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Improving Copper-Ceramic Bonding through Interface Engineering
Keywords: Copper-Alumina, Interface, Adhesion
The problem of delamination or detachment is a very serious failure path for all the microelectronic packaging systems [1, 2]. This underlies the critical importance of metallization adhesion to the substrate, especially for devices operating under harsh environments. Metallization on ceramic substrate is an important topic for microelectronic applications since the adhesion of metal films on ceramic substrates is intrinsically low. Various methods have been explored in order to obtain optimized bonding. For example, effect of surface morphology and surface cleanliness on the bonding interface has been studied in [3,4]. In this work, 96% purity of polycrystalline alumina substrate was metallized by 99.99% copper using DC magnetron sputtering method. A number of factors, such as surface pre-treatment, surface cleanliness and surface roughness have been investigated. With a proper treatment step applied, the bonding strength was improved from about 6 ± 2.5MPa up to 40.0 ± 3.0MPa without modified the surface structure and morphology of the substrate. Furthermore, the effect of the substrate surface morphology to the interface bonding has also been analyzed. Three groups of alumina substrate with the surface roughness in the range of 10nm - 150nm; 200nm - 350nm and 350nm to 500nm were used and the adherence of copper onto the Al2O3 shows an improvement up to 50% with rougher surface structure. This was due to the enlargement of contact area at the interface with the addition award from the physical locking effect on the porous area during the sputtering process. In summary, various surface treatments have been applied prior to coating and significant improvement was shown in the adhesion strength. With the help of XPS and SEM, the effect of substrate surface condition was elucidated. In addition, the bonding between copper film and the alumina substrate was improved with higher surface roughness. With larger area in contact, more bonds have been created in between the bonded materials. Thus, higher energy is needed to initiate the breakage at the interface during the tensile test and results in greater adhesion strength.
Lim Ju Dy, Ph.D Student
Nanyang Technological University
Singapore, Singapore

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