BONDING METAL TO CERAMIC LIKE MATERIALS

Abstract: The bonding of an external metal taken from the group of Cu, Ni, Fe, Ti, Mo and alloys thereof to an oxide ceramic substrate is accomplished through the use of an ionic dif­ fusion accommodating metal oxide where the ionic diffusion oxide metal is taken from the group of Fe, Mn, Ti and the combination 32 Ni 67 V. The bond adhesion and processing parameters can be enhanced by addition of Li, Ni, Cu, Co and Mo and the ceramic can be at least one member of the group of glass, pyrex, Al₂O₃ and SiO₂ glass. More particularly there is disclosed the process of bonding an external metal to a ceramic comprising in com­ bination the steps of oxidizing a coating of a metal having at least one ingredient taken from the group of Fe, Mn, Ti, and the combination of 33 Ni 67 V on the surface of a ceramic member having at least one ingredient taken from the group of glasses, quartz, Al₂O₃ and SiO₂, and interdiffusion bond­ ing a layer of a metal taken from the group of Cu, Ni, Fe, Ti, Mo and alloys thereof into said oxidized coating.

Description: Technical Field The technical field of the invention is in the bonding of metal to ceramic. In a number of applications, particularly in the electrical, electronic and decorative arts, it is desirable to tightly fasten a metal member such as a conductor to an inert, insulating or specific conductivity ceramic like member for use under conditions where a long lifetime, wide temperature cycles, resistivity, expansion match strength and economy are considerations. Background Art In the electrical arts, external metal members are usually caused to adhere to insulating materials such as high silica content substrates by applying a first metal selected for an adherence property to the substrate and thereover applying usually by plating a second metal selected for another property such as resistivity. The technique provides well bonded films but limitations are encountered in having several materials with different properties. This technique is described in U.S. Patent 4,153,518. There is also a recognition in these arts that a copper film could be caused to adhere to an aluminum oxide substrate by forming an aluminate oxide, a spinel structure oxide of the metal of the substrate in this case which would provide a gradual change instead of a well-defined boundary. The formation of aluminate spinels under these conditions requires temperatures in excess of 1000°C. This technique provides a good bond but the spinel is limited to an ingredient of the substrate ceramic. This work was reported in Thin Solid Films 33 (1976) pages 99-105. NL-A- 6413472 discloses a process for forming a firmly bonding, metallic coating on a glass or ceramic substrate in which a first layer of Fe, Cr, Sn or In is vapour deposited in an oxidising atmosphere onto the substrate, followed by a second layer of Cu or Ag. In a particular process, a first layer of Fe is deposited onto a glass substrate at a temperature of c.250°C in an oxidising atmosphere, followed by deposition of a layer of Cu. FR-A- 1117800 discloses an article comprising a glass substrate coated with an adhesive intermediate layer of a metal oxide such as iron oxide and an outer layer of a gold alloy containing 1 to 5 per cent of a metal such as iron or nickel. The intermediate metal oxide layer is said to adhere very strongly to both the glass substrate and the gold alloy layer. Chemical Abstracts Vol. 99 Abstract no. 9750W describes a process for bonding a nickel film to a soda-lime glass plate by coating the glass plate with TiO₂, coating the TiO₂ with the nickel film and firing the structure at 270°C for 10 minutes. The invention provides a structure comprising an external copper metalisation attached to an oxide ceramic taken from the group of glasses, quartz,' SiO₂, Al₂O₃ and combinations thereof, through the use of an intermediate metal oxide layer taken from the group of Fe, Mn, Ti and the 33Ni 67 V combination, optionally including additional elements from the group Li, Ni, Cu, Co and Mo, there being an oxygen-metal bond between the intermediate metal oxide layer and said ceramic and an ionic diffusion type bond between the intermediate metal oxide layer and said external metalisation, wherein said intermediate oxide layer has a spinel type lattice, formed by heating the structure in the temperature range of 780 to 950°C in an atmosphere having an oxygen partial pressure of 10⁻⁷ to 1 Pa. Brief Description of the Drawings FIG. 1 is a sketch of the elements of a metal bonded to a ceramic like material of the invention. FIG. 2 is a block diagram illustrating the principal process steps involved in the structure of FIG. 1. FIG. 3 is a photomicrograph illustrating the details of the metal bond. Disclosure of the Invention It has been found that a certain group of metals will form an oxide layer that not only will adhere with an oxide bond to ceramic-like materials but also will bond with an interstitial mixing similar to ionic diffusion to an external metal. The invention permits fastening an external metal bond to a substrate at much lower temperatures. In the ceramics art it has been well known that since the structure of the ceramic, which includes glasses, is that of oxygen atoms linked together by metal atoms then a metal oxide which is also oxygen atoms linked together by metal atoms