[labnetwork] Heating of BCl3 lines

[Robert M. HAMILTON]

Nava Ariel,

I recommend you do not heat (heat-trace) a BCl3 delivery line. Liquid BCL3
will then condense at any location along that line that is cooled and will
pool as a liquid. I say this with decades of experience delivering BCl3 as
an etch gas and as a dopant. There are several simple ways to deliver BCl3;
the easiest being a low pressure or sub atmospheric pressure regulator.

The vapor pressure of BCl3 at room temp is ~ 19.4 psia or about 4.7 psi
gauge. Use a regulator to reduce this pressure by ~ 50% of cylinder
pressure, for the delivery you are assured BCl3 will remain a gas everwhere
along the delivery line and within the tool. This pressure is also low
enough to preclude adiabetic expansion with an associated phase change
across the orifice of a gas flow controller or mass flow controller. We
have been able to deliver several hundred sccm's, to multiple etchers using
this delivery scheme. Note, our typical BCL3 cylinder is a 15 lb supply
kept in a ventilated gas cabinet. Air movement in the cabinet adds enough
heat to keep the cylinder temperature relatively constant given our
delivery rates (we the same scheme for SiCl4).

The only cylinder gas issues I've seen in a research lab delivering a gas
where the addition of heat was considered was at high NH3 flow rates. The
cylinder temperature dramatically dropped at high flows thus reducing the
available pressure and starving the line. Nitrous oxide is touted to have
similar issues; however, our use rates are too small to be an issue.

There's a caveat, however. We do not use outdoor storage our online
cylinders and we live along a coast with moderated temperatures. A cold
winter day might obviate the above approach.

Regards,
Bob Hamilton




Robert Hamilton
University of CA, Berkeley
Marvell NanoLab Equipment Manager
Rm 520 Sutardja Dai Hall, MC 1754
Berkeley, CA 94720
Phone 510-809-8618 (desk - preferred)
Mobile 510-325-7557 (my personal mobile)
E-mail preferred: bob at eecs.berkeley.edu
http://nanolab.berkeley.edu/



On Tue, Aug 23, 2016 at 5:51 AM, Nava Ariel Sternberg <na2661 at columbia.edu>
wrote:

> Dear all,
>
> We have recently purchased a new Oxford Plasma Pro System100 Cobra RIE
> that we intend to use with Cl chemistry (III-V etc.). Oxford recommended
> heating the gas lines of BCl3. Does anyone have experience with it? We are
> low on $$$ right now. How necessary that is? What is the best way to do
> this?
>
> Any thought would be appreciated.
>
> Thanks!
>
> Nava
>
> Nava Ariel-Sternberg, Ph.D.
> Director of CNI Facilities
> Columbia University
> 530 W120th Street, NY 10027
> Room 1015/MC 8903
> Office: 212-854-9927
> Cell: 201-562-7600
>
>
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