WO2002028597A1 - Method and apparatus for electrochemical planarization of a workpiece - Google Patents

Method and apparatus for electrochemical planarization of a workpiece Download PDF

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Publication number
WO2002028597A1
WO2002028597A1 PCT/US2001/031120 US0131120W WO0228597A1 WO 2002028597 A1 WO2002028597 A1 WO 2002028597A1 US 0131120 W US0131120 W US 0131120W WO 0228597 A1 WO0228597 A1 WO 0228597A1
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WO
WIPO (PCT)
Prior art keywords
brushing
workpiece
motion
electrochemical planarization
metallized
Prior art date
Application number
PCT/US2001/031120
Other languages
French (fr)
Inventor
Saket Chadda
Chris Barns
Original Assignee
Speedfam-Ipec Corporation
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Filing date
Publication date
Application filed by Speedfam-Ipec Corporation filed Critical Speedfam-Ipec Corporation
Priority to AU2002211432A priority Critical patent/AU2002211432A1/en
Publication of WO2002028597A1 publication Critical patent/WO2002028597A1/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
    • B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces
    • B24B37/046—Lapping machines or devices; Accessories designed for working plane surfaces using electric current
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
    • B23H5/00—Combined machining
    • B23H5/06—Electrochemical machining combined with mechanical working, e.g. grinding or honing
    • B23H5/08—Electrolytic grinding
    • 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
    • B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces
    • B24B37/07—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool
    • B24B37/08—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool for double side lapping
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
    • B24D13/00—Wheels having flexibly-acting working parts, e.g. buffing wheels; Mountings therefor
    • B24D13/14—Wheels having flexibly-acting working parts, e.g. buffing wheels; Mountings therefor acting by the front face
    • B24D13/145—Wheels having flexibly-acting working parts, e.g. buffing wheels; Mountings therefor acting by the front face having a brush-like working surface
    • 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 potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table 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
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
    • H01L21/321—After treatment
    • H01L21/32115—Planarisation
    • 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 potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table 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
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
    • H01L21/321—After treatment
    • H01L21/32115—Planarisation
    • H01L21/3212—Planarisation by chemical mechanical polishing [CMP]
    • H01L21/32125—Planarisation by chemical mechanical polishing [CMP] by simultaneously passing an electrical current, i.e. electrochemical mechanical polishing, e.g. ECMP
    • 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 potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
    • H01L21/283—Deposition of conductive or insulating materials for electrodes conducting electric current
    • H01L21/288—Deposition of conductive or insulating materials for electrodes conducting electric current from a liquid, e.g. electrolytic deposition
    • H01L21/2885—Deposition of conductive or insulating materials for electrodes conducting electric current from a liquid, e.g. electrolytic deposition using an external electrical current, i.e. electro-deposition

Definitions

  • the present invention relates, generally, to systems for polishing or planarizing workpieces, such as semiconductor wafers. More particularly, it relates to an apparatus and method for electrochemical planarization of a wafer having a metallized surface.
  • metallization which generally refers to the materials, methods and processes of wiring together or interconnecting the component parts of an integrated circuit located on the surface of a wafer, is critical to the operation of a semiconductor device.
  • the "wiring" of an integrated circuit involves etching trenches, or "vias", in a planar dielectric (insulator) layer and filling the trenches with a metal.
  • the primary metallization material used in semiconductor fabrication was aluminum due to the leakage and adhesion problems experienced with the use of gold and the high contact resistance with silicon experienced with copper.
  • Other metallization materials have included Ni, Ta, Ti, W, Ag, Cu/Al, TaN, TiN, CoWP, NiP and CoP.
  • the semiconductor industry has slowly been moving to the use of copper for metallization due to the alloying and electromigration problems that are seen with aluminum.
  • a barrier layer of another material is first deposited to line the trenches and vias to prevent the migration of copper into the dielectric layer.
  • Barrier metals may be W, Ti, TiN, Ta, TaN, various alloys, and other refractory nitrides, which may be deposited by CVD, PFD, or electroless or electrolytic plating.
  • extra metal is deposited in the process, such metal covering areas of the wafer above and outside the trenches and vias.
  • planarization is typically conducted to remove the extra metal down to the dielectric surface. Planarization leaves the trenches and vias filled and results in a flat, polished surface.
  • an extremely flat surface is generally needed on at least one side of the semiconductor wafer to ensure proper accuracy and performance of the microelectronic structures being created on the wafer surface.
  • the need for precise wafer surfaces becomes more important. Therefore, between each processing step, it is usually necessary to polish or planarize the surface of the wafer to obtain the flattest surface possible.
  • CMP Chemical mechanical planarization
  • Arai et al. U.S. Pat. No. 4,805,348, issued February 1989; Arai et al., U.S. Patent No. 5,099,614, issued March 1992; Karlsrud et al., U.S. Pat. No. 5,329,732, issued July 1994; Karlsrud, U.S. Pat. No. 5,498,196, issued March 1996; and Karlsrud et al., U.S. Pat. No. 5,498,199, issued March 1996.
  • a CMP machine typically includes a wafer carrier configured to hold, rotate, and transport a wafer during the process of polishing or planarizing the wafer.
  • a pressure applying element e.g., a rigid plate, a bladder assembly, or the like
  • the carrier and the polishing surface are rotated, typically at different rotational velocities, to cause relative lateral motion between the polishing surface and the wafer and to promote uniform planarization.
  • the polishing surface comprises a horizontal polishing pad that has an exposed abrasive surface of, for example, cerium oxide, aluminum oxide, fumed/precipitated silica or other particulate abrasives.
  • Polishing pads can be formed of various materials, as is known in the art, and which are available commercially.
  • the polishing pad may be blown polyurethane, such as the IC and GS series of polishing pads available from Rodel Products Corporation in Scottsdale, Arizona. The hardness and density of the polishing pad depend on the material that is to be polished.
  • CMP tends to work very well for planarization if the correct slurry and process parameters are used, it may leave stresses in the worked workpiece, leading to subsequent cracking and shorting between metal layers.
  • the semiconductor industry is increasing use of low k dielectrics, which tend to be fragile materials. CMP may result in shearing or crushing of these fragile layers. CMP also has a tendency to cause dishing into the center of wide metal features, such as trenches and vias, oxide erosion between metal features, and oxide loss of the dielectric.
  • Electrochemical planarization is an attractive alternative to CMP because it does not create stress in the workpiece and, consequently, does not reduce the integrity of the low k dielectric devices to the extent CMP may. Further, electrochemical planarization is less likely to cause dishing, oxide erosion and oxide loss of the dielectric layer.
  • Electrochemical planarization is based on electropolishing and electrochemical machining, that is, the removal of metal from a substrate by the combination of an electrochemical solution and electricity.
  • Figure 1 shows a conventional electroetching cell available in the prior art.
  • a tank 2 holds a liquid electrolyte 4, an aqueous solution of a salt.
  • Two electrodes, an anode 6 and a cathode 8, are wired to a voltage source, such as a battery 10.
  • metal atoms in the anode 6 are ionized by the electricity and go into the solution as ions.
  • the metal ions from anode 6 either plate the cathode 8, fall out as precipitate, or stay in solution.
  • FIG. 2 shows a dielectric layer 12 having trenches, or vias, and having a barrier metal layer 20 thereon.
  • a metal layer 14 is deposited on the wafer over the barrier layer, filling the trenches. After being deposited on barrier layer 20, metal layer 14 may not be completely flat but, rather, may have areas of high topography 16 and low topography
  • step-height reduction is desired, that is, the selective removal of the metal layer at the high topography areas, followed by uniform removal of the metal layer. Step-height reduction should result in metal remaining only in the trenches and vias with a flat surface therein, as illustrated in Figure 3.
