Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/7055—Exposure light control in all parts of the microlithographic apparatus, e.g. pulse length control or light interruption
  • G03F7/70575—Wavelength control, e.g. control of bandwidth, multiple wavelength, selection of wavelength or matching of optical components to wavelength
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
  • G03F1/68—Preparation processes not covered by groups G03F1/20 - G03F1/50
  • G03F1/82—Auxiliary processes, e.g. cleaning or inspecting
  • G03F1/84—Inspecting
  • G03F1/86—Inspecting by charged particle beam [CPB]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/33—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using ultraviolet 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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
  • G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
  • G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
  • G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
  • G01N23/2255—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident ion beams, e.g. proton beams
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
  • G03F1/22—Masks or mask blanks for imaging by radiation of 100nm or shorter wavelength, e.g. X-ray masks, extreme ultraviolet [EUV] masks; Preparation thereof
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
  • G03F1/68—Preparation processes not covered by groups G03F1/20 - G03F1/50
  • G03F1/72—Repair or correction of mask defects
  • G03F1/74—Repair or correction of mask defects by charged particle beam [CPB], e.g. focused ion beam
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/70605—Workpiece metrology
  • G03F7/70616—Monitoring the printed patterns
  • G03F7/7065—Defects, e.g. optical inspection of patterned layer for defects
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/70605—Workpiece metrology
  • G03F7/706835—Metrology information management or control
  • G03F7/706837—Data analysis, e.g. filtering, weighting, flyer removal, fingerprints or root cause analysis
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P72/00—Handling or holding of wafers, substrates or devices during manufacture or treatment thereof
  • H10P72/06—Apparatus for monitoring, sorting, marking, testing or measuring
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P74/00—Testing or measuring during manufacture or treatment of wafers, substrates or devices
  • H10P74/20—Testing or measuring during manufacture or treatment of wafers, substrates or devices characterised by the properties tested or measured, e.g. structural or electrical properties
  • H10P74/203—Structural properties, e.g. testing or measuring thicknesses, line widths, warpage, bond strengths or physical defects
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P74/00—Testing or measuring during manufacture or treatment of wafers, substrates or devices
  • H10P74/27—Structural arrangements therefor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/33—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using ultraviolet light
  • G01N2021/335—Vacuum UV
• • 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
  • G01N2021/95676—Masks, reticles, shadow masks

Definitions

• This invention generally relates to tire Field of photomask inspection and defect disposmouing, More particularly, tire present invention relates to methods n systems for inspectio an review of photomasks designed for use at extreme ultraviolet wavelength s).
• Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a large number of semiconductor fabrication processes to fern various features and multiple levels of the semi conductor devices.
• lithography is a semiconductor fabrication process that involves transferring a pattern frotn a photomask to a resist arranged on a 5 semiconductor wafer.
• semiconductor fabrication pr Des include, but are not limited to, ehentical-mechauicai polishing (CMP), etch, deposition, and ion implantation, Multiple senseondtietor devices may be fabricated i a arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
• CMP ehentical-mechauicai polishing
• etch etch
• deposition etch
• ion implantation ion implantation
• DUV inspection tool wit various illu inatiou: conditions : to maximize defect sensitivity and/or main pattern modulation are being explored for initial EUV defect detection. Due to the generally low signal-to-noise in DUV inspection imaging of EUY masks, these inspections often result in hundreds or thousands of defects getting detected. And if one oul like to extend the detection capability ev en further, then there may he hundreds of thousands of detections on eac BUY inspection. Eac one of these detections then needs to he accurately reviewed and disposUioued. Visually 5 reviewing! each defect is difficult due to poor DUV resolution and the risk of manual defect mise!asslficstlot goes up with defect counts.
• EUV photomask detect disposltioning: that do not have one or more of: the disadvantages described above.
• One embodiment relates to a photomask inspection system that includes an0 inspection subsystem configure for directing energy to a photomask and detecting energy from the photomask.
• the photomask is configured for use at one or more extreme ultraviolet (EUV) wavelengths of light.
• EUV extreme ultraviolet
• the system also e I «ties one or more computer subsystems configured for detecting defects on the photomask based on the detected energy in addition, the sy tem includes a charged particle beam subsystem configured5 for generating charged panicle beam images of the photomask at locations of the detected defects determined b the one or more computer subsystems.
• the one or more computer subsystems are configured for dispositio ng the detected detects based on the charged particle beam images generated for the detected defects.
• the photomask inspection: system may be further configured as described herein.
• Another embodiment relates to a method for inspecting a photomask.
• the method includes directing energy 10 a photomask ami detecting energy from the photomask. he photomask is configured for use at one or more EUV wavelengths of light.
• the method also includes detecting defects on the photomask based on the detected energy.
• the method includes generating charged panicle beam images of the photomask at locations of the detecte defects.
• The: method further inelades dispositioning: the detected defects based on the charged particle beam images generated tor the detected defects.
• the method described: above: may include any other step(s) of any Other taethod(s) described herein
• the method described above may fee performed by any of the systems described herein.
• Another embodiment relates to a non-transitory computer-readable medium storin program insU action executable on computer system for performing computer-implemented method for inspecting a photomask.
• the computer-implemented method includes the steps of the method described above.
• the computer-readable medium may be further configured as described herein.
• the steps of the computer- implemented method ma be performed as described further herein.
• the computer-implemented method for which the program instructions are executable may include any other step(s) of any other ethodf s) described herein.
• FIG. 1 is a schematic diagram illustrating a side view of one embodiment of a photo as mspeettou and defect ispositioning system
• FIG. 2 is a schematic diagram illustrating a side view of one embodiment of an 5 optical subsystem that ma fee included hi embodiments of a photomask inspection system;
• FIG. 3 is a schematic diagram illustrating a side vie w of atm example of a portion of an extreme ultraviolet (EUV) photomask;
• EUV extreme ultraviolet
• FIG. 4 is a sc e atic diagram illustrating a plan view of one example of a portion of anEITV photomask pattern without any defects;
• FIG. 5 is a schematic diagram illustrating a plan s tew of the portion of the EUV5 photomask pattern of Fig. 4 with various examples of defects that may be detecte therein;
• Fig 6 is a (low chan illustrating one embodiment of steps that may fee performed fey the embodiments described herein for dispositicmin defects detected on an BUVb photomask performed using a diarged panicle bea subsystem
• Fig. 7 is a schematic diagram illustrating a side view of one example of a portion of an EUV photomask with different examples of fuseded defects formed thereon; 5 [0022] Fig. 8 is a H w chart illustrating one embodiment of steps that n3 ⁇ 4y be performed fey the embodiments described herein for dispositioning defects detected on an EUV photomask er rmed using an atomic orce microscopy subsystem; an
• FIG. 9 is a block diagram illustrating one embodiment of a non-transitoryb computer-readable medium storing program instructions executable on a computer system for performing one: or more of the computer-implemented methods described herein,
• the terms‘"design” and‘design data” used herein refers to information and data 15 that is generated by semiconductor device designers in a design process and is therefore available for use in the embodiments described herein well in advance of printing of the design on an physical substrates: Therefore, the terms“design” and“design data” as vised herein generally refer to the physical design ⁇ layout) of an IC and data derived iron* the physical design through complex simulation or simple geometric and Boolean 0 operations.
• a ⁇ 30331 file is one of a class of files used for the representation of design layout data.
• Such files include Gl.,1 and OASIS files attd proprietary file formats such as RDF data, which is proprietary to KLA, 5 ilpitas, Calif
• the sign ay include any other design data or design data proxies described in commonly owne D S Patent Nos 7,570,796 issued on August 4, 2009 to Za&r et ah t ci 7.676.077 issue : on March 9, 2010 to Kulkarni ei ah, both of which are incorporated by reference as if fully set forth herein.
• the design data can be standard cell library data integrated layout data design data for one or more layers, 30 derivati ves of the design data, an full or partial ch ip design data.
• the ' ' design” or“ h sical design” may also be the design a ir would be ideally formed on the photomask.
