The Fraunhofer Institute (FEP) in Dresden has done a lot of work using
additional plasma to help densify the coating to make it very smooth, matching
the substrate surface roughness.  
 
Another method of smoothing the growth of thick coatings is to use
a disruptive layer periodically. Uninterupted deposition of the aluminium will
allow any nucleated crystals to grow and it is possible that a column will
grow. Depending on the crystal orientation some orientations will grow faster
than others and will increase in size and also become faceted which results in
surface roughness.  By interupting the aluminium growth periodically the
continuous growth can be prevented. Each time the aluminium is stopped and some
other material deposited and the aluminium restarted the aluminium has to
re-nucleate and so the large crystals and  faceted surface can be prevented. 
  
 
Best regards
Charles Bishop
C.A.Bishop Consulting Ltd
www.cabuk1.co.uk
 

________________________________
From: "eyepin@..." <eyepin@...>
To: PVD_coatings@yahoogroups.com
Sent: Thursday, 9 February 2012, 23:49
Subject: [PVD_coatings Forum] aluminum on Au/Ti/Si


 
Hi,

I've been trying to obtain thick smooth aluminum coatings. I've used a KJL AXXIS
system to sputter onto the silicon substrate in this order:
1. 5 nm Ti
2. 10 nm Au
3. 500 nm Al

I've tried with the substrate 20 C and 350 C and both result in rough surfaces
(0.5 - 2.0 um grains).

Any recommendations on how to achieve smooth (and thick) aluminum layers?

Thanks




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