Overview

Electronic devices that make up 99% of the computer processor and memory market are based on silicon (semiconductor) and silicon dioxide (insulator) technology. Unfortunately the key transistor gate stack structure within the traditional technology has reached an intrinsic physical scaling limit; the ultrathin gate oxide, already at 1nm thickness, cannot be made thinner without resulting in an intolerably high leakage current and reduced drive current. This limitation can be avoided by replacing the thin gate dielectric with a thicker film of an alternative material with a permittivity higher than that of SiO2, an accomplishing that has been realized in production just as this thesis goes to press. To further increase device performance, replacing the Si semiconductor with germanium as an alternative channel material is an attractive option for its high mobility and narrow band gap. However, the lack of a stable insulating oxide with high quality electrical properties prevents the fabrication of competitive Ge-based metal oxide semiconductor field effect transistors (MOSFETs). This dissertation reports the study of potential future-generation transistors with high-k dielectrics (HfO2 and Al2O3) on Ge substrates. A brief review of current research and development is first given followed by an introduction of the thin film characterization techniques used in this work. Various cleaning treatments as well as surface passivation methods using wet chemistry have been investigated on Ge substrates. Next, thin high-k dielectric films of HfO2 and Al2O3 have been deposited on Ge using atomic layer deposition (ALD). ALD permits films to be grown with monolayer control and excellent film conformality. Physical, chemical and electrical characterization has been performed on the multilayer film structures. Optimization of the film growth has been developed and we have demonstrated high quality with Au/HfO2/Ge nMOS devices. Capacitance-voltage electrical measurements show that sulfur passivation methods on Ge greatly decrease the interface state density and improve the device electrical properties. The same improvements have also been observed on the similarly processed Ge-based MOS capacitors with Al 2O3 dielectric layers.

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9781243582539

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