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 (∼5×10¹¹ cm^-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 P_b 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 T_an∼420 °C. Yet, in the range T_an∼420-550 °C, the interface starts to "degrade"to standard Si/SiO₂ properties, as indicated by the gradually increasing P_b density and attendant appearance of the EX center, an SiO₂-associated defect. At T_an∼700 °C, [P_b] has increased to about 1.3 times the value for standard thermal (111)Si/SiO₂, to remain constant up to T_an∼1000 °C, indicative of an unaltered interface structure. Annealing at T_an>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) 10¹⁰ cm^-2 eV^-1 level, which would disfavor c-Lu₂O₃ as a suitable future high-∼ 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. [ABSTRACT FROM AUTHOR]