M. Eizenberg

Carbon monolayer phase condensation on Ni(111)

A condensed monolayer of carbon on the (111) surface of C-doped nickel single crystals has been observed at different bulk doping levels in the range of 10−1 to 1 at%. This phase persists over a range of temperatures of more than 100 K; it is bounded at high temperatures by the formation of a dilute carbon phase at TS and at a lower temperature, TP, by the formation of a thick graphite precipitate. The ratio TSTP is about 1.11 at all doping levels investigated. The dependence of the precipitation and the phase transition temperatures on the bulk doping level allow the binding energy per carbon atom in the monolayer phase relative to that in the bulk solution to be determined; it is approximately 10% greater than for bulk graphite with a value of 0.55 eV. The partial atomic entropy in the monolayer phase was also determined; it is about 0.03 k greater than for bulk graphite.

Uniform tungsten silicide films produced by chemical vapor depostiton

A tungsten silicide film is deposited from WF6 and SiCl2 H2 onto a substrate so that the tungsten to silicon ratio is substantially uniform through the thickness of the WSix film, and the WSix film is substantially free of fluorine. The film can be deposited by a multi-stage process where the pressure in the chamber is varied, or by a high temperature, high pressure deposition process in a plasma cleaned deposition chamber. Preferably the SiCl2 H2 and the WF6 are mixed upstream of the deposition chamber. A seeding gas can be added to the process gases.

Interfacial reactions between Ni films and GaAs

The metallurgical examination of solid‐state reaction between nickel thin films and single‐crystal GaAs substrates and the resultant electrical properties of the contacts are reported. Annealing at 100–300 °C in forming gas led to formation of a metastable hexagonal phase Ni2GaAs which was stabilized due to its epitaxial growth on (001) and (111) GaAs substrates, as follows: (1011)Ni2GaAs∥(001)GaAs and (0001)Ni2GaAs∥(111)GaAs. Nickel atoms were found to be the dominant diffusing species during the ternary phase growth. Ni2GaAs is stable on (111)GaAs up to at least 600 °C, compared to 350 °C on (001)GaAs. The larger stability on (111) is explained by the better epitaxial match found in this case. Reaction on (001)GaAs in the temperature range of 350–550 °C resulted in decomposition of Ni2GaAs by NiAs precipitation. After annealing at 600 °C the reacted film was composed of two phases: NiGa and NiAs. The electrical properties of the contacts were correlated to the phase interfacing the substrate. The Ni2Ga...

Characterization of electroless deposited Co(W,P) thin films for encapsulation of copper metallization

Abstract Thin Co(W,P) films, 100–200 nm thick, were electroless deposited on oxidized silicon wafers using sputtered copper or cobalt as catalytic seed layers. The purpose of these films is to encapsulate copper preventing its corrosion or to serve as a diffusion barrier against copper contamination of silicon oxide and silicon in ULSI interconnect and packaging applications. The electroless cobalt layers were integrated with electroless copper and found to function as barriers up to a temperature of 500°C. The microstructure of the barrier film was found to consist of grains of h.c.p. cobalt, ∼10 nm in diameter, in which the grain boundaries are most probably enriched by phosphorus and tungsten. It was found that the phosphorus and tungsten impurities stabilize the h.c.p. phase, postponing the transition to the f.c.c. phase by more than 80°C, compared to pure bulk cobalt. The observed good barrier properties can be explained by the nano-sized grains along with the blocking effect of the impurities at the fast diffusion path of the grain boundaries. An advantage of these layers, relative to alternative diffusion barriers for copper, is their low electrical resistivity, 40 μΩ cm.

Annealing-induced interfacial toughening using a molecular nanolayer

Self-assembled molecular nanolayers (MNLs) composed of short organic chains and terminated with desired functional groups are attractive for modifying surface properties for a variety of applications. For example, organosilane MNLs are used as lubricants, in nanolithography, for corrosion protection and in the crystallization of biominerals. Recent work has explored uses of MNLs at thin-film interfaces, both as active components in molecular devices, and as passive layers, inhibiting interfacial diffusion, promoting adhesion and toughening brittle nanoporous structures. The relatively low stability of MNLs on surfaces at temperatures above 350–400 °C (refs 12, 13), as a result of desorption or degradation, limits the use of surface MNLs in high-temperature applications. Here we harness MNLs at thin-film interfaces at temperatures higher than the MNL desorption temperature to fortify copper–dielectric interfaces relevant to wiring in micro- and nano-electronic devices. Annealing Cu/MNL/SiO2 structures at 400–700 °C results in interfaces that are five times tougher than pristine Cu/SiO2 structures, yielding values exceeding ∼20 J m-2. Previously, similarly high toughness values have only been obtained using micrometre-thick interfacial layers. Electron spectroscopy of fracture surfaces and density functional theory modelling of molecular stretching and fracture show that toughening arises from thermally activated interfacial siloxane bridging that enables the MNL to be strongly linked to both the adjacent layers at the interface, and suppresses MNL desorption. We anticipate that our findings will open up opportunities for molecular-level tailoring of a variety of interfacial properties, at processing temperatures higher than previously envisaged, for applications where microlayers are not a viable option—such as in nanodevices or in thermally resistant molecular-inorganic hybrid devices.

