WO2005001577A1 - Systeme et procede de metrologie optique de plaquettes semi-conductrices - Google Patents

Systeme et procede de metrologie optique de plaquettes semi-conductrices Download PDF

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Publication number
WO2005001577A1
WO2005001577A1 PCT/US2004/014547 US2004014547W WO2005001577A1 WO 2005001577 A1 WO2005001577 A1 WO 2005001577A1 US 2004014547 W US2004014547 W US 2004014547W WO 2005001577 A1 WO2005001577 A1 WO 2005001577A1
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WIPO (PCT)
Prior art keywords
geometry
recited
probe beam
light
features
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PCT/US2004/014547
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English (en)
Inventor
Abdurrahman Sezginer
Michelle Zimmerman
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Therma-Wave, Inc.
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Publication date
Priority claimed from US10/459,631 external-priority patent/US7046376B2/en
Application filed by Therma-Wave, Inc. filed Critical Therma-Wave, Inc.
Publication of WO2005001577A1 publication Critical patent/WO2005001577A1/fr

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    • 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
    • G03F7/70633—Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching
    • 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
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
    • G01N21/956—Inspecting patterns on the surface of objects
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • 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
    • G01N21/21—Polarisation-affecting properties
    • G01N21/211—Ellipsometry

Definitions

  • the subject invention relates to optical metrology equipment for measuring critical dimensions and feature profiles of isolated and aperiodic structures on semiconductor wafers. This invention further relates to measuring the overlay alignment accuracy of a pair of patterned layers on a semiconductor wafer, possibly separated by one or more layers, made by two or more lithography steps during the manufacture of semiconductor devices.
  • the measurements are analyzed using scattering theory, for example, a Rigorous Coupled Wave Analysis, to determine the geometry of the periodic structure.
  • Rigorous Coupled Wave Theory and other similar techniques rely upon the assumption that the structure which is being inspected is essentially periodic.
  • the diameter of the light beam spot on the sample is typically significantly larger than individual features on the test structure and encompasses many cycles of the grating.
  • Most prior art systems operate wherein the probe light beam spot overlaps at least twenty repeating patterns so that the diffraction analysis will have statistical significance.
  • the results of the analysis represent an average of the geometry illuminated by the probe beam.
  • many features are isolated or aperiodic. These isolated structures cannot not evaluated with the grating analysis approaches described above.
  • test structures on the "streets” of "scribe lines” separating the dies. These test structures are periodic but are intended to have the same geometry (e.g. width, shape) as individual features within the die. By measuring the shape of the test structures, one can gain information about the structure in the dies or overlay registration. This latter approach has been finding acceptance in the industry. Examples of prior art systems which rely on scatterometry techniques can be found in U.S. Patent Nos. 5,867,276; 5,963,329; and 5,739,909. These patents describe using both spectrophotometry and spectroscopic ellipsometry to analyze periodic structures and are incorporated herein by reference.
  • the assignee manufactures a commercial device, the Opti-Probe which takes advantage of some of these simultaneous, multiple angle of incidence systems.
  • a summary of all of the metrology devices found in the Opti-Probe can be found in U.S. Patent No. 6,278,519, incorporated herein by reference.
  • a probe beam from a laser is focused with a strong lens so that the rays within the probe beam strike the sample at multiple angles of incidence.
  • the reflected beam is directed to an array photodetector.
  • the intensity of the reflected beam as a function of radial position within the beam is measured.
  • Each detector element captures not only the specularly reflected light but also the light that has been scattered into that detection angle from all of the incident angles.
  • the radial positions of the rays in the beam illuminating the detector correspond to different angles of incidence on the sample plus the integrated scattering from all of the angles of incidence contained in the incident beam.
  • the portion of the detector signal related to the specularly reflected light carries information highly influenced by the compositional characteristics of the sample.
  • the portion of the detector signal related to the scattered light carries information influenced more by the physical geometry of the surface.
  • U.S. Patent No. 5,042,951 describes an ellipsometric version of the BPR, which, in this disclosure will be referred to as Beam Profile Ellipsometry (BPE).
  • the arrangement of the BPE tool is similar to that described for the BPR tool except that additional polarizers and/or analyzers are provided. In this arrangement, the change in polarization state of the various rays within the probe beam are monitored as a function of angle of incidence.
  • Both the BPR and BPE tools were originally developed for thin film analysis.
  • One advantage of these tools for thin film analysis is that the laser beam could be focused to a small spot size on the sample.
  • the lens can produce a spot of less than five microns in diameter and preferably on the order of 1 to 2 microns in diameter. This small spot size permitted measurements in very small regions on the semiconductor.
