E. Jároli

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 ...

Thickness‐dependent formation of Gd‐silicide compounds

Gd‐silicide phases were investigated by x‐ray diffraction. The results showed that not only one phase exists in a Gd thin‐film and silicon substrate reactions. The first phase formed was hexagonal GdSi≊1.7, the second orthorhombic GdSi2. The ratio of the two phases depends on temperature of the heat treatment, and at a given temperature and time of annealing, a dependence of the thickness of the evaporated Gd layer was found. At ∼100‐nm Gd thickness the dominant phase was orthorhombic GdSi2, at ∼250 nm hexagonal GdSi≊1.7. In the 300–1000‐nm interval orthorhombic GdSi2 was the main component again. Rutherford backscattering analysis showed that the phases were found mixed within the layer. This thickness‐dependent formation could be described with a simple model proposed by Gosele and Tu [J. Appl. Phys. 53, 3252 (1982)].Gd‐silicide phases were investigated by x‐ray diffraction. The results showed that not only one phase exists in a Gd thin‐film and silicon substrate reactions. The first phase formed was hexagonal GdSi≊1.7, the second orthorhombic GdSi2. The ratio of the two phases depends on temperature of the heat treatment, and at a given temperature and time of annealing, a dependence of the thickness of the evaporated Gd layer was found. At ∼100‐nm Gd thickness the dominant phase was orthorhombic GdSi2, at ∼250 nm hexagonal GdSi≊1.7. In the 300–1000‐nm interval orthorhombic GdSi2 was the main component again. Rutherford backscattering analysis showed that the phases were found mixed within the layer. This thickness‐dependent formation could be described with a simple model proposed by Gosele and Tu [J. Appl. Phys. 53, 3252 (1982)].

Investigation of ion-implanted semiconductors by ellipsometry and backscattering spectrometry

Abstract Ion-implanted silicon and GaP were investigated by ellipsometry and channelling effect measurements to determine the validity of the Bruggeman thoery for partially amorphous layers. It was found that the effective medium approximation (EMA) gives a satisfactory description of the disordered layer for heavy ions and low doses. The thickness of the disordered layer and the degree of amorphousness are independent parameters and can be determined from ellipsometry alone. Low dose nitrogen implantation is cited as an example of the limitations of EMA.

Epitaxy of orthorhombic gadolinium disilicide on 〈100〉 silicon

Epitaxial orthorhombic GdSi2 was grown by in situ vacuum annealing of a 50‐nm Gd layer on 〈100〉 silicon. The epitaxy was proved by x‐ray diffraction, electron diffraction, and ion channeling measurements. The lattice mismatch between the orthorhombic GdSi2 and 〈100〉 silicon substrate was found to be 4%.

Nondestructive determination of damage depth profiles in ion-implanted semiconductors by multiple-angle-of-incidence single-wavelength ellipsometry

Abstract Four-parameter fitting of multiple-angle-of-incidence (MAI) ellipsometry data is developed to characterize near-surface layers on semiconductors damaged by implantation. We used coupled half-Gaussians to describe the damage depth profiles. The method was tested on Ge-implanted silicon layers (at a wavelength of 632.8 nm) and was cross-checked with high depth resolution RBS and channeling.

Optical properties of thermally stabilized ion implantation amorphized silicon

We have investigated the optical properties of thermally stabilized, ion implantation amorphized silicon by ellipsometry in the wavelength region 632.8–365.0 nm during solid phase epitaxial regrowth (SPEG) process. The Si wafers were amorphized by implantation of Si, P and Xe ions in the 40–700 keV energy region. Furnace annealing was done at 550°C for different times. It was found that the optical properties (complex dielectric function and complex refractive index) of the thermally stabilized amorphous silicon are between those of the as-implanted and monocrystalline silicon. We propose a very simple fine-grain polycrystalline model for thermally stabilized silicon with a grain size of about or less than 2 run.

Investigation of solid phase epitaxial regrowth on ion-implanted silicon by backscattering spectrometry and ellipsometry

Abstract During solid phase epitaxial regrowth (SPEG) of ion-implanted silicon the thickness of the remaining amorphous layer decreases with increasing annealing time. This amorphous layer is optically different from the as-implanted one in the wavelength region of 1–10 μm. We have investigated the thermally stabilized state by ellipsometry at a wavelength of 632.8 nm. To establish an appropriate optical model and to check the thickness data obtained from ellipsometry. we used high depth resolution backscattering spectrometry combined with channeling (BS). Using special arrangements in backscattering spectrometry such as glancing detection and 16O(α, α)16 elastic nuclear scattering, we were able to construct realistic optical models both for amorphization and recrystallization experiments. The complex refractive index for as-implanted amorphous silicon is 4.63-0.76i and for thermally stabilized silicon is 4.55-0.35i. The thickness data of amorphous layers obtained by ellipsometry are in good agreement with values deduced from BS.

The effect of ion beam treatment and subsequent annealing on Au/GaAs contacts

The effect of Xe++ and Ar+ ion beam treatment and subsequent annealing on the Au (55 nm)/n‐GaAs system was studied using cross‐sectional transmission electron microscopy. The maximum depth of observed defects caused by Xe++ ions (700 keV, 1×1014 ions/cm2) was about 400 nm from the interface in excellent agreement with the results of capacitance‐voltage measurements. The formation of about 50‐nm‐thick polycrystalline region of GaAs was observed. The ion beam treatment resulted in the formation of defects (stacking faults, twins) down to a depth of 200 nm measured from the interface. Between 200 and 400 nm depth dislocation loops were formed. Amorphization has not been observed. The sharp Au/GaAs interface has been only slightly destroyed in the as‐implanted sample. In contrast to pits in unirradiated samples, large flat grains of Au(Ga) solid solution grown into the highly damaged region of GaAs were found in the samples annealed at 450 °C after the ion beam treatment. The formation of a regrown GaAs cover...

Effect of ion beam treatment on thermal annealing of GaAs-Au layer structures

Comparison of thermal annealing and ion mixing + thermal annealing on (100) GaAs-Au evaporated layers was made. The structures were investigated by SEM, X-ray diffraction, RBS + channeling and AES. Phase formation is retarded by ion implantation both for Ar and Xe, interdiffusion, however, is enhanced for Xe. Phases, as β-phase and GaAu2, were detected. An anomalous interdiffusion was found after low-dose Xe mixing, as gold penetration was deeper for 400°C post-annealing than for 500°C. Current-voltage characteristics of the diodes show that implantation procedure brings them nearer to ohmic behavior. Electrical measurements also point to a decrease of the number of defects as the annealing temperature increases up to 475°C in contrast to thermal annealing only [1].

Charge carrier lifetime modification in silicon by high energy H+ or He+ ion implantation

Abstract H + or He + was implanted at energies of 1, 2.5 and 4 MeV into n-type 〈100〉 4–7.5 Ω cm CZ-Si with doses in the range from 3 × 10 10 /cm 2 to 1 × 10 12 /cm 2 . A reduction in minority carrier lifetime was measured by the microwave photoconductive decay (μ-PCD) method using a 904 nm laser pulse. It was shown that the modified lifetime can be directly measured by μ-PCD when the damaged region and the excess charge pocket generated by the laser pulse exactly overlap. This was the case for 4 MeV H + implantation. For shallower defects, the measured lifetime value is influenced by the diffusion process of excess minority carriers. To extract the real lifetime in this case, a three layer model is presented.