Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D19/00—Degasification of liquids
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D19/00—Degasification of liquids
  • B01D19/0031—Degasification of liquids by filtration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D19/00—Degasification of liquids
  • B01D19/0068—General arrangements, e.g. flowsheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
  • B01D63/02—Hollow fibre modules
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/30—Polyalkenyl halides
  • B01D71/32—Polyalkenyl halides containing fluorine atoms
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/12—Process control or regulation
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/38—Electroplating: Baths therefor from solutions of copper

Definitions

• This invention relates to a process for removing all dissolved gasses from aqueous electroplating and electroless plating bath solutions. More particularly, this invention relates to a process for removing dissolved gasses including oxygen from aqueous copper plating and electroless plating bath solutions.
• Copper electrochemical deposition process for the damascene structures of high aspect ratios for semiconductor manufacturing is a new application of the conventional electroplating process.
• the electroplating of high aspect ratio devices involves the use of copper plating to fill high aspect ratio sub-micron trenches and vias positioned on semiconductor chips.
• An acidic copper sulfate solution of optimized composition has proven to be the best formula for plating micro-features.
• the process consists of circulating a plating solution from a reservoir to a plating cell and back to the reservoir.
• a copper anode in the plating cell provides the source of copper, which is deposited on the cathode comprising a silicon wafer with the damascene structure.
• the final performance of the plated wafer depends on the electrical and morphological properties of the deposited copper film.
• the electrochemical bath composition plays a significant role in deposited copper film properties.
• the solution concentration of copper and suliate ions, chloride ions, metallic impurities, and organic additives all are important parameters for providing acceptable copper deposition.
• the organic additives added to the bath include accelerators, brighteners, suppressors, and levelers.
• the combination of these additives determines filling properties as well as the film's initial grain size, brightness or roughness.
• the optimum bath composition is maintained by periodic analysis and replenishing of the plating bath.
• the solution is constantly exposed to environmental oxygen as the surrounding air is entrained into the recirculating plating solution. It has been determined that some of the organic additives are sensitive to oxidative decomposition. Accelerated organic additive consumption changes the chemical composition of the bath which, in turn, can adversely affect the acceptability of the deposited copper film.
• the bath chemical composition can be changed both by the depletion of one or more organic additives and by the increased concentration of organic decomposition produced.
• dissolved gas such as oxygen in the plating bath
• the presence of dissolved gas such as oxygen in the plating bath also can cause the formation of undesirable micro voids in the plated copper film. This, in turn, can cause reduced electrical conductivity in the copper pathways formed in the semiconductor surface. Accordingly, it would be desirable to provide a copper electrochemical deposition process wherein decomposition of organic additives in a copper plating bath is controlled and minimized. In addition, it would be desirable to provide such a process wherein dissolved gas in a copper plating bath is removed.
• oxygen can be removed from an aqueous copper plating bath containing organic additives to stabilize the bath against decomposition of the organic additives by passing the bath through a degasser apparatus comprising a shell (housing) having hydrophobic hollow porous membranes (fibers) which extend through the shell.
• the hollow hydrophobic porous membrane permits passage of gas therethrough while preventing passage of liquid therethrough.
• the plating bath solution can be passed either through the shell to contact the outer surfaces of the hollow hydrophobic porous membrane or through the lumens of a hydrophobic hollow porous membranes under conditions that prevent significant intrusion of the bath solution into the membrane pores while permitting passage of oxygen gas through the pores.
• the degasser wherein the bath solution is introduced into the shell to contact the outer surfaces of the hollow membrane is referred to in the art as a "shell side degasser".
• a copper anode and a cathode comprising a substrate such as a silicon wafer, upon which an electrically conductive copper pathway is to be plated, are immersed in an acidic aqueous copper plating bath in a plating step.
• the plating bath contains organic additives which facilitate plating of copper including accelerators, brighteners, suppressors and levelers.
• Aqueous copper plating solution is directed to the plating step by being passed through a filter to remove particles therein and then through the hollow fiber membrane degasser to remove dissolved oxygen from the solution. Degassing is effected with the hollow fiber membranes under conditions that intrusion of liquid through the pores of the membranes is prevented.
