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WO1992008104A1 - Appareil destine a produire des images topographiques de surfaces - Google Patents

Appareil destine a produire des images topographiques de surfaces Download PDF

Info

Publication number
WO1992008104A1
WO1992008104A1 PCT/US1991/007995 US9107995W WO9208104A1 WO 1992008104 A1 WO1992008104 A1 WO 1992008104A1 US 9107995 W US9107995 W US 9107995W WO 9208104 A1 WO9208104 A1 WO 9208104A1
Authority
WO
WIPO (PCT)
Prior art keywords
sample
recited
probe beam
scan
angular deviation
Prior art date
Application number
PCT/US1991/007995
Other languages
English (en)
Inventor
Walter L. Smith
Clifford G. Welles
Albert Bivas
Alan R. George
Jon Opsal
Original Assignee
Therma-Wave, Inc.
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 Therma-Wave, Inc. filed Critical Therma-Wave, Inc.
Publication of WO1992008104A1 publication Critical patent/WO1992008104A1/fr

Links

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
    • 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
    • G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
    • G01B11/303—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces using photoelectric detection means

Definitions

  • the subject invention relates to a device for generating surface topographical images.
  • the device can produce images of angstrom size features and is particularly suitable for analyzing semiconductor wafers.
  • the subject invention includes laser for generating a collimated probe beam.
  • a high numerical aperture lens is used to focus the probe beam onto the surface of the sample with a spot size of about one micron in diameter.
  • the reflected probe beam is directed to a photodetector which can monitor changes in position of the beam that are result of angular deviations produced by surface features of the sample.
  • a high precision stage is provided to scan the sample with respect to the probe beam.
  • Surface features will induce angular deviations of the beam both parallel and perpendicular to the direction of the scan.
  • the angular deviations are converted to lateral displacements when the reflected probe beam passes back up through the lens. These lateral deviations are measured by the photodetector.
  • Images of the surface are created using displacement measurements which are either parallel or perpendicular to the direction of the scan. Images can also be created using various combinations of both orthogonal displacements. As discussed in detail below, different combinations can be used to enhance different kind of topological features.
  • An image of the absolute height of surface features can also be generated by integrating the angular deviation measurements with respect to incremental positions of the scanned probe beam.
  • Figure 1 is a schematic diagram of an apparatus constructed in accordance with the subject invention.
  • Figure 2 is a bottom plan view of a quad cell photodetector.
  • Figures 3a through 3d illustrate the interaction between the probe beam and a surface feature of the sample.
  • Figure 4 is a perspective view of a surface feature which runs along one of the scan directions.
  • FIGS 5a through 5c are simplified illustrations of the images which can be generated with the subject system.
  • Figures 6 through 10 are photographs of various images taken of the surface of a sample highlighting one particular surface feature.
  • Figure 6 is an image which is generated with the subject system using angular deviation measurements parallel to the direction of the scan.
  • Figure 7 is an image which is generated with the subject system using angular deviation measurements perpendicular to the direction of the scan.
  • Figure 8 is an image which is generated with the subject system wherein angular deviation measurements both parallel and perpendicular to the direction of the scan are combined.
  • Figure 9 is an image which is generated with the subject system wherein angular deviation measurements both parallel and perpendicular to the direction of the scan are combined in a different manner.
  • Figure 10 is an image which is generated with the subject system wherein angular deviation measurements both parallel and perpendicular to the direction of the scan are combined in the same manner as in Figure 9 and then inverted.
  • Figure 11 is a line scan which is generated with the subject system using angular deviation measurements to illustrate absolute height variations.
  • Figure 12 is a diagram illustrating an approach for generating a two dimensional image which displays absolute height information.
