Kinetic study on the wet etching of La₂O₃ in acidic solutions

The etching of La₂O₃, Al₂O₃, HfSiON, SiO₂ and photoresist films in various concentrations of HCl and H₂SO₄ solutions was studied. The wet etch selectivity of La₂O₃ to other thin films was very high. The etch rate of La₂O₃ is strongly related to the H concentration in the both HCl and H₂SO₄ solutions. Further, the etching mechanism of La₂O₃ in HCl was investigated. The studys two major new findings are: i) etching of La₂O₃ thin films occurs in H₂O containing LaCl₃ without addition of HCl, which may result from the production of HCl in solution, and ii) addition of La(OH)₃ in HCl suppresses the etch rate of La₂O ₃. Based on these experimental results, an etching reaction of La₂O₃ in HCl is proposed.