[labnetwork] SnO2 via ALD

[Martin, Michael]

Hi Mac,
  Thanks so much for input. The precursor is only a few weeks old but we’ve been all over the place with the bubbler temperature (50 to 100C) and only had about 5g of material to start with. So I’m betting if there’s anything left it’s toast, though we were still seeing some pressure pulses. We do have a glove box and will clean up the bubbler and reload with heated lines.
   Beneq sent a recipe that had the bubbler at 57C and substrate at 97C which we thought was a curious choice but now that makes a little more sense.
    I also received some great info from Alex Kozen of U. of Vermont that is pretty valuable:

“Yes, we do ALD SnO2. Yes, TDMA-Sn decomposes slowly about 60C. We heat our TDMA Sn to 65C when doing depositions then turn the heat off immediately after any depositions are completed. This gives us ~4X lifetime out of the precursor.

HEAT THE DELIVERY LINES! They are likely already clogged if unheated. Temp should ALWAYS increase from precursor source to deposition chamber i.e. 100C (bubbler) -> 125C (manifold)  -> 150C (lines)  -> 200C (chamber).  Beneq’s are a huge pain to repair and clean so if clogged this will likely be a Beneq service visit and thousands of dollars in repair costs + months of delay.”

   He also mentioned that not cleaning out the degraded precursor may catalyze the breakdown of a new batch.

Thanks again for taking the time to help us out!

-Michael

On Feb 6, 2026, at 3:56 PM, Hathaway, Malcolm R <hathaway at cns.fas.harvard.edu> wrote:


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Hi Michael,

So, tin oxide is interesting, in that the TDMASn is, in my estimation, very sensitive and not particularly shelf- or bottle-stable.  How old is your precursor?

I have had this tin precursor precipitate all the tin out while the ampule was still sealed (very light sensitive, as it turns out.  They put a "light sensitive" sticker on the bottle for me the next time...)

It also dies pretty quickly while on the machine, if the cylinder temp is too hot.  I don't have my notes in front of me, but it seems to prefer the lower end of the TDMAx range (50-60C, perhaps).

Do you see pressure pulses when you pulse the precursor?  If not, the precursor is dead (or the valve is blocked/stuck).  Even if you do, the precursor could be decomposed in the bottle.  There will still be liquid present, perhaps sending vapor to the chamber, but the Sn stays back in the bottle.

We have crafted glass precursor cylinders (for non-pyrophorics) specifically to be able to see the state of the precursor in the cylinder, which is pretty helpful in situations like this.

If you have a glove-box, you could do some things to see what's the status of the precursor.  We can walk through those off-line if you have an interest.

Heating of lines:  As I'm sure you know, you generally want the line heated to at least the temperature in the bottle, and sometime a bit higher, to avoid any chance of precursor condensation in the line before it gets to the chamber.  This can happen in a very short distance (a "cold spot") of unheated line.   If this is happening, it will manifest as a lack of pressure pulses in the chamber when the TDMASn valve is pulsed.  It may be that the parts of the line that are heated are close enough to the "unheated" segments that the unheated segments stay warm enough.  If the system is still "stock" I would imagine the line heating should be okay, but worth checking with a temperature gauge.

On the other hand, if some part of the plumbing is too hot, it could lead to thermal decomposition of the precursor before it gets to the chamber.   Our system with valve manifold heated to 150C did not show any issue like this.

It may be worth giving Beneq a call to see if they have specific suggestions.  I don't have one of their tools but they seem to know their way around ALD, so they probably have some suggestions.


Mac
Harvard CNS
617-259-0859



________________________________
From: Martin, Michael <michael.martin at louisville.edu>
Sent: Wednesday, February 4, 2026 4:01 PM
To: Network Fab <labnetwork at mtl.mit.edu>
Cc: Hathaway, Malcolm R <hathaway at cns.fas.harvard.edu>; Naveed, Abdul Basit <abdulbasit.naveed at louisville.edu>
Subject: SnO2 via ALD

Hello everyone,
   We are having a heck of a time depositing SnO2 in our ALD onto bare (with native oxide) silicon at a substrate temperature of 100 to 200C.  This is our first time attempting this material in our Beneq TFS200.  We are using TDMASn + H2O as precursors. We have tried heating the TDMASn anywhere between 50 to 100C, using headspace loading and via the material's vapor pressure.  We have looked at TDMASn pulse times from 200ms to 1.4 seconds with dwell times of 1 to 3 seconds. Water vapor is pulsed at our usual 100ms and a purge of 3 seconds.
  So here's a couple of questions: 1. I have read anecdotally that the material will decompose above 60C. Do you have any experience with this? 2. While the line between our heated bubbler and the reactor is quite short, it is not heated. Do your tools depositing tin oxide require a heated line to the reactor?
   Any advice would be fantastic.

Regards,

   Michael


Engineering Senior Researcher

Micro/Nano Technology Center

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