Adhesion of Reactive Ion Implanted Copper Films on Al2O3 and SiO2

Implantation of reactive ions at the Cu-Al2O3 or Cu-SiO2 interface has been explored as a means of producing adhesion of thin copper films on these otherwise inert substrates. The process may promote complex chemical bonding at the interface due to the presence of a reactive implanted species; it may also enhance adhesion by interface layer mixing. Thin copper films (400–800Å) were deposited on fused quartz or sapphire substrates. After implantation and, in some cases, heat treatment thick Cu stripes were added to enable peel testing of adhesion strength. The reactive ion species implanted were oxygen (100 keV), or titanium (120 keV) or chromium (80 or 160 keV), to doses ranging from 1015 to 1017 ions/cm2. In each case, the energy was chosen to place the reactive implant at the interface region. For comparison with simple ion beam mixing, a similar set of samples was implanted with krypton ions at 2 MeV to doses of 1 or 3.6 × 1016 ion/cm2. The peel strength was found to be about 0.5 gm/mm for the unimplanted Cu-sapphire samples; 1.3 gm/mm for those implanted with oxygen; 18 gm/mm for those implanted with krypton; 90 gm/mm for those implanted with chromium; and more than 200 gm/mm for the titanium implanted samples. No significant increase in adhesion was achieved for the implanted Cu-quartz samples, except for the titanium implant, which gave an average peel strength of 66 gm/mm after anneal for the dose of 5 × 1016 Ti+/cm2. Studies of the interfaces and of the peeled surfaces were made, using RBS. Changes in both chemical bonding and interface morphology appear to contribute to the phenomena of enhanced adhesion.

Effects on Metal/Metal-Oxide Interface Adhesion Due to Electron and Ion Irradiation

The influence of electron and ion irradiation on the adhesion at chromium-copper thin film interfaces has been studied. The measurements were carried out with different types and thicknesses of well-characterized oxides at the interfaces. The electron energies were varied between 5 and 10 keV, with doses up to 1018cm−2. lons of He+Ne+and P+were used in the range of energies between 150 keVand 1.0 MeV, with fluences ranging from 1015cm−2to 6× 1016cm−2. Substantial improvement of the adhesion is observed in cases where the beam has a significant nuclear stopping power component. Electronic processes may also play a role in improving adhesion, although they are not dominant in the case of the present films.

Ion Beam Enhanced Adhesion of Thin Films

Ion beam enhanced adhesion has been studied for the case of thin Cu films deposited on substrates of alumina, fused quartz and glass-ceramic. Beams of He+ (200 keV) and Ne+ (280 keV) were used, in order to test the respective roles of nuclear and electronic interactions in this process. Peel tests were used to produce the first quantitative studies of adhesion strength as a continuous function of ion dose. Bond strengths improved after irradiation at modest doses, sometimes by a factor of 20. Subsequent heating in a helium furnace produced as much as an order of magnitude further adhesion improvement in irradiated samples. Similar tests for Cu on Teflon produced excellent bonding for ion doses of ∼ 1014/cm2. The results indicate bond breaking and reconstruction at a sharp interface, with no significant metalsubstrate intermixing. The new bond is stable under heat cycling.

Adhesion at Metal-Ceramic Interfaces: Ion Beam Enhancement and the Role of Contaminants

Enhanced adhesion of a film of non-reactive metal deposited on a ceramic or glass substrate can be produced by irradiating the interface with an ion beam. The resulting bond can be improved by subsequent heat treatment. The interface remains abrupt. The mechanism of this bonding is discussed, and the effects of interface contaminants are examined for the Cu-Al2O3 and Au-Al2O3 systems. Finally it is noted that strong adhesion is produced when Al2O3 is subjected to preferential sputtering at the time of Cu deposition; the resulting interface chemistry is discussed.

Polymer mediated self-assembly of magnetic nanoparticles

We present a simple polymer-mediated process of assembling magnetic FePt nanoparticles on a solid substrate. Alternatively absorbing the PEI molecule and FePt nanoparticles on a HO-terminated solid surface leads to a smooth FePt nanoparticle assembly with controlled assembly thickness and dimension. Magnetic measurements show that the thermally annealed FePt nanoparticle assembly as thin as three nanoparticle layers is ferromagnetic. The magnetization direction of this thin FePt nanoparticle assembly is readily controlled with the laser-assisted magnetic writing. The reported process can be applied to various substrates, nanoparticles, and functional macromolecules and will be useful for future magnetic nanodevice fabrication.

Photoneutrons from Natural Magnesium

Recent experiments on photoneutron production from natural magnesium have produced contradictory results. Katz et al. (1954) have used brems-strahlung from a 22 MeV betatron to irradiate a natural magnesium target. The emitted neutrons were detected with boron trifluoride (BF3) counters placed in a paraffin block.