J. J. Cuomo

Amorphous metallic films for magneto‐optic applications

It has been demonstrated that perpendicular uniaxial anisotropy and compensation points in the vicinity of room temperature can be obtained in amorphous thin films of rare‐earth—transition‐metal alloys. The magneto‐optic properties of these films are reported, and it is shown that a remarkably good signal‐to‐noise ratio can be obtained in a thermomagnetically written film.

Pulsed laser deposition of diamond‐like carbon films

Carbon thin films have been prepared by 248 nm excimer laser vaporization of graphite targets. The effect of a variety of process parameters on the film properties is investigated. Deposition at or below room temperature yields diamond‐like films with low hydrogen content, high optical transmission, and high resistivity. Electron energy loss spectra indicate sp3 bond fractions of 70–85%. Detailed analyses of the pseudodielectric functions, measured using spectroscopic ellipsometry, show the films to have normal dispersion and an index of refraction of 2.5 in the visible wavelength region. The effects of a low pressure hydrogen background and the use of auxiliary pulsed and dc plasma enhancements are also examined.

Vapor deposition processes for amorphous carbon films with sp3 fractions approaching diamond

Trends in recently reported data on high sp3 fraction (up to 85%), nonhydrogenated amorphous diamond‐like carbon films deposited by ion beam sputtering and laser vaporization are examined. The degree of diamondlike film character is found to depend upon the deposition technique as well as the substrate temperature and thermal diffusivity. The data suggest that the combination of incident particle kinetic energy and surface accommodation determine the physical properties of the resultant film. A model is proposed for the condensation of energetic carbon atoms into diamondlike films in which a quench‐type surface accommodation mechanism is operative.

Electron‐beam fabrication of 80‐Å metal structures

Metal structures 100 A high with sharply defined linewidths of 80 A have been produced using an electron‐beam fabrication process. A contamination resist pattern is written with a 5‐A 45‐keV scanning electron beam in a 100‐A‐thick Au‐Pd film supported by a 100‐A carbon foil. The unprotected Au‐Pd is removed by dc ion etching with 1‐keV Ar ions. Unlike most electron‐beam microfabrication processes, the resolution of the resulting structure is not limited by electron scattering, but by the grain size of the metal films. These structures should have direct application in a large number of device fabrication problems in electron and x‐ray beam technology and they should provide masks for other microfabrication processes such as x‐ray lithography.

Langmuir probe measurements of a radio frequency induction plasma

In this work a planar, radio frequency induction plasma source is characterized in terms of ion density, electron temperature, and plasma potential using a single Langmuir probe in oxygen and noble gases. Probe measurements of density were also verified using microwave interferometry. Measured argon ion densities increase nearly linearly with power from 1×1011 cm−3 at 300 W rf power to 6×1011 cm−3 at 1.2 kW at 1×10−3 Torr. Krypton ion densities are also linear with power but saturate above 1 kW at a density of 2×1012 cm−3 at 1×10−3 Torr. Electron temperatures increase with decreasing pressure from 3 eV at 26×10−3 Torr to 7 eV at 0.3×10−3 Torr. Plasma potentials are typically 15–30 V and increase with decreasing pressure. Ion saturation current in oxygen at 5×10−3 Torr is 2.5% uniform over diagonals of 20 cm when a magnetic multipole bucket is used to confine the plasma. Ion generation energy cost in argon is 100–250 W/A.

Technology and applications of broad-beam ion sources used in sputtering. Part II. Applications

The developments in broad‐beam ion source technology described in the companion paper (Part I) have stimulated a rapid expansion in applications to materials processing. These applications are reviewed here, beginning with a summary of sputtering mechanisms. Next, etching applications are described, including microfabrication and reactive ion beam etching. The developing area of surface layer applications is summarized, and related to the existing fields of oxidation and implantation. Next, deposition applications are reviewed, including ion‐beam sputter deposition and the emerging technique of ion‐assisted vapor deposition. Many of these applications have been stimulated by the development of high current ion sources operating in the energy range of tens of hundreds of eV. It is in this energy range that ion‐activated chemical etching is efficient, self‐limiting compound layers can be grown, and the physical properties of vapor‐deposited films can be modified. In each of these areas, broad ion beam techn...

Technology and applications of broad‐beam ion sources used in sputtering. Part I. Ion source technology

The technology of broad‐beam ion sources used in sputtering applications is reviewed. The most frequently used discharge chambers are described, together with procedures for predicting performance. A new, compact ion source is described. Ion acceleration is reviewed, with particular emphasis on recent low‐energy techniques. Some of these techniques include three‐grid, small‐hole two‐grid, and one‐grid ion optics. A new material for fabrication of high‐precision ion optics is silicon. Because no stresses are introduced with the etching techniques used, the finished grid can be held to very close tolerances. A recent innovation for sputtering applications is the use of Hall‐current acceleration. This technique uses a magnetic field interacting with an electron current to provide the accelerating electric field, thereby avoiding the usual space‐charge limit on ion current density that is associated with gridded optics. Electron emission is also reviewed, with new hollow cathodes promising improved lifetimes....

Sputter deposition of dense diamond‐like carbon films at low temperature

Thin carbon films were deposited by ion beam sputtering at temperatures of 77–1073 K. Using Rutherford backscattering spectrometry and electron energy loss spectroscopy, the trends in film density and bonding were examined as a function of deposition conditions. It has been found that film density and sp3 bonding character unexpectedly increased with increased substrate thermal conductivity and decreasing substrate temperature, reaching values of 2.9 g/cc and 50%, respectively.

Picosecond optical studies of amorphous diamond and diamondlike carbon: Thermal conductivity and longitudinal sound velocity

A picosecond pump‐probe technique is used to measure the room‐temperature thermal conductivity κ and longitudinal sound velocity cl of amorphous diamond (a‐D) and diamondlike carbon (DLC) thin films. Both κ and cl were found to decrease with film hydrogen content. Depending on the film deposition technique, κ is in the range 5–10×10−2 W cm−1 K−1 for a‐D, and 3–10×10−3 W cm−1 K−1 for DLC. Values of cl were found to be in the range 14–18×105 cm s−1 for a‐D, and 6–9×105 cm s−1 for DLC.

Electrical and Optical Properties of rf‐Sputtered GaN and InN

GaN and InN thin films were grown on sapphire, silicon, and metallic substrates using rf sputtering at temperatures of 25–750°C and presputtering vacuum of 10−8 Torr. The GaN films were high in resistivity (> 108 Ω cm), but the InN layers were highly conducting with an electron concentration of 7×1018 cm−3. The refractive index for GaN ranged from 2.1 to 2.4 at long wavelengths and was dispersive below 8000 A; the index for InN is higher, 2.9. The absorption coefficient was measured from wavelengths of 2 μ to 2000 A.