Anthony F. Bernhardt

Electrochemical Planarization for Multilevel Metallization

The authors describe an electrochemical planarization technology involving electroplating followed by electropolishing, resulting in a very flat surface containing embedded conductors. Electrochemical planarization technology has been used to produce silicon substrate multichip modules. Both the electroplating and electropolishing processes have a thickness uniformity of better than [+-] 2% ([+-]3[sigma]) across a 100 mm wafer.

Laser-Lathe Lithography—a Novel Method for Manufacturing Nuclear Magnetic Resonance Microcoils

A novel 3-dimensional laser-lathe process for manufacturing magnetic resonance microcoils is presented. The process has been used to print coils on a variety of materials, including glass and Teflon. The dimensions of these coils can be varied easily to allow any number of different coil designs, including solenoids and saddle coils. In our fabrication process, capillary tubes sputter-coated with a thin titanium-copper multilayer are plated with a positive electrodeposited photoresist. The resist is exposed with a computer-controlled laser-lathe apparatus consisting of an argon-ion laser, an acousto-optic modulator, a movable aperture, a lead screw stage and a spindle stage. After exposure and development, copper is electrolytically deposited through the resist mask. Following copper deposition the resist mask is removed and the sputtered copper and titanium are etched away, leaving a microcoil firmly adhered to the capillary. The resistivity of the laser-lathe copper windings is 7.6% higher than the resistivity of hand-wound coils (1.85 μΩ-cm for laser-lathe copper compared with 1.72 μΩ-cm for bulk annealed copper). For laser-lathe and hand-wound microcoils of similar size and geometry, the coil quality factor, Q, of the laser patterned coils would be 7.6% lower than the hand-wound coils. Examples of 13C NMR spectra obtained using laser-lathe coils are shown, and a relative improvement of 68 in the NMR sensitivity is calculated for a laser-lathe microcoil compared with a conventional 5 mm NMR sample tube.

Construction and Operation of a Double‐Discharge TEA CO2 Laser

We have operated a double‐discharge transversely excited atmospheric pressure (TEA) CO2 laser with a Marx bank system at high output energies and efficiencies over a large discharge volume. The typical laser energy output is approximately 17 J/liter at an efficiency of 24% and a pulse‐to‐pulse variation of less than 10%. The parameters that govern the operation of the system are discussed.

Separation of isotopes by laser deflection of atomic beam. I. Barium

Spatial separation of isotopes of barium in an atomic beam has been demonstrated, using radiation pressure of light from a tunable dye laser which resolved the unusually narrow isotopic hyperfine structure of the Ba (I) 5535.7‐A resonance line. Observations of the deflected monoisotopic beam indicate an average of 25 photons scattered per atom in the deflected beam.

Arrays of field emission cathode structures with sub-300 nm gates

A novel field emission cathode process has been developed to produce cathode arrays with individual emitter structures having gates with <300 nm diameters. Ion tracking lithography was utilized to pattern submicron features, which can be controlled over the range 30–300 nm, and to create self-aligned and nanosized, gated emitter structures. Nanocone emitter tips were deposited into the gate structure using a variation of the Spindt process. Field emitter arrays having ∼300  nm gate diameters and an emitter density of 108/cm2 exhibited a current density of 4  mA/cm2 for a 45 V gate bias. This ion tracking lithographic approach is suitable and scalable for large flat panel video displays and appears to be commercially viable.

Isotope separation by laser deflection of an atomic beam

Separation of isotopes of barium has been accomplished by laser deflection of a single isotopic component of an atomic beam. With a tunable narrow linewidth dye laser, small differences in absorption frequency of different barium isotopes on the 6s21S0− 6s6p1P1 5536 Å resonance were exploited to deflect atoms of a single isotopic component of an atomic beam through an angle large enough to physically separate them from the atomic beam.It is shown that the principal limitation on separation efficiency, the fraction of the desired isotopic component which can be separated, is determined by the branching ratio from the excited state into metastable states. In barium, repeated absorptions and emissions on the 5536 Å transition eventually result in decay from the 6s6p1P1 state to the metastable 6s5d1D2 state. This was observed to occur for all but 3% of the138Ba atoms. As a result, the efficiency of separation was about 0.7 for the 8 mrad atomic beam divergence employed. (Throughput was nearly 1 mg/day. No attempt was made to maximize this value.)The isotopic purity of the separated atoms was measured to be in excess of 0.9, limited only by instrumental uncertainty. The effects of near resonant atomic scattering and excitation exchange on isotopic purity are considered.

