Interface reactions at TiN/HfSiON gate stacks: Dependence on the electrode structure and deposition method

We systematically investigated intrinsic and extrinsic thermal reactions at TiN/HfSiON gate stacks. The formation of an ultrathin TiO2 interlayer was found to be an intrinsic reaction at the metal/insulator interface, but growth of SiO2 underlayers between HfSiON and Si substrates, which determines the electrical thickness of metal-oxide-semiconductor (MOS) devices, depends on the structure and deposition method of the gate electrodes. Physical vapor deposition (PVD) grown TiN electrodes covered with W overlayers exhibited excellent thermal stability at up to 1000 1C. Formation of ultrathin TiO2 interlayers reduced gate leakage current (Ig), and growth of the oxide underlayer was suppressed by less than a few angstroms even for 1000 1C annealing. In contrast, we found that halogen impurities within CVD-grown metal electrodes enhance interface SiO2 growth, resulting in deterioration of equivalent oxide thickness (EOT) versus Ig characteristics of the gate stacks.