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
  • G01N21/956—Inspecting patterns on the surface of objects
  • G01N21/95607—Inspecting patterns on the surface of objects using a comparative method
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
  • Y10T428/24479—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness
  • Y10T428/24521—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness with component conforming to contour of nonplanar surface
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]

Definitions

• This invention deals with improving the sensitivity of defect inspection on patterned surfaces where the patterned structures are not fabricated as intended.
• the inspection of these surfaces may involve directing light onto such surfaces, collecting light from the surface and processing the collected light to determine whether defects are present.
• An example of this can be in semiconductor wafer manufacturing where thin-film layers are processed with lithography creating patterns in the surface that are subsequently etched and processed to create semiconductor devices.
• lithography process a layer of photoresist is deposited on the surface and the photoresist is illuminated with a pattern that is developed and processed to establish a pattern that will be etched into the surface to create a layer for the semiconductor device.
• Defects within photoresist layers are an example of low-signal producing defects where some amplification of detection signals may be required to adequately identify defects. This need may be higher when considering the extreme ultraviolet (EUV) lithography requirements for detecting printed defects from the mask.
• Prior methods for accounting for low level signals included optimization of the inspection parameters of light, spectral band, aperture mode and tool speed/pixel to identify an optimal inspection recipe.
• a method for wafer defect inspection may include, but is not limited to: providing an inspection target; applying at least one defect inspection enhancement to the inspection target; illuminating the inspection target including the at least one inspection enhancement to generate one or more inspection signals associated with one or more features of the inspection target; detecting the inspection signals; and generating one or more inspection parameters from the inspection signals.
• FIG. 1 shows a cross-sectional profile of a wafer surface with a periodic structure and a defect
• 2A shows signal responses for an inspection system operating in a brightfield mode as a function of wavelength for various defect inspection enhancement layer materials
• 2B shows signal responses for an inspection system operating in a darkfield mode as a function of wavelength for various inspection enhancement layer materials
• 3 shows signal values using the best inspection band/mode recipe for various inspection enhancement layers
• FIG. 5 shows a cross-sectional profile of a wafer surface with a periodic structure and a defect
• 1 1 shows a signal response as a function of resist refractive index n and extinction index k for both reflective and absorptive underlayers.
• Brightfield microscopes e.g. a 2830 Brightfield Patterned Wafer Defect Inspection System produced by KLA-Tencor Corporation, Milpitas, CA
• Such devices may operate in several modes including: (1 ) brightfield mode where the specular reflection from a surface of an inspection target and any propagating diffraction modes that returned to the microscope aperture may be captured thereby measuring the loss via signal inspection that it is not returned to the microscope; (2), unresolved dark-field (DF) mode where the wafer's surface is imaged and scattered light from the defect and scattered signals from random noise events are captured; and (3) resolved DF where an image of the wafer's surface may contain both scattered light from the defect as well as diffracted orders from the structure.
• DF dark-field
• NIL nano-imprint lithography
• Another candidate for next generation lithography may be nano-imprint lithography (NIL) which uses a multiple-use template that may be pressed into the photoresist establishing a pattern in photoresist.
• NIL nano-imprint lithography
• an inspection enhancement may include at least one of an application of an topical inspection enhancement layer over an inspection layer, an application of an inspection enhancement underlayer beneath an inspection layer, transfer of a patterned layer of the inspection target to an inspection enhancement layer of a second inspection target and /or selection of inspection layer materials exhibiting particular optical properties.
• the inspection target may be subjected to inspection by an inspection tool.
• an inspection tool e.g. a 2830 Brightfield Patterned Wafer Defect Inspection System produced by KLA-Tencor Corporation, Milpitas, CA
• an inspection tool may be used to illuminate an inspection target which as been subjected to an inspection enhancement with electromagnetic radiation across various spectral bands to generate one or more inspection signals (e.g. reflected signals, scattered signals, and the like) associated with one or more physical features of the inspection target.
• Those inspection signals may be detected by the inspection tool and analyzed to produce one or more inspection parameters indicative of the physical features of the inspection target.
• FIG. 1 shows a cross-sectional view of an inspection target 100 patterned to include a line-space array of parallel lines.
• the inspection target 100 may include an inspection layer 101 (e.g. a photoresist layer subject to inspection) including one or more defect structures 102, to which a topical inspection enhancement layer 103A may be applied.
