Antimony In Silicon Research Articles

Specific features of doping with antimony during the ion-beam crystallization of silicon

A method of doping during the growth of thin films by ion-beam crystallization is proposed. By the example of Si and Sb, the possibility of controllably doping semiconductors during the ion-beam crystallization process is shown. A calibrated temperature dependence of the antimony vapor flow rate in the range from 150 to 400°C is obtained. It is established that, an increase in the evaporator temperature above 200°C brings about the accumulation of impurities in the layer growth direction. Silicon layers doped with antimony to a concentration of 1018 cm–3 are grown. It is shown that, as the evaporator temperature is increased, the efficiency of the activation of antimony in silicon nonlinearly decreases from ~100 to ~10–3.

THE EFFECT OF DOPANT DOSE LOSS DURING ANNEALING ON HEAVILY DOPED SURFACE LAYERS OBTAINED BY RECOIL IMPLANTATION OF ANTIMONY IN SILICON

The aim of our investigation is focused on studying the effect of dopant dose loss during annealing treatments on heavily doped surface layers, obtained by recoil implantation of antimony in silicon. We are interested particularly by the increase of sheet resistance consequently to the shallow junctions obtained at the surface of substrate and the contribution of the dopant dose loss phenomenon following the high concentration of impurities at the surface. In this work, we report some quantitative data concerning the dopant loss at the surface of silicon implanted and its dependence with annealing treatments. Electrical measurements associated with Rutherford backscattering (RBS) technical analysis showed interesting values of sheet resistance compared with classical ion implantation and despite dopant dose loss phenomenon.

Ab initiocalculations for point defect clusters with P, As, and Sb in Si

We present results of ab initio calculations for point defect clusters with phosphorus, arsenic, and antimony in silicon, including mixed clusters. We show that these dopant species interact, modifying their diffusion and activation. Most importantly, mixed clusters can exist in similar concentrations as pure clusters, reducing the fraction of active dopants. Furthermore, we analyze the influence of cluster composition on the configurations and energetics. Phosphorus and arsenic atoms take similar roles in the cluster configurations, whereas antimony leads to different configurations. The binding to self-interstitials is weaker for As than for P and weaker for Sb than for As. The binding to a vacancy is stronger for As than for P and stronger for Sb than for As. For all clusters with one vacancy and up to four dopant atoms, the constant binding energy per dopant atom is $\ensuremath{-}1.17\text{ }\text{eV}$ for P, $\ensuremath{-}1.27\text{ }\text{eV}$ for As, and $\ensuremath{-}1.34\text{ }\text{eV}$ for Sb. Finally, we derive reaction enthalpies from the calculated formation energies and discuss the implications for dopant diffusion and activation.

Diffusion of antimony in silicon in the presence of point defects

We have investigated the diffusion of Sb in Si in the presence of defects injected by high-energy implantation of Si ions at room temperature. MeV ion implantation increases the concentrations of vacancies, which induce transient-enhanced diffusion of Sb deposited in Si. We observed a significant enhancement of Sb diffusion. Secondary ions mass spectroscopy has been performed on the implanted samples before and after annealing. Rutherford-backscattering spectrometry has been used to characterize the high-energy implantation damage. By fitting diffusion profiles to a linear diffusive model, information about atomic scale diffusion of Sb, i.e. the generation rate of mobile state Sb and its mean migration length were extracted.

低真空下における電子ビーム溶解法によるシリコン中リンおよびアンチモンの除去

The removal of phosphorus and antimony from molten silicon under low vacuum conditions has been investigated by using a glow discharge electron gun. The gun could generate electron beam and melt silicon at the low vacuum of 5-7 Pa. Phosphorus and antimony in silicon were evaporated and removed from silicon by the electron beam melting: the concentration of phosphorus decreased from about 200 ppm to about 1 ppm in one hour and that of antimony was reduced from about 300 ppm to below 0.1 ppm in 5 minutes. The removal rates obtained at the low vacuum were almost the same as those observed under high vacuum conditions.

