The suspension behavior of Al2O3 and silicate glass powders was investigated using two nonaqueous liquids — methanol (MEOH) and methyl isobutyl ketone (MIBK). The effects of liquid ratio (MIBK/MEOH) and polyvinyl butyral resin additions on suspension properties were determined. Rheological and sedimentation measurements showed that all suspensions without polymer were at least partially flocculated. However, increased flocculation was observed at high MIBK contents. Electrokinetic measurements revealed that this was due to decreased electrostatic repulsion between particles. Rheological and sedimentation measurements indicated that small polymer additions promote good dispersion (via steric stabilizazation) in glass — 3:1,MIBK/MEOH suspension. In contrast, bridging flocculation apparently occurs in glass — MEOH suspensions containing polymer. These differences in suspension behavior are associated with differences in the adsorption behavior of the polymer onto the glass particles.

A sol-gel process was developed to produce continuous mullite fibers. Spinnability of the sol was achieved by controlling hydrolysis and polycondensation conditions. The rheological properties needed for continuous fiber spinning were determined. The effect of aging of spun fibers on mullite formation was determined. Under optimum processing conditions, mullite formation was observed at ∼1000°C and theoretical density was approached at ∼1300°C. Fibers heat treated at 1500°C showed approximately 1 μm grain sizes. Exposure to a concentrated HF solution had no discernable effect on the fibers which suggested that little or no siliceous glass was present.

Sic fibers were prepared with boron nitride (BN) coatings using an in-situ processing method. Scanning Auger electron spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy showed that the coatings were uniformly distributed, well-crystallized, hexagonal BN. The coated fibers had high strength (∼ 3 GPa) and excellent creep resistance based on bend stress relaxation tests.

High-density compacts, up to 88% theoretical density, of Al2O3-SiC whiskers were prepared by a pressure casting and impregnation technique. Starting with these green bodies, composites of Al2O3−20 vol% SiC whiskers were pressureless sintered to higher than 95% theoretical density. They were further densified by hot isostatic pressing up to 99% theoretical density, resulting in a rupture strength of 680 MPa and a fracture toughness of 4.70 Mpa m1/2.

Polymer-derived SiC-based fibers with fine-diameter (∼ 10–15 μm) and high strength (∼ 3 GPa) were prepared with carbon-rich and near-stoichiometric compositions. The creep resistance of these fibers (as assessed by bend stress relaxation, BSR, measurements) could be improved significantly by annealing heat treatments in nonoxidizing atmospheres. Fibers also showed excellent strength retention after annealing heat treatments up to 1700°C for the carbon-rich fibers and up to 1950°C for the near-stoichiometric fibers. The near-stoichiometric fibers could be prepared with ∼ 3 GPa tensile strength and BSR creep behavior which was significantly better than previously reported for other types of polymer-derived SiC- based fibers.

Al2O3/SiC whisker and Al2O3/ZrO2/SiC whisker compacts with high green density (66–69%) and homogeneous microstructure were prepared by suspension processing. Procedures for optimizing particle/whisker codispersion and subsequent consolidation by slip casting are described. Although densification is severely inhibited by Sic whiskers, compacts prepared by suspension processing show significantly higher sintered densities compared to dry-pressed samples. Suspension-processed samples containing 15 vol% whiskers could be pressureless sintered to relative densities in the range 93–99%.

SiO2/Si3N4 composites were fabricated using submicrometer composite particles which consisted of inner cores of Si3N4 and outer coatings of amorphous SiO2 Powder compacts prepared with these “microcomposite” particles showed enhanced densification compared to compacts prepared from a mixture of SiO2 and Si3N4 powders. Electron microscopy observations on sintered composites indicated that densification of the mixed powder samples was constrained by the development of rigid networks of the “non-sinterable” Si3N4 particles. In contrast, the controlled spatial distribution of phases (core + coating) in the microcomposite particles inhibited the formation of Si3N4 particle-particle contacts during sintering. Compacts with 40 vol% Si3N4 were sintered to full density (is., zero porosity) at temperatures ⩽ 1300°C. The low sintering temperature was attributed to densification by viscous flow of the SiO2 coatings. This was consistent with the deformation mechanism determined in compressive creep experiments on dense composite samples.

