Help in making aluminum mirrors by vacuum coating(2001)
I need some help/suggestions on making aluminum mirrors by vacuum coating.
My problem is: the adhesion is not good enough, the aluminum layer does not survive the tape peeling test.
My running conditions are:
--Pressure: around 10^-5
--temperature: around 30 C
--Al thickness: 500 A
I do have oil backstreaming to the chamber from the diffusion pump since we do not have a cold trap there. So, does any of my friends have any ideas of what the adhesion problem is?
Any input/suggestions/responses are highly appreciated.
Thanks in advance.Charlie Smith
I'm not surprised that you have poor adhesion. To get good adhesion you need to deposit on a very clean surface. One good step would be to add a water-cooled baffle between the pump and the chamber. You can also help if you bombard the substrate with ions both before and during the deposition. Ion bombardment at energies around 1 keV before the deposition will sputter away contaminants; during the deposition, ion bombardment densifies the coating and mixes the interface (ion peening). If your substrate is a conductor, you can use a negative bias to create a glow discharge (you'll need to backfill with argon gas to 3-10 mtorr). An alternative is to use an ion beam, if the geometry permits. The ion beam is needed if your substrate is an insulator.
PVD Consultant - San Diego, California
Thank you very much for your reply. I definitely will need the cold trap there. Thanks for all your advice.
One more thing, if possible: when making aluminum mirror, what would be the thickness of aluminum? I have seen records of 1000 nm of aluminum being used, while I was using 70 nm. A friend told me that 70 nm is too thin. What would you suggest?
Once again, thank you in advance for any more advice.Charlie Smith
This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site