EP0806497A1 - Verfahren zur Absetzen von Kupfer oder von einer Kupferlegierung auf ein Aluminium enthaltendes Substrat - Google Patents

Verfahren zur Absetzen von Kupfer oder von einer Kupferlegierung auf ein Aluminium enthaltendes Substrat Download PDF

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Publication number
EP0806497A1
EP0806497A1 EP97870063A EP97870063A EP0806497A1 EP 0806497 A1 EP0806497 A1 EP 0806497A1 EP 97870063 A EP97870063 A EP 97870063A EP 97870063 A EP97870063 A EP 97870063A EP 0806497 A1 EP0806497 A1 EP 0806497A1
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EP
European Patent Office
Prior art keywords
copper
solution
deposition
substrate
aluminum
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Withdrawn
Application number
EP97870063A
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English (en)
French (fr)
Inventor
Roger Palmans
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Interuniversitair Microelektronica Centrum vzw IMEC
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Interuniversitair Microelektronica Centrum vzw IMEC
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Publication of EP0806497A1 publication Critical patent/EP0806497A1/de
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/38—Coating with copper

Definitions

  • the present invention is related to a method for depositing a copper or a copper alloy on a second metal substrate, made of aluminum or of an aluminum alloy such as Al(Si) or Al(Cu) or Al(Si, Cu) or any similar alloy.
  • the present invention is also related to applications making use of this method.
  • Electroless deposition of metals on substrates made of aluminum or of aluminum alloys has always been hampered by the susceptibility of aluminum to dissolution in the deposition baths due to the aggressive nature of these solutions. Usually, this results in an imperfect adhesion between the metal coating and the aluminum substrate.
  • Complete and reliable coverage of a substrate made of aluminum alloys with a metal requires that the native Al 2 O 3 layer is removed, and that the subsequent reoxidation of the Al surface has to be avoided when the substrate is transferred to the metal deposition bath.
  • Another recurrent problem is the formation of an insulating Al 2 O 3 layer on the aluminum substrate during metal deposition, such as the one observed during autocatalytic electroless copper deposition in an alkaline formaldehyde bath.
  • Such bath typically contains a source of Cu(II)ions, a complexing ligand for Cu(II) ions, formaldehyde as a sacrificial reductant as well as sodium hyroxide to adjust the pH of the solution to the level required for formaldehyde to work as electron donor (see document JP-A-2310375 of Toshiba Corp.)
  • the dissolution of the aluminum in the copper deposition bath is a critical item.
  • Aluminum films or Al(Si) or Al(Si, Cu) films as thin as 200 nm have to be treated for VLSI applications.
  • the state-of-the-art fails to disclose a method for depositing Cu on thin films of Al using a simple and cheap process and such that no degradation of the Al thin film occurs.
  • a classical solution to the problem of depositing a metal on an aluminum substrate is the application of a zincate treatment prior to metal deposition.
  • zincate treatment aluminum present on the surface of the substrate is displaced by Zn which protects the substrate surface against reoxidation.
  • the Zn coating is redissolved and another metal can be deposited on the oxide-free aluminum substrate.
  • the substrate has to be prepared in order to yield a uniform Zn deposit before the zincate treatment can be applied.
  • This procedure involves first an alkaline cleaning of the substrate, and secondly a conditioning of the Al substrate in a concentrated nitric acid solution (50 % by volume) which imparts a uniform thin Al 2 O 3 coating on the aluminum substrate and removes alloying elements from the surface. Standardized processing with this technology however has proven to be difficult.
  • Document US-A-4400415 describes a process for electroless deposition of a coating of nickel on an aluminum or aluminum alloy substrate.
  • the process comprises the steps of immersing the substrate in a hydroxide solution and electrolytically or electrolessly coating a layer of nickel thereon.
  • the solution has a pH of about 12 or above, a nickel or cobalt compound soluble therein and a non-cyanide complexing agent for the nickel or cobalt compound capable of maintaining the nickel or cobalt metal in solution at a pH of about 12 or above.
  • the aluminum or aluminum alloy substrate is expected to be attacked or degraded substantially.
  • the aim of the present invention is to disclose a method which yields in a reproducible way immersion metal deposition on a second metal substrate made of aluminum or of an aluminum alloy.
  • the process can be used for further electroless metal plating (e.g. with Ni/Au), and is much simpler and cheaper compared to the methods as described in the state of the art.
  • Another aim of the present invention is to suggest an immersion metal deposition method on an aluminum substrate which does not require any cleaning or conditioning of the substrate surface prior to the deposition in contrast to zincate processing.
  • a further aim of the present invention is to suggest a method which will result in immersion plated metal layers which show good uniformity and good adhesion to the aluminum substrate even without a subsequent thermal treatment.
  • the present invention is related to a method for depositing copper or copper alloy on a second metal substrate, made of aluminum or containing aluminum alloys, comprising the steps of :
  • Said solution is preferably an aqueous solution and does not contain a reductant such as formaldehyde.
  • the additive to adjust the pH of the solution is preferably sodium hydroxide.
  • the pH adjusted to a value comprised between 10.0 and 11.5 and more particularly between 10.2 and 11.0.
  • the deposition of the copper or copper alloy on the second metal substrate can be achieved by immersing said substrate in a single solution.
  • the method further comprises the step of:
  • the inert gas is Argon or Nitrogen.
  • the method further comprises the step of:
