Application of the modified electrostatic model to the impurity diffusion in nickel

The modified electrostatic model (Neumann and Tölle 1995) is applied to the impurity diffusion in nickel.Z ₀ = 0.4 is used for the effective charge of the nickel ion.The comparison of calculated and experimental diffusion parameters reveals that the sign of J Q, the difference between impurity diffusion and self-diffusion energy, and the sign of the difference between impurity diffusion and self-diffusion coefficient is correctly predicted in all cases. On the other hand the comparison exhibits some systematic deviations for 5p impurities, which cannot be explained in terms of the current impurity diffusion models.     

Diffusion of Ta in α-Ti

The diffusion of Ta in the hcp (α) phase of high-purity Ti (99.99%) was studied at different temperatures from 911 K up to 1123 K. The Rutherford Backscattering Spectrometry (RBS) and Heavy Ion RBS (HIRBS) techniques were used to obtain the penetration profiles. The evolution of the diffusion coefficient, D, as a function of temperature follows prediction of the Arrhenius law. The activation energy of the diffusion process is (318±7)kJ/mol, similar to that corresponding to self-diffusion in α-Ti. On the other hand, the measured values of D are systematically lower than those corresponding to self-diffusion by a factor of approximately 5. This reduction could be explained by taking into account the mass difference between Ta and Ti. An increase of the diffusion coefficient was measured when the diffusion proceeds on a less pure Ti (99.9%) matrix. This increment is higher at lower temperatures. Received: 12 November 2001 / Accepted: 12 March 2002 / Published online: 5 July 2002 RID="*" ID="*" RID="*" ID="*" RID="**" ID="**"Corresponding author. Fax: +54-11/6772-7362, E-mail: dyment@cnea.gov.ar RID="*" ID="*"Members of the Carrera del Investigador Científico del Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina     

XPS surface analysis of monocrystalline silicon solar cells for manufacturing control

X-ray photoelectron spectroscopy (XPS) has been applied to surfaces of silicon wafers in the different stages of the assembly line for large-scale monocrystalline silicon solar cell manufacturing (ISOFOTON, Malaga, Spain). XPS results have shown that a considerable amount of carbon is present on the pyramidal-textured monocrystalline silicon surface. This amount decreases slightly but is still present after the process of phosphor diffusion (p-n junction), as well as after subsequent calcination in humid air for SiO₂ film formation (passivation). This amount of carbon may be buried during the process of CVD coating an anti-reflection TiO₂ film. After calcination of the film in order to obtain the TiO₂ rutile phase, an even higher amount of carbon is detected on the TiO₂ anti-reflection coating surface. This indicates that not all organics from the tetra-isopropile ortho-titanate (TPT) precursor were released from the film. Furthermore, in this case phosphor is found in excess on the SiO₂ wafer surface (dead layer) and also on the rutile TiO₂ surface, indicating that an extra phosphor diffusion from the bulk silicon through the TiO₂ film has taken place during calcination. These results demonstrate how thermal treatments applied in the solar cell manufacturing assembly line can influence and may change the intended compositional distribution. These treatments may also introduce defects that act as recombination centres for charge carriers in the solar cell device. Received: 13 September 2000 / Accepted: 10 January 2001 / Published online: 3 May 2001     

On the migration of defects and impurities in microelectromechanical systems subject to a large number of light pulses

The migration of defects in light-irradiated microelectromechanical systems (MEMS) is treated theoretically. The effects of temperature gradients on atomic demixing are considered. It is found that, when the migration energy of defects and impurities is less than about 0.5 eV, their migration has to be introduced in the modelling of ageing of MEMS. Received: 17 July 2000 / Accepted: 31 March 2000 / Published online: 27 June 2001     

Lead diffusion in α-Zr

Pb diffusion in α-Zr matrix between 823 and 1123 K was measured using heavy ion Rutherford backscattering spectrometry (HIRBS) technique. A deviation from the Arrhenius law was observed, with two different regions. At low temperatures the activation energy Q is close to the expected value for a substitutional diffuser but the pre-exponential factor D₀ is higher than expected. Close to the phase transition temperature the opposite occurs, with a low Q value. This behavior is similar to the one observed for Hf and self-diffusion in α-Zr. Received: 29 September 1998 / Accepted: 29 January 1999 / Published online: 28 April 1999     

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.     

Oxygen diffusion barriers using a new sacrificial design concept for future high-density memory devices

We emphasize the importance of the new design concept for diffusion barriers in high-density memory capacitors. RuTiN and RuTiO films are proposed as sacrificial oxygen diffusion barriers. They showed much lower sheet resistance up to 800 °C than various barriers including binary and ternary nitrides, reported by others. The contact resistance for both the Pt/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si and the Pt/RuTiO/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si contact structures, the most important electrical parameter for the diffusion barrier in the bottom-electrode structure of capacitors, exhibited values as low as 5 kΩ, even after annealing up to 750 °C. When each RuTiN and TiN film is inserted as a glue layer between the bottom electrode Pt layer in the CVD–BST simple stack-type structure, the thermal stability of the RuTiN glue layer is observed to be 150 °C higher than that of the TiN glue layer. Moreover, the capacitance of the PVD–BST simple stack-type structure with a TiN glue layer initially degrades after annealing at 500 °C, and thereafter failed completely. In the case of RuTiN and the RuTiO/RuTiN glue layers, however, the capacitance continuously increased up to 550 °C. These new experimental results accommodate the introduction of the sacrificial design concept of diffusion barriers against oxygen in high-density memory capacitors. Received: 6 February 2002 / Accepted: 4 March 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +82-31/360-4545, E-mail: dongsoo.yoon@hynix.com     

