Investigation of wet etching properties and annealing effects of Hf-based high-k materials

Abstract

Wet etching properties of Hf based high- k dielectrics of HfO2, (HfO2) x (Al2 O3) 1-x, Hf oxynitride and Hf silicate were investigated, using various chemicals employed for the current CMOS device fabrication. Experimental results show that fluorides species such as F-, HF2- HF and H2 F2 are very effective for dissolving Hf and HfO2 in acids. HfF4 is highly soluble in HF with a solubility of ∼1.48 molL, which is much higher than the calculated result, and its solubility increases with reduced pH value. Etching properties of those high- k dielectrics in HF and annealing effects on their microstructure were explored. It is observed that the etch rates of Hf and HfO2 increase with increasing HF concentration and after HF etch, Hf and HfO2 surfaces become F terminated. Although the mechanisms responsible for the change in HF etch rates after the Hf based high- k films have undergone annealing are dependent on their chemical property, it is universally observed that the formation of the crystalline phase of HfO2 is the primary attributor to the reduced etch rates. The HF etching of Hf based high- k films occurs via weak points in the films, e.g., Hf-N, Al-O and Si-O bonds, as well as amorphous areas of HfO2. © 2006 The Electrochemical Society. All rights reserved.