WO2009008594A1 - End point detecting apparatus for semiconductor wafer polishing process - Google Patents

End point detecting apparatus for semiconductor wafer polishing process Download PDF

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Publication number
WO2009008594A1
WO2009008594A1 PCT/KR2008/002781 KR2008002781W WO2009008594A1 WO 2009008594 A1 WO2009008594 A1 WO 2009008594A1 KR 2008002781 W KR2008002781 W KR 2008002781W WO 2009008594 A1 WO2009008594 A1 WO 2009008594A1
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WO
WIPO (PCT)
Prior art keywords
optical fiber
end point
platen
fiber cable
polishing
Prior art date
Application number
PCT/KR2008/002781
Other languages
French (fr)
Inventor
Chang Il Kim
Pan Ki Kwon
Original Assignee
Doosan Mecatec Co., Ltd.
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 Doosan Mecatec Co., Ltd. filed Critical Doosan Mecatec Co., Ltd.
Publication of WO2009008594A1 publication Critical patent/WO2009008594A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B37/00—Lapping machines or devices; Accessories
    • B24B37/005—Control means for lapping machines or devices
    • B24B37/013—Devices or means for detecting lapping completion
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
    • H01L21/304—Mechanical treatment, e.g. grinding, polishing, cutting

Definitions

  • the present invention relates to an apparatus for detecting an end point in a process of polishing a semiconductor wafer, and more particularly, to an end point detecting apparatus capable of completely sealing an optical fiber cable and maintaining the sealing state by coupling an elastic ring member having high elasticity to a front end of the optical fiber cable, which is positioned adjacent to a polishing surface of a wafer in light irradiation equipment using the optical fiber cable, without separately performing a sealing process to the respective optical transmission through-holes of a platen and polishing pad; preventing the optical fiber cable from being damaged due to a slurry by covering the front end of the optical fiber cable with an optical transmission film; and detecting the end point, without forming a separate polishing monitoring window.
  • a semiconductor fabricating method comprises a CVD (Chemical Vapor
  • Deposition for stacking a plurality of interconnection layers which can serve as a dielectric or conductor, on the surface of a wafer so as to implement densification of a semiconductor device
  • CMP Chemical Mechanical Polishing
  • the CMP process is one of planarization methods requiring high precision to eliminate a step height of the surface of a wafer according to densification and mi- cronization of a semiconductor device and layered design of an interconnection structure.
  • the CMP process is fine machining technology which has been recently developed and generalized, and the technology development for the CMP process is actively carried out at present.
  • a slurry 2 is supplied onto the surface of wafer 1 to induce chemical reaction on the surface, while the wafer 1 comes in contact with the surface of a polishing pad 12.
  • a platen (alternatively, a polishing table 11) with the polishing pad 12 attached to the surface thereof and a wafer carrier fixing the wafer 1 are relatively moved, thereby physically planarizing recessed portions of the surface of the wafer 1. More specifically, while the platen 11 is simply turned, the wafer carrier is simultaneously turned, and is pressed by a predetermined pressure, so that the wafer 1 is polished by the polishing pad 12 and the slurry 2.
  • a polishing speed and a degree of planarization play an important role in the polishing process, and are determined depending upon process conditions of the equipment, a kind of slurry, a kind of pad, or the like.
  • polishing end point In the process of polishing the surface of the wafer 1, it is very important that the surface condition is checked out on occasion, and the process is completed when the surface condition reaches a proper level.
  • a process completing point for the surface polishing process is referred to as a polishing end point or end point.
  • the end point is a point to be primarily considered so as to minimize process errors and wafer defective.
  • optically end point detecting technique utilizes optical interference which irradiates a laser beam or white light onto the machining surface of the wafer 1 through through-holes 12a formed on the polishing pad 12 and tracks intensity variation of a reflected light with the lapse of time.
  • the residual thickness of the wafer is measured by using the intensity variation of the reflected light with the lapse of time, and the time when the thickness reaches a specific value is detected as the end point.
  • the end point detecting apparatus is one to verify the polishing state while the wafer 1 is polished. It may be called as a preliminary detecting means that can predict a time when the surface polishing process of the wafer 1 mounted on the platen 11 is completed.
  • FIG. 1 shows main parts of an end point detecting apparatus of laser beam illumination type that is disclosed in U.S. Patent Nos. 5,964,643 (filed Feb. 22, 1996) and 6,045,439 (filed Feb. 26, 1999), the patent being assigned to Applied Materials Inc.
  • the laser beam emitted from a laser collimator LC is irradiated on the surface of the wafer 1 through a transparent window 160 having a specific structure installed in a through-hole 1 Ia of the platen 11 and a through-hole 12a of the polishing pad 12, and a portion of the beam is reflected by the wafer.
  • the reflected beam is refracted by a beam splitter BS, and is incident on a detector D to measure the uniformity of the surface and detect a spectral interference signal thereof.
  • the transparent window 160 is attached to the through-hole 12a of the polishing pad 12, and the lower end of the transparent window is laid in the through-hole 1 Ia of the platen 11.
  • a light source is not closely disposed on the transparent window 160, it should utilize only a light having high straightness and coherence should be utilized, for example, a laser beam.