  • an apparatus 10 for detecting topological features on the surface of a sample 12 and generating images of those features includes a laser 20 for generating a probe beam 22.
  • laser 20 is a linearly polarized HeNe laser generating an output beam 22 of 633 nm having a
  • the probe beam 22 is directed downwardly by a polarizing beam splitter 30 through a quarter wave plate 32.
  • the beam then passes through lens 36 and onto the surface of the sample 12 with 3 mW of incident power.
  • NA 36 is a powerful microscope objective having a high numerical aperture (NA) .
  • the NA of the lens should be at least 0.5 and is preferably on the order of 0.95.
  • This diffraction limited optical arrangement is arranged to produce spot sizes on the sample having a diameter on the order of one micron.
  • the spot size is set to 0.8 microns.
  • the lens is spaced from the surface of the sample an amount substantially equal to its focal length. This position is maintained using an autofocus mechanism discussed in greater detail below.
  • a stage 40 is provided to support the sample 12 and for scanning the sample with respect to the probe beam in two orthogonal directions.
  • a dc servo stage is used, manufactured by Kensington Labs.
  • the stage utilizes an optically encoded feedback control system so movements in either the X or Y direction can be controlled to within 500 angstroms. This stage also provides for rotation of the sample.
  • the reflected probe beam will pass back up through lens 36 and quarter wave plate 32.
  • the two passes through the quarter waveplate 32 function to rotate the polarization of the beam a full 90 degrees so that when the beam reaches splitter 30 it will pass therethrough to fall on photodetector 50.
  • Photodetector 50 is of the type which can detect displacements of the probe beam.
  • a photodetector having an two dimensional array of detecting elements could be used.
  • a quad cell detector is used and the optics are arranged such that the probe beam will underfill the detector. The use and operation of quad cell detectors is well known in the art.
  • the surface of the quad cell detector is illustrated in Figure 2.
  • each of the four quadrants (52, 53, 54, 55) generates -1- separate voltage levels proportional to the power of the light falling on that segment.
  • each of the four quadrants will generate the same voltage.
  • the position of the beam moves from the center (shown schematically as 22a)
  • the voltage levels will vary and position information can be determined.
  • the sum of the output voltage generated by the two quadrants (52, 55) on the left side of Figure 2 would be subtracted from the sum of the output voltage generated by the two quadrants (53, 54) on the right side of the Figure.
  • the displacement in the Y direction would be determined in a similar manner comparing the outputs from the top two quadrants (52, 53) with the bottom two quadrants (54, 55).
  • the difference voltages are divided by the sum of the voltages of all the quadrants to normalize the result.
  • Figures 3a through 3d illustrate how angular deviations of the beam due to changes in surface topography are converted into lateral displacements of the beam at the detector.
  • Figure 3a when the beam is reflected off a flat surface, it will pass back through the center of the lens 36 and strike the detector at the center.
  • the beam will deviate angularly backwards (negative X) , parallel to the direction of the scan as shown in Figure 3b. Since the surface of the sample is substantially in the focal plane of the lens, the reflected beam will be redirected by the lens along a path parallel to but laterally displaced from the incoming probe beam.
  • the amount of negative displacement is proportional to the local slope of the surface feature 60. By monitoring the extent of this displacement, the slope of the surface feature can be determined.
  • Figure 3c illustrates that at the crest of the hillock, where the slope is zero, there will be no displacement and the beam will be once again centered on the detector.
  • the angle of the beam will again deviate in a plane parallel to the direction of the scan but in a forward sense.
  • a positive lateral displacement will occur proportional to the slope of the feature but have an opposite sign (positive X) .
  • a feature which initially produces a negative displacement followed by a positive displacement will be feature which is raised from the surface.
  • a depression or hole will characteristically produce an initial displacement of the probe beam in the positive direction and then a displacement in the negative direction (with an intermediate, zero displacement) .