Effect of the tilt angle on antimony in silicon implanted wafers

A dose of 5.0×1014 antimony (Sb+) ions cm−2 was implanted into silicon wafers at an energy of 70 keV, at different tilt angles (0°, 15°, 30°, 45°, and 60°). One set of samples was preamorphized with 160 keV germanium (Ge+) ions with a dose of 1×1015 cm−2. The second set consisted of implants into single crystal silicon. After implantation the samples were annealed at 700 °C for 30 s in a pure nitrogen ambient. Secondary ion mass spectroscopy was performed to evaluate the atomic profile and the retained dose as a function of the tilt angle before and after annealing. Rutherford backscattering spectroscopy and ion channeling measurements were performed to quantify the retained dose and the subtitutional fraction of antimony in the preamorphized and crystalline samples. Hall measurements were performed in order to calculate the proportion of the dopant which was electrically active. It was found that the substitutional fraction was a function of the tilt angle for all of the implanted samples. A correlation was also found between the electrical activation and the subtitutional fraction with the highest electrical activation being found at 15° tilt (90% for antimony implants into crystalline silicon) and 0° tilt (94% for antimony implants into amorphous silicon). For all implant angles the substitutional fraction and dopant activation was greater for the implants into amorphized silicon than for those into the crystalline phase.

Diffuse x-ray scattering and transmission electron microscopy study of defects in antimony-implanted silicon

Ion implantation followed by laser annealing has been used to create supersaturated and electrically active concentrations of antimony in silicon. Upon subsequent thermal annealing, however, these metastable dopants deactivate towards the equilibrium solubility limit. In this work, the formation of inactive antimony structures has been studied with grazing incidence diffuse x-ray scattering, and transmission electron microscopy, and the results are correlated to previous high-resolution x-ray diffraction data. We find that at a concentration of 6.0×1020 cm−3, small, incoherent clusters of radius 3–4 Å form during annealing at 900 °C. At a higher concentration of 2.2×1021 cm−3, deactivation at 600 °C occurs through the formation of small, antimony aggregates and antimony precipitates. The size of these precipitates from diffuse x-ray scattering is roughly 15 Å in radius for anneal times from 15 to 180 seconds. This value is consistent with the features observed in high-resolution and mass contrast transmission electron microscopy images. The coherent nature of the aggregates and precipitates causes the expansion of the surrounding silicon matrix as the deactivation progresses. In addition, the sensitivity of the diffuse x-ray scattering technique has allowed us to detect the presence of small clusters of radius ∼2 Å in unprocessed Czochralski silicon wafers. These defects are not observed in floating zone silicon wafers, and are tentatively attributed to thermal donors.

ANTIMONY DIFFUSION IN SILICON GEMANIUM ALLOYS UNDER POINT DEFECT INJECTION

Antimony diffusion in in-situ doped strained Si 0.9 Ge 0.1 epitaxial layers, subjected to point defects injection by rapid thermal anneal in oxygen atmosphere, was investigated as a function of temperature at range from 890°C to 1000°C. In this work, the effect of point defect injection on the diffusion of antimony in silicon and silicon-germanium alloys has confirmed the predominant mechanism for diffusion of Sb in Si and SiGe to be vacancy mediated. Diffusivities were obtained using computer simulations. Activation energies were calculated while the diffusivity of antinomy in SiGe under point defect injection as a function of temperature was presented.

Fraction of Interstitialcy Component of Phosphorus and Antimony Diffusion in Silicon

The effect of nitride films on the diffusion of phosphorus and antimony in silicon has been investigated, in order to extract the fractional interstitialcy component of these dopant diffusion. Nitride film deposited on silicon substrate is used as an extrinsic source of vacancies. The phosphorus diffusion is retarded and the antimony diffusion is enhanced in silicon under nitride films. By observing the variation of the retardation in phosphorus diffusion and the enhancement in antimony diffusion, it is determined that the fraction of interstitialcy component in phosphorus and antimony diffusion is approximately 0.96 and 0, respectively.

Simulation of redistribution of donor impurity in silicon during rapid thermal annealing with regard for percolation effect

Abstract A model for the impurity redistribution in heavily doped silicon layers suggested by Mathiot and Pfister6 is modified. Two channels of impurity diffusion are taken into account: a redistribution of impurity inside of a percolation cluster and a standard diffusion outside of that cluster. The parameters of the model are identified for the case of rapid thermal annealing of antimony in silicon. The modified model better describes the observed diffusivity dependences on temperature and doping level.

