Detection of process-dependent changes in Hf (1-x) Si x O 2 /Si(100) - - PowerPoint PPT Presentation

Detection of process-dependent changes in Hf(1-x)SixO2/Si(100) barrier heights by Second Harmonic Generation

Jimmy Price, Yongqiang An, and Michael C. Downer Physics Dept., University of Texas, Austin

Conference on Laser and Electro-Optics May 7th, 2008

ω 2ω

Si substrate

3nm HfSiO 1nm SiO2

Energy (eV) Distance (nm) Silicon SiO2 Hf(1-x)SixO2

1 2 3 4

• 4
• 3
• 2
• 1

Valence band

• ffsets

Conduction band

• ffsets

Multiple barrier heights

We exploit internal photoemission using time dependent SHG to determine barrier heights.

• J. Bloch, et al., PRL, 1996.
• Z. Marka, et al., PRB, 2003.

• Hole trapping initiates at hω = 1.57 eV
• Nonlinear 3rd order process = 4.68 eV
• Valence band offset (VBO) = 3.58 eV

Photon energy dependent threshold for hole injection!

• No transition energy threshold
• bserved for annealed HfO2.
• This indicates that VBO is beyond

spectral range.

A femtosecond, laser-induced, multi-photon absorption approach to determine barrier heights.

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*.

Extending the application with a UV pump to determine the change in barrier heights of HfO2.

*C. J. Yim, et. al., APL, 2007.

HfO2 as- deposited bands HfO2 annealed bands

Understanding how changes in film composition affect barrier heights.

• Plan to extend the application to other novel material systems

(III-V, higher-k, etc.) of interest to nano- & microelectronics.

Summary & looking forward:

• We use non-invasive, time-

dependent SHG to measure barrier heights of Hf(1-x)SixO2/Si film stacks as a function of thermal processing and composition.

• Unlike competing methods

(e.g. XPS, IPE), SHG can be used in-situ while the films are being grown.

HfO2 HfO2 HfOx HfSiO2 As

• d

e posited Annealed