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Interactions between thick film resistors and aluminium nitride substrates

: Kretzschmar, C.; Hentsche, M.; Reppe, G.

International Microelectronics and Packaging Society -IMAPS-:
International Symposium on Microelectronics 2006. Proceedings : October 8 - 12, 2006, San Diego, California, USA
Washington, DC: IMAPS, 2006
ISBN: 0-930815-80-7
International Symposium on Microelectronics <39, 2006, San Diego/Calif.>
Fraunhofer IKTS ()
Dickschichtwiderstand; Aluminiumnitrid; Halbleitersubstrat; Wärmeleitfähigkeit; Dielektrizitätskonstante; Yttriumaluminat; Materialwechselwirkung; Siebdruck; Rutheniumoxid

Resistors on aluminium nitride (AlN) are very interesting for microwave applications because of the high thermal conductivity and the excellent dielectric properties of AlN. During the firing process the conductive phase RuO2 of the resistor film can react with AlN. This reaction depends on surface quality of the substrate as roughness and content and composition of yttrium aluminates which are formed if yttria is used as additive to AlN for sintering. The yttrium aluminates on the AlN surfaces were identified by X-ray diffraction and quantified by Rietvelt analysis. The interactions between the resistor and AlN were investigated by cross section, FESEM and EDX. Four kinds of surface states were microscopically found: tight AlN, AlN with pores, residuals of yttrium aluminate after treatment of the as-fired surface and yttrium aluminate crystallites embedded in AlN. Each of this state can show another interactions with the resistor film. If yttrium aluminate is on the AlN surface the reaction between RuO2 and AlN is inhibited. On the other hand pores in the AlN increase the reaction rate. The resistance were related to the surface properties of AlN. High standard deviation of resistance was observed on some substrates. The reason for this phenomenon was investigated by different methods. The resistance correlates with the content of YAlO3 on the substrate surface. The increased resistance can be explained by reaction between RuO2 containing in the resistors as conductive phase and AlN. As result of this reaction Ru metal and gaseous nitrogen are formed. Four kinds of areas were microscopically identified: tight AlN, porous AlN, residuals of yttrium aluminates on the surface and crystallites of yttrium aluminate embedded in AlN. The reaction between RuO2 and AlN on this four areas is different. A porous AlN surface accelerates and yttrium aluminates can inhibits this reaction. Therefore the surface treatment and the homogeneity of the substrate surface are very important requirements for small standard deviation of the resistance.