Advanced Metallization Processes for Complex Structures in Microelectronics by Direct-Liquid-Evaporation Chemical Vapor Deposition
AbstractWith the rapid advancement of semiconductor industry, fabrications of complex microelectronic devices are going beyond the conventional planar geometries into three-dimensionality (3D). Besides, since the emerging of flexible and wearable consumer electronics, it is also desired to break the limitation of conventional rigid electronic devices and transform toward flexible devices. In order to provide fundamental frameworks for 3D electronics and flexible electronics, strategies to create complex structures at nano-/micro-scales, including interconnect architectures, need to be developed. For nano-scale high-aspect-ratio metal interconnects, great challenges are yet to be overcome because of the rigorous requirements of high-precision fabrication, high metal uniformity and conformality, as well as special liner and capping layers. Promising solutions to these challenges are offered by direct-liquid-evaporation chemical vapor deposition (DLE-CVD) technique developed in recent years. DLE-CVD is able to quantitatively deliver high-throughput precursor into deposition chambers with high controllability and vaporization efficiency, which provides high-quality metallization layers even deep inside complex structures, or on flexible polymer substrates.
In this thesis, advanced metallization processes based on DLE-CVD are described. The deposited metallic materials from these processes, including cobalt (Co), nickel (Ni), nickel silicide (NiSi) and copper (Cu), are thoroughly characterized and studied by electron microscopies, elemental analysis tools, atom probe tomography (APT), etc. Applications of these metallization processes in 3D electronics are demonstrated directly on high-aspect-ratio structures fabricated by reactive ion etching (RIE) technique. Furthermore, potential utilization of DLE-CVD processes to metallize the surface of polymer fibers, which can be used as flexible interconnects, is also discussed.
Chapter 1 provides a background introduction to the basics of metallization strategies and applications, and discusses potential applications of these strategies.
Chapter 2 describes detailed methods to fabricate well-defined high-aspect-ratio structures, and introduces an intriguing self-smoothing phenomenon observed in aluminum-catalyzed silicon dioxide (SiO2) atomic layer deposition (ALD), which can be used to create smooth-wall trench structures with ultrahigh aspect ratios up to 100:1.
Chapter 3 presents in-detail study of DLE-CVD cobalt (Co), in which the deposition process of highly conformal, pure, and smooth nanocrystalline Co metal films is described. All-around encapsulation of nano-scale copper (Cu) interconnect by DLE-CVD Co is demonstrated to be an effective strategy to enhance interconnect reliability, stability, and operation life.
In chapter 4, APT technique is used to study our metallic materials deposited by DLE-CVD. Compositional and structural information are acquired with atomic resolution.
And chapter 5 explores the potential application of DLE-CVD Co as the initial metallization layer on polymer fibers, to create conductive flexible interconnects.
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