  • a process of accurately coupling the polishing pad 12 having the transparent window 160 to the platen 11 is performed by visual inspection, it is not easy to match the transparent window 160 to the position of the through-hole 11a.
  • FIG. 2 shows main parts of the end point detecting apparatus disclosed in
  • U.S. Patent No. 5,433,651 (filed Dec. 22, 1993) which is assigned to International Business Machines Corporation.
  • the patent is to detect an end point by verifying a polishing degree of a semiconductor wafer using a polishing monitoring window provided on a polishing platen. Since the monitoring window is provided on the polishing platen and only a through-hole is formed in the polishing pad, a surface of the monitoring window provided on the polishing platen is coplanar with the polishing platen, or placed at a position lower than the polishing platen. Therefore, a step height occurs at a portion of the through-hole of the polishing pad thereby to form an irregular surface.
  • an end point detecting apparatus including a polishing monitoring window made of a transparent material formed on a polishing pad which is mounted on the upper portion of a platen to monitor a degree of a polishing progress of the semiconductor wafer.
  • a polishing monitoring window made of a transparent material formed on a polishing pad which is mounted on the upper portion of a platen to monitor a degree of a polishing progress of the semiconductor wafer.
  • a surface of the polishing monitoring window is scratched by a pad conditioner for adjusting the roughness of the polishing pad when polishing.
  • the scratched surface of the polishing monitoring window leads a light source used to monitor the polishing level of the wafer to irregularly reflect, so that the end point is not accurately measured to induce loss of the wafer.
  • An object of the present invention is to provide an end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer which can detect an end point of the polishing process by fixing an optical fiber cable in a through-hole of a polishing pad by means of an elastic ring member, without installing a polishing monitoring window on a platen or the polishing pad.
  • Another object of the present invention is to provide an end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer which can completely seal an optical fiber cable, without separately performing a sealing process to the through-hole of a polishing pad.
  • the apparatus can block penetration of the slurry to be used at the polishing, thereby accurately detecting the end point.
  • Still another object of the present invention is to provide an end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer which can prevent an optical fiber cable from being damaged due to slurry by covering a front end of the optical fiber cable with an optical transmission film.
  • an end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer, comprising: a platen having at least one through-hole formed in an axial direction; a polishing pad detachably mounted on an upper portion of the platen and pressed by a wafer carrier to which a semiconductor wafer is attached, the polishing pad having a through-hole coaxially corresponding to the through-hole of the platen; an optical fiber cable inserted in the through-hole of the platen and having an elastic ring member mounted on a front end of the optical fiber cable, in which a portion of the optical fiber cable corresponding to the elastic ring member is hermetically received in the through-hole of the polishing pad, and in which the optical fiber cable is composed of a light emitting fiber and a light receiving fiber; and a controller each connected to the light emitting fiber and the light receiving fiber of the optical fiber cable for detecting an end point of the semiconductor wafer.
  • the platen is subject to any one of rotational motion, straight-line motion and translational motion with respect to the wafer carrier, and the wafer carrier is subject to orbital motion with respect to the platen which is in translational motion, or is subjected to rotational motion with respect to the platen which is in straight-line motion.
  • an upper surface of the front end of the optical fiber cable which is fixed in the through-hole of the polishing pad is coplanar with an upper surface of the polishing pad, or is not positioned higher than the upper surface.
  • a reference point is set at a portion of the wafer carrier, and a sensor is attached to a predetermined position of the rotatable platen provided with the optical fiber cable, and wherein the optical fiber cable emits light at least once when the sensor of the platen passes the reference point of the wafer carrier.
  • one of the optical fiber cables measures a polishing degree of the wafer, and the other measures uniformity of the wafer.
  • the wafer carrier is divided into multiple regions so as to correct uniformity of the semiconductor wafer to be polished, in which the respective regions is freely adjusted and/or pressed.
  • the elastic ring member is made of any one selected from the group consisting of natural rubber, synthetic rubber and synthetic resin.
  • a size of the through-hole of the polishing pad is larger than an outer diameter of the optical fiber cable, and is smaller than an outer diameter of the elastic ring member.
  • the front end of the optical fiber cable is detachably covered by an optical transmission film.
  • the optical transmission film has a thickness of 0.01 mm to 2 mm.
  • the optical transmission film has light transmittance of 0.1% to 100% and properties of chemical resistance and hydrophobicity.
  • FIG. 1 is a cross-sectional view schematically illustrating an end point detecting apparatus of laser irradiation type according to one example of the prior art
  • FIG. 2 is a cross-sectional view schematically illustrating an end point detecting apparatus with a polishing monitoring window provided in a polishing platen according to another example of the prior art
  • FIG. 3 is a perspective view illustrating CMP equipment employing an end point detecting apparatus according to the present invention
  • FIG. 4 is a cross-sectional view illustrating the installation state of an end point detecting apparatus according to the present invention.
  • FIG. 5 is a perspective view illustrating a front end of an optical fiber cable with a elastic ring member that is employed in an end point detecting apparatus according to the present invention.
  • FIG. 6 is a perspective view illustrating a polishing platen with an optical fiber cable that is employed in an end point detecting apparatus according to the present invention.
