US20040000638A1 - Undercut measurement using sem - Google Patents
Undercut measurement using sem Download PDFInfo
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- US20040000638A1 US20040000638A1 US10/186,797 US18679702A US2004000638A1 US 20040000638 A1 US20040000638 A1 US 20040000638A1 US 18679702 A US18679702 A US 18679702A US 2004000638 A1 US2004000638 A1 US 2004000638A1
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- incident angle
- feature
- angles
- electron beam
- undercut
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
- G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
- H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/26—Electron or ion microscopes
- H01J2237/2611—Stereoscopic measurements and/or imaging
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/26—Electron or ion microscopes
- H01J2237/28—Scanning microscopes
- H01J2237/2813—Scanning microscopes characterised by the application
- H01J2237/2814—Measurement of surface topography
- H01J2237/2815—Depth profile
Definitions
- the present invention relates generally to specimen inspection. More particularly, the present invention relates to e-beam inspection systems.
- Semiconductor manufacturing processes include deposition and etching of various material layers on a semiconductor wafer. During the processing, various microscopic features (trenches, islands, and so on) are created on the wafer. Often times, the cross-sectional profile of a microscopic feature may be of interest to the manufacturer. In particular, the angle of undercut of a sidewall of the feature may be of interest.
- SEM Scanning electron microscopy
- FIB focus ion beam
- FIB systems impinge a focused beam on ions (for example, gallium ions) onto a specimen.
- the focused ion beam may act to precision mill the specimen at high beam currents or to image the specimen at low beam currents (in which case less material is sputtered).
- IEM transmission electron microscope
- Recent FIB systems may be utilized for in-situ cross-section preparation and high-resolution imaging.
- FIB techniques are disadvantageously destructive due to the sputtering or milling of material from the sample.
- FIG. 1A is a conventional image of a cross section of a feature 170 that is slightly undercut on both left and right sides.
- the image of the cross section was obtained by the conventional focused ion beam (FIB) technique.
- FIB focused ion beam
- the FIB technique is disadvantageous in that it requires destruction of the specimen. This is because the FIB technique thins the sample by ion milling.
- FIG. 1B shows a conventional analysis of the cross-sectional FIB image of the feature 170 to determine the undercut angles.
- the analysis gives an outline of the feature 170 .
- the undercut angle may be determined by comparing the actual left 172 -L and right 172 -R sidewalls to vertical reference lines 174 -L and 174 -R, respectively. (The slight asymmetry seen in the reference lines is thought to be due to the milling of the sample.) Analysis of this FIB image indicates a left undercut of about five (5) degrees and a right undercut of about two (2) degrees.
- FIG. 1A is a conventional image of a cross section of a feature that is slightly undercut on both left and right sides.
- FIG. 1B shows a conventional analysis of the cross-sectional FIB image of the feature to determine the undercut angles.
- FIG. 2 is a diagram providing an overview of the technique for measuring undercut angles in accordance with an embodiment of the invention.
- FIGS. 3A and 3B shown experimental electron scans of the undercut feature depicted in FIGS. 1A and 1B.
- FIG. 4A is a graph showing the analysis of data from a series of electron scans at different incidence angles to measure the left undercut in accordance with an embodiment of the invention.
- FIG. 4B is a graph showing the analysis of data from a series of electron scans at different incidence angles to measure the right undercut in accordance with an embodiment of the invention.
- FIGS. 5A through 5D depict simulated electron scans based on a hypothetical feature with ten-degree undercuts on each side.
- FIG. 6 is a graph showing the analysis of the simulated data from FIGS. 5A through 5D in accordance with an embodiment of the invention.
- FIG. 7 depicts one type of SEM system with which the invention may be utilized.
- FIG. 8 depicts another type of SEM system with which the invention may be utilized.
- Embodiments of the invention relates to methods for measuring an undercut of a feature on a specimen using a scanning electron microscope (SEM).
- One method includes illuminating the feature with a primary electron beam at an incident angle, changing the incident angle of the primary electron beam over a set of angles, measuring an intensity of scattered electrons from the feature for each incident angle in the set of angles, and determining a discontinuity in the intensities as a function of the incident angle.
- Another method includes illuminating the feature with primary electrons at an incident angle, measuring an intensity of scattered electrons from the feature by a plurality of detectors at a set of scattering angles, and determining a discontinuity in the intensities as a function of the scattering angle.
- SEM scanning electron microscope
- the SEM includes an electron illumination system for illuminating the feature with a primary electron beam at an incident angle, a mechanism for changing the incident angle of the primary electron beam over a set of angles, a detector for measuring an intensity of scattered electrons from the feature for each incident angle in the set of angles, and a processor for determining a discontinuity in the intensities as a function of the incident angle.
- Another embodiment of the invention relates to an apparatus for measuring an undercut of a feature on a specimen.
- the apparatus includes means for illuminating the feature with a primary electron beam at an incident angle, means for changing the incident angle of the primary electron beam over a set of angles, means for measuring an intensity of scattered electrons from the feature for each incident angle in the set of angles, and means for determining a discontinuity in the intensities as a function of the incident angle.