when placed on the surface of the ceramic will, when heated to the vicinity of fusion, bond to the ceramic by continuing the basic oxygen atom metal atom interlinkage. In accordance with the invention an oxide of a metal that forms ionic diffusion accommodating sites in the oxide will, when placed between a ceramic-like material and an external metal, not only bond in the well known way to the ceramic material at a minimal temperature, but also will provide a bond with the external metal in which ions from the metal enter and interstitially intermingle with the oxide. The ionic diffusion type of bond is like the bond in articles formed by fusing glass to nickel-iron alloys, and that of sealed-in leads for light bulbs and electron tubes. In accordance with the invention, it has been found that an ionic diffusion receiving layer can be formed of oxides of Fe, Mn, Ti and the combination 33 Ni 67 V. The oxides of these metals can be used singly or in combination. It has further been found that the oxides of these metals can have the properties of the bond and the processing conditions modified by additions from the group of Li, Ni, Cu, Co and Mo. The ionic diffusion receiving oxide adhesion layer will bond copper to an oxide ceramic such as glasses, SiO₂ and Al₂O₃. Referring to FIG. 1, an illustration is provided of the bonding of metal to ceramic material technique of the invention wherein on an oxide ceramic member 1, such as glass, SiO₂ or Al₂O₃ or mixtures thereof, an external metal ionic diffusion receiving oxide interlayer 2 is oxygen bonded at an interface 3 where the oxygen and metal interlinkage of the ceramic 1 is continued across the interface 3 into the oxide 2 which has metal ions different from that of the metal ions in the ceramic 1. A metal conductor 4 is bonded to the oxide interlayer 2 at an ionic diffusion interface 5. The interface 5 is shown schematically wide to emphasize the ionic interstitial intermingling between the metal oxide 2 and the metal 4. The ceramic member 1 in FIG. 1 to which the external member is to be bonded is an oxygen and metal ion interlinked material taken from the group consisting of glasses, SiO₂, sapphire or Al₂O₃ and various mixtures of glasses and crystalline phases. The metal oxide 2 in FIG. 1 is defined as being capable of accommodating a bond of the ionic diffusion type from the external metal 4 of FIG. 1 and is an oxide of a metal that forms at less than 1000°C in a structure that can accommodate both monoatomic and ionic diffusion. The 1000°C temperature is a temperature above which many chemical and physical processes move so rapidly that damage to what is being made takes place. It is always desirable to stay as low as possible. The metal of the oxide 2 need not be the metal in the ceramic 1 since the bond at the interface 3 involves oxygen rather than the metal of the ceramic as is the case in the Thin Solid Film prior art. At this state of the art, all metal members of oxide ceramics require processing in the vicinity of 1000°C or above. The metal oxide structure 2 must accommodate ionic diffusion from the external metal 4. This property of having the ability to accommodate bonds of more than one valence has been attributed to molecular structures of the spinel type. The metal oxide 2 includes oxides of Fe, Mn, Ti and the combination of 33 Ni 67 V, either singly or in combination with optional additions of Li, Ni, Cu, Co, and solid solutions thereof. The metals in the interlayer oxide are considered to be present as ions with either or both of the following valences: Fe²⁺ or Fe³⁺, Mn²⁺ or Mn³⁺, Ti³⁺ or Ti⁴⁺ and Ni²⁺, V³⁺. The additions to the ingredients of the interlayer oxide are considered to be present as ions with either or both the following valences: Li⁺, Cu⁺ or Cu²⁺, Ni²⁺, Co²⁺ or Co³⁺. The inclusion of the additions has been found to lower the temperature for bonding and to improve the bond strength. The external metal member 4 is a metal chosen for a performance property. It must be capable of providing at least one ionic diffusant which is an atom with a valence from 1 to 4. The selected external metal 4 is Cu having either or both a ⁺ or a ⁺⁺ valence. Referring next to FIG. 2, a schematic flow chart is provided to illustrate the principal steps involved in bonding the external metal member to the ceramic. There are three general steps. In the first general step a coating of a metal or a compound of the metal that will form the oxide 2 of FIG. 1 is applied to the ceramic 1. The coating is oxidized at less than 1000°. Where the coating is the metal only, oxygen is environmentally supplied. Some coatings oxidize in air. In the second general step, the external metal is applied. This can be done by machine processes such as sputtering, evaporation, spinning and vapor deposition and can even by positioning a stamped preform on the surface of the oxide interlayer. In the third general step, a heat treatment cycle at between 780°C and 950°C takes place that provides the oxide bond 3 to the ceramic 1, forms the intermediate metal oxide layer 2 in a structure capable of accommodating ionic diffusion and causes the ionic diffusion type interstitial mixing bond 5 between the external metal 4 and the metal oxide interlayer 2. Referring to FIG. 3, a photomicrograph of a sample is provided illustrating the elements of the bond of the invention. In FIG. 