Deposition of TiCx films on Al2O3 substrates by chemical vapor deposition using TiCl4 and CH4 sources in H2 was studied as a function of growth temperature and inlet feed composition. Arrhenius-type behavior was observed with an apparent activation energy of 129.9 kj/mole. The stoichiometry of the film was measured as a function of inlet composition. The carbon content increased slightly with increasing CH4 partial pressure, in agreement with equilibrium predictions. The TiCx grain size increased with deposition rate, and grains were highly oriented.

We report two novel routes, sol-gel and electroless plating, for the synthesis of lead-free solders. Novel processes with these routes were developed and demonstrated for Sn-Ag-Cu, Sn-Ag systems to achieve thin bonding layers for assembly of fine pitch integrated circuits onto substrates. Sol-gel route can be used to accurately control the final alloy composition and incorporate additives leading to the designed thermomechanical properties. In this process, the inorganic polymer solutions were spin coated and then heat-treated in a reducing atmosphere to form thin films of lead-free solders. The presence of Ag and Cu enabled easy reduction of tin oxide to tin at 400degC that was not possible with Sn precursor. With the alternate solution reduction (electroless plating) approach, bonding layers can be deposited at almost room temperatures directly on organic substrates. With this approach, the deposition selectively occurs on the metal bonding pads, which eliminates the need for any lithography. Using this approach, electroless Sn-Ag films were demonstrated on organic laminates. These thin film synthesis routes can enable short interconnections that are critical for high density, high frequency, and embedded active component packaging.

This paper presents four organic-compatible thin film processing techniques for embedding capacitors into organic PWBs. Hydrothermal synthesis allows integration of pure nano-grained barium titanate films with capacitance density of about 1 /spl mu/F/cm/sup 2/. Sol-gel and RF-sputtering in conjunction with a foil transfer process can be used to integrate a variety of perovskite thin films with the capacitance in the range of 200-400 nF/cm/sup 2/. Thermal oxidation of titanium foil also emerges as a viable process for integrating capacitance of 100s of nF using a foil transfer process. The dielectric properties of the films synthesized by these techniques as a function of various process parameters are presented. Observed dielectric properties like dielectric constant, leakage current and breakdown strengths have been correlated to structural defects and stoichiometry of the films.

Sol-gel ceramic films were fabricated for organic system-on-package compatible integral capacitor applications. The films were synthesized on Ti and Ni foils which were then transferred onto organic boards using a lamination step. SrTiO/sub 3/ and BaTiO/sub 3/ films were synthesized with capacitance as high as 700 nF/cm/sup 2/ and loss as low as 0.005. It should be noted that the high permeability of Ni (approximately 100 in bulk form) and lower conductivity compared to copper decreases the skin depth and increases the resistivity of copper. This can have a deleterious effect on Q. More studies are underway to investigate this effect.

Zirconium carbide (ZrC) and hafnium carbide (HfC) powders were produced by the carbothermal reduction reaction of carbon and the corresponding metal oxide (ZrO2 and HfO2, respectively). Solution-based processing was used to achieve a fine-scale (i.e., nanometer-level) mixing of the reactants. The reactions were substantially completed at relatively low temperatures (<1500°C) and the resulting products had small average crystallite sizes (∼50–130 nm). However, these products contained some dissolved oxygen in the metal carbide lattice and higher temperatures were required to complete the carbothermal reduction reactions. Dry-pressed compacts prepared using ZrC-based powders with ∼100 nm crystallite size could be pressurelessly sintered to ∼99% relative density at 1950°C.

