Boron electrical activation in dual B+ + N+ + and B+ + Ar+ ion-implanted silicon

Silicon wafers were implanted with 40 keV B⁺ ions and then with 50 keV N⁺ or 100 keV Ar+ ions to doses from 1.2 x 1014 to 1.2 x 1015 cm^–2. The implanted samples were studied using the Hall effect and standard van der Pauw methods. The dependences of the sheet resistivity and the sheet concentration of charge carriers on the annealing temperature in the range from 700 to 1300 K were obtained. Models describing the influence of additional implantation of nitrogen and argon ions on the process of boron electrical activation during annealing are proposed.     

Some studies of BF2 and B+F implanted Silicon

Ion-implanted shallow junctions have been investigated using BE₂ (molecular ions) by the anodic oxidation method coupled with a four-point probe technique. BF₂ ions were implanted through screen oxide at doses of 3–5 × 10¹⁵ ions/cm² and energies of 25 and 45 keV which is equivalent to 5.6 keV and 10 keV of boron ions. The effect of energy, dose and annealing temperature on shallow junctions is presented in this paper. The shallow junctions in the range of 0.19 μm to 0.47 μm were fabricated.

The effect of fluorine on sheet resistivity of boron implanted silicon at various doses, treated with two-step and three-step annealing, is also presented for comparison in the paper.     

Influence of implant dose and target temperature on crystal quality and junction depth of boron-doped silicon layers

30 keV boron ions are implanted at doses of 2×10¹⁴ and 2×10¹⁵ cm^–2 in 100 silicon wafers kept at room or liquid-nitrogen temperatures. The samples are analyzed by double-crystal X-ray diffraction, transmission electron microscopy and secondary ion-mass spectrometry before and after furnace annealing at 800°C. The low-dose implant does not amorphize the substrate at any of the temperatures, and residual defects together with a remarkably enhanced boron diffusion are observed after annealing. The high-dose implant amorphizes the substrate only at low temperature. In this case, unlike the room-temperature implant, the absence of any residual defect, the incorporation of the dopant in substitutional position and a negligible profile braodening of boron are obtained after annealing. In principle, this process proves itself a promising step for the fabrication of p ⁺/n shallow junctions with good electrical characteristics.     

Optical investigation of phosphorous-ion-implantation induced InAs/GaAs quantum dots' intermixing

This work reports on InAs/GaAs quantum dots (QDs) intermixing, induced by phosphorous ion implantation and subsequent rapid thermal annealing. The implantation process was carried out at room temperature at various doses (5×¹⁰¹⁰-¹⁰¹⁴ ions/cm²), where the ions were accelerated at 50 keV. To promote the atomic intermixing, implanted samples are subjected to rapid thermal annealing at 675 °C for 30 s. Low temperature photoluminescence (PL) measurements are carried out to investigate the influence of the interdiffusion process on the optical and electronic properties of the QDs. PL emission energy; linewidth and integrated intensity are found to exhibit a drastic dependence on the ion implantation doses. The band gap tuning limit has been achieved for an implantation dose of 5×¹⁰¹³ ions/cm². However, our measurement reveals that the accumulated defects for implantation doses higher than ¹⁰¹² ions/cm² drive the system towards the degradation of the QDs structure's quality.     

Effect of implantation energy and dose on low-dose SIMOX structures

In order to form silicon (Si)-on-insulator (SOI) layers with various thicknesses, oxygen implantation with doses between 1.0×10¹⁷/cm² and 6.0×10¹⁷/cm² and at energies between 40 and 240 keV has been carried out into 300 mm diameter (100)Si wafers at a temperature of 560 °C. After implantation, Si wafers are annealed in dry Ar mixed with 1% O₂ at a temperature of 1350 °C for 4 h. The quality of buried oxide (BOX) layers and the microstructure in implanted layers before and after annealing is characterized by transmission electron microscopy. The results reveal that the appreciable number of threading dislocations (TDs) is generated in SOI layers implanted at energies above 200 keV under the optimum dose-energy conditions for the continuous BOX layer formation. Whereas, in the case of discontinuous BOX layers, the TD generation is observed in samples implanted at energies above 120 keV. The generation of TDs is discussed with the emphasis on the effect of implantation energy. PACS 61.72Ff; 61.72Lk     

Influence of annealing on the concentration profiles of boron implantations in silicon

