Effect of Composition in Ternary La–Al–O Films on Flat-Band Voltage for Application to Dual High-$k$ Gate Dielectric Technology

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We examined the relationship between the flat-band voltage ($V_{\text{fb}}$) and the $\text{La}/(\text{La}+\text{Al})$ atomic ratio in a La–Al–O ternary oxide film for stacks with and without a SiO2 interfacial layer. A clear dependence of $V_{\text{fb}}$ on $\text{La}/(\text{La}+\text{Al})$ atomic ratio was observed for both stacks. However, the dependence for the stack with the SiO2 layer was particularly large at $\text{La}/(\text{La}+\text{Al})$ atomic ratios below 40%, leading to a large maximum difference in $V_{\text{fb}}$ ($\Delta V_{\text{fb}}$) of 1.2 eV. The results obtained indicate that dipoles with opposite orientations at La–Al–O/SiO2 interfaces contribute substantially to the large $\Delta V_{\text{fb}}$. These findings imply that precise control of Al concentration and the use of an interfacial layer with low permittivity are important in achieving both the threshold voltage ($V_{\text{th}}$) control of p-metal insulator semiconductor field effect transistors (p-MISFETs) and equivalent oxide thickness (EOT) scaling.
2009-05-25