Stephen M. Rossnagel

Ionic Field Effect Transistors with Sub-10 nm Multiple Nanopores

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.

Diffusion barrier properties of transition metal thin films grown by plasma-enhanced atomic-layer deposition

Ta thin films were grown on Si(001) and polycrystalline Si substrates by plasma-enhanced atomic-layer deposition (PE-ALD) using TaCl5 and atomic hydrogen as precursors. The grown films have resistivity of 150–180 μm cm with a small Cl concentration between 0.5 and 2 at. %. The diffusion barrier properties were investigated using bilayer structures consisting of 200 nm Cu deposited by sputtering on ALD Ta films with various thicknesses. Three in situ analysis techniques consisting of x-ray diffraction, elastic light scattering, and resistance analysis were used to determine the diffusion barrier failure temperature of Ta films. The barriers were annealed at a temperature ramp rate of 3 °C/s from 100 to 1000 °C in forming gas. For this method using x-ray diffraction, the barrier failure temperatures were determined by monitoring the disappearance of the Cu(111) x-ray diffraction peak and appearance of Cu silicide diffraction peaks. At the diffusion barrier failure temperature, elastic light scattering indic...

Film modification by low energy ion bombardment during deposition

Abstract Concurrent energetic particle bombardment can have a significant effect on the properties of evaporated and sputter-deposited films. However, in many experiments, particularly those using ion beam sputtering, the magnitude of the energetic bombardment by neutrals is ignored or underestimated. The effects of energetic bombardment include significant physical changes in the crystal sizes and orientations, defect densities, electrical and optical properties, chemical stoichiometry and surface morphologies. While there exists no general model for the effect of energetic bombardment on growing film properties, in a range of experiments researchers have started to explore systematically the interrelations of the various physical and chemical effects. These results will be helpful in elucidating what phenomena are relevant in any particular experimental system.

Phase transformation of thin sputter-deposited tungsten films at room temperature

Thin films of W have application in semiconductor interconnect structures as diffusion barriers and potentially as seed layers for electroplating. Thin W films have been deposited by sputtering [physical vapor deposition (PVD)] at near-room temperature, using Ar as the working gas, for evaluation of the electrical and structural properties of the films in the thickness range of 3 to 150 nm. Films deposited at 45 nm or greater thickness are composed of alpha (bcc) phase (only) with an electrical resistivity of 12 μΩ cm. Films deposited at thicknesses below 5 nm are mostly beta (A15 cubic) phase as-deposited with significantly higher resistivity, which is due partly to the phase and partly to electron-surface scattering (the “size effect”). In the thickness range of 5 to 45 nm, the as-deposited films are mostly beta phase and undergo transformation to the alpha phase at room temperature in tens of hours to several days. The resistivity also declines concurrently, as much as 70%. The exact mechanism driving ...

Sputter deposition for semiconductor manufacturing

Sputter deposition, also known as physical vapor deposition, or PVD, is a widely used technique for depositing thin metal layers on semiconductor wafers. These layers are used as diffusion barriers, adhesion or seed layers, primary conductors, antireflection coatings, and etch stops. With the progression toward finer topographical dimensions on wafers and increasing aspect ratios, the broad angular distribution of depositing, sputtered atoms leads to poor or nonexistent coverage in deep features. This has been partially addressed using directional sputtering techniques such as collimated sputtering or long-throw sputtering. More recently, work originating in IBM has moved toward the deposition of films from metal-rich plasmas fed by sputtering, a technique known as I-PVD (for ionized PVD). This technique, based on fairly minor modifications of existing PVD systems, solves many of the intrinsic problems of PVD and appears headed for widespread manufacturing applications.

Directional and preferential sputtering-based physical vapor deposition

Abstract Physical sputtering techniques are characterized by a mostly isotropic deposition profile, which is useful for depositing films over steps, edges and lines. However, it fails for deposition into modest (>1 : 1) aspect ratio features due to overhang formation and subsequent void formation. A number of techniques have addressed this issue. Sputtering at high sample temperatures has been used to allow some degree of surface tension to help fill structures. Bias sputtering has been found to be useful for reducing void formation in low aspect ratio features. Collimated sputtering has been developed to filter the depositing atoms, resulting in mostly-normal incidence deposition. Finally, post-ionization of the sputtered atoms has been developed to deposit films primarily from metal ions, which are accelerated to the sample surface by means of a d.c. sample bias. Each of these techniques can lead to deposition within high aspect ratio features and will allow the application of sputter deposition for future semiconductor manufacturing processes.

