light, P surf (A 2 ), has been measured from a given sample surface
  • the power of scattered light expected when the same sample surface is illuminated by a wavelength X x can be calculated as follows:
  • P ps i (P,/A bea mr(1-cos 2 ( ⁇ )/2R 2 )*(2 ⁇ /2 ) 4 *((n 2 -1)/(n 2 +2)) * (d/2) 6 *( ⁇ D 2 /4).
  • One of the difficulties encountered with a system of this type is achieving the necessary dynamic range to size larger (> 125 nm) particles. This may be accomplished by capturing two frames at each location, one of the frames captured with either a very short integration time or low illumination power level for the purpose of sizing those particles that are saturated when captured under set up conditions for maximum sensitivity.
  • inspection system 10 does not rely on expensive high power lasers and complex high speed scanning systems, it can be produced for a fraction of the cost of present day laser- and photomultiplier-based systems.
  • Inspection system 10 is also scalable to much higher power levels (and better sensitivity) without danger of wafer damage. With higher power levels, the sensitivity can reach 22 nm defect size levels.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
  • Testing Or Measuring Of Semiconductors Or The Like (AREA)

Abstract

L'invention porte sur un procédé de détection de défauts (60) dans ou sur une surface sans motif (26) d'un échantillon (28), lequel procédé met en jeu le balayage d'un faisceau de lumière (20) sur la surface sans motif et la collecte avec une caméra (42) d'une lumière de mesure diffusée par des défauts dans ou sur la surface sans motif. La caméra coopère avec des éléments optiques d'imagerie (40) et comprend un réseau d'éléments détecteurs sensibles à la lumière. Des parties de la lumière de mesure se propageant à partir des éléments optiques d'imagerie et incidente sur les éléments détecteurs sensibles à la lumière correspondent à des zones d'éléments détecteurs imagés (64) de différentes régions de diffusion de lumière de la surface sans motif où des défauts sont présents. Les parties de la lumière de mesure sont sensiblement exemptes de contributions de lumière de fond diffusée par les zones d'éléments détecteurs imagés de régions voisines des régions de diffusion de lumière englobées à l'intérieur de la zone de spot de faisceau à tout instant où le faisceau de lumière est balayé. Le résultat est un degré supérieur de sensibilité de détection de défauts.
PCT/US2009/050151 2008-07-11 2009-07-09 Système d'inspection d'échantillon à bas coût, sensible à une détection de petits défauts WO2010006197A1 (fr)

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US13468208P 2008-07-11 2008-07-11
US61/134,682 2008-07-11

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9399562B2 (en) 2010-07-12 2016-07-26 Otis Elevator Company Elevator speed and position detection system using an optical sensor
US10060861B2 (en) 2017-01-10 2018-08-28 Sunspring America, Inc. Technologies for identifying defects

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020162979A1 (en) * 2001-05-02 2002-11-07 Lasertec Corporation Optically scanning apparatus and defect inspection system
US20030137318A1 (en) * 2002-01-23 2003-07-24 Marian Enachescu Methods and systems employing infrared thermography for defect detection and analysis
US6636302B2 (en) * 1994-12-08 2003-10-21 Kla-Tencor Corporation Scanning system for inspecting anamolies on surfaces
US20040207836A1 (en) * 2002-09-27 2004-10-21 Rajeshwar Chhibber High dynamic range optical inspection system and method
US6809809B2 (en) * 2000-11-15 2004-10-26 Real Time Metrology, Inc. Optical method and apparatus for inspecting large area planar objects
US20070081151A1 (en) * 2005-10-06 2007-04-12 David Shortt Methods and systems for inspection of a wafer
US20080144921A1 (en) * 2005-04-26 2008-06-19 Lizotte Todd E Inspection method and apparatus for partially drilled microvias

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6636302B2 (en) * 1994-12-08 2003-10-21 Kla-Tencor Corporation Scanning system for inspecting anamolies on surfaces
US6809809B2 (en) * 2000-11-15 2004-10-26 Real Time Metrology, Inc. Optical method and apparatus for inspecting large area planar objects
US20020162979A1 (en) * 2001-05-02 2002-11-07 Lasertec Corporation Optically scanning apparatus and defect inspection system
US20030137318A1 (en) * 2002-01-23 2003-07-24 Marian Enachescu Methods and systems employing infrared thermography for defect detection and analysis
US20040207836A1 (en) * 2002-09-27 2004-10-21 Rajeshwar Chhibber High dynamic range optical inspection system and method
US20080144921A1 (en) * 2005-04-26 2008-06-19 Lizotte Todd E Inspection method and apparatus for partially drilled microvias
US20070081151A1 (en) * 2005-10-06 2007-04-12 David Shortt Methods and systems for inspection of a wafer

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9399562B2 (en) 2010-07-12 2016-07-26 Otis Elevator Company Elevator speed and position detection system using an optical sensor
US10060861B2 (en) 2017-01-10 2018-08-28 Sunspring America, Inc. Technologies for identifying defects
US10768120B2 (en) 2017-01-10 2020-09-08 Sunspring America, Inc. Technologies for identifying defects

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