Gary E. McGuire

Formation of epitaxial CoSi2 films on (001) silicon using Ti‐Co alloy and bimetal source materials

Using coevaporated Ti‐Co alloy and sequentially evaporated Ti‐Co bimetallic layer source materials, CoSi2 films have been grown on (001) Si. The film resistivity and resistance thermal stability are excellent. The CoSi2 are epitaxial single‐crystal films containing antiphase domains in the Ti‐Co bimetallic layer cases and are polycrystalline films containing a substantial portion of epitaxial grains in the Ti‐Co alloy cases. The epitaxial or substantially epitaxial nature of these CoSi2 films is the reason for the excellence in the film resistivity and resistance thermal stability. We believe that the epitaxial nature of the CoSi2 films results from two roles played by Ti. In the first, Ti served as a getterer for removing the native oxide layer on the Si wafer surfaces, which causes the nucleation of CoSi2 grains with random orientations. In the second, Ti silicides formed in the early stage of the annealing process served as Co diffusion barriers preventing Co2Si and CoSi formation, which would also lea...

Resistance and structural stabilities of epitaxial CoSi2 films on (001) Si substrates

The resistance and structural stabilities of the epitaxial CoSi2 films, grown on (001) Si substrates using sequentially deposited Ti‐Co bimetallic layer source materials, have been investigated by further anneals under extended conditions. In contrast to reported polycrystalline silicide film cases, the epitaxial CoSi2 films are very stable under the additional rapid thermal annealing treatment at 1100 °C for times from 10 to 60 s. This means that such CoSi2 films are able to stand the further heat treatment required in the ultralarge‐scale integration regime of Si integrated circuit fabrication. The quality of the further annealed films has been actually improved: The film resistivity has decreased to reach a value as low as 10 μΩ cm, and the film structure has become more perfect, e.g., the densities of antiphase domains and film‐Si interface facets have been decreased. For technological applications, it is necessary to remove the Ti‐Co‐Si alloy layer formed concomitantly on top of the as‐grown CoSi2 fi...

High field emission reproducibility and stability of carbon nanosheets and nanosheet-based backgated triode emission devices

The authors have characterized field emission properties of freestanding, 1nm thick graphene layers, called carbon nanosheets (CNSs), which were grown perpendicular to the growth surface using a radio-frequency plasma-enhanced chemical vapor deposition technique. The CNSs are metallic impurity-free and have uniform height distribution (standard deviation of 200h at 1.3mA emission current level. Over this time, no degradation has been observed, the variability of the individual I-V curves is small among 7216 voltage cycles, and the standard deviation at the maximum current was no more than 2.3%. A nanosheet-based backgated triode emission device has been developed to take advantage of the nanosheet field emission performance. Prototype devices have confirmed triode operation and stable electron emission.

Incorporation of metal silicides and refractory metals in VLSI technology

The advantages and issues associated with the incorporation of metal silicides and the selective deposition of refractory metals into VLSI device technology are illustrated using examples from 1 to 0.25 μm CMOS technology where the silicide or metal are formed over a pre-existing junction. While the drive current characteristics, latch-up resistance, and series resistance of junction-clad devices ae generally improved, other characteristics, such as hot electron stability, threshold voltage control, and short channel effect may be adversely effected. Reducing the metal (silicide) thickness to reduce silicon consumption and thereby allow scaling the junction depth results in films having considerably higher resistivity and poorer thermal stability. The use of silicide as a diffusion source is shown to be one possible way to scale the technology to smaller dimensions while minimizing the scaling of the silicide thickness. Here we report low leakage (<10 nA/cm2)n+ and p+ junctions where the junction motion beyond the silicide is believed to be less than 1 nm.

Selective plasma deposition

A deposition process provides selective areal deposition on a substrate surface having separate areas of different materials comprises forming a plasma over the substrate, injecting coating species into the plasma by either of sputtering or gaseous injection, adding a reactive gas for altering surface binding energy at the coating surface, and biasing the substrate during deposition to bombard the substrate with ionic species from the plasma. Surface binding energy is altered, in the general case, differently for the separate areas, enhancing selectivity. Bias power is managed to exploit the alteration in surface binding energy. In the case of gaseous injection of the coating species, and in some cases of sputtering provision of the coating material, the temperature of the substrate surface is managed as well. In an alternative embodiment, selectivity is to phase of the coating material rather than to specific areas on the substrate, and a selected phase may be preferentially deposited on the substrate.

