WO2007088552A9 - Apparatus and method for imaging integrated circuits and the like - Google Patents

Apparatus and method for imaging integrated circuits and the like

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Publication number
WO2007088552A9
WO2007088552A9 PCT/IL2007/000145 IL2007000145W WO2007088552A9 WO 2007088552 A9 WO2007088552 A9 WO 2007088552A9 IL 2007000145 W IL2007000145 W IL 2007000145W WO 2007088552 A9 WO2007088552 A9 WO 2007088552A9
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WO
WIPO (PCT)
Prior art keywords
wavelength
imaging
imaging system
internal component
previous
Prior art date
Application number
PCT/IL2007/000145
Other languages
French (fr)
Other versions
WO2007088552A1 (en
Inventor
Moshe Tshuva
Joshua Altman
Original Assignee
4Id Ltd
Moshe Tshuva
Joshua Altman
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 4Id Ltd, Moshe Tshuva, Joshua Altman filed Critical 4Id Ltd
Publication of WO2007088552A1 publication Critical patent/WO2007088552A1/en
Publication of WO2007088552A9 publication Critical patent/WO2007088552A9/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J5/60—Radiation pyrometry, e.g. infrared or optical thermometry using determination of colour temperature
    • G01J5/602—Radiation pyrometry, e.g. infrared or optical thermometry using determination of colour temperature using selective, monochromatic or bandpass filtering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J5/0096—Radiation pyrometry, e.g. infrared or optical thermometry for measuring wires, electrical contacts or electronic systems
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J2005/0077—Imaging
    • 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
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
    • G01N2021/3568—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor applied to semiconductors, e.g. Silicon
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/72—Investigating presence of flaws
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/28—Testing of electronic circuits, e.g. by signal tracer
    • G01R31/302—Contactless testing
    • G01R31/308—Contactless testing using non-ionising electromagnetic radiation, e.g. optical radiation
    • G01R31/311—Contactless testing using non-ionising electromagnetic radiation, e.g. optical radiation of integrated circuits

Definitions

  • the present invention relates to the imaging of a structure or an object, in particular the imaging of a structure having internal components that are internal to or behind a layer or material that is opaque at a given wavelength range.
  • the invention is particularly suited to the imaging of integrated circuits (IC) 3 and will be generally described with reference thereto; however, the invention is applicable to a wide range of objects and technologies including biological structures, reconnaissance applications and so on.
  • IC integrated circuits
  • IC integrated circuits
  • the manufacture of integrated circuits (IC) requires very high quality with a tight tolerance. As such, their inspection is an extremely vital part of the overall process of IC manufacturing. Therefore, much effort has been expended in evaluating such components, which may comprise several layers with intricate and thin deposits of conductive circuitry.
  • the conductive materials are usually metals such as gold, aluminum and copper, typically on/within a silicon substrate, and commonly also comprising silicon dioxide (SiO 2 ).
  • SiO 2 silicon dioxide
  • Gallium- arsenide ICs are also fairly common.
  • IC developers typically inspect ICs by imaging them after production, using known optics in the visible and NIR spectrum for surface inspection and/or after removal outer layer(s) of the chip - for example, as described in US 6,387,715; and by checking defects and the temperature via radiation emission using a LWIR sensor at particular (suspicious) locations.
  • Radiation in the visible wavelength spectrum is not typically used to evaluate the internal circuitry of ICs because silicon substrates are opaque at wavelengths of under about 1.2 microns (see Fig. IA), which includes the visible wavelength spectrum (about 0.35 - 0.75 microns) and so such wavelengths are not transmitted through the silicon.
  • the physical dimensions of the circuitry are typically on the order of 0.1 to 1 microns and as IR spectrum wavelengths are used to penetrate the silicon dioxide layer and "view" the circuitry, a good high resolution image
  • mapping is not obtained. This is because the resolution obtained is roughly equal to the wavelength used or detected multiplied by a factor which is close to one, thus the resolution obtained is essentially equal to the wavelength.
  • IC developers have expressed the need for a system (e.g. imaging system) that allows real-time visualization to aid in the development and production of ICs.
  • Development procedures can be significantly shortened using a tool that produces real-time thermal mapping photos with high resolution.
  • Low resolution cameras presently do not allow identification and confirmation of factors causing problems.
  • analysis of the thermal characteristics of ICs includes issues such as: - To process thermal emission data and temperature measurements, the material needs to be opaque.
  • - Transparent material has no emissivity or thermal signature at IR wavelengths (LWIR/MWIR).
  • - Material that is transparent in the IR range cannot be thermally mapped and silicon and silicon dioxide are transparent within that (relevant) range.