- the present invention relates to a technique for measuring undercut angles in an advantageously non-destructive manner.
- the technique may be performed using a scanning electron microscope and may be applied to measure undercut angles of features on a semiconductor wafer or other types of specimens.
- the technique may still be applied to measure undercut angles.
- FIG. 2 is a diagram providing an overview of the technique for measuring undercut angles for an undercut feature 202 in accordance with an embodiment of the invention.
- An electron beam 204 with an incident angle of less than the undercut angle (for example, zero degrees) is illustrated on the left side (situation labeled “a”), and an electron beam 210 with an incident angle that is greater than the undercut angle is illustrated on the right side (situation labeled “b”).
- Corresponding electron intensity profiles 206 (for situation “a”) and 214 (for situation “b”) are depicted below.
- the electron intensity profile 206 for the feature 202 is seen to be relatively symmetrical. There is a peak 208 -L on the left side of the profile 206 and a nearly equal sized peak 208 -R on the right side. These peaks in electron intensities are believed by the applicants to be due to emission and collection of scattered electrons from the sidewalls of the feature 202 .
- the electron intensity profile 214 for the feature 202 is seen to be substantially asymmetrical.
- the right-side peak 216 -R is now substantially higher than the left-side peak 216 -L.
- This asymmetry is believed by the applicants to be due to the electron beam 210 being incident from the right side at an angle exceeding the undercut angle of the right sidewall. As a result, it is believed that the incident beam 210 directly illuminates the right sidewall and so causes the emission of a greater number of scattered electrons 212 .
- FIGS. 3A and 3B show experimental electron scans of the undercut feature 170 depicted in FIGS. 1A and 1B.
- the beam tilt was at zero degrees for FIG. 3A and was at 6 . 6 degrees for FIG. 3B.
- Both FIGS. 3A and 3B show electron intensity versus position in the region of the undercut feature 170 .
- the electron scans of FIGS. 3A and 3B do not require destruction of the specimen and were performed prior to the destructive FIB cross sectioning of FIGS. 1A and 1B.
- undercut angles may be determined without the use of destructive FIB sectioning.
- the electron intensity profile 302 for the feature 170 is seen to be relatively symmetrical. There is a peak 304 -L on the left side of the profile 302 and a nearly equal sized peak 304 -R on the right side. The symmetry shown is expected given the zero degree incidence angle of the primary electron beam.
- the electron intensity profile 312 for the feature 170 is seen to be asymmetrical.
- the right-side peak 314 -R is now substantially higher than the left-side peak 314 -L.
- This asymmetry is believed by the applicants to be due to the electron beam being incident from the right side at an angle (6.6 degrees) that exceeds the undercut angle of the right sidewall (approximately 4 degrees).
- the incident beam directly illuminates the right sidewall and so causes the emission of a greater number of scattered electrons.
- the undercut angle is somewhere between zero degrees and 6.6 degrees.
- FIG. 4A is a graph showing the analysis of data from a series of electron scans at different incidence angles to measure the left undercut in accordance with an embodiment of the invention.
- the y-axis shows the ratio between the left peak intensity l(left) and the right peak intensity l(right).
- the x-axis shows the incidence angle of the primary beam (the rock angle) in degrees.
- the peak intensities are measured by the peak heights. However, in other embodiments, it may be possible also to measure the peak intensities using integrated peak areas.
- FIG. 4A we see that there is a discontinuity in the slope of the data at an incident angle of about 4 degrees. This indicates that the left undercut is approximately 4 degrees. This is in relatively close agreement with the FIB cross section measured left undercut of about 5 degrees.
- FIG. 4B is a graph showing the analysis of data from a series of electron scans at different incidence angles to measure the right undercut in accordance with an embodiment of the invention.
- the y-axis shows the ratio between the right peak intensity l(right) and the left peak intensity l(left).
- the x-axis shows the incidence angle of the primary beam (the rock angle) in degrees.
- FIGS. 5A through 5D depict simulated electron scans based on a hypothetical feature with ten-degree undercuts on each side. Each of these figures depicts electron intensity (in arbitrary units) on the y-axis as a function of position on the x-axis.
- FIG. 5A corresponds to low incident angles of six degrees or less and shows a relatively symmetrical profile.
- FIG. 5B corresponds to an incident angle of eleven degrees and shows asymmetry in that the right peak is higher than the left peak.
- FIG. 5C corresponds to an incident angle of seventeen degrees and shows the asymmetry increasing as the right peak becomes even higher.
- FIG. 5D corresponds to an incident angle of twenty-five degrees and shows that a reduction in asymmetry as the right peak is lower than in FIG. 5C.
- FIG. 5D shows that the asymmetry does not continue to increase at very high angles.
- FIG. 6 is a graph showing the analysis of the simulated data from FIGS. 5A through 5D in accordance with an embodiment of the invention.