  • Standard equipment in conventional semiconductor processing facilities includes wafer cleaning machines which thoroughly clean and rinse processed wafers to ensure that debris is removed from the wafers.
  • the apparatus further includes a first driver assembly, configured to cause relative motion between the workpiece and the first brushing surface, and a first conductive element disposed adjacent the first brushing surface.
  • a first power supply is configured to effect an electric potential difference between the metallized surface of the workpiece and the first conductive element.
  • the apparatus further includes a first solution application mechanism configured to supply an electrolytic solution to the first metallized surface.
  • an electrochemical planarization apparatus is further configured to planarize a workpiece having a second metallized surface opposing the first metallized surface.
  • the apparatus further includes a second brushing surface configured to press against the second metallized surface of the workpiece, a second conductive element disposed adjacent the second brushing surface and a second solution application mechanism configured to supply an electrolytic solution to the second metallized surface.
  • the first brushing surface is disk-shaped.
  • the first brushing surface is a roller configured to rotate about a longitudinal axis. In accordance with yet another embodiment of the present invention, the first brushing surface is perforated.
  • the first brushing surface is porous.
  • the second brushing surface is disk-shaped.
  • the second brushing surface is a roller configured to rotate about a longitudinal axis.
  • the second brushing surface is perforated.
  • the second brushing surface is porous.
  • a method of planarizing a metallized surface on a workpiece includes the steps of: providing a brushing surface configured to press against a metallized surface of the workpiece; providing a conductive element disposed adjacent the brushing surface; pressing the brushing surface against the metallized surface while causing relative motion between the workpiece and the brushing surface; supplying an electrolytic solution to the metallized surface; and effecting an electric potential difference between the metallized surface of the workpiece and the conductive element.
  • an apparatus for the electrochemical planarization of a workpiece having at least one metallized surface includes a plurality of brushing rollers, each roller having a conductive element and a longitudinal axis and each configured to press against the metallized surface.
  • a motor assembly is configured to rotate the brushing rollers about their respective longitudinal axes.
  • the apparatus further includes a power supply configured to effect an electric potential difference between the metallized surface of the workpiece and the conductive elements, and a solution application mechanism configured to supply an electrolytic solution to the metallized surface.
  • Figure 1 is a schematic illustration of an electroetching cell of the prior art
  • Figure 2 is a cross-sectional view of a substrate with a metal layer
  • Figure 3 is a cross-sectional view of a substrate with metal-filled trenches
  • Figure 4 is a schematic side view representation of an exemplary embodiment of an ECP apparatus of the present invention.
  • Figure 5 is a schematic side view representation of another exemplary embodiment of an ECP apparatus of the present invention.
  • Figure 6 is a schematic cross-sectional side view representation of yet another exemplary embodiment of an ECP apparatus of the present invention.
  • ECP apparatus 30 may employ a standard cleaning apparatus which uses "pancake"-style brush pads.
  • a typical cleaning apparatus using pancake-style brush pads is disclosed in U.S. Patent No. 5,144,711, issued to Gill on September 8, 1992, and U.S. Patent No. 5,870,793, issued to Choffat et al. on February 16, 1999, the contents both of which are incorporated herein by reference.
  • a cleaning apparatus of this nature typically is used to scrub semiconductor wafers after chemical mechanical planarization to remove particles of the slurry left on the surface of the wafer.
  • Such flat pancake pads are typically fixed onto a mounting plate with an adhesive and the mounting plate is attached to a holder by bolts, machine screws, or other mechanical fasteners.
  • the pad is part of a wafer cleaning machine which rotates the mounting plate and pad against the major flat surface of the semiconductor wafer being cleaned.
  • a wafer 40 having opposing metallized surfaces 40b and 40c is supported by a plurality of wafer holders 50 which contact wafer 40 along a peripheral side surface 40a.
  • Apparatus 30 includes three cleaning members.
  • the first two cleaning members are disc-shaped brushes 60a and 60b which are disposed on opposite surfaces 40b and 40c of wafer 40 and which are frictionally engageable with the opposite surfaces of wafer 40 for cleaning the same.
  • the surfaces of brushes 60a and 60b that are proximate to surfaces 40b and 40c, respectively, have a plurality of perpendicularly extending nubs 130.
  • Each nub has a cylindrical shape with a flat exposed end that is substantially coplanar with the exposed ends of the other nubs.
  • Brushes 60a and 60b are configured to rotate about a vertical axis 80.
  • brushes 60a and 60b may oscillate relative to wafer 40 in the directions of arrows B, D.
  • brushes 60a and 60b may move in an orbital motion relative to wafer 40.
  • the third cleaning member a roller 70
  • roller 70 is frictionally engageable with the peripheral side surface 40a of wafer 40 for cleaning this edge.
  • Roller 70 is configured to rotate about a vertical axis 90. While apparatus 30 is illustrated in Figure 4 using only one roller 70, it will be appreciated that two or more rollers 70 may be used. Alternatively, apparatus 30 may not employ roller 70, relying on brushes 60a and 60b to remove copper debris from side surface 40a.
  • the hardness and density of brushes 60a and 60b and roller 70 are selected based on the type of material to be planarized.
  • the brushes may be made from polyvinyl acetate (PVA), polyurethane or any other suitable material capable of frictionally engaging wafer 40 to planarize wafer 40 and remove copper debris therefrom.
  • PVA polyvinyl acetate
  • polyurethane any other suitable material capable of frictionally engaging wafer 40 to planarize wafer 40 and remove copper debris therefrom.
  • Brushes 60a and 60b should be sufficiently thick to prevent wafer 40 from coming into direct contact with conductive members 120a and 120b, described below.
  • brushes 60a and 60b are preferably uniformly perforated with a plurality of perforations 160 so as to permit conduction between wafer. surfaces 40b and 40c of wafer 40 and conductive members 120a and 120b.
  • brushes 60a and 60b may be porous so as to permit conduction between wafer surfaces 40b and 40c of wafer 40 and conductive members 120a and 120b.
  • Wafer 40 may be held in a stationary position by wafer holders 50 or wafer holders 50 may be configured to rotate about their vertical axes so that wafer 40 rotates about an axis 100 at the same time as brushes 60a and 60b are rotating about their axes 80.
  • apparatus 30 may use orbital motion of wafer 40 rather than rotational motion to planarize wafer 40.
  • An example of polishing a wafer by orbital motion is disclosed more fully in U.S. Patent No. 5,554,064, issued September 10, 1996 to Brievogel, et al., which patent is incorporated herein by reference.
  • apparatus 30 also includes conductive members 120a and 120b, which are disposed above and below wafer 40 adjacent brushes 60a and 60b.
  • Conductive members 120a and 120b may be made from a metal, such as copper, or any suitable conductive material.
  • An electric potential difference is effected between conductive members 120a and 120b and the metallized surfaces 40b and 40c, respectively, of wafer 40 by voltage sources 140, 150 which apply a positive charge to surfaces 40b and 40c of wafer 40 and a negative charge to conductive members 120a and 120b. While the exemplary embodiment of Figure 4 shows two voltage sources, it will be appreciated that any number of any conventional techniques for effecting an electric potential difference between conductive members 120a and 120b and wafer 40 may be employed.
  • An electrolytic planarizing solution may be applied by conduits 110.
  • the electrolytic planarizing solution may be supplied through brushes 60a and 60b through a manifold apparatus (not shown) and perforations 160, or by any suitable distribution device.