• a design as described herein may include all of the features of the design that would be printe on the photomask including any optical 5 proximity correction (CPC) features, which are added to the design ro enhance printing of the features oft the wafer without actually being printed themselves.
• CPC optical 5 proximity correction
• EUV photomask defect inspection using a hot inspection (e g., a deep ultraviolet (DUVh e g., 193 nm optical inspection) followed by substantially fast defect disposition using secondary charged particle beam Images.
• EUV lithography is the leading technology for P next-generation lithography OIGL), whose viability relies on the availability of a properly functional EUV photomask inspection toe!, which can: capture ail of the erlt&ai yield-impacting defects.
• the use of existing photomask inspection tools can he extended to EUV photomask inspection by tunrtmg them "hof :> in order to achieve the required defect sensitivity, despite the Substantially high number of defects that will be detected in 5 the inspection, and then repositioning each detected defect (or at least a substantial portion of the detected: defects) using: charge particle beam imaging (such as scannin electron microscopy (SE ) ⁇ , and possibly atomic force microscopy (AFM), based classification and printabi!ity modeling.
• SE scannin electron microscopy
• AFM atomic force microscopy
• the embodiments may be configured to use charged particle beam i ages and optionally AFM images to 30 disposition the detected defects.
• some embodiments described herein are configured for automated algorithm and work flow of charged particle beam imaging/analysis and Optionally ATM analysis including defect isolation, etsssiffeafion, and printability analysis.
• One embodiment relates to a photomask inspection system.
• a systerri is shown in Fig 1
• the photomask inspection system includes an inspection subsystem configured lot directing energy to a photomask and detecting energy from the photomask.
• the energy directed to the photomask by the inspection subsystem includes one or more DUV wavelengths of light.
• the :H) photomask is configured for nse :at one or more FUV wavelengths of light
• the photomask is configured: to be «set!
• the actinic wavelength of the photomask i.e.. the wavelength of light that is used to transfer 15 a pattern from the photomask to a wafer thereby causing a photochemical reaction in one or more materials on the wafer, e.g.,.
• the energy directe to the photomask by the inspection : subsystem includes light having a wavelength of 193 urn.
• the energy directed to the photomask by the inspection subsystem includes light having one or more wavelengths: 1 ⁇ 2 a range from 1 3 nm to: 257 nm.
• the energy directed to the photomask by the inspection subsystem includes light having a 5 wavelength of 13 5 nm (or another EUV wavelength of light)
• the photomask inspection system includes inspectio subsystem 100.
• fee photomask inspection system is shown in Fig. 1 as including one inspection subsystem, it is to be understood that the photomask inspection 30 system may include only one inspection subsystem or more than one inspection subsystem such as hispeeti on subsystem 100 shown in Fig 1 and inspection subsystem 20Q shown in Fig, 2 and described further herein,
• inspection subsystem: 100 includes light source 102.
• Light source 102 ay Include an suitable light source known in the art such as a laser.
• Light source 10:2 is configured to direct light to beam splitter 104, which is configured to reflect the light from light source 102 to refractive optical element 106.
• Refractive optical element I ⁇ is configured to focus light from beam splitter 104 to photomask 108.
• Beam .splitter 104 may include any suitable beam splitter such as a 50/50 beam splitter, in Refractive optical element: 1 6 may include any suitable refractive optical element, and although retractive optical element 1 6 is shown in Fig 1 3 ⁇ 4$ a single refractive optical element, t may be replaced: with one or more refractive optical elements and/or one or more reflective optical elements.
• the illumination: channel may include any other suitable elements (not shown in Fig. 1) such as one or more polarizing components., diffractive optical elements (DOEs), and one or more filters such as spectral filters.
• DOEs diffractive optical elements
• filters such as spectral filters.
• the. light source beam splitter and refractive 0 optical element are configured such that the light is directed to the photomask at a normal or substantially normal angle of incidence.
• the inspection subsystem may be condgured to scan the light over the photomask in: any suitable manner.
• the refractive: optical element, beam splitter, and detector may form a detection channel of the inspection subsystem.
• The: defector may include any suitable imaging detector known in the art such as a charge couple device (CCD) or time- delayed integrator t'TDl)
• This detection channel may also include one or more additional 30 components (sot shewn in Fig 1 ) such as one nr more polarizing components, one or more spatial filters, one or more spectra filters, and the like.
• Detector 110 k configured to generate output that is responsive to the reflected light detected by the detector. Th output may include signals, signal data, images image data, and any other suitable output.
• the inspection subsystem may be configured to have there than one mod ⁇ in any suitable manner.
• the inspection subsystem can have more than one mode sequentiall (e.g.. b changing one or more parameters of an imaging lens of the inspection subsystem such as numeiicai aperture ( At between scans of a photomask ⁇ lb
• th inspection subsystem can scan the photomask with some modes sinmiianeousl and other modes sequentially.
• the photomask inspection system may be configured to control the optical mode(s) used for any scan of an photomask in any suitable manner.
• the photomas inspection syste a include a number of other components that are not shown in Fig. 1.
• the system ma ⁇ include a load module, an: alignmentmo ide, a handler sueh as a robotic transfer arm, and an ei romnental eoutoi module and may include any such components known in the art.
• the photomask inspection system also includes one or more computer subsystems configured lot detecting: defects on the photomask based on the defected energy.
• the computer srtbsystem(s) nmy be configured to detect the delects in one or more different ays.
• the computer subsystem(s) may be configured to compare the output generated by the detector of the inspection subsystem that is responsi e to the detected 5 energy (e.g , images, imag date, etc, ⁇ to corresponding design information for the photomask :(e,g. ; GDS or oilier design data that may be stored in a design database .
• defect detection is therefore commonly referred to as dierto-datafease t po inspection.
• Results of the comparison may be compare to one or more thresholds. Output that is above the threshoid(s) may be identified as corresponding to defects or 30 potential defects, and output that is not above the Häsho!d(s) may not be identified as corresponding to defects or potential defects.
• the outpu generated by the detector of the inspection subsystem that is responsive to the detected energy an that is generated at the same location in different dies on the photomask may be compared to each other by the computer subsystemfs).
• defect detection is therefore 5 commonly referred to as die-to-die type inspection Results of such comparisons may be used as described above to identify defects on the photomask.
• the computer subsystemfs) are configured for detecting the defects using a hot threshold
• the threshold! s) used in the above described it) defect detection may be“hot” threshold! s
• A“hot” threshold is generally defined as a threshold : that is at, within, or substantially near the noise floor of the output generate fey the inspection subsystem for the photomask, hr this maimer, the defect detection can he quite a bit more aggressive (hotter) than would normally be performed for a tuned inspection recipe, so that more events including defects and nuisance events, are detected 15 than desired in a tuned inspection. In this manner, such an inspection would not normally be useful for production monitoring due to the substantially high nuisance defect detection. Inspection performed with such a threshold is commonly referred to as a ' ‘hot” inspection and tie scanning of the photomask performed during such an inspection may be commonly referred to as a“hot " scan.
• the photomask inspection system includes computer subsystem 116 coupled to Inspection subsystem 100
• tie computer subsystem ay be coupled: to a detector, e.g , detector 1 It), of ibe inspection subsystem ⁇ e.g., by one or more transmission media shown by the dashed line in Fig. I , 5 which may include any suitable transmission media known in the art).
• the computer subsystem may be coupled to tie detector in any suitable manner such that output (e.g., images) and an other information for the photomask generated fey tie inspection subsystem can fee sent to the computer subsystem and, optionally, such that the computer subsystem can send instructions to the inspection subsystem to perform one or more0 steps.
• This computer subsystem (as well as other computer subsystems described herein) ma also be referred to herein as computer system! s).
• Each of the computer subsystem* s> or systetn ⁇ s described herein may take various forms, including a personal computer 5 system, imag computer, mainframe computer system, workstation, network appliance, internet appliance, or other device.
• the term '‘computer system” may be broadly defined to encompass any device having one or more processors, which executes instructions fro a memory medium.
• the computer suhsystem(s) or system(s) may also include any suitable processor known in the an such as a parallel processor.
