WO2001084590A2 - Procede et appareil d'imagerie d'un echantillon, par utilisation de la detection indirecte en colonne d'electrons secondaires dans une microcolonne - Google Patents

Procede et appareil d'imagerie d'un echantillon, par utilisation de la detection indirecte en colonne d'electrons secondaires dans une microcolonne Download PDF

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Publication number
WO2001084590A2
WO2001084590A2 PCT/US2001/012172 US0112172W WO0184590A2 WO 2001084590 A2 WO2001084590 A2 WO 2001084590A2 US 0112172 W US0112172 W US 0112172W WO 0184590 A2 WO0184590 A2 WO 0184590A2
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WO
WIPO (PCT)
Prior art keywords
target
electrons
specimen
electron
detector
Prior art date
Application number
PCT/US2001/012172
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English (en)
Other versions
WO2001084590A3 (fr
Inventor
Stuart L. Friedman
Original Assignee
Etec Systems, 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 Etec Systems, Inc. filed Critical Etec Systems, Inc.
Priority to AU2001255373A priority Critical patent/AU2001255373A1/en
Publication of WO2001084590A2 publication Critical patent/WO2001084590A2/fr
Publication of WO2001084590A3 publication Critical patent/WO2001084590A3/fr

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Classifications

    • 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
    • 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
    • H01J37/02—Details
    • H01J37/244—Detectors; Associated components or circuits therefor
    • 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
    • H01J2237/2817—Pattern inspection

