Optimum Ion Energy Research Articles

Deposition mechanisms for promoting sp 3 bonding in diamond-like carbon

Deposition of amorphous carbon from medium energy ion beams promotes sp 3, diamond-like bonding. It is proposed that the sp 3 bonding arises from an increased density, owing to carbon ions entering subsurface atomic sites. An optimum ion energy arises from a balance between the incident carbon ions having sufficient energy to penetrate the surface atomic layer, while minimizing any excess energy dissipated in a thermal spike which can anneal out the density increment.

Deposition of Cu film on SiO2 using a partially ionized beam

Ion bombardment during deposition can significantly modify the film properties. In the partially ionized beam deposition, ions derived from the depositing material, i.e., the self‐ions, are used during deposition. Cu films were deposited on SiO2 substrates at room temperature using 1% Cu self‐ions with an energy ranging between 0–4 keV. We studied the microstructures of the Cu films using x‐ray diffraction and transmission electron microscopy, measured the impurity level inside the films using secondary ion mass spectrometry, and performed the resistivity measurements using a four point probe. The results indicate that there is an optimum ion energy around 2 keV at which, the integrated x‐ray intensity ratio I(111)/I(200) reaches its maximum value indicating a strong 〈111〉 texture, while the impurity concentration and resisitivity are minimum. The correlation between the structural, compositional and electrical properties are discussed in the framework of Mayadas and Shatzkets’s theory of grain boundary r...

Cobalt silicide formation induced by neon bombardment

Cobalt silicide formation by ion beam mixing has been studied, under bombardment with inert (neon) ions. Mixing is found to be impeded by the presence of an interfacial oxide layer. Stoichiometric silicide formation is dependent upon the use of optimum ion dose and energy. In contrast to argon and xenon bombardment high doses of neon lead to exfoliation of the surface due to migration and localisation of the gas in the sub-surface layer. The mixing behaviour is discussed in terms of both radiation enhanced diffusion and thermal spike models.

Optimization of the ion-to-atom arrival rate for ion beam assisted Ge deposition

Structural and electrical properties of Ge films deposited under simultaneous argon ion irradiation were investigated by changing both the ion-to-atom arrival-rate ratio and the ion energy. The apparent optical bandgap energy of the films showed a minimum value at an ion-to-atom ratio of about 5 × 10 −3 and an optimum ion energy of 100 eV, approaching the crystalline value of 0.67 eV. According to Hall measurements, the films exhibited an n-type conduction and an electron mobility at a maximum value of about 700 cm 2/Vs for the same ion-irradiation conditions. These facts strongly suggest that both the growth of crystalline grains in the films and the crystallinity within the grains were appreciably improved under optimum irradiation conditions of the ion beam during the film deposition.

Film deposition and buried layer formation by mass-analyzed ion beams

We have developed ion-beam equipment which can produce metal ions in the energy range from very low energy (less than 10 eV) to high energy (400 keV). High-energy neutrals and secondary electrons which would be extremely harmful in low-energy experiments are removed from the beam. With this equipment, metallization of Si by low-energy ion beam deposition and by high-energy ion implantation has been performed. Film formation mechanisms and properties of deposited films were studied in the case of a low-energy Pd ion beam. The optimum ion energy, in terms of the collection efficiency and the condition of the film-substrate interface, was found to be 50–100 eV. Films with resistivity of the same order as that of the bulk material, and as thin as a few nanometers were obtained. It was confirmed by transmission electron microscopy that these films were already continuous and covered the entire substrate surface. In the case of metallization by high-energy ions, Pd, Ag, and Al ions were implanted into Si. It was found that a buried conductive layer is obtained only when concentration of implanted species exceeds a certain threshold. The buried PdSi layer formed by 320-keV Pd implantation at a dose level of 2.0 × 10 17 cm −2 had sheet resistance on the order of a few ohms and was stable under 800°C, 30 min anneal. Crystallinity of the implanted Si substrate surface was recovered after 600–800°C, 30 min anneal.