In Situ Studies of the Surface Chemistry Reactions Involved in Gas-Phase Deposition and Etching of Thin Dielectric Films
Pena Orduna, Luis Fabian
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In this dissertation, key aspects of the surface chemistry associated with gas phase deposition and etching are discussed. Atomic layer deposition (ALD) is a gas-phase deposition technique primarily known for its superior self-limiting binary process that affords precise control, uniform and conformal thin film growth. Despite the extensive work done with ALD, the mechanisms behind nucleation and steady state growth remain unclear for many ALD processes. Additionally, in an effort to meet today's device integration requirements, e.g., scaling down nanostructures and thermal budget restrictions during film deposition, thermal ALD processes requiring high temperatures (>300 C) are now being forced out of production due to adverse thermally induced side effects, e.g., device degradation. To address this challenge and promote reactivity at low temperatures (<300 C), the surface reactivity of the substrate is increased by creating defects, dangling bonds or reactive sites using a plasma enhanced process, consequently lowering the thermal budget requirement for film deposition. However, this enhancement adds substantial complications due to complex surface reactions, which demands fundamental studies to sort out and to understand the mechanisms involved. Similarly, efforts have been undertaken to investigate gas-phase cleaning, passivation and characterization of transition metal substrates. It is well known that alcohols and acids are capable of reducing the native oxide on transition metals, e.g., cuprous oxide (Cu₂O), at relatively low temperatures (<325 C). However, the surface functionalization of the final surface after oxide reduction with organic agents has yet to be determined, particularly under industrially relevant processing conditions. The main challenge hindering a fundamental understanding of the surface science is the lack of in situ characterization sensitive enough to detect adsorbates, essential in developing reaction mechanisms. To this end, the investigations presented in this dissertation are devoted to the elucidation of a fundamental understanding of the surface chemistry. They combine in situ Fourier-transform infrared spectroscopy (FTIR) using both transmission and refection geometries to investigate the surface reaction mechanisms involved during growth of plasma enhanced ALD of silicon nitride and the etching of Cu₂O thin dielectric films at temperatures <300 C.