Definition of hydrogen chloride (HCl)

1. a colorless, pungent, corrosive gas having a suffocating odor. It is heavier than air and fumes strongly in moist air. Hydrogen chloride is very soluble in water and alcohol and less soluble in ether. In semiconductor processing, hydrogen chloride is used in such processes as etching, oxidation, passivation, and epitaxy. It also is used as a plasma and reactive ion etch of silicon and polysilicon, as well as aluminum metallization. [SEMI C3.3-88]