Au In Si Research Articles

Similarities in the electrical properties of transition metal–hydrogen complexes in silicon

We review our recent studies on the reactions of hydrogen with transition-metals (Pd, Pt, Ag, and Au) in crystalline Si. Hydrogen was incorporated into the samples by wet-chemical etching. Deep-level transient spectroscopy (DLTS) on Schottky diodes reveals several transition metal–hydrogen complexes in n- and p-type samples. From DLTS profiling, we are able to estimate the number i of hydrogen atoms in the TM–H i complexes. All complexes with i=1, 2 are electrically active. Striking similarities are found for isoelectronic complexes, e.g. Pt–H 2 and Au–H 1. Transition metal complexes with more than three hydrogen atoms are likely to be electrically passive. All hydrogen related complexes disappear after heat treatments above 600 K for several hours.

Gold Diffusion in Silicon During Gettering by an Aluminum Layer

ABSTRACTPrevious modeling of Al gettering of Au in Si indicated that, for an Al gettering layer placed on one surface of a Si wafer, Au will be gettered from both surface regions of the wafer to progressively greater depths with time. This is because, in Si, Au is a substitutional-interstitial (Aus-Aui) species with its diffusion governed by the kick-out mechanism which is mediated by Si self-inter-stitials (I). During gettering by the Al-Si liquid at one wafer surface, Aus atoms change over to Au atoms to rapidly migrate out of Si into the liquid. The changeover process consumes I. At the two wafer surface regions, the consumed I will be quickly replenished, while in the wafer interior an I undersaturation develops which hinders the Aus-Aui changeover and hence the gettering process. Experimental evidences which confirm the predictions have been obtained. Au was indiffused into a FZ Si wafer at 950°C for 16 hr. After removing the Au source and etching, samples from the in-diffused wafer were annealed at 1000°C without or with an Al layer on one surface. For samples without Al, there is no change in the net Au content, while the U-shaped indiffused profile becomes flatter. For samples with an Al layer, both wafer surface region Au concentrations were significantly decreased in 30 min while the wafer interior Au concentrations decreased only after annealing for longer times. The model predictions, the experimental results, and the implications on Si self-diffusion parameters will be discussed.

Diffusion of Gold into Heavily Boron-Doped Silicon

ABSTRACTDiffusion of Au into dislocation-free and highly dislocated Si with high B-background doping levels has been investigated with the aid of neutron activation analysis in conjunction with mechanical sectioning. The high B-doping level causes extrinsic conditions, i.e., the hole concentration exceeds the intrinsic carrier concentration even at diffusion temperatures between 900°C and 1100°C. All profiles are accurately described on the basis of the kick-out diffusion model and a mechanism which takes into account segregation of Au at dislocations. Our analysis provides solubility data of Au in Si and effective diffusion coefficients related to interstitial Au and Si self-interstitials I. The dependence of these quantities on the B-background doping level is well described by the Fermi-level effect. This analysis supports singly positively charged states in p-type Si of Au on interstitial (Aui) and substitutional (Aus) sites and of Si self-interstitials. Successful fitting of additionally requires an acceptor level of Aus. The electrical properties deduced for Aui, Aus and I are summarized in Table 2. Au profiles in highly dislocated Si obtained especially after diffusion at 900° C give evidence of Au trapped at dislocations. From our preliminary experimental results we determine an enthalpy difference of 2.7 eV between Au on substitutional sites and Au captured at dislocations.

Kinetics of Interstitial-Substitutional Exchange of Zn, Pt, and Au in Si: Experimental Results and Theoretical Calculations

The diffusion behavior of Zn, Pt, and Au in Si is completely described on the basis of interstitial-substitutional exchange mechanisms namely the dissociative and the kick-out diffusion mechanism. Recently, diffusion profiles of Zn in Si obtained after diffusion at temperatures between 870 and 1208 °C were analysed yielding information about equilibrium concentrations of intrinsic point defects involved in the diffusion process. Moreover, analysis of Zn diffusion yields the fraction of Zn on interstitial and substitutional sites and the mass action constants of the underlying diffusion-reaction processes which are presented in the present paper. From the temperature dependence of these quantities the enthalpy difference between interstitial and substitutional Zn and the reaction enthalpies for the diffusion processes were obtained. Total energy calculations for Zn, Pt, and Au on substitutional and tetrahedral interstitial sites were additionally. carried out and compared with experimental result obtained for Zn and estimates for Pt and Au. Finally, given the formation enthalpy of Si self-interstitials determined from theoretical work, reaction energies for the kick-out process are obtained.