Fabrication of high-k embedded capacitors on printed wiring board (PWB) is limited due to the inherent low-temperature process required for organic packaging. Current dielectrics for embedded capacitors are mostly organic with insufficient dielectric constant. Integration of high-k thin films on PWB is hindered by high processing temperature of ceramics. The goal of this work, is to develop low-cost/low-temperature, aqueous/non-aqueous based processes for embedded capacitors. Hydrothermal synthesis was used for synthesis of nanograined barium titanate films. Films synthesized at 95/spl deg/C on titanium foils yielded nanograined films (<80 nm grains) with higher capacitor yield in comparison to conventional hydrothermal films from Ti precursors or sputtered Ti. Films with capacitance of more than 1.0 pF/cm/sup 2/ and thickness of 300 nm (corresponding to a dielectric constant of above 350) were developed. Oxygen plasma treatment of hydrothermal films was found to lower the loss significantly to 0.06 from 0.28. Sol-gel technique was also explored an alternate low cost large area process for synthesis of high K low loss films. Sol-gel derived films are typically crystallized and densified at temperatures that are not compatible with organic build-up processes. This limitation has been addressed using a modified sol-gel process to deposit films on a carrier foil that was subsequently laminated onto the printed wiring board. All high-temperature processing steps required by the oxide dielectrics were performed before the embedding process. High-k barium titanate (BaTiO/sub 3/) and strontium titanate (SrTiO/sub 3/) thin film capacitors were synthesized on base-metal nickel (Ni) and titanium (Ti) foils as carrier. Rapid thermal processing (RTP) lowers the process time for the development of a well-crystallized titanate film to 3 minutes as opposed to the few hours of processing time required for conventional heat treatment. Capacitance densities ranging from /spl sim/45-700 nF/cm/sup 2/ have been achieved by varying the film thicknesses from /spl sim/250 to 900 nm and the heat treatment conditions. By following the RTP with a 1 hr heat treatment in nitrogen (N/sub 2/) atmosphere, the dielectric loss was reduced to 0.005. These sol-gel and hydrothermal films were subsequently integrated onto organic boards using conventional lamination and lithography methods, followed by low-cost wet etching.

We propose new IC packaging technologies that have the potential to bring about disruptive innovations in interconnect pitch, best electrical and mechanical properties, low-cost and chip size. Current approaches for chip to package interconnections are limited in terms of either pitch or electrical-mechanical trade-off properties. For example, lead free solder interconnects fail mechanically as the pitch is brought down from current 200 micron pitch to 20 micron. Compliant leads, on the other hand, solve mechanical reliability but at the expense of electrical performance. Solution-derived materials for reworkable nano-interconnects can be a viable technology to meet these two challenges. Nano-grained electroplated copper is chosen as the primary interconnect material. Compliancy was addressed by tuning the process to electroplate high-aspect-ratio structures. Reworkability was addressed by a thin, liquid lead-free solder interface between the interconnect and the package. Two approaches, sol-gel and electroless plating were used in this work to deposit these liquid interface films of lead free solders of the order of 50-300 nm. In the sol-gel process, metal-organic polymer solutions were heat-treated in a reducing atmosphere at 300/spl deg/C to form lead-free solders (Sn-Ag-Cu). In the other approach, lead-free alloy films were deposited from aqueous plating solutions consisting of suitable metal salts and reducing agents. This process was done at temperatures of 45/spl deg/C. The lead-free solder composition was controlled by altering the plating bath formulation. Lead-free solder films formed from both the above approaches were demonstrated to bond copper pads. Solution-derived nano-solder technology is an attractive low-cost method for bump-less nano-interconnects and other applications such as MEMS hermetic packaging and compliant interconnect bonding.

This work reports synthesis, characterization and integration of sub-micron thick nano-grained barium titanate films on organic Printed Wiring Boards (PWB). Barium titanate films were synthesized on titanium foils at 95∘C. SEM of films revealed 80 nm grains. The films were characterized using XRD, FTIR and Raman spectroscopy. As-synthesized films exhibited high capacitance densities and dielectric loss. The films were treated with oxygen plasma to reduce entrapped hydroxyl groups and this resulted in improved dielectric properties. The plasma treated films exhibited a capacitance density of 1 μ F/cm2 and a dielectric loss of 0.06. The high frequency dielectric properties were extracted from s-parameter measurements on CPW structures on these films and were found to be stable up to 8 GHz.

