N.Q. Khánh

Nondestructive determination of damage depth profiles in ion‐implanted semiconductors by multiple‐angle‐of‐incidence single‐wavelength ellipsometry using different optical models

Several‐parameter fitting of multiple‐angle‐of‐incidence ellipsometry data is developed to characterize near‐surface layers on semiconductors damaged by implantation. The damage depth profiles were described by either rectangular, trapezoid‐type, or coupled half‐Gaussian (realistic) optical models. The rectangular model has three parameters: the average damage level and effective thickness of the implanted layer, plus the thickness of the native oxide. The trapezoid‐type model is enhanced with a fourth parameter, the width of the back (a/c) interface. The realistic optical model consists of a stack of layers with fixed and equal thicknesses and damage levels determined by a depth profile function (presently the coupled half‐Gaussians). Five parameters were used: the center, the height, and two standard deviations of the profile, plus the thickness of the native oxide. The complex refractive index of each layer is calculated from the actual damage level by the Bruggeman effective medium approximation. The ...

Ion beam irradiated channel waveguides in Er3+-doped tellurite glass

Erbium-doped tellurite glasses are of great interest for the fabrication of active integrated circuits because of their unique properties in terms of bandwidth and rare earth solubility. The fabrication of multimode channel waveguides in a glass of this family, namely, a sodium-tungsten-tellurite glass, is demonstrated using a high-energy ion beam irradiation technique. Nitrogen ions with dose of 1.0×1016ions∕cm2 and 1.5MeV energy were used for this aim. The waveguiding effect was investigated using the end-fire coupling technique.

Ellipsometric study of polycrystalline silicon films prepared by low-pressure chemical vapor deposition

Polysilicon layers with thicknesses between 8 and 600 nm deposited by low-pressure chemical vapor deposition at temperatures ranging from 560 to 640 °C were characterized by spectroscopic ellipsometry (SE) to determine the layer thicknesses and compositions using multilayer optical models and the Bruggeman effective-medium approximation. The dependence of the structural parameters on the layer thickness and deposition temperature have been investigated. A better characterization of the polysilicon layer is achieved by using the reference data of fine-grained polysilicon in the optical model. The amount of voids in the polysilicon layer was independently measured by Rutherford backscattering spectrometry (RBS). The SE and RBS results show a good correlation. The comparison of the surface roughness measured by SE and atomic force microscopy (AFM) shows that independently of the AFM window sizes, a good correlation of the roughness determined by SE and AFM was obtained.

Ion-implantation induced anomalous surface amorphization in silicon

Spectroscopic ellipsometry (SE), high-depth-resolution Rutherford backscattering (RBS) and channeling have been used to examine the surface damage formed by room temperature N and B implantation into silicon. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fraction of the amorphous silicon component in the layers) by linear regression. The dependence of the thickness of the surface-damaged silicon layer (beneath the native oxide layer) on the implantation parameters was determined: the higher the dose, the thicker the disordered layer at the surface. The mechanism of the surface amorphization process is explained in relation to the ion beam induced layer-by-layer amorphization. The results demonstrate the applicability of Spectroscopic ellipsometry with a proper optical model. RBS, as an independent cross-checking method supported the constructed optical model.

Ellipsometric characterization of damage profiles using an advanced optical model

Damage created by ion implantation into single crystalline silicon was characterized with an optical model based on the coupled half-Gaussian model developed by Fried et al [J. Appl. Phys. 71, 2835 (1992)]. In the improved optical model the damage profile was described by sublayers with thicknesses inversely proportional to the slope of the profile. This method allows a better resolution at the quickly changing parts of the profile, and a better approximation of the Gaussian profile with the same number of sublayers. A fitting procedure, which we call “multipoint random search,” was applied to minimize the probability of getting in a local minimum. The capabilities of our method were demonstrated for amorphizing doses using different ions and energies. The improved fit quality and the correlation with results of backscattering spectrometry basically supported the optical model.