  • Silicon/silicon dioxide does not provide thermal information in most wavelength ranges, for example, in the IR wavelengths, employed to process information because it is transparent and inactive in these ranges. In those ranges in which it emits and provides thermal information (where it is opaque), silicon enables collection of information from its surface only.
  • the present invention relates to an apparatus and method that enables real-time thermal mapping and high-resolution imaging of integrated circuits (ICs) and the like.
  • the imaging apparatus includes an imaging system capable of penetrating through a silicon substrate or protective coating, to thereby map the internal structure/circuitry including its posterior with an optical and thermal resolution approaching about 1.2 micron (e.g., when using wavelengths in the NIR range).
  • UV rays UV rays
  • X-rays 0.001 microns
  • Such improved resolution can be useful, for example, in biological applications.
  • One example is for determining foreign bacteria in a culture, those bacteria being identified by use of radiating at a wavelength at which they react whereby parameters such as increase in temperature, volume change and so on can be determined.
  • an apparatus for imaging an internal component of a non-homogeneous structure comprising: an imaging system adapted for imaging in a wavelength range wherein an external portion of said structure allows passage of radiation at a wavelength in said wavelength range and said internal component is essentially opaque at said wavelength.
  • the imaging system can comprise a broad wavelength range camera and a plurality of filters; or a plurality of cameras with integral filter(s) or filter(s) associated therewith.
  • optical and thermal images are combined whereby an improved thermal resolution can be obtained.
  • a method of imaging an internal component of a non-homogeneous structure such as an integrated circuit and the like using an apparatus comprising an imaging system, the method comprising: aligning said structure with said imaging system or vice versa; and imaging the structure using a wavelength at which an external portion of said structure allows passage of said wavelength and said internal component is essentially opaque at said wavelength.
  • silicon is significantly transparent in the wavelength range of about 1.2 - 8 microns.
  • silicon dioxide SiO 2 - crystal quartz
  • SiO 2 - crystal quartz which is often a component in ICs, is transparent in the UV, visible and NIR wavelengths, in particular the 0.17 - 2.5 micron range (see Fig IB) and as such, radiation in that wavelength range can be used to image the internal structure of ICs comprising silicon dioxide.
  • wavelengths in the 1.2 — 2.5 micron range can pass through a silicon-silicon dioxide IC.
  • the present invention could be adapted for use with gallium-arsenide ICs, which are also fairly common as well as adapted for use outside of the IC manufacturing/inspection field.
  • the wavelength range of approximately 3-15 microns provides for a convenient "effective" thermal area (as understood from the area under the curve(s) in Fig. 2)
  • a camera capable of imaging in both the visible and SWIR wavelength ranges e.g. visible/infrared imager VIIRS by Raytheon corporation, USA
  • imaging is performed using at least two cameras at different wave length bands
  • the apparatus further comprises: a narrow band radiation energy source(s) for radiating on the IC in order to induce a reaction from the materials tested by which it may be identified and improved resolution may be achieved.
  • a narrow band radiation energy source(s) for radiating on the IC in order to induce a reaction from the materials tested by which it may be identified and improved resolution may be achieved.
  • the apparatus comprises a heat source. Heating the IC increases the intensity of its emitted energy (see Fig. 2). This improves determination of the location and resolution of the conductors.
  • the conductors are within the silicon, which is transparent at IR wavelengths.
  • the conductors' emissions can be determined thereby improving the resolution.
  • improved information can be achieved by means of image processing. For example, production defects can be more easily detected (e.g. wide or narrow wiring, etc.) can be determined by comparison with the obtained images.
  • cracks and defects which reach the surface are also characterized by significant changes in their reflectivity and emissivity. This information can be used for mapping them.
  • Additional embodiments involve processing of the image by looking at the derivative of the changes between the pixels, allowing improved definition of the resolution.
  • the derivative is typically used as it is rare that a conductor's dimensions exactly coincide with the edge of the pixels.
  • reactive spectrum it is meant the emissivity as a function of wavelength.
  • the material will emit in a characteristic wavelength band and the present apparatus can be used to identify the material.
  • the present invention can also take advantage of the phenomenon of Becke lines to evaluate ICs.
  • Becke lines occur in regions of sudden change in the material (cracks, breaks, sharp corners) and is caused by refraction, whereby greater emissions result.
  • the phenomenon is especially intense with IR radiation because if there is a defect such as a crack, there will be a higher thermal emission at the crack. It is also possible to discern Becke lines in the internal layers of the IC. Emissions can also be identified even when the layers are hidden.
  • a silicon-silicon dioxide substrate is opaque at visible and UV wavelengths, and therefore in those wavelength ranges, in which it is possible to theoretically obtain good resolution, it is not possible to see beneath the Si/SiO2 surface.
