Conference on Laser and Electro-Optics May 7 th , 2008 Detection of process-dependent changes in Hf (1-x) Si x O 2 /Si(100) barrier heights by Second Harmonic Generation Jimmy Price, Yongqiang An, and Michael C. Downer Physics Dept., University of Texas, Austin Multiple barrier heights 4 3 Conduction 2 band offsets ω Energy (eV) 1 2 ω 0 -1 3nm HfSiO -2 1nm SiO 2 Valence band -3 offsets -4 Si substrate Silicon SiO 2 Hf (1-x) Si x O 2 Distance (nm)
We exploit internal photoemission using time dependent SHG to determine barrier heights. J. Bloch, et al., PRL, 1996. Z. Marka, et al., PRB, 2003.
A femtosecond, laser-induced, multi-photon absorption approach to determine barrier heights. Photon energy dependent threshold for hole injection! • No transition energy threshold • Hole trapping initiates at h ω = 1.57 eV observed for annealed HfO 2 . • Nonlinear 3 rd order process = 4.68 eV • This indicates that VBO is beyond • Valence band offset (VBO) = 3.58 eV spectral range.
Extending the application with a UV pump to determine the change in barrier heights of HfO 2 . As-deposited bands • Decrease in SHG intensity occurs for a pump photon energy of ~ 5.7 eV. • Accounting for a 1.1 eV Si bandgap, hole injection over a VBO = 4.6 eV. • Consistent with XPS reports * . *C. J. Yim, et. al., APL, 2007.
Understanding how changes in film composition affect barrier heights. HfO2 as- deposited bands HfO 2 annealed bands
Summary & looking forward: We use non-invasive, time- • dependent SHG to measure barrier heights of Hf (1-x) Si x O 2 /Si film stacks as a function of thermal processing and composition. HfO 2 HfO 2 HfSiO 2 HfO x Unlike competing methods • Annealed As - d e posited (e.g. XPS, IPE), SHG can be used in-situ while the films are being grown. Plan to extend the application to other novel material systems • (III-V, higher- k , etc.) of interest to nano- & microelectronics.
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