Electrical and backscattering measurements of arsenic implanted silicon

Measurements of doping concentration and mobility of arsenic implanted silicon at high energies and at low energies with following drive-in diffusion are presented. The electrical measurements are compared with and supported by backscattering measurements. Tails which are present after short time anneals vanish during drive-in diffusion. A temperature of at least 825°C is required to fully activate the arsenic and to obtain the same mobility as in diffused samples. Backscattering data reveal an anomaly in the annealing behavior of the damage. After prolonged annealing As shows some accumulation at the surface. For drive-in diffusions lattice location experiments were performed.     

Electrical properties of silicon implanted with boron ions of MeV energy

Abstract

A knowledge of the interaction energy between two atoms as a function of their separation is important in many aspects of radiation damage theory. Recent calculations of this energy from first principles are reviewed in this article, particular attention being paid to calculations based fin the Thomas-Fermi and Thomas-Fermi-Dirac statistical theories of the atom. The advantages and limitations of these theories are discussed from the radiation damage point of view. The energy ranges over which experimental results or theoretical calculations are more useful at present are also discussed.     

Flash-lamp annealing of boron implanted silicon

Structure and impurity behaviour of silicon doped by B⁺ ion implantation up to dose of 2 × 10¹⁵ ion/cm² have been investigated after lamp pulse annealing. It has been demonstrated that the implanted layer structure strongly depends on the implantation dose, light energy density, as well as the crystallographic orientation. The optimal annealing result in the structure, which is equivalent to that obtained in the thermal treatment, The impurity diffusive redistribution proved to be rather weaker then in the case of thermal treatment.     

Range parameters of boron implanted into silicon

The range parameters of boron in silicon have been measured using the¹⁰B(n,α)⁷ Li-nuclear reaction. The results indicate that the distributions can be perfectly modeled using Pearson IV distributions with 4 moments. The range is very well described by theoretical calculations, whereas the higher moments show a strong deviation from theory.     

Electrical properties of indium implanted silicon

Electrical conductivity and Hall effect were measured from 100° to 278°K as a function of layer removal to determine the indium ionization energy and the presence of compensating centers resulting from the implantation of indium into silicon. The implants were fully annealed to reduce the influence of radiation damage. For comparison, similar measurements were performed on silicon shallow diffused with indium. Differential analysis methods were used to compute carrier concentration, mobility, and resistivity for the stripped layers. In addition, Hall measurements were performed on silicon uniformly doped with indium. In all three cases an indium energy level of 160 meV was observed. Mobility plots versus temperature were also consistent. However, significant compensation effects were noticed in the implants.     

Damage dependent electrical activation of boron implanted silicon

The important role of damage dependent electrical activation in the case of boron implanted silicon layers is whown by comparing measured acceptor concentration profiles in differently amorphized silicon layers. It is shown that the amorphous layer is completely recrystallized after a 650° C anneal for 10 min and the implanted boron is electrically active. In the heavily damaged but not amorphous region underneath the amorphous layer the implanted boron is hardly electrically active after this temperature treatment. At higher annealing temperatures the electrical activity increases, but 900° C are required for complete activation of the implanted boron. These results indicate that the process to activate the implanted boron electrically is strongly damage dependent. We thus found a new contribution to the understanding of the annealing behavior of implanted layers.     

Free-running ruby laser annealing of boron implanted silicon

An analytical treatment of the thermal phenomena during free-running ruby laser annealing of boron implanted silicon is presented. The heat equation was solved for a simplified shape of the pulse train consisting of a uniform succession of triangular spikes, identical in energy. During one spike the optical and thermal parameters of the sample were taken constant, but for each new spike, new values of these parameters were calculated taking into account their temperature dependence. Such a model predicts the melting of the top surface before the laser pulse has ended, for energy densities higher than 9×10⁴ J/m². RHEED confirms the presence of recristallization at about the same value of the laser-pulse energy densities.     

High concentration effects of ion implanted boron in silicon

The diffusion behaviour of implanted boron in silicon was investigated using the¹⁰B(n,α)⁷ Li nuclear reaction. An anomalous behavior with a strong reduction of the diffusivity above an effective solubility limit at 1.5×10¹⁹, 6×10¹⁹, and 1.1×10²⁰ cm⁻³ was found for annealing temperatures of 800, 900, and 1,000°C, respectively.     