  • the ratio of the concentrations of tartrate/Cu(II) should be higher than 2 and preferably around 4.6.
  • the concentration of Cu(II) ions in the solution is comprised in the range of 0.7 10-2 - 7.2 10-2 molar.
  • the Al alloy is Al(Si), Al(Cu), Al(Si, Cu) wherein the percentage of Si and/or Cu does not exceed 2%.
  • the present invention is also related to specific applications of the method of the invention such as selective deposition or flip-chip applications.
  • Figure 1 schematically represents a device which permits to achieve the method of the present invention.
  • the device consists of a reaction vessel (1) having a rubber-O ring (2) to seal the lid by means of safety bolts (3).
  • a 3-way valve diffuser (4) is also provided in order to let the inert gas such as N 2 to bubble through the solution present in the reaction vessel (1) with the aim of deoxygenating the solution prior to the metal deposition.
  • a magnetic stirrer (6) is provided in order to have a good diffusion of the inert gas into the solution.
  • the flow path of the inert gas is symbolized by arrows A, B, C, D while the arrow E represents the rinsing water going through the rinsing nozzle (10) used after plating.
  • a substrate or wafer (8) is fixed on a wafer support (9) and is covered by a protection plate (7).
  • the substrate is immersed in the solution after the solution is deoxygenated (typically after 10-20 minutes).
  • the copper deposition preferably is to performed while the solution is kept under an inert atmosphere (nitrogen or argon) in order to avoid in situ oxidation of the copper layer during deposition in the bath.
  • the deposition can be performed in a glass reactor as shown in figure 1 for a period of 10 to 20 minutes with nitrogen purge of the deposition solution before the substrate is immersed in the bath. During the deposition step the flow of nitrogen is maintained over the solution. Stirring of the solution is not necessary but can be applied. Stirring results in the deposition of a slightly thicker copper layer. After the required deposition time in the copper deposition bath, the wafer is rinsed with deionized water and can be either dried in a gas flow or used as such for further processing such as a nickel deposition.
  • a preferred embodiment is hereunder described with reference to a substrate made of an Al(1% Si) alloy.
  • a thin uniform film of copper can be deposited on the substrate made of Al(1% Si) alloy. This is deposited by immersing the substrate directly in a single bath containing CuSO 4 .5H 2 O (1.44 10 -2 molar) as the source of copper ions, disodiumtartrate (6.65 10 -2 molar) as the complexing agent for Cu 2+ ions, and NaOH to adjust the pH to the required value.
  • CuSO 4 .5H 2 O (1.44 10 -2 molar) as the source of copper ions
  • disodiumtartrate (6.65 10 -2 molar) as the complexing agent for Cu 2+ ions
  • NaOH NaOH
  • the deposition bath is made up by mixing stock solutions of copper(II)sulphate and disodiumtartrate in deionized water, diluting this solution to about 3/4 of the final volume, adjusting the pH of this solution with NaOH, and finally by diluting this solution to the final volume with deionized water.
  • the preferred concentration range of the copper(II) ions and tartrate extends preferably from about half the original concentration values to about two-fold these values.
  • a copper deposition using the method of the present invention is also possible outside this specific range.
  • the mechanism of copper deposition on an Al containing substrate according to the present method is believed to be based on a substitution redox reaction occurring at the substrate surface.
  • the second metal (Al) is oxidized at the surface and goes into the solution whereas the copper ions are reduced at the interface of the solution and the surface of the Al substrate and are deposited on the substrate.
  • This deposition method does not need a previous treatment of the substrate in order to remove the native oxide layer. After copper deposition, only a minor concentration of oxygen is found at the interface between the copper layer and the Al substrate.
  • a copper layer grows quickly on the aluminium substrate to a limited thickness.
  • a very fast deposition of 100 - 120 nm of copper occurs at room temperature with the above described deposition bath.
  • the complete aluminum surface is covered with copper.
  • further copper deposition is almost negligible with a deposition rate of only 7 nm per minute (for up to 10 minutes deposition time).
  • the process is not autocatalytic.
  • the copper growth comes to an end because of the lack of driving force which is the oxidation of the underlaying aluminum substrate.
  • the advantage of the displacement plating process is that an exact control of the immersion time in the deposition bath is not necessary.
  • the present method of deposition on an Al substrate with copper is a selective deposition process being applicable at room temperature : when the substrate surface contains Al alloy structures together with non-conductive parts such as dielectric layers, only the Al parts will be covered with copper.
  • the present invention also relates to applications wherein said copper deposition method is used as a first step whereby a copper seed layer is deposited on an aluminum substrate for subsequent deposition of metals such as Ni or nickel alloys.
  • This approach can be used for microelectronics applications.
  • Another application is the deposition of a protecting layer of copper in via holes in microelectronic circuits on top of aluminum for further selective autocatalytic electroless metal deposition with e.g. (copper or) nickel (alloys).
  • a further application of the method of the present invention is the electroless plating of metal bumps for flip-chip applications.
  • a thick electroless Ni layer covered with a thin gold layer is plated on the immersion Cu layer/Al structure.
  • the aluminum substrate layer is used for the bonding pad of integrated circuits.
EP97870063A 1996-05-09 1997-05-05 Verfahren zur Absetzen von Kupfer oder von einer Kupferlegierung auf ein Aluminium enthaltendes Substrat Withdrawn EP0806497A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US1748596P 1996-05-09 1996-05-09
US17485 2001-12-14