  • an incoherent light source is used as the probe beam.
  • the incoherent source creates a spot size significantly larger than the laser source and thus could be used to analyze gratings.
  • Semiconductor manufacturers continually strive to reduce the size of features on a wafer. This size reduction also applies to the width of the streets, typically used as the location for the test structures including overlay registration markings. With narrower streets, the size of the test structures need to be reduced.
  • test structures could be developed that were not periodic gratings but closer in form to the actual isolated or aperiodic structures on the dies. Even more desirable would be to develop an approach which would permit measurement of the actual structures within the dies.
  • An isolated structure would correspond to, for example, a single line, trench, hole or via or a specific alignment mark.
  • Such a structure can have extremely small dimensions (i.e., a single line can have a width of about a tenth of a micron).
  • a very small illumination spot is desirable.
  • the probe beam spot size is relatively large, on the order of 50 microns in diameter. If this probe beam was focused on an isolated structure, the portion of the measured signal attributable to the isolated structure would be extremely small.
  • Overlay metrology is the art of checking the quality of alignment after lithography.
  • Overlay error is defined as the offset between two patterned layers from their ideal relative position.
  • Overlay error is a vector quantity with two components in the plane of the wafer. Perfect overlay and zero overlay error are used synonymously. Depending on the context, overlay error may signify one of the components or the magnitude of the vector.
  • Overlay metrology provides the information that is necessary to correct the alignment of the stepper-scanner and thereby minimize overlay error on subsequent wafers. Moreover, overlay errors detected on a given wafer after exposing and developing the photoresist can be corrected by removing the photoresist and repeating the lithography step on a corrected stepper-scanner. If the measured error is minor, parameters for subsequent steps of the lithography process could be adjusted based on the overlay metrology to avoid excursions.
  • Figure 1 is a schematic diagram of an apparatus for performing the method of the subject invention.
  • Figure 2 is a graph of normalized reflectivity as a function of angle of incidence and comparing actual measured data to predicted data associated with an isolated trench.
  • Figure 3 is a graph of normalized reflectivity as a function of angle of incidence and comparing actual measured data to predicted data associated with an unpatterned thin film.
  • Figure 4 is a cross-section shape of a trench predicted by an analysis of the measured data illustrated in Figure 2.
  • Figure 5a is a schematic diagram of a first embodiment of an apparatus arranged to measure overlay registration.
  • Figure 5b is a schematic diagram of a second embodiment of an apparatus arranged to measure overlay registration.
  • Figure 6 is provided to illustrate the results of moving a baffle to different positions.
  • Figure 7 is a plan view of one form of overlay target made up of isolated features that simultaneously provide information about X and Y offsets.
  • Figure 8 is a plan view of another form of overlay target that includes isolated lines.
  • Figure 9 is plan view of another form of overlay target that includes a combination of lines and circular features.
  • FIG. 1 a basic schematic diagram of a simultaneous multiple angle of incidence apparatus 30 is illustrated. Further details about such a device are described in U.S. Patent Nos. 4,999,014; 5,042,951; 5,159,412; 5,412,473 and 6,429,943, all incorporated herein by reference.
  • the assignee's Opti- Probe device incorporates portions of this technology and markets the measurement subsystem under the trademarks Beam Profile Reflectometry or BPR (as well as a Beam Profile Ellipsometry (BPE) variant described in U.S. Patent No. 5,181,080).
  • BPR Beam Profile Reflectometry
  • BPE Beam Profile Ellipsometry
  • the basic measurement system includes a light source 32 for generating a probe beam 34.
  • the light source should be a laser for generating a coherent beam of radiation.
  • Laser diodes are suitable laser sources for this application. If the output of the laser is not itself polarized, a separate linear polarizer can be provided. The laser output can be coupled to a fiber delivery system as described in PCT WO 01/55671.
  • the probe beam 34 is focused onto the feature 12 on the sample 10 using a lens 40 in a manner so that the rays within the probe beam create a spread of angles of incidence.
  • the sample is shown supported by a stage 44.
  • the beam is directed normal to the surface of the sample but can be arranged off-axis as illustrated in U.S. Patent No. 5,166,752, incorporated by reference.
  • Lens 40 can be a high numerical aperture lens (on the order of 0.90 NA) to create angles of incidence from zero to about 70 degrees.
  • a lens having an NA of at least 0.5 is preferred.
  • a total range of angles of incidence of at least thirty degrees is also preferred.
  • the lens creates rays having predominantly S-polarized light along one axis and predominantly P-polarized light along an orthogonal axis. At intermediate angles, the polarization is mixed. In certain measurement situations, it may be desirable to have the probe beam 34 underfill lens 40 resulting in a lower effective numerical aperture.
  • the beam may be configured so that the effective numerical aperture is 0.5 which would create a spread of angles of incidence from zero to about 30 degrees.
  • the actual larger NA of the lens (0.9) would be beneficial in collecting a larger portion of the reflected and scattered light.
