|~2% technical grade HF from Price Chopper|
I have a pair of Norfoil (Silver Shield) gloves around that I use for this kind of work. They're rather stiff so a common practice to improve dexterity is to double-glove with an XL nitrile glove over the Norfoil. When combined with a lab coat, splash goggles, and a face shield there's little chance of anything getting through. (EDIT: A fume hood is significantly safer; at the time of this post I didn't have one so I just tried to work with the smallest volume possible. I do now and wouldn't repeat the experiment outside it.)
|Nitrile outer glove (blue) over Norfoil glove (silver), tucked into sleeve of Tyvek lab coat (white)|
|My standard lab PPE|
Before getting dressed I placed a 10 ml beaker of distilled water on my hot plate and preheated it to a warm but not boiling temperature (exact temp isn't critical).
The next step is to pour a bit under 1 ml of the HF solution into a plastic test tube. HF will eat glass so using glass labware with it isn't a good idea!
|HF solution in the test tube|
|Sample etching in the water bath|
When the time is up, remove the tube from the heat and suction the HF with a pipette. The acid can usually be re-used for many etches, though it does get weaker over time. Drop the die into a beaker of acetone to remove any acid residue.
Remove the sample from the acetone using solvent-resistant plastic tweezers. (Many common plastics, such as polycarbonate, will dissolve into the acetone and contaminate your sample. Metal tweezers have a nasty habit of chipping edges of dies.)
Rapidly blow-dry the sample, holding it down with tweezers so it doesn't go flying. I used a can of R-134 duster spray. (If you let the solvent evaporate slowly large crystals can form from dissolved materials.)
|Drying the sample|
The other main delayering method I plan to explore is CMP with colloidal silica. At the moment MTI is sold out, but when a new shipment arrives expect a post on CMP!