Publications (1)

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EP0806497A1 true EP0806497A1 (de) 1997-11-12

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114853554A (zh) * 2022-05-25 2022-08-05 北京理工大学 一种具有催化效应的铝铜核壳结构金属燃料及其制备方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2872346A (en) * 1956-05-21 1959-02-03 Miller Adolph Metal plating bath
NL7900504A (nl) * 1979-01-23 1980-07-25 Maria Jacoba Gerardus Antonius Werkwijze voor het vervaardigen van munitie.

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2872346A (en) * 1956-05-21 1959-02-03 Miller Adolph Metal plating bath
NL7900504A (nl) * 1979-01-23 1980-07-25 Maria Jacoba Gerardus Antonius Werkwijze voor het vervaardigen van munitie.

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
DATABASE INSPEC INSTITUTE OF ELECTRICAL ENGINEERS, STEVENAGE, GB; ASCHENBRENNER R ET AL: "Electroless nickel/copper plating as a new bump metallization", XP002038809 *
IEEE TRANSACTIONS ON COMPONENTS, PACKAGING AND MANUFACTURING TECHNOLOGY, PART B: ADVANCED PACKAGING, MAY 1995, USA, vol. 18, no. 2, ISSN 1070-9894, pages 334 - 338 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114853554A (zh) * 2022-05-25 2022-08-05 北京理工大学 一种具有催化效应的铝铜核壳结构金属燃料及其制备方法

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