Diffusion of zinc into ion implanted iron doped indium phosphide

A study has been made on the diffusion of zinc into iron-doped InP slices which have been previously implanted with various ion species. Chemical profiles of zinc and iron and hole profiles have been measured. The profiles depend strongly on the implanted ion species (argon, oxygen, fluorine, chlorine). The results cannot be attributed solely to radiation damage, but suggest the chemical influence of the particular ion species on the zinc diffusion mechanism. During the indiffusion of zinc from the surface to the bulk, there is, in the same time, a diffusion of iron in an opposite direction. The rearrangement of the iron distribution is mainly due to the presence of zinc impurities.     

Hydrogen implanted silicon oxidation

The oxidation rate and the oxide thickness of the hydrogen ion implanted silicon wafers were examined. It was observed that the native oxide thickness is higher for the H⁺ implanted Si(100) compared to the Si(111). Also the native oxide thickness depended on the implanted hydrogen distribution. The thickness increased with the hydrogen con-centration. The oxide thickness after wet oxidization of the H⁺ implanted Si(111) was higher than that of the unimplanted wafers. The oxide thickness also depended on the resistivity of the H⁺ implanted Si wafers. The suggested explanation is that in high energy H⁺ implanted Si the oxidation rate is higher as a result of the higher diffusion and reaction kinetics. All these measurements were done with the assumption that the implanted and the unimplanted samples have the same indices of refraction for the oxide as well as for the substrate.     

Transient-enhanced diffusion in shallow-junction formation

Shallow junctions are formed in crystalline Si by low-energy ion implantation of B⁺, P⁺, or As⁺ species accompanied by electrical activation of dopants by rapid thermal annealing and the special case of spike annealing. Diffusion depths were determined by secondary ion-mass spectroscopy (SIMS). Electrical activation was characterized by sheet resistance, Hall coefficient, and reverse-bias diode-leakage measurements. The B⁺ and P⁺ species exhibit transient-enhanced diffusion (TED) caused by transient excess populations of Si interstitials. The electrically activated fraction of implanted dopants depends mainly on the temperature for B⁺ species, while for P⁺ species, it depends on both temperature and P⁺ dose. The relatively small amount of diffusion associated with As⁺ implants is favorable for shallow-junction formation with spike annealing.     

Polymers as masks for Ion implantation

Polymers such as polyimides and photoresists, commonly used in semiconductor processing, have been investigated as high resolution masks for ion implantation. Thin films consisting of these materials were subjected to various implant doses of H⁺, Ne⁺ and Ar⁺ ions and the post implantation surface morphologies investigated. Polyimides maintained their integrity under severe H⁺ and Ne⁺ implant doses as high as 2.4 × 10¹⁶ cm⁻² and 1.0 × 10¹⁶ cm⁻², respectively, whereas photoresists began to degrade at implant doses of 9.6 × 10¹⁵ cm⁻² and 1.9 × 10¹⁵ cm⁻², respectively. When polyimide was H⁺ implanted with doses up to 10¹⁶ cm⁻² its dielectric constant and breakdown strength remained unchanged at 3.5 and 150 V/μm, respectively. However, a gradual increase in the dielectric constant was observed for doses above this level. It was also observed that under the influence of H⁺ implants with beam current densities exceeding 10⁻⁷ A-cm⁻² a hardening of the polyimide occurs, resulting in reduction of the etching rate in an O₂ plasma. The stopping powers of various polymers for H⁺ implants have been measured. The results show that the experimental energy loss rate for protons in these materials lies between 75–100 keV/μm.     

Comparison of Mg and Zn gate implants for GaAs n-channel junction field effect transistors

Zinc and magnesium implants into GaAs were profiled with secondary ion mass spectroscopy and etching capacitance-voltage to measure the as-implanted and annealed profiles for the eventual formation of shallow p⁺/n junction gates for junction field effect transistors (JFETs). The larger mass of the zinc ions results in shorter projected range with significantly less tailing than magnesium implants. High dose, shallow zinc implants annealed under tungsten gate metal showed good activation with negligible diffusion. The improved profile of the zinc implant, as compared to a similar magnesium implant, allowed a tighter JFET design with increased performance. Zn gated n-channel enhancement mode GaAs JFETs with 0.9 μm gate lengths showed transconductances up to 200 mS/ mm with a f_t of 18 GHZ and a f_max of 37 GHz. The performance of these self-aligned fully implanted JFETs compare favorably with comparably sized implanted MESFETs.     