  • any scan in the Y direction will not produce any angular deviation of the probe beam in that direction and therefore will be reflected back through the lens 36 with no displacement in the Y direction as shown in Figure 4. For this reason, it is desirable to be able to generate images of a sample in both the X and Y directions and images that are based on a combination of both signals so that all features can be imaged.
  • the lens 36 is maintained a distance from the surface of the sample an amount substantially equal to the focal length of the lens. In the case of the preferred 0.95 NA lens, this distance is about 300 microns.
  • the autofocus mechanism includes a servo motor 70 for varying the vertical position of the lens 36.
  • the servo is driven by an analog detection loop which determines if the lens 36 is properly focusing the probe beam.
  • a partially reflective mirror 72 picks off a small portion of the reflected probe beam and directs it to a chopper wheel 74.
  • a lens 76 is positioned in the path of the reflected probe beam such that the chopper wheel 74 is in the focal plane of the lens.
  • the light passing the chopper wheel 74 is imaged on a split cell photodetector 78.
  • the output from quad cell detector can be used to generate images of the surface topography of the sample. This output can be combined in various ways to achieve different results.
  • the combination process can be performed in a processor 90 and then sent to an image generation apparatus 92.
  • the imager 92 can be a video monitor or video hard copy printer.
  • the probe beam is scanned across the sample using the stage along a plurality of parallel lines.
  • the direction of the scan can be referred to as the X direction.
  • the scan will move across a first line taking measurements at discrete intervals.
  • the spacing between the intervals can be adjusted from 500 angstroms to 16,000 angstroms.
  • the increments utilized should be 2000 angstroms or less.
  • the sample is shifted over one increment in a direction perpendicular to the scan line and a new scan' is started. If the smallest measurement increment is chosen, a magnification of 13,600 times can be achieved.
  • features with a height in the range of a few crystallographic dimensions have been clearly observed. For example, a slip line in a silicon wafer approximately 8 angstroms in height, which created a slope of 0.015 degrees over a linear distance of 3 microns was observed.
  • Scans can be executed over regions of different sizes.
  • the preferred embodiment is programmed to generate images ranging from 12 square microns to 800 square microns.
  • FIGS. 5a though 5c are simplified illustrations of basic scans of three different features which are obtained using signals either parallel or perpendicular to the scan (X) direction. In these figures, the imager is programmed such that a zero signal or no displacement will be represented by the middle of a grey scale.
  • Figure 5a illustrates the images which would be generated of a hillock using this convention.
  • the signals parallel to the direction of the scan (X direction) will first have a large negative value (dark) move to neutral and then increase to a maximum positive value.
  • This convention is not unlike having a light source illuminate the feature from the top of the figure.
  • the displacements of the beam which are perpendicular to the scan direction (Y direction) will generate an image where the illumination source appears to be from the left.
  • the illumination analogy applies for each of the Figures and is useful in interpreting the images.
  • Figure 5b shows the images generated from the parallel (X) and perpendicular (Y) signals when scanning a pit or depression in the sample surface. It should be noted that the shading patterns are reversed from Figure 5a.
  • Figure 5c illustrates the images that would be generated from a notch or depression at the edge of the sample.
  • Figures 6 through 11 are photographs of actual images taken with the device of the subject invention.
  • the surface feature imaged consists of an engraved letter "C" enclosed within an engraved octagon design.
  • the octagon design is 100 microns across and the engravings have a depth of 0.1 microns (1000 angstroms) .
  • the scanning increment was set to 4000 angstroms.
  • Figure 6 is an image of the feature using signals generated from displacements parallel to the direction of the scan (X direction) .
  • this convention tends to produce images where a light source appears to illuminate the feature from the top of the image.
