Nanoscale simulation of the Atomic Layer Deposition process of Hafnium Dioxide

Miniaturisation has been the driving force of the microelectronics industry for the past few decades to achieve more powerful devices. Scaling rules indicate that as the transistor’s channel length is shortened, the gate oxide thickness must also shrink to maintain the electrostatic control of the gate stack while mitigating undesired short-channel effects. However, a thinner insulator layer between the gate and the channel risks amplifying the gate tunnelling current, and thus, increases the power consumption of the device. Therefore, scaled-device manufacturers have switched to utilising high permittivity materials, for example, hafnium dioxide or zirconium dioxide, in substitution of silicon dioxide as the gate dielectrics to prevent excessive gate currents. Furthermore, the downsizing of the gate oxide brings new challenges to film deposition technologies. Traditional vapour deposition techniques either suffer from poor conformality and thickness control of the film or are performed at high temperatures, which exacerbates short-channel effects by diffusing the doping profile near the channel region. Therefore, Atomic Layer Deposition (ALD) was introduced as a superior solution. By building thin films one atomic layer at a time, ALD attains a very uniform, conformal and nanometre-precise film. There have been many experimental studies into the ALD process of hafnium dioxide. Nonetheless, computer simulations of this process remain little known, leaving a gap between experiments and mathematical models. In this thesis, a novel reactive force field was developed to describe interactions between five atom types Si/O/H/Hf/Cl. Then, the same force field was employed to perform molecular dynamics simulations of the growth process. The growth per cycle obtained from the simulation is 1.42 Hf/nm2, which is in good agreement with experimental data. Observations from the simulation also confirm the theoretical growth mechanism of the ALD process. Lastly, the simulated HfO2 film was characterised by its electrical properties. Technology Computer-Aided Design (TCAD) simulations of a scaled transistor with a high-k/metal-gate (HKMG) stack were conducted, which demonstrated an improved performance over the conventional silica gate oxide.