The behaviour of boron molecular ion implants into silicon

Implants of boron molecular ions into silicon have been studied using a variety of experimental techniques, but with emphasis on sheet resistance annealing characteristics and transmission electron microscopy. Boron halide compound molecules have been implanted and equivalent dose sequential implants of atomic species used as control conditions. The implants studied were B⁺, BCl₂⁺, BCl⁺, Cl⁺ + B⁺, BF₂⁺, BF⁺ and B⁺ + F⁺ at 25 keV/B atom and B⁺, BBr₂⁺ and Br₂⁺ + B⁺ at 12 keV/B atom.The implantation of molecular ions enables conditions of varying damage to be studied with constant dose, dose rate and energy of the dopant species. In addition to damage effects the halogen atoms produce species effects in the implanted zone. The escape of the halogen atoms has been measured as a function of the annealing temperature.The significant differences which exist between the behaviour of silicon implanted with these various conditions are considered with reference to the damage structures observed by transmission electron microscopy. The boron-fluorine molecular implants are shown to offer some advantages as a means of implanting boron.     

Damage related deep electron levels in ion implanted GaAs

A study has been made of the deep electron levels in semi-insulating GaAs implanted with either ⁷⁸Se⁺ or ²⁹Si⁺ ions and rendered n-type by subsequent annealing without encapsulation in partial pressures of arsenic or arsine. Three implantation related deep states were detected with concentration profiles approximating to the type of Gaussian distributions expected for point defects related to ion implantation damage. Further heat treatment of the samples at 500°C in a gas ambient of N₂/H₂ substantially reduced concentrations of these deep levels. Two of these states were thought to be related to displacements of the substrate atoms. The third, at E_c − 0.67 eV, was found in only ⁷⁸Se⁺ ion implanted GaAs substrates and was thought to be a defect involving both Se and As atoms, rather than intrinsic lattice disorder. It is proposed that the annealing rate of these implantation related deep levels depends crucially on the in-diffusion or creation of arsenic vacancies during heat treatments.     

Zinc diffusion in tellurium doped gallium antimonide

Zinc diffusion into tellurium doped gallium antimonide, GaSb, has been carried out as a function of time, temperature, and antimony over-pressure. Total zinc profiles as well as carrier concentration profiles have been measured. Results favor a substitutional-interstitial vacancy (Frank-Turnbull)¹ or kick-out (Gösele-Morehead)² mechanism, although there is insufficient evidence to conclusively distinguish between them. There is also an inverse dependence of the diffusivity on antimony over-pressure, this is discussed in terms of zinc diffusion superimposed on gallium vacancy diffusion. Tellurium doping seems to have little effect on the diffusion because of its low level in comparison to that of zinc. Furthermore, at high zinc concentrations, the profiles indicate an additional component associated with a non-electrically active zinc species which has a small, strongly temperature dependent diffusion coefficient.     

Rapid thermal annealing of magnesium implanted GaAs-GaAIAs heterostructures experimental and simulated distributions

The use of rapid thermal annealing (RTA) techniques to anneal ion implanted GaAs compounds is expected to have a significant impact on device technology. Due to the short duration of the heat treatment, the implanted impurities may be activated without significant diffusion. For heterojunction bipolar transistor (HBT) applications, high doses of p-type impurities are required to compensate the doping levels of N-GaAlAs emitter and n⁺ GaAs contact layers. Multi-implantations were chosen to maintain a flat profile down to the base layer. Energies of 30, 60, 150, and 340 keV with doses of 6 × 10¹³, 9 × 10¹³,6 × 10¹⁴, and 9 × 10¹⁴ cm⁻², respectively, have been used. Annealing cycles with time durations of a few seconds and temperature in the range of 850–950°C are described. Electrical properties of the annealed samples have been investigated using an electrochemical measurement technique. It was found that hole concentrations as high as 4 × 10¹⁹ cm⁻³ and electrical activities near to 75 percent can be obtained. There is no evident indiffusion and no significant outdiffusion at the optimal annealing conditions. Simulation of multilayer implantations are also carried out by an accurate model available in TITAN 2D process simulator using Pearson IV laws and taking into account the diffusion effects on profile distribution caused by RTA. A first approximation using a simple model allows a rapid evaluation of the data fitting operation. In a second approach, concentration dependent diffusivity and the contribution of the electric field at the interface are covered to perform an improved data fitting of ion implanted and annealed dopant profiles. A comparative study shows a good agreement between experimental and simulated distributions.     