• the computer sahsystemfs ⁇ or syste (s) may include a computer platform with high speed processing an : software, either as a standalone or a networked tool
• the different computer subsystems may be coupled to each other such that images, data, information, 15 instructions, etc can be sent between the computer subsystems as described further herein.
• computer subsystem 110 may be coupled to computet site-system il3 ⁇ 4 (as shown by the dashed line in Fig ! by any suitable transmission media, which may include any suitable w ired aud or wireless transmission media known in the art Two or more of such computer subsystems may also be effectively coupled by a shared 0 computer-readable storage medium ⁇ not shown).
• the photomask inspection system also includes a charged particle beam subsystem configured lor generating charged particle beam images of the photomask at locations of the detected defects determined by the one or more computer subsystems ft 5 one embodiment, the charged particle beam subsystem is configured as an electron beam subsystem.
• the electron beam subsystem ma include electron column 1:22, which is txmpled to computer subsystem 134,
• the electron column includes electron beam source 124 configured to generate 30 electrons that are focused to photomask 128 by one or more elements 126
• the electron beam source may include, lor example, a cathode source or emitter tip, and one or mere elements 126 ma include, for example. a gu lens, an ano e a beam limiting aperture, a gate waive, a beam current selection aperture, an objective lens, and a scanning subsystem, all of which may include any such satiable elements known in the art
• Electrons returned from fee photomask may be focused by one or more elements 130 to detector 132,.
• One or more elements: I30 ay include, tor example, a scanning subsystem,, which may he the same scanning subsystem included in dementis) 126
• the electron column may include any other suitable elements known in the art.
• the electron column may fee further configured as; described in U.$.
• the electron column is shown in Fig. 1 as feeing configured such that fee electrons are directed to fee photomask : t an oblique angle of incidence and am scattered from the photomask at another oblique angle, it is to be understood that the electron beam 0 may be directed to and scattere from fee photomask at any suitable angles.
• the electron beam subsystem may fee configured to use multiple modes to generate images of the photomask (e.g., wife different illumination angles, collection angles, etc. ⁇ . The multiple modes of the electron beam subsyste may be different in any image generation parameters) of the subsystem.
• the charged particle beam subsystem is configured as an ton beam subsystem.
• fee electron beam source may be replaced with another charged particle beam source such as an ion beam source, which may include any suitable ion beam source known in the art.
• the charged particle beam subsystem may have any other sui able ion beam tool configuration such as those included in commercially available focused ion beam (FIB) sptems, helium Ion microscopy (HI 1 to stems, and secondar ion mass spectroscopy (SIMS) systems.
• Computer subsystem: 134 may be coupled to detector 13:2 as described above.
• Tile detector may detect charged particles returned from tie surface of tie photomask thereby forming charged panicle beast [mages of the photomask.
• the charged particle bears images may Include any suitable charged particle beam images.
• Computer aiibsysf.em 134 may be confgured ro perform any of the functions described herein using the output of the detector and/or the charged particle beam images.
• Computer subsystem 134 may he configured to perform any additional siepts) described herein * Computer subsystem 134 may also be fruther configured as described herein.
• ffee charged particle beam subsystem may be referred to us a scanning electron microscope S EM) and the charged awakele beam images ma be referred to as“SEM images, none of the embodiments described herein are limited to a SEM or SEM images.
• the charged particle beam subsystem may base any suitable configuration for generating the charged particle beam images including SEMs and other types of electron beam tools, e.g , transmission electron microscopes (TEMs).
• the charged particle beam subsystem included in the system may include a commercially available electron bea tool such s the Mask DR-SEM E56O0 Series and Mash MYM-SEM R FJ60O Scries of tools that are commercially available: fro Adcantest America, hie., Sau Jose, Calif.
• the computer subsyste fsi included in the system may also include a computer subsystem such as computer subsystem US that is not coupled to the inspection or charged particle bea subsystem in this manner, one of the computer subsystems may be a stand alone type computer subsystem, which may be coupled to the other computer subsystems shown in Fig.
• a stand alone type computer subsystem may fee configured to acquire the images described herein and to perform other ⁇ steps described herein.
• computer subsystems 1 16 and 134 may be configured to store images receive from their respectivel coupled inspection an charged particle beam subsystems and to store the images in storage media 120, which may be further configured as described herein.
• the stand alone type computer subsystem ma then 5 acquire the images: from the storage media an perform one or more steps describe herein using some combination of the images.
• the photomask inspection system may include more than on inspection subsystem.
• the inspection subsystem shown in Fig. 2 may also be used in in combination with or: instead of the inspection subsyste shown in Fig 1 in the embodiments described herein.
• inspection subsystem 200 Includes an illumination subsystem and a collection subsystem as described m more detail herein.
• the illumination 15 subsystem includes light source 20:2.
• Light source 202 may be a coherent light source such as laser, The light source may be configured to emu. monochromatic light having a wavelength of 248 a3 ⁇ 4 193 nm, and/or another Dl.'V or EIJV wavelength described herein. Alternatively, the light source may be configured to emit light have a range of wavelengths an may be coupled to a spectral filter mot shown).
• An example of a 0 broadband light source includes, but is nor limited rt ⁇ a He ⁇ Xe arc lamp that generates light in the DUV wavelength regime.
• the light source and the filter ay emit monochroma tic light having a wavelength as described above.
• the light source rosy be configured to emit light continuously or at various time intervals m pulses.
• Thg illumination subsyste may als include a number of optical components coupled to the light source.
• light front light source 202 may first pass through homogenize! 204
• Ftcnnogenizer 204 may be configured to reduce speckle of the Sight from the light source.
• the illumination subsystem may also include aperture 20b Aperture 206 may have an adjustable NA.
• the aperture may be coupled to a 30 control mechanism that may be configured to mechanically alter the aperture depending upon a control signal received front a user or front program instructions received from a program recipe being run on the system " In this manner.. the light may have variou partial coherence factors, a.
• aperture 206 may be altered to adjust a pupil of condenser lens 20$.
• the pupil of the condenser lens controls the NA of the system, As the pupil of the condenser is reduced, coherence of the iltetninatiou increases thereby decreasing the value of e.
• the value of s may he expressed as the ratio of the NA of the condenser lens to the NA of the objects e lens.
• Exposure systems may have a ⁇ alue of a? in a range between about 0.3 to about 0 9. Therefore, aperture 206 may be altered such that the inspection subsystem has a value of s between about 0.3 and about 0.9.
• the value of s may be altered : de ending upon the features on the photomask. For example, a higher value fo c> may be used if the photomask includes lines and spaces than if the photomask includes contact holes.
• the control mechanism may also be configured to alter the aperture to provide annular or offeaxis illumination.
• the aperture may also be configure to provide other types of illumination such as quadrapole or dipolar illumination.
• the aperture may be further configured to alter a shape of the beam of light.
• the aperture may be a diffraction optical element or an apodizatiO» aperture,
• the illumination subsystem may also include a number of additional optical components ⁇ not shown).
• the illumination subsystem may also include a telescope configured to alter the beam diameter of the light.
• the illumination subsystem ax include one or more rela lenses, additional lenses such as a field lens, folding mirrors additional apertures, and beamsplitters.
• the illumination subsystem may also include condenser lens 208 Condenser lens
• Bea splitter 209 may include any suitable beam : splitter known in the art.
• the stage i configure to support t e photomask by contacting the photomask proximate outer lateral edg s of tie photomask.
• Stage 212 may be configure to move the photomask such that an alignment of the photomask may be altered and such that light may scan across the photomask.
• the illumination system may include a scanning element (not 5 shown) sue! as an aconsto-epiieal deflector or a mechanical scanning assembly such that the photomask may remain substantiall stationary while the Kgbt is scanned across the photomask.
• Stage 212 may also he configured to move the photomask through focus thereby altering a focus setting of the inspection subsystem.
• the Stage may also be coupled to an autofocusing device ( . not shown) that is configured to alter a position of the it) stage thereby altering a position of the photomask to maintain a focus setting of the inspection subsystem during a inspection
• a autofocusmg device ma be coupled to the objective lens to alter a position of the objective lens to maintain the focus setting during an inspection.