  • FIG. 3 is a perspective view illustrating CMP equipment employing an end point detecting apparatus according to the present invention.
  • a CMP apparatus 10 includes a platen 11 with a polishing pad 12 mounted on an upper portion thereof, an optical fiber cable 30 mounted on a portion of the polishing pad 12 through the platen for detecting a surface polishing state of a wafer 1, a wafer carrier 13 holding the wafer 1 and pressed downwards so that the polishing pad 12 comes in contact with a surface of the wafer 1, a slurry supply nozzle (not shown) for supplying a slurry on the polishing pad 12, and a conditioner carrier 16 holding and rotating a conditioner 16a for dressing a surface of the polishing pad 12 to prevent deformation or contamination of the polishing pad 12 and thus continuously maintain polishing capability of the polishing pad 12.
  • a slurry supply nozzle not shown
  • reference numeral 13a denotes a polishing head for receiving the wafer 1 with vacuum suction
  • reference numeral 13b denotes a retainer ring for retaining the wafer 1, in which the wafer 1 is fixed to a bottom surface of the polishing head 13a with surface tension or vacuum suction
  • reference numeral 15 denotes a spindle (not shown) for rotating the wafer carrier 13 and the conditioner carrier 16.
  • FIGs. 4 and 5 illustrate the structure of an optical fiber cable according to a preferable embodiment of the present invention.
  • FIG. 4 is a cross-sectional view illustrating the installation state of the end point detecting apparatus according to the present invention
  • FIG. 5 is a perspective view illustrating a front end of the optical fiber cable with the elastic ring member.
  • the end point detecting apparatus includes a platen 11 having at least one through-hole 11a formed in an axial direction, a polishing pad 12 detachably mounted on an upper portion of the platen and pressed by a wafer carrier 13 to which a semiconductor wafer is attached, the polishing pad 12 having a through-hole 12a coaxially corresponding to the through-hole 1 Ia of the platen 11, an optical fiber cable 30 inserted in the through-hole 1 Ia of the platen 11 and having an elastic ring member 31 mounted on a front end of the optical fiber cable, in which a portion of the optical fiber cable corresponding to the elastic ring member is hermetically received in the through-hole 12a of the polishing pad 12, and the optical fiber cable is composed of a light emitting fiber and a light receiving fiber, and a controller 40 each connected to the light emitting fiber and the light receiving fiber of the optical fiber cable for detecting the end point of the semiconductor wafer.
  • the surface of the wafer 1 comes in contact with the polishing pad 12 by load of the wafer carrier 13 itself and a pressing force of the wafer carrier.
  • the slurry is flowed in a fine clearance between the contact surfaces, so that mechanical polishing is performed by polishing particles contained in the slurry and surface bosses of the polishing pad 12 and simultaneously chemical polishing is performed by chemical components contained in the slurry, thereby polishing the surface of the wafer 1.
  • the platen 11 is subject to any one of rotational motion, straight- line motion and translational motion with respect to the wafer carrier 13, and the wafer carrier 13 is subject to orbital motion with respect to the platen 11 which is in translational motion, or is subjected to rotational motion with respect to the platen which is in straight-line motion.
  • the optical fiber cable 30 is inserted in the through-hole 1 Ia of the platen 11.
  • the platen 11 or the polishing pad 12 may be provided with at least one through-hole 11a and 12a.
  • One end of the optical fiber cable 30 is each connected to the controller 40 for detecting the end point of the wafer polishing process via the light emitting fiber and the light receiving fiber, and the other end protrudes from the surface of the platen 11 to be inserted in the through-hole 12a of the polishing pad 12. If the optical fiber cable 30 with the elastic ring member 31 fixed to a distal end is secured to the polishing pad 12 of the platen 11, the optical fiber cable 30 is not moved with respect to the polishing pad 12.
  • the polishing pad 12 is attached to or detached from the elastic ring member 31 of the optical fiber cable 30 by a constant force applied by an operator (see FIGs. 4 and 6).
  • the upper surface of the front end of the optical fiber cable 30 which is inserted in the through-hole 1 Ia of the platen 11 is coplanar with the upper surface of the polishing pad 12, or is positioned lower than the upper surface. If the upper surface of the distal end is positioned lower than the upper surface of the polishing pad 12, the front end of the optical fiber cable 30 does not come in contact with the pad conditioner for maintaining the roughness of the polishing pad 12 in process of polishing the semiconductor wafer, thereby prevent the surface of the front end of the optical fiber cable 30 from being damaged.
  • the elastic ring member 31 closely contacts the outer periphery of the front end of the optical fiber cable 30 so as to protect the front end of the optical fiber cable 30 which is inserted in the through-hole 12a of the polishing pad 12 via the through-hole 1 Ia of the platen 11 and block penetration of the slurry used at the polishing.
  • a size of the through-hole 12a of the polishing pad 12 is preferably larger than an outer diameter of the optical fiber cable 30, and is smaller than an outer diameter of the elastic ring member 31.
  • the elastic ring member 31 is made of a material having an elastic characteristic, such as natural rubber, synthetic rubber or synthetic resin.