  • Lens 40 is positioned to create a probe beam spot 42 on the sample.
  • a spot size having a diameter as small as two microns or less can be achieved. If a lens with a smaller NA is used, the spot size would typically be larger. In most measurements situations, it would appear desirable to have the spot size less than five microns in diameter. However, in the situation discussed above, where the lens is underfilled, the spot size could be larger than five microns.
  • Light reflected by the feature both specular and scattered
  • the reflected light is redirected by a splitter 46 to an imaging lens 48.
  • Lens 48 magnifies and relays an image of the sample at the focal plane of the lens.
  • a spatial filter 50 having an aperture is placed in the focal plane of the lens 48 for controlling size of the area of the sample which is measured.
  • the probe beam is then passed through a 50-50 splitter and directed to two photodetectors 54 and 56 having a linear array of detector elements.
  • the photodetectors are arranged orthogonal to each other to measure both the S and P polarization components.
  • each of the detecting elements in the array measures light specularly reflected from different angles of incidence.
  • the radial position within the reflected probe beam is mapped to the angle of incidence, with the rays closer to the center of the beam having the smallest angles of incidence and the rays in the radially outer portion of the beam corresponding to the greatest angles of incidence.
  • each detector element simultaneously generates an independent signal that correspond to a different angle of incidence on the sample plus the integrated scattering from all of the angles of incidence contained in the incident beam.
  • the output signals from the detector arrays are supplied to the processor 60.
  • Processor 60 will analyze the signals based on algorithms that consider the reflected and scattered light. The algorithms rely on the Fresnel equations. As noted above, since the structure is not periodic, Rigorous Coupled Wave Theory would not be well suited to the analysis. Rather, and as discussed below, boundary or volume integral approaches, are better suited to this problem.
  • the selected algorithms will correlate the variation in reflectivity as a function of the position on the detector with the geometry of the aperiodic structure. The type of analysis will depend on the application.
  • the processor can compare the detected signals to an expected set of signals corresponding to the desired geometry of the aperiodic structure. If the detected signals do not match the expected signals, it is an indication that the process is not falling within the specified tolerances and should be terminated and investigated. In this approach, no sophisticated real time analysis of the signals is necessary. The reflected output signals can be more rigorously analyzed to determine the specific geometry of the aperiodic structure. While there are a number of different approaches, most have certain traits in common. More specifically, the analytical approach will typically start with a theoretical "best guess" of the geometry of the measured structure.
  • s is the equivalent of sin ⁇
  • the s are the Guassian quadrature nodes, in contrast to the periodic systems where s are equally spaced
  • the w are the weights.
  • E 0 k ° d E 0 (s,z)e' k °" J-s 0 where s 0 ⁇ 1.
  • the electric field as a function of s is not analytic, therefore we need to perform the integration in at least 3 regions, (-oo,-l),(-l,l),(l, ⁇ ) .
  • TM mode we use the equivalent of TM1 implementation.
  • Boundary Integral Approach As noted above, although a Fourier expansion approach can be used, boundary or volume integral methods are ideal for isolated features in that they provide a more robust solution.
  • the boundary integral formulation relies on the Green's theorem, the properties of the wave function and Green's functions.
  • T represents the boundary of the region of interest. In our case, it is simply a curve since the y dimension is of no concern. Since the boundary conditions require that ⁇ (x) , G(x,x ) , d n ⁇ (x) , axt ⁇ d n G(x,x') be continuous across material boundaries, the volume can be extended over several materials provided that G is obtained.
  • ⁇ (X') !dT'_n ⁇ [ ⁇ (X)VG'(X, X') - V ⁇ (X)G'(X, X')]
  • the wafer was silicon with a 650nm top layer of silicon dioxide.
  • the isolated trench had a nominal width of about 500 nanometers (0.5 microns) and a nominal depth of about 650 nanometers.
  • a beam profile reflectometer of the type illustrated in Figure 1 and found in the assignee's Opti-Probe system was used to measure the sample.
  • the photodetector arrays in this system generate output signals corresponding to angles of incidence ranging from about +70 degrees to - 70 degrees around the normal to the sample.
  • Figures 2 and 3 illustrate measurements made on the sample wafer.
  • Figure 2 illustrates measurements with the probe beam over the trench while Figure 3 illustrates measurements with the probe beam positioned on an unpattemed portion of the wafer.
  • the output of the detector elements includes both a specularly reflected component and a scattered light component. It may be desirable to minimize the specularly reflected component and maximize the scattered light component. This can be important if the primary interest is in characterizing the physical structure of the scatterer and less information is needed about the underlying structure.
  • One approach for achieving the latter goal is described in copending provisional application Serial No. 60/394,201 filed July 5, 2002, assigned to the same assignee herein and incorporated by reference.
  • This disclosure proposes inserting a baffle 80 (shown in phantom in Figure 1) into a portion of the probe beam path.
  • the baffle is intended to block a semi-circular portion of the probe beam.