Optimization of RTA parameters to produce ultra-shallow, highly activated B+, BF 2 + , and As+ ion implanted junctions

The effects of time, temperature, ramp-up, and ramp-down rates with rapid thermal annealing employing a STEAG AST SHS3000 were investigated on 1.0 and 2.0 keV ¹¹B⁺, 2.2, 5.0, and 8.9 keV ⁴⁹BF ₂ ⁺ , and 2 KeV ⁷⁵As⁺, 1E15/cm² samples implanted in a Varian VIISion-80 PLUS ion implanter at 0^o tilt angles. These annealed samples were analyzed by four-point probe, secondary ion mass spectrometry (SIMS), and in select cases by spreading resistance profiling (SRP) and transmission electron microscopy (TEM). To ensure reproducibility and to minimize oxidation enhanced diffusion as an uncontrolled variable, the O₂ background concentration in N₂ was maintained at a controlled low level. Under these conditions, ramp-rates alone were found not to be significant. Spike anneals (1050°C, ～ 0 s) with fast ramp-rates (240°C/s) and fast cool down rates (86°C/s) provided the shallowest junctions, while still yielding good sheet resistance values. Post annealed samples were examined for extended defect levels (by TEM) and trapped interstitial concentrations. Fluorine concentration measurements were employed to qualitatively explain differences in the B diffusion from ¹¹B⁺ and ⁴⁹BF ₂ ⁺ ion implants at various energies. The 2.2 keV ⁴⁹BF ₂ ⁺ “fast” spike annealed sample at 1050°C exhibited limited, if any, enhanced diffusion, yielding a SIMS junction depth of 490Å, an electrical junction of 386Å (by SRP) and a sheet resistance of 406 ohm/sq.     

Cubic Perovskite Fluoride as Open Framework Cathode for Na‐Ion Batteries

Exploring novel structure prototype and mineral phase, especially open framework material, is crucial to developing high‐performance Na‐ion battery cathodes in view of potentially faster intrinsic diffusion of Na⁺ in lattices. Perovskite phases have been widely applied in solar cells, fuel cells, and electrocatalysis; however, they are rarely attempted as energy storage electrode materials. This study proposes pre‐expanding perovskite iron fluoride (KFeF₃) framework by stuffing large‐sized K⁺ as a channel filler, which is advantageous over Na⁺, NH₄⁺, and H₂O molecule filler in terms of structure robustness, symmetry, and connectivity. K⁺ stuffing leads to the preservation of a more “regular” cubic phase with fast isotropic 3D diffusion as a consequence of no distortion of FeF₆ octahedra during K‐Na electrochemical exchange and following Na‐insertion cycling. High‐rate Na‐storage is achievable with a reversible capacity of 110, 70, and 40 mAh g^?1 at 0.1, 2, and 10 C, respectively, for this open framework fluoride cathode, benefiting from solid solution electrochemical behavior and high intrinsic diffusion coefficient. It is thought that this rate performance is currently the best among Na‐storage fluoride materials.     

The electrical characteristics of InP implanted with the column IV elements

A study of the electrical characteristics of InP implanted with C, Si, Ge and Sn demonstrates that all of these column IV elements are donors, although the net electrical activation achieved with the light ion C was only about 5%. Samples implanted at temperatures of 150–200°C generally had lower sheet resistivities, higher mobilities and except for high doses, higher sheet carrier concentrations than those done at room temperatures. Implants at 150–200°C with 1 × 10¹⁴cm^?2 of the heavier ions, Si, Ge or Sn, resulted in layers with sheet carrier concentrations of 7.8 × 10¹³, 5.6 × 10¹³ and 4.7 × 10¹³cm^?2, respectively. Carrier concentration profiles of samples implanted at 200°C with 1 × 10¹⁴cm^?2 of Si agreed reasonably well with LSS theory. Higher doses gave rise to substantial diffusion of the implanted Si, whereas room temperature implants showed poor activation near the surface.     

Superhydrophilic All-pH-Adaptable Redox Conjugated Porous Polymers as Universal and Ultrarobust Ion Hosts for Diverse Energy Storage with Chemical Self-Chargeability