Definitions

  • the invention generally relates to the design of microcolumns for scanning electron microscopes used in lithography and inspection of articles.
  • the invention relates to design of microcolumns which utilize indirect detection of secondary electrons.
  • a specimen under investigation is irradiated using a primary electron beam.
  • the interaction of the primary electron beam with the specimen causes the latter to emit secondary electrons with kinetic energies of up to 50 eN.
  • the secondary electrons emitted by the specimen typically carry information about the topographical structure of the specimen.
  • the interaction of the primary electron beam with the specimen also causes the emission of a second class of electrons, called backscattered electrons.
  • the backscattered electrons have energies ranging from 50 eN and up to the kinetic energy of the electrons in the primary electron beam, and carry information about the material composition of the specimen.
  • the secondary and backscattered electrons emitted by the specimen are collected using an electron detector.
  • the electron detector collects the electrons emitted by the specimen and generates an output electrical signal representative of the cumulative charge of the collected electrons, multiplied by the amplification factor of the detector.
  • the electrical signal produced by the electron detector is used in creating an image of the specimen.
  • the created image is indicative of either the topographic or the material structure of the specimen.
  • the scanning of the specimen with the electron beam can be accomplished either by moving the specimen with respect to the stationary electron beam, or by moving the electron beam with respect to the stationary specimen. In some designs, both the specimen and the beam are moved. In the vast majority of such applications the electron beam moves over a fine region (from less than a micron to tens of microns), while the specimen itself moves over a coarser region (from a few tens of microns to many millimeters or even centimeters).
  • the secondary electrons emitted by the specimen typically have a wide kinetic energy distribution. Therefore, the amount of time required for various electrons to reach the electron detector of the column can vary substantially.
  • a wide disparity in the arrival times of the secondary electrons from the specimen results in a decrease in scanning speed of the electron microscope, because the microscope has to "wait" for the slowest electrons emitted by the irradiated spot of the specimen to reach the detector, before the microscope can move on to scan the next spot.
  • the width of the collection time distribution is proportional to the length of the electron's travel path, it is highly advantageous to have a microscope column with small linear dimensions. Such microscope columns have been developed and are known in the art as microcolumns.
  • a typical scanning electron microscope microcolumn 10 is shown in Fig. 1.
  • a primary electron beam 1 produced by the primary beam source S enters the microcolumn 10 from the left and passes through a middle channel 2 thereof.
  • the passing electron beam 1 irradiates a spot on the specimen 3.
  • a set of electron lenses 6 is used to "focus" the primary electron beam 1 on the specimen 3, which may be an article to be inspected.
  • Secondary electrons 4 emitted by the specimen 3 travel back into the column 10, where they are detected by means of an electron detector disposed at either position 5 or position 15.
  • the electron detector can be placed close to the specimen 3, preferably between the specimen 3 and the electron lens 6, at the location designated by numeral 15 in Fig. 1.
  • MCP microchannel plate electron multiplier
  • the electron detector 15 is very close to the specimen 3 and is subject to contamination from specimen outgassing and poor specimen chamber vacuum.
  • the primary electron beam 1 passes through the center of the electron detector 15. Because it is difficult to fabricate an MCP with an active area within a short distance of the primary electron beam axis, the central cone of electrons emitted by the specimen is not detected.
  • One way to avoid the detector contamination problem is to place the electron detector inside the microcolumn, preferably at location 5 in Fig. 1.
  • An in-lens (or in- column) detector would suffer less contamination from the specimen and would permit shorter working distances.
  • achieving large collection efficiencies with an in- column detector remains challenging.
  • a relatively long distance between the specimen and the in-column detector can lead to an unacceptable spread in transit times for the electrons corresponding to a given image pixel.
  • a specimen is induced to emit secondary electrons. This can be accomplished by irradiating the specimen with a primary electron beam. However, the exact manner in which the specimen is induced to emit secondary electrons is not critical to the present invention and, therefore, other methods for inducing secondary electron emission can be used.
  • the inventive method also involves providing a target in the electron microscope microcolumn. The secondary electrons incident on the target produce tertiary electrons, which, in turn, are used to obtain information regarding the specimen. To this end, the tertiary electrons can be detected by an electron detector disposed in, or about the microcolumn.
  • the target is preferably provided with a central opening through which the beam of primary electrons passes towards the specimen.
  • Such opening can have a size slightly exceeding the size of the cross-section of the primary electron beam. Typically, the size of the opening will be between 100 and 400 microns.
  • the shape and the material of the target are optimized to provide for effective operation of the microcolumn.
  • the target can be textured, have an angled structure, a conical structure, a sawtooth shape, or a rough surface.
  • the material of the target can be specially chosen to maximize the yield of tertiary electrons produced thereon, or the target can be coated with such a material.
  • the target can be produced by micromachining or otherwise. It is yet another feature of the invention that the target is arranged such that a normal to its surface points away from a dead region of a detector for detecting the tertiary electrons.
  • the inventive apparatus comprises an electron beam generation and transport system for providing a primary electron beam.
  • the primary electron beam irradiates the specimen and induces it to emit secondary electrons.
  • the secondary electrons strike a target and produce tertiary electrons.
  • the inventive apparatus also includes an electron detector for detecting the tertiary electrons to obtain information regarding the specimen.
  • the inventive apparatus can be further provided with a set of electrostatic electron lenses for focusing the primary electron beam on the specimen.
  • the apparatus can be also provided with a cylindrical electrode for shielding the primary electron beam and the secondary electrons from a bias applied to an input surface of the electron detector.
  • the electron detector is disposed between the target and the specimen, while the electron lenses are placed between the electron detector and the specimen.
  • Fig. 1 shows a schematic diagram of a scanning electron microscope microcolumn.
  • Fig. 2 shows a simulation of the secondary electron trajectories in the inventive microcolumn.
  • Fig. 3 shows a simulation of the tertiary electron trajectories in the inventive microcolumn.
  • Fig. 4 shows an embodiment of the inventive microcolumn.
  • Fig. 5 shows another embodiment of the inventive microcolumn.
  • Fig. 6 shows yet another embodiment of the inventive microcolumn.
  • the inventive indirect in-column detection scheme offers a number of clear and distinct advantages over other detection schemes.
  • the indirect electron detection scheme is defined as one wherein the secondary or backscattered electrons from the specimen first strike a target rather than an active detector. The secondary electrons ⁇ generated at the target ("tertiary" electrons) are then collected using any conventional, active electron detector.