  • the elastic ring member 31 integrally coupled to the outer periphery of the front end of the optical fiber cable 30 has elasticity, the elastic ring member 31 can be easily inserted in the through-hole 11a even though the outer diameter of the distal end is larger than the size of the through- hole 1 Ia. In this instance, the inserted distal end comes in close contact with the through-hole 12a to block the penetration of the slurry.
  • the front end of the optical fiber cable 30 coupled with the elastic ring member 31 is covered by the optical transmission film 35 to seal and protect the front end.
  • An adhesive may be applied on one side of the optical transmission film 35 to enable the optical transmission film to easily attach or detach.
  • the optical transmission film 35 has a thickness of 0.01 mm to 2 mm, light transmittance of 0.1% to 100%, chemical resistance and hydrophobicity.
  • the upper surface of the front end of the optical fiber cable 30 can be protected against the slurry used when polishing the wafer or deionized water used when cleaning the wafer (see FIG. 5).
  • the controller 40 is each connected to the light emitting fiber and the light receiving fiber of the optical fiber cable 30 to measure the end point of the semiconductor wafer polishing process.
  • the optical fiber cable 30 is generally composed of one light emitting fiber and at least two light receiving fibers.
  • the light emitting fiber is positioned at a center portion of the optical fiber cable 30, and the light receiving fibers are disposed around the light emitting fiber.
  • the optical fiber cable 30 sets a reference point at a portion of the wafer carrier 13, and a sensor (not shown) is attached to a predetermined position of the rotatable platen 11 provided with the optical fiber cable.
  • the optical fiber cable emits light at least once when the sensor of the platen passes the reference point of the wafer carrier 13.
  • the optical fiber cable emits light periodically as stated above, and so the light reflected from the surface of the wafer to be polished is collected and transmitted to the controller 40 to measure the status change of the wafer to be polished and thus detect the end point.
  • the wafer carrier 13 is preferably divided into multiple regions so as to correct the uniformity of the semiconductor wafer to be polished. The respective regions is freely adjusted and/or pressed.
  • the sensor may comprise an optical sensor and a high frequency sensor.
  • the present invention does not require a separate polishing monitoring window, and fixes an end of an optical fiber cable with an elastic ring member, thereby effectively blocking penetration of slurry used at the polishing. Also, the end of the optical fiber cable is covered by an optical transmission film to prevent the optical fiber cable from being damaged by the slurry.
  • the present invention can detect an end point accurately in a process of polishing, irrespective of penetration of the slurry and scattered reflection of a light source.

Abstract

An end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer is disclosed. The apparatus includes a platen having at least one through-hole formed in an axial direction, a polishing pad detachably mounted on an upper portion of the platen and pressed by a wafer carrier to which a semiconductor wafer is attached, the polishing pad having a through-hole coaxially corresponding to the through-hole of the platen, an optical fiber cable inserted in the through-hole of the platen and having an elastic ring member mounted on a front end of the optical fiber cable, in which a portion of the optical fiber cable corresponding to the elastic ring member is hermetically received in the through-hole of the polishing pad, and in which the optical fiber cable is composed of a light emitting fiber and a light receiving fiber, and a controller each connected to the light emitting fiber and the light receiving fiber of the optical fiber cable for detecting an end point of the semiconductor wafer. The apparatus can measure a polishing degree of the wafer to detect the end point, without forming a window for monitoring the polishing state of the wafer, thereby improving a process ability of a polishing apparatus.

Description

Description
END POINT DETECTING APPARATUS FOR SEMICONDUCTOR WAFER POLISHING PROCESS
Technical Field
[1] The present invention relates to an apparatus for detecting an end point in a process of polishing a semiconductor wafer, and more particularly, to an end point detecting apparatus capable of completely sealing an optical fiber cable and maintaining the sealing state by coupling an elastic ring member having high elasticity to a front end of the optical fiber cable, which is positioned adjacent to a polishing surface of a wafer in light irradiation equipment using the optical fiber cable, without separately performing a sealing process to the respective optical transmission through-holes of a platen and polishing pad; preventing the optical fiber cable from being damaged due to a slurry by covering the front end of the optical fiber cable with an optical transmission film; and detecting the end point, without forming a separate polishing monitoring window.
[2]
Background Art
[3] In general, a semiconductor fabricating method comprises a CVD (Chemical Vapor
Deposition) process for stacking a plurality of interconnection layers which can serve as a dielectric or conductor, on the surface of a wafer so as to implement densification of a semiconductor device, and a CMP (Chemical Mechanical Polishing) process for eliminating a step height between a plurality of interconnection layers formed on the surface of a wafer through mechanical polishing and chemical reaction.
[4] The CMP process is one of planarization methods requiring high precision to eliminate a step height of the surface of a wafer according to densification and mi- cronization of a semiconductor device and layered design of an interconnection structure. The CMP process is fine machining technology which has been recently developed and generalized, and the technology development for the CMP process is actively carried out at present.
