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Notes: 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 coordinated, whereas at the B-type interfaces they appear to be eightfold coordinated.It is shown that these interface configurations introduce defects in the three-dimensional CoSi2 precipitates and Si matrix. As a result, the nuclei are subjected to compressive strain. It is argued that the combination of interface energy and strain results in a larger stability of small B-type nuclei as compared to A type. When the precipitates grow beyond a critical size of some 20–30 nm, A-type precipitates become more stable, finally resulting in a buried layer of aligned orientation if the layer thickness is larger than about 30 nm. If smaller, it is argued that upon prolonged annealing the layer will have a twinned orientation (B type). Annealed layers of aligned orientation in (100) Si are found to contain interfacial dislocations of edge type with Burgers vectors b=a/4〈111〉 and b=a/2〈100〉. These dislocations are associated with boundaries separating domains having different interface structures. For (111) Si, there exist edge-type dislocations with Burgers vector b=a/2〈110〉. The final state of strain can be attributed to the difference in thermal expansion between CoSi2 and Si. The strain at room temperature corresponds to a fully relaxed layer at about 700 °C. Below this temperature, dislocations become immobile.

Notes: CoSi2 layers formed by the thermal reaction of vapor-deposited Co films on Si(100) substrates have been studied by transmission electron microscopy, and x-ray diffraction. It is shown that first a layer of CoSi is formed between Co and Si. Only thereafter is the formation of CoSi2 initiated at the Si/CoSi interface. In view of the similarity of the crystal structure and the small lattice mismatch between the Si and the CoSi2, epitaxy of aligned (100) CoSi2 is expected to occur. However, in addition to an aligned (100) orientation, CoSi2 occurs in a number of orientations, including a (110) preferential orientation. Many individual grains are composed of subgrains, slightly rotated with respect to each other and connected by small-angle boundaries. It is shown that the observations can be largely attributed to the geometrical lattice match between CoSi2 and Si. A computer program has been developed that searches systematically for a large number of possible geometrical matches. It allows us to calculate epitaxial relationships between CoSi2 and the Si(100) substrate. The probability of various fits is estimated on the basis of their strain energy and coincidence site density, showing good correspondence with the experimental observations.

Notes: The diffusion of In and Tl implanted into SiO2 has been investigated by means of Rutherford backscattering spectrometry. The diffusion of these elements is shown to be strongly dependent on their chemical state in SiO2. By combining these results with previous results for Ga, a general model has been formulated which describes the incorporation and diffusion of Group III elements in SiO2. The most important parameter of this model is the valence state of these elements in SiO2. In their trivalent state these elements are incorporated on Si sites of the SiO2 network, where they are virtually immobile. On the other hand, interstitial monovalent Group III ions are observed to show rapid diffusion. In addition to this, there is a second independent diffusion process, which is attributed to interstitial migration of InOH or TlOH molecules. After high-temperature annealing of SiO2 covered with Si3N4, the In and Tl diffusion profiles exhibit a peak at the SiO2-Si interface. This segregation is tentatively explained by stress relief at the SiO2-Si interface.

Notes: 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.

Notes: Heteroepitaxial Si/CoSi2/Si structures have been synthesized by high-dose implantation of Co into (100) and (111) Si at an energy of 170 keV and subsequent annealing. In the as-implanted state the implanted Co is found to be present as CoSi2. For a dose of 2×1017 Co/cm2, the Co is present in the form of epitaxial precipitates, which exhibit both the aligned (A-type) CoSi2 and twinned (B-type) orientation. For a higher dose of 3×1017 Co/cm2, a monocrystalline epitaxial CoSi2 layer near the top of the implanted Co distribution is formed during the implantation. The heteroepitaxial structures that are formed in this way are fully aligned. In contrast, when these structures are formed by sequential surface deposition techniques, twinning occurs at every Si/CoSi2 interface. The formation of the aligned orientation of the buried CoSi2 layer can be attributed to the larger stability of aligned precipitates as compared to twin-oriented precipitates.

