[labnetwork] Anneal temp for aluminum on silicon with forming gas

[John Shott]

Julia:

Fouad is correct that things like epitaxial reactors and MOCVD equipment 
run pure hydrogen at high temperatures.  They also have careful pre- and 
post-run purging to remove residual air before hydrogen is introduced 
and typically also have some form of hydrogen burning/scrubbing at the 
exhaust end.  In short, epi reactors and MOCVD systems go to great 
lengths to make sure that oxygen and hydrogen NEVER mix at high 
temperatures.  I certainly wouldn't want to be in the room if you tried 
to run pure hydrogen at 800 C in a typical horizontal annealing 
furnace.  I suspect that Fouad would agree that this would be a very bad 
idea.  Long ago, when running an oxidation furnace with a hydrogen torch 
to generate steam, I learned why you want to make sure that the ratio of 
hydrogen to oxygen is safely less than 2.0: I turned a cassette of 
wafers into fine glitter all over the laboratory floor.

But, back to the issue of forming gas anneals:

For a comparatively open forming gas anneal setup, I believe that your 
numbers of 5% forming gas at 400 C or slightly higher are right in the 
proper ball park.  I'll be surprised if others aren't very close to this 
range in their own usage.

We at Stanford run 4% forming gas and the great majority of our lab 
members likely do their annealing at either 400 or 450 C typically for 
about 30 minutes.  The furnace used for this typically idles close to 
400 C so there isn't  too much of a ramp up/down even if the actual 
anneal will be at 450 C.

At 450 you probably get slightly better annealing of interface traps 
than you would at 400 C ... but you can also see more in the way of 
hillock formation if you have aluminum or aluminum-alloy metalization on 
your wafers.

Good luck,

John


On 11/13/2012 2:07 PM, Fouad Karouta wrote:
>
> Hi Julia,
>
> Pure H2 is commonly used in epitaxy reactors at temperature well above 
> 600°C. MOCVD of GaAs/AlGaAs is performed at T=600-800C.
>
> In the past I did liquid phase epitaxy of GaAs/AlGaAs around 800C in 
> pure H2.
>
> Moreover Flammability of H2 in air is between 4 to 80%. So in inert 
> gas like N2 the flammability are different.
>
> Hope this would help.
>
> Fouad Karouta
>

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