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 on the outer surface, creating a
passivation layer which prevents further oxidation of the chromium, and of the underlying metal (if any), even in corrosive environments. Chromium plating on steel
for automotive use involves three diffusion barrier layers—copper, nickel, then chromium—to provide long term durability where there will be many large temperature changes. If chromium is plated directly onto the steel, then their different
thermal expansion coefficients will cause the chrome plating to peel off the steel.
Nickel,
Nichrome,
tantalum,
hafnium,
niobium,
zirconium,
vanadium, and
tungsten are a few of the metal 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. ==Integrated circuits==