Laser annealing of Bi implanted <111> and <100> silicon

The influence of surface orientation in Bi implanted silicon, annealed by Q-switched ruby laser pulse irradiation was investigated. Depth distributions and lattice location of the Bi atoms were obtained using⁴He backscattering and channeling techniques and the electrical behavior studied by sheet resistance measurements. The dopant profiles show partial surface accumulation and in-depth broadening without influence of the substrate orientation. These profiles can be fitted by a numerical calculation based on the normal freezing model with an interfacial segregation coefficient much higher than the equilibrium one. The impurity atoms located in the in-depth profile are shown to be electrically active when their maximum concentration does not exceed 10²⁰ atoms/cm³.     

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.     

Annealing behaviour of implanted nitrogen in bulk and evaporated Ni

The diffusion coefficients of nitrogen in N-implanted polycrystalline Ni have been deduced. Both bulk and Ni-evaporated samples implanted with nitrogen were annealed at 150–500° C. The nitrogen profiles were probed using the nuclear resonance broadening technique. The value of 0.99±0.12 eV for the activation energy and (3.0 _–2.8 ⁺⁴⁰ )×10^–6 cm²/s for the frequency factor were obtained for implanted N in bulk Ni. The solubilities for both the bulk and evaporated Ni samples are given. In evaporated Ni nitrogen migration is enhanced due to the defects arising during evaporation.     

Diffusion and solubility of zinc in dislocation-free and plastically deformed silicon crystals

Floating-zone Si crystals enclosed in quartz ampoules were exposed to Zn vapour released by an elemental diffusion source. Penetration profiles of Zn in Si were recorded using the spreading-resistance technique or neutron activation analysis. Both the erfc-type distributions observed in plastically deformed specimens and the non-erfc profiles determined on dislocationfree wafers are consistently interpreted within the framework of the kick-out model. As an implication, Si self-interstitials generated in excess by interstitial-to-substitutional transitions of in-diffusing Zn atoms annihilate not only at the surface but also at dislocations. On the other hand, dislocation-induced segregation of Zn appears to be rather minor, as revealed by transition electron microscopy. Combining the Zn incorporation rate in dislocation-free Si with solubility data from saturated specimens yields the self-interstitial contribution to the Si self-diffusion coefficient.Dedicated to H.J. Queisser on the occasion of his 60th birthday     

Rapid thermal annealing of high dose arsenic-implanted silicon

A model for rapid thermal annealing of high dose arsenic-implanted silicon layers is proposed. The kinetics of arsenic clustering was taken into account. Assuming that all arsenic is initially electrically active, the clustering rate is found to be enhanced during the early stage of annealing in comparison with results reported for conventional furnace tempering [1]. An influence of a low temperature preannealing on the diffusion behaviour of arsenic has not been observed.     

Microstructure and thermal stability of Fe,Ti, and Ag implanted yttria-stabilized zirconia

Yttria-stabilized zirconia (YSZ) was implanted with 15 keV Fe or Ti ions up to a dose of 8×10¹⁶ at cm^–2. The resulting dopant concentrations exceeded the concentrations corresponding to the equilibrium solid solubility of Fe₂O₃ or TiO₂ in YSZ. During oxidation in air at 400° C, the Fe and Ti concentration in the outermost surface layer increased even further until a surface layer was formed of mainly Fe₂O₃ and TiO₂, as shown by XPS and ISS measurements. From the time dependence of the Fe and Ti depth profiles during anneal treatments, diffusion coefficients were calculated. From those values it was estimated that the maximum temperature at which the Fe- and Ti-implanted layers can be operated without changes in the dopant concentration profiles was 700 and 800° C, respectively. The high-dose implanted layer was completely amorphous even after annealing up to 1100° C, as shown by scanning transmission electron microscopy. Preliminary measurements on 50 keV Ag implanted YSZ indicate that in this case the amorphous layer recrystallizes into fine grained cubic YSZ at a temperature of about 1000° C. The average grain diameter was estimated at 20 nm, whereas the original grain size of YSZ before implantation was 400 nm. This result implies that the grain size in the surface of a ceramic material can be decreased by ion beam amorphisation and subsequent recrystallisation at elevated temperatures.     

Hydrogen implantation and diffusion in silicon and silicon dioxide

Depth profiles of hydrogen implanted into crystalline silicon in random direction at different fluences have been measured by the¹⁵N technique and by SIMS. Whereas hydrogen implanted at a fluence of 10¹⁵ ions/cm² shows some limited mobility, no such mobility is observed for higher implantation fluences. In these cases, ballistic computer codes describe the depth distributions well, within the ranges of both experimental and theoretical accuracy. Annealing up to 510 K does not change the hydrogen distributions.Furthermore, high-fluence hydrogen implantation into silicon dioxide has been examined. There is some indication for radiation-enhanced diffusion during the implantation process. Upon subsequent thermal annealing, the hydrogen is found to diffuse, probably via a trapping/detrapping mechanism associated with an OH/H₂ transformation of the hydrogen bonding.     

High-temperature diffusion of phosphorus and boron in silicon via vacancies or via self-interstitials?