• the inspection subsystem may also include a number of optical components arranged to form a collection stfosystem.
• the collection subsystem includes objective lens 214. Light reflecte by the photomask is collected by objective lens 2 14.
• the collection subsystem also includes aperture 216 having an adjustable NA The NA of aperture 216 may also be selected such that light exiting the aperture has a selecte 0 magnification
• Aperture 216 is positioned between objective lens 214 and lens 218, which may be configured as a tube lens, Light horn lens 218 may be directed to beamsplitter 220. Beamsplitter 220 may be configured to direct the fight to three detectors 222, 224, and 226.
• the collection subsystem may also include a .number of additional optical component! (not shown) such as a magnification lens. The 5 magnification lens may be positioned between lens 218 and beamsplitter 220.
• the detectors may include lot example CCDs or IDs cameras.
• the detectors ma also have a one-dimensional or two-dimensional array of pixels.
• Each of the three defectors may have a different focus setting. In this manner, the three detectors may form images of the photomask at three different focus- settings substantially simultaneously. For example, one detector may be substantially in focus, and the Other two detectors may be out of focus in opposite directions with respect to the in-focus 5 condition in addition, the inspection subsystem ma include any number of such detectors depending on the mechanical or physical constraints of the inspection subsystem.
• a iu*r natively, rhe inspection subsystem may only include one detector configured0 to form an image of the photomask.
• the detector may have a focus setting approximately equal to a focus setting of an exposure system images of th photomask at different focus settmgs: may be forme by altering the focus setting of the detector alter each image is formed. Is such as embodiment, beamsplitter 220 would sot be necessary to split the light to multiple detectors.
• Computer subsystem 228 «lay fee couple to inspection subsystem 200.
• the computer subsystem may be coupled fo a detector, e g , detectors 222, 224, and 226, of the inspection subsystem fe.g., by one or more transmission media shown by the dashed lines in Fig. 2, which may include any suitable transmission media known in0 the art).
• the computer : subsyste ma be couple to the: detectors in an suitable: manner.
• the computer subsyste may he coupled to the inspection subsystem in any other suitable manner such that intagef s) an an other information for the photomask generated by the inspection subsystem can he sent to the computer subsystem and, optionally such that the computer subsystem Can send instructions to the inspection5 subsystem to perform one or more steps described herein,
• Figs. 1. anti 2: are provided: herein to generall illustrate s me configurations of inspection and charged particle beam subsystems that may be included in the embodiments described herein.
• the configurations of the inspection and0 charged particle beam subsystems described herein ma be altered to optimize the performance of the system as is normally performed when designing: a. commercial inspection system in addition the photomask; inspection systems: described here n may be implemented using existing inspection and charged particle beam subsystems (e.g.. by adding functionality described herein to an existing inspection and/or charged particle 5 beam inspection system) such as the photomask inspection tools that am commercially available from XA.
• the embodiments described herein may be provided as optional functionality of the system (e.g , addition to other functionality of the system).
• the photomask inspection systems described herein may be designed from scratch" to provide a completely new system.
• the inspection subsystem may be configured as an optical inspection subsystem that is configured to scan the photomask with tight having one or more wavelengths.
• the inspection subsystem can be a different type of inspection subsystem.
• the energy directed to th 15 photomask by the inspection subsystem includes electrons.
• the energy directed to the photomask by the inspection (subsystem Includes ions in suc embodiments, the inspection subsystem ma he configured in a similar manner as shown by electron column 122 in Fig, 1 (possibly with the electron source replaced by an ion beam source).
• the optical inspection subsystem shown in Fig 1 Stay he 6 replaced with an electron beam or ion beam inspection subsystem, and the system ma include two charged particle beam subsystems (one for inspection and the other for generating the charged particle beaut images for the detected delects).
• the wo charged particle beam -subsystems may be different in one or more 5 pa amete s such that one of the su syst ms is particularly suited bar inspection while the other is particularly suited for generating the charged particle beam images, Bor exam le, the two subsystems may be different in resolution capability (such that the subsystem used for inspection lias a Sower resolution capability than the one used for charged pat tide beam imaging).
• the system may include one 30 charged pat ude beam subsystem that is used for both inspection and charged particle beam imaging., and one or more parameters of the subsystem can be altered between inspection and imaging such that the subsystem can be used for both tasks.
• the charged panicle beam subsystem shown in Fig 1 may be configured to have a higher resolution if it is to be used for imaging rather than for inspection.
• the embodiments of the charged particle beam subsystem shown in Fig, 1 describe some general an various configurations fer charged particle beam subsystems : that can be tailored hi a number of manners that will be obvious to one skilled in the an to produce subsystems having different imaging capabilities that are more or less suitable for different applications.
• Electron beam inspection pf the photomask may also be performed as described in apabilit of Model EBEYE M for EUV Mask Production 5 b Mafca ei ah, November 8, 2012, SP1E Photomask Technolog 2012, Proceedings Volume SS22, 14 pages, which is incorporated: by reference as if felly set ferth herein.
• the embodiments describe herein may be further configured as described in this reference.
• typical EUV plioioip sk stac is illnsimted in Fig. 3.
• the mask substrate (not shown) is covered with 40 pairs of " molybdenum (Moksiiicon (St) multilayer (ML) thin films capped with a relatively thin layer of ruthenium (Ru , shown collectively as thin ft 1ms 300 in Fig. 3.
• a bilayer film of tantalum boron nitride (TaB ) 302 and tantalum boron oxide (TaBO) 304 acts as the absorber, which is selectively etched to form the mask pattern.
• EUV mask inspection can be done by a DUV inspection tool to capture defect sites.
• the number of defect sites can be thousands ami hundreds of thousands when the DUV inspection tools are used in a relatively high sensitivity mode.
• the computer snbsystem(s) are configured for disposhionirig the detected defects based on the charged particle bea images generated for the detected defects.
• Positioning as that term is used herein is defined as determining additional Information for a detected defect that can be used to make a final decision tor how to appropriately deal with the detected defect, s,g , that a detected defect should foe repaired, that a detected defect is a nuisance and can foe ignored, that a detected defect do s not need to foe repaired but the wafers printed with die photomask should be monitored for the detected defect s impact on the wafer patterns formed with the photomask:, etc.
• secondary charged particle beam (e-beam or ion) imaging of tire mask described herein provides higher resolution than inspection with relatively high acceleration voltage allowing tor much better review of detected defects on masks. Therefore, the charged particle beam images can be used to determine information for the detected defects more accurately (with greater resolution) than the inspection images of IP the detected defects thereby enabling additional information to be determined from the charged particle beam images: that can he rrsed to make decisions abend (disposition) the detected defects: more effectively.
• Recent advances in multi-beam and multi-column electron beam imaging also allows for massive SEM data collection.
• SEM images can be captured on a mask review, 15 CD-SEM, or electron beam inspection tool (or ion beam images can be captured «sing one of the ion beam tools described herein) at each detected defect Ideation (or a selected subset of the detected defect locations) determined front the previous step of inspection output.
• Each vest charged particle beam image may then he disposi tinned from one or more of the following aspects described further herein - defect isolation, classification, ?.P and priutahility
• fte one or pore computer subsystems are configured for detecting fire : defects using; a hot threshold, hich pay foe performed as described further herein. in this manner the embodiments described herein can provide a substantially 5 high sensitivity EUV photomask defect inspection using: a foot inspection run followed by subsequent classification and wafer printabilitv simulation of the substantially large number of detected defects using secondary charged particle beam images, Sinc the charged particle beam images provide higher resolution of the detected detects than the inspection, the charged particle beam images provide more accurate information for the detected delects
• disposition ing the detected detects includes determining 5 if it3 ⁇ 4e detected defects are real defects or false defects.
• each charged particle beam image may fee revie ed to assess if the detected defect is real.
• Determining if the detected defects are real may include determining one or more characteristics of the detected defects and comparing the one or more characteristics to predetermined criteria that separates real defects from false defects.
