Comparative electron spin resonance study of epi-$Lu2O3/(111)Si$ and $a-Lu2O3/(100)Si$ interfaces: Misfit point defects

An electron spin resonance study has been carried out on heteroepitaxial Si/insulator structures obtained through growth of epi-$Lu2O3$ films on (111)Si (⁠$∼4.5%$ mismatch) by molecular-beam epitaxy, with special attention to the inherent quality as well as the thermal stability of interfaces, monitored through occurring paramagnetic point defects. This indicates the presence, in the as-grown state, of $Pb$ defects $(∼5×1011cm−2)$ with the unpaired $sp3$ Si dangling bond along the [111] interface normal, the archetypical defect (trap) of the standard thermal $(111)Si/SiO2$ interface, directly revealing, and identified as the result of, imperfect epitaxy. The occurrence of $Pb$ defects, a major system of electrically detrimental interface traps, is ascribed to lattice mismatch with related introduction of misfit dislocations. This interface nature appears to persist for annealing in vacuum up to a temperature $Tan∼420°C$⁠. Yet, in the range $Tan∼420–550°C$⁠, the interface starts to “degrade” to standard $Si/SiO2$ properties, as indicated by the gradually increasing $Pb$ density and attendant appearance of the EX center, an $SiO2$-associated defect. At $Tan∼700°C$⁠, $[Pb]$ has increased to about 1.3 times the value for standard thermal $(111)Si/SiO2$⁠, to remain constant up to $Tan∼1000°C$⁠, indicative of an unaltered interface structure. Annealing at $Tan>1000°C$ results in disintegration altogether of the $Si/SiO2$-type interface. Passivation anneal in $H2$ $(405°C)$ alarmingly fails to deactivate the $Pb$ system to the device grade (sub) $1010cm−2eV−1$ level, which would disfavor $c-Lu2O3$ as a suitable future high-$κ$ replacement for the $a-SiO2$ gate dielectric. Comparison of the thermal stability of the $c-Lu2O3/(111)Si$ interface with that of molecular-beam deposited amorphous-$Lu2O3/(100)Si$ shows the former to be superior, yet unlikely to meet technological thermal budget requirements. No $Lu2O3$-specific point defects could be observed.