Abstract
As the conventional hydrogen-termination method has a limited ability to improve the interface quality between SiO2 and its Si substrate, an alternative termination method to reduce the influence of interface states is necessary. Interface engineering using first-principles calculations to suppress the influence of interface states is proposed based on the findings that silicon with dangling bonds is their primary origin. First-principles calculations indicate that the interface states can be terminated with oxygen when incorporated into the SiO2/Si interface without additional oxidation, which generates other interface states from an appropriate oxygen-anneal process. It is experimentally shown that such an oxygen termination can be realized in slow and low-temperature annealing, and the oxygen-termination method is a promising alternative for hydrogen termination. The stronger Si–O bond introduced from the oxygen termination compared with the Si–H bonds from hydrogen termination ensures a better interface quality. As one oxygen atom terminates two silicon atoms, the oxygen-termination method can efficiently suppress the number of interface defects compared with hydrogen and fluorine termination. The mobility degradation due to the interface states was improved more from oxygen termination than from hydrogen termination because the strength of Coulomb scattering due to Si–O dipoles is reduced from the heavier oxygen mass. Theoretical predictions were verified using experiments, indicating that the oxygen-termination method under appropriately optimized annealing conditions (speed and temperature) is a promising candidate to improve the interface quality by reducing the influence of interface states.
Highlights
Aggressive device scaling of metal-oxide-semiconductor fieldeffect transistors (MOSFETs) requires highly scaled gate oxides, such as ultrathin gate oxides,[1] oxynitride films,[2] or high-k gate films.[3]
As the interface states are negatively charged under strong inversion conditions of MOSFETs (Fig. 2), they form a dipole and become the origin of dipole scattering
Samples were prepared on silicon wafers to evaluate the density of Pb centers under various annealing conditions and is explained as follows:[21] The experiments allowed measuring the number of Pb centers using the electron spin resonance (ESR) method[47] because it enables the detection of Pb centers
Summary
Aggressive device scaling of metal-oxide-semiconductor fieldeffect transistors (MOSFETs) requires highly scaled gate oxides, such as ultrathin gate oxides,[1] oxynitride films,[2] or high-k gate films.[3]. The interface states significantly impact key MOSFET parameters, such as the threshold voltage (Vth), linear (Idlin) and saturation (Idsat) drain currents, and transconductance (gm).[4] The generation of interface states leads scitation.org/journal/adv to unexpected flat-band voltage (Vfb) shifts and mobility degradation due to Coulomb scattering associated with the interface states. The random dopant fluctuation increases as the scaled-down device size enhances the random telegraph noise (RTN) and Vth-fluctuations as caused by the interface states because of the increased leakage current from the shallow Vth distribution associated with the random dopant distribution. Such fluctuations in RTN and Vth are enhanced more in the corner region of FinFETs because of the electric field crowding effect. A careful control of the passivation–repassivation process to improve the interface quality, such as the fin sidewall, has become an increasingly important issue for large scale integration (LSI)-process technologies
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