Abstract:
Electron-beam generators have wide area and directional beam generation capability. The generators include anode and cathode electrodes, which are disposed in spaced-apart and opposing relationship relative to each other. A clustered carbon nanotube array is provided to support the wide area and directional beam generation. The clustered nanotube array extends between the anode and cathode electrodes. The nanotube array also has a wide area emission surface thereon, which extends opposite a primary surface of the anode electrode. The clustered nanotube array is configured so that nanotubes therein provide conductive channels for electrons, which pass from the cathode electrode to the anode electrode via the emission surface.

Description:
REFERENCE TO PRIORITY APPLICATION  
       [0001]     This application claims priority to Korean Application Serial No. 2004-00854, filed Jan. 7, 2004, the disclosure of which is hereby incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to electron-beam inspection tools used in manufacturing and, more particularly, to electron-beam inspection tools using in semiconductor wafer fabrication and methods of operating the same.  
       BACKGROUND OF THE INVENTION  
       [0003]     Various defects can occur during the fabrication of semiconductor devices and many of these defects can cause device malfunction and failure. The defects introduced during fabrication of the semiconductor devices can generally be divided into two categories including physical defects, such as particles, which can cause physical abnormalities on the surface of a semiconductor substrate, and electrical defects, which accompany physical defects but may bring about electrical failure in the semiconductor devices even in the absence of physical defects. Physical defects can generally be detected by conventional image observation equipment. However, electrical defects typically cannot be detected by such conventional observation equipment.  
         [0004]     It is known to test contact holes (e.g., through-holes) extending to an electrically conductive region within a semiconductor substrate using an electron beam inspection apparatus. Such inspection apparatus may provide in-line monitoring to determine whether a contact hole formed in an electrically insulating layer is in an open or not-open state. If an unetched portion of material (e.g., an oxide or nitride residue) is present in the contact hole, primary electrons from the electron beam may not flow properly to the substrate for collection and may accumulate on the surface of the unetched material. If this occurs, a large quantity of secondary electrons may be emitted from the surface of the substrate. Depending on a difference in secondary electron yields, a brighter (white) or darker (black) image may be displayed for each portion of the substrate where a large amount of secondary electrons are emitted, that is, portions where unetched material is present, relative to portions where the unetched material layer is not present. By detecting these differences, physical defects may be identified. One example of an ion inspection apparatus is disclosed in commonly assigned U.S. Pat. No. 6,545,491 to Kim et al., entitled “Apparatus for detecting defects in semiconductor devices and methods of using the same.” Another example of an ion inspection apparatus is disclosed in commonly assigned U.S. Pat. No. 6,525,318 to Kim et al., entitled “Methods of Inspecting Integrated Circuit Substrates Using Electron Beams.” The disclosures of these Kim et al. patents are hereby incorporate herein by reference. One drawback of conventional electron beam inspection tools is the requirement that each contact hole on a semiconductor substrate (e.g., silicon wafer) be individually checked one-at-a-time. This one-at-a-time checking can result in long inspection times for large substrates having large quantities of contact holes. This drawback may also be present in those tools that perform inspection by evaluating wafer leakage current (e.g., electron current passing through the substrate to an electrode). However, some of these tools may use relatively large area cathode electrodes that provide wide area electron emission onto an opposing portion of an underlying substrate. This wide area emission technique may eliminate the requirement to check each contact hole one-at-a-time, but may also lead to detrimental arc discharging when high voltages are applied to the cathode electrode.  
         [0005]     Thus, notwithstanding these conventional electron beam inspection tools, there continues to be a need for improved tools that provide high speed inspection without unwanted side effects such as arc discharging resulting from high voltage levels.  
