UC San Diego

Novel materials are great demand for boosting transistor performance in scaled integrated electronic circuits especially as the channels approach atomic dimension stretching traditional scaling limits. The high effective carrier mobility of SiGe in p-channel field effect transistors (pFETs) promises enhanced transport for high speed electronics. SiGe is a very convenient alternative channel material because unlike III-V semiconductors, SiGe can be readily grown epitaxially on Si substrates. However, formation of localized surface states in the bandgap hence the trapped charges at the interface during gate oxide deposition on SiGe hinders SiGe integration into pFETs.

Surface passivation prior to gate oxide growth is incapable of preventing GeOx formation during atomic layer deposition (ALD) due to diffusion of oxidant species which react with the SiGe surface thereby deteriorating the interface. Therefore, control over the structure and composition of high-k gate oxide/SiGe interface with layer by layer ALD oxide growth is not attainable.

ALD reactant species can be utilized to passivate the interface defects during or after oxide deposition by benefiting from facile diffusion through gate oxide. In this dissertation, investigation and suppression of electronic defects at SiGe/high-k oxide interface during and after gate oxide deposition is investigated. Correlations are made between the interface charge trap density (Dit) determined by impedance measurements and the chemical - physical structure of the interfaces obtained with advanced nanoscale characterization techniques. In all these studies, unlike ideal layer-by-layer oxide ALD, unconventional oxidation on SiGe is observed during ALD. This non-ideality which is the source of defect formation at the high-k/SiGe interface, is exploited to suppress interface defects.

Ultra-low defect (9.4×1010cm-2) HfO2/SiGe interfaces (<0.5nm thick) are formed using selective oxygen scavenging from the SiGe interface using oxygen reactive metal gates or highly reactive ALD precursors. These processes form SiOx rich and GeOx deficient interfaces by utilizing the difference in Si versus Ge oxidation enthalpy. A nearly inverse process is found using a strong oxidant ozone which can readily diffuse to the interfaces, promote GeOx out diffusion and sublimation leaving SiOx rich low defect interface