[5] With the principle of the CMP technology, as shown in FIG. 1, a slurry 2 is supplied onto the surface of wafer 1 to induce chemical reaction on the surface, while the wafer 1 comes in contact with the surface of a polishing pad 12. A platen (alternatively, a polishing table 11) with the polishing pad 12 attached to the surface thereof and a wafer carrier fixing the wafer 1 are relatively moved, thereby physically planarizing recessed portions of the surface of the wafer 1. More specifically, while the platen 11 is simply turned, the wafer carrier is simultaneously turned, and is pressed by a predetermined pressure, so that the wafer 1 is polished by the polishing pad 12 and the slurry 2. A polishing speed and a degree of planarization play an important role in the polishing process, and are determined depending upon process conditions of the equipment, a kind of slurry, a kind of pad, or the like.
[6] In the process of polishing the surface of the wafer 1, it is very important that the surface condition is checked out on occasion, and the process is completed when the surface condition reaches a proper level. Generally, a process completing point for the surface polishing process is referred to as a polishing end point or end point. The end point is a point to be primarily considered so as to minimize process errors and wafer defective.
[7] Diverse structures of end point detecting apparatuses have been proposed to detect the end point of the process. Since an optically end point detecting technique comes up to high precision, this technique is widely used in present. The optically end point detecting technique utilizes optical interference which irradiates a laser beam or white light onto the machining surface of the wafer 1 through through-holes 12a formed on the polishing pad 12 and tracks intensity variation of a reflected light with the lapse of time. The residual thickness of the wafer is measured by using the intensity variation of the reflected light with the lapse of time, and the time when the thickness reaches a specific value is detected as the end point.
[8] As described above, the end point detecting apparatus is one to verify the polishing state while the wafer 1 is polished. It may be called as a preliminary detecting means that can predict a time when the surface polishing process of the wafer 1 mounted on the platen 11 is completed.
[9] FIG. 1 shows main parts of an end point detecting apparatus of laser beam illumination type that is disclosed in U.S. Patent Nos. 5,964,643 (filed Feb. 22, 1996) and 6,045,439 (filed Feb. 26, 1999), the patent being assigned to Applied Materials Inc.
[10] In the above patents, the laser beam emitted from a laser collimator LC is irradiated on the surface of the wafer 1 through a transparent window 160 having a specific structure installed in a through-hole 1 Ia of the platen 11 and a through-hole 12a of the polishing pad 12, and a portion of the beam is reflected by the wafer. The reflected beam is refracted by a beam splitter BS, and is incident on a detector D to measure the uniformity of the surface and detect a spectral interference signal thereof. The transparent window 160 is attached to the through-hole 12a of the polishing pad 12, and the lower end of the transparent window is laid in the through-hole 1 Ia of the platen 11.
[11] With the end point detecting technique employing the laser beam irradiation, if the slurry 2 comes in the polishing pad 12 and the platen 11 via the through-holes 11a and 12a, an optical signal is deformed to disturb the signal of the reflected beam. As a result, clearances between the transparent window 160 and the through-holes 11a and 12a should be sealed so as to prevent the slurry 2 from penetrating in the polishing pad 12 and the platen 11.
[12] As a light source is not closely disposed on the transparent window 160, it should utilize only a light having high straightness and coherence should be utilized, for example, a laser beam. In addition, since a process of accurately coupling the polishing pad 12 having the transparent window 160 to the platen 11 is performed by visual inspection, it is not easy to match the transparent window 160 to the position of the through-hole 11a.
[13] Otherwise, FIG. 2 shows main parts of the end point detecting apparatus disclosed in
U.S. Patent No. 5,433,651 (filed Dec. 22, 1993) which is assigned to International Business Machines Corporation. The patent is to detect an end point by verifying a polishing degree of a semiconductor wafer using a polishing monitoring window provided on a polishing platen. Since the monitoring window is provided on the polishing platen and only a through-hole is formed in the polishing pad, a surface of the monitoring window provided on the polishing platen is coplanar with the polishing platen, or placed at a position lower than the polishing platen. Therefore, a step height occurs at a portion of the through-hole of the polishing pad thereby to form an irregular surface.
[14] This causes a problem in that the polishing slurry stays around the window during polishing. If the staying slurry is not properly removed, the slurry is cured to induce diffused reflection. Also, the cured slurry is detached from the window to form scratch on the wafer. The polishing slurry penetrates between the polishing platen and the polishing pad to deteriorate an adhesion force of the polishing pad adhesive, so that the pad of the monitoring window comes off. As a result, the apparatus may lead to poor machining in the semiconductor wafer.
[15] Also, there is another end point detecting apparatus including a polishing monitoring window made of a transparent material formed on a polishing pad which is mounted on the upper portion of a platen to monitor a degree of a polishing progress of the semiconductor wafer. As an edge of the polishing monitoring window is coplanar with an end of the polishing pad, a surface of the polishing monitoring window is scratched by a pad conditioner for adjusting the roughness of the polishing pad when polishing. The scratched surface of the polishing monitoring window leads a light source used to monitor the polishing level of the wafer to irregularly reflect, so that the end point is not accurately measured to induce loss of the wafer.
[16] Also, because of damage of the polishing monitoring window, a use cycle of the polishing pad is shortened, so that a maintenance cost of the equipment is increased. Moisture is generated in a lower space of the polishing monitoring window by the heat produced at the polishing, so that light interference causes reduction in transmittance or adhesion force of an adhesive between the polishing pad and the polishing monitoring window. In the latter case, there is a danger that the polishing monitoring window may protrude from the polishing pad. [17]
Disclosure of Invention Technical Problem
[18] Therefore, the present invention has been made in view of the above-mentioned problems.
