KR20040002420A - Method of making a nickel-coated copper substrate and thin film composite containing the same - Google Patents

Abstract

The present invention relates to a method of making a copper / nickel substrate by annealing nickel coated copper. After the nickel deposition step, a dielectric such as lead zircon titanate (PZT) may be deposited on the substrate by known methods such as sol-gel or vacuum deposition techniques. The invention also relates to thin film composite materials. Such composite materials include pre-annealed nickel coated copper substrates and dielectrics such as PZT.

Description

METHOD OF MAKING A NICKEL-COATED COPPER SUBSTRATE AND THIN FILM COMPOSITE CONTAINING THE SAME}

In the past, efforts have been made to develop high capacitive electrochemical energy storage elements, in particular capacitors and batteries, used for reduced volumes. Both capacitors and batteries store energy by separating positive and negative charges. New research continues because of the need to store more energy in a smaller package.

Energy storage devices made from thin film composites are known to be useful in electronic and optoelectronic applications such as ferroelectric memory devices, superthermal conductivity sensor devices, waveguide modulators, and acoustic sensors. Thin film composite materials, for example, are used in various semiconductor integrated circuit devices such as analog circuits, rf circuits, and DRAMs.

Composite materials generally consist of a substrate, a dielectric, and an electrode, the dielectric being between the substrate and the electrode. Substrates are typically composed of copper, silicon, fused silica, platinum coated silicon, alumina, sapphire, platinum coated sapphire, or single crystal SrTiO ₃ substrates.

Copper substrates are often preferred in view of their easy availability. Unfortunately, thin film composite materials with copper substrates cause heat transfer and outgassing. Thermal transfer is the movement of copper ions to a dielectric at elevated temperatures and the movement of ions in the dielectric to a substrate. Degassing occurs when gaseous copper atoms exit the substrate and enter the oven or dielectric where deposition of the dielectric occurs. Therefore, there is a need for a copper substrate that can eliminate this disadvantage.

The present invention relates to a method for producing a nickel coated copper substrate used in a thin film composite material and a thin film composite material including the nickel coated copper substrate.

1 is a graph showing the optimal temperature and time for annealing a nickel coated substrate in accordance with the method of the present invention,

2 is an internal structure of a nickel coated copper substrate preannealed at a temperature of 400 ° C. for 120 minutes using a scanning electron microscope,

3 is an internal structure of a nickel coated copper substrate preannealed at a temperature of 900 ° C. for 5 minutes using a scanning electron microscope,

4 and 5 show the internal structure of the nickel coated copper substrate preannealed at a temperature of 800 ° C. for 20 minutes using a scanning electron microscope,

6 is an internal structure of a nickel coated copper substrate preannealed at a temperature of 500 ° C. for 90 minutes using a scanning electron microscope,

7 is an internal structure of a nickel coated copper substrate preannealed for 30 minutes at a temperature of 650 ° C. using a scanning electron microscope,

8 shows a thin film composite material according to the present invention having a copper substrate coated with nickel on its top and bottom surfaces, a dielectric, an optional barrier or buffer layer, and a top dielectric,

9 shows a thin film composite material according to the present invention having a copper substrate completely sealed by nickel.

The present invention relates to a method of making a nickel deposited copper substrate. The present invention also relates to a thin film composite material comprising such a nickel coated copper substrate. Nickel coated substrates are made by depositing nickel on copper and then annealing the final substrate. The copper may be in foil form. After annealing, the dielectric may be deposited on the substrate by methods known in the art, such as sol-gel techniques or vacuum deposition techniques.

The thin film composite material according to the present invention comprises a nickel coated copper substrate and a dielectric. The substrate is made by depositing nickel on copper. Nickel may be deposited on one or both sides of the copper substrate. In a preferred embodiment, nickel encapsulates the copper substrate.

The nickel deposited copper substrate is then annealed at a temperature in the range of about 400 ° C. to 820 ° C., preferably about 800 ° C. The optimum annealing time varies with the annealing temperature. For example, annealing at 400 ° C. preferably lasts for about 120 minutes and annealing at 800 ° C. lasts for about 20 minutes. 1 shows the optimum annealing temperature and time with the most preferred temperature and time being points on the line. The unacceptable consequence of causing a defective substrate occurs at the point where the distance from the line is increased. Defective substrates exhibit unacceptable dielectric constants, high voltage leakage, or delamination.

Generally, the thickness of the substrate (prior to nickel deposition) is in the range of about 20 to about 50 microns. The Ni thickness on the side that contacts the dielectric ranges from about 0.10 microns to about 2.0 microns. The thickness of Ni on the bottom surface of the substrate (when no dielectric is in contact therebetween) ranges from 0.1 to about 10 microns.

Nickel may also be applied to the copper substrate by sputtering or other means known in the art. The preliminary annealing and nickel deposition steps preferably take place in an oxygen free atmosphere, such as a gaseous atmosphere of argon or nitrogen. (Preliminary annealing as used herein refers to annealing before deposition of the dielectric material.)