  • light in the left hand portion of the incident beam reaches the sample while light in the right hand portion of the incident beam is blocked. Specularly reflected light is collected by the right hand side of lens 40 but is blocked from reaching the detector by baffle 80.
  • only light which has been scattered from the sample and captured by the left hand side of the lens will reach the detector. In this manner, the light reaching the detector will be primarily scattered light and not specularly reflected light. Additional measurements can be taken after moving the baffle to block the left hand side of the incident beam.
  • the output generated by the detectors does not correspond to specific incidence angles as in a conventional BPR arrangement. Rather, the detectors measure an integration of scattered light from various angles of incidence.
  • a measurement system including a baffle in the manner describe above can be used to measure scattered light from both isolated structures as well as periodic structures.
  • Such a baffle structure can be used to analyze overlay registration as discussed below.
  • the application of the system that includes a baffle to measure overlay registration is illustrated in Figure 5a.
  • Figure 5a is similar to Figure 1 with like numbers corresponding to like parts.
  • a light 32 is collimated by collimator 135 and reflected by a beam splitter 140.
  • the light source 32 can be monochromatic.
  • the wavelength of the light source 32 can be variable.
  • the light source 32 is a bank of lasers or a laser with multiple emission lines or a tunable laser.
  • light source 32 can be the output of a broadband light source coupled to a monochrometer.
  • the light that is reflected off the beam splitter 140 is focused by the objective 40 onto the overlay target 150 on the wafer 155 under test.
  • the light that is reflected and scattered by the overlay target is mapped onto an array detector 160.
  • Detector 160 is a 2-dimensional array such as a CCD.
  • Movable baffle 80 has three states shown in Figure 6: open, blocking half of the aperture, blocking the other half of the aperture.
  • the baffle can be a dark sheet that is moved mechanically.
  • the baffle can be a two-segment, liquid crystal neumatic or ferroelectric shutter.
  • the output of detector array 160 is recorded in each of the three states of the baffle, for each wavelength.
  • the detector only measures the scattered light when the baffle is inserted.
  • the baffle blocks the specular reflection.
  • the reason for blocking the specular reflection and measuring the scattered light in isolation is that the specular reflection can dominate the total light intensity and may contain little information about isolated small features that make up the target.
  • the purpose of taking a measurement with the baffle fully open is to gather information about the film stack in which the isolated target is embedded. Knowledge of the film stack is necessary for interpreting the scattering of the electromagnetic waves.
  • FIG. 6 illustrates the baffle covering either the left or right hand side of the aperture corresponding to movement along an axis parallel to the page in Figure 5. Additional information could be obtained by making additional analogous measurements along an axis perpendicular to the page of Figure 5 (which would correspond to an illustration in Figure 6 where the baffle covered either the top or bottom half of the aperture). Taking measurements with the baffle in different positions may aid in evaluating asymmetries of the features.
  • the instrument is similar to Beam Profiling Reflectometer (BPR). (See U.S. Patent Nos.
  • a particular location on the array detector 160 corresponds to a particular angle of incidence on the target.
  • the recorded light intensity depends on the stack of materials on the wafer as well as the features that make up the target.
  • the baffle partially blocks the aperture, the measured field strongly depends on the features on the target including overlay but also on the stack of materials on the wafer.
  • the fields acquired by detector array 160 for multiple states of the baffle 60 and multiple wavelengths are processed to obtain the parameters of the film stack and the target.
  • the parameters of the target are quantities such as feature thickness, linewidth or diameter, sidewall angle and overlay offset.
  • An alternative embodiment is shown in Figure 5b.
  • the numerical aperture of the illumination is substantially smaller than the numerical aperture of detection.
  • the aperture of illumination is controlled by the collimator or beam expander 135, or optionally by iris 137.
  • the specular illumination hits a small portion 162 of the detector array 160.
  • the outputs of pixels in the specular region 162 of detector array 160 are ignored. These pixels are optionally blocked by a baffle 164 to prevent blooming of the detector array.
  • the rest of the detector array 160 measures diffracted light. If the illumination overfills the target, the target is surrounded by an unpattemed film stack.
  • the general processing steps used to analyze the measured signals will be similar to those discussed above.
  • a model is seeded with an initial guess of target parameters.
  • a calculation is made to predict the electromagnetic wave scattering.
  • Figure 7 illustrates a single target grid which would provide information about overlay registration in both X and Y directions simultaneously. More specifically, any overlay error in either direction will vary the scattered light pattern created by this structure. While the target grid of Figure 7 theoretically can be used to analyze overlay error, it may be difficult to isolate the changes induced by the error in the X direction from the error in the Y direction.
  • Figures 8 and 9 illustrate targets where the errors in the X and Y direction may be more easily decoupled. When using a target as shown in Figure 8, it may be desirable to scan the probe beam in a direction perpendicular to the lines.