       SUMMARY OF THE INVENTION  
       [0006]     Embodiments of the invention include electron-beam generators having wide area and directional beam generation. In some of these embodiments, anode and cathode electrodes are disposed in spaced-apart and opposing relationship relative to each other and powered by a power source. A clustered nanotube array is also provided to support the wide area and directional beam generation. The clustered nanotube array extends between the anode and cathode electrodes. The array also has a wide area emission surface thereon, which extends opposite a primary surface of the anode electrode. The clustered nanotube array is configured so that nanotubes therein provide conductive channels for electrons, which pass from the cathode electrode to the anode electrode via the emission surface. According to preferred aspects of these embodiments, the clustered nanotube array includes an array of carbon nanotubes. The embodiments may also include an electromagnetic field generator, which is configured to establish an electromagnetic field in a space between the anode and cathode electrodes.  
         [0007]     Additional embodiments of the invention include electron-beam inspection tools. These inspection tools include anode and cathode electrodes, which are disposed in spaced-apart and opposing relationship relative to each other. The anode electrode has a primary surface thereon, which is configured to receive a semiconductor wafer. A clustered nanotube array is also provided to enhance electron-beam emission efficiency. The array extends between the anode and cathode electrodes and has an emission surface thereon, which extends opposite the primary surface of the anode electrode. The clustered nanotube array is configured so that nanotubes therein provide conductive channels for electrons passing from the cathode electrode to the anode electrode via the emission surface. An ammeter is also provided to measure leakage current passing from the semiconductor wafer to the primary surface of the anode electrode. This ammeter is electrically coupled to the anode electrode.  
         [0008]     Still further embodiments of the invention include another electron-beam inspection tool. This tool includes anode and cathode electrodes, which are disposed in spaced-apart and opposing relationship relative to each other. The anode electrode has a primary surface thereon and an array of emission holes therein. A clustered nanotube array is also provided. The array extends between the anode and cathode electrodes. The array has an emission surface thereon that extends opposite the primary surface of the anode electrode. The clustered nanotube array is configured so that nanotubes therein provide conductive channels for electrons passing from the cathode electrode to the anode electrode via the emission surface. A power source is electrically coupled to the anode and cathode electrodes, so that an electric field can be established therebetween. A supporting stage, which is configured to receive a semiconductor wafer on a primary surface thereof, is also provided and an ammeter is electrically coupled to the stage. In these embodiments, the anode electrode is disposed between the stage and the cathode electrode, so that electrons passing through the emission holes in the anode electrode are received by the wafer.  
         [0009]     Additional embodiments of the invention include methods of inspecting a semiconductor substrate by emitting beams of electrons from a wide area emission surface of a clustered carbon nanotube array to a semiconductor substrate having a plurality of contact holes thereon. The substrate includes a semiconductor wafer and an electrically insulating layer on the semiconductor wafer. The electrically insulating layer has the plurality of contact holes therein that expose corresponding portions of the semiconductor wafer. This emitting step is performed in a presence of an electromagnetic field, which has flux lines extending in a substantially orthogonal direction relative to the emission surface. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of an electron-beam inspection apparatus according to a first embodiment of the invention.  
         [0011]      FIG. 2  is a flow diagram of operations that illustrate methods of inspecting substrates using the apparatus of  FIG. 1 .  
         [0012]      FIG. 3  is a perspective view of an electron-beam inspection apparatus according to a second embodiment of the invention.  
         [0013]      FIG. 4  is a flow diagram of operations that illustrate methods of inspecting substrates using the apparatus of  FIG. 3 .  
         [0014]      FIG. 5  is a perspective view of an electron-beam inspection apparatus according to a third embodiment of the invention.  
         [0015]      FIG. 6  is a flow diagram of operations that illustrate methods of inspecting substrates using the apparatus of  FIG. 5 .  
         [0016]      FIG. 7  is a perspective view of an electron-beam inspection apparatus according to a fourth embodiment of the invention.  
         [0017]      FIG. 8  is a flow diagram of operations that illustrate methods of inspecting substrates using the apparatus of  FIG. 7 . 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]     The present invention now will be described more fully herein with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity of description. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Like reference numerals refer to like elements throughout.  