Infrared resonance excitation of δ-layers-a silicon-based infrared quantum-well detector

The resonant excitation of sub-bands in the self-consistent potential well formed by a δ-layer of antimony in silicon has been measured. The density-tuneable resonance of a single δ-layer has an absorption strength of the order of 50%. The expected splitting of the quantum states into two different sub-band ladders, caused by the multi-valley property of silicon, is obtained. Good agreement with self-consistent calculations can be obtained if an additional background of deep levels near the δ-layer is assumed. An IR detector concept is discussed.

The effect of phosphorus background concentration on the diffusion of tin, arsenic and antimony in silicon

The effect of phosphorus background concentration on the diffusion of tin, arsenic and antimony in silicon has been studied for phosphorus concentrations between about 9 × 10 19 and 5 × 10 20 cm −3 , corresponding to 10 ⪅ n/n i ⪅ 60 . The effective diffusion coefficients are found to be proportional to high power of n/n i for all three impurities. These results are discussed within the framework of the percolation model.

Investigation on the electrically inactive antimony at thermal equilibrium in silicon

We report the results of concentration profile measurements performed to determine the amount of electrically inactive antimony in silicon for a carrier density close to the equilibrium value n e (i.e. the one corresponding to equilibrium with precipitates). No measurable amount of inactive antimony could be detected and this supports the conclusion that the n e values we reported previously correspond to the dopant solubility.

Equilibrium Carrier Density and Solubility of Antimony in Silicon

The equilibrium solid solubility of antimony in silicon was determined in the range 850°–1300°C by carrier density measurements on polysilicon films doped by ion implantation. Up to 1150°C this property follows very tightly the exponential dependence with and . The values at higher temperatures show a smaller increase, the figures at 1200°, 1250°, and 1300°C being , respectively. The attainment of the two‐phase equilibrium was confirmed by carrier profile measurements on isothermally annealed single‐crystal specimens doped in a wide range of concentrations, as well as by TEM examinations which detected a high density of particles having the hexagonal structure of antimony. It is shown that the new solubility values, unlike the previous ones, fully comply with the conditions for phase equilibrium. According to this treatment, the values of 0.58 eV and of are deduced for the partial molar enthalpy and, respectively, for the excess partial molar entropy of the dopant in silicon relative to the standard liquid state of antimony.

Steady-state solubility of substitutional impurities in silicon

A theoretical approach in impurity solubility calculations for semiconductor crystals is developed. The steady-state solubility of boron, phosphorus, arsenic, and antimony in silicon at 900 to 1200 °C is experimentally investigated and compared to the previously published values. Thermodynamic parameters related to impurity interaction in silicon matrix are derived from the correct experimental data. [Russian Text Ignored].

Two-dimensional modeling of ion implantation with spatial moments

We present a two-dimensional model of ion implantation which allows for position dependent lateral moments. The lateral standard deviation and the lateral kurtosis as a function of depth have been calculated by 2-D Monte-Carlo simulations for boron, phosphorus, arsenic, and antimony in silicon for energies in the range of 10–300 keV. The lateral moments as a function of depth and energy as well as the vertical moments as a function of energy have been fitted by simple formulae. We specify two types of distribution functions the parameters of which can be adjusted to given values of standard deviation and kurtosis. In this way the depth dependent lateral moments can be included into analytical distribution functions.