Diffusion of gold and platinum in amorphous silicon and germanium

195Au radiotracer atoms produced via the radioactive decay of implanted 195Hg ions have been used to investigate systematically the diffusivities of Au in amorphous Si and Ge by means of serial Ar +-beam sectioning as a function of the diffusion temperature, doping with Au and/or charging with hydrogen. Less extensive studies of the same type have been carried out for the diffusion of Pt in Pt-doped amorphous silicon. The Au diffusion data are interpreted in terms of direct diffusion in which the diffusing 195Au atoms are temporarily trapped by different kind of vacancy-like defects. These traps can be saturated with Au or hydrogen. Their nature and concentrations are found to change as a result of annealing-induced structural relaxation of the amorphous specimens.

Diffusion, Precipitation, and Cavity-Wall Reactions of Ion-Implanted Gold in Silicon

AbstractThe diffusion of Au in Si and its binding to cavities and to precipitates of the equilibrium Au-Si phase were investigated in the temperature range 1023-1123 K using ion implantation and Rutherford backscattering spectrometry. The diffusivity-solubility product for interstitial Au was found to be about an order of magnitude greater than the extrapolation of previous, indirect determinations at higher temperatures. Chemisorption on cavity walls was shown to be more stable than Au-Si precipitation by 0.1-0.3 eV in the investigated temperature range, indicating that cavities are effective gettering centers for Au impurities.

Comment on "Gold, self-, and dopant diffusion in silicon"

In the subject publication, Mathiot casts doubt upon our Monte Carlo simulations of Au diffusion in Si with the kick-out mechanism. We argue that our simulations were correct. In addition, we observe that Mathiot's treatment of diffusion lacks information on boundary conditions which is necessary for accurate modeling. Mathiot's model also ignores the possible existence of vacancy clusters. Mathiot concluded that diffusion of Au in Si is dominated by the kick-out mechanism. We argue that this conclusion is unjustified.

Defect Trapping and Precipitation Processes During Annealing of Cu and Au Implanted Si

AbstractThe behaviour of metallic impurities in Si is an issue of primary concern in advanced device processing. This paper addresses the annealing behaviour of Cu and Au in Si when nanocavities are present within the substrate as potential gettering and precipitation sites. In-situ, ‘hot’ Rutherford backscattering has been used to study metal accumulation to cavities at the annealing temperature. Transmission electron microscopy has been used to study the final microstructure of the Au-Si and Cu-Si system. A range of interesting phenomena have been observed, including very efficient transient gettering of both Cu and Au to cavities at the annealing temperature and precipitation of second phases at cavities. Dissolution of accumulated metal from defect bands into solution occurs for long-time annealing. This behaviour is discussed in terms of supersaturated solid solubility processes, diffusion, defect-trapping and precipitation of Cu and Au in Si.

Three-dimensional concentration profiles of hybrid diffusers in crystalline silicon

The diffusion of ion-implanted Au, Pt, and Zn in crystalline Si has been investigated. The implantation was performed in photolithographically defined areas of the wafer and a spreading resistance technique was used to measure the three-dimensional concentration profiles of the metal atoms after high temperature diffusion anneals. We found that the lateral spread under the mask is larger than the vertical diffusion, especially on the sample side opposite to the implanted diffusion source. All the significant features of the measured profiles can be explained as a consequence of the kick-out mechanism of diffusion for these transition metals. In fact, the peculiar shape of the concentration profiles is determined by the interplay between the influx of interstitial metal atoms and the outflux of silicon self-interstitials generated by the kick-out reaction. Despite the high lateral diffusion, it will be shown that by a suitable combination of implantation fluence and annealing temperature it is possible to limit this lateral spread inside ∼200 μm, while maintaining a high metal concentration in the region under the implanted area. This demonstrates the possibility of using transition metal diffusion to control minority carrier lifetime in a selected area of a semiconductor device.