Herein, a new fibrous conjugated microporous polymer bearing phenazine species (PNZ-CMP) is reported as a universal and ultrastable electrode to host various mono- and multi-valent charge carriers for diverse aqueous rechargeable cells combining rapid kinetics, ultralong lifespan, and chemical rechargeability. The porous cross-linked structure, interconnected donor-acceptor network, and readily accessible active sites endow PNZ-CMP with highly-reversible redox activity, superhydrophilicity, facile electron transport, high ion diffusion coefficient, and all-pH-adaptability (−1 to 15) in aqueous electrolytes. Thus, adopting PNZ-CMP electrodes enables good compatibility with H⁺/Li⁺/Na⁺/K⁺/Zn²⁺/Al³⁺ ions and fast surface-controlled redox reactions for diverse aqueous battery chemistry. Multiple PNZ-CMP-based full cells show superior electrochemical performance especially ultralong lifespan, e.g., ≈84% capacity retention over 200 days for K⁺, ≈100% over 127 days for Zn²⁺, and ≈76% over 47 days for anion-coordinated Al ions, surpassing small molecule counterparts and most previously-reported corresponding systems. The spontaneous redox chemistry of reduced phenazine species with O₂ is first explored to render PNZ-CMP with repeatable chemical self-chargeability in four electrolytes. Especially in 0.05 m H₂SO₄, an accumulative discharge capacity up to 48505 mAh g⁻¹ is achieved via facile self-charging, which can originate from the “reactive antiaromaticity to stable aromaticity” conversion of the redox moieties as revealed by theoretical studies.     

Boron implantation and epitaxial regrowth studies of 6H SiC

Implantation of B has been performed into an epitaxially grown layer of 6H SiC, at two different B concentrations, 2×10¹⁶ cm⁻³ and 2×10¹⁸ cm⁻³. Subsequently, an epitaxial layer was regrown on the B implanted layer. The samples were investigated by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). In the highly B-doped layers plate-like defects were found, associated with large strain fields, and an increased B concentration. These defects were stable at the originally implanted region during regrowth and at anneal temperatures up to 1700°C. In the samples implanted with the lower B concentration, no crystal defects could be detected by TEM. No threading dislocations or other defects were observed in the regrown epitaxial layer, which shows the possibility to grow a layer with high crystalline quality on B implanted 6H SiC. By SIMS, it was found that B piles up at the interface to the regrown layer, which could be explained by enhanced diffusion from an increased concentration of point defects created by implantation damage in the region. B is also spread out into the original crystal and in the regrown layer at a concentration of below 2×10¹⁶ cm⁻³, with a diffusion constant estimated to 1.3×10⁻¹² cm²s⁻¹. This diffusion is most probably not driven by implantation damage, but by intrinsic defects in the grown crystal. Our investigation shows that the combination of implantation and subsequent regrowth techniques could be used in SiC for building advanced device structures, with the crystal quality in the regrown layer not being deteriorated by crystal defects in the implanted region. A device process using B implantation and subsequent regrowth could on the other hand be limited by the diffusion of B.     

Rapid thermal diffusion of zinc into GaAs

Rapid thermal diffusion of zinc into semi-insulating GaAs from spin-on Zn doped silica film was performed. Spin-on films act both as Zn diffusion sources and GaAs surface encapsulant layer against decomposition during the rapid thermal diffusion. The very shallowp ⁺ layers were obtained at a diffusion temperature of 900° C for 5 sec. Non-alloyed ohmic contacts to thesep ⁺ layers were achieved with an average contact resistivity of 2.4 × 10⁻⁶ Ω cm². The interface is very smooth. The zinc diffusion coefficient for rapid thermal diffusion with effective diffusion time of 6 sec at 900° C was numerically calculated from SIMS profiles. In contrast to the common Longini-Weisberg-Blanc model, the rapid thermal diffusion is under nonequilibrium condition. Complications due to interstitial-substitutional nonequilibrium, vacancy supply resulted from the interface stress field, and zinc precipitation are briefly discussed.     

Beryllium and sulfur ion-implanted profiles in gaas

Atomic profiles of ion-implanted Be and S in GaAs have been measured as a function of implant fluence and annealing temperature. Concentration versus depth profiles were ob-tained by means of secondary ion mass spectrometry (SIMS) techniques. Pyrolytically deposited and sputter-coated Si0₂ and Si₃N₄ films were used as encapsulants for the 500 to 900° annealing study. Semi-insulating GaAs was implanted with 200 keV³⁴S⁺ to fluences of 1 × 10¹⁴ and 5₂× 10¹⁴/cm², and 100 keV⁹Be⁺ in the 1 × 10¹³ to 1 × 10¹⁵/cm² fluence range. The S profiles did not change significantly after annealing at 800°C, although there was some skewing after annealing above 600°C. In contrast, the Be profiles showed significant changes and a decrease in the peak concentration for the ≥ 5 × 10^T4/cm² implants after a 700°C anneal. After a 800°C anneal the Be profile was essentially flat with a monotonic decrease from the surface into the implanted re-gion and a 900°C anneal caused a further decrease in the Be concentration. Profiles of Be implants of ≤ 1 × 10¹⁴/cm² did not change significantly after annealing indicating that the higher fluence cases were related to solubility effects. This work supported by the Naval Electronic Systems Command and the Office of Naval Research.     