  • the IC is imaged in a wavelength range of about 1.2 - 2.5 microns where the Si-SiO 2 substrate is significantly transparent and thus a resolution of about 1.2 microns of the IC circuitry is obtainable.
  • radiation of various wavelengths can be radiated on the IC using an energy source whose wavelengths pass through Si/SiO2 and are absorbed and emitted by the conductor, thereby improving the imaging.
  • the energy source could be of different spectra.
  • the apparatus and method of the present invention does not require the removal (milling, drilling, etc) of any portion of the IC in order to expose the ICs internal components.
  • the manufacturing process may be halted and the IC may be imaged and its temperature may be measured by a camera adapted to measure this temperature (i.e. an IR camera).
  • Thermodynamic Background A body which is above 0 K (absolute zero) emits radiation which is a function of its temperature and wavelength (consistent with the Planck Energy Distribution Formula).
  • the emission coefficient as a function of the wavelength expresses the intensity of the emitted radiation relative to the intensity of that emitted by a black body.
  • An example of this can be seen in the graph of Fig. 2. As seen in the graph, as the temperature of the body increases, the intensity of the radiation increases and the wavelength coinciding with the maximum intensity decreases.
  • Fig. 3 there is a graph showing the emissivity of a material (diamond) in which there are two wavelength bands (the 5 micron region and in the 8 micron region) in which the diamond absorbs about 90% of the radiation radiated on it.
  • the Y-axis (I/ I 0 ) is the intensity of radiation (I) absorbed by the diamond divided by the radiation radiated on it (I 0 ) and the X-axis is the wavelength in microns.
  • the absorption coefficient is equal to the emission coefficient, at the same wavelength, i.e. the above mentioned spectrographic bands are those in which the diamond both absorbs and emits.
  • the conductors are disposed within the silicon, which is transparent at IR wavelengths. Since the silicon is transparent, it is possible to differentiate between the radiation emitted by the conductors for mapping the transparent areas using appropriate algorithms.
  • the reactive spectrum and emissivity of the common conductor materials are known, and by imaging in a narrow window of wavelengths the radiation emitted by each material can be isolated and their location identified. Thus, each of the materials is identified and information of the emissivity obtained can be used for more accurately calculating their temperature.
  • Becke lines can be determined also in internal locations. In this manner one can better identify the emissions, even where the layers are hidden. Because in the IR range the emissions are internal and no external light is directed inward, Becke lines will be more prominent in the IR range.
  • Figs. IA and IB are graphs of the transmittance of silicon and silicon dioxide, respectively, as a function of wavelength
  • Fig. 2 is a graph of the energy emitted by a black body at various temperatures as a function of wavelength
  • Fig. 3 is a graph showing the emissivity/absorbance of a material (diamond) as a function of wavelength
  • Fig. 4 is a schematic view of the imaging components of an apparatus according to the present invention.
  • Fig. 5 is a schematic view of an apparatus according to the present invention.
  • FIG. 4 there is shown a schematic of the imaging components of an apparatus, according to the present invention for inspecting an object; in this embodiment an integrated circuit or IC 10.
  • the IC 10 - which, as illustrated, for example, could be a normal chip 11a or a flip chip lib - typically contains a silicon mount or substrate 12, a layer with silicon dioxide (SiO2) 14 and conductors, such as aluminum (Al) 16a and gold (Au) 16b.
  • the IC 10 also comprises a connector 15 and optionally a protective layer 17.
  • the apparatus For imaging the IC 10, the apparatus comprises a plurality of sensors or cameras 18a, 18b, 18c ... 18n, each having optics comprising lenses 20 and filters 22a, 22b, 22c ... 22n associated therewith.
  • the imaging path of the cameras is directed to an area or target region of the IC 10 via reflectors or selective mirrors 24.
  • camera 18a is a near-IR. (NIR) camera, imaging, for example, in the 1-2 micron wavelength band; camera 18b is a MWIR camera, imaging, for example, in the 3-5 micron wavelength band; and camera 18c is a LWIR camera for imaging, for example in the 10-15 micron wavelength band.
  • Filter 22a is a 1.4-1.6 band pass filter; filter 22b is a 4.0-4.6 band pass filter; and filter 22c is a 10-12 band pass filter.
  • Fig. 5 shows further aspects of the apparatus according to the present invention.
  • the IC 10 may be located on a positioning surface or table 30 with an energy source 32 adjacent thereto.
  • the apparatus further comprises a processor 34, which typically includes a user interface, and has associated therewith a controller 36.
  • the processor 34 which provides an output 35, is operationally connected to the cameras 18a and 18b and to the controller 36.
  • the apparatus preferably comprises a heat source 38 capable of uniformly heating the IC 10.
