Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
• • 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
  • G03F7/70625—Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
  • H01L22/10—Measuring as part of the manufacturing process
  • H01L22/12—Measuring as part of the manufacturing process for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions
• • 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

Definitions

• the invention relates to the field of characterization - applied in particular to the need for microelectronics - which makes it possible to determine the shapes of patterns on the surface of a substrate. This technique allows a characterization on an isolated object called "unique".
• Lithography combined with deposition and etching techniques, allows to "transfer”, optically, the image of a mask, on which patterns are represented, in a resin deposited on the surface of substrates.
• the resin once insolated, is developed and generally serves as a mask for the etching processes and / or deposits that allow the realization of the manufacturing steps of the integrated circuits.
• the quality of photogravure processes is controlled in the production line by means of various characterization methods listed as "Critical Dimension Metrology”. We seek to measure nanometric dimensions (up to 100 nm) with accuracies of the order of a few cents.
• the scatterometric technique is put into practice in various ways.
• One of the methods consists of a goniometric analysis of the diffraction of the gratings illuminated by a directive source [Spectroscopic Critical Dimension (SCD) Metrology for CD Control and Stepper Characterization, John Allgair, KLA-Tencor Corporation, hrtp: // www. kla -tencor. corn / company / magazine / fal101 / SCD. pdf].
• SCD Critical Dimension
• This technique is limited by the information acquisition time which imposes the mechanical movement of the detectors.
• Another approach is to make this recording in an integrated way, by means of an optical system which forms, on an image detector, a cartography of the luminous intensity according to two angles of the space, azimuth and declination [http; // www. eldim. en / ezcontrast / semiconducior. htm. ].
• the optical system makes the image of the "Fourier plane" of the characterization network on the detector.
• the source used is "extended” and placed in the Fourier plane of the object network. Under these conditions, the object network is illuminated with light beams more or less parallel to each other.
• the invention relates to a new technique of scaterometry, which makes it possible to measure on so - called "unique" objects.
• These may be lines or pads that can be found anywhere on a surface of a substrate and that result from the implementation of a micro-technology process or microelectronics. These lines or pads do not need to have been specifically provided, unlike the characterization networks used in the known techniques.
• the infinite diffraction pattern generated by such a single object is observed by means of an optical system.
• An examination method according to the invention comprises:
• a spatially coherent light beam preferably originating from a directional source optics, focused on the object with a strong numerical openness, - the formation of the image of the TF
• the diffraction pattern obtained, and thus its optical TF, is highly dependent on the object.
• This is for example a stud, rectangular or rounded, or a log, elongated, or a trench of rectangular or rounded section.
• the present invention thus relates to the analysis of a "single" object on the surface of a substrate using a beam of a coherent source focused with focusing means with a high numerical aperture (between 0.5 and 1.8 or 3).
• This opening depends on the index of the medium considered and the acceptance angle of the focusing means.
• This association between a coherent source and focusing means with high numerical aperture makes it possible to simultaneously achieve all the effects on the object. With the maximum opening, or with a large opening, we work on a very small area of the object and the surrounding substrate. This avoids the use of selection means of a particular incidence.
• the invention also relates to a device for measuring dimensional and / or structural characteristics of a single object, comprising:
• the focusing means with a high numerical aperture, or a part of these means can be placed directly in contact with the object or in a position very close to the object.
• the distance between the object and these focusing means is preferably less than a few tens of nm, for example less, in the air, at 10 nm or 30 nm or 50 nm or, in the presence of a fluid film, at 100 nm.
• An interface liquid, or index matching may be disposed between the object and the lens. The distance between them is then about 30 nm to 100 nm.
• the lens is for example a solid immersion lens, whose proximity to the object and the index will allow to work with a large numerical aperture.
• the use of focusing means or of a lens close to the object makes it possible to work at an effective wavelength of analysis, at the level of the object, equal to a fraction of the wavelength from the source. This use of a smaller wavelength makes it easy to analyze objects of small characteristic dimensions.
