Transformation of electrically active defects as a result of annealing of silicon implanted with high-energy ions

Deep-level transient spectroscopy is used to study both the concentration profiles of defects introduced into silicon during the implantation of 14-MeV boron ions and the transformation of these defects as a result of subsequent annealing at temperatures in the range from 200 to 800°C. It is ascertained that implantation gives rise to a standard set of vacancy-containing radiation defects (the oxygen-vacancy and phosphorusvacancy complexes and divacancies) and to a center with the level located at E _c − 0.57 eV. Heat treatments at temperatures of 200–300°C bring about the disappearance of all vacancy-containing complexes at a distance from the surface h > 12−9 μm. Most likely, this phenomenon is caused by the decomposition of interstitial-containing complexes located at a depth h > 12−9 μm and their annihilation with the vacancy-containing complexes. Heat treatments at higher temperatures bring about both a further narrowing of the layer that still contains the vacancy-type defects to h ≈ 6 μm at 500°C and a change in the set of observable electrically active centers in the temperature range from 400 to 500°C. Specific features of the annealing of radiation defects after high-energy ion implantation are caused by spatial separation of the vacancy-and interstitial-containing defects. Original Russian Text ? I.V. Antonova, S.S. Shaĭmeev, S.A. Smagulova, 2006, published in Fizika i Tekhnika Poluprovodnikov, 2006, Vol. 40, No. 5, pp. 557–562.     

Ion implanted GaAs varactor diodes: capacitance uniformity

Gallium arsenide varactor diodes with low series resistance (~0.25 ?) for u.h.f. t.v. tuners are developed. Uniformity and reproducibility of diode capacitance is improved markedly by using improved ion implantation and l.p.e. techniques. The standard deviation of diode capacitance distribution is 0.74% at V = 3.0 V within a wafer. A good r.f. tracking characteristic can be obtained in varactor tuners.     

Photoluminescence in silicon implanted with silicon ions at amorphizing doses

Luminescent and structural properties of n-FZ-Si and n-Cz-Si implanted with Si ions at amorphizing doses and annealed at 1100°C in a chlorine-containing atmosphere have been studied. An analysis of proton Rutherford backscattering spectra of implanted samples demonstrated that an amorphous layer is formed, and its position and thickness depend on the implantation dose. An X-ray diffraction analysis revealed that defects of the interstitial type are formed in the samples upon annealing. Photoluminescence spectra measured at 78 K and low excitation levels are dominated by the dislocation-related line D1, which is also observed at 300 K. The peak position of this line, its full width at half-maximum, and intensity depend on the conduction type of Si and implantation dose. As the luminescence excitation power is raised, a continuous band appears in the spectrum. A model is suggested that explains the fundamental aspects of the behavior of the photoluminescence spectra in relation to the experimental conditions.     

Properties of silicon implanted with boron ions through thermal silicon dioxide

The properties of silicon implanted with boron ions through thermal SiO₂ films were studied using sheet resistivity measurements (corroborated by Hall data). Electrical properties for implants through 0.1 μm of SiO₂, as compared to bare silicon, showed no unusual behavior as a function of anneal temperature. Sheet resistivity measurements as a function of SiO₂ thickness for fixed ion energy, and as a function of energy for fixed oxide thickness were made after 525 and 925°C anneals, for boron doses of 10¹³, 10¹⁴ and 10¹⁵ ions/cm². The profile of boron ions in SiO₂ is near Gaussian for the energy range investigated and the stopping power is 0 to 20% lower than the theoretical value currently in the literature. Considerations for device manufacture are discussed in light of the results.     

Breakdown and capacitance properties of hyperabrupt epitaxial Schottky barrier diodes

An analysis of the breakdown and capacitance properties of punch-through hyperabrupt epitaxial Schottky barrier diodes has been carried out. Results are given for the dependence of breakdown voltage of such a device on surface concentration and epitaxial layer thickness. Design curves are given for epitaxial hyperabrupt schottky varactor diodes. The design procedure yields an optimal impurity profile in which just-punch-through occurs at the highest voltage of operation. This gives a maximum dynamic range of operation still keeping the series resistance to a minimum. A corrected boundary condition to determine the profile constants associated with an n/n⁺ (high/low) junction is also given.     

Electrical properties of silicon layers implanted with ytterbium ions

It is ascertained that implantation of 1-MeV ytterbium ions with a dose of 10¹³ cm^?2 into silicon with subsequent annealing at temperatures of 600–1100°C gives rise to donor centers. The donor-center concentration is higher in the samples implanted additionally with oxygen ions. The results show that at least two types of donor centers are formed; these centers contain either ytterbium or oxygen impurity atoms. The dependence of electron mobility on the concentration of electrically active centers in the silicon layers implanted with the ytterbium rare-earth ions is determined in the concentration range of 7×10¹⁵–10¹⁷ cm^?3.     