  • the processor 34 may include the capability to combine (or unify) the images obtained by the apparatus (e.g. the optical and thermal images).
  • the apparatus can be used to inspect the IC 10 using the following operational steps, or method:
  • Heating the IC to a third uniform temperature e.g. 60 C.
  • the method can further include radiating the IC using the energy source 32. This is performed preferably at a wavelength in a first wavelength band where the internal component (conductor) has a relatively high absorbance, while imaging at a second wavelength (band) where the internal component (conductor) has a relatively high emission.
  • this can be used to identify the material of the internal component, this can be used to thermally activate it at a particular wavelength, instead of, or in addition to, heating the entire IC or components thereof by operating the IC.
  • thermal resolution that is better than the thermal resolution that would otherwise be obtained can be achieved.
  • the improvement can be significant; for example, a resolution about twice as good as without combining the images, or better, can be obtained.
  • the apparatus and method of the present invention are applicable to various structures and types of ICs.
  • the various ICs there is a different emissivity profile and behavior as a function of wavelength and temperature of the material. Integrating the images at different wavelengths allows achieving high resolution at short wavelengths and a good thermal image in the SWIR wavelength range.
  • the apparatus and method of the present invention is not limited to the above-described application, rather there are potentially various applications of this invention.
  • the apparatus and/or method can be used with non-silicon based ICs (e.g.
  • gallium-arsenide ICs gallium-arsenide ICs
  • it could be used to determine the location of a person (or other mammal) within a building and to provide an enhanced view thereof.
  • the invention can be used to determine whether the person is carrying a metallic item, to provide an accurate image of the item and potentially to determine the item's composition; and for a plethora of biological/microbiological and medical applications, etc.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
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  • Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
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Abstract

An apparatus for imaging an internal component of a non-homogeneous structure comprising an imaging system with either at least one camera having a plurality of filters of different wavelength pass bands associated therewith, or, a plurality of cameras of different imaging wavelength for imaging in one or more wavelength ranges wherein an external portion of the structure allows passage of radiation at a wavelength in the wavelength range and the internal component is essentially opaque at the wavelength.

Description

APPARATUS AND METHOD FOR IMAGING INTEGRATED CIRCUITS AND THE LIKE
FIELD OF INVENTION
The present invention relates to the imaging of a structure or an object, in particular the imaging of a structure having internal components that are internal to or behind a layer or material that is opaque at a given wavelength range.
The invention is particularly suited to the imaging of integrated circuits (IC)3 and will be generally described with reference thereto; however, the invention is applicable to a wide range of objects and technologies including biological structures, reconnaissance applications and so on.
BACKGROUND OF THE INVENTION The manufacture of integrated circuits (IC) requires very high quality with a tight tolerance. As such, their inspection is an extremely vital part of the overall process of IC manufacturing. Therefore, much effort has been expended in evaluating such components, which may comprise several layers with intricate and thin deposits of conductive circuitry. The conductive materials are usually metals such as gold, aluminum and copper, typically on/within a silicon substrate, and commonly also comprising silicon dioxide (SiO2). Gallium- arsenide ICs are also fairly common.
Presently, IC developers typically inspect ICs by imaging them after production, using known optics in the visible and NIR spectrum for surface inspection and/or after removal outer layer(s) of the chip - for example, as described in US 6,387,715; and by checking defects and the temperature via radiation emission using a LWIR sensor at particular (suspicious) locations.
Radiation in the visible wavelength spectrum is not typically used to evaluate the internal circuitry of ICs because silicon substrates are opaque at wavelengths of under about 1.2 microns (see Fig. IA), which includes the visible wavelength spectrum (about 0.35 - 0.75 microns) and so such wavelengths are not transmitted through the silicon.
However, the physical dimensions of the circuitry are typically on the order of 0.1 to 1 microns and as IR spectrum wavelengths are used to penetrate the silicon dioxide layer and "view" the circuitry, a good high resolution image
(mapping) is not obtained. This is because the resolution obtained is roughly equal to the wavelength used or detected multiplied by a factor which is close to one, thus the resolution obtained is essentially equal to the wavelength. With the present technology, one cannot typically obtain a thermal map of a silicon IC with a resolution better than about 30 microns. Also, one cannot achieve an image of a silicon IC with a resolution below about 1.2 microns; nor can one view/produce a thermal map where the IC is multi-layered and its active layer does not face a camera/sensor or when it is coated with a protective coating.
IC developers have expressed the need for a system (e.g. imaging system) that allows real-time visualization to aid in the development and production of ICs. Development procedures can be significantly shortened using a tool that produces real-time thermal mapping photos with high resolution. Low resolution cameras presently do not allow identification and confirmation of factors causing problems.
