Parker T

Low Temperature Wafer Bonding by Copper Nanorod Array

A vast array of Cu nanorods with a diameter of 10-20 nm grown by an oblique angle deposition technique was utilized as an adhesive layer for bonding 200 mm Si wafers at low temperatures. The focus ion beam/scanning electron microscope images illustrate that the Cu nanorod array underwent coalescence readily upon a bonding temperature at 200°C. Upon 400°C, a dense Cu bonding layer with homogeneous structure was achieved. A fully dense bonding structure was also obtained upon a lower bonding temperature at 300°C followed by a postannealing at 400°C in a reducing ambient.

Surface texture evolution of polycrystalline and nanostructured films: RHEED surface pole figure analysis

In this topical review, we outline the construction of a reflection high-energy electron diffraction (RHEED) surface pole figure from a polycrystalline film by recording multiple RHEED patterns as the substrate is rotated around the surface normal. Due to the short penetration depth of electrons, the constructed pole figure is a surface pole figure. It is in contrast to the conventional x-ray pole figure which gives the average texture information of the entire polycrystalline film. Examples of the surface pole figure construction processes of a fibre texture and a biaxial texture are illustrated using Ru vertical nanorods and Mg nanoblades, respectively. For a biaxially textured film, there often exists an in-plane morphological anisotropy. Then additional intensity normalization must be applied to compensate for the effects of anisotropic morphology on RHEED surface pole figure construction. Rich information on the texture evolution, such as the change in the tilt angle of the texture axis, has been obtained from the in situ study of oblique angle vapour deposition of Mg nanoblades using RHEED surface pole figures. Finally we make a comparison between the RHEED surface pole figure and the conventional x-ray pole figure techniques.

Size control of Cu nanorods through oxygen-mediated growth and low temperature sintering

Control of the size of Cu nanorods vapor-deposited at an oblique angle (approximately 85 degrees) by oxygen-mediated growth was investigated using scanning electron microscopy (SEM) and x-ray diffraction (XRD). It was observed that exposure of Cu nanorods to the oxygen ambient periodically resulted in a reduction in the diameter of the nanorods as well as an increase in the areal density of the nanorods. This oxygen-induced modification to the nanorod growth is attributed to the higher energy barrier for Cu adatom migration on the oxide surface at room temperature; this reduces the rod diameter. At a low annealing temperature of approximately 300 degrees C, the SEM images show that the nanorods have densified and formed a continuous film structure, which is consistent with the sintering phenomenon. The XRD and SEM analyses show that the coalescent/grain growth rate for Cu nanorods with smaller diameters is enhanced due to the size effect. This low temperature sintering characteristic of the Cu nanorod array has great potential for being utilized in wafer bonding for three-dimensional integration of devices.

Epitaxial multilayered Co/Cu ferromagnetic nanocolumns grown by oblique angle deposition

Slanted Co/Cu multilayer nanocolumns were grown on Si and gold-coated Si substrates by two-source oblique-angle vapour deposition. The respective column lengths and layer thicknesses were varied from ∼400 to ∼700 nm and ∼ 6t o∼16 nm. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show the column diameters to be less than 65 nm. The ferromagnetic nature of the nanocolumns was verified by vibrating sample magnetometry. Compositional analysis using electron energy loss spectroscopic elemental mapping and energy dispersive x-ray spectrometry of a single nanocolumn showed alternating bands of Co and Cu, indicating a multilayer structure. X-ray diffraction (XRD) results showed that the Co and Cu layers are predominantly face-centred cubic (fcc) and a minor hexagonal close packed (hcp) Co phase was also detected. The hcp phase may be due to a high density of stacking faults in the fcc Co. TEM studies have shown an epitaxial relationship between the Co and Cu layers within the individual columns. By comparing the XRD and TEM results, we conclude that the (020) planes are parallel to the column axis, and the column growth is nearly parallel to the [101] direction.