[mems-talk] Pin Holes on the Al Surface

[Brad Cantos]

Hi Shifeng,

When you say "black stuff," are you viewing it with an optical  
microscope?  If so, you may also want to look at it with an SEM if you  
have one available.  What you describe sounds very much like spitting  
during aluminum deposition with an ebeam evaporator.  This will cause  
relative large spheres of Al to be forcefully ejected from the melt  
and deposited on the wafer surface.  When they adhere to the surface,  
they will block further deposition in that area by shadowing the metal  
vapor.  These spheres do not adhere well and will drop off during  
subsequent process steps leaving a pinhole that often appears black  
optically.  One thing you can do is reduce the evaporation rate,  In  
my experience 5-10Å/sec will eliminate most of this type of spitting.   
There is a paper from IBM back in the 1970's that describe the  
phenomenon and solve it by adding a small amount of another metal  
(maybe Ta or W - I can't remember) to the melt.  I'll try to look up  
the reference for you if you need it.

Brad Cantos
brad.cantos at holage.com
http://holage.com

LinkedIn: http://www.linkedin.com/in/bradcantos

On Apr 1, 2009, at 9:47 AM, li shifeng wrote:

> Hi, I used to ebeam to deposit Al on the glass substrate. I found  
> some black stuffs distributed on the entire Al surface after  
> deposition. Following dry etching transfer these to the glass  
> substrate and make the surface very rough. I do not what are these  
> black stuffs and how to get ride of them. Anyone has the similar  
> experiences and solution.
>
> Thanks!
>
> shifeng