Selection
While the choice of diffusion barrier depends on the final function, anticipated operating temperature and service life are critical parameters to select diffusion barrier materials. Many thin film metal combinations have been evaluated for their adhesion and diffusion barrier properties. Aluminum provides good electrical and thermal conductivity, adhesion and reliability because of its oxygen reactivity and the self-passivation properties of its oxide. Copper also easily reacts with oxygen but its oxides have poor adhesion properties. As for gold its virtue relies in its inertness, and ease of application; its problem is its cost. Chromium has excellent adhesion to many materials because of its reactivity. Its affinity for oxygen forms a thin stable oxide coat, a passivation layer which prevents further oxidation and provides inertness to corrosive environment. Nickel, Nichrome, tantalum, hafnium, niobium, zirconium, vanadium, and tungsten are a few of the metals combinations used to form diffusion barriers for specific applications. Conductive ceramics can be also used, such as tantalum nitride, indium oxide, copper silicide, tungsten nitride, and titanium nitride.
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