  • the structure of Figure 9 mimics contacts (vias) and interconnections in a Damacene process.
  • the spacing and size of the features are the same as in the actual device. This ensures that the metrology target and the devices are subject to the same aberrations of the lithography projector.
  • the present invention differs from the prior art approaches that use imaging to evaluate overlay in that no attempt is made to form a sharply resolved image of the test target.
  • the features of the target are preferably as small as the critical dimensions of the devices. Such small features cannot be imaged by visible-light optical microscopy.
  • the present invention does not use spatially periodic targets.
  • the targets are not diffraction gratings.
  • One advantage of the present approach is that the isolated targets are smaller than the ones used in prior art. Further, the critical dimensions of the overlay target and the actual devices on the wafer can be the same. Therefore, lens aberrations of the stepper/scanner affect the overlay targets and devices similarly.
  • overlay measurements using spatially periodic targets are ambiguous up to an arbitrary multiple of the period. The measurement described here is not ambiguous by a period because it does not use periodic structures. It should be noted that the targets illustrated in Figures 7 to 9 might be usable with many other prior art optical metrology systems.
  • these targets might be measured with an ellipsometer (spectroscopic or otherwise) or a beam profile reflectometer (BPR) without baffle 80, or beam profiling ellipsometer (BPE), a spectroscopic reflectometer, or a variable angle reflectometer or ellipsometer.
  • the optical instrument can be any instrument that measures properties of light that has interacted with the overlay target as a function of one or more of the independent variables: wavelength, polar angle of incidence, azimuthal angle of incidence, polarization states of the incident and detected light.
  • the data can be processed by a neural-network which is trained previous to the measurements.
  • the neural network can be trained on a set of calculated or measured fields corresponding to known target parameters.
  • the data can be processed by looking up the measured field in a library of previously computed or measured library of fields. The look-up is performed by finding the library entry whose difference from the measured field has the least variance from the norm.
  • the optical components of the analyzer can be of any type typically used in an ellipsometer such as a polarizer or a retarder.
  • the ellipsometric output signals are analyzed in a fashion similar to the prior art approaches for using ellipsometric data to evaluate the geometry of an aperiodic structures.
  • U.S. Patent No. 5,181 ,080 describes a variant of the BPE approach. In this system, a quadrant detector is used to measure the power of the reflected probe beam along two orthogonal axes. Each quadrant generates a response proportional to the integration of all angles of incidence. By manipulating the output of the quadrants, ellipsometric information can be derived.
  • the assignee's Opti-Probe device has multiple measurement technologies in addition to the Beam Profile Reflectometry system. These other technologies include broadband reflectometry and broadband ellipsometry.
  • these measurement technologies include broadband reflectometry and broadband ellipsometry.
  • an incoherent polychromatic probe beam is focused onto the sample.
  • the reflected polychromatic probe beam is monitored at a plurality of wavelengths.
  • reflectometry changes in intensity of the polychromatic probe beam are monitored.
  • ellipsometry changes in polarization state of the polychromatic probe beam are monitored.
  • the output from these additional modules might be useable in combination with the BPR and BPE signals to more accurately evaluate the geometry of the isolated structure.
  • most of the basic hardware elements discussed herein have been known in the prior art. The developments intended to be covered by this disclosure relate to certain applications of that technology. More specifically, it is believed that the BPR and BPE techniques can be used to measure isolated, single (non-repeating) structures which have dimensions in the micron and sub-micron range. These would include, for example, single lines, single vias, single holes and single trenches. It is believed that by focusing a coherent probe beam on the structure and measuring the reflected response, one can rely on scattered light effects to determine the geometry of the structure.
  • the subject invention is also intended to cover the situation where a periodic structure has a size or extent smaller than the probe beam spot. For example, consider a repeating structure having only five or ten lines. If the probe beam spot is greater than the structure, the reflected field would be aperiodic and could not be analyzed with a grating approach. However, using the techniques described herein one could still derive information about the sample.
  • the probe beam spot size would be at least about twice the width of the structure so the grating effects would be minimal.
  • initial experiments have shown that isolated and aperiodic structures can be monitored with the probe beam spatially fixed with respect to the feature, it is within the scope of the subject invention to scan the probe beam with respect to the feature. In such a case, measurements are taken at various positions of the probe beam and the data combined to analyze the sample.
  • Such an approach may be particularly useful with a system operating in accordance with U.S. Patent No. 5J 81 ,080, discussed above.
  • the relative motion of the probe beam with respect to the sample can be achieved using a conventional motion stage. It is also possible to move the optics.