• the topical inspection enhancement layer 103A may have increased inspection properties relative to the inspection layer 101 (e.g. enhanced reflectivity, scattering, refractive index, etc.).
• the application can be done with a deposition tool such as a chemical vapor deposition process.
• the increased scattering capabilities of the topical inspection enhancement layer 103A may enhance the scattering signal due to its material properties. For example, a metallic defect will scatter much more light than a dielectric defect.
• Such a topical inspection enhancement layer 103A may also serve to increase the volume of a particular defect, thereby further increasing the scattering associated with that defect.
• Various materials may be used to coat a wafer to provide a topical inspection enhancement layer 103A.
• materials incorporated into the topical inspection enhancement layer 103A may include, but are not limited to titanium nitride, aluminum, silver, gold, tantalum nitride and/or chromium.
• materials incorporated into the topical inspection enhancement layer 103A may include, but are not limited to titanium nitride, aluminum, silver, gold, tantalum nitride and/or chromium.
• some topical inspection enhancement layer 103A materials may include those that are commonly used in wafer fabrication processes for other purposes (e.g. adhesion layers).
• FIGs. 2A and 2B show the respective signals (e.g.
• gray levels (GL) out of a possible 255) produced from a full-height bridge-type defect using a darkfield (DF) mode (HPEC) and a brightfield (BF) mode on a 2830 Brightfield Patterned Wafer Defect Inspection System produced by KLA-Tencor Corporation, Milpitas, CA, for an inspection target having a 5nm coating of inspection enhancement material over a 30nm DR NIL structure with a 40nm depth photoresist (e.g. as shown in FIG. 1 ) as a function of the inspection wavelength.
• aluminum provides signal enhancement in both DF and BF that increases associated defect signals above the uncoated case.
• FIG. 3 shows signals in BF and DF for the 2830 Brightfield Patterned Wafer Defect Inspection System produced by KLA-Tencor Corporation, Milpitas, CA, using the inspection recipe for the various topical inspection enhancement layer 103A materials optimized to result in the maximum signal responses.
• a particular topical inspection enhancement layer 103A material may have properties that allow resonant surface plasmons to occur.
• the potential for such occurrences is a function of the permittivity of the topical inspection enhancement layer 103A.
• the occurrence of surface plasmon modes for some materials and their use as a component of the topical inspection enhancement layer 103A may be desirable.
• FIGs. 4A and 4B show scattering cross sections as a function of wavelength where values >1 indicate a potential signal improvement due to a topical inspection enhancement layer 103A.
• FIG. 4B shows a large potential signal enhancement using a typical noble metal as a topical inspection enhancement layer 103A material having a negative permittivity relative to surrounding material permittivity, a necessary condition to support surface plasmon resonance modes.
• FIG. 4A shows moderate potential signal enhancement from a typical dielectric material that cannot readily support surface plasmon resonance modes.
• the inspection target 100 may include at least one inspection enhancement underlayer 103B configured as a transparent underlayer disposed under an inspection layer 101 .
• Such a configuration may result in a thin-film interference effect having an interference maximum at the location of defect structures 102.
• the thin- film interference can be caused by light reflecting off a substrate 104, and may also reflect off of interlayer boundaries between transparent or semi- transparent materials in the stack (e.g. the boundary between inspection layer 101 and inspection enhancement underlayer 103B) interfering with incident and other reflected light thereby producing standing waves of maximum and minimum electric field intensities.
• the optical properties e.g.
• the inspection target 100 may also include at least one inspection enhancement underlayer 103B configured as a opaque underlayer disposed under an inspection layer 101 .
• this underlayer may have the added advantage of reducing wafer inspection noise from underlying process variation and previous layer defects.
• the inspection layer 101 may be generally applied in a thin layer 40- 100nm thick over a Si blank wafer substrate 104 and then developed for the purpose of testing a stepper tool's focus and exposure or to qualify the mask by inspecting a print-check wafer for mask defects. It may be the case that an optimal wavelength for inspecting such samples may be shorter than current wafer inspection tools utilize. Developing a wafer inspection tool that operates at shorter wavelengths may be costly due to limited and very expensive light sources available, expensive optics and poor optical coating performance, increased risk of photo contamination, wafer damage from high- energy photons to name a few disadvantages.
• the signal producing properties of the sample may be adjusted such that the maximum inspection wavelengths are moved to within the operating wavelength range for an inspection tool.