  • the electrolytic planarizing solution may include such materials as ammonium phosphate, phosphoric acid, copper sulfate, sulfuric acid, chromic acid and/or additives, or may be a combination of such materials and a conventional CMP slurry.
  • brushes 60a and 60b are pressed against surfaces 40b and 40c, respectively, with a desired amount of force while rotating about their respective vertical axes.
  • brushes 60a and 60b are pressed against surfaces 40b and 40c at a pressure of approximately 0.5 psi or less, although it may be appreciated that any suitable pressure which promotes planarization may be used.
  • Wafer carriers 50 may also be rotated about their vertical axes so that wafer 40 rotates about axis 100.
  • An electrolytic planarizing solution is supplied to both surfaces 40b and 40c of wafer 40.
  • any remaining metal from the metallized surface and the remaining exposed barrier layer 20, shown in Figure 2 may be removed by standard etching processes, such as wet etch, vapor etch, spray etch, plasma etch or chemical mechanical planarization, since the surface of the wafer had just previously been substantially planarized with the present invention. Selection of the etch method and chemistry depends on the barrier layer chemistry.
  • apparatus 30 could be modified so that electrochemical planarization is performed on only one surface of the wafer.
  • wafer 40 could be supported on side 40c by a conventional rotating platen and electrochemical planarization could be performed selectively on side 40b.
  • An advantage of the ECP apparatus of the present invention is that, with concurrent electrochemical etching and mechanical scrubbing of wafer, the metallized surface is removed first from high topography areas, and subsequently uniformly etched and planarized.
  • the electrochemical etching aspect of the invention enables high removal rates at low pressure, which reduces dishing and oxide erosion.
  • a further advantage is that, because a standard washing apparatus may be retrofitted to perform ECP as described herein, specialized ECP machines do not need to be purchased and additional equipment costs are thereby reduced.
  • an alternative embodiment 200 of the ECP apparatus of the present invention may use brush rollers to planarize a wafer having metallized surfaces on opposing surfaces of the wafer.
  • brush rollers For a discussion of a cleaning apparatus using rollers, see U.S. Patent No. 5,975,094 issued to Shurtliff on November 2, 1999, the contents of which are incorporated herein by this reference.
  • a wafer 210 having opposing metallized surfaces 210b and 210c is supported by a plurality of wafer holders 220 which contact wafer 210 along a peripheral side surface 210a.
  • Apparatus 200 includes three cleaning members.
  • the first two cleaning members are brush rollers 240a and 240b which are disposed adjacent the metallized surfaces 210b and 210c of wafer 210 and which are frictionally engageable with the opposite sides of wafer 210 for cleaning the same.
  • Brush rollers 240a and 240b are preferably substantially cylindrical in shape and are configured • to rotate about their respective longitudinal axes 250a and 250b, while moving translationally over the surface of the wafer 210.
  • Brush rollers 240a and 240b may be made from polyvinyl acetate (PVA), polyurethane or any other suitable material.
  • brush rollers 240a and 240b are preferably uniformly perforated with a plurality of perforations 320 so as to permit conduction between wafer surfaces 210b and 210c of wafer 210 and conductive members 260a and 260b, discussed below.
  • brush rollers 240a and 240b may be porous so as to permit conduction between wafer surfaces 210b and 210c of wafer 210 and conductive members 260a and 260b.
  • a third cleaning member is a roller 270 which is frictionally engageable with the peripheral side surface 210a of wafer 210 for cleaning this edge.
  • Roller 270 is configured to rotate about a vertical axis 280. While apparatus 200 is illustrated in Figure 5 using only one roller 270, it will be appreciated that two or more rollers 270 may be used. Alternatively, apparatus 200 may not employ roller 270, relying on brush rollers 240a and 240b to remove copper debris from side surface 210a. Wafer 210 may be held in a stationary position by wafer holders 220 or, alternatively, wafer holders 220 may be configured to rotate about their vertical axes so that wafer 210 rotates about an axis 290 at the same time as brush rollers 240a and 240b are rotating about their axes 250a and 250b.
  • each brush roller 240a and 240b includes a conductive member, conductive members 260a and 260b, respectively.
  • Conductive members 260a and 260b are positioned within brush rollers 240a and 240b, respectively, and extend approximately the entire length of brush rollers 240a and 240b.
  • An electric potential difference is effected between conductive members 260a and 260b and the metallized surfaces 210b and 210c of wafer 210 by voltage sources 300 and 310 which apply a positive charge to the surfaces 210b and 210c of the wafer and a negative charge to conductive members 260a and 260b.
  • An electrolytic planarizing solution which may include an electrolytic solution or an electrolytic solution combined with a conventional CMP slurry, may be supplied through brush rollers 240a and 240b and perforations 320, or by any suitable distribution device.
  • brush rollers 240a and 240b are pressed against surfaces 210b and 210c, respectively, while rotating about their respective longitudinal axes.
  • Wafer carriers 220 may also be rotated about their vertical axes so that wafer 210 rotates about axis 290.
  • An electrolytic planarizing solution is supplied to both surfaces 210b and 210c of wafer 210.
  • metal ions are liberated from sides 210a, 210b and 210c of wafer 210, thereby resulting in deplating of the metallized surfaces from the wafer.
  • Figure 5 illustrates an exemplary embodiment of the present invention which employs two brush rollers positioned on opposite surfaces 210b and 210c of wafer 210 to electrochemically planarize those surfaces simultaneously
  • the present invention could employ only one roller brush on one surface of the wafer to planarize that surface.
  • multiple brush rollers may be positioned on one surface of the wafer to planarize that surface.
  • FIG. 6 illustrates yet another embodiment of the present invention, a cleaning station 400, configured for the electrochemical planarization of a wafer having at least one metallized surface.
  • Cleaning station 400 may be incorporated within a larger machine for processing or cleaning semiconductor wafers (or other workpieces) e.g., as described in U.S. Patent No. 5,950,327, issued to Peterson et al. on September 14, 1999, the entire content of which is incorporated by reference herein.
  • Cleaning station 400 preferably comprises an enclosure, e.g., a scrubber box, enclosing a plurality of pairs of brush rollers.
  • Cleaning station 400 comprises a bottom panel 412, a top panel 414, side panels 410, a rear panel (not shown) and a front panel (not shown).
  • the panels comprise a self-contained box, which can be quickly and easily removed using a handle 420 and replaced when it is desired to replace one or more of the brush rollers.
  • Cleaning station 400 comprises a plurality of brush roller pairs configured to drive wafers through the scrubber box and to simultaneously electrochemically planarize the top and/or bottom flat surfaces of wafers passing therethrough.
  • cleaning station 400 preferably includes a wafer input 416 configured to receive wafers into the enclosure. When a wafer enters the enclosure, the first pair of drive rollers (described below) "grabs" the wafer and feeds it forward to the next pair of rollers.
  • Cleaning station 400 may have any number of pairs of rollers, although for convenience Figure 6 illustrates a cleaning station having six pairs of rollers.
  • the scrubber box includes a first brush roller pair comprising respective rollers 430 and 432; a second roller pair comprising upper brush roller 434 and lower brush roller 436; a third roller pair comprising upper brush roller 438 and lower brush roller 440; a fourth pair comprising upper brush roller 442 and lower brush roller 444; a fifth pair comprising upper brush roller 446 and lower brush roller 448; and a sixth terminal roller pair comprising upper brush roller 450 and lower brush roller 452.
  • Cleaning station 400 is configured such that wafers enter from the far left, are sequentially urged through the station, and are discharged from the station at the far right position (proximate rollers 450 and 452).