In addition, analysis of the thermal characteristics of ICs (and other non- homogenous structures with one or more internal components) includes issues such as: - To process thermal emission data and temperature measurements, the material needs to be opaque.
- For visualizing through material, it needs to be transparent.
- Transparent material has no emissivity or thermal signature at IR wavelengths (LWIR/MWIR). - Material that is transparent in the IR range cannot be thermally mapped and silicon and silicon dioxide are transparent within that (relevant) range. Thus, the IC industry is confronted by the problem of obtaining thermal and optical information on ICs made of silicon and like material. Silicon/silicon dioxide does not provide thermal information in most wavelength ranges, for example, in the IR wavelengths, employed to process information because it is transparent and inactive in these ranges. In those ranges in which it emits and provides thermal information (where it is opaque), silicon enables collection of information from its surface only. As a result, current methods for the measurement of temperature are mediocre and intrusive - generally based on removal of silicon layers in order to image or the insertion of probes for temperature measurement. These methods are cumbersome, imprecise, and alter the thermal behavior of the component in the vicinity being examined.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus and method that enables real-time thermal mapping and high-resolution imaging of integrated circuits (ICs) and the like. The imaging apparatus includes an imaging system capable of penetrating through a silicon substrate or protective coating, to thereby map the internal structure/circuitry including its posterior with an optical and thermal resolution approaching about 1.2 micron (e.g., when using wavelengths in the NIR range).
For applications other than silicon-based ICs, shorter wavelengths may be used and the resolution can be better, for example 0.1 microns (UV rays) or 0.001 microns (X-rays).
Such improved resolution can be useful, for example, in biological applications. One example is for determining foreign bacteria in a culture, those bacteria being identified by use of radiating at a wavelength at which they react whereby parameters such as increase in temperature, volume change and so on can be determined.
According to an embodiment of the invention, there is provided an apparatus for imaging an internal component of a non-homogeneous structure comprising: an imaging system adapted for imaging in a wavelength range wherein an external portion of said structure allows passage of radiation at a wavelength in said wavelength range and said internal component is essentially opaque at said wavelength.
The imaging system can comprise a broad wavelength range camera and a plurality of filters; or a plurality of cameras with integral filter(s) or filter(s) associated therewith.
According to another embodiment of the present invention, optical and thermal images are combined whereby an improved thermal resolution can be obtained. According to yet another embodiment of the invention, there is provided a method of imaging an internal component of a non-homogeneous structure such as an integrated circuit and the like using an apparatus comprising an imaging system, the method comprising: aligning said structure with said imaging system or vice versa; and imaging the structure using a wavelength at which an external portion of said structure allows passage of said wavelength and said internal component is essentially opaque at said wavelength.
As noticed in Fig. IA, silicon is significantly transparent in the wavelength range of about 1.2 - 8 microns. In addition, silicon dioxide (SiO2 - crystal quartz), which is often a component in ICs, is transparent in the UV, visible and NIR wavelengths, in particular the 0.17 - 2.5 micron range (see Fig IB) and as such, radiation in that wavelength range can be used to image the internal structure of ICs comprising silicon dioxide. Thus, wavelengths in the 1.2 — 2.5 micron range can pass through a silicon-silicon dioxide IC. It should be understood that the present invention could be adapted for use with gallium-arsenide ICs, which are also fairly common as well as adapted for use outside of the IC manufacturing/inspection field.
The wavelength range of approximately 3-15 microns provides for a convenient "effective" thermal area (as understood from the area under the curve(s) in Fig. 2)
A camera capable of imaging in both the visible and SWIR wavelength ranges (e.g. visible/infrared imager VIIRS by Raytheon corporation, USA) could be used in conjunction with various filters as part of the apparatus of the present invention.
According to an embodiment of the method of the present invention, imaging is performed using at least two cameras at different wave length bands
(e.g. 1-2 microns and 3-5 microns) in combination with appropriate optics and filters. This can be achieved by using different camera (sensor) types or different band filters in front of the cameras.
According to a further embodiment of the present invention, the apparatus further comprises: a narrow band radiation energy source(s) for radiating on the IC in order to induce a reaction from the materials tested by which it may be identified and improved resolution may be achieved. The combination of the cameras' output and analysis of the information received, enables production of an image having a high optical and thermal resolution. For all intents and purposes, a real time picture of what is thermally occurring in the ICs can be obtained.
The spatial resolution of the obtained image will be determined by the shortest wavelengths imaged, and thus a resolution of approximately 1.2 microns is possible (and potentially much better if not limited by the opaqueness of silicon below 1.2 microns). According to a still further embodiment, the apparatus comprises a heat source. Heating the IC increases the intensity of its emitted energy (see Fig. 2). This improves determination of the location and resolution of the conductors.