• the charged particle beam :fo image of a detected defect may be processe fey the computer siibsystem(s1 to determine dimensions o the defected defect. The determined dimensions: may then fee compared fey the computer subsystem(s) to a threshold that separates real defects from false defects base on size.
• Other characteristic ⁇ ) of the deteeted defects determined fro the charged particle beam images can be used in a similar manner to separate the real defects 15 from false delects,
• the computer snbsystem(s) may fee configured for detecting defects on the photomask by applying a hot threshold to the output of the inspection subsystem, a majority of the detected defects may include“false” or“nuisance defects.
• “False 0 defects” as that term is used herein is generally defined as defects that are detected on the photomask as such hut; are not really actual defects on the photomask instead,“idse defects” may fee detected due to non-defect noise sources on the photomask (e.g., line edge roughness (I..ER), relatively small crtical dimension (CD) variation in patterned features, thickness variations, etc.) and/or due to matginalities in the Inspection,5 subsystem itself or its configuration use for inspection,
• non-defect noise sources on the photomask e.g., line edge roughness (I..ER), relatively small crtical dimension (CD) variation in patterned features, thickness variations, etc.
• the computer subsystem! s may run a hot scan (i.e., a scan in which output is generated for the photomask as energy 30 is scanned across it and a hot threshold is applied to the output to detect defects thereby rendering it a“hot scan”) to ensure that all real defects (even those with relatively low SNR) are captured by inspection in other words, because it is a hot. scan, a significant number of false defects will be detected an at least some real defects or defects of interest ( DO Is) w ill also be detected (because they will also be detected by a hot scan).
• DO Is real defects or defects of interest
• the real defects can be separate ferns the false defects using the charged particle beam images
• ‘rea defects as that term is used herein can be generally defined as delects feat are detected by Inspection and confirmed as actual defects and/or DO Is by charged panicle beam image processing. What ultimately qualifies as a teal defect or a false defect therefere may be: eontro I led by fee quality specifications set by the photomask user.
• di positiomng the detecte defects includes determining if the detected defects are real defects or false defects, which may be performed as described farther herein, and determining a printabdiiy of the real defects on a wafer if the wafer is printed with fee photomask in a lithography process.
• determining fee printabilitv simulates the wafer printing (lithography) process that would be performe using the photomask therein predicting how the real defects would affect the paterns printed on the wafer. For example, each charged particle beam image generated for a detected detect may be reviewe to assess if fee detected defect is real, and if real, whether I would be critical and cause relatively large errors at wafer print or nuisance ant!
• an automate and substantially accurate way of modeling the EUV lithographic process is provided by fee embodiments described herein thereby enabling substantially accurate prediction of the printebillry of mask absorber defects starting with the detected defect charged particle beam images.
• determining the pontability includes inputting the charged particle beam linages generated for the real defects into a mode! of the lithography process thereby generating simulated wafer images illustrating how the real defects affect; one or more patterns printed on the wafer in the lithography process. Determining tire prin lability predicts the defect printing impact by wafer exposure condition simulation.
• This simulation may include mask near-field simulation, which can use either Kirchoff approximation, rigorous finite difference time domain (FDTD) solver, 5 rigorous coupled wave analysis (RCWA), or a compact approximation model such as a Defect: Priutabilit Simulator (DPS) mask mode!
• dispositioiutig the detected defects includes determining a pri nahiliiy of the detected defects on a wafer if fee wafer is printed with the photomask in a lithograph process, and : determining the printahilhy includes inputting design information for the photomask into a model of the charged particle beam subsystem thereby generating simulated charged particle beam reference images of a defect free5 version of the photomask, S ula ring aerial images for the charged particle beam images generated: for the defected defects and fer the simulated charged particle beam reference hnages, and determining how fee detected defects affect one or more patterns printed on the wafer in the lithography process based on the simulated aerial images.
• the defecfoifee mask may he rendered from the post- OPC design database: clips corresponding to the positions: of fee detecte defects: in a die- to-database type approach.
• the charged particle beam-based disposition workflow then involves three main phases as shown in Fig. 6,
• the original images from the charged particle beam tool may be first de-noised and refined to improve the quality of the images.
• original charged particle beam image 600 may be denoised and refined to generate It) de-noised test image 602.
• Denotsing and refining of the original charged particle beam image may be performed in any suitable manner known in the art.
• the post-QPC design database at the same loeation as the detected defect is clipped (ie,, extracted), and a charged particle beam model is applied to render a defect-free reference charged particle beam Image
• the charged panicle beam model may include any appropriate15 charged particle beam model known in th a t.
• design data clip 604 e.g., 60S data portion
• data lookup ma be performe using the test charge particle: beam image
• a charged particle beam model is applie to the design data clip to generate defect-free reference charged particle beam image >606
• the rendering may be calibrated using b actual defect free charged particle beam images and their corresponding design data clips.
• the rendered defect-free charged particle beam image may be a gray scale image.
• the de-noised test and rendered reference charged particle beam images are aligned and then subtracted to generate a grayscale difference image that is: then used to Isolate the defect site by local gray level variation. Alignment and subtraction may be performed in any,5 suitable manner known in the art As shown in Fig 6. reference image 606 may be subtracted from de-noised test: image 60 to generate difference gray scale image 6 S, The defect isolation may be performed as described further herein using difference image 608 to generate defect position image 6 IQ. [0074] lit the second phase, binary contours may be extracted from the demoised charged particle bea test image to generate the test binary image containing die detected defect and also from the rendered charged particle beam image to generate the reference binary image.
• Contour extraction may be applied to both the test and rendered charged particle 5 beam images in any suitable manner known in the art
• binary contours may be extracted fro de-noised test image 602 thereby generating test binar image 612, and binary contours may he extracted from defect-free reference charged particle beatn image 606 thereby generating reference binary' image 614.
• a binary difference image may then be generated by .subtracting the reference binary image bom in die test bi nary image.
• reference binary image 614 may be subtracted from rest binary image 612: thereby generatingbinary difference image 616.
• the gray and binary difference images thus generated ma then be used to calculate defect metrics iiom the defect isolated in the first phase and to effectively 15 determine the type of defect* e.g,, tine edge roughness ( LFRy PinHole, PinDof Intrusion, Extrusion, etc.
• defect metrics may be organized in a data structure such as a defect information fable and may include information such as defect area in the binary difference image, size in the k and y 0 directions in the binary difference image, defect area in the gray scale difference image, and size i the x and directions n the gra scale difference image.
• the defect metrics may be used with or inpu to guidelines 620 that define different defect types to generate defect: classifications: 622.
• the defect metrics may otherwise be determined from the gray scale difference image and ie binary ⁇ difference image in any suitable manner 5 know in the art Defect : classification may also be performed as described further herein.
• an appropiate mash model may be applied to both the test an reference binar images with ihe associated scanner exposure conditions to generate test 30 arid reference EUV aerial images.
• the mask model may be applied to the images as described further herein.
• the eomputer subsyste fs ⁇ may run prmtahifity simulations With scanner optical: conditions.
• test binary image 612 may be input to an EUV lithography simulation to generate test aerial image 624
• ami reference binary image bid may be input to the LUV lithography simulation to
• Aerial Image Anal zer (A 1 A) may then be run to compute priiitability Of all features withih the field of view (FGV) of the: charged particle beam subsystem in which the defect is located.
• FGV field of view
• test aerial image 624 and reference aerial image 626 may be input to AIA that may generate simulated image 628 snowing how the defect would affect the features of the o mask in the aerial image pro ected on a wafe during a lithograph process.
• Examp 1 es of the AIA that may be used in the embodiments describe herein are described in
• the charged particle beam subsystem is configured for automated generation of the charged particle beam images at all of the locations of theb detected defects, dispositioning the detected defects includes etet mining if the detecte defeefe are real defects or false detects, and; the one or more computer subsystems are configured for automated dispositioning o all of the detected defects determined to be the real defects.
• the charged particle beam subsystem may be configured to automatically generate charged particle beam images for each of the detected defects5 repotted by the inspection.