• the source is preferably a directional source, or of small geometrical extent (in the optical sense, that is to say at the same time of reduced surface and low divergence), for example a bright source such as a laser or an LED.
• Polarization means make it possible to work with polarized incident light.
• the focus of the source on the object defines the area illuminated thereon and on a portion of the surrounding substrate. The definition of this illuminated area does not require means such as a diaphragm disposed on the path towards the object.
• the means of analysis, or to form the image of the TFO of the light diffracted or reflected by the object make it possible to establish the conjugation of the plan of the object and the plan of its Fourier transform. Detection of one or more polarization state (s) of the beam reflected or diffracted by the object can be realized.
• means for polarizing such a beam may be provided, possibly allowing analysis of various polarizations.
• a treatment can be performed at the detector output; the sight of only diffracted field figures allows a first characterization.
• Numerical processing can also be used to determine a sketch of the shape of the single object. We can get rid of the phenomenon of
• FIGS. 1A-1C represent various objects, each being unique on a substrate
• FIG. 2 represents a device according to the invention
• FIG. 3 represents details of a device according to the invention
• FIGS. 4A and 5A represent objects.
• FIGS. 4B-4D and 5B-5D are diffraction images, respectively of the patterns of FIG. 4A and FIG. 4B.
• the object 1 and its support or substrate 5 come for example from a component production unit such as those used in microelectronics.
• the object 1 rests, or is formed on, the upper surface 3 of the support or substrate 5.
• it has a non-zero thickness or dimension, in a direction perpendicular to this surface 3, that this thickness is measured above above or below (case of trenches, figure IC) of this surface.
• the support or substrate 5 is made of a semiconductor material, for example silicon or SiGe. It can also be a stack of layers such as an SOI.
• This substrate 5 can be a "wafer” as used today in the field of semiconductor industry or microelectronics. Such a “wafer” usually has a size or diameter of 200 mm or 300 mm, and a thickness of a few tens or hundreds of microns, for example less than 50 microns or 100 microns or 200 microns or 500 microns.
• the reference 6 designates the surface of this single object, on which an incident beam will be focused.
• the single object is a strip 1 on the surface 3 of the substrate 5.
• the object 1 is said to be unique in that there is no other object on the surface 3 of the substrate 5 at a distance of less than 2 times the area illuminated by the incident beam. For example, there is no other surface object 3 of the substrate 5 at a distance from the single object less than 2 times the maximum diameter or dimension, measured in the plane of the surface 3, of the illuminated area. by the incident beam. In fact we address a single object during lighting.
• the unique object can have other forms. This may be for example a rectangular pad 60 (FIG. 1B) or of rounded shape, or a trench 61, 62 of shape or of rectangular or rounded section (FIG. 1C). For convenience, two trenches are shown in Figure 1C, but each is in principle unique on the substrate.
• the smallest dimension of the object (this dimension is here measured perpendicularly to the substrate 5) is of the order of 300 nm for a wavelength close to 0.4 ⁇ m.
• this minimum dimension is related to ⁇ . It can be said that both the maximum dimensions and the minimum dimensions of the object depend on the wavelength ⁇ , the numerical aperture and the signal-to-noise ratio of the measured signal.
• the other dimensions are such that they define a surface of size greater than the size of the spot in the plane 6 of the incident beam 9.
• the single object is a pad 60, for which each of the dimensions d, d
• the surface 6 of the object 1 is illuminated by means of radiation or a beam 9 coming from a source 24.
• the spot of this incident beam 9 coming from the source is focused on the surface of the pattern, included in planes parallel to plane 3.
• a spot 90, 91, 92 is shown in each of Figures IA, IB and IC; this spot covers respectively the area delimited by the upper surface of the pad 60, or a zone or a portion of the trench 61, 62, but also a portion of the substrate 5 which provides a phase reference.
