Doctoral Dissertations

Jae-Won Park

Date of Award

12-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Metallurgical Engineering

Major Professor

Anthony J. Pedraza

Committee Members

D. H. Lowndes, W. R. Allen, R. A. Buchanan, H. Weitering

Abstract

One of the most fundamental aspects of the metal/ceramic couple applications is strong adhesion. For this reason, a substatial effort has been made in this work to establish the processing conditions that enhance the adhesion between two dissimilar materials and discover the adhesion mechanisms responsible for the strong bonding. In this work, representative systems chosen included gold and copper as the metallic films and Al2;O3; and AIN as the ceramic substrates. These metals and ceramics are non-reactive with each other under thermodynamic equilibrium and, for this reason, the ceramic surfaces were modified to increase the reactivity between the ceramics and the metals. Laser irradiation and ion bombardment methods were used for the surface modifications and aimed at disordering and debonding the surface atomic arrangement and chemical changes of the ceramics. The surface characterizations were conducted with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) before and after surface modifications. The results were compared with TEM analysis. These ceramics were decomposed leaving metallic aluminum and/or substoichiometric ceramics on the surface, followed by the reoxidation of the utmost layers. The metallic films were sputter-deposited on the as-received and surface modified ceramic substrates, and the film/substrate couples were annealed to increase the atomic mobility at the interface. Pull adhesion testing was conducted next, and then the interfaces of the strongly and weakly adhered couples were analyzed with AES technique. The analysis of the interface of the metal/ceramic couples using AES is usually not easy due to the sample charging and decomposition of ceramic substrates. Hence, a new method was devised, in which the analysis is performed on the film using the Auger electron escape depth. This method can also eliminate the problems during the AES analysis of the ceramics. The analysis takes advantage of various film thickness and the variation of Auger electron kinetic energies of the elements of interest.

The interfacial reactions of the metallic films and alumina and aluminum nitride couples were greatly affected by the laser energy densities and irradiation atmospheres used for the substrate treatment and annealing temperatures of the couples. Also, the surface contaminants played a very important role for the enhanced adhesion. In the copper/Al2;O73; couple, the strong bonding mechanisms were i) the formation of double oxides at the interface which could be achieved by the laser irradiation of the ceramics in air followed by the low temperature (300°C) annealing of the couple and ii) direct interaction between the copper film and metallic aluminum and/or substoichiometric alumina that could be obtained by the laser irradiation in Ar-4%H2; followed by 500°C annealing of the couple. In the gold film/Al2;O3; couple, the gold was also reacted with the substrate when the substrate was irradiated in the oxygen atmosphere at 1 J/cm2; energy density and the couple was annealed at 300°C.

The amount of the metallic aluminum that formed by the decomposition ofAIN was much more than that formed in alumina. Since the metallic aluminum is easily reoxidized, the bonding mechanism in these couples were not much different to the copper-alumina couples. In the strongly bonded couple, Cu-O-Alcompound was always found at the interface. Gold reacted with laser irradiatedAIN substrate in the strongly bonded Au/AIN couple.

When Ar+ ions bombardment of sapphire (single crystalline Al2;O3;) andgold film deposition were conducted simultaneously, pull adhesion testing of the couple also showed very strong bonding without a following anneal of the couple. The effects of ion beam bombardment on the sapphire substrate were investigated in situ with AES. Metallic aluminum was detected on the surface of sapphire substrate after irradiating for 3 min. with 7 keV Artions, These results were consistent with TRIM calculations that yield preferential sputtering of oxygen. An AES analysis revealed that Au-Al-O compound formed at the interface that may have caused the strong bonding. The compound must have been favored by the surface cleaning and the reduction of the sapphire due to theion bombardment prior to the gold film deposition.

A study on the copper diffusion into SiO2; substrate was also conducted in this work. Copper deposited on the thermally grown SiO2; substrate drifted into the substrate upon annealing at 300°C under 1 MV /cm2; electric field application. AES analysis showed formation of a copper oxide at the interface of this couple.

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