         [0019]      FIG. 1  illustrates an electron-beam inspection tool  100  according to a first embodiment of the invention. This tool  100  includes an anode electrode  110  and a cathode electrode  120 , which are powered by a power source  130 . This power source  130  establishes a sufficient voltage between the anode electrode  110  and cathode electrode  120  to thereby promote electron emission in a downward direction from the cathode electrode  120  to the anode electrode  110 . The anode electrode  110  has a primary surface (e.g., upper surface) that is configured to support a semiconductor substrate. This substrate may include a semiconductor wafer (W) having an electrically insulating layer (not shown) thereon. This electrically insulating layer may have a plurality of contact holes therein that expose underlying portions of the semiconductor wafer (W). These contact holes can be inspected for the presence of residues by evaluating the magnitude of leakage current passing from a backside of the wafer (W) to the anode electrode  110 . This leakage current may be measured by an ammeter  150 , which is electrically coupled to the anode electrode  110 .  
         [0020]     The inspection tool  100  also includes a clustered nanotube array  140 , which is mounted to an emission surface of the cathode electrode  120 . The clustered nanotube array  140  has a wide area emission surface  140   a  thereon, which extends opposite a primary surface of the anode electrode  110 . This emission surface  140   a  is filled with a high density of closely-spaced nanotube openings, which may have diameters in a range from about 1 nm to about 10 nm. The clustered nanotube array  140  is configured so that nanotubes therein provide conductive channels for electrons (e−), which under the influence of an electric field pass from the cathode electrode  120  to the anode electrode  110  via the emission surface  140   a . The clustered nanotube array  140  may be a carbon nanotube array having carbon nanotubes therein. As understood by those skilled in the art, carbon nanotubes may have closed hexagonal honeycomb structures, which enclose cylindrical channels. Examples of carbon nanotube arrays are described in articles by: B. J. Hinds et al., entitled “Aligned Multiwalled Carbon Nanotube Membranes,” Science, Vol. 303, Jan. 2, 2004, pp. 62-64; A. Cao et al., entitled “Grapevine-like Growth of Single Walled Carbon Nanotubes Among Vertically Aligned Multiwalled Nanotube Arrays,” App. Phys. Letters, Vol. 79, No.  9 , August 2001, pp. 1252-1254; and W. Hu et al., entitled “Growth of Well-Aligned Carbon Nanotube Arrays on Silicon Substrates Using Porous Alumina File as a Nanotemplate,” App. Phys. Letters, Vol. 79, No.  19 , November 2001, pp. 3083-3085.  
         [0021]      FIG. 2  is a flow diagram of operations that illustrate an inspection method performed by the apparatus of  FIG. 1 . These operations include emitting electrons from a cathode electrode  120 , Block ST 11 , and forming a wide area and uniformly downward emission of these electrons from an emission surface of the nanotube array  140  by passing these electrons through carbon nanotubes within the array  140 , Block ST 12 . This uniform emission of electrons is irradiated onto an exposed surface of a substrate, Block ST 13 . This substrate may include a semiconductor wafer having an electrically insulating layer thereon containing a plurality of contact holes. These contact holes may include some contact holes that are at least partially filled with insulating residues that block passage of electrons therethrough. As illustrated by Block ST 14 , a leakage current from the underside surface of the wafer is measured with an ammeter to identify the presence of blocked contact holes. Techniques to identify the presence of blocked holes from leakage current measurements are well known to those skilled in the art and need not be described further herein.  
         [0022]     During operation of the inspection tool  100 , the power source  130  supplies a field emission current (I) to the cathode electrode  120 . The magnitude of this emission current (I) may be determined from the following Formula 1: 
 
 I=aV   2  exp[−( bφ   1.5 )/(βV)]  (1) 
 
 where “a” and “b” are constants, V represents an applied voltage established by the power source, which extends between the anode and cathode electrodes, V represents a field enhancement factor and (p represents a work function. 
