Low Energy Ion Beam Deposition Research Articles

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.

Composition and properties of the so-called “diamond-like” amorphous carbon films

The composition of amorphous “diamond-like” films made by direct low energy ion beam deposition, r.f. discharge and sputtering was determined by nuclear reaction analysis, IR spectroscopy and microcombustion chemical analysis. The nuclear reaction analysis showed very similar hydrogen depth profiles for all three types of samples. The atomic ration of hydrogen to carbon was approximately 0.2 at the film surface and rose to approximately 1.0 at a depth of 500 Å. The integrated intensity of the CH stretching band at about 2900 cm -1 indicates that the amount of chemically bonded hydrogen is less than the total hydrogen content. Combustion analysis confirmed the overall atomic ratio of hydrogen to carbon determined by nuclear reaction analysis. The chemical state of the non-bonded hydrogen was not determined; however, the effective diffusion coefficient computed from the hydrogen depth profile was extremely low. This indicates either that the films are exceedingly impermeable or that the non-bonded hydrogen requires an additional activated step to leave the films, e.g. desorption or chemical reaction.

Direct ion beam deposition for thin film formation

Thin film formation by direct ion beam deposition is described. The advantages of the low energy ion beam deposition method are discussed together with limitations of this method. The description of a prototype ion beam deposition system and lead and magnesium ion beam deposition using this system are given in detail. The lead and magnesium deposits are characterized by Rutherford backscattering analysis and electron microscopy. The most important advantage of the low energy ion beam deposition method is the precise controllability of deposition parameters.

Low-energy mass-separated ion beam deposition of materials

A low energy mass-separated ion beam deposition system was developed. Ge + ions of 100 μA were obtained at an acceleration energy of 100 eV with a beam spot size of 5 mm ø at 5 × 10 −8 Torr. Material buildup has been observed at the range of ion energy where the self-sputtering yield is below unity. The incident ion energy dependence of the reactions of the F + and CF x + ions with a silicon substrate has been measured, as well as the physical phenomena conventionally observed between impinging ions and a substrate material. Epitaxial growth of Ge films on Ge and Si single crystal substrates has been observed at 300°C with a Ge + ion energy of 100 eV. Deposited Ge crystal properties were evaluated.

Germanium and Silicon Film Growth by Low-Energy Ion Beam Deposition

The design and characteristics of a low-energy ion beam deposition system are discussed. In the system, metal ions with an energy of 100 eV are deposited onto the substrate at a current density of 4–5 µA/cm2. Germanium single crystalline films are deposited on germanium (111) and silicon (111) substrate at substrate temperatures above 300°C. In the case of deposition below 200°C, films are found to be amorphous and re-crystallized by annealing above 300°C. When the ion energy over 500 eV is used, sputtering of the substrate is dominant and deposition is not observed for Ge+ ions and the silicon substrate combination. The results demonstrated the feasibility of growing thin film by low-energy ion beam deposition.