- Data points in FIG. 6 are at zero degrees (from FIG. 5A), six degrees (from FIG. 5A), eleven degrees (from FIG. 5B), seventeen degrees (from FIG. 5C), and twenty-five degrees (from FIG. 5D).
- the undercut angle is between six degrees and eleven degrees. This is a good result because the simulations are based on an undercut angle of ten degrees. Of course, further simulations at closer angles may be performed to more precisely determine the undercut angle.
- SEM Scanning electron microscope
- the SEM system 10 depicted in FIG. 7 is particularly suitable for measurement of critical dimensions and is described in detail in U.S. Pat. No. 5,869,833, entitled “Electron Beam Dose Control for Scanning Electron Microscopy and Critical Dimension Measurement Instruments,” issued to Richardson et al. and assigned to KLA-Tencor Corporation of San Jose, Calif.
- the disclosure of U.S. Pat. No. 5,869,833 (the Richardson patent) is hereby incorporated by reference.
- the SEM 10 of FIG. 7 includes an electron beam source 12 , a focusing column and lens assembly 14 , and a scan controller 16 .
- the scan controller 16 scans an electron beam across selected regions of the specimen 20 .
- a detector subsystem 24 to detect secondary and backscattered electrons from the specimen 20 .
- the electron beam source 12 at the top of the SEM system 10 produces an electron beam 34 .
- One implementation that could be used includes an electron source 36 that consists of a thermal field emitter with electrons accelerated by a surface field generated by power supply 32 .
- Alternative electron source embodiments may instead be employed.
- the electrons emitted by the electron source 36 are then, within the beam source 12 , directed through the electrodes 38 and the source lens 39 (each also controlled by the power supply 32 ) to form the electron beam 34 that enters the focusing column and lens assembly 14 to be directed to the specimen 20 .
- the electron beam 34 passes through an aperture 41 , reducing the beam current.
- the beam current may be reduced from approximately 300 pA (pico Amperes) to a range of 5 to 100 pA forming the electron beam that is labeled 34 ′.
- the electron beam 34 ′ then passes through an objective lens 42 that includes magnetic coils 43 and pole pieces 44 to generate a strong magnetic field. That magnetic field is used to focus beam 34 ′ into an electron beam 18 with a spot size that may be, for example, about 5 nm (nanometers) when directed at the specimen 20 .
- a bias may be applied by a power supply 52 to the specimen 20 to create a decelerating field to slow down the electrons in the beam 18 as the electrons approach the specimen 20 .
- the electron beam 18 may be raster scanned over the specimen 20 and the secondary and backscattered electron signal 28 may be detected by the detector subsystem 24 .
- the secondary and backscattered electrons 28 are released as a result of the interaction of the electron beam 18 with specimen 20 and are directed back toward the objective lens 42 .
- electrons 28 may spiral through the objective lens 42 (as a result of the magnetic field), and then travel toward the detector subsystem 24 as they leave the field within the lens 42 .
- the specimen 20 may be comprised of a variety of materials that may be conductive, insulating, or semiconducting.
- a sub-area within the specimen 20 may be of particular interest for scanning to determine features of that sub-area.
- An image processor and display subsystem 26 may develop the image of the sub-area.
- the specimen 20 may be a semiconductor wafer and a sub-area of the wafer may be a portion of a circuit die on the wafer.
- the detector subsystem 24 may be selected to have a bandwidth that is at least adequate to detect the secondary and backscattered electrons that form the electron signal 28 .
- the detector subsystem 24 may include a micro-channel plate, micro-sphere plate, semiconductor diode, or a scintillator and photo-multiplier assembly.
- the detector subsystem 24 illustrated in FIG. 7 includes a detector 55 and collector plat 56 .
- the secondary and backscattered electron signal 28 is received by the detector 55 and then collected by the collector plate 56 .
- the collector plate 56 generates a signal that is received by the image processor and dispay subsystem 26 .
- the image processor and display subsystem 26 may amplify the signal by an amplifier 58 before the signal is input into an image generator 59 .
- the location of the electron beam 18 on the specimen 20 is controlled by the scan controller 16 .
- the scan controller 16 illustrated in FIG. 7 includes scan plates 45 that are located within the magnetic field created by coils 43 and pole pieces 44 .
- the scan plates 45 are powered by a raster generator 48 (via signals on lines 46 and 47 ) to direct the electron beam 18 in both the x and y directions across the specimen 20 .
- FIG. 8 is a simplified schematic representation of the paths of the primary, secondary, backscattered and transmitted electrons through the electron optical column and collection system for electron beam inspection.
- FIG. 8 shows a schematic diagram of the various electron beam paths within the column and below substrate 57 . Electrons are emitted radially from field emission cathode 81 and appear to originate from a very small bright point source. Under the combined action of the accelerating field and condenser lens magnetic field, the beam is collimated into a parallel beam. Gun anode aperture 87 masks off electrons emitted at unusable angles, while the remaining beam continues on to beam limiting aperture 99 .
- An upper deflector (not depicted) is used for stigmation and alignment, ensuring that the final beam is round and that it passes through the center of the objective lens 104 comprising elements 105 , 106 and 107 .