• a recipe ⁇ i.eflower a set of instructions) used to generate the chatted particle beam images may instruct the charged particle bea subsystem to generate charged: particle beam Images at each of the locations of the detected defects determined by the computer subsystem ⁇ thereby enabling automatic generation of the charged particle beam images for all of the detected defects.
• the computer subsy?tem(s) may be configured to automatically process each of the charged particle beam images generated for the detected defects to disposition the detected defects automatically, which may include determining if the detected defects are real or false defects, possibly in combination with any other disposition ing described herein. Once the computer ubsysiemts) determine which of the detected defects are real or false, any further dispositioning may onl he performed fo the real defects thereby making the dispositioning more efficient.
• dispositioning the detected defects includes determining isolation of the detected defects with respect to patterned tea fines hi a FOV of the charged particle beat» subsystem centered on the locations of the detecte defects (or in which the locations of the detected defects are positioned).
• Defect isolation identities the detected defect location within the FOV of the charged particle beam image.
• the detected defect location may be determined using local gray level variation and a difference image generated from the charged particle beam image acquired at the defect location hi one such example, the local gray level variation may be determined as a function of position within the difference image, and the maximum value of the local gray level variation may be determined as the defect location. Determining the location of the defect within the FOV of the charged particle beam image may, however, he performed in any other suitable manner known in the art.
• Determining the defect isolation may also include determining which of the tterned : features of the photomask im the FOV of the charged particle beam image that a detected defect is closest to and ho close the detected defect is to those paterned features. For example, once the location of a detected defect within the FOV of the charged particle beam image has been determined as described above, that defect location information can be used to identify spatial information for the detected defect relative to patterned features m the photomask using the test image For the detected defect.
• Determining the defect isolation may include identifying which of the patterned features that a detected defect overlaps with, which may be the case if the defect Is located within or at least partially overlaps with one or more patterned features, or which of the patterned: features: is defeeti
• Detect isolation may also include determining the location of a defected defect with respect to the patterned ieamres in the FOV [regardless of whether or not the detected defect overlaps with or is within a patterned feature itself! For example if a detected defect is fat least partially) spatially coincident with a 5 patterned feature, determining the defect isolation may: include determining the location of the defected defect with respect to the perimeter or outer bounda of the patterned feature.
• determining the defect isolation may include identifying the patterned feature that the defect is closest to and then determining0 ho close the defect is to the patterned feature.
• the defect isolation may also include determining how close (i some length dimensions that a detected defect 3 ⁇ 4 to a particular part of a patterned feature (e g., a corner, a side, an end, etc ⁇ .
• the space between the detected defect and the patterned feature that it is closest to may be expressed as a single value, a range of values, an average, a function, or in am other5 suitable manner in addition, a user may particularly care about how close a detected defect is to a subset of the patterned features of the photomask than other patterned features of the photomask. For example, one or mor parameters of the defect isolation step ma he set Snc that the detected defect location relative to its closest patterned fca re is determined and or the detected defect location relative to any one type of0 patterned feature is determined if that one type of patterned feature is within the FOV of the charged particle beam subsystem.
• the computer subsystem ⁇ are configured for sending the determined isolation of the detected defects to a photomask repair tool, an the photomask repair tool uses the determined isolation of the detected defects In a repair process performed on the photomask hi this manner, the defect isolation information can be used In the repair tool when the mask needs to be fixed.
• 1ft one such example as0 shown in Fig. 1, compute subsystem 118 tor any other computer subsystem of the system) may be configured to send the determined i olation of the detected defects to photo ask repair tool 140, which may or may not: be part of the system.
• the photomask repair tool may have any suitable configuration known in the art in addition, the photomask repair tool may be a comnserc tally available photomask repair tool such as the 5 MeRiT iieXT system that is commercially available from Carl Zeiss SBE, LLC, Thomwood, Mew York
• the photomask repair tool may use the: determine isolati n to determine one or more parameters of the repair process such as repair position and area wit the aim of repairing the detected delects without altering any correctly formed features proximate the detected defects.
• disposing the detected defects nclu es classif ing the detected defects based on the charged particle beam images generated for the detected defects by identifying a type of the detected defects.
• Gassifrcaiion defines the type of defect.
• Pig. 4 shows one example of a defect free mask pattern 400. where color areas 15 indicate absorber and non-color areas indicates Mi.., Fig. 5 shows some examples of different types of defects ; if there is no significant detect and only local line edge roughness (LER) contributes to the detecte inspection signal or image, the detected defect is calle LER as hown by defect example 500.
• LER line edge roughness
• the detected defect is called a hard-defect as shown 0 by defect example 502. If the absorber has a pin-hole and the bottom ML is exposed by the pin-hole, the detected defect; is a pin-hole defect as shown by defect example 504. If a portion of a particle or a: whole particle is located on the ML, the particle or particle portion has a pnntahiiity impact on wafer exposure and i classified as a pertainie-on-ML as shown by defect example 506. if a particle is completely on the absorber, the particle 5 does not ha ⁇ e any printability impact on the wafer exposure and goes to a different bin which is particie-on-ahsorber as show by defect example 508.
• Classifying the detected defects based on the charged particle beam image generated for the detected defects may be performed in any suitable manner.
• the comp mer su b system (s ⁇ may determine one or more charactettxues of the detected effectss based on the charged particle beam images.
• Those cbaracicrlsi!c(s) may include, for exam le, size, shape, orientation, location, location r l ti e to any nearby patterned features, texture, and the like. Any determined characteristic ⁇ ) and possibly the charged particle beam images may be input to a defect classifier by the computer snhsystemfs).
• the defect classifier may be configured for determining the class (or type, bin, etc ⁇ of the detected defects based on their determined characteristic si and or charged particle beam images.
• Tbe defect classifier may be any suitable defect classification method or algorithm known in the art.
• One example of snch a defect classifier is a relatively simple decision tree in which different types of defects are separated b applying different eotlines t the defect characters $tk(ss that separate different types of defects from each other.
• Other examples of suitable defect classifiers are machine teaming type defeet classifiers, some examples of which are described in IAS.
• Patent Application Publication Nos. 2018/0107928 published April 19, 2018 b Zhan et a I. and 2019/0073568 published March 7, 2019 by fie et al.. which are incorporated by reference as if fully set forth herein.
• the embodiments describe herein may be further configured as described in these publications
• the system inclu es a atomic force microscopy (AF ) subsystem configured for scanning the photomask at the locations of the detected defects thereby generating height info! atron for the locations of the detecte defects.
• AF atomic force microscopy
• the embodiments described herein can he used for buried defects in ML, where the defect is mostly located on the bottom of the ML stack but that morphology is transferred from the bottom to the surface, e,g,, as shown in Tig % Fig 7 shows examples of typical ML buried defects op an iOY photomask
• Diagram 700 shows a bump type defect and diagram 702 shows a pit type defect. As shown in diagrams 700 and 702, .
• the HUY photomask includes L stack 704 and patterned absorber stack 706,
• ML hump defect 708 on the bottom of the ML stack may be transferred to the uppermost surface of the ML stack a ML bump defect 710 on the surface.
• ML, pit. defect 7G2 on the bottom of the ML stack ma be transferred to the uppermost surface of the ML stack as ML. pit defect 714 an the surface.
• the nature of the defects comes from the bottom of the ML, and they can transfer the morphology up to the uppermost surface of the ML, Such defects may therefore induce printable defects on wafers ue to the phase differences they can cause in the light that is projected onto the wafers.
• An AFM tool can therefore he used to scan the surface of the EIJV photomask to obtain height information as m image (he;, height information as a fimetion pf k and y position across the EIJV photomask), which can he used to disposiitos the defects;.
• the system may include AFM subsystem 136 that is coupled to computer subsystem 138, Computer subsystem 138 may h eoapjed to other computer subsystem; s ) of the system as described Farther herein such that Information, data, etc * can be transmitted between the computer subsystem(s).
• the AFM subsystem may have any suitable configuration known in the art.