Abstract

L'invention concerne un système de métrologie optique qui est conçu pour réduire au minimum la mesure de la lumière réfléchie spéculairement et mesurer essentiellement la lumière diffusée. Ledit système s'apparente aux systèmes actuels de mesure de profil de faisceau mais comprend un déflecteur mobile permettant de bloquer sélectivement la lumière réfléchie spéculairement. L'invention concerne en outre certaines cibles isolées non périodiques, appropriées pour évaluer une superposition.
PCT/US2004/014547 2003-06-11 2004-05-10 Systeme et procede de metrologie optique de plaquettes semi-conductrices WO2005001577A1 (fr)

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US10/459,631 US7046376B2 (en) 2002-07-05 2003-06-11 Overlay targets with isolated, critical-dimension features and apparatus to measure overlay
US10/459,631 2003-06-11

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5181080A (en) * 1991-12-23 1993-01-19 Therma-Wave, Inc. Method and apparatus for evaluating the thickness of thin films
US5412473A (en) * 1993-07-16 1995-05-02 Therma-Wave, Inc. Multiple angle spectroscopic analyzer utilizing interferometric and ellipsometric devices
US6317211B1 (en) * 1996-05-02 2001-11-13 International Business Machines Corporation Optical metrology tool and method of using same

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5181080A (en) * 1991-12-23 1993-01-19 Therma-Wave, Inc. Method and apparatus for evaluating the thickness of thin films
US5412473A (en) * 1993-07-16 1995-05-02 Therma-Wave, Inc. Multiple angle spectroscopic analyzer utilizing interferometric and ellipsometric devices
US6317211B1 (en) * 1996-05-02 2001-11-13 International Business Machines Corporation Optical metrology tool and method of using same

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