No abstract

A comparative electron spin resonance study is reported on (100)Si/SiO2 entities, grown by thermal oxidation of biaxial tensile strained (100)Si (sSi) layers, epitaxially grown on a strain relaxed Si0.8Ge0.2 buffer layer, and standard (100)Si. In the as-oxidized state a significant decrease (∼50%) of inherently incorporated interface defects, Pb0 and Pb1, is observed, i.e., the sSi/SiO2 interface is found to be inherently significantly improved in terms of electrically detrimental interface traps (Pb0). After vacuum-ultraviolet irradiation two more SiO2-associated defects appear, namely Eγ′ (generic entity O3≡Si·) and EX. Interestingly, a decrease (∼50%) of Eγ′ defect density is observed compared to standard Si/SiO2. This reduction in inherent electrically active interface (Pb0) and near-interface (Eγ′) traps would establish sSi/SiO2 as a superior device structure for all electrical properties where (near)-interfacial traps play a detrimental role. For one, the reduction of detrimental (near)-interface defects may be an additional reason for the commonly reported mobility enhancement in sSi/SiO2 based metal–oxide–semiconductor structures over standard Si/SiO2 ones, and at the same time account for the reported reduction of 1/f noise in the former structures. The data also confirm the generally accepted notion that Pb-type defects are mismatch induced defects.

A multi-frequency electron spin resonance (ESR) study has been carried out the Ge Pb1 dangling bond (DB)-type interface defect in SiO2/GexSi1−x/SiO2/(100)Si heterostructures of different Ge fraction manufactured by the condensation technique. The notable absence of Si Pb-type centers enables unobscured spectral analysis as function of magnetic field angle, reassured by coinciding multi-frequency ESR data. The center features monoclinic-I (C2v) symmetry with principal g values g1 = 2.0338 ± 0.0003, g2 = 2.0386 ± 0.0006, g3 = 2.0054, with the lowest value, g3, axis 24 ± 2° off a 〈111〉 direction towards the [100] interface normal n. The defect appearance shows a systematic variation as function of x, reaching maximum densities of ∼6.8 × 1012 cm−2 per Si/SiO2 interface for x ∼ 0.7, to disappear for x outside the ]0.45–0.87[ range. The ESR signal width is dominated by inhomogeneous broadening arising from strain-induced Gaussian spread in g, resulting in frequency (ν)-dependent peak-to-peak broadening of ΔBppSB/ν = 0.62 G/GHz and 1.13 G/GHz for the applied magnetic field B//g3 principal axis and B//n, respectively. Compared to the familiar Si Pb-type interface defects in (100)Si/SiO2, the enhanced ν-dependent broadening scales with the spin-orbit coupling constant ratio λ(Ge)/λ(Si). The natural inhomogeneous broadening due to unresolved 73Ge hyperfine interaction is found to be below ∼1.56 G, the inferred residual (ν→0) width. The core of the defect, previously depicted as a Ge Pb1-type center, concerns an asymmetrically back bonded trivalent Ge atom where the total of all data would suggest a back bond arrangement involving two Ge and one Si atoms and/or a strained bond. Initial studies show the defect to exhibit reversal hydrogen passivation/depassivation kinetics, where defects can be substantially, yet only partially, ESR-inactivated by heating in H2. The properties and nature of the center are discussed within the context of the their inherent incorporation as interface mismatch centers, where assessing the defect’s nature and modalities of occurrence may provide a link to unraveling the role of point defects in adapting interfacial mismatch.

An electron spin resonance study has been carried out on heteroepitaxial Si/insulator structures obtained through growth of epi-Lu 2 O 3 films on ͑111͒Si ͑ϳ4.5% mismatch͒ 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 P b defects ͑ϳ5 ϫ 10 11 cm −2 ͒ with the unpaired sp 3 Si dangling bond along the ͓111͔ interface normal, the archetypical defect ͑trap͒ of the standard thermal ͑111͒Si/ SiO 2 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 ϳ 420°C. Yet, in the range T an ϳ 420-550°C, the interface starts to "degrade" to standard Si/ SiO 2 properties, as indicated by the gradually increasing P b density and attendant appearance of the EX center, an SiO 2-associated defect. At T an ϳ 700°C, ͓P b ͔ has increased to about 1.3 times the value for standard thermal ͑111͒Si/ SiO 2 , to remain constant up to T an ϳ 1000°C, indicative of an unaltered interface structure. Annealing at T an Ͼ 1000°C results in disintegration altogether of the Si/ SiO 2-type interface. Passivation anneal in H 2 ͑405°C͒ alarmingly fails to deactivate the P b system to the device grade ͑sub͒ 10 10 cm −2 eV −1 level, which would disfavor c-Lu 2 O 3 as a suitable future high-replacement for the a-SiO 2 gate dielectric. Comparison of the thermal stability of the c-Lu 2 O 3 / ͑111͒Si interface with that of molecular-beam deposited amorphous-Lu 2 O 3 / ͑100͒Si shows the former to be superior, yet unlikely to meet technological thermal budget requirements. No Lu 2 O 3-specific point defects could be observed.