Wet Etch Characteristics of Hafnium Silicate Layers

To facilitate selective removal of the gate dielectric towards the gate electrode, wet etch characteristics of HfSiOx and HfSiOx(N) in acidified HF solutions were determined as function of several process parameters. Etch behavior of Hf- silicates was found to be little influenced by the various CVD deposition processes. The top part (0-2 nm) of thick Hf- silicate layers etched similar to as-deposited thin layers (< 2nm) while the bulk part was etching significantly slower. However, etch rates were strongly dependent on composition (lower for Hf-rich silicates). Also, the removal rate of HfSiOx (N) was mainly depending on the amount of incorporated nitrogen and crystallization temperature. Thermally nitrided layers were easier to remove compared to plasma nitrided layers. Post nitridation anneals at high temperature in nitrogen environment decreased the etch rate. After removal, Hf concentrations below 1e11 at/cm2 for most of the HfSiOx(N) layers under study were observed after a short (typically a few seconds) etch process in a single wafer spin cleaning tool.