page_title: Hydrofluoric acid
section_title: Etchant, cleaner
hierarchical_section_title: Hydrofluoric acid / Uses / Etchant, cleaner
caption_attribution_description: English: etching tanks used to perform Piranha, Hydrofluoric acid or RCA clean on 6-inch wafer batches at LAAS-CNRS technological facility in Toulouse, France. Français&#160;: Bacs de gravure chimique utilisés pour des nettoyages RCA, à l'acide fluorhydrique ou au mélange piranha sur des lots de wafers de 6 pouces à la centrale de technologie du LAAS-CNRS à Toulouse, France.
context_page_description: Hydrofluoric acid is a solution of hydrogen fluoride in water. Solutions of HF are colourless, acidic and highly corrosive.
  It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepressant medication fluoxetine and the material PTFE. Elemental fluorine is produced from it. It is commonly used to etch glass and silicon wafers.
  When hydrofluoric acid comes into contact with human skin it causes deep burns.
context_section_description: It is used in the semiconductor industry as a major component of Wright Etch and buffered oxide etch, which are used to clean silicon wafers. In a similar manner it is also used to etch glass by treatment with silicon dioxide to form gaseous or water-soluble silicon fluorides. It can also be used to polish and frost glass.
  SiO₂ + 4 HF → SiF₄(g) + 2 H₂O
  SiO₂ + 6 HF → H₂SiF₆ + 2 H₂O
  A 5% to 9% hydrofluoric acid gel is also commonly used to etch all ceramic dental restorations to improve bonding. For similar reasons, dilute hydrofluoric acid is a component of household rust stain remover, in car washes in "wheel cleaner" compounds, in ceramic and fabric rust inhibitors, and in water spot removers. Because of its ability to dissolve iron oxides as well as silica-based contaminants, hydrofluoric acid is used in pre-commissioning boilers that produce high-pressure steam.  Hydrofluoric acid is also useful for dissolving rock samples (usually powdered) prior to analysis. In similar manner, this acid is used in acid macerations to extract organic fossils from silicate rocks.  Fossiliferous rock may be immersed directly into the acid, or a cellulose nitrate film may be applied (dissolved in amyl acetate), which adheres to the organic component and allows the rock to be dissolved around it.
caption: Wet etching tanks
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