 
         [0023]     This Formula 1 demonstrates that when a conventional cathode electrode having a wide emission area is used as an emission source, a very high voltage of about 10 4 V/μm may need to be established between the cathode and anode electrodes to obtain emission. Unfortunately, this high voltage may contribute to uneven emission of electrons from the cathode electrode and arc discharge or material breakdown at a surface of the cathode electrode. In contrast, the use of a clustered nanotube array  140  containing carbon nanotubes may result in electron emission at much lower voltages. For example, although a carbon nanotube array may have a work function (e.g., 4.5 eV) similar to a work function of a metal tip, the field enhancement factor β of the carbon nanotube array may be greater than about 1,000. This high field enhancement factor translates to a requirement that only a relatively small voltage of about 10V/μm is required to obtain electron emission from an emission surface  140   a  of the carbon nanotube array.  
         [0024]     As described in the aforementioned articles, carbon nanotube arrays may be fabricated using a variety of techniques. These techniques include arc-discharging, laser vapor deposition, plasma-enhanced chemical vapor deposition, thermal chemical vapor deposition, vapor phase growth and other techniques. In an arc-discharging technique, a direct current is applied between a positive graphite electrode and a negative graphite electrode to generate an electron discharge. Electrons emitted from the negative graphite electrode collide against the positive graphite electrode and are converted into carbon clusters. The carbon clusters may be condensed on a surface of the negative graphite electrode, which is cooled at a very low temperature, to thereby form a carbon nanotube array. In a laser vapor deposition method, a laser is irradiated onto a graphite target in an oven to thereby evaporate the graphite target. The evaporation of the graphite target results in the condensation of carbon clusters at very low temperature. In a plasma chemical vapor deposition method, a high-frequency voltage is applied to a pair of electrodes to generate a glow discharge in a reaction chamber. Examples of reaction gases include C 2 H 4 , CH 4  and CO, for example. Examples of catalyst metals include Fe, Ni, Co, which may be deposited on a substrate that includes Si, SiO 2 , and glass. The catalyst metal on the substrate is etched to form catalyst metal particles having nano-dimensions. The reaction gases are then introduced into the reaction chamber and a glow discharge is performed to thereby grow a carbon nanotube array on the catalyst metal particles.  
         [0025]     A carbon nanotube array of high purity may also be manufactured using thermal chemical vapor deposition. In this technique, a catalyst metal including Fe, Ni or Co is deposited on a substrate. The substrate is then wet-etched using a hydrogen fluoride (HF) solution. The etched substrate is received in a quartz boat. The quartz boat is then loaded into a chemical vapor deposition (CVD) chamber. The catalyst metal is etched in the chamber using a NH 3  gas at a high temperature, to thereby form catalyst metal particles having nano-dimensions.  
         [0026]     In a vapor phase growth technique, reaction gases including carbon and a catalyst metal are directly used under a vapor phase state. The catalyst metal is vaporized at a first temperature to form catalyst metal particles having nano-dimensions. The catalyst metal particles are heated at a second temperature greater than the first temperature so that carbon atoms are decomposed from the reaction gases. The carbon atoms are chemisorbed and diffused on the catalyst metal particles.  
         [0027]      FIG. 3  illustrates an electron-beam inspection tool  200  according to a second embodiment of the invention. This tool  200  includes an anode electrode  210  and a cathode electrode  220 , which are powered by a power source  230 . This power source  230  establishes a sufficient voltage between the anode electrode  210  and cathode electrode  220  to thereby promote electron emission in a downward direction from the cathode electrode  220  to the anode electrode  210 . The tool  200  also includes a pair of electromagnets  260  and  270  that operate together to establish a magnetic field in a space between the anode and cathode electrodes. The flux lines in the magnetic field extend vertically in a direction parallel to the electron emission path and orthogonal to an electron emission surface  240   a.    