Comparative study of ion implantation caused anomalous surface damage in silicon studied by spectroscopic ellipsometry and Rutherford backscattering spectrometry

Damage created by ion implantation of 150 keV Ne+ and 800 keV Ar+ ions in single-crystalline silicon was characterized using Spectroscopic Ellipsometry (SE) and Rutherford Backscattering Spectrometry (RBS) in combination with channeling. Results from both methods unambiguously show the presence of a heavily damaged thin layer at the surface that is not predicted by TRIM calculations. The amorphization rate at the surface was found to be proportional to the nuclear energy deposition at the surface. It is demonstrated that SE cross-checked with RBS could be used for quantitative and accurate evaluation of the thickness of the damaged surface layer. The formation of this thin amorphous layer could be attributed to the redistribution of Si interstitials produced by the implantation process from the buried damaged region towards the surface and to a subsequent segregation process (W. Fukarek et al., Nucl. Instr. and Meth. B 127/128 (1997) 879).

Nondestructive characterization of nitrogen-implanted silicon-on-insulator structures by spectroscopic ellipsometry

Silicon‐on‐insulator structures implanted by 200‐keV nitrogen with a dose of 7.5×1017 atoms/cm2 were studied by spectroscopic ellipsometry (SE). The SE measurements were carried out in the 300–700‐nm wavelength (4.13–1.78‐eV photon energy) range. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and compositions) by linear regression. Calculated data were in good agreement with measurements when a seven‐layer model, consisting of surface oxide layer, thick silicon layer, upper two interface layers, thick nitride layer, and lower two interface layers, was applied. Results obtained by SE were compared with those from Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy. In contrast with RBS measurements, we found that the sensitivity of our optical model combined with the fitting technique was good enough to resolve the silicon‐rich transition layers at the upper and lower in...

Comparative study of ion implantation caused damage depth profiles in polycrystalline and single crystalline silicon studied by spectroscopic ellipsometry and Rutherford backscattering spectrometry

Abstract Damage created by ion implantation of Ar+ ions into polycrystalline (p-Si) and single-crystalline silicon (c-Si) was characterized using Spectroscopic Ellipsometry (SE), Rutherford Backscattering Spectrometry (RBS), and Transmission Electron Microscopy (TEM). To create buried disorder, Ar+ ions with an energy of 100 keV were implanted into the samples. Ion doses were varied from 5×1013 to 6.75×1014 cm−2. The parameters of the implantation were kept identical for both p-Si and c-Si. Damage depth profiles have been investigated using SE, RBS, and TEM, in case of c-Si, and SE and TEM in case of p-Si. The results prove the applicability of spectroscopic ellipsometry for characterizing ion implantation caused damage even in polycrystalline silicon, where the RBS method cannot be applied. The RBS and TEM results basically supported the optical model of SE.

Damage accumulation in nitrogen implanted 6H-SiC: Dependence on the direction of ion incidence and on the ion fluence

The influence of crystallographic orientation and ion fluence on the shape of damage distributions induced by 500keV N+ implantation at room temperature into 6H‐SiC is investigated. The irradiation was performed at different tilt angles between 0° and 4° with respect to the ⟨0001⟩ crystallographic axis in order to consider the whole range of beam alignment from channeling to random conditions. The applied implantation fluence range was 2.5×1014–3×1015cm−2. A special analytical method, 3.55MeV He+4 ion backscattering analysis in combination with channeling technique (BS∕C), was employed to measure the disorder accumulation simultaneously in the Si and C sublattices of SiC with good depth resolution. For correct energy to depth conversion in the BS∕C spectra, the average electronic energy loss per analyzing He ion for the ⟨0001⟩ axial channeling direction was determined. It was found that the tilt angle of nitrogen implantation has strong influence on the shape of the induced disorder profiles. Significantl...

Amorphous alloy formation and thickness dependent growth of Gd–silicides in solid phase thin film reaction

Abstract The formation of amorphous and equilibrium phases was investigated during the solid-phase reaction of Gd thin film with (111) and (100) oriented Si substrate as a function of thickness and annealing by X-ray diffraction, Rutherford backscattering and transmission electron microscopy. For Gd films thinner than 30 nm, the phase formation was affected by the substrate orientation. At low temperature (320°C), amorphous phase developed on Si(100). At higher temperatures epitaxial hexagonal GdSi1.7 was found on Si(111), while on Si(100), epitaxial orthorhombic GdSi2 was formed. For thicker gadolinium films on Si(111), a conventional diffusion–reaction process appeared. The hexagonal GdSi1.7 phase formed first and then transformed to the second phase (orthorhombic GdSi2). The ratio of these phases could be described by a model. On Si(100) substrate at each thickness and annealing, only orthorhombic GdSi2 phase was formed. The phase formation depended on the time and temperature of the annealing and even on the initial Gd film thickness and substrate orientation.