J. J. M. Ottenheim

Synthesis of heteroepitaxial Si/CoSi2/Si structures by Co implantation into Si

Heteroepitaxial Si/CoSi2/Si structures have been formed in both (100) and (111)Si by high‐dose implantation of Co. During the implantation, Co is incorporated in the Si lattice as CoSi2 with the same orientation as the Si substrate. Upon annealing the implanted Co distribution is transformed into an epitaxial Si/CoSi2/Si layered structure. Sputtering of Si during the implantation of Co was studied using an implanted Si3N4 marker layer. The Si/CoSi2/Si/Si3N4/Si multilayer structure that is formed in this way demonstrates the potential of the ion beam synthesis technique.

Ion beam synthesis of heteroepitaxial Si/CoSi2/Si structures

The formation of buried single crystalline CoSi2 layers within a monocrystalline Si substrate by high‐dose ion implantation of Co has been studied. Comparison of measured Co distributions with profiles obtained from Monte Carlo calculations has revealed the two basic phenomena that are responsible for the formation of buried layers. The enhanced stopping due to the incorporation of high concentrations of Co into Si has been identified as the dominant effect in the ion beam synthesis of buried layers. The high stopping near the top of the implanted distribution causes accumulation of Co at this point, which promotes buried layer formation. Sputtering brings the entire Co profile closer to the surface. After implantation at a temperature of 450 °C, Co is present in the form of coherent CoSi2 precipitates. Precipitates occur both in a twinned and an aligned orientation and are highly strained due to the lattice mismatch with Si. For high doses a buried monocrystalline and aligned CoSi2 layer forms within the...

Ion beam synthesis of cobalt silicide: effect of implantation temperature

Abstract In order to understand the physical processes which occur during ion beam synthesis of CoSi2, we have studied the effect of implantation temperature. The experiment consisted of 170 keV Co implantations (dose =1.7 × 1017 ions/cm2) in Si(100) targets at temperatures varying between 250°C and 500°C. Both as-implanted and annealed samples have been analyzed by several techniques, such as cross-section transmission electron microscopy, X-ray diffraction, Rutherford-backscattering spectrometry and the four-point probe technique. Our data indicate that an optimum implantation temperature interval exists where pinhole-free buried layers of CoSi2 can be synthesized. Outside this interval, the evolution of the precipitate size distribution and/or strain situation in the as-implanted state effectively reduce the necessary depth variation in precipitate stability.

Microstructure of buried CoSi2 layers formed by high‐dose Co implantation into (100) and (111) Si substrates

Heteroepitaxial Si/CoSi2/Si structures have been synthesized by implanting 170‐keV Co+ with doses in the range 1–3×1017 Co+ions/cm2 into (100) and (111) Si substrates and subsequent annealing. The microstructure of both the as‐implanted and annealed structures is investigated in great detail by transmission electron microscopy, high‐resolution electron microscopy, and x‐ray diffraction. In the as‐implanted samples, the Co is present as CoSi2 precipitates, occurring both in aligned (A‐type) and twinned (B‐type) orientation. For the highest dose, a continuous layer of stoichiometric CoSi2 is already formed during implantation. It is found that the formation of a connected layer, already during implantation, is crucial for the formation of a buried CoSi2 layer upon subsequent annealing. Particular attention is given to the coordination of the interfacial Co atoms at the Si/CoSi2 (111) interfaces of both types of precipitates. We find that the interfacial Co atoms at the A‐type interfaces are fully sevenfold ...

Single crystalline CoSi2 layers formed by Co implantation into Si

Abstract The formation of buried single crystalline CoSi 2 layers by high-dose implantation of Co into Si has been studied. Comparison of Monte Carlo calculations and measured profiles showed that the enhanced stopping due to the incorporation of high concentrations of Co into Si plays an essential role in the formation of the buried layers. The implanted Co has been shown to be present in the form of coherent CoSi 2 precipitates, which are tetragonally distorted. The process of coalescence into a buried layer during annealing has also been studied and Co diffusion in Si was found to be the rate-determining step.

Thin buried cobalt silicide layers in Si(100) by channeled implantations

Si(100) wafers have been implanted with 50 keV Co ions at elevated substrate temperatures (320 °C) in the dose range 7.8×1014–7.8×1016 at. cm−2. A comparison is made between channeled (along the Si 〈100〉 surface normal) and random (tilted by 7°) implantations. Co depth distributions are measured with secondary‐ion mass spectrometry and compared to marlowe and trim simulations. Annealed samples are characterized by Rutherford backscattering spectrometry and transmission electron microscopy. Our data indicate that for channeled implantations the sputtering effect is strongly reduced as compared to random implantations. Also, the average penetration depth is increased by about 20%. As a consequence, annealing of our high‐dose implanted samples yields either a discontinuous surface silicide layer (random case) or a pinhole‐free buried silicide layer (channeled case).