Dielectric deposition on nickel coated copper substrates generally requires low processing temperatures to minimize cross diffusion and reaction between the foil and the dielectric. Such dielectrics may also be applied to the substrate by sol-gel where the deposition takes place at room temperature and the annealed nickel coated copper substrate is cooled to room temperature or by vacuum deposition (including sputtering, electron beam deposition, and other techniques). It is also possible, where the annealed product is cooled to the temperature at which deposition occurs. For example, when vacuum deposition is used, the dielectric is applied at elevated temperatures ranging from 300 ° C to about 400 ° C. Deposition of the dielectric may occur in a single step or multiple steps. The thickness of the dielectric varies with the amount of voltage required for the final product, such as a capacitor. The higher the applied voltage, the thicker the dielectric will be. Typical thickness for the dielectric is about 600 nm.

In a preferred embodiment, the dielectric is lead zircon titanate (PZT) of formula Pb _a L _b Zr _x Ti _y O _z , where L is a lanthanide metal, preferably La or Nb, and x and y are each about 0.35 to about 0.6 ranges from about 2.5 to about 5.0, a ranges from about 0.95 to about 1.25, and b ranges from about 0.02 to about 0.10. Such dielectrics include lead acetate [Pb (CH ₃ COO) ₂ H ₂ O], zirconium n-propoxide [Zr (O-nC ₃ H ₇ ) ₄ ], titanium isopropoxide [Ti] as initial materials (O-iC ₃ H ₇ ) ₄ ] and lanthanum isopropoxide [La (O-iC ₃ H ₇ ) ₃ ] or niobium ethoxide [Nb (OC ₂ H ₅ ) ₅ ]. In a preferred embodiment, such a dielectric may be prepared by dissolving lead acetate trihydrate in 2-methoxyethanol to obtain lead acetate and dehydrating the composition at vacuum and 110 ° C. Zirconium n-propoxide and titanium isopropoxide in 2-methoxyethanol are mixed with the final product at room temperature and refluxed at 110 ° C. for about 2-3 hours under vacuum, from which the formula Pb (Zr _0.52 Ti Polymeric precursors such as _0.48 ) O ₃ can be obtained. Finally, a 0.3 M stock solution may be obtained by dilution with toluene, formamade suitable for protection from cracks, and addition of 10 mol% or more of Pb suitable for the removal of lead oxide during final annealing processing.

Conventional dielectrics known in the art to which the present invention pertains may also be used, but in particular the formula Ba _a Ti _b O _c (where a and b are respectively 0.75 to 1.25, c is in the range of 2.5 to about 5.0) as well as M _a B _b Ti _c O _d where a is from about 0.01 to about 0.1, b is from about 0.75 to about 1.25, c is from about 0.75 to about 1.25, d is from about 2.5 to about 5.0, and M is non- More desirable results are obtained by using a barium titanate dielectric of reactive electroconductive metal). As M, gold, copper, intermetallic compounds such as Ni ₃ Al, Ru and InSn are preferable. Such barium dielectrics are described in PCT WO / 98/07167, incorporated herein by reference and published February 19, 1998.

After deposition, the article is annealed for about 20 minutes in the range of 500 ° C to 600 ° C. At this stage annealing time will be shorter if higher temperatures are used. Annealing terminates when the desired result is achieved. The preliminary annealing step must occur at a temperature higher than the annealing temperature for dielectric deposition on the substrate, the latter being referred to as the "post-annealing" step. If the preannealing step is at a lower temperature than the post annealing step, the preannealing will proceed for a longer time, typically 20 minutes or more.

As shown in FIG. 2, a flat laminate surface is obtained for the final substrate preannealed at a temperature of 400 ° C. for 120 minutes. A dielectric constant of 86 was obtained and a Tgδ (%) of 14 was obtained. 3 shows the preferred results obtained under pre-annealing conditions at 900 ° C. for 5 minutes. The substrate has a dielectric constant of 110 and a Tgδ (%) of 7. 4 and 5 show the preferred results obtained when preannealing is carried out at 800 ° C. for 20 minutes. The dielectric constants measured were 75 and 113, respectively. 6 and 7 show the results in preliminary annealing conditions, which are undesirable than the conditions of the previous figures. 6 is a scanning electron micrograph of a substrate preannealed at 500 ° C. for 90 minutes. The final substrate was rough and showed peeling. 7 is a scanning electron micrograph of a substrate pre-annealed at 650 ° C. for 30 minutes. The final substrate was rough. All substrates shown in FIGS. 2-7 were obtained in an Ar atmosphere and used PZT as the dielectric deposited on the substrate by spin coating. The thickness of Cu is about 33 to 35.6 microns. Tests were performed and the thickness of Ni on the top surface in contact with the dielectric in FIG. 5 was 1.78 microns. The thickness of Ni on the lowest side of the substrate (not in contact with any dielectric) was 6.35 to 7.62 microns. In FIGS. 2-4 and 6 and 7, the thickness of Ni on the topmost surface in contact with the dielectric was 0.1270 microns and the thickness of Ni on the bottommost surface of the substrate (not in contact with a predetermined dielectric) was 0.3556-0.5080 microns. The thickness of all copper foils for thin film composites in FIGS. 2-7 is about 34 microns.