Also, further information can be obtained by imaging the IC while electric current is flowing in the circuitry (metal conductors), thereby increasing their emission. This also transfers heat to the silicon substrate causing it to heat up.
The conductors are within the silicon, which is transparent at IR wavelengths.
Due to the transparency of the silicon at IR wavelengths, the conductors' emissions can be determined thereby improving the resolution. By combining the obtained images and comparing them to schematics of the ICs circuitry system, if available, improved information can be achieved by means of image processing. For example, production defects can be more easily detected (e.g. wide or narrow wiring, etc.) can be determined by comparison with the obtained images. In addition, cracks and defects which reach the surface are also characterized by significant changes in their reflectivity and emissivity. This information can be used for mapping them.
Additional embodiments involve processing of the image by looking at the derivative of the changes between the pixels, allowing improved definition of the resolution. The derivative is typically used as it is rare that a conductor's dimensions exactly coincide with the edge of the pixels.
The reactive spectrum of each material used in the IC is known. By reactive spectrum it is meant the emissivity as a function of wavelength.
By imaging in a narrow window of wavelengths, isolation of the emissions of the various materials is possible; and the materials can be identified (although they are typically known in the case of ICs) and located in the image. For example, for identifying the material exhibiting the absorbance shown in Fig. 3 (a diamond in this case), one could radiate an object having such material with such an absorbance/emission spectrum in a wavelength range that the material absorbs well (e.g. about 7.8 - 8.5 microns) and identify the material due to its high emission in another wavelength range (e.g. 4.7 - 5.1 microns in this example).
Even without radiating the material (diamond in this example), the material will emit in a characteristic wavelength band and the present apparatus can be used to identify the material.
The present invention can also take advantage of the phenomenon of Becke lines to evaluate ICs. Becke lines occur in regions of sudden change in the material (cracks, breaks, sharp corners) and is caused by refraction, whereby greater emissions result. The phenomenon is especially intense with IR radiation because if there is a defect such as a crack, there will be a higher thermal emission at the crack. It is also possible to discern Becke lines in the internal layers of the IC. Emissions can also be identified even when the layers are hidden.
A silicon-silicon dioxide substrate is opaque at visible and UV wavelengths, and therefore in those wavelength ranges, in which it is possible to theoretically obtain good resolution, it is not possible to see beneath the Si/SiO2 surface. According to the present invention, the IC is imaged in a wavelength range of about 1.2 - 2.5 microns where the Si-SiO2 substrate is significantly transparent and thus a resolution of about 1.2 microns of the IC circuitry is obtainable.
In addition, radiation of various wavelengths can be radiated on the IC using an energy source whose wavelengths pass through Si/SiO2 and are absorbed and emitted by the conductor, thereby improving the imaging. In other applications (non Si-based ICs or applications other than ICs), the energy source could be of different spectra.
In addition to the advantage of higher resolution imaging, the apparatus and method of the present invention does not require the removal (milling, drilling, etc) of any portion of the IC in order to expose the ICs internal components. Thus, it is also convenient for inspection at various steps in the manufacturing process of an IC. The manufacturing process may be halted and the IC may be imaged and its temperature may be measured by a camera adapted to measure this temperature (i.e. an IR camera).
Thermodynamic Background: A body which is above 0 K (absolute zero) emits radiation which is a function of its temperature and wavelength (consistent with the Planck Energy Distribution Formula). The emission coefficient as a function of the wavelength expresses the intensity of the emitted radiation relative to the intensity of that emitted by a black body. An example of this can be seen in the graph of Fig. 2. As seen in the graph, as the temperature of the body increases, the intensity of the radiation increases and the wavelength coinciding with the maximum intensity decreases.
In Fig. 3 there is a graph showing the emissivity of a material (diamond) in which there are two wavelength bands (the 5 micron region and in the 8 micron region) in which the diamond absorbs about 90% of the radiation radiated on it. The Y-axis (I/ I0) is the intensity of radiation (I) absorbed by the diamond divided by the radiation radiated on it (I0) and the X-axis is the wavelength in microns.
In accordance with the 2n Law of Thermodynamics, the absorption coefficient is equal to the emission coefficient, at the same wavelength, i.e. the above mentioned spectrographic bands are those in which the diamond both absorbs and emits.
For each material one can establish a characteristic spectrographic graph. The applicable information in these graphs is used to determine the location and temperature of the components.
The conductors are disposed within the silicon, which is transparent at IR wavelengths. Since the silicon is transparent, it is possible to differentiate between the radiation emitted by the conductors for mapping the transparent areas using appropriate algorithms. The reactive spectrum and emissivity of the common conductor materials are known, and by imaging in a narrow window of wavelengths the radiation emitted by each material can be isolated and their location identified. Thus, each of the materials is identified and information of the emissivity obtained can be used for more accurately calculating their temperature.
