[labnetwork] considerations for hot phosphoric acid etches

Tue Apr 21 02:37:00 EDT 2026

Hi Nathanael,

I had a similar situation in which I couldn't use our hot phos station for
initial fear of cross contamination, so I set up a hotplate process at our
general wet bench.

First you need a quartz beaker since pyrex will be damaged over time (even
after one use). I used a 1L beaker. Unfortunately they aren't cheap.

I put the beaker in a metal pan (dry) as containment in case of spillage or
worst case a crack in the beaker. I found at 350C the hot phos in the
beaker, through the metal pan, would reach a stable 160C (but you'll have
to determine your own hot plate settings). I covered the beaker with a
teflon dish. The spout or beak of the beaker allows vapour to escape. It is
also perfect to put a thermometer in (good to over 160C of course) to
monitor the temperature. The spout also allows you to occasionally squirt
small quantities of DI in to maintain concentration. Don't go nuts since
you're technically breaking the AAA rule.

The die should be placed in a teflon basket for controlled submersion since
they will tend to float. Also when the etch is complete it makes it easier
to remove the die to be washed with DI. Turn the hotplate off and let the
beaker cool so you can aspirate or otherwise safely dispose of the
phosphoric acid.

It's not the most repeatable setup, but it worked nicely if you don't have
a proper heated phosphoric acid bath with DI dripper and N2 bubbler. Of
course, you should wear full PPE during the process.

-Chris
-- 
Quantum Fabrication Engineer - R&D4
Quantum Nanoelectronics Laboratory
University of California, Berkeley
125 LeConte Hall
Berkeley, CA.
Email: craum at berkeley.edu

On Mon, Apr 20, 2026 at 6:59 PM 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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