3 the region labelled A is the ceramic substrate, the region labelled B is the external metal and the region labelled C is the ionic interdiffused region. The jagged shapes are an illustration of what remains after an attempt to peel off the external metal layer. Best Mode For Carrying Out The Invention The preferred method of carrying out the invention in general is to apply the interlayer coating to the ceramic by a dry process such as sputtering or a wet process such as spinning followed by the application of the external metal with the interdiffusion heat treatment, either during or after application, being at the minimum temperature to provide the required bond, and yet be consistent with the properties of the materials involved. In order to permit one skilled in the art to have a starting place in practicing the invention, specific examples illustrating the principles involved are provided. In general the interlayer is applied as a film in a dry process such as sputtering or evaporation or in a wet process such as by spinning. In Magnetron sputtering, for example, a Ti film of 500nm (5000A °) thickness is generally grown at a 10nm per minute rate. In sputtering the metals can be applied as mixtures, for example MnFe or NiFe followed by oxidation to form the oxide interlayer. In spinning the film of the Fe, Mn, Ti or V compound is spun on the glass or ceramic substrate and is then heated in the range between 450°C and 900°C in air. The interlayer film strength and adhesion to the substrate is enhanced with a 700 to 900°C heat treatment. EXAMPLE Copper External Metal A fused quartz ceramic is coated with Fe₂O₃ approximately 200nm thick. A layer of Cu approximately 4 micrometers (µm) thick is vacuum evaporated over the Fe₂O₃ coating on the quartz. The combination is heated in the range of 780 to 950°C in an oxygen partial pressure of 1 to 10⁻⁷ Pa (10⁻⁵ to 10⁻¹² atm). The intermediate ionic diffusion accommodation layer formed from the Fe₂O₃ was determined by magnetic resonance to be magnetic and from x-ray diffraction to have a spinel like structure with a lattice parameter in the field CuFe₂O₄-Fe₃O₄-CuFe₅O₈. The average bond strength measured by a pull test is 2.8 x 10⁷ ± 7 x 10⁶ Pa (4.0 ± 1.0 kilopounds per square inch (Kpsi)). The failure appears in the fused quartz not at the bond. Care is indicated to minimize dissolving Cu during step 3 into the quartz which may weaken the quartz. The photomicrograph of the bond cross section shown in FIG. 3 illustrates the ionic diffusion in the region labelled C. A reduction in the oxygen partial pressure to 10⁻⁸ Pa (10⁻¹⁸ atm) reduces the pull strength to 4.8 x 10⁶ Pa (0.7 Kpsi). It is considered that the low oxygen pressure does not permit formation of the needed copper ions. The identical procedure using a glass ceramic provides a pull test of 7.1 x 10⁷ Pa (10.3 ± 1.0 Kpsi) which, when the oxygen partial pressure is reduced to 10⁻⁸ Pa (10⁻¹⁸ atm) is reduced to 7 x 10⁵ Pa (0.1 Kpsi). Tio₂ and V₂O₅ do not react as easily as Fe₂O₃ but are responsive to the following procedure: The heat treatment temperature range is increased to between 800°C and 1000°C in the presence of a gas containing H₂ between 0.15% and 0.65% and N₂ between 99.85% and 99.35%. The gases are mixed and passed through a water reactor at 20° to 30°C which imparts a water content. Cu external metal using the above techniques in addition to quartz may also be bonded to the following glass ceramic materials: SiO₂, glass, 90-100% Al₂O₃ ceramics and Al₂O₃-SiO₂ ceramics.

Claims: A structure comprising an external copper metalisation attached to an oxide ceramic taken from the group of glasses, quartz, SiO₂, Al₂O₃ and combinations thereof, through the use of an intermediate metal oxide layer taken from the group of Fe, Mn, Ti and the 33Ni 67 V combination, optionally including additional elements from the group Li, Ni, Cu, Co and Mo, there being an oxygen-metal bond between the intermediate metal oxide layer and said ceramic and an ionic diffusion type bond between the intermediate metal oxide layer and said external metalisation, wherein said intermediate oxide layer has a spinel type lattice, formed by heating the structure in the temperature range of 780 to 950°C in an atmosphere having an oxygen partial pressure of 10⁻⁷ to 1 Pa. A process of bonding an external metal to a ceramic comprising oxidising a coating of a metal having at least one ingredient taken from the group of Fe, Mn, Ti and the combination 33Ni 67 V, optionally including additional elements from the group Li, Ni, Cu, Co and Mo on the surface of a ceramic member having at least one ingredient taken from the group of glasses, quartz, Al₂O₃ and SiO₂, depositing an external layer of copper metal onto the oxidised coating and subjecting the structure to a heat treatment in the temperature range of 780 to 950°C, in an atmosphere having an oxygen partial pressure of 10⁻⁷ to 1Pa, in order to form an interdiffusion bond between the oxidised coating and the external metal layer and a spinel type lattice structure in the oxidised coating. A process as claimed in claim 2, wherein said oxidising step occurs during the application of the metal coating.

Inventors: BROWNLOW, JAMES MERRITT, PLASKETT, THOMAS STANLEY
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1985
Main classification: C03C27
IPC codes: C03C17, C04B41, C04B37, C23C14