Study of range distribution parameters for bismuth-ion implantation in silver gallium diselenide

Range distributions for bismuth ions implanted in AgGaSe₂ in the energy range 80–300 keV were investigated by using 2.1-MeV He²⁺ Rutherford backscattering spectrometry (RBS). A convolution calculation method was used to extract the true distributions of bismuth from the measured RBS spectra. The range distribution parameters, R_p and ΔR_p, were obtained and compared with those obtained from Monte Carlo simulation. The experimental R_p values agree with the Monte Carlo simulation values very well, but the experimental ΔR_p values are systematically larger than those from the theoretical simulation. Received: 28 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-531/856-5167, E-mail: xdliu@sdu.edu.cn     

Study of phase separation in Ti-Co-N thin films on silicon substrate

73 Co₂₇ and Ti₇₃Co₂₇- N during thermal annealing has been studied by SIMS, AES and XRD methods. It has been shown that in case of Ti₇₃Co₂₇ the CoSi₂ layer was not formed and the formation of ternary silicide compounds CoTiSi and Co₃Ti₂Si took place. At the same time in case of Ti₇₃Co₂₇- N the bottom layer CoSi₂ and the upper layer based on TiN were formed. The interaction behaviour has been found to depend on nitrogen concentration in initial film. For high amount of nitrogen the diffusion of Si atoms into upper layer and Si₃N₄ phase formation were observed. The possible variants of solid-phase interaction between silicon and the alloys containing intermetallic compounds and influence of nitrogen on this process are discussed. Received: 25 September 1996 / Accepted: 11 October 1996     

Field-enhanced neutralization of electrically active boron in hydrogen implanted Schottky diodes

We have observed that hydrogen implantation in p-type boron-doped silicon material induces a neutralization of boron in a 10 m deep region after the Schottky diodes have been heated at a 90° C temperature under reverse-biasing. The profile of neutralized acceptors can be reversibly shaped by successively applying different reverse biases.     

Carbon precipitation and diffusion in SiGeC alloys under silicon self-interstitial injection

In this work we investigate the diffusion and precipitation of supersaturated substitutional carbon in 200-nm-thick SiGeC layers buried under a silicon cap layer of 40 nm. The samples were annealed in either inert (N₂) or oxidizing (O₂) ambient at 850 °C for times ranging from 2 to 10 h. The silicon self-interstitial (I) flux coming from the surface under oxidation enhances the C diffusion with respect to the N₂-annealed samples. In the early stages of the oxidation process, the loss of C from the SiGeC layer by diffusion across the layer/cap interface dominates. This phenomenon saturates after an initial period (2–4 h), which depends on the C concentration. This saturation is due to the formation and growth of C-containing precipitates that are promoted by the I injection and act as a sink for mobile C atoms. The influence of carbon concentration on the competition between precipitation and diffusion is discussed. Received: 19 October 2001 / Accepted: 19 December 2001 / Published online: 20 March 2002 / Published online: 20 March 2002     

Transient-diffusion effects

Transient effects on diffusion and activation during post-implantation anneals are a major obstacle for the further miniaturization of ultra-large-scale integrated semiconductor devices. The article reviews recent developments in the simulation of such phenomena with particular emphasis on models for the kinetics of self-interstitial agglomerates and boron–interstitial clusters. Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-9131/761-212, E-mail: pichler@iis-bfhg.de     

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 characteristics of platinum diffusion in n-type GaN

The electrical and optical characteristics of platinum (Pt) diffusion in n-type gallium nitride (GaN) film are investigated. The diffusion extent was characterized by the SIMS technique. The temperature-dependent diffusion coefficients of Pt in n-GaN are 4.158 × 10⁻¹⁴, 1.572 × 10⁻¹³ and 3.216 × 10⁻¹³ cm²/s at a temperature of 650, 750 and 850 °C, respectively. The Pt diffusion constant and activation energy in GaN are 6.627 × 10⁻⁹ cm²/s and 0.914 eV, respectively. These results indicate that the major diffusion mechanism of Pt in GaN is possibly an interstitial diffusion. In addition, it is also observed that the Pt atom may be a donor because the carrier concentration in Pt-diffused GaN is higher than that in un-diffused GaN. The optical property is studied by temperature-dependent photoluminescence (PL) measurement. The thermal quenching of the PL spectra for Pt-diffused GaN samples is also examined.     

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     

The reflectivity of Mo/Ag/Au ohmic contacts on p-type GaN for flip-chip light-emitting diode (FCLED) applications

The Mo/Ag/Au contact for flip-chip light-emitting diode (FCLED) applications is examined on its contact resistance and light reflectance. A high reflectance of 90% is achieved in un-annealed contact, but a strong inter-diffusion of ohmic metals and GaN during the annealing process is found to result in poor reflectance (55% at the wavelength of 465 nm). The secondary ion mass spectrometry (SIMS) depth profiles indicate that a wide inter-diffusion region existed in the annealed contacts; thus the low reflectivity of the Mo/Ag/Au-annealed contacts can be attributed to the strong inter-diffusion of Au and Ag.     

On an application of the causality principle to the theory of ion transport processes

We suggest an approach for ion transport processes that is motivated by analogies with the S-matrix theory. By using causality-based analyticity assumptions, conductivity frequency pre-factors are expressed in terms of the transfer amplitude. This provides a means of dealing with a unified scheme that includes ionic oscillations in wells and classical-like escaping. As an application, we use this technique to reproduce results obtained in terms of the Kramers problem without invoking the Kramers’ Fokker-Planck equation or details of the transfer mechanism in solid electrolytes.