• suitable AFM tools that ean be used as the AFM subsystem described herein are commercially available from Broker Corp., Billerica, Mass (such as the XnSight; family of products) anti in photomask repair tools sueh as the rapid probe microscope (RF ) In the MeliX neXT syste that is commercially available front 23 ⁇ 4iss.
• the AF subsystem ma also not be part of the system, but may be couple to the system in some manner te . by their computer subsystem; s)).
• the computer subsysiem(s) may be: configured to send results of the delect detection to the AFM subsyste feg , as an inspection results f e), and: the AFM subsystem may generate height information for all of the detected defects automatically.
• the computer subsystem; s) may Identify one or more of rhe defected defects a$ described further herein and select the identified one or more detecte defect for scanning hy the AFM subsystem. If fewer than all of the defected: defects are selected fee AFM scanning, only the defect detection resells for the selected detects may be sent to the AFM subsystem or a computer subsystem coupled thereto.
• the AFM subsystem may be configure for automatic scanning of the detected defects, and the: scanning may be automated as described farther herein.
• Parameters of the AF scanning that are used for the detected defects may alt be the same (some predetermined best known AFM parameters) or may be selected dynamically based on any information generated for the detected defects prior to or during AFM scanning.
• the computer subsystem(s ⁇ are configured for: identifying one or more of the delected delects that do not appear in the charged particle beam images generated at the locations of the one or more of the detected defects, and the AFM subsystem is configured for automated seaiming of the phototnask at only the0 locations of the identified one or more of the detected defects.
• the AFM subsystem can be used to scan the surface at foe5 location of the non-redeteeted defect to obtain heigh information as an image that can be used for dispositioning the detected defect.
• a defect location re orted by inspection is scanned by the charged particle beam subsystem as described herein and no defect can be found in the charged particle beam imagefs ⁇ generated for that defect location (which can be determined by performing any suitable defect location method ond the charged particle beam tmagefs) ⁇ , then that defect location may be selected for AFM subsystem scanning.
• the defect re-detecuon performed using foe charged particle beam images may be perforated as described further herein with respect to inspection or in any other suitable manner known in the: art.
• the information generated by the AFM subsystem5 may be mom suitable for defect dispositioning than the available inspection images (or information determined therefrom) and the available charged particle beam images in which no defect was re-detccfed,
• the computer subsystem* s) are configured for0 acquiring information for additional defects defected on a blank substrate prior to fabrication of the photomask wit the blank substrate, and the AFM subsystem is configured : for scanning the photomask at locations of the additional defects thereby generating height information for the locations of the additional defects.
• a blank substrate fe.g., $ substrate consisting of the ML stack shown: In Fig.
• the patterned absorber layer may be formed on the blank substrate thereby forming a photomask. That photomask can then be inspected as described herein. If actinic blank inspection of die photomask noticed the location of ML defects prior to absorber patterning, the AF tool can be used to scan the: surface to obtain height information tha is then used as the images for dis osk. toning the detected ⁇ U lects performed as described heroin.
• the computer subsystem ⁇ can acquire the information for the additional defects detected by blank substrate inspection k any suitable manner ⁇ e.g.lie from ike inspection system (not shown) that performed the blank substrate inspection or foam a storage medium, e.g., storage media 120 shows in Fig. 1, in which the blank substrate inspection results are stored).
• the information for the additional defects may include any and/or all of the information for the additional defects reported by blank substrate inspection, which will include information for the blank substrate defects that can be used by the computer s bs ste 's;) described herein to determine the locations on the photomask at which ATM scanning will be performed to generate; height : infermati on for those blank substrate defects.
• the AFM subsyste ma scan the photomask: at the location s of the additional defects as described further herein.
• the computer subsystem(s) are configure for dispositkming die detected defects based on the height mformatfon generated for the detected defects.
• Dispositioning the detected defects based on the height information may be performed in any suitable manner.
• the height information may be input to a defect classifier as described further herein, and the detect classifier may determine a defect wpe based on the height information.
• the defect classifier may determine that the defect is an ML ⁇ bump defect such as that show n in Fig. 7.
• the defec dispositioniug may determine that the detect is aft M pit defect such as that shown in Fig. 7. Dispositioniug the detected defects based on the height information may also or alternatively include any of the ot e disposifioning described herein as performed using the dunged particle beam images.
• dis psftidfitintg the detected defects based on the height Information includes determining priniabtli!y of the defected defects on a wafer if the wafer is primed with the photomask in a lithography process, and determining the prinfabiliry includes inputting design information for the photomask into a model of the AFM subsystem thereby generating: simulated reference height information for a defect free version of the photomask, sirnolating aerial images for the height information generated for the detected defects and for the simulated r ference height information, and determining how the detected defects affect One or more patterns primed on the wafer in the lithography process based on the simulated aerial images.
• a defect-free mask may be rendered from the conespondiftg post-OPC design database clips in a dle-to-database type approach.
• the AFM-base workflow then Involves three main phases, as shown in Fig. 8.
• the original images from the AFM tool av first be de-noi cd and refined to Improve the quality of the images, For example, as shown in ihg $ test AFM image 800 may be dc- noised, correcte for tilt, an refined to generate refined test image 802.
• Denoising and refining the original AFM images m y be performed in any suitable manner known in the art
• a portion of the post-OPC design database at the same location as the defect is clipped (extracted), and an AFM model is applied ro render a defect- free reference AFM image.
• the refined test image may be used with a lookup fenefron to search the design database for the photomask to i3 ⁇ 4 the corresponding design clip Shown in Fig 8 as design clip 804.
• An AFM model may thou be applied to the design clip to generate a defect-free reference AFM image shown in Fig 8 as reference AFM image 806.
• the AFM model may be calibrated using known defect free AFM test 5 images and their corresponding design clips.
• the AFM model may include any suitable AFM model known in the art.
• the de-noised test an rendered reference AFM images ma be aligned, corrected for frit and subtracted to generate a grayscale difference image, which is then used to isolate the defect site by local heigh ⁇ information.
• the alignment tilt correction and subtraction of the rest and reference AFM images may be lb performed in an suitable manner known in the art.
• the defect site may he isolated by local height information in the AFM difference image in any suitable manner known in
• binary contours and ML morphologies may be extracted from 15 the de-noised AFM test image to generate both a test biliary image and test ML morphology containin the detected defect and also from the rendered AFM image to generate a reference binary mask and Hat ML morphology. For example, as shown in
• test image 802 may be processed to extract the absorber contours thereby generating binary contour image SOS.
• the de-noised A FM test image may also 0 be processed for ext efro of the; ML morphology thereby generating ; test ML morphology image 810.
• the binary contours and ML morphologies may be extracted in any suitable manner known in the art.
• the test ML motphology image may be used to caknlaie defect metrics from the defect isolated in the firs! step, and the defect metrics may include, for example, defect area size, height, percentage of defect lying on the ML, 5 etc, For example, as shown in Fig 8, test.
• motphology image 810 may bo used to determine defect metrics S 12, which may be stored in a defect information table or any other suitable data structure.
• the defect information that is determined and store may include any suitable information that can be determine from the extracted ML morphology image such as ML height.
• the defect information may be extracted from the 30 test ML morpho logy image in any suitable manner known in the art. Tins information can then be used to determine the exact type of defect, for example, pit, bump, etc.
• defect metrics 812 may be input defect classific tion 814, which determines the type of defects from the information in the defect metrics.
• Defect classification 814 may be performed as described further herein (e.g., using a defec classi ier) or in any other suitable manner known in the art.
• the DP'S mask model is applied to both the test and reference &FM Images with the associated scanner exposure conditions to generate test and reference EUY aerial images.
• This step may he performed as described further herein.
• this simulation may include rigorous FDTU solver and RCWA
• binar contour Image 808 an test ML morphology image 810 may be input : to m EUY simulation model to generate test aerial image ib
• reference APM image 80b ma be inpat to the EUV simulation model to generate reference aerial image SI 8.
• conformal Ml conformal Ml .
