Scanning tunneling microscopy study of nitrogen incorporated HfO2

The impact of nitrogen incorporation on the physical and electrical characteristics of the HfO2 is examined. X-ray photoelectron spectroscopy shows that nitrogen can be incorporated into the HfO2 via a two-step thermal anneal--first in ultrahigh vacuum (UHV) and subsequently in N2. Following the N2 anneal, scanning tunneling microscopy in UHV reveals a marked reduction in the low-voltage leakage current under gate injection biasing. From band theory and existing first-principles simulation results, one may consistently attribute this improvement to the passivation of oxygen vacancies in the HfO2 by nitrogen. Improvement in the breakdown strength of the HfO2 subjected to ramp-voltage stress (substrate injection) is also observed after the N2 anneal. The local current-voltage curves acquired concurrently during the ramp-voltage stress exhibit 'space-charge limited conduction', which implies that the observed improvement in breakdown strength may be related to a limitation of the current flow through the gate stack in the high stress voltage regime