Etching of Zirconium Oxide, Hafnium Oxide, and Hafnium Silicates in Dilute Hydrofluoric Acid Solutions

Oxides and silicates of zirconium and hafnium are actively being considered and tested to replace SiO₂ as the gate material. Though these materials have the high-dielectric constant (k ∼ 20–25) needed to provide a larger equivalent oxide thickness, they are very refractory and difficult to etch by wet and dry methods. In this paper, work done on wet etching of ZrO₂, HfO₂, and HfSi_xO_y in dilute hydrofluoric acid (HF) solutions is presented and discussed. Experiments were done on various high-k films deposited by metalorganic chemical vapor deposition. It was found that the as-deposited high-k films can be dissolved with a good selectivity over SiO₂ in dilute HF solutions, but heat-treated high-k films are difficult to etch with good selectivity over SiO₂ under the same conditions.