• the plating solution is removed from the plating bath and is directed to a reservoir for the solution where its composition can be monitored to determine whether additional organic additive or acid should be added thereto in order to maintain the desired composition which is efficient for attaining satisfactory copper plating in the plating step.
• Figure 1 is a schematic flow sheet illustrating the process of this invention.
• Figure 2 is a graph showing consumption of organic additives in a copper plating bath without removing oxygen in Example 1.
• Figure 3 is a graph showing consumption of two organic additives with oxygen removal in Example 1.
• Figure 4 is a graph showing consumption of an organic additive with and without oxygen removal in Example 1.
• Figure 5 is a graph showing consumption of an oxygen additive utilizing the degassing steps in parallel in Example 1.
• Figure 6 is a graph of efficiency in removing gas in the degasser of Example 4.
• Figure 7 is a graph showing consumption of additives in the degasser of Example 4.
• Degassing of an aqueous acidic copper plating solution to remove oxygen is effected by passing the solution through a degasser comprising a shell through which extend hydrophobic hollow porous membranes.
• the plating solution can be passed through the shell to contact the outer surfaces of the hollow porous fiber membranes or through the lumens of the hollow porous fiber membranes.
• the solution is passed through the degasser under conditions to prevent liquid flow through the pores of the membranes while permitting gas flow through the membrane pores.
• the membrane surfaces are not wet by the solution thereby preventing significant liquid intrusion into the membrane pores.
• a subatmospheric pressure is effected on the surfaces of the membranes opposite the membrane surfaces contacted by the bath by removing gas either from the lumens of the membrane or from the housing.
• the hollow porous fiber membrane are formed from a hydrophobic polymer having a surface energy equal to or greater than about 23 dynes/ cm, preferably greater than about 25 dynes/cm.
• suitable hydrophobic polymers include skinned hydrophobic polymers such as perfluoroalkoxy polymers (PFA) such as perfluoro (alkoxy vinylether), fluorinated ethylene-propylene polymer (Teflon FEP) or the like.
• PFA perfluoroalkoxy polymers
• Teflon FEP fluorinated ethylene-propylene polymer
• the membranes typically have a bubble point greater than about 100 psi.
• Suitable skinned membranes can be produced by the process of U.S. patent application 60/117,854, filed January 29, 1999 which is incorporated herein by reference.
• the vacuum utilized to effect degassing to remove oxygen from the solution positioned either within the shell or within the lumens of the hollow porous fiber membranes is between about 10 inch Hg and about 29 inch Hg, preferably between about 25 inch Hg and about 28 inch Hg.
• the fibers range in length between about 8 inches and about 20 inches although fibers of shorter or longer length can be employed.
• Typical conditions of flow of the aqueous solution through the shell or through the fibers are between about 10 and about 30 liters/minute. Under these process conditions, oxygen concentration in the solution is reduced to below about 6 ppm, preferably below about 3ppm.
• the degassing apparatus of the invention generally is made by potting the hollow fiber porous membrane to both ends of a shell (housing) so that liquid flow through the degasser is effected through the lumens of the hollow fibers or through the portion of the shell interior not occupied by the hollow fibers. Potting is a process of forming a tube sheet having liquid tight seals around each fiber.
• the tube sheet or pot separates the interior of the final contactor from the environment.
• the pot is thermally bonded to the housing vessel to produce a unitary end structure.
• the unitary end structure comprises the portion of the fiber bundle which is encompassed in a potted end, the pot and the end portion of the hydrophobic thermoplastic housing, the inner surface of which is congruent with the pot and bonded to it.
• the perfluorinated thermoplastic end seals are preferably made of poly (tetrafluoroethylene-co-perfluoro (alkylvinylether)) having a melting point of from about 250°C to about 260°C.
• a preferred potting material is Hyfion® 940 AX resin, from Ausimont USA Inc. Thorofare, NJ.
• Low viscosity poly (tetrafluoroethylene-co- hexafluoropropylene) with low end-of-melt temperatures as described in US Patent 5,266,639 is also suitable.
• the process involves heating the potting material in a heating cup at around 275 °C until the melt turns clear and are free of trapped bubbles.
• a recess is made in the molten pool of potting material that remains as a recess for a time sufficient to position and fix the fiber bundle and housing in place. Subsequently, the recess will fill with the molten thermoplastic in a gravity driven flow.
• a unitary end structure by which is meant that the fibers and the pot are bonded to the housing to form a single entity consisting, for example, of perfluorinated thermoplastic materials is prepared by first pretreating the surfaces of both ends of the housing before the potting and bonding step. This is accomplished by melt-bonding the potting material to the housing. The internal surfaces on both ends of the housing are heated close to its melting point or just at the melting point and immediately immersed into a cup containing powdered (poly (PTFE-CO-PFVAE)) potting resin. Since the surface temperature of the housing is higher than the melting point of the potting resins, the potting resin is then fused to the housing resin - a condition for bonding to occur. The housing is then taken out and polished with a heat gun to fuse any excess unmelted powder. Without this pretreatment step, the housing surfaces often detach from the potting surfaces because of absence of intermixing of the two resins.