By providing energy (radiation) at one wavelength (active excitation) and imaging at a different wavelength the reaction of each of the materials/components can be isolated (e.g., as understood from Fig. 3).
If a schematic of the IC is available, production defects/deviations relative to the schematic can be determined.
In addition, information can be obtained from Becke lines - a situation wherein areas of sudden change (cracks, breaks, corners and the like) produce a higher emission. This effect is pronounced in the IR wavelengths (at which heat radiation is emitted). Becke lines can be determined also in internal locations. In this manner one can better identify the emissions, even where the layers are hidden. Because in the IR range the emissions are internal and no external light is directed inward, Becke lines will be more prominent in the IR range.
Cracks and other defects reaching the surface are also characterized in significant changes in their reflectivity and emissivity. This information can be used for mapping any defects.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be more clearly understood upon reading of the following detailed description of non-limiting exemplary embodiments thereof, with reference to the following drawings, in which:
Figs. IA and IB are graphs of the transmittance of silicon and silicon dioxide, respectively, as a function of wavelength;
Fig. 2 is a graph of the energy emitted by a black body at various temperatures as a function of wavelength; Fig. 3 is a graph showing the emissivity/absorbance of a material (diamond) as a function of wavelength;
Fig. 4 is a schematic view of the imaging components of an apparatus according to the present invention; and
Fig. 5 is a schematic view of an apparatus according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Fig. 4, there is shown a schematic of the imaging components of an apparatus, according to the present invention for inspecting an object; in this embodiment an integrated circuit or IC 10. The IC 10 - which, as illustrated, for example, could be a normal chip 11a or a flip chip lib - typically contains a silicon mount or substrate 12, a layer with silicon dioxide (SiO2) 14 and conductors, such as aluminum (Al) 16a and gold (Au) 16b. The IC 10 also comprises a connector 15 and optionally a protective layer 17.
For imaging the IC 10, the apparatus comprises a plurality of sensors or cameras 18a, 18b, 18c ... 18n, each having optics comprising lenses 20 and filters 22a, 22b, 22c ... 22n associated therewith. The imaging path of the cameras is directed to an area or target region of the IC 10 via reflectors or selective mirrors 24.
In this embodiment, camera 18a is a near-IR. (NIR) camera, imaging, for example, in the 1-2 micron wavelength band; camera 18b is a MWIR camera, imaging, for example, in the 3-5 micron wavelength band; and camera 18c is a LWIR camera for imaging, for example in the 10-15 micron wavelength band. Filter 22a is a 1.4-1.6 band pass filter; filter 22b is a 4.0-4.6 band pass filter; and filter 22c is a 10-12 band pass filter. Fig. 5 shows further aspects of the apparatus according to the present invention. During inspection, the IC 10 may be located on a positioning surface or table 30 with an energy source 32 adjacent thereto. The apparatus further comprises a processor 34, which typically includes a user interface, and has associated therewith a controller 36. The processor 34, which provides an output 35, is operationally connected to the cameras 18a and 18b and to the controller 36. In addition, the apparatus preferably comprises a heat source 38 capable of uniformly heating the IC 10. The processor 34 may include the capability to combine (or unify) the images obtained by the apparatus (e.g. the optical and thermal images).
The apparatus can be used to inspect the IC 10 using the following operational steps, or method:
1) Attaching the IC 10 to the positioning table 30.
2) Connecting the IC 10 to an electric system (e.g. mains - not shown). 3) Imaging the IC 10 at a first uniform temperature (e.g. room temperature).
4) Imaging the IC 10 at different wavelengths with the cameras 18a,b,c...n typically in the UVC to IR wavelength range.
5) Storing the results in the processor 34. 6) Moving the IC via the table 30 to different locations and repeating steps 4 and 5 until all desired portions of the IC 10 are imaged. 7) Heating the IC to a second uniform temperature (e.g. 45 C). An exemplary technique is described in US 2003/722588 (WO 05052540), "Detection of Imperfections in Precious Stones". 8) Repeating steps 4 and 5.
9) Heating the IC to a third uniform temperature (e.g. 60 C).
10) Repeating steps 4 and 5. (At this point the IC need not continue to be heated).
11) Analyzing all of the results in each target region. 12) Determining, from the analysis at each temperature, an accurate emissivity coefficient at each target region and identifying the material(s) present in each target region.
13) Operating the electricity to the IC and imaging while the IC is operating to obtain a real-time image thereof in operation.
14) Calculating the temperature by way of measuring the level of radiation and wavelength band width of the material at each point.