[19] An object of the present invention is to provide an end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer which can detect an end point of the polishing process by fixing an optical fiber cable in a through-hole of a polishing pad by means of an elastic ring member, without installing a polishing monitoring window on a platen or the polishing pad.
[20] Another object of the present invention is to provide an end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer which can completely seal an optical fiber cable, without separately performing a sealing process to the through-hole of a polishing pad. The apparatus can block penetration of the slurry to be used at the polishing, thereby accurately detecting the end point.
[21] Still another object of the present invention is to provide an end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer which can prevent an optical fiber cable from being damaged due to slurry by covering a front end of the optical fiber cable with an optical transmission film.
[22]
Technical Solution
[23] According to an aspect of the present invention, there is provided an end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer, comprising: a platen having at least one through-hole formed in an axial direction; a polishing pad detachably mounted on an upper portion of the platen and pressed by a wafer carrier to which a semiconductor wafer is attached, the polishing pad having a through-hole coaxially corresponding to the through-hole of the platen; an optical fiber cable inserted in the through-hole of the platen and having an elastic ring member mounted on a front end of the optical fiber cable, in which a portion of the optical fiber cable corresponding to the elastic ring member is hermetically received in the through-hole of the polishing pad, and in which the optical fiber cable is composed of a light emitting fiber and a light receiving fiber; and a controller each connected to the light emitting fiber and the light receiving fiber of the optical fiber cable for detecting an end point of the semiconductor wafer. [24] In a preferred embodiment of the present invention, the platen is subject to any one of rotational motion, straight-line motion and translational motion with respect to the wafer carrier, and the wafer carrier is subject to orbital motion with respect to the platen which is in translational motion, or is subjected to rotational motion with respect to the platen which is in straight-line motion. [25] In a preferred embodiment of the present invention, an upper surface of the front end of the optical fiber cable which is fixed in the through-hole of the polishing pad is coplanar with an upper surface of the polishing pad, or is not positioned higher than the upper surface. [26] In a preferred embodiment of the present invention, a reference point is set at a portion of the wafer carrier, and a sensor is attached to a predetermined position of the rotatable platen provided with the optical fiber cable, and wherein the optical fiber cable emits light at least once when the sensor of the platen passes the reference point of the wafer carrier. [27] In a preferred embodiment of the present invention, one of the optical fiber cables measures a polishing degree of the wafer, and the other measures uniformity of the wafer. [28] In a preferred embodiment of the present invention, the wafer carrier is divided into multiple regions so as to correct uniformity of the semiconductor wafer to be polished, in which the respective regions is freely adjusted and/or pressed. [29] In a preferred embodiment of the present invention, the elastic ring member is made of any one selected from the group consisting of natural rubber, synthetic rubber and synthetic resin. [30] In a preferred embodiment of the present invention, a size of the through-hole of the polishing pad is larger than an outer diameter of the optical fiber cable, and is smaller than an outer diameter of the elastic ring member. [31] In a preferred embodiment of the present invention, the front end of the optical fiber cable is detachably covered by an optical transmission film. [32] In a preferred embodiment of the present invention, the optical transmission film has a thickness of 0.01 mm to 2 mm. [33] Also, in a preferred embodiment of the present invention, the optical transmission film has light transmittance of 0.1% to 100% and properties of chemical resistance and hydrophobicity. [34]
Brief Description of the Drawings [35] The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in con- junction with the accompanying drawings in which:
[36] FIG. 1 is a cross-sectional view schematically illustrating an end point detecting apparatus of laser irradiation type according to one example of the prior art;
[37] FIG. 2 is a cross-sectional view schematically illustrating an end point detecting apparatus with a polishing monitoring window provided in a polishing platen according to another example of the prior art;
[38] FIG. 3 is a perspective view illustrating CMP equipment employing an end point detecting apparatus according to the present invention;
[39] FIG. 4 is a cross-sectional view illustrating the installation state of an end point detecting apparatus according to the present invention;
[40] FIG. 5 is a perspective view illustrating a front end of an optical fiber cable with a elastic ring member that is employed in an end point detecting apparatus according to the present invention; and
[41] FIG. 6 is a perspective view illustrating a polishing platen with an optical fiber cable that is employed in an end point detecting apparatus according to the present invention.
[42]
Best Mode for Carrying Out the Invention
[43] Reference will now be made in detail to the preferred embodiments of the present invention. It is to be understood that the following examples are illustrative only and the present invention is not limited thereto.
[44] FIG. 3 is a perspective view illustrating CMP equipment employing an end point detecting apparatus according to the present invention.