- a condenser lens (not depicted) is mechanically centered to the axis defined by cathode 81 and beam limiting aperture 99 . The deflection follows the path shown, so that the scanned, focused probe (beam at point of impact with the substrate) emerges from the objective lens 104 .
- Wien filter deflectors 112 and 113 deflect the secondary electron beam 167 into detector 117 .
- the transmitted beam 108 passes through electrode system 123 and 124 that spreads the beam 108 before it hits the detector 129 .
- the secondary electron beam is directed by stronger Wien filter deflections toward the low voltage secondary electron detector 160 that may be the same detector used for backscatter imaging at high voltage. Further detail on the system and its operation is described in the Meisberger patent.
- the incidence angle of the primary electron beam may be varied by appropriate adjustment of the currents in the objective lenses that focus the beam onto the specimen.
- the incidence angle of the primary electron beam may be varied by tilting the stage holding the specimen.
- this embodiment may avoid the blurring of the scanned image that occurs when the incident beam is tilted.
- electron detection at a range of angles may be used to measure the undercut angle.
- Such an embodiment may include multiple electron detectors at different scattering angles and application of a non-uniform extracting field to differentiate between scattered electrons at the different scattering angles.
- the multiple detectors would be oriented such that the sidewall of interest is within direct line-of-sight of the detectors at higher detecting angles so that a discontinuity occurs between a first detector without direct line-of-sight and a second detector with direct line-of-sight.
- the measured undercut angle may correspond to the detecting angle at which the discontinuity is determined to occur.
Abstract
Description
- 1. Field of the Invention
- The present invention relates generally to specimen inspection. More particularly, the present invention relates to e-beam inspection systems.
- 2. Description of the Background Art
- Semiconductor manufacturing processes include deposition and etching of various material layers on a semiconductor wafer. During the processing, various microscopic features (trenches, islands, and so on) are created on the wafer. Often times, the cross-sectional profile of a microscopic feature may be of interest to the manufacturer. In particular, the angle of undercut of a sidewall of the feature may be of interest.
- Scanning electron microscopy (SEM) may be used to inspect a wafer, and the rock angle of the incident beam may be varied in an attempt to view an undercut. Unfortunately, SEM images tend to have significant resolution degradation when taken at large rock angles. This blurring of the images makes impractical the determination of large undercut angles by viewing SEM images at large rock angles.
- Another conventional technique for determining undercut angles is by way of focus ion beam (FIB) sections. FIB systems impinge a focused beam on ions (for example, gallium ions) onto a specimen. The focused ion beam may act to precision mill the specimen at high beam currents or to image the specimen at low beam currents (in which case less material is sputtered). Hence, an FIB system may be used in preparing a cross-section specimen for transmission electron microscope (IEM) imaging. Recent FIB systems may be utilized for in-situ cross-section preparation and high-resolution imaging. However, FIB techniques are disadvantageously destructive due to the sputtering or milling of material from the sample.
- FIG. 1A is a conventional image of a cross section of a
feature 170 that is slightly undercut on both left and right sides. The image of the cross section was obtained by the conventional focused ion beam (FIB) technique. As mentioned above, the FIB technique is disadvantageous in that it requires destruction of the specimen. This is because the FIB technique thins the sample by ion milling. - FIG. 1B shows a conventional analysis of the cross-sectional FIB image of the
feature 170 to determine the undercut angles. The analysis gives an outline of thefeature 170. Using the outline of thefeature 170, the undercut angle may be determined by comparing the actual left 172-L and right 172-R sidewalls to vertical reference lines 174-L and 174-R, respectively. (The slight asymmetry seen in the reference lines is thought to be due to the milling of the sample.) Analysis of this FIB image indicates a left undercut of about five (5) degrees and a right undercut of about two (2) degrees. - FIG. 1A is a conventional image of a cross section of a feature that is slightly undercut on both left and right sides.
- FIG. 1B shows a conventional analysis of the cross-sectional FIB image of the feature to determine the undercut angles.
- FIG. 2 is a diagram providing an overview of the technique for measuring undercut angles in accordance with an embodiment of the invention.
- FIGS. 3A and 3B shown experimental electron scans of the undercut feature depicted in FIGS. 1A and 1B.
- FIG. 4A is a graph showing the analysis of data from a series of electron scans at different incidence angles to measure the left undercut in accordance with an embodiment of the invention.
- FIG. 4B is a graph showing the analysis of data from a series of electron scans at different incidence angles to measure the right undercut in accordance with an embodiment of the invention.
- FIGS. 5A through 5D depict simulated electron scans based on a hypothetical feature with ten-degree undercuts on each side.
- FIG. 6 is a graph showing the analysis of the simulated data from FIGS. 5A through 5D in accordance with an embodiment of the invention.
- FIG. 7 depicts one type of SEM system with which the invention may be utilized.
- FIG. 8 depicts another type of SEM system with which the invention may be utilized.
- Embodiments of the invention relates to methods for measuring an undercut of a feature on a specimen using a scanning electron microscope (SEM). One method includes illuminating the feature with a primary electron beam at an incident angle, changing the incident angle of the primary electron beam over a set of angles, measuring an intensity of scattered electrons from the feature for each incident angle in the set of angles, and determining a discontinuity in the intensities as a function of the incident angle. Another method includes illuminating the feature with primary electrons at an incident angle, measuring an intensity of scattered electrons from the feature by a plurality of detectors at a set of scattering angles, and determining a discontinuity in the intensities as a function of the scattering angle.
- Another embodiment of the invention relates to a scanning electron microscope (SEM) for measuring an undercut of a feature on a specimen. The SEM includes an electron illumination system for illuminating the feature with a primary electron beam at an incident angle, a mechanism for changing the incident angle of the primary electron beam over a set of angles, a detector for measuring an intensity of scattered electrons from the feature for each incident angle in the set of angles, and a processor for determining a discontinuity in the intensities as a function of the incident angle.
- Another embodiment of the invention relates to an apparatus for measuring an undercut of a feature on a specimen. The apparatus includes means for illuminating the feature with a primary electron beam at an incident angle, means for changing the incident angle of the primary electron beam over a set of angles, means for measuring an intensity of scattered electrons from the feature for each incident angle in the set of angles, and means for determining a discontinuity in the intensities as a function of the incident angle.
- The present invention relates to a technique for measuring undercut angles in an advantageously non-destructive manner. The technique may be performed using a scanning electron microscope and may be applied to measure undercut angles of features on a semiconductor wafer or other types of specimens. In accordance with one embodiment, even if the images have substantial resolution degradation (due to large rock angles), the technique may still be applied to measure undercut angles.
- FIG. 2 is a diagram providing an overview of the technique for measuring undercut angles for an
undercut feature 202 in accordance with an embodiment of the invention. Anelectron beam 204 with an incident angle of less than the undercut angle (for example, zero degrees) is illustrated on the left side (situation labeled “a”), and anelectron beam 210 with an incident angle that is greater than the undercut angle is illustrated on the right side (situation labeled “b”). Corresponding electron intensity profiles 206 (for situation “a”) and 214 (for situation “b”) are depicted below. - For situation “a”, the
electron intensity profile 206 for thefeature 202 is seen to be relatively symmetrical. There is a peak 208-L on the left side of theprofile 206 and a nearly equal sized peak 208-R on the right side. These peaks in electron intensities are believed by the applicants to be due to emission and collection of scattered electrons from the sidewalls of thefeature 202. - For situation “b”, the
electron intensity profile 214 for thefeature 202 is seen to be substantially asymmetrical. The right-side peak 216-R is now substantially higher than the left-side peak 216-L. This asymmetry is believed by the applicants to be due to theelectron beam 210 being incident from the right side at an angle exceeding the undercut angle of the right sidewall. As a result, it is believed that theincident beam 210 directly illuminates the right sidewall and so causes the emission of a greater number of scatteredelectrons 212. - FIGS. 3A and 3B show experimental electron scans of the undercut
feature 170 depicted in FIGS. 1A and 1B. The beam tilt was at zero degrees for FIG. 3A and was at 6.6 degrees for FIG. 3B. Both FIGS. 3A and 3B show electron intensity versus position in the region of the undercutfeature 170. The electron scans of FIGS. 3A and 3B do not require destruction of the specimen and were performed prior to the destructive FIB cross sectioning of FIGS. 1A and 1B. By using the present invention, undercut angles may be determined without the use of destructive FIB sectioning. - As can be seen from FIG. 3A, the
electron intensity profile 302 for thefeature 170 is seen to be relatively symmetrical. There is a peak 304-L on the left side of theprofile 302 and a nearly equal sized peak 304-R on the right side. The symmetry shown is expected given the zero degree incidence angle of the primary electron beam. - On the other hand, in FIG. 3B, the
electron intensity profile 312 for thefeature 170 is seen to be asymmetrical. The right-side peak 314-R is now substantially higher than the left-side peak 314-L. This asymmetry is believed by the applicants to be due to the electron beam being incident from the right side at an angle (6.6 degrees) that exceeds the undercut angle of the right sidewall (approximately 4 degrees). As a result, it is believed that the incident beam directly illuminates the right sidewall and so causes the emission of a greater number of scattered electrons. In accordance with an embodiment of the invention, it may be determined from FIGS. 3A and 3B that the undercut angle is somewhere between zero degrees and 6.6 degrees. - Note that the peaks are wider in FIG. 3B than the peaks in FIG. 3A. This broadening of the peaks corresponds to the blurring of the detected image that occurs when the incident beam is tilted in the SEM. It is believed that this blurring that makes the asymmetry between right and left intensities difficult to detect visually from the scanned image. Hence, a preferred embodiment of the invention quantitatively analyzes the scanned data.