Shot noise in silicon Schottky barrier diodes

Noise measurements have been performed on forward and reverse-biased silicon Schottky barrier diodes. Measurements were performed in the frequency range of 100 Hz to 50 kHz. Apart from excess noise observed for some diodes in a portion of this frequency range, the noise for the diodes was found to be in excellent agreement with shot-noise theory. Some refinements of the shot-noise theory have been considered, but the difference between the refined and the simple theories was not resolvable in our measurements. A useful noise-measurement technique is described.     

RF burnout dependence on variation in barrier capacitance of mixer diodes

A novel scheme to measure the VSWR and the "phase variation" of mixer diodes at high RF power levels is described. This experimental test system provides a nondestructive way of determining the power-handling capability of a mixer diode and also serves as an important tool in improving the burnout performance of point contact and Schottky barrier diodes.     

Relaxation of a defect subsystem in silicon irradiated with high-energy heavy ions

The relaxation of a silicon defect subsystem modified by the implantation of high-energy heavy ions was studied by varying the electrical properties of irradiated Si crystal annealed at a temperature of 450°C. It is shown that quenched-in acceptors are introduced into Si crystals as a result of irradiation with comparatively low doses of Bi ions and subsequent relatively short annealing (no longer than 5 h); the distribution of these quenched-in acceptors has two peaks located at a depth of about 10 μm and at a depth corresponding approximately to the ions’ projected range (43.5 μm). The peaks in the distribution of quenched-in acceptors correspond to the regions enriched with vacancy-containing defects. As the heat-treatment duration increases, the acceptor centers are transformed into donor centers with the centers’ spatial distribution remaining intact. Simultaneously, an almost uniform introduction of quenched-in donors occurs in the entire crystal beyond the depth corresponding to the projected range of ions. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 5, 2003, pp. 565–569. Original Russian Text Copyright ? 2003 by Smagulova, Antonova, Neustroev, Skuratov.     

Photoluminescence in silicon implanted with erbium ions at an elevated temperature

Photoluminescence spectra of n-type silicon upon implantation with erbium ions at 600°C and oxygen ions at room temperature and subsequent annealings at 1100°C in a chlorine-containing atmosphere have been studied. Depending on the annealing duration, photoluminescence spectra at 80 K are dominated by lines of the Er³⁺ ion or dislocation-related luminescence. The short-wavelength shift of the dislocation-related luminescence line observed at this temperature is due to implantation of erbium ions at an elevated temperature. At room temperature, lines of erbium and dislocation-related luminescence are observed in the spectra, but lines of near-band-edge luminescence predominate.     

Investigation of double barrier MOS tunnel diodes with PECVD silicon quantum well

Double barrier metal-oxide-semiconductor tunnel diodes with ultrathin PECVD Si and thermal SiO₂ layers were fabricated. The measured capacitance-voltage and current-voltage characteristics were interpreted and physical parameters of the structures were extracted by means of a theoretical model.     

Behavior of various silicon Schottky barrier diodes under heat treatment

Variations of Schottky forward voltage with heat treatment have been observed for AlPd₂Si Si and Si-doped AlPd₂Si Si Schottky barrier diodes. These variations have been reduced to a minimum by the use of a barrier metal such as TiW between Al and the silicided contacts.     

Negative annealing in silicon after the implantation of high-energy sodium ions

The implantation of sodium ions with an energy of 300 keV is carried out into high-resistivity p-Si. The annealing of defects at T _ann = 350–450°C and related activation of atoms (the latter occurs at the “tail” of atom distribution) are described by a first-order reaction. At T _ann = 450–525°C and irrespective of the ion dose, negative annealing is observed; this annealing is accompanied by an appreciable increase in the surface resistance ρ _s . According to estimations, the activation energy of this process amounts to ~2 eV. It is our opinion that the annealing is related to the precipitation of sodium donor atoms, which occurs at a depth exceeding by two–three times the projected range R _p of ions. The annealing of defects at T _ann = 525–700°C, which leads to a further decrease in ρ _s , features an activation energy of ~2.1 eV. The hypothesis that the “tail” in the profiles of sodium atoms measured by secondary-ion mass spectroscopy is due to the diffusion of these atoms from the walls of the crater to its center is verified. It is shown that this process is not implemented since the profiles of sodium atoms measured at room temperature do not differ from those measured at–140°C.     