15) Combining/unifying the imaging results at different wavelengths to improve the integrated image.
The method can further include radiating the IC using the energy source 32. This is performed preferably at a wavelength in a first wavelength band where the internal component (conductor) has a relatively high absorbance, while imaging at a second wavelength (band) where the internal component (conductor) has a relatively high emission.
Not only can this be used to identify the material of the internal component, this can be used to thermally activate it at a particular wavelength, instead of, or in addition to, heating the entire IC or components thereof by operating the IC.
It should be noted that by combining or unifying the (optical and thermal) imaging results, a thermal resolution that is better than the thermal resolution that would otherwise be obtained can be achieved. The improvement can be significant; for example, a resolution about twice as good as without combining the images, or better, can be obtained.
It should be understood that the apparatus and method of the present invention are applicable to various structures and types of ICs. For each of the materials used the various ICs, there is a different emissivity profile and behavior as a function of wavelength and temperature of the material. Integrating the images at different wavelengths allows achieving high resolution at short wavelengths and a good thermal image in the SWIR wavelength range. It should be understood that the apparatus and method of the present invention is not limited to the above-described application, rather there are potentially various applications of this invention. For example, mutatis mutandis, the apparatus and/or method can be used with non-silicon based ICs (e.g. gallium-arsenide ICs); and also it could be used to determine the location of a person (or other mammal) within a building and to provide an enhanced view thereof. Further the invention can be used to determine whether the person is carrying a metallic item, to provide an accurate image of the item and potentially to determine the item's composition; and for a plethora of biological/microbiological and medical applications, etc.

Claims

1. An apparatus for imaging an internal component of a non-homogeneous structure comprising an imaging system with either at least one camera having a plurality of filters of different wavelength pass bands associated therewith, or, a plurality of cameras of different imaging wavelength for imaging in one or more wavelength ranges wherein an external portion of said structure allows passage of radiation at a wavelength in said wavelength range and said internal component is essentially opaque at said wavelength.
2. The apparatus according to claim 1, wherein the imaging system comprises a plurality of cameras of different imaging wavelengths.
3. The apparatus according to claim 1, wherein the imaging system comprises at least one camera and a plurality of filters of different wavelength pass bands.
4. The apparatus according any of the previous claims, wherein it is adapted for combining optical and thermal images.
5. The apparatus according any of the previous claims, wherein the imaging system is adapted for thermal mapping in a wavelength range less than approximately 30 microns.
6. The apparatus according any of the previous claims, wherein the structure is an integrated circuit of the type comprising silicon and silicon dioxide and the imaging system is adapted for optical imaging in the wavelength range of approximately 1.2 to 2.5 microns.
7. The apparatus according any of the previous claims, wherein the imaging system is adapted for imaging using UV rays and/or X-rays; at wavelengths of approximately 0.1 microns and 0.001 microns, respectively.
8. The apparatus according any of the previous claims, wherein the imaging system is adapted for imaging at particular wavelength ranges whereby the material of the internal component can be identified.
9. The apparatus according to any of the previous claims, further comprising an energy source for providing energy to the structure.
10. The apparatus according to claim 9, wherein the energy source is adapted to provide energy to the structure at a wavelength band corresponding to a wavelength band at which the internal component has a relatively high absorbance.
11. The apparatus according to either of claims 9 or 10, wherein the imaging system is further adapted to image at one or more wavelength bands corresponding to a band at which the internal component has a relatively high emission.
12. The apparatus according to any of the previous claims, further comprising a heating source capable of heating the structure, preferably to an essentially uniform temperature.
13. The apparatus according to any of the previous claims, wherein the imaging system comprises at least one camera and at least one reflective mirror for aligning the cameras and the structure or an area thereof.
14. The apparatus according to claim 1, further adapted to detect increased emissions related to Becke lines.
15. A method of imaging an internal component of a non-homogeneous structure such as an integrated circuit and the like using an apparatus comprising an imaging system, the method comprising: aligning said structure with said imaging system or vice versa; and imaging the structure using a wavelength at which an external portion of said structure allows passage of said wavelength and said internal component is essentially opaque at said wavelength.
16. The method according to claim 15, further comprising combining optical and thermal images in order to obtain an improved thermal resolution.
17. The method according to either of claims 15 or 16, further comprising heating the structure, preferably to an essentially uniform temperature.
18. The method according to any of claims 15-17, further comprising radiating the structure at a first wavelength band whereat the internal component has a particularly high absorbance; and imaging at a second wavelength band whereat the internal component has a particularly high emission.
PCT/IL2007/000145 2006-02-05 2007-02-05 Apparatus and method for imaging integrated circuits and the like WO2007088552A1 (en)

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