[labnetwork] Silicon Nitride question

Mon Apr 16 12:47:19 EDT 2012

Chris Balicki,

Re: less than ideal N2 pump purge gas purity/lpcvd nitride 
pumps:

I have found my conversations with Edwards constructive and 
their pump staff well informed. My first suggestion is to 
call Edwards for some guidance on the issue of your N2 
quality, the partial pressures of O2 and its affects on 
their pumps. The iQ series pump have been our stalwarts for 
decades. We continue to have them rebuilt as needed. For the 
nitride process we see lifetimes of three years and better. 
We operate our nitride with iQ's and Edwards QMB blowers.

Appended is an excerpt from the Q-series instruction manual 
which offers insight into the N2 purge circuits. I am 
attaching the pdf to this reply; however, it may not be 
deliverable to the rest of the labnetwork list e-mails 
because of IT security.

4.2 Gas flow rates and pressures
Table 2 (see Section 2) shows the maximum flow rates for the 
shaft-seals purge, 3/4-interstage
purge and 2/3-interstage purge gas flows. During operation, 
you must set the flow rates of the 3/4-interstage purge and 
the 2/3-interstage purge pipelines to the required values. 
These values are dependent on the process in which the
pump is used and you should adjust the flow rates according 
to your experience. If you exceed
the flow rates specified in Table 2, the performance of the 
pump may be reduced.
You must set the pressure of the shaft-seals purge as 
specified in Table 2 and Section 3.11. You
must not attempt to adjust the flow rate of the shaft-seals 
purge (which is determined by the
pumpitself). The nominal flow rate of the shaft-seals purge 
is 12 l.min-1 . If the flow rate is higher
than the nominal value, you may reduce the flow rate of the 
3/4-interstage purge by
[F-12] l.min-1 (where F is the actual shaft-seals flow 
rate). This will reduce the amount of nitrogen
exhausted from the pump.

As you can see, the purge gas on an iQ series pump goes to 
several locations, the gear box to protect the transmission 
and seals, two interstage areas and the exhaust. I would 
guess the interstage will be the area of most concern given 
your O2 partial pressure as this is where most of the 
reaction products are likely to form. Part of the purpose of 
this interstage purge is to prevent a phase change to a 
liquid of the pumped gases, during compression. Given the 
nitride process you may be able to operate by completely 
shutting off the interstage N2 purge (for safety, the 
exhaust gas purge should remain in spec. as this is part of 
dilution).

Call Edwards tech support. They can offer you better guidance.

Note, our lpcvd nitride tubes deliver a variety of nitride 
films and are also used for HTO (high temperature oxide). 
The Pareto numbers for the two tubes, (one restricted to MOS 
and one for MEMS) are, for the last 12 months:
MOS:    86.94% availability
MEMS: 85.50%     "

Prior to H2O our uptimes were in the mid 90%. I expect to 
improve our current numbers with modifications to the way we 
add N2O for the HTO process and the way we manage our N2O 
recipes.

I'd be interested in learning your results. Liquid 
nitrogen/N2 is one of our largest operating costs. We've 
toyed with on-sight N2 generation; however, installation is 
a "big bite" and a plant not without operating costs. So far 
we've passed this up given the purities such on-site 
generation delivers.

Bob Hamilton

Robert M. 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 (Emergencies)
On 4/13/2012 4:47 PM,

Chris Balicki wrote:
> Hello Everyone,
>
> Here at Simon Fraser University, we are also optimizing our SiN LPCVD setup. Certainly, we appreciate the recent responses and recommendations.
>
> The dry pump (Edward iQDP80 in our case) requires significant N2 purge flow. Currently, we supply this N2 via a membrane generator. Since the generator capacity has been taxed, current O2 levels are between 1.5-2.0%. Our pump exhaust is fed to an Edwards TPU via a ~15ft run of unheated SS tubing.
>
> 1. Are O2 levels of 1.5-2.0% harmful to dry pump operation? If so, what N2 purity is recommended?
> 2. What further measures are recommended to minimize pump exhaust buildup due to O2 content and unreacted silanes/byproducts?
>
> Thanks,
>
> Chris
>
> ---
> Christopher Balicki
> Clean Room Technician, EIT
> 4D LABS, Simon Fraser University
> 8888 University Drive
> Burnaby, BC V5A 1S6
> t: 778-782-8026 e: balicki at 4dlabs.ca w: www.4dlabs.ca
>
> ----- Original Message -----
> From: "Richard H. Morrison, Jr."<rmorrison at draper.com>
> To: labnetwork at mtl.mit.edu
> Sent: Wednesday, April 11, 2012 5:08:56 AM
> Subject: [labnetwork] Silicon Nitride question
>
>
>
>
>
> Hi Everyone,
>
>
>
> I am restarting a Silicon Nitride LPCVD process and I have a few questions. The process will use a EBARA dry pump therefore should I use a trap on the vacuum pump inlet to catch any particulate generated?
>
>
>
> Any issue with excess hydrogen from the process going into the dry pump, do I need a burn box on the vacuum pump exhaust?
>
>
>
> 2 nd question has anybody tried to run the LPCVD process on a wafer with a platinum metal pattern on the surface? I was wondering if there maybe some adverse effect because of the catalytic nature of Platinum.
>
>
>
> Thanks
>
> Rick
>
>
>
>
>
> Rick Morrison
>
> Senior Member Technical Staff
>
> Group Leader Microfabrication Operations
>
> Draper Laboratory
>
> 555 Technology Square
>
> Cambridge, MA 02139
>
>
>
> W 617-258-3420
>
> C 508-930-3461
>
>
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