Interface band alignment in high-k gate stacks

In order to successfully implement alternate high-K dielectric materials into MOS structures, the interface properties of MOS gate stacks must be better understood. Dipoles that may form at the metal/dielectric and dielectric/semiconductor interfaces make the band offsets difficult to predict. We have measured the conduction and valence band densities of states for a variety MOS stacks using \textit{in situ} using inverse photoemission (IPE) and photoemission spectroscopy (PES), respectively. Results obtained from clean and metallized (with Ru or Al) HfO$_{2}$/Si, SiO$_{2}$/Si and mixed silicate films will be presented. IPE indicates a shift of the conduction band minimum (CBM) to higher energy ($i.e$. away from $E_{F})$ with increasing SiO$_{2}$. The effect of metallization on the location of band edges depends upon the metal species. The addition of N to the dielectrics shifts the CBM in a way that is thickness dependent. Possible mechanisms for these observed effects will be discussed.