HF

One of the most dastardly things that I’ve encountered after switching to an experimental group in my PhD, is this stupid chemical called hydrofluoric acid (HF). A little background: during semiconductor processing, you encounter process where you want to deposit oxide on top of your sample, and then remove them in a certain pattern. Or, when you leave your sample for a while, there will be chance that a thin layer of oxide naturally forming on top of your sample, several nanometers thick. Before you do any further processing you want to etch away this thin layer of oxide. This is where HF comes into play.

*Shudders*

It is capable of etching away silicon dioxide, which is also why it is infamous for being capable of etching away any glass containers. And does it pose any kind of health hazard to humans? Well..

Oh God..

The blue diamond on the left indicates the health hazard, with the highest being 4. So it’s 4 out of 4. A little excerpt from wiki:

Hydrogen fluoride gas is an acute poison that may immediately and permanently damage lungs and the corneas of the eyes. Aqueous hydrofluoric acid is a contact-poison with the potential for deep, initially painless burns and ensuing tissue death. By interfering with body calcium metabolism, the concentrated acid may also cause systemic toxicity and eventual cardiac arrest and fatality, after contact with as little as 160 cm2 (25 square inches) of skin

So some points:

  • It looks just like water
  • If you get exposed by it, initially you won’t notice anything
  • After a while, you will feel some burning sensation on your skin, and the bone near your exposed part might start to deform
  • Not satisfied with horribly disfiguring the exposed area, it actually enters your system to mess with your magnesium and calcium composition, and end up in lethality

When I took the nanofabrication clean room training, the person in charge just had to warn us repeatedly about this particular chemical. He even add some personal experience where his friend, even with all the personal protective equipment, suffers one finger due to a tiny hole in his glove. That’s the problem: you won’t even notice that you’re exposed until a while, because you have no idea whether it’s water, perspiration, or something else. A quick google search for hydrofluoric acid will show all kinds of horrible images related to HF spill.

Whenever I need to load silicon sample to the MBE, I had to dip my wafers in HF while wearing additional gloves, face shield, and apron. And all the while when pouring the thing, I keep repeating in my mind “God please don’t let it spill, God please don’t let it spill”.  Urgh.

Moral of the story: make sure you have calcium gluconate gel around you when using HF, and a quick access to 911. And say basmalah before starting. Oh and your life is more important than your experiment.

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