• the interference effect may also be used to maximize the signal by moving the standing wave maximum to the location of the defect.
• a resulting signal may be a function of the electric field at the defect location and, as such, may change with wavelength of the incident light as the wavelength determines where the maximum and minimum of the standing wave interference will occur.
• Changing the thickness or material of the underlying layer may alter the interference properties of the stack to maximize the electric field at the defect. This may be done for a particular wavelength or, if a wavelength is known, at a particular location within the structure where the defect is located. It should be noted that such techniques may be used with the other methods to increase signal as well (e.g., the pattern transfer technique as will be discussed below).
• the optimum inspection wavelength may be moved to a wavelength range where the potential damage from the inspection photons altering the chemistry of the inspection layer 101 is minimized.
• a variable thickness SiN inspection enhancement underlayer 103B was simulated beneath an inspection layer 101 and the defect signal in a brightfield low-sigma mode (VIB) from a full-height bridge defect was calculated as a function of the thickness of the SiN inspection enhancement underlayer 103B and inspection wavelength.
• FIG. 6 shows various signal responses for various inspection enhancement underlayer 103B thicknesses across various wavelengths. As shown in FIG. 6, the uncoated inspection layer 101 may have a maximum wavelength sensitivity at about 230nm.
• Such sensitivity may be below inspection thresholds for broadband wafer inspection tools that operate between 260 and 450nm.
• the maximum may be moved to about 300nm, inside the broadband spectrum and much above the uncoated inspection layer 101 signal.
• Other thicknesses may be employed to move the signal responses toward other portions of the spectrum that might be advantageous for minimizing noise (which may also be a function of the wavelength) or minimizing wafer damage by photochemical processes.
• the maximum of the defect signal can be tuned to that wavelength by varying the depth and/or material properties (e.g. n, k) of the inspection enhancement underlayer 103B.
• FIG. 7 illustrates this effect by showing the signal as a function of the depth of a SiN inspection enhancement underlayer 103B for 313nm and 365nm.
• a SiN inspection enhancement underlayer 103B depth of either about 40nm or about 140nm may be selected depending upon which thickness might be better suited to the requirements of other wafer processing steps.
• transparent materials other than SiN may be used to create a thin-film interference effect (e.g., SiO2).
• signal response may be improved by transferring a patterned inspection layer 101 of an inspection target 100A onto an inspection enhancement underlayer 103B of a second inspection target 100B.
• an inspection enhancement underlayer 103B that has stronger scattering properties, the corresponding defects of the inspection layer 101 may be easier to capture.
• Such processes are similar to after-etch inspection techniques but are, instead, applied to a short loop wafer (e.g. wafers used to test a particular step in the fabrication process) with one or more under-layer materials that has optimum inspection properties rather than a processed full- loop wafer (e.g. a wafer in a production line).
• an image pattern and an image of the defect may be transferred into a material stack with a selected depth, materials and composition.
• Defect sensitivity may be greater in after-clean inspection (ACI) layers (e.g. as shown in FIG. 8C) than after-develop inspection (ADI) layers (as shown in FIG. 8A).
• ACI after-clean inspection
• ADI after-develop inspection
• the stack may be designed to exploit material contrast versus wavelength, scattering power of materials (i.e. higher index of refraction), and interference effects as described above. If the wavelengths in a selected inspection band are able to penetrate a stack, the overall volume of the defect scattering center may be increased by increasing defect height.
• line -space structures (common in photo short loop studies) that have behaved like optical waveguides when the material, dimension, wavelength and incident angle are correctly tuned have been observed. This waveguide effect may be exploited to amplify the E-field in the direct vicinity of the defect of interest.
• FIGs. 8A-8C a pattern transfer technique for an inspection target 100 is shown.
• An original pattern of an inspection layer 101 on a silicon substrate 104 of an inspection target 100A (as shown in FIG. 8A) may be patterned on a stack (e.g. a thicker SiN inspection enhancement underlayer 103B with an underlying SiO 2 adhesion layer 105 as shown in FIGs. 8B and 8C) of a second inspection target 100B.
• the inspection layer 101 pattern of the inspection target 100A may be etched into the SiN inspection enhancement underlayer 103B of the second inspection target 100B, and then cleaned prior to inspection (e.g. ACI) to remove etched portions of the SiN topical inspection enhancement layer 103A to leave a patterned inspection enhancement underlayer 103B as shown in FIG. 8C.
• the patterned inspection enhancement underlayer 103B may then be subjected to inspection.
