To speed-up etching rate by incorporating an etching soln. contg. hydrogen fluoride and ammonium fluoride with a salt of the other strong acid as well.
Into an aq. soln. contg. hydrogen fluoride and ammonium fluoride, the other salt is moreover incorporated to prepare an etching soln. The other salt to be incorporated is a salt of a strong acid, and the other salt is selected from the groups consisting of the salts of hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, sulfuric acid, hexafluorosilicic acid and tetrafluoroboric acid. More in details, the other salt is selected from one or ≥two kinds selected from the groups consisting of alikali metallic salts of strong acid, ammonium salt of strong acid and quaternary ammonium salt of strong acid. Preferably,the concn. of hydrogen fluoride in the etching soln. is about 0.05 to 10 mol/kg, the concn. of ammonium fluoride is about 0.05 to 11 mol/kg, and the concn. of the other salt is about 0.05 to 5 mol/kg. The etching soln. in used ordinarily at pH≥2, desirably at about ≥3.
SUYAMA MAKOTO
ITANO MITSUSHI
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