• Means (for example a set of lenses) forming a measurement objective 2 make it possible to form the image of the Fourier transform of the surface 6 of the single object 1 in the image focal plane 8 of this objective.
• the surface of the object and a portion or zone in the vicinity of the object that provides a phase reference are illuminated.
• the surface of the object is illuminated as much as the neighboring surface.
• the optical Fourier transform is an optical method for imaging the angular response of an object to a light excitation.
• the invention thus makes it possible to visualize this angular response of the light reflected or diffracted by the object.
• a transfer objective 10, 12 then forms the image of the Fourier transform of the surface 6 on a sensor 14 formed of detectors.
• This transfer objective comprises for example a pair of lenses 10, 12.
• the lens 10 may be a field lens.
• the senor 14 it is for example a CCD camera.
• a CCD camera as means 14 for forming an image makes it possible to acquire, in a single acquisition, as much data as illuminated pixels of the CCD camera.
• the sensor 14 makes it possible to capture the intensity emitted by the surface 6, according to each transmission direction indicated by the torque ( ⁇ , ⁇ ) as illustrated in FIG.
• the illumination can be done from a Fourier plane 18 offset from the optical axis AA 'of the device by a semi-transparent plane 20.
• a lens system 22 is disposed on the path of the beam 9 emitted by the source 24 to form a parallel light beam in the Fourier plane 8.
• This radiation source 24 is a coherent source that can be a bright point source such as a laser or a quasi-point source such as a super radiant LED. It is preferably placed at the focal point of an optical system 22 of sufficient focal length so that the diameter of the beam covers all or most of the Fourier plane.
• the incident beam 9 of the source 24 is focused on the single object 1 by the focusing means of the system 2 arranged in the path of this beam.
• a lens 4 is disposed in contact or object 1 or in quasi-contact with this object, very close to it, at a distance for example less than a few tens of nanometers, for example less than 10 nm or 50 nm or 100 nm.
• the lens 4 is a ball lens, with a flat 7 (see Figure 3). It may have a diameter ⁇ of the order of about 1 mm. The object 1 is then almost in contact with the flat 7.
• This lens can be rutile TiO2 (index 2.6) or diamond (index 2.4).
• This lens is preferably of solid immersion type, or SIL, which allows to pass the tunnel barrier for large numerical apertures.
• the source may be polarized by means 23 of polarization arranged in the path of the beam 9 from the source 24 towards the object 1.
• a linear polarization, or circular or radial or torus, the incident beam 9 can be achieved.
• Means 28 forming a polarization device may be arranged in the path of the analyzed beam, towards the means 14 for forming an image.
• Each polarization means 23, 28 or each polarizer may comprise 2 blades A / 4, or quarter wave, arranged consecutively (possibly electrically controlled) to address all possible polarization states (including circular, torus .. .etc.).
• Polarizers Linear can also be used. Radial states are more generally obtained by 1/4 wave blades behind the polarizers, generally in liquid crystals. The rays coming from the source 24 are then collinear (parallel) to the optical axis AA 'at the Fourier plane 8 of the optical system.
• the infinite diffraction pattern which can be analyzed by the optical system described above, depends very substantially on the shape of the single object.
• a method according to the invention makes it possible to analyze the shape of objects with an accuracy of a few nanometers.
• the diffraction pattern can be analyzed in intensity and polarization.
• the diffraction patterns at infinity are compared with 2 single object cases (log, or object of parallelepipedal shape, as in FIG. 1A) which differ from one another by their thickness.
• one has a thickness el of 0.05 ⁇ m (measured along the z axis of FIG. 4A, perpendicular to the plane 3 of the substrate 5 on which the object is formed), the other has a thickness e 2 of 0 , 1 ⁇ m (measured along the same axis z, FIG. 5A).
• the wavelength is 0.5 ⁇ m
• the SIL lens index is 2
• the object width is 100 nm.