Simulation of boron diffusion during low-temperature annealing of implanted silicon

Modeling of ion-implanted boron redistribution in silicon crystals during low-temperature annealing with a small thermal budget has been carried out. It was shown that formation of “tails” in the low-concentration region of impurity profiles occurs due to the long-range migration of boron interstitials.     

Electron irradiation assisted annealing of boron and phosphorus implanted silicon layers

Radíatíon annealing due to a 1.0 MeV election beam of intensity 25 μA/cm² was studied in silicon samples implanted with phosphorus and boron ions and annealed at 350–500°C. A significant annealing enhancement as compared to thermal annealing has been observed in phosphorus-implanted samples. In boron-implanted samples, a fast initial rise of electrical activity is followed by a continuous decrease of carrier concentration. The results are interpreted in terms of two competing processes: electron irradiation induced removal of post-implantation defects and introduction of simple electrically active defects.     

The effect of annealing ambient on carrier recombination in boron implanted silicon

The selection of either an oxidising or inert ambient during high temperature annealing is shown to affect dopant activation and electron–hole recombination in boron implanted silicon samples. Samples implanted with B at fluence between 3 × 10¹⁴ cm^–2 to 3 × 10¹⁵ cm^–2 are shown to have lower dopant activation after oxidation at 1000 °C compared to an equivalent anneal in an inert ambient. In addition, emitter recombination is shown to be up to 15 times higher after oxidation compared with an inert anneal for samples with equivalent passivation from deposited Al₂O₃ films. The observed increase in recombination for oxidised samples is attributed to the enhanced formation of boron‐interstitial defect clusters and dislocation loops under oxidising conditions. It is also shown that an inert anneal for 10 minutes at 1000 °C prior to oxidation has no significant impact on sheet resistance or recombination compared with a standard oxidation process.

     

Channeling study of boron implanted silicon: Liquid nitrogen temperature implantation

Silicon samples have been boron implanted at 150 keV at liquid nitrogen temperature to a dose of 3.6 × 10¹⁵/cm². This dose rendered the implanted layer amorphous as viewed by helium ion backscattering. Four kinds of room temperature measurements were made on the same set of samples as a function of the isochronal annealing temperature. The measurements made were the determination of the substitutional boron content by the channeling technique using the B¹¹(p, α) nuclear reaction, observation of the disorder by helium ion backscattering, determination of the carrier concentration by van der Pauw Hall measurements, and the sheet resistivity by four point probe measurements. These measurements are compared with results from samples implanted at room temperature. The carrier concentration correlates well with the substitutional boron content for both room temperature and liquid nitrogen temperature implantations. Following annealing temperatures in the 600 to 800°C range, a much larger percentage of the boron lies on substitutional lattice sites, and therefore the carrier concentration is larger, if the implantation is done at liquid nitrogen temperature rather than at room temperature. Following liquid nitrogen temperature implantation, reverse annealing is observed from 600 to 800°C in the substitutional boron content, carrier concentration and sheet resistivity. The boron is more than 90 per cent substitutional after annealing to 1100°C for both the room temperature and liquid nitrogen temperature implantations. The low temperature implantation produced a buried amorphous layer, and this layer was observed to regrow from both the surface and substrate sides at approximately equal rates.     

Thermal redistribution of boron implants in bulk silicon and SOS type structures

The redistribution of boron profiles in bulk silicon and SOS (silicon-on-sapphire) type structures is investigated in this paper. Experimental data on thermally redistributed profiles are correlated with predictions based on a computer program whose numerical algorithm was described in an earlier paper. Three cases were considered which involved the thermal redistribution of 1) a high dose (2×10¹⁵ and 5×10¹⁴ cm^–2) 80keV boron implant in (111) bulk silicon, in an oxidizing ambient of steam at 1000°, 1100°, and 1200°C, respectively; 2) a high dose (2.3×10¹⁵ cm^–2) 25 keV boron implant in (100) silicon-on-sapphire, in a nonoxidizing ambient of nitrogen at 1000 °C; and 3) a low dose (3.2×10¹² cm^–2) 150 keV boron implant in (100) bulk silicon, in oxidizing and nonoxidizing ambients that make up the fabrication schedule of an-channel enhancement mode device. For all three cases the overall correlation of computer predictions with experimental data was excellent. Correlations with experimental data based on SUPREM predictions are also included.     