• the reference aerial image may be subtracted ffom the test aerial image to generate difference aerial image: 820, which can then be used for printability analysis lie MA is then ru : to compute printabiilty of all features within the FOV.
• the eorapitter subsyste (s) are eon!!gpfed for automated disposition g the detected defects based on the height information generated for the detected defects.
• an or all of the dispositioning described herein may be performed automatically by the computer subsystem? s). in other words, once the AGM subsystem has generated height information for a detected defect, the computer subsyste Cs) may automaticall perform defect dispositioning using the height Information and any other information for the detected defect generated by the system o otherwise made available to the system. Enabling the automatic dispositioning, which is provided by the embodiments described herein, is advantageous as described further herein.
• one or more computer subsystems are configured for dispositioning the detected defects based on the charged particle beaut images generated for the detected defects in combination with images generated from the energy from the 5 photomask detected by the inspection subsystem.
• the images may be generate as described forthsr herein.
• the energy directed to the photomask by the inspection subsystem Includes light having a wavelength of 1 93 nm.
• inspection of the photomask may be performed with 193 nm light thereby making 193 ntn images of the photomask readily available for defect dispositioning.
• the It) computer subsystem(s) may store the output of the inspection subsystem for any defects detected on the photomask and then may use the stored output for dispositioning the defects in combination with the charged particle images.
• Using such images in conjunction with charged particle images may be particularly advantageous fen relatively shallow, multilayer defects dial do not have any signal in the charged particle beam 15 images.
• the defect may not generate a signal in the charged particle beam images.
• Reviewing optical 193 n images together with the charged particle beam images to thereby disposition the delects may also be particularly advantageous if the high resolution AFM is not fast or stable enough for some applications.
• the computer 9 subsyste 's may also use the charged particle beam images in combination w th an other inspection Images (L&,, not just 193 nm images) and/or other optical images that are avai lable for the defects defecte on the photomask.
• the defeef isposltloning performe using charged particle beam in combination with other images may otherwise be performed as described further herein.
• the computer snbsystemfs may also be configure lair : defect: dis ositioning usin ofoer combinations of imag s an information generated or acquired by the systems described herein Bor example, height: information for the detects determined using the AFM subsystem may be used in combination with optical images tor the defects.
• the one or more computer subsystems are configure for dispositioning the detected defects based on the height mfematiori generated for the detecte defects in combination with images generated from the energy from the photomask detected b the inspection subsystem.
• the images may include any of the images described herein. In one such example, the images may he IPS nm optical 5 images.
• the energy directed to the photomask by the inspection subsyste include light having a avelength of 193 nm.
• the optical images used whh the height information for defect dispositioning may also include any other optical images described above. The defect dispositioning performed using the optical images and the height information ma otherwise be performed as it) described further herein
• sane advantage of die embodiments described herein is that they are able to isolate the exact defect location by comparing the secondary images te.g., the charged particle beam images and/or the ATM images) to the design database.
• Another advantage is that the embodiments enable the 0 defect type classification by substantially high resolution charged particle beam/AFM images.
• An add tional advantage Is that printahiiity ca he predicted without relying on any operator’s experience or actinic imaging tool. Moreo ver, since the who ie work flow can be fully antomated by software and processe in parallel by a computing server, tire throughput of the entire dispositioning can be much faster than manual dispositioning. 5
• the embodiments described herein result from the first atempt of implementing a fusion of substantially high sensitivity EUV mask inspection followed by dispositioning capability via fully automated charged particle beam/AFM image analysts, which advantageously extends FUV photomask inspection 30 capability and improves defect dispositioning accuracy and throughput of patterned EUV mask inspection t!hlike the embodiments describe herein, an actinic imaging too! such as an AIMS tool commercially available from Zeiss can be used tor EUY photomask defect disposittontng, but it is too slow to get through hundreds to thousands of defects in a production tine.
• Another alternative to the embodiments described herein might be 5 defect dispositioning with an: actinic inspection tool with tow numerical aperture (NA) inspection (LNI), but such an inspection tool is not currently available,
• the embodiments described : herein are also different than wafer inspection methods and systems in a number of ways for example, for photomasks, generally, it is id desirable: to perform inspection at the actinic wavelength of the photomasks for several reasons including that the prfetab!lhy of th detected defects can fee assessed with a properly configured inspection tool: and the use of the actinic wavelength ensures that defects can be detected on the photomasks with sufficient sensitivity in contrast wafer inspection methods and systems are often designed based primarily on the smallest si3 ⁇ 4e 15 of the defeets that need to be detected on the wafer Such wafer inspection does not, however, need to be performed to determine the printa thirty of any defects on: the wafer since the defects are already printed on the wafers and the wafers are not used to print any other substrates.
• an actinic ieview tool captures images by scanner optics (which is low' resolution) to mimic the wafer impact.
• the actinic wavelength of a photomask and a wafer primed with the photomask may be the same (i.e. call the 5 wavelength of light that is used to transfer a pattern from the photomask to the wafer thereby causing a photochemical reaction in one or mo materials on the wafer, e g , a photoresist), but wafer inspection processes arc not designed: based on that actinic wavelength or any lack of a wafer inspection tool that: Is capable of inspection at that actinic wavelength.
• the embodihients describe herein have been designed to overcome the lack of a suitable inspection method or system for EUV photomasks.
• the features of the embodiments described herein that enable the inspection of EUV photomasks include that the enormous number of defects detected by inspection of EUV photomasks can be dealt w ith efficiently by using the charged particle beam images (an optionally the AT images) for defect dispositioning.
• This feature enables using a hot threshold is the inspection that results in detection of both real and false defects in great numbers without significantly impacting the inspection process. Therefore, the inspection can detect the smallest size defects that arc required to fee detected for Eli A photomask inspection and the resulting detected false defects can be separated from the real defects by the dispositioning described herein.
• the embodiments described herein w ill be efficient, easy to use, and accurate, especially compared to other available options lor EUV photon task inspection .
• Another embodiment relates to a method : for inspection : of a photomask.
• the method includes dheetiug energ to a photomask and detecting energy from the photomask.
• the photomask is configured as described herein.
• the method also includes detecting defects on the photomask based on the detected energy and generating chai ned particle beam images of the photomask at locations of the detected defects.
• the method further includes dispositioning the detected defects : based on the charged: particle beam images generated: for the detected defects. [0l03j Eatjh of ’ the steps of the method may be performed as described further herein,
• the method may als include any other step(s) that can he performed by the inspection subsystem, charged particle beam subsystem.. ATM subsystem:, and/or computer subsystem* s) or system(s) described Herein which may be configured according to any of the embodiments described herein in addition the method described above may he performed b any of tire system embodiments described herein.
• An additional embodiment relates to a non-transitory computer-readabl medium storing program instructions executable on a computer s stem for performing a computer-i mplememed method for inspecting a hotomask.
• One such embodiment is 5 shown in Fig. 9. In particular, as shown in Fig. 9.
• non-transitory computer-readable medium 900 includes program instructions 902 executable on computer system 904 T he compitter-mipfe ented method may include any slept is) of any method(s) described herein. it) [010S] Program instructions 902: implementing methods such as those described herein may be stored on computer-readable medium 900, The computer-readable medium may fee a storage medium sued as a magnetic of optical disk, a magnetic tape, or any other suitable uou-traository computer-readable medium known in the art. 15 [0106] The progra instructions may be implemented in any of various wavs mduting procedure-based techniques, component-based techniques, and/or object-oriented techniques, among others. For example, the program instructions may be implemented using ActiveX controls, CT+ objects, JavaBeans, Microsoft Foundation Classes fMFC ’ ). SSE (streaming SIMD Extension) or other technologies or methodologies as ?.o desired
• Computer system 904 ma be configured according to any of the embodiments : described herein. 5 [0108] Further modifications and alternative embodiments of various aspects of the invention will he apparent : to those skilled in the art in view of this description, Bor example, methods and systems for dis positioning detects beteeiod on a photomask are provided. Accordingly, this description is to be construe as illustrative only and is for tbs purpose of teaching those skilled in the art the general manner of carrying out the 30 invention.

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