K. Kyllesbech Larsen

Heavy doping effects in the diffusion of group IV and V impurities in silicon

Studies of the diffusion of Ge, Sn, As, and Sb in Si at high donor concentrations provided by phosphorous doping have been performed. It is found that for donor concentrations, CD below ∼2×1020 cm−3, the diffusivity depends linearly on CD; for doping concentrations above ∼2×1020 cm−3, however, the diffusivity increases dramatically with increasing donor concentrations. This behavior has been successfully modeled within the vacancy–percolation model, and it is concluded that collective phenomena play a significant role at high donor concentrations.

On the chemical diffusion in layered thin films containing amorphous Co-Zr, Ni-Zr, and Fe-Zr

The chemical diffusion in thin trilayer films of TM–TM 100− x Zr x –TM with an amorphous middle layer where TM = Co, Ni, or Fe and in amorphous Fe–Zr and Ni–Zr films with composition gradients has been investigated using Rutherford backscattering spectrometry. The growth of the amorphous layer in the trilayers, due to in-diffusion of cobalt and nickel, is initially found to be proportional to the square root of the time, t 1/2 , and subsequently found to level off before the compositions corresponding to metastable equilibria are reached. Irradiation, with 500 keV Xe + ions, is found to promote the in-diffusion. This behavior is discussed in terms of structural relaxation effects and their influence on the metastable equilibrium. In amorphous Fe–Zr the chemical diffusivity is observed to be very sluggish. Contrary to the behavior in Co–Zr and Ni–Zr trilayers, the direction of the iron diffusion in Fe–Zr trilayers suggests a broad positive peak in the Gibbs free energy at a composition around 50 at. % Zr. It is argued that the sluggish chemical diffusivity of iron is directly related to the unusual composition-dependence of the Gibbs free energy for amorphous Fe–Zr.

The effect of phosphorus background concentration on the diffusion of tin, arsenic and antimony in silicon

The effect of phosphorus background concentration on the diffusion of tin, arsenic and antimony in silicon has been studied for phosphorus concentrations between about 9 × 1019 and 5 × 1020cm−3, corresponding to 10 ⪅ n/ni ⪅ 60. The effective diffusion coefficients are found to be proportional to high power of n/ni for all three impurities. These results are discussed within the framework of the percolation model.

High temperature annealing effects on the electrical characteristics of C implanted Si

We have investigated the electrical characteristics of p+–n Si junction diodes implanted with 300 keV C ions at fluences of 0.5 and 1×1015 cm−2 and annealed at 900 or 1100 °C. In all cases cross‐sectional transmission electron microscopy shows an excellent crystalline quality, with no extended defects, and the C‐rich region is characterized by an n‐type doping. In the material annealed at 900 °C the C‐rich region shows a low electron mobility and the presence of deep donor levels, and, as a consequence, the diode characteristics are nonideal. These effects can be attributed to the formation of C–Si self‐interstitial‐type complexes after the 900 °C anneal. At 1100 °C part of the C–Si complexes dissolve and the electrical characteristics of the materials noticeably improve.

Indiffusion of cobalt in amorphous Co–Zr

Abstract By use of trilayers consisting of ∼ 35 nm cobalt ∼ 45 nm amorphous CoZr, and ∼ 35 nm cobalt, the indiffusion of cobalt into the amorphous structure was studied by means of Rutherford Backscattering Spectroscopy (RBS). At temperatures between 650 K and 690 K, an initially high diffusion essentially stopped after 20–40 min annealing before equilibrium was reached. It is proposed that the effect is related to the diffusional asymmetry in the amorphous phase. The relatively immobile zirconium atoms cannot relax their configuration to permit cobalt indiffusion up to the equilibrium value.