• Figures 4B (respectively 5B), 4C
• 4D represent the magnitudes
• for the object of FIG. 4A (respectively 5A), that is to say the norm of the amplitude of the field along the x axis (defined with respect to the direction of polarization of the wave incident), the intensity of the global field, and the intensity of the field along the y-axis (defined as the direction perpendicular to the polarization direction of the incident wave).
• the state of polarization Ex used to illuminate the object, then also for detection, is particularly sensitive to the object used, so here to the thickness of each log.
• the information relating to the polarization Ey is however interesting insofar as it can differ substantially in intensity depending on the shape of the object. If the shape of the log varies, the polarization figure also varies.
• an object of another form for example a stud such as that of FIG. 1B, or a trench (as in FIG. 1C), another polarization figure is obtained.
• Digital data processing means 26 make it possible to process the data coming from the detection means or the means making it possible to form the image of the optical TF of the diffracted light 19. For example, an image of a diffraction pattern, such as that of FIGS. 4B-4D, 5B-5D, can be displayed on display means 27. Given the very great sensitivity of the measurement to the shape of the object, an operator can, depending on the image that he perceives, deduce if this form is that expected.
• the visualization means 27 make it possible to display the image of this form. As already indicated above, the sensitivity of the process is such that this approximation can be very good.
• the focusing means 4 are in contact or in quasi-contact with the pattern 1. It is also possible to put an index matching fluid (for example ethylbenzene, index 1.49) between these means. 4 and the object 1.
• the index layer has for example a thickness of about 100 nm.
• a wavelength as short as possible to increase the influence of diffraction.
• a wavelength close to 405 nm it is possible to use a wavelength close to 405 nm.
• the shape of the beam is approximately circular with an intensity distribution which depends on the polarization states chosen by the polarization means 23.
• the diameter or size of the spot is preferably less than 1 ⁇ m.
• the FWHM (this is the total width at mid-height of the intensity curve of the beam in the plane near the surface 6 of the object) is less than 300 nm given the depth of field.
• means for example a piezoelectric translation unit.
• This displacement may be oscillating over a range that may be of the order of a fraction of a micrometer, for example less than or equal to 0.1 ⁇ m, or 0.5 ⁇ m or 1 ⁇ m.
• a translation in the object plane induces a rotation of the Fourier plane.
• the phase of the diffracted wave then undergoes a rotation which scrambles any stationary speckel figure. In fat it is enough that one of the elements moves, any combination is possible from there.
• means such as for example described in the article by LPGhislain et al., Applied Physics Letters, Vol. 74, No. 4, 1999, allow a relative translation between the focusing means 4 and the object 1.
• This translation allows to vary the distance between these two elements in the direction of the optical axis AA '.
• the distance between the lens 4 and the object 1 can move during the acquisition. This allows to enrich the signature of the scaterometric signal and to break, and thus eliminate, the coherence.
• the focusing means 4 are separated from the rest of the optical system so that the substrate assembly 5 (with the object 1) - focusing means 4 is displaced along the optical axis AA '. relative to the rest of the characterization device (the amplitude of this displacement is of the order of microns).
• Means for carrying out this movement are, for example, piezelectic means.
• the invention may be associated with a component manufacturing unit such as those made in microelectronics.
• the object 1 comes from this production unit, passes a device such as that described above in connection with the figures, the data processing means 26 comprising for example a microcomputer specially programmed to implement a method treatment as described above.
• the data processing means 26 comprising for example a microcomputer specially programmed to implement a method treatment as described above. An operator can thus have the result of the analysis at the place of production and modify it accordingly if the analysis indicates dimensional and / or structural characteristics different from those expected.

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• 2006
  • 2006-08-02 FR FR0653248A patent/FR2904690B1/fr not_active Expired - Fee Related
• 2007
  • 2007-08-01 WO PCT/EP2007/057956 patent/WO2008015230A1/fr active Search and Examination
  • 2007-08-01 EP EP07788125A patent/EP2047209A1/de not_active Withdrawn
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