• the unitary end structure(s) is cut and the lumen of the fibers exposed.
• the potted surfaces are then polished further using a heat gun to melt away any smeared or rough potted surfaces.
• a solder gun can be used to locally remelt and repair any defective spot, sometimes with the help of a drop of melted resin.
• a plating bath 10 which includes a housing 12, an inner tube 14 which includes a copper anode 16 and a cathode substrate to be plated such as a silicon wafer 18.
• the surface of the solution in housing 12 can be blanketed with nitrogen or an inert gas such as argon, helium or the like to reduce oxygen dissolved in the solution.
• Degassed aqueous acidic copper solution containing organic additives is directed through conduit 20 into inner tank 14 wherein a voltage is established between anode 16 and cathode 18.
• Spent solution is removed from tank 14 as indicated by arrows 22 and 24 through conduit 26 and is directed to reservoir 28.
• the spent solution 30 can be analyzed for organic concentration and concentration of additive decomposition product. Based on the analyses, organic additives can optionally be added to solution 30.
• the solution 30 then is pumped by pump 32 through particle filter 34, conduit 33 and then through degasser 42 containing the hollow porous fiber membranes in a housing as described above and wherein a vacuum is drawn through conduit 44.
• the degassed solution with reduced oxygen concentration is returned to tank 12 through conduit 20. It is to be understood that a plurahty of degassing units 42 can be utilized either in parallel or in series to reduce oxygen content of the solution being cycled through the process of this invention.
• the plating solution from a reservoir (-75 liters) is circulated (-17 liters/min flow rate) through a plating cell - 1 - containing a silicon wafer cathode and a copper anode.
• the solution additives are maintained at adequate level by periodically analyzing the bath for composition and adding the make up amount.
• Example 2 A second set of experiments were conducted as described in Example 1 but with a degasser unit turned on ( -26 Hg vacuum).
• the degasser unit included 10 inch hollow fiber skinned PFA ultrafiltration membranes.
• the dissolved oxygen and additive concentration in the bath were monitored as profiled in Figure 3.
• Example 3 Three Degassers and Nitrogen Blanket Three degasser modules of the type uses in Example 2 were installed (in a parallel configuration) in the copper plating unit. The objective was to determine incremental improvements in degassing efficiency and its effect on the additive consumption, over time. The system performance was also improved by reducing/eliminating the sources of oxygen entrainment into the plating solution at the cell overflow, drain pipe return line, and the solution reservoir by infusing nitrogen and covering these areas with appropriate plastic lids or plastic sheeting.
• This example illustrates the process of this invention utilizing a shell side degasser wherein a plating solution contacts the outer surfaces of hollow hydrophobic fiber membranes positioned within a shell.
• the integrity of the degasser was very good. There was no sign of weeping of leaking.
• the single pass efficiency was 37 +/- 8% at 4.5 GPM solution flow rate.
• the total system efficiency was about 73 +/ -5%, which was calculated based on the saturated O 2 level in the bath.
• the analysis of additives showed that the degasser reduced the consumption rate of Additive X.
• the integrity is determined in two ways.
• the degasser single pass efficiency was 37 +/ -8% throughout the testing period.
• the total system efficiency was about 73 +/ -5%, which was calculated based on the saturated O 2 level in the bath.
• Additive consumption rate was measured with and without degasser. As shown in Figure 7, the degasser reduced the consumption rate of additive "X" by nearly 50%; degassing had less effect on the consumption rate of additive "Y”. Based on the normal consumption rate of 0.15 ml/Amp. hrs (as circular points shown) for Gen6b3, degasser reduced the consumption rate by 38%.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Automation & Control Theory (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Degasification And Air Bubble Elimination (AREA)

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Cited By (14)

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Citations (9)

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• 2002
  • 2002-01-31 EP EP02707656A patent/EP1357989A4/en not_active Withdrawn
  • 2002-01-31 KR KR1020037010414A patent/KR100824910B1/ko not_active Expired - Fee Related
  • 2002-01-31 CN CNA028075315A patent/CN1499992A/zh active Pending
  • 2002-01-31 WO PCT/US2002/002924 patent/WO2002062446A1/en not_active Ceased
  • 2002-01-31 JP JP2002562449A patent/JP2004531640A/ja active Pending
  • 2002-01-31 US US10/467,245 patent/US7014679B2/en not_active Expired - Fee Related
  • 2002-02-06 TW TW091102093A patent/TW593783B/zh not_active IP Right Cessation

Patent Citations (9)

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