Electronic properties of the Zr-ZrO ₂-SiO ₂-Si (100) gate stack structure

The interface electronic structure of a layered Zr-ZrO ₂-SiO ₂-Si (100) system was studied with x-ray (hv=1254 eV) and ultraviolet (hv=21.2 eV) photoemission spectroscopies. In situ growth and characterization allow the structures to be deposited and studied in a stepwise manner without the risk of contamination. This study discusses the electronic properties including electron affinities and work functions, valence band maxima, band bending in the Si, and internal fields in a layered high- κ gate stack. With this information the band alignments can be reconstructed and compared to predictions of the vacuum alignment models (i.e., the Schottky-Mott model for metal-semiconductor interfaces or the electron affinity model for heterojunctions) and the interface induced gap states model. The vacuum alignment models are first order approaches to determine the electronic barrier height for a heterojunction, and interface bonding can contribute to charge transfer across the interface, affecting the dipole contribution and altering the barrier heights. In this study, the band offsets and vacuum levels are independently measured, thereby determining the deviation from the vacuum level alignment models. The valence band offsets at the Si-Si O ₂, Si O ₂ -Zr O ₂, and Zr O ₂ -Zr are found to be 4.4±0.1, 0.67±0.24, and 4.9±0.44 eV, respectively. For these same interfaces the deviations from the electron affinity or Schottky-Mott model are determined to be 0.2±0.14, -1.43±0.29, and 1.3±0.39 eV, respectively.