Enhanced interdiffusion in amorphous Ni–Zr thin films under tensile strain

Abstract Amorphous thin films of Ni-Zr have been deposited on different substrates using electron-beam evaporation. The films were compositionally graded and, in order to determine the interdiffusivity [dtilde] the time evolution on annealing of their depth profiles were measured using Rutherford backscattering spectrometry. Owing to the difference between thermal expansions of the film and substrate, strain was induced on heating to the annealing temperature. The observed interdiffusivity at 523 K in Ni-Zr films deposited on single crystals of NaCl, giving a tensile strain in addition to the initial strain, was found to be four to seven times larger than for Ni-Zr films deposited on sapphire, where no or only a small compressive additional strain was built up. The difference between the strain contributions from these substrates was estimated from available thermal expansion data to be 0.8%.

The Effect of Oxygen on The Electrical Activation and Diffusion of Ion-Implanted Boron

Transient enhanced diffusion (TED) and electrical activation (EA) of ion-implanted boron during rapid thermal annealing has been investigated using three types of boron doped p-type Si (100) substrates: (a) Cz 20 Ωcm, (b) 3 μm thick 20 Ωcm epitaxial Si layer (epi-layer) grown on a 20 Ωcm Cz substrate, and (c) 3 μm thick 20 Ωcm epi-layer grown on a 5 mΩcin Fz substrate. The level of oxygen is known to decrease from material type (a) to (c). The samples were implanted with 20 keV, 5×10 13 cm −2 boron and subjected to rapid thermal annealing (RTA) at various temperatures and times. The EA and TED were studied using spreading resistance profiling (SRP) and secondary ion mass spectrometry (SIMS), respectively. Although the amount of TED is almost identical for the three substrates, the EA is found to be significantly higher in the epi-layers compared to Cz substrates. It is speculated that the trapping of vacancies by oxygen in the ion-damaged region leads to an increase in the interstitial supersaturation during annealing, which then results in enhanced boron clustering and reduced electrical activation in the peak of the implanted profile.

Characterization of C coimplanted GexSi1−x epitaxial layers formed by high dose Ge ion implantation in (100) Si

We have investigated electrical and structural characteristics of C coimplanted GexSi1−x layers formed by high dose Ge implantation in (100) Si followed by rapid thermal annealing at 1100 °C for 10 s. In the absence of C the layers, with Ge peak concentrations of about 15 at. %, are epitaxial and fully strained but show extrinsic dislocation loops in the Ge end of range region. In C coimplanted GexSi1−x the crystalline quality of the materials is improved since the formation of defects at the end of range is suppressed and the strain is reduced. From an electrical point of view the situation is reversed. The electrical characterization of p+/n diodes shows that, without C coimplantation, in GexSi1−x the hole mobility is larger than in Si, and the bandgap narrowing results in an increase of the minority carrier concentration. Moreover, the diffusion of minority carriers does not appear to be influenced by the presence of the secondary defects at the end of range. Vice versa, in C coimplanted GexSi1−x, even...

On the phase formation during ion beam mixing of Al-Ti

Abstract The phase formation during ion beam mixing of elemental multilayered Al1−xTix films has been investigated. The irradiations were carried out with 500 keV Xe+ ions. The whole compositional range has been covered for substrate temperatures between 100 and 500 K. Between 300 and 500 K only extended terminal solid solutions of hcp and fcc were found. Nonequilibrium solubilities of up to 60 at.% Al in hcp and 25 at.% Ti in fcc were observed. At lower temperature an amorphous phase was found to form for Al-rich compositions. Gibbs free energies were calculated using the CALPHAD method, and metastable phase diagrams were constructed. Reasonable agreement between the predicted phase formation estimated from free energies and the experimental results was found. However, to thermodynamically justify the formation of the amorphous phase at low temperatures, the estimated free energies of the terminal solid solutions at low temperatures had to be increased relative to the amorphous phase, which is attributed to radiation induced defects.

Evidence for phase separation in amorphous Fe-Zr from chemical diffusion

Abstract The chemical diffusion of iron in layered films of amorphous Fe-Zr and b.c.c. Fe and in amorphous Fe-Zr films with a composition profile have been investigated using Rutherford backscattering spectrometry. The compositional changes after annealing observed in these films provide evidence for a broad positive peak in the Gibbs free energy of amorphous Fe-Zr at around 50 at% Zr consistent with phase separation of the amorphous state.