We report a new method to fabricate electrode-embedded multiple nanopore structures with sub-10 nm diameter, which is designed for electrofluidic applications such as ionic field effect transistors. Our method involves patterning pore structures on membranes using e-beam lithography and shrinking the pore diameter by a self-limiting atomic layer deposition process. We demonstrate that 70-80 nm diameter pores can be shrunk down to sub-10 nm diameter and that the ionic transport of KCl electrolyte can be efficiently manipulated by the embedded electrode within the membrane.

The resistivity of thin Cu films depends on film thickness as the dimensions approach the electron mean-free-path for Cu of 39 nm. The key size-dependent contributions are from electron–surface scattering, grain boundary scattering, and surface roughness-induced scattering. Measurements with pseudoepitaxial Cu films deposited on Si have been undertaken to reduce effects of grain boundaries and surface roughness and suggest an electron-scattering parameter of p=0.12. Overlayers of metal films on the Cu generally increase the resistivity for Ta and Pt overlayers, and may reduce the resistivity for Au and Al. The resistivity increase may also be reversed if the overlayer oxidizes.

A technique has been developed for highly efficient postionization of sputtered metal atoms from a magnetron cathode. The process is based on conventional magnetron sputtering with the addition of a high density, inductively coupled rf (RFI) plasma in the region between the sputtering cathode and the sample. Metal atoms sputtered from the cathode due to inert gas ion bombardment transit the rf plasma and can be ionized. The metal ions can then be accelerated to the sample by means of a low voltage dc bias, such that the metal ions arrive at the sample at normal incidence and at a specified energy. The ionization fraction, measured with a gridded mass-sensitive energy analyzer is low at 5 mTorr and can reach 85% at 30 mTorr. Optical emission measurements show scaling of the relative ionization to higher discharge powers. The addition of large fluxes of metal atoms tends to cool the Ar RFI plasma, although this effect depends on the chamber pressure and probably the pressure response of the electron temperature. The technique has been scaled to 300 mm cathodes and 200 mm wafers and demonstrated with Cu, AlCu, and Ti/TiN. Deposition rates are equal to or in some cases larger than conventional magnetron sputtering. A primary application of this technique is lining and filling semiconductor trenches and vias on a manufacturing scale.

A new deposition technique has been developed which combines conventional magnetron sputter deposition with a rf inductively coupled plasma (RFI). The RFI plasma is located in the region between the magnetron cathode and the sample position, and is set up by a metal coil immersed in the plasma. A large fraction of the metal atoms sputtered from the magnetron cathode are ionized in the RFI plasma. By placing a negative bias on the sample, metal ions are then accelerated across the sample sheath and deposited at normal incidence. Results from a gridded energy analyzer configured with a microbalance collector and located at the sample position indicate the level of ionization is low at a few mTorr and rises to ≳80% at pressures in the 25–35 mTorr range. Optical measurements of metal ion and neutral emission lines show scaling of the relative ionization to higher discharge powers. Significant cooling of the plasma electron temperature is observed when high concentrations of metal atoms were sputtered into the plasma.

The electrical resistivity of thin films of Ta and TaN has been examined as a function of film thickness and other processing parameters. The films were deposited by magnetron sputtering of Ta cathodes with Ar, or mixtures of Ar and N 2 for the case of TaN. Ta films deposited on silicon dioxide or Cu surfaces were always beta phase, and showed little resistance increase as the thickness was reduced. The TaN films were deposited in a broad range of compositions, depending on reactive gas flow and system configuration, and showed strong increases in resistivity as thickness was decreased. Ta films deposited on TaN x with x equal to or greater than 1, an electrical resistivity greater than 300 m⍀ cm, and with thickness greater than 2 nm were alpha phase, and showed significant increases in resistivity as thickness was reduced. The application and electrical properties of these films as diffusion barriers in interconnect structures depends strongly on the thicknesses at the contact points at the bottoms of vias and only weakly on the phase of the Ta. The resistivity of the barrier films on via and trench sidewalls is high enough to be irrelevant to circuit performance.