US Patent 7592231 MOS transistor and fabrication thereof

A method of fabricating a MOS transistor is described. A substrate is provided, and then a composite layer for forming a gate structure and a carbon-containing mask material layer are formed thereon in turn, wherein the carbon-containing mask material layer is formed with a carbon-containing precursor gas and a reaction gas. The carbon-containing mask material layer and the composite layer are patterned into a carbon-containing hard mask layer and a gate structure, respectively. A spacer is formed on the sidewalls of the gate structure and the carbon-containing hard mask layer. A passivation layer is formed over the substrate, and then a portion of the passivation layer is removed to expose a portion of the substrate. A doped epitaxial layer is formed on the exposed portion of the substrate.