The influence of annealing on the concentration profiles of boron implanted into silicon with does of 10¹⁴ ions/cm² up to 10¹⁶ ions/cm² and an energy of 70 keV was studied. The concentration profiles were measured with Secondary Ion Mass Spectrometry (SIMS). The broadening of the concentration profiles during annealing can be described as a superposition of effects resulting from a relatively immobile and a mobile boron fraction. The properties of the immobile boron fraction were studied by measuring the influence of a boron implantation on the distribution of a homogeneous boron background dope. From these experiments it was concluded that the immobile boron fraction consists of boron precipitates. The properties of the mobile fraction were studied from concentration profiles that were obtained after annealing during different periods at the same temperature. It was found that during the initial stage of the annealing process a fast broadening of the profile occurs; this was assumed to be due to an interstitial type boron diffusion. After prolonged annealing the much slower substitutional type diffusion prevails, due to trapping of the interstitial boron atoms by vacancies. The reliability of the SIMS method, as applied to profile measurements, was checked for the high boron doses used in this investigation. Excessive boron precipitates, obtained after annealing of a high dose, such as 10¹⁶ ions/cm² at about 1000°C, appear to give some increase of the ion yield.     

Ion dose and anneal temperature dependent studies of silicon implanted AlxGa1−xN

Electrical and optical activation studies of Al_xGa_1−xN (x = 0.11 and 0.21) implanted with silicon were made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1 × 10¹⁴ to 1 × 10¹⁵ cm⁻² at room temperature. The implanted samples were subsequently annealed from 1100 to 1300 °C for 20 min in a nitrogen environment. A maximum electrical activation efficiency of 91% was obtained for the Al_0.11Ga_0.89N implanted with the highest dose of 1 × 10¹⁵ cm⁻² even after annealing at 1150 °C. 100% activation efficiencies were successfully obtained for the Al_0.21Ga_0.79N samples after annealing at 1300 °C for both doses of 5 × 10¹⁴ and 1 × 10¹⁵ cm⁻². The mobility of the Si-implanted Al_xGa_1−xN increases with annealing temperature, and the highest mobilities are 109 and 98 cm²/V·s for Al_0.11Ga_0.89N and Al_0.21Ga_0.79N, respectively. The cathodoluminescence (CL) spectra for all the samples exhibited a sharp neutral-donor-bound exciton peak, and the CL intensity increases with annealing temperature, indicating successive improved implantation damage recovery as the annealing temperature is increased. These results provide the optimum annealing conditions for activation of implanted Si ions in Al_xGa_1−xN.     

The electrical behaviour of abrupt ion implanted and diffused P+N junctions

Abstract

Results are reported of measurements of the properties of diodes formed by ion implantation, and for comparison boron diffused P⁺N diodes of similar area close by on the same chip. The four group III acceptor impurities were implanted separately to a dose of 5 × 10¹⁵ ions/cm² at room temperature into similar samples of suitably masked silicon. Boron ions were also implanted at liquid nitrogen temperature and 450°C. Annealing was limited to a maximum temperatare of 550 °C.

Measurements have been made of sheet resistance, forward and reverse I-V characteristics (from 10^?9 amps/cm²), reverse breakdown voltage, noise, minority carrier storage time and junction series resistance.

The bulk properties of boron implanted diodes were found to be reproducible. The introduction of recombination centres by implantation is the major factor influencing variation in these properties between one implantation condition and another. Changes in surface oxide conditions probably affect reverse leakage currents and breakdown voltages.

The properties of boron implanted diodes are considered suitable for applications such as the MOSFET, and are superior to those of the AI, Ga and In implanted diodes.     

Analysis of the effect of annealing on the photoluminescence spectra of Cu ion implanted ZnS nanoparticles

In the present study, we report the photoluminescence (PL) study of nanoparticles of ZnS implanted with Cu⁺ ions at the doses of 5×10¹⁴, 1×10¹⁵ and 5×10¹⁵ ions/cm² and annealed at 200 and 300 °C. The photoluminescence spectra of the samples implanted at lower doses of 5×10¹⁴ and 1×10¹⁵ ions/cm² and annealed at 200 and 300 °C showed peaks at around 406, 418 and 485 nm. The PL emission peak at 485 nm was attributed to the transition of electrons from conduction band of ZnS to the impurity level formed by the implanted Cu⁺ ions. In the PL spectrum of the sample implanted at the highest dose of 5×10¹⁵ ions/cm², in addition to the emission peaks observed in the PL spectra of the samples implanted at lower doses, a peak at around 525 nm, the intensity of which decreased with increase in the annealing temperature, was observed. The emission peak at 525 nm was attributed to the transitions between sulfur and zinc vacancy levels. The full width at half maximum (FWHM) of the emission peak at 406 nm was observed to decrease with increase in annealing temperature, indicating lattice reconstruction. The observation of copper ion impurity related peak at 485 nm in the PL spectra of samples of the present study indicated that the doping of copper ions into the ZnS lattice is achievable by implanting Cu⁺ ions followed by annealing.     

