Title: Point defects at and near interfaces of functional semiconductor(Si, Ge)/insulator stacks probed by multifrequency electron spin resonance
Other Titles: Puntdefecten aan en nabij grenslagen van functionele halfgeleider(Si, Ge)/isolatorstructuren gekarakteriseerd d.m.v. multifrequentie elektron spin resonantie
Authors: Nguyen, Anh Phuc Duc; S0197857
Issue Date: 12-Sep-2012
Abstract: Relentless downward scaling serves as main red wire in progressing the field of very large scale integration (VLSI) based on the metal-oxide-semiconductor field effect transistor (MOSFET). This Si-based transistor technology, in which the superb Si/Si-oxide entity has played an overruling role, has revolutionized the society with respect to informatics and communication, and has thus taken us to the current semiconductor-based information age. Yet, inevitably, with continued scaling some fundamental limits are reached, requiring drastic and innovative new steps to be taken. One element considered is the incorporation of new semiconductor/insulator heterostructures with high-mobility (higher than Si) semiconductors such as Ge, GexSi1-x, GaAs, InGaAs, in combination with adequate alternative insulators. The current work situates within the field of fundamental aspects of semiconductor/insulator structures, including both traditional Si/SiO2 and newly conceived ones. More specifically, the study concerns fundamental probing of unavoidably occurring (near) interfacial point defects at the origin of interface traps, generally much detrimental to the performance of the MOS entity. Their impact must be reduced to below critical level. The study has been carried out by means of the multifrequency electron spin resonance (ESR), with ultimate goal the atomic identification of point defects, for which purpose the ESR method has emerged as an exclusive technique. Additionally, valuable information is also inferred regarding stability, quality, and interfacial matching arrangements In a first experimental part, an ESR study has been carried out of interface properties of a newly developed epitaxially grown c-Ge3N4/(111)Ge entity. This has resulted in the observation a remarkable interface defect with axial (trigonal) symmetry. In combination with theoretical considerations, the defect was identified as the intrinsic Ge K center, a thus far unknown intrinsic point defect. The data point to a superior inherent quality of the epi-Ge3N4/(111)Si entity, at least in terms of occurring paramagnetic point defects, leading to the overall conclusion that a thin epitaxial Ge-nitride layer may serve as an adequate passivating interlayer for functional Ge/insulator structures. The second part deals with the study of a non-thermal Si/SiO2 structure where, in contrast with the standard thermal oxide grown at elevated temperature, the SiO2 layer was deposited on (100)Si substrates at low temperature using a newly developed atomic layer deposition method, of much interest for implementation in device manufacturing not compatible with high temperature steps. Besides confirming a generally good quality of the Si/SiO2 structure, however, two types of defects were revealed conclusively identified as concerning Cri+ and Fei0 (3d metal) contamination in top Si substrate layers. The inferred defect densities together with the defect depth profiling led to the conclusion that the contamination likely originates from the reactor-environment during cleaning process in connection with the particular ALD method. A final part presents the results of the low-temperature K-band ESR study of (111)Si/AlN and (111)Si/AlN/AlxGa1-xN structures epitaxially grown on p+-(111)Si substrate wafers using the metal organic chemical deposition method applied at 1130 oC. A first important fact here, revealed by physical morphology mapping tools, is the presence an epitaxial c-Si3N4 interlayer at the (111)Si interface, so that, in fact, the crucial operational interface concerns the epitaxial c-Si3N4/(111)Si interface. Two main ESR-active defects were observed both involving an unpaired electron at a defected 3-fold coordinated Si atom: As first one, this includes the D-defect residing in amorphous-Si like patches likely located in near-interfacial Si layers. The second one was identified as the PbN center residing right at the (111)Si/Si-nitride interface, which occurrence was not totally unexpected. Yet, surprising was the detection, besides the regular [111]PbN centers, of the unusual 19o-PbN variants pointing to a less ideal (111)Si/Si-nitride interface in terms of interface morphology (excess roughness). The results may well be reconciled with results obtained by means of deep level transient spectroscopy (DLTS) carried out in conjunction with ESR probing on the same samples.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Semiconductor Physics Section

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