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Interface Engineering for High-k Dielectrics

To improve the performance of conventional MOSFET devices, it was proposed to replace the conventional SiO2 gate dielectric with a thicker dielectric with a higher dielectric constant, such as HfO2 or ZrO2. However, two main issues were met while integrating the new metal oxide dielectrics into the standard semiconductor technology: (1) high threshold voltages and (2) polysilicon (poly-Si) depletion. Researchers from Freescale Semiconductor together with the Kintech Lab team have investigated the role of the poly-Si–MeOx interface and the effect of interfacial atomic bonding on the threshold shift. The results obtained indicate that pinning due to the interfacial Si–Hf and Si–O–Al bonds occurs for HfO2 and Al2O3, respectively. Oxygen vacancies at polysilicon / HfO2 interfaces also lead to Fermi pinning.

The role of Hf-Si bonds in the Fermi level pinning at the high-k dielectric / poly-Si interface is schematically ilustrated in the figure below

Interface Engineering, high-k, MOSFET, higher dielectric constant, Fermi pinning, polysilicon depletion, band structure, band gap, HfO2, semiconductor technology, MD-kMC, atomistic modeling, first principles, transistor,  field-effect, material design