[labnetwork] LPCVD film anomaly

Wed Aug 4 10:11:57 EDT 2021

The soft pump, (sometimes called the half gate) should be non interlocked and allow you to open while you are pulling the load. We did custom tools with a slow pump valve with standard 1/2 inch nupro, a medium pump with a NW25 gate, and a main vacuum valve with ISO 80 valve, gave more options in the pump down and backfill.
The ammonium chloride will build up on Nitride, so blanket heaters are always important.
The N2 backfill should be able to flow while the process door is open, but make sure the flow it attached to the load area either through a connection to the front flange, or through an rear connected injector.
We had built some CVD polysilicon configurations with a blanket or curtain purge in the scavenger box so the wafers would pass through N2.

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________________________________
From: labnetwork <labnetwork-bounces at mtl.mit.edu> on behalf of Mary Tang <mtang at stanford.edu>
Sent: 03 August 2021 17:03
To: Tony Whipple <whipp003 at umn.edu>; Terre Briggs <terreb at umich.edu>
Cc: Labnetwork <labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] LPCVD film anomaly

Thanks Tony!

Yes, I was trying to remember what Ted Berg, our furnace guy at the time, did about the "champagne nitride".  I don't recall the plumbing solution exactly, but he took a cue from Berkeley and found a way to ensure a constant, low draw during unload.

Mary

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Mary X. Tang, Ph.D.
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Stanford Nanofabrication Facility
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mtang at stanford.edu<mailto:mtang at stanford.edu>

On 8/3/2021 2:29 PM, Tony Whipple wrote:
Hello Terre;
I thought I saw this type of image before and we had a similar problem with our LSN process, see image below.
It turned out that with our setup we were having a reaction with residual that would react when we vented the tube.  This
reaction would cause particles to fall ( rain ) on the wafers when the tube was vented and being unloaded. We had talked
with Bob Hamilton at Berekley while visiting there and noticed his LPCVD setup and his solution before we noticed the
same problem with our LPCVD.    After installing the fix we did not have this issue anymore.

The solution is to provide a very limited small low flowing path around the gate valve so that when the gate valve is closed
( such as during tube vent ) the tube still has a small draw on it pulling any reactions toward the pump and away from the
wafers.  If you have this type of bypass already, the only thing would be to confirm that it is still working I guess. We had a
pressure gauge installed next to this to confirm that it was working and not plugged.  We would see a pressure change
that indicated it needed cleaning soon.

Regards, Tony W.

[image.png]

On Tue, Aug 3, 2021 at 11:20 AM Terre Briggs <terreb at umich.edu<mailto:terreb at umich.edu>> wrote:
Hello All,
    We are currently having film quality issues with our LPCVD Low Stress Nitride, HTO and Nitride films. Without getting into all of the details just yet I am sharing with you some SEM images. The anomaly, as our furnace manufacturer describes it, are what look like spheres, or bubbles on the surface of the films. We are pretty confident that the spheres are only on the surface and not down into the film itself.
It is very random across the wafers and across the wafer load. After further processing, the spheres come off and leave behind a divot, or crater on the surface. This can also be seen in the SEM images.
   My question is, has anyone ever seen anything like this with any of your LPCVD films? I have been working with Tempress for the last several months to resolve the issue, but they have never seen anything like this, and so far we have not made any progress in determining the source. Any help would be appreciated.

Thanks.....Terre

Terre Briggs
Engineer in Research Sr.
Lurie Nanofabrication Laboratory
University of Michigan
1301 Beal Ave.
Ann Arbor, MI 48109
734-320-4470

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Expert Semiconductor Technology, Inc.

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