8 illustrates an embodiment according to the invention, wherein the illustrated thin film composite material includes a copper substrate 10 coated with nickel 20, a dielectric 50, and, optionally, a top electrode 60. Coated copper substrates. The nickel coating may also completely or partially seal the copper substrate. Optionally, the copper substrate may be sealed on only two sides. 8 also uses a barrier or buffer layer 30 applied to a nickel coated substrate prior to the deposition of the dielectric. The purpose of the barrier layer, which is generally made of noble metal, and the buffer layer, which is made of glass, is to prevent atomic migration between the substrate and the dielectric.

Finally, the thin film composite material according to the present invention further comprises an upper or electrically conductive layer. The upper electrode may be composed of any electrically conductive metal, such as aluminum, gold, platinum, or a known metal. The thin film composite material shown in FIGS. 2 to 7 has Al as the upper electrode.

9 shows a thin film composite material in which the copper substrate 10 is completely sealed with nickel 20. In addition, the thin film composite material may further include a barrier or buffer layer 30, a dielectric 20, and an electrode 60.

Various modifications of the nature, composition, function and arrangement of the various elements, steps and processes may be possible without departing from the spirit and scope of the invention as defined in the following claims.

Claims (24)

(a) a nickel coated copper substrate, (b) a thin film composite material comprising a dielectric layer on the nickel coated copper substrate. The method of claim 1, A thin film composite material wherein the top and bottom surfaces of the nickel coated copper substrate are coated with the dielectric. The method of claim 2, And the copper of the nickel coated copper substrate is encapsulated by nickel and encapsulated. The method of claim 3, wherein The dielectric is Ba _a Ti _b O _c , wherein a and b are each about 0.75 to about 1.25 and c is in a range from about 2.5 to about 5.0. The method of claim 3, wherein The dielectric is Pb _a L _b Zr _x Ti _y O _z , where L is a lanthanide metal, x and y are each in the range of about 0.35 to about 0.65, z is in the range of about 2.5 to about 5.0, and a is about 0.95 To 1.25 and b in a range from about 0.02 to about 0.10. The method of claim 1, And a barrier or buffer layer positioned between the nickel coated copper substrate and the dielectric layer. The method of claim 1, Further comprising an electrically conductive layer, And the dielectric is positioned between the electrically conductive layer and the nickel coated copper substrate. The method of claim 6, And the barrier layer comprises a precious metal. The method of claim 6, And the buffer layer comprises glass. The method of claim 6, Further comprising an electrically conductive layer, And the dielectric is located between the barrier or buffer layer and the nickel coated copper substrate. The method of claim 2, And a bottom barrier or buffer layer positioned between the dielectric and the bottom surface of the substrate, and a top barrier or buffer layer positioned between the top dielectric and the top surface of the substrate. The method of claim 11, Wherein said nickel coated copper substrate is encapsulated and encapsulated by nickel. As a manufacturing method of the copper substrate for thin film composite materials, (a) depositing nickel on the copper substrate to provide a nickel coated copper substrate, (b) annealing the nickel coated copper substrate. The method of claim 13, And the nickel coated copper substrate is annealed at a temperature in a range from about 400 ° C to about 820 ° C. The method of claim 13, And the nickel coated copper substrate is encapsulated by nickel and encapsulated. The method of claim 13, And the nickel coated copper substrate is annealed at the time and temperature set in FIG. 1. The method of claim 14, And the nickel coated copper substrate is annealed at a temperature in the range of about 650 ° C to about 800 ° C. The method of claim 16, And the nickel coated copper substrate is annealed at a temperature of about 400 ° C. for about 120 minutes. The method of claim 14, And the nickel coated copper substrate is annealed at a temperature of about 800 ° C. for about 20 minutes. As a manufacturing method of a thin film composite material, (a) depositing nickel on the copper substrate to provide a nickel coated copper substrate, (b) annealing the nickel coated copper substrate for a time sufficient to provide a nickel coated copper substrate at a temperature ranging from about 400 ° C. to about 800 ° C., and (c) depositing a dielectric on said nickel coated copper substrate. The method of claim 20, And the nickel coated copper substrate is annealed at the time and temperature set in FIG. The method of claim 20, Depositing an electrically conductive layer on the dielectric layer. The method of claim 20, After step (a), a barrier or buffer layer is deposited on the nickel coated copper substrate. The method of claim 20, Wherein said nickel coated copper substrate is a copper substrate that is encapsulated and encapsulated by nickel.