Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

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Diamond-like amorphous carbon

▪ Abstract The synthesis of nanocrystalline diamond films from carbon-containing noble gas plasmas is described. The nanocrystallinity is the result of new growth and nucleation mechanisms, which involve the insertion of C2, carbon dimer, into carbon-carbon and carbon-hydrogen bonds, resulting in hetereogeneous nucleation rates on the order 1010 cm−2 s−1. Extensive characterization studies led to the conclusion that phase-pure diamond is produced with a microstructure consisting of randomly oriented 3–15-nm crystallites. By adjusting the noble gas/hydrogen ratio in the gas mixture, a continuous transition from micro- to nanocrystallinity is achieved. Up to 10% of the total carbon in the nanocrystalline films is located at 2 to 4 atom-wide grain boundaries. Because the grain boundary carbon is π-bonded, the mechanical, electrical, and optical properties of nanocrystalline diamond are profoundly altered. Nanocrystalline diamond films are unique new materials with applications in fields as diverse as tribolo...

Nanocrystalline diamond films1

Modern computer microprocessor chips are marvels of engineering complexity. For the current 45 nm technology node, there may be nearly a billion transistors on a chip barely 1 cm2 and more than 10 000 m of wiring connecting and powering these devices distributed over 9-10 wiring levels. This represents quite an advance from the first INTEL 4004B microprocessor chip introduced in 1971 with 10 μm minimum dimensions and 2 300 transistors on the chip! It has been disclosed that advanced microprocessor chips at the 32 nm node will have more than 2 billion transistors.1 For instance, Figure 1 shows a sectional 3D image of a 90 nm IBM microprocessor, containing several hundred million integrated devices and 10 levels of interconnect wiring, designated as the back-end-of-the-line (BEOL). Since the invention of microprocessors, the number of active devices on a chip has been exponentially increasing, approximately doubling every two years. This trend was first described in 1965 by Gordon Moore,2 although the original discussion suggested doubling the number of devices every year, and the phenomenon became popularly known as Moore’s Law. This progress has proven remarkably resilient and has persisted for more than 50 years. The enabler that has permitted these advances is known as scaling, that is, the reduction of minimum device dimensions by lithographic advances (photoresists, tooling, and process integration optimization) by ∼30% for each device generation.3 It allowed more active devices to be incorporated in a given area and improved the operating characteristics of the individual transistors. It should be emphasized that the earlier improvements in chip performance were achieved with very few changes in the materials used in the construction of the chips themselves. The increase of performance with scaling * Corresponding author. E-mail: gdubois@us.ibm.com. † IBM Almaden Research Center. ‡ Stanford University. Willi Volksen received his B.S. in Chemistry (magna cum laude) from New Mexico Institute of Mining and Technology in 1972 and his Ph.D. in Chemistry/Polymer Science from the University of Massachusetts, Lowell, in 1975. He then joined the research group of Prof. Harry Gray/Dr. Alan Rembaum at the California Institute of Technology as a postdoctoral fellow and upon completion of the one-year appointment joined Dr. Rembaum at the Jet Propulsion Laboratory as a Senior Chemist in 1976. In 1977 Dr. Volksen joined the IBM Research Division at the IBM Almaden Research Center in San Jose, CA, where he is an active research staff member in the Advanced Materials Group of the Science and Technology function.

Low dielectric constant materials.

We have determined the dielectric functions of ZnO:Ga and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}:\mathrm{Sn}$ with different carrier concentrations by spectroscopic ellipsometry. The dielectric functions have been obtained from ellipsometry analyses using the Drude and Tauc-Lorentz models. With increasing Hall carrier concentration ${N}_{\text{Hall}}$ in a range from ${10}^{19}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}{10}^{21}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, the dielectric functions of ZnO:Ga and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}:\mathrm{Sn}$ show drastic changes due to increases in (i) free-carrier absorption in a low-energy region and (ii) the Burstein-Moss shift in a high-energy region. The analyses of the dielectric functions revealed reductions in high-frequency dielectric constant ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}$ and increases in plasma energy ${E}_{\mathrm{p}}$ as ${N}_{\text{Hall}}$ in the films increases. From a set of the parameters $({N}_{\text{Hall}},\phantom{\rule{0.2em}{0ex}}{\ensuremath{\epsilon}}_{\ensuremath{\infty}},\phantom{\rule{0.2em}{0ex}}{E}_{\mathrm{p}})$ determined experimentally, effective mass ${m}^{*}$ of ZnO:Ga and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}:\mathrm{Sn}$ is extracted. In contrast to previous studies, we found linear increases in ${m}^{*}$ with increasing ${N}_{\text{Hall}}$. When the variations of ${m}^{*}$ with carrier concentration are taken into account, carrier concentrations determined optically from spectroscopic ellipsometry show remarkable agreement with those estimated by Hall measurements. Nevertheless, the electron mobility obtained from spectroscopic ellipsometry and Hall measurements indicates rather poor agreement. We attributed this to the presence of grain boundaries in the films. In this article, we discuss various effects of carrier concentration on the optical properties of transparent conductive oxides.