         [0028]     The anode electrode  210  has a primary surface (e.g., upper surface) that is configured to support a semiconductor substrate. This semiconductor substrate may include a semiconductor wafer (W) having an electrically insulating layer (not shown) thereon. This electrically insulating layer may have a plurality of contact holes therein that expose underlying portions of the semiconductor wafer (W). These contact holes can be inspected for the presence of residues by evaluating the magnitude of leakage current passing from a backside of the wafer (W) to the anode electrode  210 . This leakage current may be measured by an ammeter  250 , which is electrically coupled to the anode electrode  210 .  
         [0029]     The inspection tool  200  also includes a clustered nanotube array  240 , which is mounted to an emission surface of the cathode electrode  220 . The clustered nanotube array  240  has a wide area emission surface  240   a  thereon, which extends opposite a primary surface of the anode electrode  210 . This emission surface  240   a  is filled with a high density of closely-spaced nanotube openings. The clustered nanotube array  240  is configured so that nanotubes therein provide conductive channels for electrons (e−), which under the influence of an electric field pass from the cathode electrode  220  to the anode electrode  210  via the emission surface  240   a.    
         [0030]      FIG. 4  is a flow diagram of operations that illustrate an inspection method performed by the apparatus of  FIG. 3 . These operations include establishing a magnetic field between the anode electrode  210  and the cathode electrode  220 , using the pair of electromagnets  260  and  270 , Block ST 21 , and emitting electrons from a cathode electrode  220 , Block ST 22 . A wide area and uniformly downward emission of these electrons is then established from an emission surface of the nanotube array  240  by passing these electrons through carbon nanotubes within the array  240 , Block ST 23 . This uniform emission of electrons is irradiated onto an exposed surface of a substrate, Block ST 24 . This substrate may include a semiconductor wafer having an electrically insulating layer thereon containing a plurality of contact holes. These contact holes may include some contact holes that are at least partially filled with insulating residues that block passage of electrons therethrough. As illustrated by Block ST 25 , a leakage current from the underside surface of the wafer is measured with an ammeter to identify the presence of blocked contact holes.  
         [0031]      FIG. 5  illustrates an electron-beam inspection tool  300  according to a third embodiment of the invention. This tool  300  includes an anode electrode  310  and a cathode electrode  320 , which are powered by a power source  330 . This power source  330  establishes a sufficient voltage between the anode electrode  310  and cathode electrode  320  to thereby promote electron emission in a downward direction from the cathode electrode  320  to the anode electrode  310 . The anode electrode  310  has a primary surface (e.g., upper surface) and an array of emission holes  311  therein that support passage of electrons (e−) emitted by the cathode electrode  320 . A stage  380  is also provided. This stage  380  is configured to support a substrate. This substrate may include a semiconductor wafer (W) having an electrically insulating layer (not shown) thereon. This electrically insulating layer may have a plurality of contact holes therein that expose underlying portions of the semiconductor wafer (W). These contact holes can be inspected for the presence of residues by evaluating the magnitude of leakage current passing from a backside of the wafer (W) to the stage  380 . This leakage current may be measured by an ammeter  350 , which is electrically coupled to the stage  380 .  
         [0032]     The inspection tool  300  also includes a clustered nanotube array  340 , which is mounted to an emission surface of the cathode electrode  320 . The clustered nanotube array  340  has a wide area emission surface  340   a  thereon, which extends opposite a primary surface of the anode electrode  310 . This emission surface  340   a  is filled with a high density of closely-spaced nanotube openings. The clustered nanotube array  340  is configured so that nanotubes therein provide conductive channels for electrons (e−), which under the influence of an electric field pass from the cathode electrode  320  to the emission holes  311  in the anode electrode  310  via the emission surface  340   a . The clustered nanotube array  340  may be a carbon nanotube array having carbon nanotubes therein.  
