Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Use of hydrofluoric acid

  1. Apr 14, 2015 #1
    Hi all,

    I have a rather specific question regarding the content of a possible job for me in science (postdoc in academia). The job would imply do deal times to times with hydrofluoric acid (HF) in cleanroom, for wet etching of Si in particular.

    My background is more in physics - I have no previous background in such techniques. Of course, I browsed the web and I know that this compound is very nasty and I am aware of the safety procedures.

    Those who have experience could tell me more in the sense, is it reasonable for me to adapt to such technique as my first experience in chemical etching? Did you feel a specific stress linked to this particular step in the processes? Is is really different from other chemicals regarding the feeling/danger of the operator?

    Thanks a lot, it would clarify the way I see this job.

  2. jcsd
  3. Apr 14, 2015 #2


    User Avatar

    Staff: Mentor

    I would definitely advice against starting with HF. Getting some experience with glass/wet chemistry using safe solutions looks much more reasonable.

    Stress thing is individual. I never had problems dealing with more dangerous stuff (not that I ever worked with really nasty chemicals), I knew people who were paralyzed even by mildly concentrated acids .
  4. Apr 18, 2015 #3
    Hmm... I confess I never understood why people are 'scared' of chemicals. That implies 'fearing' something, an irrational emotion that should have nothing to do with scientific work, and may even temporarily impair your judgment and capabilities, IMO.

    Chemicals are just inanimate objects, they can't decide to jump at your throat and kill you (unlike living things). So anything that goes wrong when using chemicals is necessarily caused by their improper/clumsy handling by the operator, which may include not wearing appropriate personal protective equipment, using faulty or inadequate equipment, being inattentive, etc.
    Sure, there are chemicals that are inherently more capable of doing us harm than others. If you spill a large amount of concentrated HF on your body, you're more likely to be harmed than if you spilled the same amount of orange juice. The thing is, when you're handling HF rather than fruit juice, you are supposed to be in a completely different environment, appropriately dressed, to pay close attention to what you're doing and to adopt all the necessary procedures that protect you from harm.

    The other element to consider of course is scale. I have seen people stress/panic because they had to use 10 mg of zinc cyanide in a reaction, which was happening in a sealed tube, under a fume hood, in a chemical lab equipped with all the emergency kits known to man.
    Sorry, but even if by a crazy accident the tube blew up, its whole content flew into your mouth and you swallowed it, chances are you would not experience any serious physical consequences - perhaps more psychological ones.
    On the other hand, the guys who work in a manufacturing plant and operate huge reactors full of cyanide or HF, well, I think they may justifiedly have a slightly higher stress level, because if something went wrong there, they may indeed be severely harmed. That's why the procedures in those cases are much more strict, rigidly regulated and controlled, to make sure that nothing is left to chance, as opposed to the comparatively more 'free' environment of a research lab.

    So, my answer to you kooglof, if you eventually take the job, would be: don't 'fear' using small amounts of hazardous chemicals. If you work rationally, in a properly equipped lab, with all the adequate counter-measures ready at hand, and following all the appropriate procedures, that's really nothing out the ordinary for a science professional.
  5. Apr 21, 2015 #4
    Thanks to both of you.

    From both answers, it seems that is more a psychological question than an actual question. Everything is about the risk management, rather than the risk itself, at least for small amount of chemicals where everything is supposedly human-controlled.

    As I gathered more and more information (which I now stopped doing), I concluded that two categories of people exist: Those who feel nothing when waking up in the morning and who know that they will handle such poisonous chemicals, and those who do not sleep two nights before having to handle the same chemicals. In both cases, the risk is the same, but the real question is how would I live, outside the lab, if I know that every day I could play with HF with no further notice (I implicitely assume that someone in my situation would acquire quickly the skills for safe handling of dangerous chemicals, as science is my profession).
  6. Apr 21, 2015 #5


    User Avatar
    Science Advisor
    Gold Member

    I'm having a hard time deciding which is more hazardous: working with HF or taking an academic postdoc job :nb)

    But seriously, it sounds like you'll be working in a semicon fab cleanroom, and HF (1% aq soln) etching of SiOx is pretty routine there. The amount of protective gear that you wear in a cleanroom should allay your concerns somewhat. Don't be cavalier (it's still HF, after all), but I wouldn't be as concerned about it as if I were working outside a cleanroom with HF.
  7. Apr 21, 2015 #6
    All this time we were talking about a 1% solution ???? :wideeyed:
    That's probably less acidic than a lemonade!

    Only joking, it has to be treated with caution, but frankly, at that concentration you would really have to drink a good amount of it, or bathe in it for a while, before it does anything to you. Please don't think that one drop of this stuff splashing on your skin will instantly kill you! We're much sturdier animals than that!

    Just today they delivered 4 bottles of phosgene (solution in toluene) in my lab. Well, *that* is something you wouldn't want to be around, believe me! :biggrin:
  8. Apr 21, 2015 #7
    Hum, 1% I don't think so. I think it will rather be in the range of 5 to 15%. Dilution starting from approx. 50% has to be done by myself, is it a critical step for a beginner?

    Easy with the phosgene... it is not really my cup of tea o0) !
  9. Apr 21, 2015 #8
    We routinely use HF acid to etch aluminum, it is referred to as a "bright dip" and is usually concentrated at 5%. I'll admit when I first started working with it, I was very leery. It didn't help that people here didn't understand some basic safety concerns with it and were storing used dip in glass containers, etc,. We also use it to etch silicon in what is called a CP4 etch.

    If your going to be dealing with concentrations of 50%, I'd be concerned. That is strong enough to cause serious harm with even a small incidental exposure. I'm sure you'll have proper protection and remedies (calcium gluconate, etc.) in case anything happens.

    PS. The thing I don't like working with most is Chromic acid (or any chromium containing compounds.) Very insidious and exposure won't be evident until your in bad shape.
  10. Apr 22, 2015 #9


    User Avatar
    Science Advisor

    I know an engineer. In the enterprise where he is working a person even fell in a bath with hydrofluoric acid they use to clean steel and he didn't get hurt. Obviously he got optimal first care and was transferred to a hospital.
    Concentrated HF is another beast.
    Chemicals are usually not a safety threat when you are aware of their properties and are carefull yourself.
    Most accidents I know from laboratories happened when people were doing things in a hurry or operated with substances with unknown properties or unexpected behaviour.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook