Modelling mobility degradation due to remote Coulomb scattering from dielectric charges and its impact on MOS device performance

The electron mobility in high-k transistors is degraded when compared to silicon oxide transistors. So far this problem has hampered the production of high-k transistors. One of the main causes of the low mobility is remote Coulomb scattering from charges in the dielectric. In this paper we analyse how the dielectric constants can change the mobility in a high-k stacked transistors. When an interface layer (IL) is used between the semiconductor and the high-k dielectric, the increase of the dielectric constant of the IL degrades the mobility. When the dielectric constant of the high-k layer is increased, the mobility is increased. These two opposite effects can be explained by an increase of the electric coupling in the first case and by an increase of the fringing field in the second. We study the electron mobility as a function of dielectric constant and thickness for three different stacks. Higher permittivity layers in combination with an interface layer free of charges are desirable to improve mobility.