Wet Etch Recipes

Wet chemical etching is most often either reaction speed limited (your acid & your material) or diffusion limited (mostly stirring, sometimes sample feature size if it's really small). The important note is that it is not as simple as dumping everything together and tossing your sample in the acid. It can come out not uniform or sometimes really rough

For some specific recipes, pay attention to the order of adding each acid!

If you don’t see a recipe for a material you are interested in etching, or you want to do something specific, it may be worth checking

Tips:

• Use dipper baskets for easier control of the etching time, and rinse samples quickly after taking them out of the acid bath! 

• Use a combination of water rinse beakers. When you remove a sample from acid etchant, do a two-step rinse. The first beaker removes most of the concentrated etchant and the second beaker removes the last of the now-diluted etchant.

• Acids/Oxidizers have standard "initial concentrations", and are not noted repeatedly in the recipe table unless specified.
  If you find other recipes from the literature, be sure to check the concentration they used.

  • Citric acid (C₆H₈O₇): anhydrous citric acid. We buy our own. This comes in small crystals so you need to mass out what you need to use.

  • H₂O₂: Hydrogen Peroxide, 35%. Supplied by MRC.

  • HCl: Hydrochloric Acid, 37%. Supplied by MRC.

  • HF: Hydrofluoric Acid, 49%. Supplied by MRC.

  • H₃PO₄: Phosphoric Acid, 85%. Used to be supplied by MRC, but we buy our own now.

• Scale recipes accordingly if you need a larger volume bath

• If the hydrogen peroxide is expired (check the label before using!) do not use it. Instead, put a waste label on the bottle, label it as “Hydrogen Peroxide, Expired - 100%” and put it next to the acid cabinet in the waste area. Get a new, unexpired bottle from the cabinet near the tube furnaces. Bad peroxide = bad etch (typically rough, uneven, and unpredictable).