- FIG. 4A is a graph showing the analysis of data from a series of electron scans at different incidence angles to measure the left undercut in accordance with an embodiment of the invention. The y-axis shows the ratio between the left peak intensity l(left) and the right peak intensity l(right). The x-axis shows the incidence angle of the primary beam (the rock angle) in degrees. In a preferred embodiment, the peak intensities are measured by the peak heights. However, in other embodiments, it may be possible also to measure the peak intensities using integrated peak areas. In the graph of FIG. 4A, we see that there is a discontinuity in the slope of the data at an incident angle of about 4 degrees. This indicates that the left undercut is approximately 4 degrees. This is in relatively close agreement with the FIB cross section measured left undercut of about 5 degrees.
- FIG. 4B is a graph showing the analysis of data from a series of electron scans at different incidence angles to measure the right undercut in accordance with an embodiment of the invention. The y-axis shows the ratio between the right peak intensity l(right) and the left peak intensity l(left). The x-axis shows the incidence angle of the primary beam (the rock angle) in degrees. In the graph of FIG. 4B, we see that there is a discontinuity in the slope of the data at an incident angle of about +3 degrees. This indicates that the right undercut is approximately 3 degrees. This is in relatively close agreement with the FIB cross section measured left undercut of about 2 degrees.
- FIGS. 5A through 5D depict simulated electron scans based on a hypothetical feature with ten-degree undercuts on each side. Each of these figures depicts electron intensity (in arbitrary units) on the y-axis as a function of position on the x-axis. FIG. 5A corresponds to low incident angles of six degrees or less and shows a relatively symmetrical profile. FIG. 5B corresponds to an incident angle of eleven degrees and shows asymmetry in that the right peak is higher than the left peak. FIG. 5C corresponds to an incident angle of seventeen degrees and shows the asymmetry increasing as the right peak becomes even higher. Finally, FIG. 5D corresponds to an incident angle of twenty-five degrees and shows that a reduction in asymmetry as the right peak is lower than in FIG. 5C. Thus, FIG. 5D shows that the asymmetry does not continue to increase at very high angles.
- FIG. 6 is a graph showing the analysis of the simulated data from FIGS. 5A through 5D in accordance with an embodiment of the invention. Data points in FIG. 6 are at zero degrees (from FIG. 5A), six degrees (from FIG. 5A), eleven degrees (from FIG. 5B), seventeen degrees (from FIG. 5C), and twenty-five degrees (from FIG. 5D). As indicated from FIG. 6, the undercut angle is between six degrees and eleven degrees. This is a good result because the simulations are based on an undercut angle of ten degrees. Of course, further simulations at closer angles may be performed to more precisely determine the undercut angle.
- Scanning electron microscope (SEM) systems are shown in FIGS. 7 and 8 as examples of SEM systems with which the invention may be utilized. The present invention may be utilized in other types of SEM systems as well.
- The
SEM system 10 depicted in FIG. 7 is particularly suitable for measurement of critical dimensions and is described in detail in U.S. Pat. No. 5,869,833, entitled “Electron Beam Dose Control for Scanning Electron Microscopy and Critical Dimension Measurement Instruments,” issued to Richardson et al. and assigned to KLA-Tencor Corporation of San Jose, Calif. The disclosure of U.S. Pat. No. 5,869,833 (the Richardson patent) is hereby incorporated by reference. - The
SEM 10 of FIG. 7 includes anelectron beam source 12, a focusing column and lens assembly 14, and ascan controller 16. Thescan controller 16 scans an electron beam across selected regions of thespecimen 20. Also included is adetector subsystem 24 to detect secondary and backscattered electrons from thespecimen 20. - The
electron beam source 12 at the top of theSEM system 10 produces anelectron beam 34. One implementation that could be used includes anelectron source 36 that consists of a thermal field emitter with electrons accelerated by a surface field generated bypower supply 32. Alternative electron source embodiments may instead be employed. The electrons emitted by theelectron source 36 are then, within thebeam source 12, directed through theelectrodes 38 and the source lens 39 (each also controlled by the power supply 32) to form theelectron beam 34 that enters the focusing column and lens assembly 14 to be directed to thespecimen 20. - In the focusing column and lens assembly14, the
electron beam 34 passes through anaperture 41, reducing the beam current. For example, the beam current may be reduced from approximately 300 pA (pico Amperes) to a range of 5 to 100 pA forming the electron beam that is labeled 34′. Theelectron beam 34′ then passes through anobjective lens 42 that includesmagnetic coils 43 and pole pieces 44 to generate a strong magnetic field. That magnetic field is used to focusbeam 34′ into anelectron beam 18 with a spot size that may be, for example, about 5 nm (nanometers) when directed at thespecimen 20. A bias may be applied by apower supply 52 to thespecimen 20 to create a decelerating field to slow down the electrons in thebeam 18 as the electrons approach thespecimen 20. - In operation, the