  • Each of the odd pairs of rollers preferably functions as a drive roller, with each drive roller pair operating at a drive speed SI.
  • brush rollers 430, 432, 438, 440, 446 and 448 operate at drive speed SI.
  • the bottom brush rollers i.e., rollers 432, 436, 440, 444, 448 and 452 rotate clockwise, as shown.
  • the top brush roller of each even brush roller pair i.e., brush rollers 434, 442 and 450
  • the top roller in each odd brush roller pair i.e., 430, 438 and 446) preferably rotates counterclockwise.
  • Each of the even pairs of rollers preferably are configured to operate at a process speed S2.
  • Each odd roller pair is preferably driven by a first drive motor (not shown) so that the wafers are driven through the cleaning station 400 at an essentially uniform rate.
  • Each even roller pair is preferably driven by a second motor at process speed S2.
  • an operator may control the drive speed SI by setting a first control associated with the first motor and may also independently control processing speed S2 by manipulating a second control associated with the second motor.
  • roller speeds are illustrated in Figure 6, it is to be understood that virtually any number of rollers and any combination of roller speeds and roller directions may be employed in the context of the present invention. For example, two, three or even more roller speeds may be employed with various permutations and combinations of speed and direction being selected to achieve optimum performance for a desired application.
  • Each of the even pairs of brush rollers 434, 436, 442, 444, 450 and 452 include conductive member 454, 456, 458, 460, 462 and 464, respectively.
  • Conductive members 454, 456, 458, 460, 462 and 464 are positioned within, and extend approximately the entire length of, the respective brush rollers.
  • Brush rollers 434, 436, 442, 444, 450 and 452 may be made from polyvinyl acetate (PVA), polyurethane or any other suitable material.
  • these brush rollers are preferably uniformly perforated so as to permit conduction between the conductive members and the wafer.
  • these brush rollers may be porous so as to permit conduction between the conductive members and the wafer.
  • Top panel 414 may further include one or more fluid inlet ports (not shown) configured to distribute fluids to a discrete portion of, or to the entirety of, the inside of cleaning station 400.
  • Top panel 414 also may include a number of manifolds (not shown) arranged to deliver fluid to specific locations within cleaning station 400.
  • top panel 414 may comprise a first manifold to deliver an electrolytic planarizing solution, a second manifold to deliver conventional slurry, and a third manifold to deliver deionized water.
  • Each individual manifold is configured such that it is fluidly distinct from each of the remaining manifolds.
  • one or more of the fluid inlet ports may be coupled together such that a single fluid may be applied to more than one manifold.
  • the manifolds may be configured to distribute fluid to locations above and/or between adjacent brush rollers. This arrangement permits the fluid to reach wafers as they pass through the cleaning station.
  • Cleaning station 400 may also include a fluid outlet (not shown) through which the electrolytic solution may flow during or after the planarization procedure. If desired, the electrolytic solution retrieved from the fluid outlet may be recycled, disposed of, or handled as desired.
  • a wafer enters cleaning station 416, is "grabbed" by brush rollers 430 and 432 and is urged forward to the outlet of cleaning station 400.
  • An electrolytic planarization solution is distributed to the rollers and an electric potential difference is effected between the conductive members of the brush rollers and the wafer.
  • metal ions are liberated from the metallized surfaces, thereby resulting in deplating of the metallized surfaces.
  • As the wafer contacts the brush rollers it is further planarized by the abrasive action of the brush rollers and any abrasive particulates in the planarization solution. As a result, the areas of high topography on the metallized surface are removed, after which uniform etching and planarizing subsequently take place.

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Abstract

An electrochemical planarization apparatus (30) for planarizing a workpiece which has at least one metallized surface (40). The apparatus (30) includes a first brushing surface (60) configured to frictionally engage the metallized surface (40) of the workpiece (40), a first driver assembly configured to cause relative motion between the metallized surface (40) of the workpiece (40) and the first brushing surface (60), and a first conductive element (120) disposed proximate the first brushing surface (60). The apparatus (30) also includes a first power supply configured to effect an electric potential difference between the metallized surface (40) of the workpiece (40) and the first conductive element (120), and a first solution application mechanism (110) configured to supply an electrolytic solution to the first metallized surface (40). The apparatus may also have a second brushing surface (60), a second conductive element (120) disposed proximate the second brushing surface, a second solution application mechanism (110), and a second power supply.

Description

METHOD AND APPARATUS FOR ELECTROCHEMICAL PLANARIZATION OF A WORKPIECE
Technical Field The present invention relates, generally, to systems for polishing or planarizing workpieces, such as semiconductor wafers. More particularly, it relates to an apparatus and method for electrochemical planarization of a wafer having a metallized surface.
Background The production of integrated circuits begins with the creation of high-quality semiconductor wafers. During the wafer fabrication process, the wafers may undergo multiple masking, etching, and dielectric and conductor deposition processes. In addition, metallization, which generally refers to the materials, methods and processes of wiring together or interconnecting the component parts of an integrated circuit located on the surface of a wafer, is critical to the operation of a semiconductor device. Typically, the "wiring" of an integrated circuit involves etching trenches, or "vias", in a planar dielectric (insulator) layer and filling the trenches with a metal.
In the past, the primary metallization material used in semiconductor fabrication was aluminum due to the leakage and adhesion problems experienced with the use of gold and the high contact resistance with silicon experienced with copper. Other metallization materials have included Ni, Ta, Ti, W, Ag, Cu/Al, TaN, TiN, CoWP, NiP and CoP. Over time, the semiconductor industry has slowly been moving to the use of copper for metallization due to the alloying and electromigration problems that are seen with aluminum. When copper is used as the filling, typically a barrier layer of another material is first deposited to line the trenches and vias to prevent the migration of copper into the dielectric layer. Barrier metals may be W, Ti, TiN, Ta, TaN, various alloys, and other refractory nitrides, which may be deposited by CVD, PFD, or electroless or electrolytic plating. To achieve good fill of the trenches and vias, extra metal is deposited in the process, such metal covering areas of the wafer above and outside the trenches and vias. After filling, planarization is typically conducted to remove the extra metal down to the dielectric surface. Planarization leaves the trenches and vias filled and results in a flat, polished surface.
Because of the high precision required in the production of integrated circuits, an extremely flat surface is generally needed on at least one side of the semiconductor wafer to ensure proper accuracy and performance of the microelectronic structures being created on the wafer surface. As the size of the integrated circuits continues to decrease and the density of microstructures on an integrated circuit increases, the need for precise wafer surfaces becomes more important. Therefore, between each processing step, it is usually necessary to polish or planarize the surface of the wafer to obtain the flattest surface possible.
Chemical mechanical planarization (CMP) is a technique conventional used for planarization of semiconductor wafers. For a discussion of chemical mechanical planarization (CMP) processes and apparatus, see, for example, Arai et al., U.S. Pat. No. 4,805,348, issued February 1989; Arai et al., U.S. Patent No. 5,099,614, issued March 1992; Karlsrud et al., U.S. Pat. No. 5,329,732, issued July 1994; Karlsrud, U.S. Pat. No. 5,498,196, issued March 1996; and Karlsrud et al., U.S. Pat. No. 5,498,199, issued March 1996.
Typically, a CMP machine includes a wafer carrier configured to hold, rotate, and transport a wafer during the process of polishing or planarizing the wafer. During a planarization operation, a pressure applying element (e.g., a rigid plate, a bladder assembly, or the like) that may be integral to the wafer carrier, applies pressure such that the wafer engages a polishing surface with a desired amount of force. The carrier and the polishing surface are rotated, typically at different rotational velocities, to cause relative lateral motion between the polishing surface and the wafer and to promote uniform planarization.
