[labnetwork] LPCVD nitride pumps

[Robert M. Hamilton]

Savitha and colleagues,

I find myself in disagreement about the use of foreline 
traps in a reactive lpcvd nitride process. Adding such a 
trap, at a location between the tube and pump, requires 
dealing with a can full of reactive, corrosive and 
pyrophoric waste. Given the quantity of effluent, I suspect 
maintenance would be frequent.

I can share the UC Berkeley NanoLab, and it predecessor the 
Microlab's experience with lpcvd low-stress, silicon-rich, 
lpcvd nitride. To meet the demands of MEMS research, where 
we found our tube running virtually 24/7, we designed an 
lpcvd tube specifically for this low stress-process. We've 
run it for close to a couple of decades now with high 
reliability and excellent pump lifetimes.

The salient features of this tube are:

1) An unheated manifold from the 50 mm process tube rear 
transition to the pump. While the rear transition of the 
process tube is 50mm the manifold is ISO 75mm and about 7 
feet long from tube-to-pump. This large foreline surface 
area, operating at close to room temp, does some trapping of 
the ammonium chloride and DCS residues; however, it never 
restricts within the lifetime of a process tube.

2) The gate valve for this process is an MKS "Jalapeno" 
valve with a heater jacket”, operating at ~200C. We worked 
with Tystar Corp's Henry Heidbreder to design a unique valve 
that allows a small amount of pumping (3-4 slpm) while the 
tube is vented thus eliminating back-streaming from the 
manifold back into the process tube during wafer loading 
(and thus eliminating re-deposition, a.k.a. “particles”). 
One of this compound valves orifice has a self-cleaning 
feature that maintains its 7 mm orifice. In addition, this 
Tystar valves has a slow-pump feature.

2) We use a 200 C heated Baratron to monitor process pressure.

3) The pump package is an Edwards QMB500/QDP80. We use a 
high-throughput pump stack to meet the ~140 mTorr process 
pressure we use in our recipes. A QDP runs at 80 C. A pump 
that ran hotter than the QDP series would likely better 
serve the process. I do not know the Bush Cobra line. It may 
run that hot or hotter. I know Kashiyama has a screw pump 
specifically designed for lpcvd nitride.

4) The effluent of this tubes pump stack exhaust is sent 
through an Edwards model 250 water-cooled abatement trap. It 
has very large surface areas. It gets continuously flooded 
with relatively high amounts of N2 from the pump-purge (35 
slpm) while in standby. It also is connected to the house 
exhaust system so it has contact with some air and moisture. 
We have not found the effluent in this trap pyrophoric (we 
have found it acidic). When we service the trap we isolate 
it and use water to react with the solids before cleaning it.

Pump lifetime for this tube is typically 2000-3000 hours of 
process run-time. For us this is presently about 2 years. 
The major "down-time" issue for this tube is the rear 
transition clogging up and pinching off because of the 
process effluent. We use a tapered reamer to clear this 
vitreous effluent and we can typically do this a few times 
before we break the rear transition. At that time we replace 
the tube and service the pumping system as necessary. I have 
found that attempting to heat this transition to a 
temperature high enough to reduce deposition destroys the 
o-ring seals.

Good luck and if you are ever in Berkeley give us a visit 
and we’ll do show & tell!

Regards,
Bob Hamilton


Bob Hamilton
Marvel NanoLab
University of CA at Berkeley
Rm 520 Sutardja Dai Hall
Berkeley, CA 94720-1754
bob at eecs.berkeley.edu
(e-mail preferred)
510-809-8600
510-325-7557 (mobile - emergencies)

On 4/30/2013 12:01 AM, Savitha P wrote:
> Hi!
>
> We wanted to buy two solutions for mainly making seed layers for plating.
> These are Gold Chloride solution (0.5%) and TRANSENE Nickelex solution.
>  From MSDS, these solutions are shown to bioaccumulate and are toxic to
> aquatic life. Nickelex comes with additional warnings of being
> carcinogenic and mutagenic with special safety requirements and disposal
> protocols.
>
> Could someone please let me know whether these chemicals are used
> routinely in the fabs and if yes, what are the disposal protocols for the
> same. Are there any other chemicals (maybe, less toxic) which can be used
> for the same purpose. We are planning to dedicate one of our general wet
> benches as the electroplating bench for the time being, so chances of
> cross contamination will be low.
>
> Thanks and regards,
>
> Savitha
>
>