Y.-M. Sun

Directly patternable, highly conducting polymers for broad applications in organic electronics

Postdeposition solvent annealing of water-dispersible conducting polymers induces dramatic structural rearrangement and improves electrical conductivities by more than two orders of magnitude. We attain electrical conductivities in excess of 50 S/cm when polyaniline films are exposed to dichloroacetic acid. Subjecting commercially available poly(ethylene dioxythiophene) to the same treatment yields a conductivity as high as 250 S/cm. This process has enabled the wide incorporation of conducting polymers in organic electronics; conducting polymers that are not typically processable can now be deposited from solution and their conductivities subsequently enhanced to practical levels via a simple and straightforward solvent annealing process. The treated conducting polymers are thus promising alternatives for metals as source and drain electrodes in organic thin-film transistors as well as for transparent metal oxide conductors as anodes in organic solar cells and light-emitting diodes.

Oxidation of Si(100) in nitric oxide at low pressures: An x-ray photoelectron spectroscopy study

Ultrathin (8–23 A) silicon oxynitrides have been studied in the temperature range of 560–1000 °C in 4 Torr of NO using a sequential growth and analysis approach. X-ray photoelectron spectroscopy indicates that with increasing growth temperature and time, a bonding structure with predominantly Si–O rather than Si–N formation is favored. Simultaneously, the average volume fraction of N (N/N+O) in the dielectric decreases, as a consequence of which the N1s binding energy increases by 0.2–0.8 eV from its initial value of 397.8 eV at a thickness of 8 A. A correlation of the electrical characteristics of NO grown oxynitrides with nitrogen content and location has been made. A film growth mechanism that takes into account the removal of previously incorporated N by NO is also proposed.

Patterning conductive copper by nanotransfer printing

We describe a method for patterning conductive copper over large areas by nanotransfer printing (nTP). This technique is purely additive and yields feature sizes in the 1–500 μm range. Unlike gold patterns printed in a similar manner, oligomers from poly(dimethylsiloxane) (PDMS) stamps used in nTP permeate through the entire thickness of printed copper resulting in nonconductive patterns. Hot leaching the PDMS stamps in toluene prior to printing removes residual oligomers; printing with pretreated stamps reproducibly yields conductive copper patterns with an average resistivity of 31μΩ-cm.

Iridium film growth with indium tris-acetylacetonate: oxygen and substrate effects

Oxygen and substrate effects on iridium film growth have been investigated by metallorganic chemical vapor deposition (MOCVD), insitu X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Iridium trisacetylacetonate, Ir(CH3COCHCOCH3)3, was used as the Ir precursor. High purity CVD Ir films were obtained when this precursor was codosed with oxygen. Without oxygen, the Ir film contains noticeable carbon. The presence of oxygen not only removes carbon, but also prevents carbon incorporation from other reactive gas components, such as acetone. Oxygen also controls the film deposition rate and has a significant impact on the film morphology. Substrate effects on the initial growth rate are evidenced by the fact that the growth rate on a titanium-carbonitride (TiCN) surface is significantly higher than that on an SiO2 surface. Selective deposition in the presence of oxygen was also observed: compared to SiO2 and Ta2O5 substrates, no deposition (or very slow deposition) was observed on sapphire at 400°C. The topography of films grown on the various substrates was compared using AFM. Ir was roughest when deposited on SiO2 using a low oxygen flow rate. This is because the initial growth of Ir films on SiO2 follows a three-dimensional growth mode on isolated islands,

Chemical vapor deposition of ultrathin Ta2O5 films using Ta[N(CH3)2]5

Tantalum oxide films were deposited on Si substrates by chemical vapor deposition using the precursor Ta[N(CH3)2]5, and an oxidizing agent—O2, H2O, or NO. Temperatures ranged between 400 and 500 °C and total pressures between 10−3 and 9 Torr. NO did not lead to satisfactory film growth rates. Insignificant (<1 at. %) N and up to a few percent C are incorporated when O2 is the oxidant and the total pressure is in the Torr regime. In the milliTorr regime, the Ta2O5 films, grown using either O2 or H2O, contain readily detectable amounts of C and N. For the films grown with O2 in the Torr regime, leakage currents were significantly lowered when the flow rate of O2 increased from 100 to 900 sccm.

Evaluation of precursors for chemical vapor deposition of ruthenium

Abstract Several commercially available organometallic precursors have been evaluated for metallorganic chemical vapor deposition (MOCVD) of pure ruthenium films. Of these, only a dimer, [RuC5H5(CO)2]2, proved suitable for CVD. On patterned Si3N4 and flat barium strontium titanate (BST), pure, conductive, conformal ruthenium films were grown from this dimer when oxygen was used as a reaction gas. Without oxygen, significant amounts of carbon were incorporated into the film. Oxygen and substrate temperature effects on ruthenium CVD film growth were investigated by resistivity measurements, in situ X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Growth conditions and possible mechanisms are discussed.

Near-monodispersed polyaniline particles through template synthesis and simultaneous doping with diblock copolymers of PMA and PAAMPSA

Well-defined block copolymers of poly(methyl acrylate) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PMA/PAAMPSA, were successfully synthesized by atom transfer radical polymerization. These amphiphilic block copolymers spontaneously form micelles with a hydrophobic PMA core and a hydrophilic PAAMPSA corona in aqueous solutions. These micelles were used to template synthesize polyaniline. Because the polymerization of aniline is restricted to the PAAMPSA corona, which also serves as the dopant, the size of the conductive particles can be controlled by tuning the molecular characteristics of the block copolymer while maintaining a narrow size distribution. When cast as films, their conductivities are influenced by the weight fraction of polyaniline present, with higher polyaniline loading resulting in higher conductivities.

Study of copper diffusion through a ruthenium thin film by photoemission electron microscopy

Photoemission electron microscopy is used to study copper diffusion through a ruthenium thin film. The photoemission electron microscopy images display a large contrast between Cu and Ru due to the differences in work function, making photoemission electron microscopy an ideal methodology to study thin film diffusion in real time. Between 175 and 290°C, Cu mainly diffuses through defect sites in the thin Ru film. Uniform diffusion of Cu through the Ru film begins at approximately 300°C. The results are confirmed by x-ray photoemission spectroscopy depth profiling and scanning electron microscopy–energy dispersive x-ray spectroscopy analysis.

Growth Chemistry of Ultrathin Silicon Nitride and Oxynitride Passivation Layers on Si(100)

We have studied the thermal growth chemistry and bonding structure of three promising ultrathin (5–20A), nitrogen rich passivation layers on Si(100), namely-Si 3 N 4 , NO/Si(100) grown oxynitride and NO annealed SiO 2 . These films are intended to serve as substrates with excellent diffusion barrier/interface properties during deposition of high- K dielectrics such as Ta 2 O 5 , with t SiO2 equivalent

Thermal and Chemical Instability Between Iridium Gate Electrode and Ta205 Gate Dielectrics

The thermal and chemical stability of thin CVD iridium films deposited on thin CVD tantalum pentoxide (Ta 2 O 5 ) films on Si(100) have been investigated by means of in-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Angle Resolved XPS (ARXPS). It was found that upon annealing in vacuum at 800 °C for more than 1 min, tantalum oxide at the Ir-Ta 2 O 5 interface was decomposed and formed metallic tantalum which diffused through Ir, while changes in iridium film itself were negligible. When annealed at 750 °C within 15 minutes, intermediate partially oxidized Ta was formed and coexisted with metallic and oxidized Ta. A portion of metallic Ta near Ir-vacuum interface was subsequently oxidized when the films were exposed in air.