Laser annealing of GaAs dual implanted with Si and P ions

Laser annealing of SI(100) GaAs:Cr implanted either with Si⁺ ions (150 keV, 6×10¹³-1×10¹⁵cm^–2) or dual implanted with Si⁺ ions (150 keV, 6×10¹⁴–1×10¹⁵cm^–2) and P⁺ ions (160 keV, 1×10¹⁴–1×10¹⁵cm^–2) has been examined using backscatteringchannelling technique and via electrical measurement of Hall effect. It has been found that at laser energy densities 0·8 J cm^–2 a full recovery of the sample surface occurs. In dual implanted samples (1×10¹⁵ Si⁺ cm^–2+1×10¹⁵P⁺cm^–2) up to 46% of Si atoms become electrically active after the laser annealing. Resultant Hall mobility of carriers is, however,lower than that obtained after common thermal annealing.The authors are pleased to take the opportunity of thanking Professor M. Kubát for his encouragement and continuous support. Accelerator staff is gratefully acknowledged for its assistance in the course of experiments.     

Observation of ferromagnetism at room temperature for Cr ions implanted ZnO thin films

Single crystalline ZnO films were grown on c-plane GaN/sapphire (0 0 0 1) substrates by molecular beam epitaxy. Cr⁺ ions were implanted into the ZnO films with three different doses, i.e., 1 × 10¹⁴, 5 × 10¹⁵, and 3 × 10¹⁶ cm⁻². The implantation energy was 150 keV. Thermal treatment was carried out at 800 °C for 30 s in a rapid thermal annealing oven in flowing nitrogen. X-ray diffraction (XRD), atomic force microscopy, Raman measurements, transmission electron microscopy and superconducting quantum interference device were used to characterize the ZnO films. The results showed that thermal annealing relaxed the stress in the Cr⁺ ions implanted samples and the implantation-induced damage was partly recovered by means of the proper annealing treatment. Transmission electron microscopy measurements indicated that the first five monolayers of ZnO rotated an angle off the [0 0 0 1]-axis of the GaN in the interfacial layer. The magnetic-field dependence of magnetization of annealed ZnO:Cr showed ferromagnetic behavior at room temperature.     

Crystalline quality of 3C-SiC formed by high-fluence C-implanted Si

Carbon ions at 40 keV were implanted into (1 0 0) high-purity p-type silicon wafers at 400 °C to a fluence of 6.5 × 10¹⁷ ions/cm². Subsequent thermal annealing of the implanted samples was performed in a diffusion furnace at atmospheric pressure with inert nitrogen ambient at 1100 °C. Time-of-flight energy elastic recoil detection analysis (ToF-E ERDA) was used to investigate depth distributions of the implanted ions. Infrared transmittance (IR) and Raman scattering measurements were used to characterize the formation of SiC in the implanted Si substrate. X-ray diffraction analysis (XRD) was used to characterize the crystalline quality in the surface layer of the sample. The formation of 3C-SiC and its crystalline structure obtained from the above mentioned techniques was finally confirmed by transmission electron microscopy (TEM). The results show that 3C-SiC is directly formed during implantation, and that the subsequent high-temperature annealing enhances the quality of the poly-crystalline SiC.     

Influence of surface morphology on the field emission properties of planar SiC/Si heterostructures formed by ion beam synthesis

The electron field emission properties of planar SiC/Si heterostructures with various surface morphology formed by high dose C⁺ implantation into Si using a metal vapor vacuum arc ion source were investigated. An implant energy of 35 keV was used with doses of 8×10¹⁷, 1×10¹⁸ and 1.2×10¹⁸ ions/cm⁻² with subsequent annealing in Ar at 1200 °C for various times. X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy showed that a thin stoichiometric SiC surface layer is formed and the surface work function is about 4.5 eV. Atomic force microscopy indicated that the size and density of the densely distributed small protrusions formed on the surface vary with preparation conditions. Results showed that there is an optimum annealing time for the corresponding implant dose at which a remarkably low turn-on field of about 1 V/μm is observed. The density and size of the small protrusions on the surface are believed to be the main factors affecting the field emission properties.     