Commensurate–incommensurate phase transition between 6×6 and √3×√3 + satellite structures of the Au/Si(111) surface

Alternate annealing in the low- (≤250 °C) and high- (≥400 °C) temperature regimes of the Au/Si(111) surface at different Au coverages prepared by room-temperature deposition and isothermal annealing in the high-temperature regime at over-(ML) coverages have been studied by means of low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and Rutherford backscattering spectroscopy (RBS). It is found that the 6×6 pattern and the √3×√3+satellite pattern are formed at 0.9–2.2 ML coverages by annealing for several minutes at 250 and 500 °C, respectively, when there exist an Au surface peak and a diffusion tail extended towards the lower energy behind the Au peak and that the phase transition between both patterns is reversible by alternate annealing in two temperature regimes as long as the diffusion tail is not diminished. From this result, the 6×6 structure is ascribed to excess embedded Au atoms situated at the ordered sites and Au atoms constituting the √3×√3 structure at the top surface. Moreover, it is found that the phase transition between the √3×√3 structure and the mixed structure of √3×√3+5×1 are also reversible by alternate annealing in the two temperature regimes at the actual coverages of 0.72–0.84 ML. Furthermore, from analysis of the isochronal annealing data at 1.7 ML, the activation energy of the diffusion of Au in Si is found to be 1.3 eV.

Thin gold and indium films on Si(111) surface

A 3-component system (AuInSi) and thin indium and gold film interactions on the Si(111)7 × 7 surface were examined using Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). A new surface phase Si(111)3 × 1-( Au, In) was detected at submonolayer metal coverages. Gold and indium were deposited under UHV conditions with further annealing at 300–500°C. It was shown that the agglomeration of gold atoms into islands covered by indium atoms takes place upon deposition of In onto the Si(111)5 × 1-Au surface phase with further annealing. This explains the absence of the gold Auger-peak (69 eV). Indium atoms in excess with respect to the Si(111)1 × 1-In surface phase are responsible for the SiAu surface phase decay and for the formation of gold islands covered by indium.

Interface-state-controlled segregation of gold during ion-beam-induced epitaxy of amorphous silicon.

Segregation coefficients and velocity enhancements for Au in amorphous Si during ion-beam-induced epitaxial crystallization were measured. At 320 {degree}C, velocity enhancements of up to 2.5 times were observed, and interface breakdown occurred at interfacial Au concentrations of 11 at. %. Although qualitatively similar to thermal solid-phase epitaxy, these velocity enhancements are substantially reduced in magnitude while the interface breakdown occurs at much higher concentrations. Between 250 {degree}C and 400 {degree}C, Au is trapped at the moving interface with segregation coefficients {ital k}, which are approximately velocity and concentration independent and vary between 0.001 and 0.012. In contrast with classical segregation, however, {ital k} increases linearly with interface position during the initial stages of growth to a temperature-dependent steady-state value. At 250 {degree}C, for example, {ital k} increases by at least a factor of 4 to 0.012 during growth. These results suggest an evolving interface structure from the initial thermal configuration to an irradiation-induced steady-state configuration with a higher trapping efficiency.

Diffusivity of gold in amorphous silicon measured by the artificial multilayer technique

Artificial multilayers of amorphous Si and amorphous Si containing 0.7 at. % Au, with repeat lengths between 44 and 48A, were fabricated by ion beam sputtering. The change, with annealing time in the intensity of the first-order x-ray diffraction peak resulting from the composition modulation, is used to determine the diffusivity of Au in amorphous Si. Diffusion lengths on the order of an interatomic distance have been measured. The diffusivities over the temperature range 200–260 °C have an Arrhenius-type temperature dependence with an activation enthalpy of about 1.3 eV, and are in agreement with the extrapolation of published higher temperature data.

Epitaxial recrystallization and diffusion phenomena in amorphous silicon produced by MeV ion beams

Diffusion and interfacial segregation phenomena occurring in the Si amorphous-crystal system under MeV Ar ion irradiation are reviewed. Implanted Au, Ag and Cu in amorphous Si undergo radiation enhanced diffusion in the temperature range 300–700 K with Arrhenius-like behavior with activation energies of 0.37, 0.39 and 0.17 eV respectively. Segregation and trapping of Au at the amorphous-crystal interface occurs when recrystallization is induced with 2.5 MeV Ar ion irradiation. The Au segregation is analogous to behavior at liquid-solid interfaces. The Au is trapped in crystalline Si at concentrations some ten orders of magnitude in excess of equilibrium concentration.