  • the left and right hand sides of the octagon and the left hand side of the letter "C" are suppressed. This result occurs because the slope of these features is constant along the axis parallel to the scan.
  • Figure 7 is an image based on beam displacement in a direction perpendicular to the scan (Y direction) .
  • the top and bottom of both the octagon and letter "C" are suppressed since these features do not change slope in the Y direction.
  • Figure 8 illustrates one of those images.
  • the displacements in both the X and Y direction are summed and then plotted. This approach has the effect of shifting the source of illumination 45 degrees so that all of the X and Y features are enhanced. It should be noted that some of the angled portions of the feature are less prominent.
  • Image value X cos ⁇ + Y sin ⁇ where ⁇ is the desired azimuthal angle. Note that when ⁇ is zero degrees, the image generated will be like that shown in Figure 6, whereas when ⁇ is 90 degrees, the image generated will be like Figure 7.
  • this formula eliminates the sign (+ or -) from the data and produces an absolute value of the displacement or slope of the feature.
  • the steeper the feature the more it will be illuminated, regardless of whether it is a down slope or an up slope. This type of image is desirable when one wants to obtain an overall picture of the variations in surface topography without regard to the type of feature being imaged.
  • the data points used to generate the image in Figure 10 are obtained by first calculating the value of R as set forth above in equation 2. Thereafter, this value is simply inverted so that the highest values are given the darkest color and the lowest values the brightest color. Similar to Figure 9, this image also gives an overall picture of variations in surface topography. However, this image has the added advantage in that it is more consistent with human observation in standard lighting conditions wherein flat areas are brightly illuminated and slopes tend to be shaded.
  • the subject invention can be further used to determine the absolute value of the height of a feature.
  • the displacements in the beam can be converted directly into the slope of the surface. Height information can be determined by integrating this slope information with respect to the increments between data points.
  • the stage is typically moved in increments that range from 500 angstroms to 2000 angstroms. Using these small increments for the integration, extremely accurate height information can be generated.
  • Figure 11 is a graph which gives height information with respect to the position of the beam on the sample along a single scan line. An image similar to Figures 6 through 10 could be generated from multiple parallel line scans. In order to generate a two dimensional image which displays absolute vertical height information, both X and Y angular deviation signals are required. This requirement can best be appreciated by referring to Figure 12.
  • Figure 12 is a schematic illustration of a rectangular scan area on the surface of the sample. Data point 93 is located at point X ⁇ , Y ⁇ , within the scanned region.
  • the first step is to integrate the individual displacement (slope) measurements along the X axis from point 94 to point 95 (X ⁇ , Y 0 ) as shown in equation (3) .
  • the value can be more accurately determined by performing the complimentary calculations along a path from the starting point 94, to point 96 (X Q , Y ⁇ ) and then to point 93 according to formulas (5) and (6) below.
  • the subject topographical imaging system has been incorporated into a thermal wave imaging system marketed by Therma-Wave, Inc., the assignee of the subject invention.
  • the thermal wave and topographical images provide a powerful tool for the analysis of semiconductor IC devices. More particularly, one can compare the images generated of an area of a wafer to determine whether the observable artifacts are caused by either surface and subsurface anomalies.
  • an apparatus for generating images of the surface topography of a sample In the apparatus, a probe beam is focused and scanned over the surface of the sample. The displacements of the reflected probe beam which are the result of angular deviations in the beam caused by surface features are measured. The displacements are used to generate images of the surface features. The images are derived from displacements either parallel or perpendicular to the direction of the scan. Additional images can be generated using a composite of both displacements.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

