Strain Dependence of Dielectric Properties and Reliability of High-k Thin Films

The effect of strain on both electronic and structural characteristics of HfO₂ used for sub-50-nm semiconductor devices was analyzed by a quantum chemical molecular dynamics analysis. The band structure of HfO₂ is strongly affected by strain in the film. Based on the change rate of band gap obtained from our simulations, the strain sensitivity of the relative permittivity of HfO₂ film is predicted to about 2.4%/1%-strain. The predicted strain sensitivity was validated quantitatively by measuring the change of the capacitance of MOS capacitors using a HfO₂ gate dielectric film. It is very important, therefore, to minimize the mechanical strain in the dielectric film to assure the reliability of MOS transistor.