Atomic layer deposition and characterization of rare earth oxides for innovation in microelectronics

The research activity described in this thesis was mainly carried out in the framework of the European project REALISE “Rare earth atomic layer deposition for innovation in electronics”. The principal project aims were to deposit high permittivity rare earth oxide layers with sub-nanometer control and integrate these dielectrics into innovative memory and communication devices. The idea was to develop and optimize the deposition process of novel ultra-thin dielectric films and to investigate and characterize their physical and chemical properties before testing them for applications in innovative microelectronic devices. The growth process which was the subject of the research is atomic layer deposition (ALD). Nowadays, this technique is one of the leading technologies employed for deposition of nanometer-scale films at an industrial level. Indeed ALD allows deposition of conformal ultra-thin layers with an extremely precise thickness control. Moreover, ALD growth processes are scalable up to 8” or 12” large area substrates making this technique very promising for the necessities of high-throughput industries. Most of the materials investigated in this study belong to the rare earth oxides (REOs) family. Rare earth-based binary and ternary oxides are high dielectric constant (high-k) materials which might be successfully employed in several microelectronic fields. Indeed, the scaling down of the device dimensions requires the employment of ever-thinner insulating dielectric layers for logic, memory and communication applications. Appropriate physical and chemical stability are required together with stringent electrical requisites in terms of permittivity value and leakage current. Thus, a variety of high-k dielectrics was identified, deposited using ALD and characterized in order to asses the potential implementation in advanced nano-scaled devices. The REOs were deposited on different semiconductor substrates in order to address different oxide/semiconductor interfaces. In addition, an in situ study of the ALD processes and of the film and interface optical properties was performed using spectroscopic ellipsometry during the deposition of the various stacks. Therefore, the research activity was balanced between the development of new ALD processes and the assessment and the discussion of more fundamental scientific issues connected with the structural, chemical and electrical properties of the thin films grown by ALD.