[labnetwork] Oxide growth in Nitrogen

[Robert M. Hamilton]

Savitha,

Back diffusion via your exhaust port may be the issue with 
high wafer oxidation rates in  your atmospheric . tube. It 
should be easy to install an orifice to test this. Assuming 
your N2 flow is ~10-20 slpm during load and remains high 
during anneals you should be able to live with ~ 3 mm 
orifice in the tube's exhaust. It can be a pretty primitive 
test - even aluminum foil.

Bob H.

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 2/13/2013 1:48 AM, Savitha P wrote:
> Hello!
>
>   We have a horizontal furnace, but the exhaust system is not a scavenger
> type. We have individual 1 inch exhaust tubes from each of the furnace,
> connecting to a common exhaust pipe which in turn is connected to a local
> scrubber system. There are 4 tubes in each of the furnace stack and we see
> this problem in all the tubes.
>
> When you say, the thickness is >5nm, could you please let me know what is
> the upper limits that you see and whether you do this experiments on the
> tubes in the stack and is there a trend in the thickness with respect to
> their position in the stack.
>
> Thanks and regards,
>
> Savitha
>
>> Savitha P.,
>>
>> It is difficult to predict the purity of the N2 in your
>> atmospheric process tube without knowing more about the
>> geometry of the tube. Is it a horizontal or vertical furnace?
>>
>> Backstreaming will play a role in the furnace atmosphere.
>> One presumes the tube has an exit opening(s) which ports
>> into a scavenger. Back-diffusion/partial pressure laws will
>> invariably increase O2, CO2 and water vapor partial
>> pressures in the furnace environment.
>>
>> At Berkeley, we reduced O2 contamination by modifying our
>> OEM's furnace tube exit port design. In addition to reducing
>> overall exit orifice area, we increased the number of exit
>> ports and positioned them symmetrically around the
>> circumference for better cross-wafer uniformity.
>>
>> Our go/no go standard for N2 atmospheres in our atmospheric
>> furnaces was >5 nm oxide/1000 C/12 hours.
>>
>> Also, the furnace pre-clean step is important. I'll defer to
>> others on the labnetwork who are more qualified to discuss this.
>>
>> 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 2/11/2013 3:22 AM, Savitha P wrote:
>>> Dear Colleagues:
>>>    We had done a N2 anneal in our atmospheric furnace for 10hrs at 1100
>>> deg
>>> C, substrate was silicon <100>, P-type. The oxide thickness obtained
> was
>>> ~16nm (variation of 15.2 - 17.6nm). For one hr anneal, the thickness
> obtained was ~5nm. It would be really helpful if we could know the
> silicon
>>> dioxide thickness expected for N2 annealing experiments. The percentage of
>>> O2 impurity in our N2 is supposed to be <1.000 ppb according to our
> purifier specs.
>>> Regards,
>>> Savitha
>>
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>>
>