Electrical measurements of boron implanted silicon on sapphire and bulk silicon

Hall effect and sheet resistivity measurements have been performed on boron implantations in 1μm silicon layers on sapphire (SOS), and in bulk silicon. The doses used were 10¹⁴, 10¹⁵ and 10¹⁶ ions/cm², and implantation energies were 150 and 300 keV. The samples were annealed at temperatures between 300 and 800°C. As a rule the effective number of carriers in SOS was found to be about twice the number of carriers in bulk silicon. However, the mobility is lower in bulk silicon, resulting in a sheet resistivity almost the same in boron implanted SOS and bulk silicon.     

Optical study of implantation damage recovery from Si-implanted GaN

Comprehensive and systematic optical activation studies of Si-implanted GaN grown on sapphire substrates have been made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10¹³ to 5×10¹⁵ cm⁻² at room temperature. The samples were proximity cap annealed from 1250 to 1350 °C with a 500-Å-thick AlN cap in a nitrogen environment. The results of photoluminescence measurements made at 3 K show a very sharp neutral-donor-bound exciton peak along with a sharp donor-acceptor pair peak after annealing at 1350 °C for 20 s, indicating excellent implantation damage recovery. The results also indicate the AlN cap protected the implanted GaN layer very well during high temperature annealing without creating any significant anneal-induced damage. This observation is consistent with the electrical activation results for these samples.     

Slow positron beam study of nitrogen implanted CZ-Si subjected to rapid thermal processing

In this experiment, nitrogen ions were implanted into CZ-silicon wafer at 100 keV at room temperature with the fluence of 5 × 10¹⁵ N₂⁺/cm², followed by rapid thermal processing (RTP) at different temperatures. The single detector Doppler broadening and coincidence Doppler broadening measurements on slow positron beam were carried out to characterize the defects in the as-implanted silicon and RTP-treated samples. It is found that both nitrogen-vacancy complexes (N-Vsi) and oxygen-vacancy complexes (O-Vsi) produced by nitrogen implantation diffuse back to the sample surface upon annealing. But the N-Vsi and the O-Vsi complete with each other and give a summed effect on positron annihilation characteristics. It is shown that the N-Vsi win out the O-Vsi in as-implanted sample and by RTP at 650 °C, 750 °C, which make the S-parameter increase; O-Vsi plays a dominant role after annealing above 850 °C, which makes the S parameter decrease.     

Ferromagnetism in ZnO doped with Co by ion implantation

The importance of doping ZnO with magnetic ions is associated with the fact that this oxide is a good candidate for the formation of a magnetic-diluted semiconductor. Most of the studies reported in Co-doped ZnO were carried out in thin films, but the understanding of the modification of the magnetic behaviour due to doping demands the study of single-crystalline samples. In this work, ZnO single crystals were doped at room temperature with Co by ion implantation with fluences ranging between 2×10¹⁶ and 1×10¹⁷ ions cm⁻² and implantation energy of 100 keV. As implanted samples show a superparamagnetic behaviour attributed to the formation of Co clusters, room temperature ferromagnetism is attained after annealing at 800 °C, but no magnetoresistance was detected in the temperature range from 10 to 300 K.     

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.     

Processing for optically active erbium in silicon by film co-deposition and ion-beam mixing

Techniques of film deposition by co-evaporation, ion-beam assisted mixing, oxygen ion implantation, and thermal annealing were been combined in a novel way to study processing of erbium-in-silicon thin-film materials for optoelectronics applications. Structures with erbium concentrations above atomic solubility in silicon and below that of silicide compounds were prepared by vacuum co-evaporation from two elemental sources to deposit 200-270 nm films on crystalline silicon substrates. Ar⁺ ions were implanted at 300 keV. Oxygen was incorporated by O⁺-ion implantation at 130 keV. Samples were annealed at 600 °C in vacuum. Concentration profiles of the constituent elements were obtained by Rutherford backscattering spectrometry. Results show that diffusion induced by ion-beam mixing and activated by thermal annealing depends on the deposited Si-Er profile and reaction with implanted oxygen. Room temperature photoluminescence spectra show Er³⁺ transitions in a 1480-1550 nm band and integrated intensities that increase with the oxygen-to-erbium ratio.