The paper re-examines the effect of oxidation on the diffusion of phosphorus and boron in silicon as well as recent results on redistribution phenomena of these dopants under irradiation and on the emitter-push effect. It is shown that at high temperatures phosphorus and boron diffuse via a defect mechanism involving silicon self-interstitials. These results support the view-point that self-interstitials are the dominating point defects in silicon under thermal equilibrium conditions. Possible generation mechanisms for the self-interstitial supersaturation causing the emitter-push effect are suggested.     

Behaviour of implanted arsenic in silicon single crystals subjected to transient heating with incoherent light

The behaviour of ion-implanted arsenic in 100-oriented silicon single crystals exposed to continuous incoherent light from a xenon arc lamp has been analyzed with sheet resistivity measurements, Rutherford backscattering spectrometry, and ion channeling including angular scans. Redistribution, substitutionality, and electrical activity of arsenic were followed as functions of exposure time (6–20s) and induced temperature (1000°–1100°C). Redistribution was observed for implanted concentrations exceeding 4×10²⁰ at.%/cm³. High substitutional fractions, between 95% and 99%, and low sheet resistivities were found for all annealed samples. Formation mechanism of arsenic substitutional solid solutions during transient heating of implanted layers is discussed.     

Thermal equilibrium concentrations and effects of negatively charged Ga vacancies in n-type GaAs

We have calculated the thermal equilibrium concentrations of the various negatively charged Ga vacancy species in GaAs. The triply-negatively-charged Ga vacancy, V _Ga ^3– , has been emphasized, since it dominates Ga self-diffusion and Ga-Al interdiffusion under intrinsic and n-doping conditions, as well as the diffusion of Si donor atoms occupying Ga sites. Under strong n-doping conditions, the thermal equilibrium V _Ga ^3– concentration, , has been found to exhibit a temperature independence or a negative temperature dependence, i.e., the value is either unchanged or increases as the temperature is lowered. This is quite contrary to the normal point defect behavior for which the point defect thermal equilibrium concentration decreases as the temperature is lowered. This property provides explanations to a number of outstanding experimental results, either requiring the interpretation that V _Ga ^3– has attained its thermal equilibrium concentration at the onset of each experiment, or requiring mechanisms involving point defect non-equilibrium phenomena.     

The influence of the solubility limit on diffusion of as implants in silicon

Enhanced diffusion of implanted arsenic impurities in silicon during subsequent thermal annealing can be interpreted in terms of a system of reaction-diffusion equations. It is shown that for high doses the local solubility limit can considerably influence the reactions between the defects involved and thus markedly change the effective diffusion of As donors. A similar effect can be brought about by the presence of predoped donors/acceptors, which also can significantly accelerate/retard the effective diffusion of As implants. Furthermore, an explanation of some precipitation/clustering processes during a rapid/slow cooling-down is proposed. Finally, several contradictory experimental results published previously will be shown to be compatible with the present model.     

CW CO2-laser annealing of arsenic implanted silicon

CW CO₂-laser annealing of arsenic implanted silicon was investigated in comparison with thermal annealing. Ion channeling, ellipsometry, and Hall effect measurements were performed to characterize the annealed layers and a correlation among the different methods was made. The laser annealing was done with power densities of 100 to 640 W cm⁻² for 1 to 20 s. It was found that the lattice disorder produced during implantation can be completely annealed out by laser annealing with a power density of 500 W cm⁻² and the arsenic atoms are brought on lattice sites up to 96±2%. The maximum sheet carrier concentration of 6×10¹⁵ cm⁻² was obtained for 1×10¹⁶ cm⁻² implantation after laser annealing, which was up to 33% higher than that after thermal annealing at 600 to 900°C for 30 min.     

Diffusion of nitrogen in vanadium and niobium

The diffusion of N in the group VB metals V and Nb has been studied in the previously uninvestigated temperature range 300–500 °C using ion-beam techniques. Diffusion couples were created by ion implantation. The time-dependent diffusion profiles were monitored by the use of the Nuclear Resonance Broadening (NRB) technique. New values for the solubility of N in Nb were obtained. The diffusion rates presented support recent observations of the diffusivity of interstitial impurities in body-centered cubic metals in which positive deviations from Arrhenius behaviour have been seen at high temperatures.     

Diffusion of Al in ion-implanted Pd and Pt

The diffusion coefficients of aluminium have been measured in polycrystalline fcc Pd and Pt. The Al-implanted palladium and platinum samples were annealed at 400°–800 °C and 450°–900 °C, respectively. The aluminium profiles were probed using the nuclear resonance broadening (NRB) technique. Values of (1.41±0.09) and (1.38±0.09) eV for the activation energy and (1.5 _–1.0 ⁺⁵ )×10^–6 and (4 _–3 ⁺¹⁰ )×10^–7cm²/s for the frequency factor were obtained for Al in Pd and Pt, respectively. These anomalous results, compared to the normal impurity diffusion, were checked using also Al-evaporated samples.     