  • the inventive detection method is indirect because the conventional electron detector never sees the electrons from the specimen, but detects only the electrons generated on the target.
  • a target is any solid object, the size and shape of which are relatively unconstrained. The target is passive and will introduce very little gain (less than 10) in the number of the electrons.
  • the active detector which is used to detect tertiary electrons produced on the target, is an MCP or any other electron multiplier.
  • the active electron detector can also be a photodetector such as a photomultiplier tube (PMT) or a photodiode.
  • PMT photomultiplier tube
  • the gain of the active electron detector can be as high as 10 6 .
  • the target can have a substantially small central aperture and secondary electrons traveling close to the optical axis of the microcolumn can strike it.
  • the tertiary electrons incident on the active detector can be spread over a large active area, limiting the saturation and aging effects in the detector that would otherwise occur if a narrow beam of secondaries and backscattered electrons struck the detector directly.
  • Fig. 2 shows simulation results of secondary electron trajectories in the inventive microcolumn, demonstrating the feasibility of the inventive indirect electron detection scheme.
  • over 60% of the secondaries 4 emitted by the specimen 3 with energy of 5 eN pass through electrostatic electron lenses 6.
  • the lenses may be positioned in an einzel mode.
  • the electrons 4 are accelerated in the electric field from the lenses 6 to the target 7.
  • Approximately 10% of the secondary electrons 4 pass through the aperture 2 in the target 7, and 50% of the secondary electrons hit the target 7.
  • the equipotential lines are designated in the figure by the numeral 11.
  • a cylindrical electrode 9 shields electrons (the primary electron beam and the secondary electrons) traveling along the optical axis from the voltage bias applied to the input surface of the electron detector 5. Further optimization of both the geometry and the applied voltages can be used to increase the fraction of the secondary electrons 4 striking the target 7 as well as the number of tertiaries 8 reaching the electron detector 5.
  • the biasing potentials can be applied to the components of the microcolumn in a manner shown in Fig. 3.
  • This figure shows a voltage source NS1 connected between the specimen 3 and the surface of the target 7.
  • the potential difference Nl created by this voltage source is responsible for accelerating the secondary and backscattered electrons before they strike the surface of the target 7.
  • the potential of the target 7 should be positive with respect to the potential of the specimen 3.
  • the second voltage source NS2 generating the potential difference N2 applied between the target 7 and the electron detector 5 is responsible for directing the tertiary electrons 8 towards the electron detector 5 and accelerating the tertiary electrons 8.
  • the potential of the electron detector 5 should be positive with respect to the potential of the target 7.
  • the primary electron beam passes through aperture 2 (which as an example, may be 400 microns in diameter) made in the target electrode.
  • This aperture can easily be reduced to, for example, 100 microns in diameter, allowing detection of electrons down to a distance of 50 microns from the optical axis.
  • MicroChannel plates which are especially desirable because of their low noise and high bandwidth, are not available with an active area within 1 mm of the axial hole.
  • the entire secondary electron current 4 would hit a only small area of the detector.
  • the large current density in the detector would lead to saturation effects and would decrease the lifetime of the detector.
  • the tertiary electrons 8 are spread over a larger area of the detector 5. Thereby, the current density in the detector is decreased.
  • the composition and configuration of the target 7 should be optimized to increase the yield of the tertiary electrons 8.
  • the chosen target material should have a high secondary yield at an energy consistent with the optical design of the system.
  • the secondaries from the specimen can easily be accelerated to, for example, 50 eN or even a few hundred eN. Any of the metals or compounds used in conventional multiplier dynodes, multichannel plates, or channeltrons are likely candidates.
  • the target itself can be fabricated from such a material, or the material can be applied as a coating to a substrate such as a silicon membrane.
  • the topography of the target also can be modified to increase the yield of the tertiary electrons.
  • a coating can be deposited onto the surface of the target so that its roughness increases.
  • the surface of the target can be roughened by sputtering or etching. With a rough target surface, the electrons would be incident at the target at larger angles with respect to the local surface normal, increasing the tertiary yield.
  • the surface of the target 7 can also be shaped or micromachined for a similar effect, as shown in the embodiments of Figs. 4-6.
  • the target's topography can also help in directing the tertiaries away from the detector's axis and toward the active area of the detector.
  • the tertiary electrons are emitted by the target consistent with a cos( ⁇ ) intensity distribution, with respect to the normal of the local surface plane.
  • ⁇ is the angle between the normal of the local surface plane and the direction of the electron emission. Therefore, more tertiary electrons will hit the detector 5 if the local normal to the target's surface does not point toward the dead center of the detector 5.
  • the sawtoothed (Figs. 4 and 5) and conical (Fig. 6) target surface shapes will aid in directing the tertiaries towards the active area of the detector 5.
  • the local surface normal of roughened or fingerlike surfaces created by sputtering, etching, or deposition will also face away from the optical axis.
  • Another benefit of the inventive indirect detection scheme stems from the fact that the secondaries and backscattered electrons 4 emitted by the specimen 3 must be accelerated inside the microcolumn 10 so that they strike the target 7 with sufficient kinetic energy to generate the tertiary electrons 8.
  • the requisite acceleration of the secondary electrons is achieved by creating an appropriate electric field inside the microcolumn 10.
  • the aforementioned accelerating electric field in the microcolumn can be produced by biasing the electrostatic lenses 6 and target 7, such as to create a suitable electrical potential difference between the electrostatic lenses 6 and the target 7.
  • a potential difference created between the target 7 and the electron detector 5 would effectuate the acceleration of the tertiary electrons 8 towards the electron detector 5. This potential difference can be achieved by suitably biasing the electron detector 5 with respect to the target 7.
  • the acceleration of the secondary electrons increases the electrons' kinetic energy E and decreases the ratio ⁇ E/E of the electrons' kinetic energy dispersion to the value of their kinetic energy. A decrease in this ratio results in a decrease of the dispersion of the secondary electrons' collection times. Therefore, the inventive microcolumn overcomes the time-of-flight problems seen in other in-lens detection techniques.
  • the detection efficiency can be made less sensitive to the inherent energy distribution of the emitted secondary electrons. Additionally, fast moving secondary electrons will be influenced less by stray external fields, limiting another source of unpredictable variations in the detected signal.
  • the specimen 3 may be an article to be inspected.
  • the specimen 3 may be a semiconductor wafer or reticle. Fine and coarse scanning motion of a beam with respect to the wafer or reticle are well known to those skilled in the art, and need not be detailed here. While the invention has been described herein with respect to preferred embodiments, it will be readily appreciated by those skilled in the art that various modifications in form and detail may be made therein without departing from the scope and spirit of the invention.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)

