What Does Diffusion Barrier Layer Mean?
A diffusion barrier layer is an intermediate layer positioned between two metals. It is a barrier to protect the metals from corrupting each other.
There are a few metal combinations used to form diffusion barrier layers for specific applications. In the past a number of different species have been explored as barrier layers, like titanium/titanium nitride and tantalum/tantalum nitride, or modifications of these, such as tungsten/titanium nitride and titanium silicon nitride. The problem with tantalum barrier layers is that they can be contaminated with small amounts of carbon and oxygen, inhibiting copper wetting and adhesion. Other barrier layers include:
- Cobalt-based diffusion barrier thin films
- Amorphous silicon carbide films
- Silicon oxynitride films
Corrosionpedia Explains Diffusion Barrier Layer
A diffusion barrier is preferably a single-phase alloy or intermetallic compound. A diffusion barrier layer is characterized by:
- Low solubility for aluminum from either the substrate or the protective coating
- Low interdiffusivity for elements from the substrate and the coating
- Minimal impact on the mechanical properties of the coated article
- Minimal thermal expansion mismatch with both the substrate and the protective coating
- Application using existing coating techniques
A good diffusion barrier requires inertness with respect to adjacent materials. Materials providing good adhesion are not necessarily good diffusion barriers and vice-versa. Consequently, there are cases where two or more separate layers must be used to provide a proper interface between substrates.
Selection of diffusion barrier materials depends on:
- Final intended function
- Anticipated operating temperature
- Service life
Non-metallic barriers have a significant advantage over metal barriers, since their coefficients of expansion are more closely matched. Conductive ceramics can be also used, such as:
- Tantalum nitride/indium oxide
- Titanium nitride