Thin, high atomic weight refractory film deposition for diffusion barrier, adhesion layer, and seed layer applications

Thin, nearly conformal films are required for semiconductor applications to function as diffusion barriers, adhesion layers and seed layers within trenches and vias. The deposition of high mass refractory films with conventional, noncollimated magnetron sputtering at low pressures shows better‐than‐expected conformality which is dependent on the degree of directionality of the depositing atoms: the conformality increases as the directionality increases. The primary cause appears to be a strongly angle‐dependent reflection coefficient for the depositing metal atoms. As the deposition is made more directional by increasing the cathode‐to‐sample distance, the depositing atoms are more likely to reflect from the steep sidewalls, leading to better conformality as well as a less columnar film structure.

Growth of cubic-TaN thin films by plasma-enhanced atomic layer deposition

Low resistivity cubic-TaN thin films were grown by plasma-enhanced-atomic layer deposition using TaCl5 as the metal precursor and hydrogen/nitrogen plasma. The deposition has been performed by alternate exposures of TaCl5 and the plasma of hydrogen and nitrogen mixture. X-ray diffraction analyses show that the film is composed of cubic TaN grains, in contrast to the previously reported highly resistive Ta3N5 films grown by Ta3N5 grown by TaCl5 and NH3 as precursors. The composition and thickness were measured by Rutherford backscattering and hydrogen concentrations were obtained by forward recoil elastic spectrometry as a function of growth parameters. The N content of the cubic TaN films was controlled from N/Ta=0.7 up to 1.3 by changing nitrogen partial pressure. The resistivity and growth rate increase with increasing N concentration in the film. The Cl and H content were found to be strong functions of plasma exposure time and growth temperatures, and TaN films with resistivity as low as 350 μΩ cm wer...

Robust TaNx diffusion barrier for Cu-interconnect technology with subnanometer thickness by metal-organic plasma-enhanced atomic layer deposition

TaNx diffusion barriers with good barrier properties at subnanometer thickness were deposited by plasma-enhanced atomic layer deposition (PE-ALD) from pentakis(dimethylamino)Ta. Hydrogen and/or nitrogen plasma was used as reactants to produce TaNx thin films with a different nitrogen content. The film properties including the carbon and oxygen impurity content were affected by the nitrogen flow during the process. The deposited film has nanocrystalline grains with hydrogen-only plasma, while the amorphous structure was obtained for nitrogen plasma. The diffusion barrier properties of deposited TaN films for Cu interconnects have been studied by thermal stress test based on synchrotron x-ray diffraction. The results indicate that the PE-ALD TaN films are good diffusion barriers even at a small thickness as 0.6nm. Better diffusion barrier properties were obtained for higher nitrogen content. Based on a diffusion kinetics analysis, the nanocrystalline microstructure of the films was responsible for the bette...

Fabrication and Performance Limits of Sub-0.1 µm Cu Interconnects

As the on-chip interconnect linewidth and film thickness shrink below 0.1 µm, the size effect on Cu resistivity becomes important, and the electrical performance deliverable by such narrow metal lines needs to be assessed critically. From the fabrication viewpoint, it is also crucial to determine how structural parameters affect resistivity in the sub-0.1 µm feature size regime. To evaluate the scaling of resistivity with thickness, we have fabricated a series of Ta/Cu/Ta/SiO 2 thin film structures with Cu thickness ranging from 1 µm to 0.02 µm. These test structures revealed a far larger (∼2.3 ×) size effect than that expected from surface scattering. We have also fabricated test structures containing 50-nm-wide Cu lines wrapped in Ta-based liners and embedded in insulating SiO 2 using e-beam lithography, high-density plasma etching, ionized PVD Cu deposition, and chemical-mechanical planarization processes. Direct current (16 nA) resistance measurements from these 50-nm-wide Cu lines have also shown a higher- than-expected distribution of resistivity. Cross-sectional TEM and surface AFM observations suggest that the observed extra resistivity increase can be attributed to small grain sizes in ultra- thin Cu films and to Cu/Ta interface roughness. Monte Carlo simulations are used to quantify the extra resistivity resulting from interface roughness.