I am trying to make some thin film microwires using Au on a SiO substrate, however, the Au delaminated and lifted off the surface.
I used a 10nm layer of Ti to act as an interface between the Au and SiO. The Au was 200 nm thick deposited by thermal evaporation at a rate of 1A/s. The substrate temperature was around 45C. Everything was done under vacuum around 6 uTorr. Prior to deposition the substrate was cleaned by a quick O2 plasma etch.
If anyone has any suggestions on how I might be able to improve adhesion, I would appreciate it. Normally I would just run test samples and vary some parameters to get an idea of what works, but Au is just too expensive to do that.
Better if you use Chromium deposition (a very thin layer) on Si O2 before depositing Au. It has a good adhesion with gold.
You need adhesion layer. It was mentioned above that chromium (Cr) is generally used for this purpose. Other common material is nickel (Ni). Keep in mind that both Ni and Cr require quite high temperature for melting and evaporation, so you will heat up your substrate a little. In addition, Ni can easily destroy the boat used for resistive heating (Ni and Al are very reactive) so you need to use crucible or boat covered by protective aluminum oxide layer. In both Cr and Ni cases you need only very thin layer (few nanomaters are fully enough, it does not need to be continuous layer).
Otherr alternative approach is to use organic self-assembled monolayer as an adhesion layer. I recommend to use (3-mercaptopropyl)trimethoxysilane (shortly MPTMS) for this purpose. This rod-like molecule has one end modified with thiol (sulphur atom reacts with gold), while the other one will create a bond with SiO2. As a result, if you put your substrates to the desiccator together with MPTMS and you will leave it for a day (MPTMS is volatile, so gas phase is formed soon) you obtain organic adhesion layer suitable for gold evaporation.
Both above-mentioned approaches are suitable for SiO2 substrates. You need to chose in accordance to your requirements and possibilities (we do not know if your power supply is strong enough to evaporate Cr or if you have Al2O3 coated boates for Ni).
Good luck. :)
Definitely, Cr is a very good option (also Mo). We typically use Cr in our lab to anchor the Au layers.
Thank you all for the responses.
Is there any benefit to using Cr over Ti as an adhesion layer between SiO2 and Au? I've also read some sources which suggest using both.
Some further information about my problem. I am using a lithography mask to do evaporation and liftoff, so rigorous cleaning of the substrate prior to deposition is difficult without damaging the mask. I believe Hydrogen contamination might be the source of my adhesion issues.
Both are high melting point materials.
1) It is easy to thermally evaporate chromium, using Chrome plated tungsten rods, to flash a thin layer of Cr for the purpose of adhesion layer before Au is deposited.
2) In case you have a sputtering machine, it is easier to sputter deposit Ti buffer layer.
So both materials (Cr. or Ti) are fine, you need a good vacuum in case of Titanium, and a convenient method to deposit ultra thin layers to be considered as adhesion layers.
K. Sreenivas
Please remember,
you should try to deposit Au-Ti (without breaking the vacuum
or alternately Au-Cr layers without breaking the vacuum.
K. Sreenivas
Silane modifications enhance the adhesion strength. There are different types of silane coupling agents available commercially according to our requirements. Please go through below link. This article might be helpful.
http://www.sciencedirect.com/science/article/pii/S0032386116301227
Chromium is a good adhesion layer between gold and SiO2. We have used Cr 25 nm layer under 200 nm gold using electron beam evaporator and it is working.
Chromium, Taitenium and Neickel are a good adhesion layers for gold.
I am doing 20nm Ti or 20nm Cr adhesion layer for 150nm of Au.
Please see our published work on improving the direct adhesion of Au to SiO2 without using any additional adhesion layer.
Article Postdeposition UV-Ozone Treatment: An Enabling Technique to ...
Cr as well as Ti will work absolutely fine as an adhesion layer for Au Deposition. We typically use Cr/Au instead of Ti/Au combination in our accelerometers and gyroscopes because of lower stiffness of Cr than Titanium.
Has people mansion here- Cr and Ti can be a good adhesive layers (its depends on your later process also, if you will wet etch SiO2 later in your process flow Ti can be problematic)
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructures
- Thin Films