electron beam 18 may be raster scanned over thespecimen 20 and the secondary and backscatteredelectron signal 28 may be detected by thedetector subsystem 24. The secondary and backscatteredelectrons 28 are released as a result of the interaction of theelectron beam 18 withspecimen 20 and are directed back toward theobjective lens 42. Aselectrons 28 are released, they may spiral through the objective lens 42 (as a result of the magnetic field), and then travel toward thedetector subsystem 24 as they leave the field within thelens 42. Typically, thespecimen 20 may be comprised of a variety of materials that may be conductive, insulating, or semiconducting. A sub-area within thespecimen 20 may be of particular interest for scanning to determine features of that sub-area. An image processor anddisplay subsystem 26 may develop the image of the sub-area. For example, thespecimen 20 may be a semiconductor wafer and a sub-area of the wafer may be a portion of a circuit die on the wafer. - The
detector subsystem 24 may be selected to have a bandwidth that is at least adequate to detect the secondary and backscattered electrons that form theelectron signal 28. For example, thedetector subsystem 24 may include a micro-channel plate, micro-sphere plate, semiconductor diode, or a scintillator and photo-multiplier assembly. Thedetector subsystem 24 illustrated in FIG. 7 includes adetector 55 andcollector plat 56. The secondary and backscatteredelectron signal 28 is received by thedetector 55 and then collected by thecollector plate 56. Thecollector plate 56 generates a signal that is received by the image processor anddispay subsystem 26. The image processor anddisplay subsystem 26 may amplify the signal by anamplifier 58 before the signal is input into animage generator 59. - The location of the
electron beam 18 on thespecimen 20 is controlled by thescan controller 16. Thescan controller 16 illustrated in FIG. 7 includesscan plates 45 that are located within the magnetic field created bycoils 43 and pole pieces 44. Thescan plates 45 are powered by a raster generator 48 (via signals onlines 46 and 47) to direct theelectron beam 18 in both the x and y directions across thespecimen 20. - The SEM system depicted in FIG. 8 is described in U.S. Pat. No. 5,578,821, entitled “Electron Beam Inspection System and Method,” issued to Meisberger et al. and assigned to KLA-Tencor Corporation of San Jose, Calif. The disclosure of U.S. Pat. No. 5,578,821 (the Meisberger patent) is hereby incorporated by reference.
- FIG. 8 is a simplified schematic representation of the paths of the primary, secondary, backscattered and transmitted electrons through the electron optical column and collection system for electron beam inspection. In brief, FIG. 8 shows a schematic diagram of the various electron beam paths within the column and below
substrate 57. Electrons are emitted radially fromfield emission cathode 81 and appear to originate from a very small bright point source. Under the combined action of the accelerating field and condenser lens magnetic field, the beam is collimated into a parallel beam.Gun anode aperture 87 masks off electrons emitted at unusable angles, while the remaining beam continues on tobeam limiting aperture 99. An upper deflector (not depicted) is used for stigmation and alignment, ensuring that the final beam is round and that it passes through the center of the objective lens 104 comprising elements 105, 106 and 107. A condenser lens (not depicted) is mechanically centered to the axis defined bycathode 81 andbeam limiting aperture 99. The deflection follows the path shown, so that the scanned, focused probe (beam at point of impact with the substrate) emerges from the objective lens 104. - In High Voltage mode operation,
Wien filter deflectors secondary electron beam 167 intodetector 117. When partially transparent masks are imaged, the transmittedbeam 108 passes through electrode system 123 and 124 that spreads thebeam 108 before it hits thedetector 129. In Low Voltage mode operation, the secondary electron beam is directed by stronger Wien filter deflections toward the low voltagesecondary electron detector 160 that may be the same detector used for backscatter imaging at high voltage. Further detail on the system and its operation is described in the Meisberger patent. - In accordance with one embodiment of the invention, the incidence angle of the primary electron beam may be varied by appropriate adjustment of the currents in the objective lenses that focus the beam onto the specimen. In accordance with another embodiment of the invention, the incidence angle of the primary electron beam may be varied by tilting the stage holding the specimen Advantageously, this embodiment may avoid the blurring of the scanned image that occurs when the incident beam is tilted.
- In accordance with an alternate embodiment, electron detection at a range of angles may be used to measure the undercut angle. Such an embodiment may include multiple electron detectors at different scattering angles and application of a non-uniform extracting field to differentiate between scattered electrons at the different scattering angles. The multiple detectors would be oriented such that the sidewall of interest is within direct line-of-sight of the detectors at higher detecting angles so that a discontinuity occurs between a first detector without direct line-of-sight and a second detector with direct line-of-sight. In that case, the measured undercut angle may correspond to the detecting angle at which the discontinuity is determined to occur.
- In the above description, numerous specific details are given to provide a thorough understanding of embodiments of the invention. However, the above description of illustrated embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the invention. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
- These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.