Notes: The atomic structure of the (111) interface between CoSi2 (type A and B) and Si is investigated by high-resolution transmission electron microscopy, combined with image simulations. Type B interfaces of CoSi2 layers formed by thermal reaction of vapor deposited Co on (111) oriented Si, of Si/CoSi2/Si heterostructures, and of CoSi2 precipitates formed by high-dose Co implantation were examined. The coordination of the Co atoms at all B-type interfaces is found to be eightfold, in accordance with theoretical predictions. Type A interfaces of CoSi2 precipitates and continuous CoSi2 layers, formed by ion implantation and subsequent annealing, showed clear evidence for the presence of sevenfold coordinated interfacial Co.

Notes: The electrical resistivity and the Hall coefficient of thin polycrystalline MoSi2 films were measured as a function of temperature from 4.2 to 300 K. The transverse and longitudinal magnetoresistances have been determined at temperatures between 2 and 50 K at fields up to 10 T. Samples of both the high-temperature tetragonal MoSi2 phase and the low-temperature hexagonal phase have been prepared. The Hall coefficient of tetragonal MoSi2 changes sign with temperature, which means that this compound is a multiband conductor, and thus no reliable value for the carrier concentration can be derived from Hall measurements alone. Magnetoresistance data have therefore been analyzed with a simple two-band model in order to determine the dominant carrier type in both MoSi2 structures. In tetragonal MoSi2, electrons and holes are present in equal concentrations, whereas in hexagonal MoSi2 holes are the dominating type of carrier.

Notes: Molybdenum disilicide films have been formed by a reaction of Mo with polycrystalline silicon. Implantation of phosphorus or arsenic prior to reaction has been shown to have a large effect on the silicidation process. The object of implantation was to enhance the silicide reaction by creating damage at the metal-silicon interface. This, then, results in silicide films with less surface roughness (and a lower electrical resistivity). Molecular P+2 ions were found to be more effective in creating damage than single P+ ions, due to the fact that for P+2 ions two simultaneous collision cascades occur which overlap. Apart from the beneficial effect of implantation damage, the introduction of phosphorus has a deleterious effect on the properties of the silicide films. This phenomenon is explained by the presence of a thin and nonuniform native oxide layer which hinders the silicide reaction. Without addition of phosphorus, new nuclei for the silicide reaction can be formed due to stress introduced by the formation of the silicide, which will act upon the oxide and cause it to break up at some weak spot. The effect of phosphorus is proposed to be that it renders the oxide more viscous which prevents this process from taking place. The x-ray diffraction spectra revealed that the orientation of the grains in the polycrystalline MoSi2 films is influenced by the method of preparation.

Notes: A study of electrical transport properties in MoSi2 thin films revealed a large resistivity difference of 57 vs 157 μΩ cm at room temperature between films formed from a codeposited Mo/Si structure and layers formed by reaction of deposited Mo with Si. The resistivity difference was found to be temperature independent. The Hall effect in the films formed from deposited Mo was a factor of four larger than in films formed from a codeposited alloy. The temperature dependencies of the Hall effect were also found to be different. Analyses of the films by Rutherford backscattering and transmission electron microscopy revealed no significant differences in thickness or grain size of the layers. The only microstructural difference is the stacking fault density, which is very high in the high-ohmic films. The mechanism by which the stacking faults influence the electrical properties of MoSi2 and other refractory metal silicides is discussed, and relations are established between the method of deposition, the microstructure of the films, and the electrical transport properties.

Notes: A study of the diffusion of ion-implanted Sb in SiO2 by means of Rutherford backscattering spectrometry showed that the major fraction of the implanted Sb is immobile in SiO2 upon annealing at temperatures as high as 1200 °C in N2, O2, or O2/H2O ambients. When the oxide is encapsulated by an Si3N4 film during annealing, no diffusion is observed at all. To mobilize implanted Sb, extra oxygen has to be supplied from the annealing ambient. The diffusion of Sb exhibits a lower activation energy in a N2 or O2 ambient (1.3 eV) than in an O2/H2O ambient (2.3 eV). The present result for the O2 ambient differs spectacularly from the data reported in the literature which gave an activation energy of 8.75 eV and a pre-exponential factor which was 27 orders of magnitude lower than value reported here. The diffusion of implanted Sb exhibits some similarity to that of implanted As. There is also evidence that Sb is incorporated on both silicon and oxygen sites of the SiO2 network, i.e., in a way similar to As.