         [0033]      FIG. 6  is a flow diagram of operations that illustrate an inspection method performed by the apparatus of  FIG. 5 . These operations include emitting electrons from a cathode electrode  320 , Block ST 31 , and forming a wide area and uniformly downward emission of these electrons from an emission surface of the nanotube array  340  by passing these electrons through carbon nanotubes within the array  340 , Block ST 32 . This uniform emission of electrons is irradiated through emission holes  311  in an anode electrode  310 , Block ST 33 , and then onto a front side of a substrate (e.g., wafer W), Block ST 34 . This substrate may include a semiconductor wafer W having an electrically insulating layer thereon containing a plurality of contact holes. These contact holes may include some contact holes that are at least partially filled with insulating residues that block passage of electrons therethrough. As illustrated by Block ST 35 , a leakage current from the underside surface of the wafer is measured with an ammeter to identify the presence of blocked contact holes.  
         [0034]      FIG. 7  illustrates an electron-beam inspection tool  400  according to a fourth embodiment of the invention. This tool  400  includes an anode electrode  410  and a cathode electrode  420 , which are powered by a power source  430 . This power source  430  establishes a sufficient voltage between the anode electrode  410  and cathode electrode  420  to thereby promote electron emission in a downward direction from the cathode electrode  420  to the anode electrode  410 . The tool  400  also includes a pair of electromagnets  460  and  470  that operate together to establish a magnetic field in a space between the anode and cathode electrodes. This magnetic field has flux lines that extend vertically between the electromagnets  460  and  470 . The anode electrode  410  has a primary surface (e.g., upper surface) and an array of emission holes  411  therein that support passage of electrons (e−) emitted by the cathode electrode  420 . A stage  480  is also provided. This stage  480  is configured to support a substrate. This substrate may include a semiconductor wafer (W) having an electrically insulating layer (not shown) thereon. This electrically insulating layer may have a plurality of contact holes therein that expose underlying portions of the semiconductor wafer (W). These contact holes can be inspected for the presence of residues by evaluating the magnitude of leakage current passing from a backside of the wafer (W) to the stage  480 . This leakage current may be measured by an ammeter  450 , which is electrically coupled to the stage  480 .  
         [0035]     The inspection tool  400  also includes a clustered nanotube array  440 , which is mounted to an emission surface of the cathode electrode  420 . The clustered nanotube array  440  has a wide area emission surface  440   a  thereon, which extends opposite a primary surface of the anode electrode  410  and orthogonal to the magnetic flux lines. This emission surface  440   a  is filled with a high density of closely-spaced nanotube openings. The clustered nanotube array  440  is configured so that nanotubes therein provide conductive channels for electrons (e−), which under the influence of an electric field pass from the cathode electrode  420  to the emission holes  411  in the anode electrode  410  via the emission surface  440   a . The clustered nanotube array  440  may be a carbon nanotube array having carbon nanotubes therein.  
         [0036]      FIG. 8  is a flow diagram of operations that illustrate an inspection method performed by the apparatus of  FIG. 7 . These operations include establishing a magnetic field between anode and cathode electrodes, ST 41 , and emitting electrons from the cathode electrode  420 , Block ST 42 . A wide area and uniformly downward emission of these electrons is also established from an emission surface of the nanotube array  440 . This emission occurs by passing these electrons through carbon nanotubes within the array  340 , Block ST 43 . This uniform emission of electrons is irradiated through emission holes  411  in an anode electrode  410 , Block ST 44 , and then onto a front side of a substrate (e.g., wafer W), Block ST 45 . This substrate may include a semiconductor wafer W having an electrically insulating layer thereon containing a plurality of contact holes. These contact holes may include some contact holes that are at least partially filled with insulating residues that block passage of electrons therethrough. As illustrated by Block ST 46 , a leakage current from the underside surface of the wafer is measured with an ammeter to identify the presence of blocked contact holes.  
         [0037]     In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.