An HF Dip stands for a hydrofluoric dip, or a composition of hydrofluoric acid. Hydrofluoric acid is a highly corrosive and dangerous chemical substance that is most commonly used as a product in cleaning wafers and should be handled quickly and under extreme care and caution. It is a colorless solution that is a precursor to most fluorine compounds, including pharmaceutical prescription drugs like the anti-depressant Prozac, and which is capable of dissolving many chemical materials and substances like oxides. It is usually stored in plastic containers due to its high reactivity to glass and more moderate reactivity to most metals.
If accidentally exposed to, or improperly handled during the cleaning of wafers, it can cause severe, immediate, and oftentimes permanent damage to the lungs and corneas of the eyes.