In general, the polishing surface comprises a horizontal polishing pad that has an exposed abrasive surface of, for example, cerium oxide, aluminum oxide, fumed/precipitated silica or other particulate abrasives. Polishing pads can be formed of various materials, as is known in the art, and which are available commercially. Typically, the polishing pad may be blown polyurethane, such as the IC and GS series of polishing pads available from Rodel Products Corporation in Scottsdale, Arizona. The hardness and density of the polishing pad depend on the material that is to be polished.
While CMP tends to work very well for planarization if the correct slurry and process parameters are used, it may leave stresses in the worked workpiece, leading to subsequent cracking and shorting between metal layers. In addition, the semiconductor industry is increasing use of low k dielectrics, which tend to be fragile materials. CMP may result in shearing or crushing of these fragile layers. CMP also has a tendency to cause dishing into the center of wide metal features, such as trenches and vias, oxide erosion between metal features, and oxide loss of the dielectric.
Electrochemical planarization is an attractive alternative to CMP because it does not create stress in the workpiece and, consequently, does not reduce the integrity of the low k dielectric devices to the extent CMP may. Further, electrochemical planarization is less likely to cause dishing, oxide erosion and oxide loss of the dielectric layer.
Electrochemical planarization is based on electropolishing and electrochemical machining, that is, the removal of metal from a substrate by the combination of an electrochemical solution and electricity. Figure 1 shows a conventional electroetching cell available in the prior art. A tank 2 holds a liquid electrolyte 4, an aqueous solution of a salt.
Two electrodes, an anode 6 and a cathode 8, are wired to a voltage source, such as a battery 10.
When the apparatus is electrified, metal atoms in the anode 6 are ionized by the electricity and go into the solution as ions. Depending on the chemistry of the metals and salt, the metal ions from anode 6 either plate the cathode 8, fall out as precipitate, or stay in solution.
When used for planarization of metal films on semiconductor wafers, conventional electrochemical planarization presents the disadvantage that the metal is not selectively removed from the wafer. Figure 2 shows a dielectric layer 12 having trenches, or vias, and having a barrier metal layer 20 thereon. A metal layer 14 is deposited on the wafer over the barrier layer, filling the trenches. After being deposited on barrier layer 20, metal layer 14 may not be completely flat but, rather, may have areas of high topography 16 and low topography
18. With conventional electrochemical planarization, the metal layer is removed uniformly, so that the areas of high topography and low topography remain. In planarization, however, "step-height reduction" is desired, that is, the selective removal of the metal layer at the high topography areas, followed by uniform removal of the metal layer. Step-height reduction should result in metal remaining only in the trenches and vias with a flat surface therein, as illustrated in Figure 3.
Due to the high cost of processing equipment, semiconductor manufacturers often prefer to use existing processing equipment to perform multiple functions. Standard equipment in conventional semiconductor processing facilities includes wafer cleaning machines which thoroughly clean and rinse processed wafers to ensure that debris is removed from the wafers.
For a discussion of existing wafer cleaning machines, see, for example, U.S. Patent No.
5,357,645, issued to Onodera on October 25, 1994, and U.S. Patent No. 6,012,193, issued to Inoue et al. on January 11, 2000. It would be desirable to modify or retrofit wafer cleaning machines to be able to perform electrochemical planarization, thereby reducing equipment costs.
Accordingly, there exists a need for an electrochemical planarization method and apparatus which accomplishes step-height reduction of metal layers on substrates, followed by uniform planarization of the metal layer. There exists a further need for an electrochemical planarization technique that may be retrofitted to existing processing equipment.
Summary of the Invention
These and other aspects of the present invention will become more apparent to those skilled in the art from the following non-limiting detailed description of preferred embodiments of the invention taken with reference to the accompanying figures.
In accordance with an exemplary embodiment of the present invention, an electrochemical planarization apparatus for planarizing a workpiece having at least one metallized surface includes a first brushing surface configured to press against the metallized surface of the workpiece. The apparatus further includes a first driver assembly, configured to cause relative motion between the workpiece and the first brushing surface, and a first conductive element disposed adjacent the first brushing surface. A first power supply is configured to effect an electric potential difference between the metallized surface of the workpiece and the first conductive element. The apparatus further includes a first solution application mechanism configured to supply an electrolytic solution to the first metallized surface.
In accordance with a further embodiment of the present invention, an electrochemical planarization apparatus is further configured to planarize a workpiece having a second metallized surface opposing the first metallized surface. The apparatus further includes a second brushing surface configured to press against the second metallized surface of the workpiece, a second conductive element disposed adjacent the second brushing surface and a second solution application mechanism configured to supply an electrolytic solution to the second metallized surface.
In accordance with another embodiment of the present invention, the first brushing surface is disk-shaped.
In accordance with yet a further embodiment of the present invention, the first brushing surface is a roller configured to rotate about a longitudinal axis. In accordance with yet another embodiment of the present invention, the first brushing surface is perforated.
In accordance with a further embodiment of the present invention, the first brushing surface is porous. In accordance with another embodiment of the present invention, the second brushing surface is disk-shaped.
In accordance with a further embodiment of the present invention, the second brushing surface is a roller configured to rotate about a longitudinal axis. In accordance with yet a further embodiment of the present invention, the second brushing surface is perforated.
In accordance with another embodiment of the present invention, the second brushing surface is porous.
In accordance with yet another embodiment of the present invention, a method of planarizing a metallized surface on a workpiece includes the steps of: providing a brushing surface configured to press against a metallized surface of the workpiece; providing a conductive element disposed adjacent the brushing surface; pressing the brushing surface against the metallized surface while causing relative motion between the workpiece and the brushing surface; supplying an electrolytic solution to the metallized surface; and effecting an electric potential difference between the metallized surface of the workpiece and the conductive element.
In accordance with yet a further embodiment of the present invention, an apparatus for the electrochemical planarization of a workpiece having at least one metallized surface includes a plurality of brushing rollers, each roller having a conductive element and a longitudinal axis and each configured to press against the metallized surface. A motor assembly is configured to rotate the brushing rollers about their respective longitudinal axes. The apparatus further includes a power supply configured to effect an electric potential difference between the metallized surface of the workpiece and the conductive elements, and a solution application mechanism configured to supply an electrolytic solution to the metallized surface.
Brief Description of the Drawings
Exemplary embodiments of the present invention will hereafter be described in conjunction with the appended drawing figures, wherein like designations denote like elements, and: Figure 1 is a schematic illustration of an electroetching cell of the prior art;
Figure 2 is a cross-sectional view of a substrate with a metal layer;
Figure 3 is a cross-sectional view of a substrate with metal-filled trenches;
Figure 4 is a schematic side view representation of an exemplary embodiment of an ECP apparatus of the present invention;
Figure 5 is a schematic side view representation of another exemplary embodiment of an ECP apparatus of the present invention; and
Figure 6 is a schematic cross-sectional side view representation of yet another exemplary embodiment of an ECP apparatus of the present invention.
Detailed Description of the Invention
The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth.
A schematic representation of an exemplary embodiment of an electrochemical planarization (ECP) apparatus 30 of the present invention is illustrated in Figure 4. ECP apparatus 30 may employ a standard cleaning apparatus which uses "pancake"-style brush pads. A typical cleaning apparatus using pancake-style brush pads is disclosed in U.S. Patent No. 5,144,711, issued to Gill on September 8, 1992, and U.S. Patent No. 5,870,793, issued to Choffat et al. on February 16, 1999, the contents both of which are incorporated herein by reference. A cleaning apparatus of this nature typically is used to scrub semiconductor wafers after chemical mechanical planarization to remove particles of the slurry left on the surface of the wafer. Such flat pancake pads are typically fixed onto a mounting plate with an adhesive and the mounting plate is attached to a holder by bolts, machine screws, or other mechanical fasteners. The pad is part of a wafer cleaning machine which rotates the mounting plate and pad against the major flat surface of the semiconductor wafer being cleaned.
