[labnetwork] Mask of Al in HF

[Gheorghe Iordache]

Hi Joe,
Masking to protect the Al contact pads from HF is tricky.
Not sure if you can change the structure but, if the sacrificial layer to free the devices would be silicon, you may consider the improved TMAH solution proposed in this paper: https://www.sciencedirect.com/science/article/pii/S092442470000546X?via%3Dihub
I used it to make sensors on suspended membranes with Al pads exposed some 20 years ago... :) and it works nicely. It's a bit time consuming to prepare... (https://www.researchgate.net/publication/237115771_Low-power_micro-scale_CMOS-compatible_silicon_sensor_on_a_suspended_membrane)
I hope it helps.

Kind regards,
=======================
Gheorghe IORDACHE, PhD Physics, MBA
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KAUST
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From: labnetwork [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Maduzia, Joseph Walter
Sent: 26 October 2021 23:49
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Mask of Al in HF

Hello,

Does anyone have any suggestions for mask materials to protect Al in HF 49% for SiO2 removal in SOI wafer? The device is SOI, ICP DRIE etched to glass, HF etch to undercut and free devices, but have Al contact pads and AL is dep'd first. Typically we use PR as pattern mask, but the Al is etching behind the PR. In this case the Al is deposited first, so although order of operations change might help, it's not a good option atm.

Thank you for any suggestions you might have!
JOE MADUZIA
MNMS Laboratory Specialist

The Grainger College of Engineering
Mechanical Science and Engineering

2239 Sidney Lu Mechanical Engineering Bldg
1206 W. Green
Urbana, IL 61801
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