Diffusion is the movement of one material into another. Sometimes this movement is a desired effect and sometimes it is not. Diffusion usually occurs more rapidly at higher temperatures. The analytical challenge when investigating diffusion is ensuring good depth resolution and low detection limits, whilst also ensuring that the analysis itself does not affect the result.
Diffusion analysis is usually done using ion beam depth-profiling methods, such as Auger Electron Spectroscopy (Auger) and Secondary Ion Mass Spectrometry (SIMS). The particular technique used depends upon the sample being tested:
- Metal layer inter-diffusion: Auger is generally used for metal layer inter-diffusion analysis because sample rotation can be used to reduce sputter etch roughening effects, making for better interface and layer definition.
- Dopant Diffusion: SIMS is generally used for implant studies in semiconductors where the best detection limits and depth resolution are required.
- Interlayer diffusion in semiconductors: SIMS is generally the method of choice, particularly in conjunction with advance sample preparation such as backside polishing.
Depth profiling using ion beam etching/sputtering can push one material forwards into another material (ion beam mixing). By using lower beam energies and/or analyzing from the sample backside, ion beam sputtering artifacts can be reduced or removed, allowing the observation of genuine diffusion.