Endovascular Catheter for Magnetic Navigation under MR Imaging Guidance: Evaluation of Safety In Vivo at 1.5T

BACKGROUND AND PURPOSE: Endovascular navigation under MR imaging guidance can be facilitated by a catheter with steerable microcoils on the tip. Not only do microcoils create visible artifacts allowing catheter tracking, but also they create a small magnetic moment permitting remote-controlled catheter tip deflection. A side product of catheter tip electrical currents, however, is the heat that might damage blood vessels. We sought to determine the upper boundary of electrical currents safely usable at 1.5T in a coil-tipped microcatheter system. MATERIALS AND METHODS: Alumina tubes with solenoid copper coils were attached to neurovascular microcatheters with heat shrink-wrap. Catheters were tested in carotid arteries of 8 pigs. The catheters were advanced under x-ray fluoroscopy and MR imaging. Currents from 0 mA to 700 mA were applied to test heating and potential vascular damage. Postmortem histologic analysis was the primary endpoint. RESULTS: Several heat-mitigation strategies demonstrated negligible vascular damage compared with control arteries. Coil currents ≤300 mA resulted in no damage (0/58 samples) compared with 9 (25%) of 36 samples for > 300-mA activations (P = .0001). Tip coil activation ≤1 minute and a proximal carotid guide catheter saline drip > 2 mL/minute also had a nonsignificantly lower likelihood of vascular damage. For catheter tip coil activations ≤300 mA for ≤1 minute in normal carotid flow, 0 of 43 samples had tissue damage. CONCLUSIONS: Activations of copper coils at the tip of microcatheters at low currents in 1.5T MR scanners can be achieved without significant damage to blood vessel walls in a controlled experimental setting. Further optimization of catheter design and procedure protocols is necessary for safe remote control magnetic catheter guidance.

Integration of vapor deposited polyimide into a multichip module packaging process

We report the first full integration of a vapor-deposited polyimide dielectric into a multichip module (MCM) electronic packaging scheme. A robust high-throughput vapor deposition polymerization (VDP) of polyimide has been developed for an interconnection scheme in which thin film metal interconnects are patterned from the top of bare die, down the sides, and onto the substrate circuit board surface. VDP polyimides films have been extensively characterized using infrared spectroscopy and prism coupling techniques. The chemical and electrical properties of the VDP polyimide films are similar to commercially available spin cast polyimides.

Vapor deposition polymerization of polyimide for microelectronic applications

We report the high-throughput vapor deposition polymerization (VDP) of smooth, uniform polyimide films for microelectronic applications. Using infrared (IR) spectroscopy, waveguiding refractive index measurements, atomic force microscopy, and matrix assisted laser desorption ionization, we have characterized both cured and uncured films. Uncured VDP films consist of oligomers (up to tetramers) and unreacted monomeric species. Cured VDP films are chemically identical to commercially available spin cast polyimides. Both IR and refractive index anisotropy are used to determine the extent of cure, and the stoichiometry of the cured film. Integration of the VDP films into a multichip module process is presented, and the application of VDP films in ultra-large-scale integrated circuit manufacturing is discussed. Finally, the vapor deposition of 3,3′,4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine, a high performance polyimide system, is presented.

Multichip packaging for very-high-speed digital systems

Abstract High-speed computing systems are limited by integrated circuit (IC) packaging technology. For system speed and compactness, ICs should be bonded in close proximity; however, this leads to heat-dissipation problems with conventional packaging. Residual inductance in chip-to-board connections also limits system speed. A packaging technology is being developed for very-high-speed, compact, and rugged computing systems, which is particularly well suited to high-power and high-I/O systems. A complete package consists of ICs bonded to a silicon circuit board (SiCB) which is, in turn, bonded to a microchannel heat-sink. The thin-film, eutectic bond between silicon dice and the SiCB provides intimate thermal and mechanical contact. The SiCB provides speed-of-light interconnect between ICs using SiO 2 as the dielectric and copper metallization. A novel electrochemical metal planarization process is used in applications requiring multiple levels of interconnection on the silicon circuit board. Laser patterning permits chip-to-SiCB interconnect to be fabricated directly on the vertical walls of attached die, which results in higher I/O density and better electrical characteristics than allowed by wire bonding or tape automated bonding (TAB). Incorporation of the microchannel heat-sink reduces overall package thermal resistance per unit area by a factor of more than 50 compared to conventional technology. Memory modules have been produced with the technology and tested according to US space qualification procedures. Enhanced thermal-shock tests (500 K temperature change, 10 s cycle time) have demonstrated the ruggedness of the technology.