Claims (21)
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US10/186,797 US6670612B1 (en) | 2002-07-01 | 2002-07-01 | Undercut measurement using SEM |
JP2003270078A JP4469572B2 (en) | 2002-07-01 | 2003-07-01 | Undercut measurement method using SEM |
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US10/186,797 US6670612B1 (en) | 2002-07-01 | 2002-07-01 | Undercut measurement using SEM |
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US20040000638A1 true US20040000638A1 (en) | 2004-01-01 |
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US20060147489A1 (en) * | 2003-03-28 | 2006-07-06 | Conor Medsystems, Inc. | Implantable medical device with beneficial agent concentration gradient |
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AU2003263776A1 (en) * | 2002-07-11 | 2004-02-02 | Applied Materials Israel, Ltd | Method and apparatus for measuring critical dimensions with a particle beam |
DE102004004597B4 (en) * | 2004-01-29 | 2008-08-07 | Qimonda Ag | Method for measuring a structure on a semiconductor wafer with a scanning electron microscope |
US7355709B1 (en) | 2004-02-23 | 2008-04-08 | Kla-Tencor Technologies Corp. | Methods and systems for optical and non-optical measurements of a substrate |
JP5367549B2 (en) | 2009-12-07 | 2013-12-11 | 株式会社東芝 | Substrate measurement method |
WO2013183057A1 (en) * | 2012-06-05 | 2013-12-12 | B-Nano Ltd. | A system and method for performing analysis of materials in a non-vacuum environment using an electron microscope |
US20160336143A1 (en) * | 2015-05-15 | 2016-11-17 | Kabushiki Kaisha Toshiba | Charged particle beam apparatus and method of calibrating sample position |
TWI797449B (en) * | 2019-05-21 | 2023-04-01 | 美商應用材料股份有限公司 | Enhanced cross sectional features measurement methodology and system |
US11264202B2 (en) * | 2020-05-18 | 2022-03-01 | Applied Materials Israel Ltd. | Generating three dimensional information regarding structural elements of a specimen |
CN112563149B (en) * | 2020-12-11 | 2023-12-01 | 苏州工业园区纳米产业技术研究院有限公司 | Method for accurately measuring drilling size and stripping process |
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JPS56114269A (en) * | 1980-02-15 | 1981-09-08 | Internatl Precision Inc | Scanning type electronic microscope |
JPH01311551A (en) * | 1988-06-08 | 1989-12-15 | Toshiba Corp | Pattern shape measuring device |
JPH02249908A (en) * | 1989-03-24 | 1990-10-05 | Dainippon Printing Co Ltd | Method for inspecting resist pattern |
JPH07111336B2 (en) * | 1990-02-07 | 1995-11-29 | 株式会社東芝 | Pattern dimension measuring method and device |
US6411377B1 (en) * | 1991-04-02 | 2002-06-25 | Hitachi, Ltd. | Optical apparatus for defect and particle size inspection |
JP3730263B2 (en) * | 1992-05-27 | 2005-12-21 | ケーエルエー・インストルメンツ・コーポレーション | Apparatus and method for automatic substrate inspection using charged particle beam |
JP3265724B2 (en) * | 1993-07-14 | 2002-03-18 | 株式会社日立製作所 | Charged particle beam equipment |
US5739909A (en) * | 1995-10-10 | 1998-04-14 | Lucent Technologies Inc. | Measurement and control of linewidths in periodic structures using spectroscopic ellipsometry |
US5869833A (en) * | 1997-01-16 | 1999-02-09 | Kla-Tencor Corporation | Electron beam dose control for scanning electron microscopy and critical dimension measurement instruments |
US6066849A (en) * | 1997-01-16 | 2000-05-23 | Kla Tencor | Scanning electron beam microscope |
US6054710A (en) * | 1997-12-18 | 2000-04-25 | Cypress Semiconductor Corp. | Method and apparatus for obtaining two- or three-dimensional information from scanning electron microscopy |
US6031614A (en) * | 1998-12-02 | 2000-02-29 | Siemens Aktiengesellschaft | Measurement system and method for measuring critical dimensions using ellipsometry |
JP4361661B2 (en) * | 2000-03-24 | 2009-11-11 | 富士通マイクロエレクトロニクス株式会社 | Line width measurement method |
US6472662B1 (en) * | 2000-08-30 | 2002-10-29 | International Business Machines Corporation | Automated method for determining several critical dimension properties from scanning electron microscope by using several tilted beam or sample scans |
US6911349B2 (en) * | 2001-02-16 | 2005-06-28 | Boxer Cross Inc. | Evaluating sidewall coverage in a semiconductor wafer |
JP4094327B2 (en) * | 2002-04-10 | 2008-06-04 | 株式会社日立ハイテクノロジーズ | PATTERN MEASURING METHOD, PATTERN MEASURING DEVICE, AND PATTERN PROCESS CONTROL METHOD |
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2002
- 2002-07-01 US US10/186,797 patent/US6670612B1/en not_active Expired - Lifetime
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Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20060147489A1 (en) * | 2003-03-28 | 2006-07-06 | Conor Medsystems, Inc. | Implantable medical device with beneficial agent concentration gradient |
US8449901B2 (en) | 2003-03-28 | 2013-05-28 | Innovational Holdings, Llc | Implantable medical device with beneficial agent concentration gradient |
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JP2004132956A (en) | 2004-04-30 |
JP4469572B2 (en) | 2010-05-26 |
US6670612B1 (en) | 2003-12-30 |
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