Referring to Figure 4, a wafer 40 having opposing metallized surfaces 40b and 40c is supported by a plurality of wafer holders 50 which contact wafer 40 along a peripheral side surface 40a. Apparatus 30 includes three cleaning members. The first two cleaning members are disc-shaped brushes 60a and 60b which are disposed on opposite surfaces 40b and 40c of wafer 40 and which are frictionally engageable with the opposite surfaces of wafer 40 for cleaning the same. The surfaces of brushes 60a and 60b that are proximate to surfaces 40b and 40c, respectively, have a plurality of perpendicularly extending nubs 130. Each nub has a cylindrical shape with a flat exposed end that is substantially coplanar with the exposed ends of the other nubs. Brushes 60a and 60b are configured to rotate about a vertical axis 80. In addition, brushes 60a and 60b may oscillate relative to wafer 40 in the directions of arrows B, D. Alternatively, brushes 60a and 60b may move in an orbital motion relative to wafer 40.
The third cleaning member, a roller 70, is frictionally engageable with the peripheral side surface 40a of wafer 40 for cleaning this edge. Roller 70 is configured to rotate about a vertical axis 90. While apparatus 30 is illustrated in Figure 4 using only one roller 70, it will be appreciated that two or more rollers 70 may be used. Alternatively, apparatus 30 may not employ roller 70, relying on brushes 60a and 60b to remove copper debris from side surface 40a. The hardness and density of brushes 60a and 60b and roller 70 are selected based on the type of material to be planarized. The brushes may be made from polyvinyl acetate (PVA), polyurethane or any other suitable material capable of frictionally engaging wafer 40 to planarize wafer 40 and remove copper debris therefrom. Brushes 60a and 60b should be sufficiently thick to prevent wafer 40 from coming into direct contact with conductive members 120a and 120b, described below. In addition, because conventional brushes are generally not conductive, brushes 60a and 60b are preferably uniformly perforated with a plurality of perforations 160 so as to permit conduction between wafer. surfaces 40b and 40c of wafer 40 and conductive members 120a and 120b. Alternatively, brushes 60a and 60b may be porous so as to permit conduction between wafer surfaces 40b and 40c of wafer 40 and conductive members 120a and 120b.
Wafer 40 may be held in a stationary position by wafer holders 50 or wafer holders 50 may be configured to rotate about their vertical axes so that wafer 40 rotates about an axis 100 at the same time as brushes 60a and 60b are rotating about their axes 80. Alternatively, apparatus 30 may use orbital motion of wafer 40 rather than rotational motion to planarize wafer 40. An example of polishing a wafer by orbital motion is disclosed more fully in U.S. Patent No. 5,554,064, issued September 10, 1996 to Brievogel, et al., which patent is incorporated herein by reference.
To perform electrochemical planarization, apparatus 30 also includes conductive members 120a and 120b, which are disposed above and below wafer 40 adjacent brushes 60a and 60b. Conductive members 120a and 120b may be made from a metal, such as copper, or any suitable conductive material. An electric potential difference is effected between conductive members 120a and 120b and the metallized surfaces 40b and 40c, respectively, of wafer 40 by voltage sources 140, 150 which apply a positive charge to surfaces 40b and 40c of wafer 40 and a negative charge to conductive members 120a and 120b. While the exemplary embodiment of Figure 4 shows two voltage sources, it will be appreciated that any number of any conventional techniques for effecting an electric potential difference between conductive members 120a and 120b and wafer 40 may be employed. An electrolytic planarizing solution may be applied by conduits 110. Alternatively, it will be appreciated that the electrolytic planarizing solution may be supplied through brushes 60a and 60b through a manifold apparatus (not shown) and perforations 160, or by any suitable distribution device. The electrolytic planarizing solution may include such materials as ammonium phosphate, phosphoric acid, copper sulfate, sulfuric acid, chromic acid and/or additives, or may be a combination of such materials and a conventional CMP slurry.
In operation of apparatus 30, brushes 60a and 60b are pressed against surfaces 40b and 40c, respectively, with a desired amount of force while rotating about their respective vertical axes. Preferably, brushes 60a and 60b are pressed against surfaces 40b and 40c at a pressure of approximately 0.5 psi or less, although it may be appreciated that any suitable pressure which promotes planarization may be used. Wafer carriers 50 may also be rotated about their vertical axes so that wafer 40 rotates about axis 100. An electrolytic planarizing solution is supplied to both surfaces 40b and 40c of wafer 40. When the electric potential difference is effected between the conductive members 120a and 120b and the metallized surfaces 40b and 40c of wafer 40, metal ions are liberated from surfaces 40a, 40b and 40c of wafer 40, thereby resulting in deplating of the metal from the wafer.
After planarization is completed, any remaining metal from the metallized surface and the remaining exposed barrier layer 20, shown in Figure 2, may be removed by standard etching processes, such as wet etch, vapor etch, spray etch, plasma etch or chemical mechanical planarization, since the surface of the wafer had just previously been substantially planarized with the present invention. Selection of the etch method and chemistry depends on the barrier layer chemistry.
While in the above embodiment, the metallized surfaces of opposing sides 40b and 40c of wafer 40 are removed simultaneously, it will be appreciated that apparatus 30 could be modified so that electrochemical planarization is performed on only one surface of the wafer. For example, wafer 40 could be supported on side 40c by a conventional rotating platen and electrochemical planarization could be performed selectively on side 40b.
An advantage of the ECP apparatus of the present invention is that, with concurrent electrochemical etching and mechanical scrubbing of wafer, the metallized surface is removed first from high topography areas, and subsequently uniformly etched and planarized. The electrochemical etching aspect of the invention enables high removal rates at low pressure, which reduces dishing and oxide erosion. A further advantage is that, because a standard washing apparatus may be retrofitted to perform ECP as described herein, specialized ECP machines do not need to be purchased and additional equipment costs are thereby reduced.
Referring to Figure 5, an alternative embodiment 200 of the ECP apparatus of the present invention may use brush rollers to planarize a wafer having metallized surfaces on opposing surfaces of the wafer. For a discussion of a cleaning apparatus using rollers, see U.S. Patent No. 5,975,094 issued to Shurtliff on November 2, 1999, the contents of which are incorporated herein by this reference.
