Investigation of Wet Etching Properties and Annealing Effects of Hf-Based High-k Materials

Abstract

Wet etching properties of Hf based high- dielectrics of , , 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 , and are very effective for dissolving Hf and in acids. is highly soluble in with a solubility of , which is much higher than the calculated result, and its solubility increases with reduced pH value. Etching properties of those high- dielectrics in and annealing effects on their microstructure were explored. It is observed that the etch rates of Hf and increase with increasing concentration and after etch, Hf and surfaces become F terminated. Although the mechanisms responsible for the change in etch rates after the Hf based high- films have undergone annealing are dependent on their chemical property, it is universally observed that the formation of the crystalline phase of is the primary attributor to the reduced etch rates. The etching of Hf based high- films occurs via weak points in the films, e.g., , and bonds, as well as amorphous areas of .