[45] Referring to FIG. 3, a CMP apparatus 10 includes a platen 11 with a polishing pad 12 mounted on an upper portion thereof, an optical fiber cable 30 mounted on a portion of the polishing pad 12 through the platen for detecting a surface polishing state of a wafer 1, a wafer carrier 13 holding the wafer 1 and pressed downwards so that the polishing pad 12 comes in contact with a surface of the wafer 1, a slurry supply nozzle (not shown) for supplying a slurry on the polishing pad 12, and a conditioner carrier 16 holding and rotating a conditioner 16a for dressing a surface of the polishing pad 12 to prevent deformation or contamination of the polishing pad 12 and thus continuously maintain polishing capability of the polishing pad 12. In FIG. 3, reference numeral 13a denotes a polishing head for receiving the wafer 1 with vacuum suction, reference numeral 13b denotes a retainer ring for retaining the wafer 1, in which the wafer 1 is fixed to a bottom surface of the polishing head 13a with surface tension or vacuum suction, and reference numeral 15 denotes a spindle (not shown) for rotating the wafer carrier 13 and the conditioner carrier 16.
[46] The end point detecting apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[47] FIGs. 4 and 5 illustrate the structure of an optical fiber cable according to a preferable embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating the installation state of the end point detecting apparatus according to the present invention, and FIG. 5 is a perspective view illustrating a front end of the optical fiber cable with the elastic ring member.
[48] Referring to FIGs. 4 and 5, the end point detecting apparatus according to the present invention includes a platen 11 having at least one through-hole 11a formed in an axial direction, a polishing pad 12 detachably mounted on an upper portion of the platen and pressed by a wafer carrier 13 to which a semiconductor wafer is attached, the polishing pad 12 having a through-hole 12a coaxially corresponding to the through-hole 1 Ia of the platen 11, an optical fiber cable 30 inserted in the through-hole 1 Ia of the platen 11 and having an elastic ring member 31 mounted on a front end of the optical fiber cable, in which a portion of the optical fiber cable corresponding to the elastic ring member is hermetically received in the through-hole 12a of the polishing pad 12, and the optical fiber cable is composed of a light emitting fiber and a light receiving fiber, and a controller 40 each connected to the light emitting fiber and the light receiving fiber of the optical fiber cable for detecting the end point of the semiconductor wafer.
[49] With the above construction, the surface of the wafer 1 comes in contact with the polishing pad 12 by load of the wafer carrier 13 itself and a pressing force of the wafer carrier. The slurry is flowed in a fine clearance between the contact surfaces, so that mechanical polishing is performed by polishing particles contained in the slurry and surface bosses of the polishing pad 12 and simultaneously chemical polishing is performed by chemical components contained in the slurry, thereby polishing the surface of the wafer 1.
[50] The platen 11 is subject to any one of rotational motion, straight- line motion and translational motion with respect to the wafer carrier 13, and the wafer carrier 13 is subject to orbital motion with respect to the platen 11 which is in translational motion, or is subjected to rotational motion with respect to the platen which is in straight-line motion.
[51] The optical fiber cable 30 is inserted in the through-hole 1 Ia of the platen 11. In this instance, the platen 11 or the polishing pad 12 may be provided with at least one through-hole 11a and 12a. One end of the optical fiber cable 30 is each connected to the controller 40 for detecting the end point of the wafer polishing process via the light emitting fiber and the light receiving fiber, and the other end protrudes from the surface of the platen 11 to be inserted in the through-hole 12a of the polishing pad 12. If the optical fiber cable 30 with the elastic ring member 31 fixed to a distal end is secured to the polishing pad 12 of the platen 11, the optical fiber cable 30 is not moved with respect to the polishing pad 12. The polishing pad 12 is attached to or detached from the elastic ring member 31 of the optical fiber cable 30 by a constant force applied by an operator (see FIGs. 4 and 6).
[52] Preferably, the upper surface of the front end of the optical fiber cable 30 which is inserted in the through-hole 1 Ia of the platen 11 is coplanar with the upper surface of the polishing pad 12, or is positioned lower than the upper surface. If the upper surface of the distal end is positioned lower than the upper surface of the polishing pad 12, the front end of the optical fiber cable 30 does not come in contact with the pad conditioner for maintaining the roughness of the polishing pad 12 in process of polishing the semiconductor wafer, thereby prevent the surface of the front end of the optical fiber cable 30 from being damaged.
[53] As described above, the elastic ring member 31 closely contacts the outer periphery of the front end of the optical fiber cable 30 so as to protect the front end of the optical fiber cable 30 which is inserted in the through-hole 12a of the polishing pad 12 via the through-hole 1 Ia of the platen 11 and block penetration of the slurry used at the polishing. In this instance, a size of the through-hole 12a of the polishing pad 12 is preferably larger than an outer diameter of the optical fiber cable 30, and is smaller than an outer diameter of the elastic ring member 31. Preferably, the elastic ring member 31 is made of a material having an elastic characteristic, such as natural rubber, synthetic rubber or synthetic resin. Since the elastic ring member 31 integrally coupled to the outer periphery of the front end of the optical fiber cable 30 has elasticity, the elastic ring member 31 can be easily inserted in the through-hole 11a even though the outer diameter of the distal end is larger than the size of the through- hole 1 Ia. In this instance, the inserted distal end comes in close contact with the through-hole 12a to block the penetration of the slurry.
[54] The front end of the optical fiber cable 30 coupled with the elastic ring member 31 is covered by the optical transmission film 35 to seal and protect the front end. An adhesive may be applied on one side of the optical transmission film 35 to enable the optical transmission film to easily attach or detach. Preferably, the optical transmission film 35 has a thickness of 0.01 mm to 2 mm, light transmittance of 0.1% to 100%, chemical resistance and hydrophobicity. The upper surface of the front end of the optical fiber cable 30 can be protected against the slurry used when polishing the wafer or deionized water used when cleaning the wafer (see FIG. 5).