• the patterned inspection enhancement underlayer 103B material may be selected to include a higher scattering material than the inspection layer 101 of inspection target 100A and its thickness and the thickness of an underlying layer (e.g. adhesion layer 105) can be used to move the best signal wavelengths into the range of a wafer inspection tool as described above. Additionally, the depth of the adhesion layer 105 may be similarly adjusted to provide an additional degree of optimization.
• FIG. 9 simulated performance by a 2830 Brightfield Patterned Wafer Defect Inspection System produced by KLA-Tencor Corporation, Milpitas, CA, on various pattern transfer materials as a function of their thickness is shown.
• the simulated signals obtained from analysis of an ADI configuration (as shown in FIG. 8A) were used as a normalization factor with the simulated plot signals obtained from an ACI configuration (as shown in FIG. 8C) relative to the ADI for both BF and DF.
• a relatively thick SiN may have the best performance especially in DF where signal increases of >30x are possible.
• Material choices for the underlayer can include SiN, SiO2, Poly Si, Si, Al, TaN, TiN, and the like.
• the wavelength response for the ACI configuration with various thickness of SiN inspection enhancement underlayer 103B compared with the wavelength response for the ADI configuration without the inspection enhancement underlayer 103B show that the wavelength for enhanced sensitivity may be optimized to correspond with favorable regions by configuring the thickness of the SiN inspection enhancement underlayer 103B.
• a similar effect can occur by varying the thickness of one or more underlying materials (e.g. adhesion layer 105) to move the best signal to a desired wavelength.
• signal response may be improved by selecting inspection layer 101 materials (e.g. photoresist layers) and/or adding dyes (e.g. to increase absorption) to the inspection layer 101 to enhance optical properties of the inspection layer 101 at inspection wavelengths.
• inspection layer 101 materials e.g. photoresist layers
• dyes e.g. to increase absorption
• the scattering enhancement can increase by 3.7 compared to a inspection layer 101 with a refractive index of 1 .58 over the spectral range of the 2830 Brightfield Patterned Wafer Defect Inspection System produced by KLA-Tencor Corporation, Milpitas, CA.
• Figure 11 A shows the increase in simulated defect signal as a function of refractive index n at the inspection wavelengths using a darkfield (DF) mode (HPEC) and a brightfield low-sigma mode (VIB) brightfield mode on a 2830 Brightfield Patterned Wafer Defect Inspection System produced by KLA- Tencor Corporation, Milpitas, CA, and for both reflective and absorptive underlayers.
• Figure 1 1 B shows the increase in simulated defect signal in a low-sigma mode (VIB) brightfield mode as a function of extinction coefficient k at the inspection wavelength for a reflective underlayer. By increasing k from 0 to 1 .0, the simulated defect signal increases by 1 .9x.
• the extinction coefficient k can be increased at inspection wavelengths by adding dyes whose absorption peaks are centered on the inspection mean wavelength.
• the refractive index can be increased at inspection wavelengths by selection of inspection layer 101 materials or by adding absorbers with absorption peaks at shorter wavelengths than the inspection wavelengths.
• the index of refraction naturally increases near the absorption peak for wavelengths longer than the absorption peak (normal dispersion).
• Examples of a signal bearing medium include, but may be not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link (e.g., transmitter, receiver, transmission logic, reception logic, etc.), etc.).
• a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.
• a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link (e.g., transmitter, receiver, transmission logic,
• electrical circuitry includes, but is not limited to, electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a general purpose computer configured by a computer program which at least partially carries out processes and /or devices described herein, or a microprocessor configured by a computer program which at least partially carries out processes and /or devices described herein), electrical circuitry forming a memory device (e.g., forms of random access memory), and/or electrical circuitry forming a communications device (e.g., a modem, communications switch, or optical-
• any two components so associated can also be viewed as being “operably connected”, or “operably coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable”, to each other to achieve the desired functionality.
• operably couplable include but may be not limited to physically mateable and/or physically interacting components, and/or wirelessly interactable, and/or wirelessly interacting components, and/or logically interacting, and/or logically interactable components.
• one or more components may be referred to herein as “configured to,” “configurable to,” “operable/operative to,” “adapted/adaptable,” “able to,” “conformable/conformed to,” etc.
• “configured to” can generally encompass active-state components and/or inactive-state components and/or standby- state components, unless context requires otherwise.

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• 2010
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