Un appareil (10) destiné à produire des images de la topographie de surface d'un échantillon (12) est décrit. Dans ledit appareil, un faisceau-sonde (22) est orienté vers la surface de l'échantillon (12) et balaie cette surface. On mesure les déplacements du faisceau-sonde réfléchi qui sont le résultat des déviations angulaires du faisceau, causées par les caractéristiques de surface. Les déplacements sont utilisés pour produire des images de caractéristiques de surface. Les images sont dérivées de déplacements soit parallèles, soit perpendiculaires à la direction de balayage. Il est possible de produire des images supplémentaires en utilisant une combinaison des deux déplacements.
PCT/US1991/007995 1990-10-24 1991-10-23 Appareil destine a produire des images topographiques de surfaces WO1992008104A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US60247590A 1990-10-24 1990-10-24
US602,475 1990-10-24
US61544790A 1990-11-19 1990-11-19
US615,447 1990-11-19

Publications (1)

Publication Number Publication Date
WO1992008104A1 true WO1992008104A1 (fr) 1992-05-14

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PCT/US1991/007995 WO1992008104A1 (fr) 1990-10-24 1991-10-23 Appareil destine a produire des images topographiques de surfaces

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6453006B1 (en) 2000-03-16 2002-09-17 Therma-Wave, Inc. Calibration and alignment of X-ray reflectometric systems
US6507634B1 (en) 2001-09-19 2003-01-14 Therma-Wave, Inc. System and method for X-ray reflectometry measurement of low density films
US6744850B2 (en) 2001-01-11 2004-06-01 Therma-Wave, Inc. X-ray reflectance measurement system with adjustable resolution
CN100427878C (zh) * 2003-04-01 2008-10-22 希捷科技有限公司 使用垂直入射束偏移法用于超光滑表面的光学轮廓测定仪
WO2009033645A3 (fr) * 2007-09-10 2009-05-07 Eppendorf Ag Système détecteur optique sur un dispositif de traitement de liquides

Citations (5)

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Publication number Priority date Publication date Assignee Title
US3885875A (en) * 1974-07-29 1975-05-27 Zygo Corp Noncontact surface profilometer
US3975102A (en) * 1974-07-29 1976-08-17 Zygo Corporation Scanning photoelectric autocollimator
US4289400A (en) * 1977-03-08 1981-09-15 Sony Corporation Apparatus for measuring a gradient of a surface
US4332477A (en) * 1979-01-09 1982-06-01 Canon Kabushiki Kaisha Flatness measuring apparatus
US4427295A (en) * 1977-12-16 1984-01-24 Canon Kabushiki Kaisha Measuring apparatus

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3885875A (en) * 1974-07-29 1975-05-27 Zygo Corp Noncontact surface profilometer
US3975102A (en) * 1974-07-29 1976-08-17 Zygo Corporation Scanning photoelectric autocollimator
US4289400A (en) * 1977-03-08 1981-09-15 Sony Corporation Apparatus for measuring a gradient of a surface
US4427295A (en) * 1977-12-16 1984-01-24 Canon Kabushiki Kaisha Measuring apparatus
US4332477A (en) * 1979-01-09 1982-06-01 Canon Kabushiki Kaisha Flatness measuring apparatus

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 13, No. 3, August 1971, R.W. HARRISON, "Laser Scanning Surface Profilometer", pages 789-790. *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6453006B1 (en) 2000-03-16 2002-09-17 Therma-Wave, Inc. Calibration and alignment of X-ray reflectometric systems
US6643354B2 (en) 2000-03-16 2003-11-04 Therma-Wave, Inc. Calibration and alignment of X-ray reflectometric systems
US6768785B2 (en) 2000-03-16 2004-07-27 Therma-Wave, Inc. Calibration and alignment of X-ray reflectometric systems
US6987832B2 (en) 2000-03-16 2006-01-17 Kla-Tencor Technologies Corp. Calibration and alignment of X-ray reflectometric systems
US6744850B2 (en) 2001-01-11 2004-06-01 Therma-Wave, Inc. X-ray reflectance measurement system with adjustable resolution
US6507634B1 (en) 2001-09-19 2003-01-14 Therma-Wave, Inc. System and method for X-ray reflectometry measurement of low density films
CN100427878C (zh) * 2003-04-01 2008-10-22 希捷科技有限公司 使用垂直入射束偏移法用于超光滑表面的光学轮廓测定仪
US7916308B2 (en) 2003-04-01 2011-03-29 Seagate Technology Llc Method and optical profiler
WO2009033645A3 (fr) * 2007-09-10 2009-05-07 Eppendorf Ag Système détecteur optique sur un dispositif de traitement de liquides
CN101842671B (zh) * 2007-09-10 2013-06-05 埃佩多夫股份公司 用于处理液体的装置上的光学传感器系统
US8507886B2 (en) 2007-09-10 2013-08-13 Eppendorf Ag Optical sensor system on a device for the treatment of liquids

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