[55] The controller 40 is each connected to the light emitting fiber and the light receiving fiber of the optical fiber cable 30 to measure the end point of the semiconductor wafer polishing process. The optical fiber cable 30 is generally composed of one light emitting fiber and at least two light receiving fibers. The light emitting fiber is positioned at a center portion of the optical fiber cable 30, and the light receiving fibers are disposed around the light emitting fiber. Preferably, the optical fiber cable 30 sets a reference point at a portion of the wafer carrier 13, and a sensor (not shown) is attached to a predetermined position of the rotatable platen 11 provided with the optical fiber cable. The optical fiber cable emits light at least once when the sensor of the platen passes the reference point of the wafer carrier 13. The optical fiber cable emits light periodically as stated above, and so the light reflected from the surface of the wafer to be polished is collected and transmitted to the controller 40 to measure the status change of the wafer to be polished and thus detect the end point. In this instance, the wafer carrier 13 is preferably divided into multiple regions so as to correct the uniformity of the semiconductor wafer to be polished. The respective regions is freely adjusted and/or pressed. Meanwhile, the sensor may comprise an optical sensor and a high frequency sensor.
[56] While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings. On the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims.
[57]
Industrial Applicability
[58] As can be seen from the foregoing, the present invention does not require a separate polishing monitoring window, and fixes an end of an optical fiber cable with an elastic ring member, thereby effectively blocking penetration of slurry used at the polishing. Also, the end of the optical fiber cable is covered by an optical transmission film to prevent the optical fiber cable from being damaged by the slurry.
[59] In addition, the present invention can detect an end point accurately in a process of polishing, irrespective of penetration of the slurry and scattered reflection of a light source.

Claims

Claims
[1] An end point detecting apparatus for use in a process of polishing a surface of a semiconductor wafer, comprising: a platen having at least one through-hole formed in an axial direction; a polishing pad detachably mounted on an upper portion of the platen and pressed by a wafer carrier to which a semiconductor wafer is attached, the polishing pad having a through-hole coaxially corresponding to the through-hole of the platen; an optical fiber cable inserted in the through-hole of the platen and having an elastic ring member mounted on a front end of the optical fiber cable, in which a portion of the optical fiber cable corresponding to the elastic ring member is hermetically received in the through-hole of the polishing pad, and in which the optical fiber cable is composed of a light emitting fiber and a light receiving fiber; and a controller each connected to the light emitting fiber and the light receiving fiber of the optical fiber cable for detecting an end point of the semiconductor wafer.
[2] The end point detecting apparatus as claimed in claim 1, wherein the platen is subject to any one of rotational motion, straight- line motion and translational motion with respect to the wafer carrier, and the wafer carrier is subject to orbital motion with respect to the platen which is in translational motion, or is subjected to rotational motion with respect to the platen which is in straight-line motion.
[3] The end point detecting apparatus as claimed in claim 1, wherein an upper surface of the front end of the optical fiber cable which is fixed in the through- hole of the polishing pad is coplanar with an upper surface of the polishing pad, or is not positioned higher than the upper surface.
[4] The end point detecting apparatus as claimed in claim 1, wherein a reference point is set at a portion of the wafer carrier, and a sensor is attached to a predetermined position of the rotatable platen provided with the optical fiber cable, and wherein the optical fiber cable emits light at least once when the sensor of the platen passes the reference point of the wafer carrier.
[5] The end point detecting apparatus as claimed in claim 1, wherein one of the optical fiber cables measures a polishing degree of the wafer, and the other measures uniformity of the wafer.
[6] The end point detecting apparatus as claimed in claim 1, wherein the wafer carrier is divided into multiple regions so as to correct uniformity of the semiconductor wafer to be polished, in which the respective regions is freely adjusted and/or pressed. [7] The end point detecting apparatus as claimed in claim 1, wherein the elastic ring member is made of any one selected from the group consisting of natural rubber, synthetic rubber and synthetic resin. [8] The end point detecting apparatus as claimed in claim 1, wherein a size of the through-hole of the polishing pad is larger than an outer diameter of the optical fiber cable, and is smaller than an outer diameter of the elastic ring member. [9] The end point detecting apparatus as claimed in claim 1, wherein the front end of the optical fiber is detachably covered by an optical transmission film. [10] The end point detecting apparatus as claimed in claim 9, wherein the optical transmission film has a thickness of 0.01 mm to 2 mm. [11] The end point detecting apparatus as claimed in claim 9, wherein the optical transmission film has light transmittance of 0.1% to 100% and properties of chemical resistance and hydrophobicity.
PCT/KR2008/002781 2007-07-06 2008-05-19 End point detecting apparatus for semiconductor wafer polishing process WO2009008594A1 (en)

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WO2015029524A1 (en) * 2013-08-28 2015-03-05 Ｓｕｍｃｏ Ｔｅｃｈｘｉｖ株式会社 Method and device for polishing semiconductor wafer
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