[labnetwork] Diborane stability

Tue Sep 24 17:14:23 EDT 2013

Hello Savitha,

Something additional to check. Diborane has a shelf life, usually a year. If you installed it in 2011, it might be past its expiration date. The expiration date should be on the cylinder vendor's documentation.

Take care,

Tom Britton
Director of Sales
Critical Systems, Inc.
Direct: 208-890-1417
Office: 877-572-5515
www.CriticalSystemsInc.com<http://www.criticalsystemsinc.com/>

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From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Tom Britton
Sent: Tuesday, September 24, 2013 11:04 AM
To: Bob Hamilton; labnetwork at mtl.mit.edu
Cc: treese at criticalsystemsinc.com
Subject: Re: [labnetwork] Diborane stability

Excellent information as usual Bob. We might be able to add on to this to help Savitha.

Hi Savitha,

In looking at your email, two things jump out at us as to what may be causing your issues.

The first is the temperature you're operating at. If you'll reference the attached electronics bulletin from Air Products, you'll see a chart showing the effects of temperature on the decomposition rate of B2H6. In a production environment our staff kept their gas at 4°C. As you rise above this temperature, the number of usable days of the gas decreases. Now when diborane decomposes it forms hydrogen and boron hydrides. These boron hydrides are the contamination that clogs small orifices, shows up as particulate on your end product and causes regulator creep. Chill the bottle to 4°C and insulate the line and you should see an improvement.

The second is the regulator in the gas cabinet. If you are not using a dual stage regulator, you should install one of these in place of the existing regulator. As diborane is so volatile, it has been well documented that the pressure drop in a single stage regulator creates a significant temperature change due to the Joule Thompson effect. By using a dual stage regulator you spread that pressure drop, and subsequent cooling change, over a wider area which reduces the amount of particulate contamination caused condensation at the pressure drop. See the attached paper by APTech on dual stage regulators.

If you need the chiller jackets and controllers, we just got 20 of the Accurate Gas Heater/Chillers in from a large gas cabinet purchase we just made and he have most sizes of cylinder jackets available. The Heater/Chillers are $2,200 and the jackets run $2,000 to $3,000 depending on cylinder size.

Good luck with your process! I hope this helps.

Thank you!

Tom Britton
Director of Sales
Critical Systems, Inc.
Direct: 208-890-1417
Office: 877-572-5515
www.CriticalSystemsInc.com<http://www.criticalsystemsinc.com/>

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-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Bob Hamilton
Sent: Monday, September 23, 2013 12:13 PM
To: labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] Diborane stability

Savitha,

The mix of diborane and Ar will not be as stable as B2H6 in H2 and higher order boranes will form faster. I regret I cannot share experience with such a mix. Voltaix, a manufacturer of hydride gases may be able to offer guidance:

http://www.voltaix.com/

Having said this you may want to look at other possible issues. Mass flow controller have a a heated bypass sensor and this capillary bypass is subject to blockage if diborane is left within the mfc at the termination of a process. For this reason, when we used diborane we used an in and out isolation valve. We'd close the supply and then pump out the mfc so there was virtually no B2H6 in the mfc at idle.

At the UC Berkeley NanoLab we are not currently using diborane as a dopant having obviated it for 1% BCl3/bal He in our LPCVD processes. We may be using it again in our epi process. The carrier gas in that case will be H2.

Regards,

Bob Hamilton

On 9/23/2013 5:21 AM, Savitha P wrote:

> Hi!

>

> We have diborane (2% in Ar carrier gas) connected to our APCVD furnace

> as the source for boron doping. For the past one month we have not

> achieved resistivity changes with any of our standard recipes. Our

> cylinder was installed in 2011 and is kept at ~22-24 deg C.

>

>   I have been reading some of the previous posts about the formation

> of

> B4H10 particles which deposit out. Has anyone noticed this kind of

> phenomena leading to only flushing of the carrier Argon gas. We tried

> rolling of our cylinder for ~1hr (on the advice of our cylinder

> supplier) but had no better results.

>

> Thanks and regards,

>

> Savitha

>

--

Robert Hamilton

University of California at Berkeley

Marvell NanoLab

Equipment Eng. Mgr.

Room 520 Sutardja Dai Hall

Berkeley, CA 94720-1754

bob at eecs.berkeley.edu<mailto:bob at eecs.berkeley.edu>

Phone: 510-809-8600

Mobile: 510-325-7557

e-mail preferred

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