Holmium redistribution upon solid-phase epitaxial crystallization of amorphized silicon layers

Concentration profiles of Ho were investigated after annealing at a temperature of 620°C of silicon layers implanted with 1-MeV Ho⁺ ions to doses of 1?3×10¹⁴ cm^?2 exceeding the amorphization threshold, as well as with O⁺ ions with energies that ensure the coincidence of the concentration maxima of implanted impurities and doses that are greater by an order of magnitude than those of Ho⁺. The crystallization of the amorphized silicon layer occurs by the mechanism of solid-phase epitaxy. The main features of the segregation redistribution of Ho are shown to be similar to the previously studied segregation behavior of Er. An increase in the Ho concentration at the initial stage of the solid-phase epitaxial crystallization is explained by the small rate of mass transfer through the amorphous layer-single crystal interface. An analytical expression was obtained to describe the variation of the segregation coefficient in the process of solid-phase epitaxial crystallization, including its initial stage, which allows the calculation concentration profiles of rare-earth elements.     

The electrical properties of zinc diffused indium phosphide

The electrical properties of p-type layers of InP, formed by the diffusion of zinc into n-type material, are studied. A wide range of diffusion conditions are used and both homogeneously doped specimens and those containing a zinc atom concentration gradient are produced. The impurity atom distribution of the diffused crystals is characterised by radiotracer analysis. p?n junction measurements on non-homogeneously doped specimens indicate that the number of zinc atoms in a diffused layer is much greater than the number of shallow acceptors. This non-correspondence of atom and carrier concentrations is confirmed by four point resistivity, Hall effect and capacitance-voltage measurements. The first two of these techniques are used to produce carrier concentration profiles which are compared with corresponding radio-tracer profiles. The carrier profiles are achieved by both serial sectioning and multiple specimen techniques. A gold probe point contacting procedure is developed for the Hall Effect measurements from which a plot of carrier mobility versus carrier concentration, in the range 5 × 10¹⁸ – 5 × 10¹⁹cm^?3, is produced for p-type InP.     

Breakdown in concentration profile diodes

Reverse breakdown capability or a concentration profiled p⁺ n n⁺ diode depends upon the surface concentration at the contra and the edge region. To study the effect of various concentration profiles on the breakdown capability, the electric field distribution in the semiconductor and the dielectric is theoretically computed. These theoretical computations are compared with the experimentally determined values. Extremely high breakdown voltages have been achieved in plane p⁺ n n⁺ junctions using this technique. The desired concentration profiles are achieved using spin-on sources for boron diffusion. These sources require a curing time, alter preparation, to yield reproducible uniform impurity eurfece concentration. To study the stj-ucturoJ changes taking place in the liquid phase during the curing time, IR spectra of the liquid spin-on source are presented. It is concluded that the interaction between B-O and Si-OH in the liquid phase is responsible for achieving uniform surface concentration, Further, if concentration profiling is used for reducing the surface electric field, one can eliminate the mechanical bevelling or chemical etching step.     

Electrical activity of iodine-diffused CdTe

The electrical activity of iodine in CdTe is discussed when iodine is introduced into the CdTe by diffusion from the vapour phase. It is compared both with the total concentration of iodine in the diffused CdTe slices and with the electrical activity in CdTe slices which have been annealed under Cd- and Te-saturated vapour pressures. Iodine-diffused slices of CdTe were profiled by secondary ion mass spectrometry (SIMS) to obtain the total iodine concentration and by capacitance-voltage (C-V) techniques to obtain the net concentration of electrically active iodine. After annealing with iodine in the form of Cdl₂, the slices were p-type, similar to those obtained when CdTe was annealed in either excess Te or Cd vapour, and they showed no significant increase in electrical activity. If Cd was added to the Cdl₂ diffusion source or the CdTe was given a subsequent anneal in cadmium vapour, the slices became n-type. The results indicated that in all cases a neutral layer composed of Cd _nI_m (m and n are integers) formed on the surface layers, whereas if Cd was involved in the diffusion, some of the iodine existed in an electrically active form deeper into the slice with a maximum concentration of active carriers given by N_D - N_A ≈ 10¹⁷ cm⁻³. © 1997 John Wiley & Sons Ltd.