Evaluation of electroless deposited Co(W,P) thin films as diffusion barriers for copper metallization

Abstract Electroless deposited Co(W,P) thin films were evaluated as diffusion barriers for copper metallization. Capacitance versus time measurements of MOS structures as well as SIMS depth profiles indicate that 30-nm-thick films can function as effective barriers against copper diffusion after thermal treatments up to 500°C. The improved barrier properties relative to sputtered cobalt are explained by the incorporation of phosphorus (8–10 at.%) and tungsten (∼2 at.%) which most probably enrich the grain boundaries of the nanocrystalline hcp cobalt grains, forming a ‘stuffed’ barrier. The phosphorus and tungsten additions stabilize the hcp crystalline structure of the cobalt grains, delaying the transition to the fcc phase by more than 80°C compared to bulk pure cobalt. An advantage of this material compared to alternative diffusion barriers for copper is its relatively low resistivity of 80 μΩ cm.

Chemical vapor deposited TiCN: A new barrier metallization for submicron via and contact applications

High quality chemical vapor deposited (CVD) TiCN films were produced in a single wafer reactor using a metalorganic precursor (tetrakisdimethylamino titanium). The films have excellent step coverage (≳80%) over high aspect‐ratio contacts as well as a very low particle level. These properties are obtained because the films were deposited under surface‐reaction controlled conditions; the measured activation energy is 0.9 eV. The stress levels of the films are relatively low, below 5×109 dyn/cm2 compressive. The films also show good barrier properties against Al, Cu, and WF6 attack, that are attributed to their amorphous component, to the high C content of the films, and to the high step coverage. The electrical properties of the CVD TiCN films were evaluated at the via level, and the resistance contribution was shown in many cases to be comparable to that of sputtered TiN. These properties make this material a suitable barrier material for contact and via applications in sub‐0.5 μm devices.

TiCN: A new chemical vapor deposited contact barrier metallization for submicron devices

High‐quality chemical vapor deposited TiCN films were produced in a single wafer reactor using a metallorganic (TDMAT) precursor. The films have excellent step coverage over high aspect‐ratio contacts as well as very low particle content. These properties are obtained because the films are deposited under surface‐reaction controlled conditions. The films show also excellent barrier properties against Al and WF6 attack. These properties make this material a superb contact barrier material for ultra‐large‐scale integrated devices.

Properties of Copper Films Prepared by Chemical Vapor Deposition for Advanced Metallization of Microelectronic Devices

Nucleation and growth of Cu by chemical vapor deposition (CVD) using hexafluoracetylacetonato-Cu(I)-trimethylvinylsilane [hfac(Cu)tmvs] on different physical vapor deposition (PVD) diffusion barriers, namely, tantalum (Ta) and tantalum nitride (TaN x with x orientation of the grains and no amorphous interlayer.

Structures of ultra-thin atomic-layer-deposited TaNx films

Atomic layer deposition (ALD) is an attractive technique in fabrication of microelectronics presently and in the future, for its accurate thickness control in atomic scale, excellent conformality, and uniformity over large areas at low temperature. It has been adapted and used in deposition of ultrathin TaNx films as diffusion barriers for Cu metallization. In this study, composition, structure, and stability of ultra-thin (1.5–10 nm) atomic layer deposited films are characterized by a set of complementary analytical techniques. The results indicate that the N to Ta atomic concentration ratio in the ALD TaNx films is approximately 2, independent of the film thickness and annealing up to 750 °C. Hydrogen, oxygen, and carbon are detected as impurities within the as-deposited films. The as-deposited ALD TaNx films have an fcc NaCl-type nanocrystalline structure even when the film thickness is 1.5 nm. Following thermal anneal at 600 °C and higher, the films do not undergo a structural change except for an inc...