Comparison of profile tailing in SIMS analyses of various impurities in silicon using nitrogen,oxygen, and neon ion beams at near-normal incidence

We have performed a systematic SIMS study into the effect of (i) the chemical nature and (ii) the energy of the primary ions on the decay length which characterizes the exponential fall-off of impurity sputter profiles. The samples consisted of low resistivity, p-type Si covered with thin metallic overlayers. Bombardment was carried out at 2° off normal. Aspect (i) was investigated for tracers of Cu and Ga using N ₂ ⁺ , O ₂ ⁺ , and Ne⁺ primary ions at an energy of 5 keV/atom. The effect of the beam energy, aspect (ii), was studied for eight different tracer species and N ₂ ⁺ primary ions at energies between 2 and 5 keV/atom. In the case of Ga, was found to be shorter with N ₂ ⁺ or O ₂ ⁺ primary ions (=7.0 and 7.5 nm, respectively) than with Ne⁺ (=12 nm). This effect is attributed to beam induced formation of Si₃N₄ or SiO₂ layers, whereby the effective width of the internal distribution of intermixed Ga impurities in the Si subsystem is reduced significantly. In contrast to Ga, the decay length for Cu is smallest under bombardment with Ne⁺ (=16 nm), quite large with N ₂ ⁺ (26 nm) and extremely large with O ₂ ⁺ (2.2 m). Segregation of Cu atoms at the Si₃N₄/Si and the SiO₂/Si interface, respectively, is responsible for this depressed impurity removal rate. Within experimental accuracy the observed variation of the decay length with N ₂ ⁺ energy E [keV/atom] can be written in the form =kE ^p, where k and p are element specific parameters which range from k=1.2 nm for Pb to 10 nm for Cu and from p=0.6 for Cu and Ag to 1.0 for Pb. The results are discussed with reference to conceivable shapes of the distribution of intermixed impurity atoms.On leave from NTT Applied Electronics Laboratories, 3-9-11, Midori-cho, Musashino-shi, Tokyo 180, Japan     

Analysis of temperature and enhanced diffusion effects in sputtering of CrSi2

Previously reported experimental results on sputtering and enhanced diffusion processes in CrSi₂ during 100 keVXe⁺ bombardment at different temperatures have been quantitatively analyzed.The framework for the analysis is a simple theoretical model in which the Si atoms are considered mobile in a matrix of Cr atoms whose density is assumed constant and diffusivity is considered zero everywhere. Erosion velocity of the matrix (due to the sputtering of Cr atoms), sputtering and enhanced diffusion processes of Si atoms are taken into account in the mathematical model.In our analysis we show that the time evolution of the total number of sputtered atoms in binary solids cannot yield an unambigous conclusion as to the existence of preferential sputtering.Further, it is found that in the case of CrSi₂ the preferential sputtering of Si atoms depends on the suicide temperature.     

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.     

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.     

Approximation to the two-step diffusion profile by a series of gaussian functions

The two-step diffusion profile is approximated by a series of gaussian functions. Its accuracy is dependent upon the number of terms used in the series, but independent of the number and the spacing of exact data points.     

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 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 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.     

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.     

Determination of the copper diffusion coefficient in silicon from transient ion-drift

We use the transient ion drift in a depletion region of a Schottky barrier to determine ion diffusivities at moderate temperatures. The pulsed reverse bias leads to temperature dependent capacitance transients similar to deep level carrier emission transients. A simple theoretical model together with classical transient signal analysis provide the means to extract the ion diffusion constant. When applied to copper in silicon, diffusion data are obtained in a not yet investigated temperature range (280–400 K) which agree well with both low and high temperature diffusion data.     

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.     

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.     

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 behaviour of C-implanted α-Hf

The annealing behaviour of C in the group IVa metal Hf has been studied in the previously uninvestigated temperature range 650–800°C using ion-beam techniques. Diffusion couples were created by ion implantation. The time evolution of the carbon profiles were monitored by the use of the Nuclear Resonance Broadening (NRB) technique. The linear Arrhenius plot extracted from the measurements indicates that the diffusivity of implanted C in polycrystalline h.c.p. -Hf can be described by the activation energyQ=3.9±0.2 eV and the pre-exponential factor D₀=(50± ₄₇ ¹²⁰ )×10⁵ cm²/s. The implanted distributions were used to determine the solubility of C in -Hf for the first time.     

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.     

Simulation of range profiles for boron implantation into SiO2/Si and Si3N4/SiO2/Si targets

The simple method of profile combination is shown to be applicable to the simulation of boron profiles in SiO₂/Si and Si₃N₄/Si layered targets. This is demonstrated by comparison with range distributions calculated by more sophisticated theoretical methods, i.e. TRIM Monte Carlo simulations and the algorithm of Christel et al., and with experimental data. The method of profile combination can also be applied to layered targets with a crystalline silicon substrate.     

Passivation of laser induced defects in silicon by low energy hydrogen ion implantation

It is well established that the pulsed-laser annealing of as-implanted Si introduces electrically active defects. The aim of this paper is to show that these defects can be neutralized by low-energy hydrogen ion implantation. The techniques used for the sample characterization are current-voltage measurements and capacitance transient spectroscopy.     

A comparison of hydrogen incorporation and effusion in doped crystalline silicon,germanium, and gallium arsenide

The incorporation of deuterium into crystalline silicon, germanium, and gallium arsenide from a plasma source is investigated as a function of sample temperature during the plasma treatment. The total amount of incorporated deuterium and its bonding states are characterized by the thermal effusion (TE) technique for different dopants and doping levels. In all samples investigated, we find a strong influence of the passivation temperature on these quantities; however, there are large differences between different semiconductors and for different doping levels or dopants. The results are discussed in terms of plasma-induced defects, dopant-deuterium complexes, and surface effects.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

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.