Diffusion of nitrogen in ion-implanted chromium and tungsten

The diffusion of N in the group VI B metals Cr and W has been studied in the previously uninvestigated temperature ranges 300°–550 °C (Cr) and 600°–800 °C (W) using ion-beam techniques. Diffusion couples were created by ion-implantation. The timedependent diffusion profiles were monitored by the use of the Nuclear Resonance Broadening (NRB) technique. The linear Arrhenius plots extracted from the measured diffusivities indicate that the diffusivity of implanted N in Cr and W can be described by the activation energyQ=1.39±0.06 eV and 2.32±0.16 eV and the pre-exponential factorD ₀=(7.0±7.2)×10^–4cm^2/s and 4.3±8.3cm^2/s, respectively. The solubilities of N in Cr and W from the implanted distributions were found to deviate from those obtained using conventional metallographical methods.     

Diffusion of Al in ion-implanted α-Zr and α-Hf

The diffusion of Al in the group IVa metals Zr and Hf has been studied for the first time in the temperature ranges 600°–800°C (Zr) and 750°–900°C (Hf) using ion-beam techniques. Diffusion couples were created by ion-implantation. The time-dependent diffusion profiles were monitored by the use of the Nuclear Resonance Broadening (NRB) technique. The linear Arrhenius plots extracted from the measured diffusivities indicate that the diffusivity of implanted Al in Zr and Hf can be described by the activation energyQ=2.9±0.2eV and 3.7±0.3eV and the pre-exponential factorD ₀=17±42cm²/s and 170±600cm²/s, respectively.     

Gold diffusion in silicon by Rapid Optical Annealing

Gold diffusion in silicon is investigated using Rapid Optical Annealing at temperatures in the range of 800°C to 1200°C and annealing times from 300 s down to 1 s. The resulting content of substitutional gold is determined by spreading resistance measurements and analyzed by comparison with extensive numerical simulations.The profiles obtained show a broader spectrum as compared to the U-shapes after long time diffusion. The cooling process affects the profiles significantly, since they depend on the wafer thickness. An unexpected penetration depth was found after 1200°C diffusion in thick wafers, which are subject to small cooling rates. This phenomenon is due to a special combination of reverse kick-out, deep diffusion of highly supersaturated interstitial gold, and again an incorporation in lattice sites, termed the RDI effect.Numerical calculations allow us to reproduce the experimentally observed profiles only if a sensitive balance between the different temperature dependencies is obeyed. These investigations, therefore, yield new information about the equilibrium concentration and diffusion of silicon interstitials. A best set of parameters is presented. The time constant of the kick-out process is quantified for the first time.     

Rapid thermal diffusion of aluminum in silicon and its interaction with phosphorus

Aluminum diffusion profiles in silicon were produced under rapid thermal processing conditions using a Si-sandwich structure to avoid losses of aluminum by reaction with the quartz reactor. The impact of phosphorus on the diffusion behaviour of aluminum was investigated by predeposition of P into Al-diffused wafers and vice versa. Dopant profiles were determined by SIMS (Secondary-Ion-Mass Spectroscopy), electrochemical CV-and SRP (Spreading Resistance) analysis. The resulting profiles after Al predeposition at 1293 K exhibit high Al-surface concentrations up to the solid solubility limit of about 2×10²⁵ m^–3. It is shown that phosphorus has a great influence on the drivein behaviour of Al, leading to an accelerated Al diffusion in front of the P profile (enhanced Al diffusion caused by self-interstitial supersaturation) and an up-hill migration of Al in the high-concentration regime, which can be explained by field-assisted diffusion. A strong retardation of aluminum diffusion combined with concentrations well above the solidsolubility limit was observed during the Al predeposition into P-diffused wafers.     

Annealing behaviour of ion-implanted nickel-aluminium alloy

The time evolution of the aluminium concentration profiles in ion-implanted nickel-aluminium alloys during annealing has been studied in the temperature range 550–800°C using the (p, γ) resonance broadening method. The surface enrichment of aluminium has been found to be balanced by a corresponding uniform decrease in the bulk concentration and hence the bulk concentration profiles can be described by the modified solution of the second diffusion equation, when the implanted concentration does not exceed the solubility limit. When the solubility limit is exceeded the time evolution follows the solubility controlled flow of the solutes. The dependence of the degree of surface enrichment on the extra irradiation of⁵⁸Ni⁺ before and after the aluminium implantation is demonstrated and is found to be significant only in the post-irradiation cases. This is taken as evidence of the importance of interstitials in the development of the bulk concentration profiles. The linear Arrhenius plot extracted from the measurements indicates that the diffusion of A 1 in Ni can be described by the activation energyE=2.69 eV and the pre-exponential factorD ₀=0.6 cm²/s. Solid solubilities of aluminium in nickel from the implanted distribution are found to agree with those obtained using conventional metallographical methods.     

Annealing kinetics of ion-implanted nickel-aluminium alloy

The first-order chemical reaction-rate formalism has been used in conjunction with diffusion to describe phenomenologically the annealing of ion-implanted nickel-aluminium alloys. An activation energy of 1.83 eV was determined for the reaction which causes a decrease in the bulk concentration. Possible participants in the reaction have been discussed.