Diffusion of Au in Amorphous Si Measured by the Artificial Multilayer Technique

AbstractThe diffusivity of Au in amorphous Si (a-Si) has been determined in the temperature range 200-260°C using and Ar-ion sputter deposited artificial multilayered films of a-Si and a-Si(0.7at%Au) with repeat lengths between 44 and 48 Å. Diffusion on lengths scales of the order of interatomic spacings have been investigated. The Au diffusivity exhibits an Arrhenius temperature dependence with an activation enthalpy of 1.2eV and shows good agreement with extrapolations of higher temperature Au diffusion data obtained by Rutherford backscattering spectrometry (RBS) in ion-implanted, CVD, and sputter deposited a-Si. The measured Au diffusivity also shows a significant time dependence.

Trapping of Au in Si during pulsed laser irradiation: A comparison with ion beam induced segregation

Liquid phase nonequilibrium segregation and trapping of Au in Si induced by Q-switched laser irradiation are reported. Depending on the incident laser energy density, irradiation results in either amorphization or recrystallization of a near surface layer. In the latter case, at interface velocities of 9 m/s, the segregation coefficient is 0.1±0.02 and Au is trapped in near-substitutional lattice sites at concentrations of 0.5 at. %. These results are compared with recent data on solid phase, ion beam induced segregation, where Au at the amorphous-crystal interface is trapped on nonunique lattice sites.

Radiation-enhanced diffusion of Au in amorphous Si

The radiation-enhanced diffusion of implanted Au markers in amorphous Si has been measured in the temperature range 77–693 K. Samples were irradiated with 2.5 MeV Ar ions. The diffusion coefficients show three well-defined regions. For temperatures <400 K, diffusion is athermal and due to ballistic mixing. For temperatures in the range 400–700 K diffusion is Arrhenius-type with an activation energy of 0.37 eV and is considerably enhanced over the normal thermal diffusion. The defects that cause the enhanced diffusion come from nuclear energy loss processes. Thermal diffusion, with an activation energy of 1.42 eV, dominates at temperatures greater than 750 K.

Diffusion of Au in Amorphous Si During Ion-Beam Irradiation

ABSTRACTWe have measured the radiation-enhanced diffusion of Au in amorphous Si in the temperature range 77–700 K. Gold was implanted to depths of 500Å at concentrations of an atomic %. The samples were than amorphized to depths of -2μm using MeV Ar implants at liquid nitrogen temperature. Radiation-enhanced diffusion was induced by a 2.5 MeV Ar beam at doses of 2×1016−2×1017/cm2 and dose rates of 7×1012−7×1013/cm2sec. The diffusion coefficients show three well defined regions. At temperatures <400K diffusion is essentially athermal and due to ballistic mixing. At temperatures between 400K and 700K the diffusion, which is considerably enhanced over the usual thermal values, has an Arrhenius behavior with an activation energy of 0.37 eV. At higher temperatures thermal diffusion, with an activation energy of 1.42 eV, dominates.

Segregation and Trapping of Gold During Ion-Induced Crystallization of Amorphous Si

ABSTRACTA novel regime of crystal growth and segregation has been observed. Amorphous Si layers were uniformly doped with Au and epitaxial crystallization was induced in the temperature range 250–420°C using 2.5 MeV Ar ion irradiation. The Au segregation at the amorphous/crystal interface is analogous to behavior at liquid/solid interfaces except that the interfacial segregation coefficient of 0.007 at 320°C is independent of velocity between 0.6 and 6A/sec. This process results in the trapping of Au in crystalline Si at concentrations some ten orders of magnitude in excess of equilibrium concentration.

Accelerator mass spectrometry solutions to semiconductor problems

A 2.5 MV Tandetron based accelerator mass spectrometry system has been used to measure several impurities (B, Cr, P, Ge, As, Sb and Au) in Si, GaAs and/or HgCdTe semiconductor samples. Modifications of the Cs ion source and sample holder have been made to reduce the introduction of impurities into the system, and this has allowed detection limits of 0.1 parts per billion atomic to be reached in some cases. Depth profiles of simple semiconductor structures have also been performed. A comparison of this method to more conventional analytical techniques such as SIMS is discussed.