O. Polgár

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 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.

Ellipsometric characterization of oxidized porous silicon layer structures

Abstract Electrochemically prepared porous silicon (PS) layers were oxidized thermally and investigated by spectroscopic ellipsometry (SE). The SE spectra were measured in the range of 270–850 nm with a rotating polarizer ellipsometer. The PS was modelled as a mixture of void and crystalline silicon or fine-grained polycrystalline silicon with enhanced absorption due to extensive grain-boundary regions, i.e. the complex refractive index of the layer was calculated by Bruggeman effective medium approximation. The dielectric function of the fine-grained polycrystalline silicon was taken from the work published by G.E. Jellison, Jr., M.F. Chisholm, S.M. Gorbatkin, Appl. Phys. Lett. 62 (1993) 3348. The porosity, the layer thickness and the composition of the oxidized PS layers were determined. Oxidation at 900°C was performed after a stabilizing heat treatment at 320°C. The oxidation at 900°C for 10 min generated only a few nm silicon dioxide on single crystalline Si while in the case of PS with 57% porosity nearly complete oxidation was found. For PS with 68% porosity complete oxidation was observed.

Ion implantation-caused damage depth profiles in single-crystalline silicon studied by Spectroscopic Ellipsometry and Rutherford Backscattering Spectrometry

Abstract Damage created by ion implantation of Ar + ions into single crystalline silicon is characterized using Spectroscopic Ellipsometry (SE) and Rutherford Backscattering Spectrometry (RBS). To create buried disorder, Ar + ions with an energy of 100 keV were implanted into the samples. Ion doses were varied from 5×10 13 atom\cm 2 to 6.75×10 14 atom\cm 2 . Damage depth profiles have been investigated using RBS combined with channeling, and SE. For the analysis of the SE data optical models were used, which consist of a stack of layers. The result proves the applicability of spectroscopic ellipsometry for the characterization of ion-implantation-caused damage. As an independent cross-checking method, Rutherford Backscattering Spectrometry was used. The RBS results basically supported the optical model of SE.

Optical models for cavity profiles in high-dose helium-implanted and annealed silicon measured by ellipsometry

Cavities created by He implantation with a dose of 5×1016cm−2 and energy of 40keV into single-crystalline silicon and annealing at 650–1000°C for 15–60min were characterized by multiple angles of incidence spectroscopic ellipsometry. Optical models of increasing complexity were developed assuming the cavity layer either to be homogeneous, or to have a Gaussian profile, or sublayers with independently fitted cavity ratios. Cavity profiles of different annealing conditions were compared and cross-checked by transmission electron microscopy. A strategy for the ellipsometric evaluation was proposed to reduce the computation time and the probability of getting in local minima using complex models with numerous parameters. High sensitivity on the angle of incidence was found, and the choice and the determination of the angle of incidence were discussed.

Ion implantation induced buried disorder studied by Rutherford Backscattering Spectrometry and Spectroscopic Ellipsometry

Abstract In this study, the damage created by ion implantation of N + 2 ions into single crystalline 〈100〉 silicon is characterized using Rutherford Backscattering Spectrometry (RBS) and Spectroscopic Ellipsometry (SE). Samples were implanted at room temperature with ion energy of 400 keV to create buried disorder RBS and channeling techniques with 1.5 MeV He + ions were used in the experiments.

Ellipsometry on ion implantation induced damage

The optical properties of semiconductors largely depend on the disorder in the crystal structure, especially in the photon energy range near the direct interband transition energies. The E1 and E2 critical point (CP) energies in silicon are about 3.4 eV (∼365 nm) and 4.2 eV (∼295 nm), respectively. These transitions are located in a photon energy range that is available in most commercial spectroscopic ellipsometers, which makes ellipsometry a powerful technique for the characterization of ion implantation-caused damage. Due to the absorption peaks at the CP energies the optical penetration depth is small. For example, in silicon it is about 10 nm and 5 nm at photon energies corresponding to the E1 and E2 CP energies, respectively. It means that current trends towards shallower junctions and lower ion implantation energies make ellipsometry even more sensitive to the near-surface crystal structure, and the sensitivity of depth profiles can further be increased preparing special samples for the measurements using wedge masks. Ellipsometry measures the complex reflectance ratio of the sample in form of a pair of ellipsometric angles (ψ,Δ) that can accurately be measured using commercial ellipsometers. It is more and more important to use proper optical models to evaluate the measured spectra. There are two key points when evaluating ellipsometric spectra measured on ion implanted semiconductors: (i) the parameterization of the dielectric function of disordered material and (ii) the parameterization of the damage depth profile. The dielectric function can be characterized using numerous methods including the generalized critical point model, the standard critical point model, and the model dielectric function. The depth profile can be described using coupled half-Gaussian profiles or error functions. Because ellipsometry is a non-invasive and non-destructive method, it is capable of the measurement of decreasing disorder in situ, during annealing in a vacuum chamber or a furnace. It has also been demonstrated that ellipsometry is a powerful tool for a quick and non-destructive mapping of large surfaces using special optical arrangements and proper optical models. Using this tool, it is possible to map the lateral homogeneity of the dose, to map the thickness of thin surface layers and any other near-surface properties that can be described by proper optical models.

Advanced optical model for the ellipsometric study of ion implantation-caused damage depth profiles in single-crystalline silicon

Damage depth profiles have been investigated by spectroscopic ellipsometry (SE) using an improved optical model for the evaluation. Damage created by ion implantation of Ar/sup +/ ions into single crystalline silicon was characterized using SE and Rutherford backscattering spectrometry (RBS). To create buried disorder, Ar/sup +/ ions with an energy of 100 keV were implanted into the samples. Ion doses of 4.65/spl times/10/sup 14/ cm/sup -2/ and 6.75/spl times/10/sup 14/ cm/sup -2/ were used. In our optical model, the damage profile is described by sublayers with thicknesses inversely proportional to the slope of the profile, in contrast to the earlier model having equal thicknesses. The thicknesses of the sublayers are automatically calculated from the four parameters of the coupled half-Gaussian profile, while the number of the layers are held constant. The improved fit quality and the results of measurements made by RBS and transmission electron microscopy basically supported the optical model of SE.