ALBERT

Notes: Amorphous Si/Ge artificial multilayers with a repeat length around 60 A(ring) have been partially mixed with 1.5-MeV Ar+ ions at temperatures in the range 77–673 K. The diffusive component of the square of the mixing length, obtained by subtracting out the ballistic contribution, does not depend on the dose rate at a given dose, and shows an Arrhenius-type temperature dependence with activation enthalpies between 0.13 and 0.22 eV. Possible mechanisms for migration and annihilation processes of defects are discussed to understand these low activation enthalpies.

Notes: 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.

Notes: The epitaxial realignment of undoped and As doped polysilicon films onto crystalline silicon substrates induced by high-temperature rapid-thermal annealing has been investigated. It is shown that the realignment mode and the kinetics of the process are intimately related to the microcrystalline structure of the layers under investigation, to the morphology of the native oxide film present at the interface, and to the presence of As atoms dispersed in the deposited layers. For layers having fine grain dimensions, compared to the film thickness, the realignment takes place via the motion of the crystal-polysilicon interface towards the surface. This is observed in undoped layers and in layers which have been subjected to a high-temperature anneal before As doping. The preimplant anneal disrupts the interfacial oxide film and reduces the thermal cycle needed to complete the realignment of the polysilicon layers. In layers which have not experienced any thermal treatment before As doping, it is seen that the grain size first increases to dimensions on the order of the film thickness, and the realignment transformation then proceeds by lateral growth of epitaxial columns in a manner similar to secondary grain growth. The kinetics of both realignment modes are thermally activated and the atomic limiting processes have been tentatively identified to be As diffusion in bulk Si for As doped layers and Si self diffusion for undoped films. The effect of the microcrystalline structure on the realignment kinetics is attributed to its relationship with the driving force governing the realignment transformation.

Notes: We have investigated the electronic properties of Er in crystalline Si using deep-level transient spectroscopy and capacitance-voltage measurements. Erbium was incorporated by ion implantation in a p+-n junction structure. In order to explore the role of oxygen and defects some samples were coimplanted with O and the annealing behavior of the deep-level spectra was explored in the temperature range 800–1000 °C for annealing times ranging from 5 s to 30 min. We show that O-codoping produces large modifications in the Er-related deep-level spectra and, in particular, a promotion from deep to shallow levels, thus enhancing the donor behavior of Er in Si. For erbium implanted in pure crystalline Si the spectrum is dominated by deep levels arising from Er-defect complexes which are easily dissociated upon thermal annealing. In O-coimplanted samples the formation of Er-O complexes with a characteristic level at EC−0.15 eV is observed. These complexes form upon thermal annealing and are stable up to 900 °C. These results are presented and possible implications for our current understanding of the mechanisms of Er photoluminescence in Si are discussed. © 1995 American Institute of Physics.

Notes: The formation and dissolution of Si-O-Al precipitates have been investigated in Czochralski silicon wafers implanted with 6 MeV Al ions and thermally processed. The data have been compared to the O precipitation in samples implanted with 6 MeV Si or P ions. The amount of precipitated O atoms is about one order of magnitude higher for Al than for Si or P implanted samples. Moreover, a strong gettering of the Al atoms by the silicon dioxide precipitates has been observed. The precipitate evolution has been studied for different annealing times and temperatures. The oxygen precipitation has been simulated by the classical theory of nucleation and growth, with the introduction of new factors that take into account the implant damage distribution, the agglomeration of point defects during the initial stages of the annealing and the oxygen outdiffusion from the sample surface.

Notes: We have studied the effect of erbium-impurity interactions on the 1.54 μm luminescence of Er3+ in crystalline Si. Float-zone and Czochralski-grown (100) oriented Si wafers were implanted with Er at a total dose of ∼1×1015/cm2. Some samples were also coimplanted with O, C, and F to realize uniform concentrations (up to 1020/cm3) of these impurities in the Er-doped region. Samples were analyzed by photoluminescence spectroscopy (PL) and electron paramagnetic resonance (EPR). Deep-level transient spectroscopy (DLTS) was also performed on p-n diodes implanted with Er at a dose of 6×1011/cm2 and codoped with impurities at a constant concentration of 1×1018/cm3. It was found that impurity codoping reduces the temperature quenching of the PL yield and that this reduction is more marked when the impurity concentration is increased. An EPR spectrum of sharp, anisotropic, lines is obtained for the sample codoped with 1020 O/cm3 but no clear EPR signal is observed without this codoping. The spectrum for the magnetic field B parallel to the [100] direction is similar to that expected for Er3+ in an approximately octahedral crystal field. DLTS analyses confirmed the formation of new Er3+ sites in the presence of the codoping impurities. In particular, a reduction in the density of the deepest levels has been observed and an impurity+Er-related level at ∼0.15 eV below the conduction band has been identified.This level is present in Er+O-, Er+F-, and Er+C-doped Si samples while it is not observed in samples solely doped with Er or with the codoping impurity only. We suggest that this new level causes efficient excitation of Er through the recombination of e-h pairs bound to this level. Temperature quenching is ascribed to the thermalization of bound electrons to the conduction band. We show that the attainment of well-defined impurity-related luminescent Er centers is responsible for both the luminescence enhancement at low temperatures and for the reduction of the temperature quenching of the luminescence. A quantitative model for the excitation and deexcitation processes of Er in Si is also proposed and shows good agreement with the experimental results. © 1995 American Institute of Physics.

Notes: Electron paramagnetic resonance measurements have been made on samples of float zone silicon, implanted with 1015 Er/cm2. One sample was coimplanted with oxygen to give an impurity concentration of 1020 O/cm3 and 1019 Er/cm3. In this coimplanted sample, sharp lines are observed which are identified as arising from a single spin 1/2 Er3+ center having a g tensor exhibiting monoclinic C1h symmetry. The principal g values and tilt angle are g1=0.80, g2=5.45, g3=12.60, and τ=2.6°. In the absence of O, the sharp lines are not observed. No Er3+ cubic centers were detected in either sample. Possible structures for the center are discussed. © 1996 American Institute of Physics.

Notes: Interfacial melting of thin (∼65 nm) Ni2Si films thermally grown on 〈111〉 Si has been observed after pulsed laser irradiation. Low-energy implanted Bi was used as a marker to detect surface melting. Rutherford backscattering spectrometry has shown that the energy density threshold for interfacial mixing was lower than the one at which changes in the Bi profile occurred. Cross-section transmission electron microscopy performed on those samples has shown the existence of a reacted layer, ∼20 nm, at the silicide/silicon interface while no change in the structure of the outermost 50 nm was observed. The reacted layer formed sharp interfaces with both the underlying silicon and the silicide. Interfacial melting has been related to the presence in the phase diagram of an eutectic between the compound and the pure silicon.

Notes: 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.

Notes: 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.