Ab initio modeling of structure and defects at the HfO2/Si interface

Using ab initio density functional calculations we study implications of film growth kinetics on the structure and defects at the HfO2/Si(001) interface region. We introduce a simplified model for the atomic layer deposition with HfCl4 as a metal precursor and H2O as the oxidant. The model suggests that the initial interface growth results in a typically less than 1 monolayer of Hf in the first metallic layer. As a consequence, the oxygen coordination at the interface is either two (one Si and one Hf atom) or three (two Hf and one Si atoms), which partially supports the kinetically motivated interface models but is in contrast with the epitaxially motivated models suggested previously. Further calculations show the oxygen vacancy formation energy at the Si-O-Hf sites is similar to 1 eV lower than that in the bulk HfO2. This makes the Si-Hf bond a likely interface defect, which is predicted to be a shallow hole trap. Calculations also predict interstitial oxygen to migrate from HfO2 into Si substrate resulting in the formation of the SiOx interface layer.