Mixing of phosphorus and antimony ions in silicon by recoil implantation

The mixing of two different ion species by recoil implantation has received considerable interest recently because the technique appears to be an attractive way of modifying the surface properties of an ion-implanted region. By recoil implantation, one could introduce almost any two ion species simultaneously into a substrate and study their respective properties or any mutual interactions. Possible applications are in the formation of low Schottky barrier contacts [1, 2] and in the formation of high-low homojunctions. This work examined the effects of mixing phosphorus and antimony in silicon by recoil implantation. The main purpose was to investigate the electrical properties after ion mixing and to compare the results with those achieved using other techniques. By investigating the annealing behaviour, we also studied the different degrees of activation. (1 00>-oriented p-type silicon was used in this work. It was supplied by Wacher Chemitronic. The resistivity was between 10 and 20f~cm. The wafers were first cleaned using standard IC cleaning procedures and rinsed dry prior to metal deposition. An Edwards E-beam evaporator was used and the thickness of the deposited layer was monitored using a quartz crystal. The film thickness should be uniform within + 1 0 % . A Varian 200-1000 ion implanter was used and the beam energy was set at 120 keV. Phosphorus was used as the ion source and the dosage was varied from 1 x 1014 to 2 × 1016 cm 2. After recoil implantation, the metal film, antimony in this case, was removed using a mixed solution of HNO3 : HC1 : H20 (1 : 1 : 1). Isochronal annealing was carried out in a nitrogen atmosphere for 30 rain durations. The annealing temperature was between 600 and 1100 ° C. Sheet resistance was measured using the standard four-point probe technique. Fig. 1 shows a typical plot of how the sheet resistance of the recoil implanted silicon samples varied with annealing temperature. The results were for samples with four different antimony thicknesses. The phosphorus dosage was 1 x 1015 cm -2. The data for samples with an antimony thickness of less than 20 nm showed no appreciable difference and the magnitudes are in basic agreement with the results reported by Dearnaley et al. [3]. From the figure, it is apparent that more than one effect influences the annealing characteristics. Fig. 2 shows the sheet resistance of the samples as a function of the implant dosage when the samples are annealed at different temperatures. The annealing time was set at 30 min. Only the results from two different types of samples were shown. The solid curves are for samples without a surface antimony layer and the dotted curves are for samples coated with 80nm antimony. The observed linear relationships for the samples with no antimony indicated that the sheet resistance has a similar power dependence on the implant dosage and that the annealing temperature (from 700°C upwards) only affected the degree of carrier activation. At very high dosages, saturation effects were observed at the lower annealing temperatures. The antimony recoil implanted samples exhibited similar behaviour when the annealing temperature was above 1000°C indicating most probably the same type of activation behaviour as the directly implanted samples. The sheet resistances were somewhat higher because of the scattering of the phosphorus ions by the antimony layer. Note the difference in the slopes between the samples annealed at 800°C and those annealed above 1000 ° C. Figs 1 and 2 clearly demonstrate the effects of antimony recoil implantation in silicon. The initial decrease of the sheet resistance with increasing anneal-

The nature of electrically inactive antimony in silicon

Supersaturated solutions of substitutional, electrically active Sb in 〈100〉 silicon single crystals have been obtained by ion implantation, followed by short-duration incoherent-light annealing. Substitutional and nonsubstitutional fractions have been studied as functions of implanted dose and anneal temperature by Rutherford backscattering and channeling techniques, transmission-electron microscopy, Hall-effect and resistivity measurements (combined with layer removal), and Mössbauer spectroscopy. The maximum electrically active concentration, which can be incorporated on undisturbed substitutional sites, is found to be 4.5×1020 Sb/cm3 for 700 °C annealing. Upon further annealing, the supersaturated solution is reduced and approaches the Trumbore solubility value at temperatures of about 1100 °C. The Sb going out of solution is shown for the first time to be created in two different surroundings: Sb is predominantly found in Sb-vacancy complexes for low doses and low annealing temperatures and in Sb precipitates for high doses and/or high annealing temperatures. Complete agreement is found between substitutional fractions derived from Mössbauer spectroscopy and electrically active fractions from Hall-effect measurements, whereas the substitutional fractions from channeling measurements are significantly higher. The experiments are not conclusive as to whether this difference is due to the fraction of Sb in Sb-vacancy complexes or in coherent Sb precipitates.

Supersaturation of antimony in silicon by vitreous carbon strip heater annealing

Abstract A description is given of a simple vitreous carbon strip heater for transient annealing of ion- implanted semiconductors. Antimony-implanted silicon samples (0.4–5.8 × 1015 cm−2 at 35 or 80 keV) were annealed for 15–600 s at temperatures in the range 650–910°C. Annealing was confirmed by Rutherford backscattering and electrical measurements. Supersaturated solid solutions of Sb in Si were observed with a maximum solubility of 1.0 × 1021 Sb cm−3 at 650°C. Electrical measurements appear to give solubilities lower than those determined by backscattering.

Formation of partially coherent antimony precipitates in ion implanted thermally annealed silicon

Thermal annealing of a supersaturated solid solution of antimony in silicon results in the formation of partially coherent antimony precipitates. Transmission electron microscopy and microdiffraction studies show the precipitates to be bounded by {112} Si surfaces with the {111} Si and {1̄012} Sb planes coherent across the interface. The role of dislocations in the growth of the precipitates is discussed.