UC San Diego

With the need for more compute performance, smaller semiconductor device dimensions and denser interconnections have required the use of ultra-thin layers conformally deposited in three-dimensional structures such as the gate-all-around MOSFET and in high-aspect-ratio interconnect vias. Atomic layer deposition (ALD), with the ability to precisely control thickness as well as selectively deposit layers on different materials, is used in current process nodes for gate oxides and barrier layers, but new channel materials such as silicon-germanium (SiGe) and new interconnect metals such as cobalt (Co) and ruthenium (Ru) require new surface preparation techniques and ALD processes.Chapter 2 of this dissertation describes the passivation of defects in gate oxides deposited by ALD in SiGe-channel devices. SiGe’s high carrier mobility shows promise for future devices, but the presence of unstable germanium oxides (GeOx) in the interface between oxide and channel results in high defect densities, limiting device performance. By nitridating the surface prior to gate oxide ALD using an RF plasma, a reduction in defect densities is demonstrated. TEM and XPS studies confirmed the formation of a GeNx interfacial layer suppressing GeOx formation during ALD, improving gate oxide nucleation and decreasing defect densities. With shrinking device dimensions, interconnect via widths correspondingly shrink. While copper has long been used for due to its low bulk resistivity, ultra-narrow (<10 nm) via widths show high resistance with Cu. Co has been proposed as an alternative as it maintains its resistivity to smaller widths, with several selective Co ALD processes developed. However, surface defects can result in unwanted deposition, and in Chapter 3, the passivation of surface defects to enhance selectivity of Co ALD is studied, with XPS and SEM studies showing that a low-temperature reflow process can further enhance selectivity. Ru is also a promising metal for interconnects due to its potential for a barrier-less via fill, and in Chapter 4, the deposition of Ru with a resistance close to the bulk value by ALD is demonstrated. XRD and TEM studies confirm the deposition of Ru layers with low O and C content and grain sizes similar to the film thickness, minimizing grain boundary scattering.