Simultaneous determination of tensile and shear strains of crystalline bilayers using three Bragg reflections of X-rays

A method for the simultaneous determination of nine strain coefficients, both shear and tensile, of crystalline bilayers is proposed and realized. The X-ray diffraction peak intensities along 2θ (vertical) and β (horizontal) scans relative to the plane of incidence of three Bragg reflections whose atomic planes are not parallel to each other can be used to obtain shear and tensile strain coefficients. The theoretical considerations and experimental examples for single-crystal GeSi/Si overlayers are reported. It is also demonstrated that, for GeSi/Si, the shear and tensile strain coefficients of the Si substrate tend to vanish when the GeSi layer is thicker than 40 nm.

STEM measurement of Ge concentration profiles in Si/GeSi/Si heterostructures with 3 Å resolution

GeSi alloys are of great interest because of potential applications to high-performance semiconductor devices. For example, the fastest heterojunction bipolar transistor (in Si-based materials) in 1990 was fabricated by using a strained GeSi layer. To accomplish this, it is necessary to keep the Ge concentration and the thickness of the GeSi films below a “critical thickness” to avoid relaxation of the GeSi alloys. It is therefore important to control the Ge concentration and the thickness of GeSi films. When the thickness of the GeSi film is under 10 nm, common characterization techniques such as RBS (Rutherford Backscattering Spectrometry), Auger analysis and SIMS (Secondary Ion Mass Spectrometry) reach resolution limits. The accurate measurement of Ge profiles in GeSi thin films becomes a difficult but important issue. In this paper, we measure Ge concentration profiles by different analytical techniques obtained from STEM and compare them with results from SIMS and Auger analysis.

Spreading Resistance Profiling Study of GeSi/Si Structures by High Dose Ge Implantation into Si

Hetero-structures of GeSi layers on Si have been produced by high dose Ge implantation into p-type (100) Si wafers at 150 or 300 keV at various doses. From spreading resistance profiling measurements, it is found that for samples implanted at 300 keV at a sufficiently high dose, there is an unexpected resistivity type conversion due to the Ge implantation. The depths of the n-p junction formed as-implanted can be larger than 1.5 /xm, far beyond the Ge projected range. Upon annealing, the junction position moves toward the surface and eventually stops at a depth corresponding to the thickness of the GeSi layer. However, no such n-p junction formation was observed in the spreading resistance profiles of the 150 keV implanted samples. These spreading resistance results are discussed in conjunction with results from RBS and SIMS experiments.

Characterization of GeSi Layer Formed by High Dose Ge Implantation into Si

ABSTRACTHigh dose Ge implantation into p-type <100> Si wafers at 150 keV has been performed at doses of 3.6×1016, 6.7×1016 and 9.0×1016 cm-2. The Ge distribution and the crystal quality of the implanted layer before and after annealing at various temperatures have been studied by RBS and channelling experiments. It is found that for the medium and high dose samples before annealing, more than 90% of the Ge atoms are in interstitial sites and after annealing at 1000°C, more than 50% of the Ge atoms have become substitutional. The situation is better for the low dose sample where less than 70% of the Ge atoms are in interstitial sites before annealing and about 80% of them become substitutional after annealing at 1000°C. The ESR spectra of these samples are of lorentzian shape with a g-value of about 2.007 and a spin density of about 6×1016 cm-3. The ESR signals of these samples have been inferred to be mainly due to Si-dangling bonds in the GeSi alloy layer and can be eliminated by annealing at 1000°C for 10 minutes. Electrical characterization of the GeSi layer by spreading resistance profiling technique shows that the implantation damage has been extended deep into the substrate before annealing. After annealing at 1000°C, these defects are removed but the spreading resistance of the surface GeSi layer is found to remain higher than that of the substrate.

Rapid Thermal Oxidation of GeSi Strained Layers

ABSTRACTA cold-wall rapid thermal processor is used for the oxidation of commensurately grown GexSi1−x layers on Si substrates. It is shown for dry oxidation that the oxidation rate of GeSi is the same as that of Si. The dry oxidationrate of GeSi is independent of Ge concentration (up to 20 % considered in this study) in the GeSi layer. For wet oxidation, however, the rate of oxidation of the GexSi1−x layer is found to be significantly higher than that of pure Si, and the oxidation rate increases with the Ge concentration in GexSi1−x layer. Employing highfrequency and quasistatic Capacitance-Voltage measurements, it is found for a thin oxide that a fixed negative oxide charge density in the range of 1011 – 1012/cm2, and the interface trap level density (in the mid-gap region) of about 1012 /cm2.eV are present. Further, the density of this fixed oxide charge at the SiO2 /GeSi interface is found.to increase with the Ge concentration in the commensurately grown GeSi layers.

Confinement of Threading Dislocations in Simox with a GeSi Strained Layer

ABSTRACTWe have investigated improving the crystalline quality of epitaxial silicon grown on SIMOX by confining threading dislocations in the original Si top layer using a GeSi strained layer. Epitaxial Si/GeSi/Si structures were grown by CVD on SIMOX and Si substrates with a GeSi alloy layer about 1000 − 1500 angstroms thick with Ge concentrations of about 0−20%. A Ge concentration in the alloy layer of about 5.5% or higher appears to be necessary in order to bend any of the threading dislocations from the original SIMOX top layer. For a higher Ge concentration of about 16%, most of the threading dislocations appear to be bent and confined by the GeSi layer. In addition, the GeSi strained layers grown by CVD (at about 1000°C) appear to be high quality and no misfit dislocations were observed in the regions studied by XTEM and plane view TEM.