[labnetwork] Predicting Solid Etch Products

Tue May 14 13:40:45 EDT 2024

Hi Emma,

This is a very good question, and one that I’ve struggled to answer as well. I’m not an etch expert but by necessity have had to try to answer some of these questions, and this<https://purdue.atlassian.net/wiki/spaces/BNCWiki/pages/6246876/Tutorial+on+Etching#TutorialonEtching-GeneralMaterials-Willitetch%3F> (reproduced below, not sure if it will come through or not) is a very rough starting point I’ve come up with that I think (hope) helps get in the ballpark. Would love to hear from other folks as to how they approach this.

Materials can generally be etched in the RIEs as long as they form volatile byproducts, or products for which the vapor pressure (at the temperature of the etch) is higher than the pressure of the chamber.

Etching is very complicated and this will be massive oversimplification...but generally volatile byproducts can be determined from literature, or as a fallback, the CRC Handbook of Chemistry and Physics Online, (4) Properties of the Elements & Inorganics, Physical Constants of Inorganic Compounds: https://hbcp.chemnetbase.com/faces/documents/04_02/04_02_0001.xhtml. From there, click "Go to Interactive Table", and find products that may be formed (i.e. chloride, fluorides, oxides, depending on the gasses). A compound is deemed volatile if it has a boiling point at a reasonable temperature range for the temperature and pressure of the system. Note that at lower pressures, boiling points decrease, so these are just a good starting point reference.

As a VERY general rule of thumb, anything with a boiling point (tbp) < 185 C will be volatile in the ICP RIEs.

As an example, aluminum chloride is volatile, and aluminum fluoride and aluminum are not.
[cid:image002.png at 01DAA604.1196DAB0]
[cid:image003.png at 01DAA604.1196DAB0]
[cid:image004.png at 01DAA604.1196DAB0]
[cid:image005.png at 01DAA604.1196DAB0]

Neither Copper chloride or copper fluoride is volatile, which is why it is not allowed in any chamber:
[cid:image006.png at 01DAA604.1196DAB0]
[cid:image007.png at 01DAA604.1196DAB0]
[cid:image008.png at 01DAA604.1196DAB0]
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[cid:image010.png at 01DAA604.1196DAB0]
[cid:image011.png at 01DAA604.1196DAB0]

Byproducts of silicon are very volatile:
[cid:image012.png at 01DAA604.1196DAB0]
[cid:image013.png at 01DAA604.1196DAB0]

Many times different fluorides/chlorides of the same material will have drastically different boiling points. It's important to research which will be formed in the plasma. Titanium is a good example of this, with TiCl2  and TiCl3 being non-volatile, and TiCl4 being volatile:
[cid:image014.png at 01DAA604.1196DAB0]
[cid:image015.png at 01DAA604.1196DAB0]
[cid:image016.png at 01DAA604.1196DAB0]

Thanks,
Justin

Justin C. Wirth, PhD
Senior Research Engineer – EBL Processes & Nanofab Process Consultation
Birck Nanotechnology Center | Room 2287A
765.494.8203 | jcwirth at purdue.edu<mailto:jcwirth at purdue.edu>
BNCWiki<https://purdue.atlassian.net/wiki/spaces/BNCWiki> | Purdue iLab<https://purdue.ilabsolutions.com/> | Book time on my calendar<https://outlook.office.com/bookwithme/user/5ad94572a9c04a4e8aa9159479128868@purdue.edu?anonymous&ep=plink>

From: labnetwork <labnetwork-bounces at mtl.mit.edu> On Behalf Of Emma Anquillare
Sent: Friday, May 10, 2024 12:07 PM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Predicting Solid Etch Products

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Dear Lab network,

First time caller here 😊

I am new to plasma etching, and working to institute better process control in our ICP and RIE etchers in an academic shared use facility. We don’t have the capacity to designate a single etcher for each process, so between our three tools, we essentially have a most-restricted, somewhat restricted, and “dirty” tool. To avoid cross contamination and chamber residue buildup, we have a technician manually scrub out the chambers with IPA every week- usually seeing the most solid residue in our ICP that handles Lithium Niobate milling.

My question is- while many products of etch reactions get pumped away as vapors, what about the reactions that do leave solid residues? Is there a systematic way to predict or look up what solids will be left from common (or unusual) reactions, and know how they will react and interact with other solids and gasses present in your chamber? Especially with such frequent manual cleaning, how do you ensure that you don’t inadvertently open the chamber to something acutely toxic, pyrophoric, shock sensitive, etc?

Very curious to learn what steps people take and tools they use (literature? calculations? databases? forums?)  when approaching this problem, and when asked to allow a new material into a tool.

Best,

Emma

_____________________________________________
Emma Anquillare, PhD
Research Scientist
ASRC Nanofabrication Facility
City University of New York

[cid:image001.jpg at 01DAA602.E64AD420]
Catalyzing Change, Celebrating Gains:
A decade of visionary science for the public good.
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