I have noticed poor adhesion between sputtered Au and Pt thin films. Why this is so, and is there a way to enhance this adhesion?
We routinely sputter Au on Pt with very good adhesion due to metallic bonding between the layers. I would suggest looking at the stress of the layers, as Pt in particular can generate very high stress as deposited. The thicker the films, the more stress you build, the more critical it is to have a low intrinsic stress process (greater than 1 µm needs a great deal of care). Optimizing pressure and/or temp can minimize stress. What is the morphology of the film. A dense (like zone T, 2 or 3) film with low stress should have very strong adhesion. A more porous zone 1 or worse film will be more susceptible to delamination. Also, are the films deposited sequentially without breaking vacuum? If no, there is a chance of interface contamination, requiring careful cleaning/substrate etch.
A Ti interlayer can help, but only masks/covers the inherent problem, and makes your films more susceptible to damage by oxidation.
try to use very thin layer of Titanium (approximately upto 5 nm) before the deposition of Au on Pt film. People generally use Titanium to adhere the Au on SiO2 substrate. Hopefully it will also work in your case.
The buffer layer, as also suggested by Mandeep, could be a solution, or you can try to enhance temperature or the energy of sputtered ions.
We typically use a Cr layer (around ~5 Å) to "anchor" Au to Si substrates. I guess it might work.
Hi .. Titanium can be used with thermal treatments ranging from 200 to 400 C.
In case you are already using Ti/Cr adhesion layer, try to UV/Ion clean the substrate before sputtering.
Using buffer layer is a common approach. Some of them might be Ti, Ta. Ta is a cheap way :D
Adhesion between Cr and gold can be enhanced by starting the deposition of the Cr layer at the lowest base pressure possible (lowest amount of oxygen in system). When oxygen is present I believe the Cr forms an oxide which interferes with the adhesion. I don't know if this approach would work for Pt ??
We are not given actual film thickness here or the application. Assuming that introducing any buffer layer is prohibitive due to application requirements, and there are technical means to do it, I would suggest an idea to explore co-sputtered Au-Pt interface layer.
Problem of adhesion for these materials are unlikely due to interface contamination and merely due to the weakness of Au/ Pt interfacing interatomic bonds and addition of bulk and interface stress ( pseudo-lattice mismatch). Some stable chemical interfacing bond bridges have to be formed in adding other metallic materials, considering that covalent bridges have reduced probability to be formed with other types of atoms (quite chemical neutral materials)and , assuming that no additional contaminants can further reduce the interfacing interatomic bonds.
Therefore, it will have to be introduced distributed additional interface atoms M with can form stronger interface bonding bridge.
Ti can be a solution, especially when atomic mixing can be achieved with adequate compromize between ion bombardment energy providing atomic mixing , diffusion by heat and achievement of reduced stress, and if no N CH and O contamination prevail.
However, other smaller metallic atoms able to diffuse inside the Au/Pt interface like In, Ag or Nb for instance can be considered, if no other heat and chemical affinity is changing the distribution of the additional atoms.
We routinely sputter Au on Pt with very good adhesion due to metallic bonding between the layers. I would suggest looking at the stress of the layers, as Pt in particular can generate very high stress as deposited. The thicker the films, the more stress you build, the more critical it is to have a low intrinsic stress process (greater than 1 µm needs a great deal of care). Optimizing pressure and/or temp can minimize stress. What is the morphology of the film. A dense (like zone T, 2 or 3) film with low stress should have very strong adhesion. A more porous zone 1 or worse film will be more susceptible to delamination. Also, are the films deposited sequentially without breaking vacuum? If no, there is a chance of interface contamination, requiring careful cleaning/substrate etch.
A Ti interlayer can help, but only masks/covers the inherent problem, and makes your films more susceptible to damage by oxidation.
I simply suggest to minimize the sputtering base pressure, as low as possible with a modest sputtering rate will get you a good adhesion. Good luck.
We typically use a bonding layer of either Ti or Cr, but the first thing is to make sure your the substrate surface is clean. We have had excellent results when we clean our substrates in-situ.
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructures
- Thin Films