Fast transient capacitance measurements for implanted deep levels in silicon

The present diffraction problem is solved by means of a perturbation calculus in the transition conditions and by repeated application of the method of steepest descent to two-dimensional Fourier integrals. We obtain a reflection coefficient for the rough surface resulting in a geometrical-optics approximation for the space wave field strength. In the case of a periodic roughness profile the application of the method of steepest descent in the transform space can be avoided and we get the electromagnetic field through differentiation of the Bromwich potentials. The numerical results of the two methods are discussed in the case of a one-dimensional cosine profile. We show that the influence of the earth's roughness increases with increasing receiver heights and fixed receiver distance. On the other hand, we point out that the geometric optical approach is a rather good approximation for the space wave field strength.     

Electrical conductivity,absorption and luminescence measurements in cubic boron nitride

Electrical and optical measurements were carried out on tiny crystals of cubic boron nitride. The dark current i_D was found to change exponentially with T, with activation energies in the range 0·2–0·4 eV. A red electroluminescence, of intensity i_EL. proportional to i_D was observed. Upon illumination at low temperatures a photocurrent i_p proportional to the square root of the excitation intensity appeared. It varied exponentially with T, with an activation energy of 0.05 ± 0.01 eV. The crystals exhibited a red thermoluminescence with several unresolved peaks covering the temperature range 100–400K, and having activation energies in the range 0·15–0·40 eV.     

Analysis of UV-Laser induced oxidation of implanted silicon by optical reflectivity measurements

The oxidation of ion implanted silicon induced by a repetitive excimer laser working in liquid phase regime has been monitored by a simple in situ technique. It consists to follow the optical reflectivity at the wavelength 633 nm of the silicon samples under irradiation. The influence of implantation and laser irradiation conditions on the oxidation process has been investigated by this technique. The results obtained have been compared using infrared absorption data. The role of the Si/SiO₂ interface roughness on the oxide film quality has been studied.     

Low energy boron implantation profiles in silicon from junction depth measurements

Some methods have been recently developed to investigate the distribution of implanted ions in semiconductors, especially into silicon. Generally, these techniques are not valid for boron due to the absence of convenient radioactive isotopes, or to a too small sensitivity when the lower part of the distribution is of interest. This corresponds to our problem, since boron implanted nuclear particle detectors prepared with high resistivity material (up to 50,000 ω.cm) are needed. The properties of these P-N junctions depend in a certain amount on the impurity distribution existing several orders of magnitude below the top of the distribution. Therefore, only the junction location method can be employed. In this method a series of N-type silicon samples, differing each from the other by an increase in resistivity are implanted with boron. The depth of the P-N junction corresponds to the point of the profile where the concentration N_A is equal to that of the substrate N_D (i.e. this latter being well known from the resistivity of the starting material). If the location of the junction can be measured, the profile can then be constructed point by point. The junction location is visualized generally by copper staining. Roosild,⁽¹⁾ Kleinfelder,⁽²⁾ Fairfield⁽³⁾ and D. E. Davies⁽⁴⁾ have used this procedure for boron implantations at energies higher than 50 keV. There is a problem due to the small penetration of the boron ion, and, for high resistivity materials, it is difficult to know the true limits of the zones stained with copper.

In our problem, when heavy particle detectors are desired, it is necessary to implant at lower energies than those indicated previously (< 20 keV). We have developed a new technique derived from the junction depth method, which is useful even at very low implant energy (≈ 10 keV). It consists in measuring the energy loss by 100 keV protons when crossing the entrance window of the P-N junctions used as detectors.

In the first part of this paper the method is described and the possible errors are analyzed and evaluated. In the second part, the distribution of 15 keV boron ions implanted under several experimental conditions is studied. Emphasis is given to the defects resulting from the silicon bombardment.