Atomic layer depositions (ALD) for advanced gate stack applications and ULSI front end of the line (FEOL) applications

Atomic layer deposition (ALD) is a unique branch of chemical vapor deposition techniques that relies solely on self-terminating surface chemical reactions. ALD offers precise control of film thickness, uniformity of film thickness over a large area and high film conformality on complex surfaces. Thanks to these features, ALD is now being used in a lot of areas, especially in microelectronics. Among many application areas of ALD, the gate dielectric application is getting the most attention. High-κ dielectrics are just being introduced as the gate dielectrics for high performance MOSFETs and the deposition of gate dielectrics generally require precise thickness control and high quality interface. ALD meets these requirements and thus is emerging as the main deposition method for high-κ gate dielectrics. The current generation of high-κ dielectrics is based on HfO 2 but HfO 2 has limitations in scaling below equivalent oxide thickness (EOT) of 0.5-0.7 nm due to small conduction band offset with respect to Si and relatively poor interface with Si. Lanthanide oxides have been suggested as the next generation of high-κ gate dielectrics because many of them have larger conduction band offsets (∼2 eV) than HfO 2 . In this thesis, ALD processes of ternary lanthanide oxides such as LaAlO 3 , PrAlO 3 and GdScO 3 and the properties of the ALD films are discussed focusing on the electrical properties. The films all showed promising electrical properties (κ ∼ 20, leakage current density 3-4 orders of magnitude smaller than SiO 2 ). Especially, GdScO 3 showed low interface trap density and low fixed charge density suitable for gate dielectric applications. Versatility of ALD is shown by use of ALD in passivating Ge surfaces for high-κ oxide deposition. Very thin (1-2 nm) insulating nitride films such as Hf 3 N 4 and AlN were deposited on wet-cleaned Ge surfaces as interfacial layers between Ge and high-κ oxide. The high-κ stacks on Ge made this way exhibited much improved interface properties than other reported high-κ stacks on Ge. ALD in other front end of the line (FEOL) applications are also demonstrated such as ALD tungsten nitride for gate electrodes and ALD nickel for silicide contacts. A novel precursor delivery method using precursor solutions and an MKS ® mole delivery device (MDD) is introduced in the last chapter of the thesis.