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

Abstract

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.