A wafer 210 having opposing metallized surfaces 210b and 210c is supported by a plurality of wafer holders 220 which contact wafer 210 along a peripheral side surface 210a. Apparatus 200 includes three cleaning members. The first two cleaning members are brush rollers 240a and 240b which are disposed adjacent the metallized surfaces 210b and 210c of wafer 210 and which are frictionally engageable with the opposite sides of wafer 210 for cleaning the same. Brush rollers 240a and 240b are preferably substantially cylindrical in shape and are configured • to rotate about their respective longitudinal axes 250a and 250b, while moving translationally over the surface of the wafer 210. Brush rollers 240a and 240b may be made from polyvinyl acetate (PVA), polyurethane or any other suitable material. In addition, brush rollers 240a and 240b are preferably uniformly perforated with a plurality of perforations 320 so as to permit conduction between wafer surfaces 210b and 210c of wafer 210 and conductive members 260a and 260b, discussed below. Alternatively, brush rollers 240a and 240b may be porous so as to permit conduction between wafer surfaces 210b and 210c of wafer 210 and conductive members 260a and 260b. A third cleaning member is a roller 270 which is frictionally engageable with the peripheral side surface 210a of wafer 210 for cleaning this edge. Roller 270 is configured to rotate about a vertical axis 280. While apparatus 200 is illustrated in Figure 5 using only one roller 270, it will be appreciated that two or more rollers 270 may be used. Alternatively, apparatus 200 may not employ roller 270, relying on brush rollers 240a and 240b to remove copper debris from side surface 210a. Wafer 210 may be held in a stationary position by wafer holders 220 or, alternatively, wafer holders 220 may be configured to rotate about their vertical axes so that wafer 210 rotates about an axis 290 at the same time as brush rollers 240a and 240b are rotating about their axes 250a and 250b. To perform electrochemical planarization, each brush roller 240a and 240b includes a conductive member, conductive members 260a and 260b, respectively. Conductive members 260a and 260b are positioned within brush rollers 240a and 240b, respectively, and extend approximately the entire length of brush rollers 240a and 240b. An electric potential difference is effected between conductive members 260a and 260b and the metallized surfaces 210b and 210c of wafer 210 by voltage sources 300 and 310 which apply a positive charge to the surfaces 210b and 210c of the wafer and a negative charge to conductive members 260a and 260b. While the exemplary embodiment of Figure 5 shows two voltage sources, it will be appreciated that any number of any conventional techniques for effecting an electric potential difference between conductive members 260a and 260b and wafer 210 may be employed. An electrolytic planarizing solution, which may include an electrolytic solution or an electrolytic solution combined with a conventional CMP slurry, may be supplied through brush rollers 240a and 240b and perforations 320, or by any suitable distribution device.
In operation of apparatus 200, brush rollers 240a and 240b are pressed against surfaces 210b and 210c, respectively, while rotating about their respective longitudinal axes. Wafer carriers 220 may also be rotated about their vertical axes so that wafer 210 rotates about axis 290. An electrolytic planarizing solution is supplied to both surfaces 210b and 210c of wafer 210. When the electric potential difference is effected between the conductive members 260a and 260b and metallized surfaces 210b and 210c of wafer 210, metal ions are liberated from sides 210a, 210b and 210c of wafer 210, thereby resulting in deplating of the metallized surfaces from the wafer.
While Figure 5 illustrates an exemplary embodiment of the present invention which employs two brush rollers positioned on opposite surfaces 210b and 210c of wafer 210 to electrochemically planarize those surfaces simultaneously, it will be appreciated that the present invention could employ only one roller brush on one surface of the wafer to planarize that surface. Alternatively, multiple brush rollers may be positioned on one surface of the wafer to planarize that surface.
Figure 6 illustrates yet another embodiment of the present invention, a cleaning station 400, configured for the electrochemical planarization of a wafer having at least one metallized surface. Cleaning station 400 may be incorporated within a larger machine for processing or cleaning semiconductor wafers (or other workpieces) e.g., as described in U.S. Patent No. 5,950,327, issued to Peterson et al. on September 14, 1999, the entire content of which is incorporated by reference herein. Cleaning station 400 preferably comprises an enclosure, e.g., a scrubber box, enclosing a plurality of pairs of brush rollers. Cleaning station 400 comprises a bottom panel 412, a top panel 414, side panels 410, a rear panel (not shown) and a front panel (not shown). Hence, the panels comprise a self-contained box, which can be quickly and easily removed using a handle 420 and replaced when it is desired to replace one or more of the brush rollers.
Cleaning station 400 comprises a plurality of brush roller pairs configured to drive wafers through the scrubber box and to simultaneously electrochemically planarize the top and/or bottom flat surfaces of wafers passing therethrough. As shown in Figure 6, cleaning station 400 preferably includes a wafer input 416 configured to receive wafers into the enclosure. When a wafer enters the enclosure, the first pair of drive rollers (described below) "grabs" the wafer and feeds it forward to the next pair of rollers.
Cleaning station 400 may have any number of pairs of rollers, although for convenience Figure 6 illustrates a cleaning station having six pairs of rollers. In the illustrated embodiment, the scrubber box includes a first brush roller pair comprising respective rollers 430 and 432; a second roller pair comprising upper brush roller 434 and lower brush roller 436; a third roller pair comprising upper brush roller 438 and lower brush roller 440; a fourth pair comprising upper brush roller 442 and lower brush roller 444; a fifth pair comprising upper brush roller 446 and lower brush roller 448; and a sixth terminal roller pair comprising upper brush roller 450 and lower brush roller 452. Cleaning station 400 is configured such that wafers enter from the far left, are sequentially urged through the station, and are discharged from the station at the far right position (proximate rollers 450 and 452).
Each of the odd pairs of rollers (e.g., the first (rollers 430 and 432), third (rollers 438 and 440), fifth (rollers 446 and 448) roller pairs) preferably functions as a drive roller, with each drive roller pair operating at a drive speed SI. As such, brush rollers 430, 432, 438, 440, 446 and 448 operate at drive speed SI. The bottom brush rollers (i.e., rollers 432, 436, 440, 444, 448 and 452) rotate clockwise, as shown. In addition, the top brush roller of each even brush roller pair (i.e., brush rollers 434, 442 and 450) also rotates clockwise. Finally, the top roller in each odd brush roller pair (i.e., 430, 438 and 446) preferably rotates counterclockwise.
Each of the even pairs of rollers (e.g., the second, fourth and sixth pairs) preferably are configured to operate at a process speed S2. Each odd roller pair is preferably driven by a first drive motor (not shown) so that the wafers are driven through the cleaning station 400 at an essentially uniform rate. Each even roller pair is preferably driven by a second motor at process speed S2. In this way, an operator may control the drive speed SI by setting a first control associated with the first motor and may also independently control processing speed S2 by manipulating a second control associated with the second motor. By allowing the operator to dynamically configure respective speeds SI and S2, substantial flexibility is achieved in cleaning station 400. Although the aforementioned roller speeds are illustrated in Figure 6, it is to be understood that virtually any number of rollers and any combination of roller speeds and roller directions may be employed in the context of the present invention. For example, two, three or even more roller speeds may be employed with various permutations and combinations of speed and direction being selected to achieve optimum performance for a desired application. Each of the even pairs of brush rollers 434, 436, 442, 444, 450 and 452 include conductive member 454, 456, 458, 460, 462 and 464, respectively. Conductive members 454, 456, 458, 460, 462 and 464 are positioned within, and extend approximately the entire length of, the respective brush rollers. Brush rollers 434, 436, 442, 444, 450 and 452 may be made from polyvinyl acetate (PVA), polyurethane or any other suitable material. In addition, these brush rollers are preferably uniformly perforated so as to permit conduction between the conductive members and the wafer. Alternatively, these brush rollers may be porous so as to permit conduction between the conductive members and the wafer.
Top panel 414 may further include one or more fluid inlet ports (not shown) configured to distribute fluids to a discrete portion of, or to the entirety of, the inside of cleaning station 400. Top panel 414 also may include a number of manifolds (not shown) arranged to deliver fluid to specific locations within cleaning station 400. For example, top panel 414 may comprise a first manifold to deliver an electrolytic planarizing solution, a second manifold to deliver conventional slurry, and a third manifold to deliver deionized water. Each individual manifold is configured such that it is fluidly distinct from each of the remaining manifolds. However, one or more of the fluid inlet ports may be coupled together such that a single fluid may be applied to more than one manifold. The manifolds may be configured to distribute fluid to locations above and/or between adjacent brush rollers. This arrangement permits the fluid to reach wafers as they pass through the cleaning station. Cleaning station 400 may also include a fluid outlet (not shown) through which the electrolytic solution may flow during or after the planarization procedure. If desired, the electrolytic solution retrieved from the fluid outlet may be recycled, disposed of, or handled as desired.
