HF dip [HFDIP]
Setup time for this process is about 5 minutes. This process takes about 5 minutes to
complete.
Hydrofluoric acid (HF) is used to remove native silicon dioxide from wafers. Since it
acts quickly, one needs to only expose the wafer fro a short time (“dip”). HF is a
dangerous chemical and protective gear must be worn when using it, in particular,
neoprene or thick nitrile gloves and eye protection must be worn.
A prepared solution should already be available to you. If not, here is how to prepare a
2% solution.
480 ml water
20 ml HF (49%)
Wear heavy protective gloves and protective eye gear. Add 480 ml water to
polyproplene beaker then, add 20 ml HF. Never use a glass beaker with HF since HF
attacks glass. Label the bottle “2% HF solution-Dangerous acid!” then, add your name
and the date.
Soak the wafer for 2 minutes in this solution. Remove the wafer and rinse in running DI
water. Check for hydrophobicity by performing a wetting test. Pour a little DI water on
the surface. If the water beads up and rolls off, the surface is hydrophobic and water will
not wet it. Since oxide is hydrophilic and pure silicon is hydrophobic, a non-wetting
surface is clean of oxides. Blow dry with nitrogen and store in a clean, dry environment.
The 2% solution may be saved for other cleaning. (It does not lose its effectiveness). To
dispose the 2% HF solution, pour into an INRF labeled waste container for 2% HF. Very
small amounts of 2% HF may be disposed by diluting with cold water, then flushing
down the drain with plenty of cold water.
Be sure to wash your neoprene gloves and return to their proper location when finished.