Fabrication and characterization of ferroelectric Hf_xZr_1-xO_y layers for novel nanosheet devices: from high-k to ferroelectric behaviors

Abstract

With the continuous advancement of semiconductor technology, the size of devices has been shrinking, making it increasingly challenging to improve device performance due to issues like gate leakage and quantum tunneling. To overcome these challenges, the concept of "More than Moore" emerged, focusing on increasing the functionality of devices at a given dimension instead of following Moore’s law, which involves scaling down device sizes. A significant breakthrough occurred in 2011 when a material, hafnium oxide, was rediscovered to possess superior performance. This material exhibited greater capacitance and stable ferroelectricity even at nanometer-scale thickness. In this thesis, we investigate Zirconium-doped Hafnium Oxides, specifically Hafnium Zirconium Oxide (HZO), a material with a higher dielectric constant than SiO2. Depending on the deposition and integration processes, HZO can exhibit strong ferroelectric properties or charge trapping capabilities, two characteristics particularly suitable for memory applications. By employing a HZO as gate oxide, it is possible to benefit from a higher dielectric constant, improved capacitance, lower power consumption, and CMOS compatibility.The thesis primarily focuses on implementing and optimizing an Atomic Layer Deposition (ALD) process to deposit sub-10 nm thick HZO films with high purity. The grown material is comprehensively characterized using a vast set of experimental techniques, to assess thedeposited thin film properties. Thanks to a careful electrical characterization, the dielectricconstants of the grown HfO2 and ZrO2 are extracted, and the ferroelectric properties of thecombined HZO are confirmed through capacitance-voltage (C-V) and polarization-voltage(P-V) analyses.Furthermore, we investigate the possibility of realizing memory devices based on the integrationof an HZO layer into monolithic and single-crystalline Aluminum-Silicon heterostructures.The fabricated devices are electrically characterized, showing the potential ofAl-Si-Al heterostructure memory devices using ferroelectric materials as charge trappingmemories, ensuring stable data retention and proposing their suitability for memory applications.In conclusion, this work successfully implemented the controlled ALD growth of HZOthin films and verified the ferroelectric behavior of the grown material . Additionally, itreveals the potential of stable memory devices, providing valuable insights into the electricalproperties of HZO and its promise as a high-k material for advanced semiconductordevices. The research sets a foundation for improved memory technologies and advancesin semiconductor materials and devices.