Nanocrystalline SiC powders were prepared at low temperature (less than or equal to1300degreesC) by carbothermal reduction reactions in silica/carbon mixtures. Fine-scale mixing of the reactants was achieved by using solution-based processing. Mechanistic studies indicated that the SiC formed in accordance with the "shrinking core" reaction model in which the rate was controlled by the reaction of silicon monoxide vapor at the carbon surface.

Most of the compliant interconnects that are currently being developed have inductance and resistance higher than desirable. There is definitive evidence that nano-structure interconnects can provide better resistance to crack growth and fatigue resistance and hence improve mechanical reliability without sacrificing the electrical properties. Current approaches to interconnects such as reflowed solder paste and electroplated interconnects cannot easily achieve nano-grained structures and also impose restrictions on the processibility. For example, screen-printing solder pastes cannot achieve very fine pitches, while electroplated interconnects are restricted to a few material systems. The current wafer level packages are at a pitch of 250-400 microns. We propose solution derived reworkable nano-interconnects as a viable technology to meet the needs of reducing pitch in the die package.This paper proposes solution derived (sol-gel based) nano-grained copper and lead free solders for fine-pitch high strength nano-structured interconnects. In this process, metal-based organic polymer solutions are heat-treated in reducing atmosphere to form metallic copper and lead-free solders (Sn-Ag-Cu). The key is to achieve ultra homogeneous mixing at atomic to molecular level. The precursors were mixed in solvent and refluxed under inert atmosphere at 125 degreesC to form metallic Cu/Sn-Ag-Cu complex solutions. The homogenous gel obtained from the hydrolysis of sol-gel precursor solution is heat treated under inert atmosphere at temperatures below 350 degreesC to achieve the desired compositions. Among a large number of methods for metal deposition, sol-gel technology, based on thermal decomposition of metal-organic compounds, can prove to be the most convenient and inexpensive for industrial applications.

Chemical-mechanical planarization (CMP), a surface preparation process used widely in integrated circuits manufacture, is currently the leading nanoscale manufacturing process worldwide, with an annual economic impact well in excess of $1 billion. Originally developed for glass polishing, CMP is used by the microelectronics industry to create silicon, silicon oxide, tungsten and copper surfaces with average roughnesses of O(10 mm). The process typically involves shearing a dilute abrasive silica or ceria nanoparticle-laden “slurry” between a compliant rough surface (the “pad”) and the surface to be polished (the “wafer”). The composition of the slurry can greatly affect material removal rates. Despite its importance, however, a lot still remains to be discovered about the fundamental mechanisms involved in this process. A multidisciplinary effort at Georgia Tech has focused upon the interfacial mechanics of this process and how nanoparticles chemomechanically wear SiO2, Si and Cu surfaces. It has been found, for example, that the wear rate of dielectric varies approximately as the particle diameter. The entrapment of particles at the asperity/dielectric interface is thought to produce the polishing, but the exact nature of this interaction is still unknown. An evanescent-wave visualization technique has therefore been developed to visualize the dynamics of fluorescent 300–500 nm diameter colloidal silica and polystyrene particles within a particle diameter of the “wafer” surface in a simplified model pad-wafer geometry. The technique has been used for the first time to the authors’ knowledge to directly measure the velocity and concentration of the interfacial particles—which presumably interact with and wear the wafer. Although the pad speeds in these studies are much lower than those encountered in the actual CMP process, the initial results suggest that there is negligible “slip” between the particle and fluid phase velocities at the wafer surface. The number of particles at the wafer surface appears, however, to be strongly affected by particle properties, including particle density and size.

Zirconium carbide (ZrC) powders were produced by the carbothermal reduction reaction of zirconia and carbon. Solution-based processing was used to achieve a fine-scale mixing of the reactants. The reaction was substantially completed at relatively low temperature (1400degreesC) and the resulting ZrC product had small average crystallite size (similar to120 nm). ZrC powder compacts were pressureless sintered to >90% relative density at 1800degreesC.