Abstract

Dans une microcolonne de microscope électronique à balayage, qui peut être utilisée pour le contrôle d'articles, une cible est utilisée afin de transformer des électrons secondaires, émis par l'échantillon, en électrons tertiaires. Ces électrons tertiaires sont ensuite détectés au moyen d'un détecteur d'électrons classique. La forme et les dimensions relativement non contraintes de la cible, par comparaison avec la forme et les dimensions du détecteur d'électrons, permettent une détection efficace des électrons secondaires qui passent à proximité de l'axe optique de l'appareil. La forme et la composition de la cible peuvent être choisies de manière à optimiser l'efficacité de détection du système.
PCT/US2001/012172 2000-05-04 2001-04-12 Procede et appareil d'imagerie d'un echantillon, par utilisation de la detection indirecte en colonne d'electrons secondaires dans une microcolonne WO2001084590A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001255373A AU2001255373A1 (en) 2000-05-04 2001-04-12 Method and apparatus for imaging a specimen using indirect in-column detection of secondary electrons in a microcolumn

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US56563500A 2000-05-04 2000-05-04
US09/565,635 2000-05-04

Publications (2)

Publication Number Publication Date
WO2001084590A2 true WO2001084590A2 (fr) 2001-11-08
WO2001084590A3 WO2001084590A3 (fr) 2002-03-28

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AU (1) AU2001255373A1 (fr)
TW (1) TW508615B (fr)
WO (1) WO2001084590A2 (fr)

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Publication number Priority date Publication date Assignee Title
US8617672B2 (en) 2005-07-13 2013-12-31 Applied Materials, Inc. Localized surface annealing of components for substrate processing chambers
US7942969B2 (en) 2007-05-30 2011-05-17 Applied Materials, Inc. Substrate cleaning chamber and components

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5466940A (en) * 1994-06-20 1995-11-14 Opal Technologies Ltd. Electron detector with high backscattered electron acceptance for particle beam apparatus
WO2000067290A2 (fr) * 1999-05-05 2000-11-09 Etec Systems, Inc. Ensemble compose d'une microcolonne et d'un microscope-sonde a balayage

Family Cites Families (2)

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Publication number Priority date Publication date Assignee Title
SU1265887A1 (ru) * 1985-03-20 1986-10-23 Институт проблем технологии микроэлектроники и особочистых материалов АН СССР Устройство дл регистрации неупругоотраженных электронов в растровом электронном микроскопе
JPH0883589A (ja) * 1994-09-13 1996-03-26 Hitachi Ltd 走査型電子顕微鏡

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5466940A (en) * 1994-06-20 1995-11-14 Opal Technologies Ltd. Electron detector with high backscattered electron acceptance for particle beam apparatus
WO2000067290A2 (fr) * 1999-05-05 2000-11-09 Etec Systems, Inc. Ensemble compose d'une microcolonne et d'un microscope-sonde a balayage

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
DATABASE WPI Section EI, Week 198724 Derwent Publications Ltd., London, GB; Class S03, AN 1987-168691 XP002182623 & SU 1 265 887 A (AS USSR MICROELECTR), 23 October 1986 (1986-10-23) *
PATENT ABSTRACTS OF JAPAN vol. 1996, no. 07, 31 July 1996 (1996-07-31) & JP 08 083589 A (HITACHI LTD), 26 March 1996 (1996-03-26) *
T ET AL: "Electron beam technology - SEM to microcolumn" MICROELECTRONIC ENGINEERING, ELSEVIER PUBLISHERS BV., AMSTERDAM, NL, vol. 32, no. 1, 1 September 1996 (1996-09-01), pages 113-130, XP004013428 ISSN: 0167-9317 *

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WO2001084590A3 (fr) 2002-03-28
TW508615B (en) 2002-11-01
AU2001255373A1 (en) 2001-11-12

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