Science and engineering of nanodiamond particle surfaces for biological applications (Review)

Diamond has outstanding bulk properties such as super hardness, chemical inertness, biocompatibility, luminescence, to name just a few. In the nanoworld, in order to exploit these outstanding bulk properties, the surfaces of nanodiamond (ND) particles must be accordingly engineered for specific applications. Modification of functional groups on the NDs surface and the corresponding electrostatic properties determine their colloidal stability in solvents, formation of photonic crystals, controlled adsorption and release of cargo molecules, conjugation with biomolecules and polymers, and cellular uptake. The optical activity of the luminescent color centers in NDs depends on their proximity to the NDs surface and surface termination. In order to engineer the ND surface, a fundamental understanding of the specific structural features and sp(3)-sp(2) phase transformations on the surface of ND particles is required. In the case of ND particles produced by detonation of carbon containing explosives (detonation ND), it should also be taken into account that its structure depends on the synthesis parameters and subsequent processing. Thus, for development of a strategy of surface modification of detonation ND, it is imperative to know details of its production. In this review, the authors discuss ND particles structure, strategies for surface modification, electrokinetic properties of NDs in suspensions, and conclude with a brief overview of the relevant bioapplications.

Advanced processing techniques for through-wafer interconnects

The fabrication of interconnects used in future microelectronic devices and for three-dimensional (3D) integration of these components will require advanced integrated circuit (IC) processing techniques. One attractive approach to providing increased connectivity is to use through-wafer interconnects. The primary challenge to implementing 3D stacking is the formation of these high aspect ratio interconnects with a sufficiently small diameter and, consequently, with sufficiently high density. Processing techniques to fabricate through-wafer interconnects in silicon for applications that require multichip stacking or contacts on both sides of the wafer will be described. The techniques used for fabrication of the vertical interconnects are compatible with complementary metal–oxide–semiconductor technology and executed within the thermal budget of a completed IC. The processing techniques to be described include: deep silicon etching (DRIE) to form small diameter vias, insulator lining, adhesion/barrier laye...

Infrared Absorption Properties of Carbon Nanotube/Nanodiamond Based Thin Film Coatings

We report on the characterization of thin-film near and short wavelength infrared absorbers comprised of carbon nanotubes dispersed in a polymer. Charged nanodiamond particles are used to effectively and uniformly disperse the carbon nanotubes in the polymer matrix, leading to a very homogenous film. Using this new technique, we demonstrate an infrared absorption of up to 95% in films with thicknesses . This remarkably high absorption is the result of low reflection off the surface and high absorption across the film thickness. The complex refractive index of the films is extracted using an effective media approximation. Calculations show the film has a wide angle for high absorption and is polarization independent. These films are easy to fabricate, robust and damage-resistant, and are compatible with post-processing techniques. These films can be used as the coating layer to boost the efficiency of uncooled infrared sensors and solar-thermal energy harvesters.

Improved stability of thin cobalt disilicide films using BF2 implantation

The thermal stability of ∼50 nm CoSi2 and TiSi2 thin films after BF2+ implantation was investigated. The electrical characteristics of silicide films were evaluated after high temperature annealing as a function of implanted BF2+ energy. It was observed that implantation with a projected range near the silicide/silicon interface produced the most stable films. The silicide/silicon interface morphology was investigated using scanning tunneling microscopy, where with appropriate BF2 implantation conditions, smoother interfaces were seen after high temperature annealing. The stabilizing effect is attributed to fluorine segregation into the silicide grain boundaries and at the silicide/silicon interface.

Field emission device with back gated structure

Analysis and performance optimization of a back-gated field emission device is provided. The device consists of an anode, electron emitting cathodes and gate electrode that are placed below the cathode (“back gate”). The role of a back gate is to control electron emission from the cathode by changing the voltage on the back gate. The top of the cathode is selectively coated with an electron emissive material/structure that presents better emission properties when compared to the material of the cathode. The role of the cathode geometry, back gate voltage, cathode-gate distance, distance between cathode electrodes, the back gate dielectric, as well as field emission characteristics of the emitting material on the top of a cathode were analyzed using continuum electrostatic simulations. The proposed design significantly facilitates fabrication of the field emitting devices while decreasing the amount of charge lost to the gate and potentially reducing the likelihood of catastrophic discharges.