During electrochemical planarization, a wafer enters cleaning station 416, is "grabbed" by brush rollers 430 and 432 and is urged forward to the outlet of cleaning station 400. An electrolytic planarization solution is distributed to the rollers and an electric potential difference is effected between the conductive members of the brush rollers and the wafer. As the wafer travels by brush rollers 434, 436, 442, 444, 450 and 454, metal ions are liberated from the metallized surfaces, thereby resulting in deplating of the metallized surfaces. As the wafer contacts the brush rollers, it is further planarized by the abrasive action of the brush rollers and any abrasive particulates in the planarization solution. As a result, the areas of high topography on the metallized surface are removed, after which uniform etching and planarizing subsequently take place.
Although the subject invention has been described herein in conjunction with the appended drawing Figures, it will be appreciated that the scope of the invention is not so limited. Various modifications in the arrangement of the components discussed and the steps described herein for using the subject device may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

ClaimsWe claim:
1. An electrochemical planarization apparatus for planarizing a workpiece, said workpiece having at least one metallized surface and a peripheral edge surface, said apparatus comprising:
(a) a first brushing surface configured to frictionally engage said at least one metallized surface of said workpiece;
(b) a first driver assembly configured to cause relative motion between said workpiece and said first brushing surface;
(c) a first conductive element disposed proximate said first brushing surface;
(d) a first power supply configured to effect an electric potential difference between said at least one metallized surface of said workpiece and said first conductive element; and (e) a first solution application mechanism configured to supply an electrolytic solution to said first metallized surface.
2. The electrochemical planarization apparatus of Claim 1 wherein said workpiece has a second metallized surface and said apparatus further comprises: (a) a second brushing surface configured to frictionally engage said second metallized surface of said workpiece;
(b) a second conductive element disposed proximate said second brushing surface; and
(c) a second solution application mechanism configured to supply an electrolytic solution to said second metallized surface.
3. The electrochemical planarization-apparatus of claim 2 further comprising:
(a) a second driver assembly configured to cause relative motion between said workpiece and said second brushing surface.
4. The electrochemical planarization apparatus of claim 2 wherein said first driver assembly is configured to cause relative motion between said workpiece and said second brushing surface.
5. The electrochemical planarization apparatus of claim 2 further comprising:
(a) a second power supply configured to effect an electric potential difference between said second metallized surface of said workpiece and said second conductive element.
6. The electrochemical planarization apparatus of claim 2 wherein said first power supply is configured to effect an electric potential difference between said second metallized surface of said workpiece and said second conductive element.
7. The electrochemical planarization apparatus of claim 1 further comprising at least one edge brush surface configured to press against said peripheral edge surface of said workpiece.
8. The electrochemical planarization apparatus of claim 2 further comprising at least one edge brush surface configured to press against said peripheral edge surface of said workpiece.
9. The electrochemical planarization apparatus of claim 1, wherein said relative motion is chosen from the group consisting of: linear motion, orbital motion, circular motion, a combination of linear and orbital motion, a combination of linear and circular motion, a combination of orbital motion and circular motion, and a combination of linear, orbital and circular motion.
10. The electrochemical planarization apparatus of claim 3, wherein said relative motion is chosen from the group consisting of: linear motion, orbital motion, circular motion, a combination of linear and orbital motion, a combination of linear and circular motion, a combination of orbital motion and circular motion, and a combination of linear, orbital and circular motion.
11. The electrochemical planarization apparatus of claim 4, wherein said relative motion is chosen from the group consisting of: linear motion, orbital motion, circular motion, a combination of linear and orbital motion, a combination of linear and circular motion, a combination of orbital motion and circular motion, and a combination of linear, orbital and circular motion.
12. The electrochemical planarization apparatus of claim 1 wherein said first brushing surface is disk-shaped.
13. The electrochemical planarization apparatus of claim 12 wherein said first brushing surface is configured to rotate about a center axis.
14. The electrochemical planarization apparatus of claim 12 wherein said first brushing surface is perforated.
15. The electrochemical planarization apparatus of claim 12 wherein said first brushing surface is porous
16. The electrochemical planarization apparatus of claim 1 wherein said first brushing surface is a roller configured to rotate about a longitudinal axis.
17. The electrochemical planarization apparatus of claim 16 wherein said first brushing surface is perforated.
18. The electrochemical planarization apparatus of claim 16 wherein said first brushing surface is porous.
19. The electrochemical planarization apparatus of claim 2 wherein said second brushing surface is disk-shaped.
20. The electrochemical planarization apparatus of claim 19 wherein said second brushing surface is configured to rotate about a center axis.
21. The electrochemical planarization apparatus of claim 19 wherein said second brushing surface is perforated.
22. The electrochemical planarization apparatus of claim 19 wherein said second brushing surface is porous.
23. The electrochemical planarization apparatus of claim 2 wherein said second brushing surface is a roller configured to rotate about a longitudinal axis.
24. The electrochemical planarization apparatus of claim 23 wherein said second brushing surface is perforated.
25. The electrochemical planarization apparatus of claim 23 wherein said second brushing surface is porous.
26. A method of planarizing a metallized surface on a workpiece, the method comprising:
(a) providing a brushing surface configured to frictionally engage said metallized surface of said workpiece;
(b) providing a conductive element disposed proximate said brushing surface;
(c) pressing said brushing surface against said metallized surface while causing relative motion between said workpiece and said brushing surface;
(d) supplying an electrolytic solution at said metallized surface; and
(e) effecting an electric potential difference between said metallized surface on said workpiece and said conductive element.
27. The method of claim 26, wherein said relative motion is chosen from the group consisting of: linear motion, orbital motion, circular motion, a combination of linear motion and orbital motion, a combination of linear motion and circular motion, a combination of orbital motion and circular motion, and a combination of linear, orbital and circular motion.
28. The method of claim 26, wherein said brushing surface is disk-shaped and said method further comprises rotating said brushing surface about a central axis.
29. The method of claim 28, wherein said brushing surface is perforated.
30. The method of claim 28, wherein said brushing surface is porous.
31. The method of claim 26, wherein said brushing surface is a roller and said method further comprises rotating said brushing surface about a longitudinal axis.
32. The method of claim 31 , wherein said brushing surface is perforated.
33. The method of claim 31 , wherein said brushing surface is porous.
34. An apparatus for the electrochemical planarization of a workpiece, the workpiece having at least one metallized surface, said apparatus comprising:
(a) a plurality of brushing rollers, each having a longitudinal axis and each configured to frictionally engage said at least one metallized surface of said workpiece, wherein each of said plurality of brushing rollers comprises a conductive element;
(b) a driver assembly configured to rotate each of said plurality of brushing rollers about said longitudinal axis;
(c) a power supply configured to effect an electric potential difference between said at least one metallized surface of said workpiece and said conductive elements; and
(d) a solution application mechanism configured to supply an electrolytic solution to said metallized surface.
35. The apparatus of claim 34, wherein each of said plurality of brushing rollers is perforated.
36. The apparatus of claim 34, wherein each of said plurality of brushing rollers is porous.
PCT/US2001/031120 2000-10-04 2001-10-04 Method and apparatus for electrochemical planarization of a workpiece WO2002028597A1 (en)

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AU2002211432A1 (en) 2002-04-15

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