[labnetwork] considerations for hot phosphoric acid etches

[Demis D. John]

We have users do this safely in beakers.

Perfectly fine for small pieces (and smaller quantities of chemical).

Certainly not that pleasant for full wafers though - once or twice with 4”
wafers is fine, but very few decide to do this 10 times without a better
setup.

-- Demis (contact info <https://wiki.nanotech.ucsb.edu/wiki/Demis_D._John>)
*Reminder*: The NanoFab has a publications policy
<https://wiki.nanotech.ucsb.edu/wiki/Frequently_Asked_Questions#Publications_acknowledging_the_Nanofab>


On Mon, Apr 20, 2026 at 18:55 Nathanael Sieb <sieb at 4dlabs.ca> wrote:

> Hi Lorenzo,
>
> Thanks for your detailed feedback and this was along the lines of my
> expectations.  Have you or anyone else seen any self-contained table-top
> baths that would fit on top of a wet-bench deck?  Most of what I've seen is
> deck-mount in a wet bench or a heater-chiller designed to heat or cool a
> bath but not contain chemicals.
>
> Does anyone do this safely without using an acid bath permanently built
> into a wet bench?  I'm guessing the answer is mainly no, but I figured I'd
> check.
>
> Thanks,
>
> Nathanael
>
>
> On 2026-04-19 9:35 a.m., Lorenzo Palmiano wrote:
>
> Here are some tips,  OSHA and SDS also breaks down all the safety
> pre-cautions is 5 parts: engineering, handling, storage, PPE and emergency
> response.
>
> At ~160 °C, phosphoric acid is highly viscous and near boiling. Risks
> include increased splashing and bumping, higher aerosol or acid mist
> generation, and severe combined thermal and chemical burns from any contact.
>
> 1. Equipment and Temperature Control
> • Use only a temperature‑controlled acid bath or certified wet etch bench
> • Do not use open beakers on generic hot plates
> • Verify bath temperature with an independent thermometer or probe
> • Avoid overshoot above setpoint; local overheating increases instability
> • Never leave heating unattended
>
> 2. Water Exclusion (Zero Tolerance)
> • Absolutely no DI water near the bath while hot
> • No wet wafers, tools, or condensation introduction
> • Do not add water to hot acid under any circumstances
> • Any water contact at this temperature can cause violent splattering
>
> 3. Required PPE at ≥160 °C
> • Chemical splash goggles AND full face shield (both required)
> • Acid‑resistant apron (front facing out)
> • Long acid‑resistant gloves with arm shields
> • Standard safety glasses alone are not sufficient
> • Do not use stained, wet, cracked, or poorly fitting PPE
>
> 4. Positioning and Handling Discipline
> • Never lean over the bath
> • Approach from the side, not directly from the front
> • Move slowly to avoid wave‑induced splashing
> • Treat all clear liquids as hot acid — never assume it is water
>
> 5. Ventilation and Airflow
> • Operate only with confirmed functioning exhaust
> • If airflow or power is lost, stop work immediately and leave the area
> • Hot phosphoric acid fumes and mist present inhalation hazards
>
> 6. Emergency Readiness (Before Starting)
> • Know the exact location of the eyewash and safety shower
> • Be prepared to cut heater power immediately if needed
> • In case of skin or eye exposure, flush with water for at least 15
> minutes and seek medical attention
>
> Bottom Line
> At ~160 °C, hot phosphoric acid must be treated as near‑boiling corrosive
> material. Strict temperature control, zero water exposure, full PPE, proper
> ventilation, and disciplined handling are mandatory.
>
> Please follow these precautions without exception.
>
> Lorenzo P
> 415.404.0565
> www.espie-electronic.com
>
> On Apr 19, 2026, at 7:23 AM, Nathanael Sieb <sieb at 4dlabs.ca>
> <sieb at 4dlabs.ca> wrote:
>
> hot phosphoric acid etching in your facilities, I would appreciate any
> safety or operational tips you have.  For us it would need to be a
> hot-plate process, and I want to make sure we are taking a cautious
> approach before allowing heating of phosphoric up to 160°C.
>
> * Nathanael Sieb *
> Director of Operations and Administration  |  4D LABS
> <http://www.4dlabs.ca/>
> Simon Fraser University
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