Study of the distribution profile of iron ions implanted into silicon

Iron ions with energies of 90 and 250 keV and a dose of 10¹⁶ cm^–2 are implanted into a silicon single crystal with the (110) orientation. The method of Rutherford backscattering in combination with channeling is used to study the distribution profiles of the introduced impurity and also the profiles of the distribution of radiation-induced defects in the crystal lattice. Experimental data are compared with the results of simulation performed using the TRIM software package. It is shown that, at an energy of 4.6 keV/nucleon, the average projected ranges coincide; however, at an energy of 1.6 keV/nucleon, the difference amounts to 35%. In addition, it is shown that the calculation incorrectly takes into account the dose dependence at energies of 1.6–4.6 keV/nucleon.     

Theory and experiment for silicon Schottky barrier diodes at high current density

Metal-silicon Schottky barrier diodes exhibit n values which theoretically vary as a function of doping and applied voltage. The expected variation depends on which theoretical model is used to describe the current transport.Titanium n-type silicon barriers were prepared. At a doping level of 3 × 10¹⁵ cm^?3 the barrier height and n-value measured at 100 mV were 0.485±0.005 V and 1.02±0.01 whereas for a doping level of 2 × 10¹⁴ cm^?3 the corresponding values were 0.500±0.005 V and 1.18±0.05.The experimental variation of the diode n value as a function of semiconductor band bending showed good agreement with the thermionic-diffusion model of Crowell and Beguwala: n values increased rapidly as the band bending β → 2, and n values were highest at a given β for diodes with the lowest doping concentration. Similar results were obtained by measurements on magnesium and aluminium barriers on n-type silicon.An analysis of the results has shown that the variation of the diode saturation current I_s follows the predictions of the thermionic-diffusion theory, although there were some anomalies at high current densities. The anomalies did not result from variation of the width of the undepleted region of the epitaxial silicon layer or from diode self-heating effects.     

Axial lifetime control in silicon power diodes by irradiation with protons, alphas, low- and high-energy electrons

Local lifetime control by proton and alpha-particle irradiation with energies from 1.8 to 12.1 MeV and doses up to 5×10¹² cm⁻² was faced with two types of electron irradiation giving the different profiles of carrier lifetime: the high-energy (4 MeV) resulting in a homogeneous lifetime distribution and the low-energy (500 and 460 keV) providing so-called sloping lifetime control. Deep and shallow levels introduced by irradiation were characterised by DLTS, HVCTS and C-V profiling and their effect on static and dynamic parameters of irradiated diodes was measured and simulated. The advantages and drawbacks of different lifetime control techniques are compared and their application aspects are discussed, as well.     

Investigations on the annealing behavior of high-energy carbon irradiated Au/n-GaAs Schottky barrier diodes

Au Schottky barrier diodes (SBDs) have been irradiated using high-energy carbon ion fluences of 1×10¹¹, 1×10¹² and 1×10¹³ cm⁻². Current–voltage characteristics of unirradiated and irradiated diodes have been analyzed. The change in reverse leakage current increases with increasing ion fluence due to the irradiation-induced defects at the interface. The diodes were annealed at 523 and 623 K to study the effect of annealing. The rectifying behavior of the irradiated SBDs improves at 523 K. But at 623 K, the diode behavior deteriorates irrespective of the fluences. Better enhancement in the barrier height and also improvement in the ideality factor of the diodes has been observed at the annealing temperature of 523 K. Scanning Electron Microscopic analysis was carried out on the irradiated samples to delineate the projected range of the defects by high-energy carbon ion irradiation.     

A pulsed synthesis of β-FeSi2 layers on silicon implanted with Fe+ ions

Continuous layers and fine-grained films of β-FeSi₂ were synthesized using the implantation of Fe⁺ ions into Si(100) with subsequent pulsed nanosecond ion-beam treatment of the implanted layers. The X-ray diffraction studies showed that the pulsed ion-beam treatment brings about the formation of a mixture of two phases: FeSi and β-FeSi₂ with strained crystal lattices. Subsequent rapid thermal annealing led to the complete transformation of the FeSi phase into the β-FeSi₂ phase with the formation of a textured layer. The data obtained using Raman spectroscopy corroborate the formation of the β-FeSi₂ phase with a high degree of silicon crystallinity. The results of measuring the optical absorption point to the formation of β-FeSi₂ layers and precipitates with a direct-gap structure, an optical gap of E _g≈0.83 eV, and an Urbach tail extent of E ₀≈220 meV. The photoluminescence band peaked at λ≈1.56 μm and caused by direct band-to-band transitions in β-FeSi₂ was observed at temperatures lower than 210 K. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 11, 2001, pp. 1320–1325. Original Russian Text Copyright ? 2001 by Batalov, Bayazitov, Terukov, Kudoyarova, Weiser, Kuehne.