Effects of carrier concentration on the dielectric function of ZnO:Ga and In 2 O 3 : Sn studied by spectroscopic ellipsometry: Analysis of free-carrier and band-edge absorption

We describe a novel method for the spectroscopic measurement of the state of polarization (SOP) of light. A pair of thick birefringent retarders is incorporated into the spectroscopic polarimeter, so the generated channeled spectrum is composed of three quasi-cosinusoidal components carrying the information about the SOP of the light that is being measured. Fourier inversion of the channeled spectrum provides significant parameters for determination of the spectrally resolved Stokes parameters of light. No mechanically movable components for polarization control or active devices for polarization modulation are used, and all the Stokes parameters can be determined at once from only the single spectrum. The effectiveness of this method is demonstrated by the generation of elliptically polarized light whose SOP varies with wave number.

Spectroscopic polarimetry with a channeled spectrum.

A multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to measure the time evolution of spectra (1.5–4.0 eV) in the normalized Stokes vector of the light beam reflected from the surface of a growing film. With this instrument, a time resolution of 32 ms for full spectra is possible. Several advantages of the rotating-compensator multichannel ellipsometer design over the simpler rotating-polarizer design are demonstrated here. These include the ability to: (i) determine the sign of the p-s wave phase-shift difference Δ, (ii) obtain accurate Δ values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the sample. We have demonstrated the use of the latter spectra to characterize instrument errors such as stray light inside the spectrograph attached to the multichannel detector. The degree of polarization of the reflected beam has also been applied to characterize the time evo...

Rotating-compensator multichannel ellipsometry: Applications for real time Stokes vector spectroscopy of thin film growth

Advances in multichannel spectroscopic ellipsometry

Effects of processing conditions on the growth of nanocrystalline diamond thin films: real time spectroscopic ellipsometry studies

A multichannel ellipsometer in the dual rotating-compensator configuration has been developed for applications in real time Mueller matrix spectroscopy of anisotropic surfaces and thin films. The sequence of optical elements for this instrument configuration can be denoted PC1r(5ω)SC2r(3ω)A, where P, S, and A represent the polarizer, sample, and analyzer. In this sequence, C1r and C2r represent the first and second compensators, rotating with angular frequencies of 5ω and 3ω, respectively, where ω=π/TC is the base angular frequency (corresponding to 2 Hz) and TC=0.25 s is the fundamental optical period. The instrument can provide 170 point spectra over the wavelength range from 235 nm (5.3 eV) to 735 nm (1.7 eV) in all 16 elements of the unnormalized Mueller matrix with minimum acquisition and repetition times of TC=0.25 s. In this study, instrumentation calibration procedures are demonstrated in the transmission geometry without a sample, including (i) alignment of the two MgF2 zero-order biplate compensators, (ii) determination of the retardance and phase spectra for the compensators, (iii) determination of the offset angles for the optical elements, and (iv) characterization of the spectral response function of the ellipsometer. Calibration procedure (iv) allows the (1,1) element of the transmission Mueller matrix to be determined; thus the unnormalized Mueller matrix can be obtained. The dual rotating-compensator multichannel ellipsometer is assessed with respect to its performance in transmission without a sample, and is then applied in the transmission geometry to study anisotropy, depolarization, and light scattering effects for a MgF2 helicoidally sculptured thin film on a glass substrate. Numerous future applications of this instrument are anticipated for real time analysis of complex surfaces and thin films in the reflection geometry as well.

Dual rotating-compensator multichannel ellipsometer: Instrument development for high-speed Mueller matrix spectroscopy of surfaces and thin films

Real time spectroscopic ellipsometry has been applied to characterize the substrate temperature (T) dependence of the deposition rates for nanocrystalline diamond thin films prepared by microwave plasma‐enhanced chemical vapor deposition on seeded Si substrates. With the real time capability, it is possible to determine the rates at which the diamond mass thickness (i.e., volume per area) increases during the early nucleation and bulk film growth regimes. The increases in the nucleating and bulk diamond growth rates with T for 400<T<800 °C are consistent with activation energies of ∼17 and 8 kcal/mol, respectively. The results reported here provide insights into the nature of the low‐T growth rate limitations for diamond films on nondiamond substrates.

Nucleation and bulk film growth kinetics of nanocrystalline diamond prepared by microwave plasma‐enhanced chemical vapor deposition on silicon substrates

Joungchel Lee

Papers

Rotating-compensator multichannel ellipsometry: Applications for real time Stokes vector spectroscopy of thin film growth

Advances in multichannel spectroscopic ellipsometry

Effects of processing conditions on the growth of nanocrystalline diamond thin films: real time spectroscopic ellipsometry studies

Dual rotating-compensator multichannel ellipsometer: Instrument development for high-speed Mueller matrix spectroscopy of surfaces and thin films

Nucleation and bulk film growth kinetics of nanocrystalline diamond prepared by microwave plasma‐enhanced chemical vapor deposition on silicon substrates