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A kinetic Monte Carlo simulation of the electromigration-induced void migration behavior of three-dimensional nanovoids at the interface between a metal conductor and its dielectric overlayer is described. The results of the simulation correlate with in situ observations as well as with simple analytical models of void trapping and detachment from grain boundaries (GBs) and their junctions.

Research is presented concerning the kinetics of the reaction of eutectic SnPb solder on Cu. Solid state solder aged at 125-170-degrees Centrigrade and liquid state solder at 200-240-degrees Centigrade are compared.

Solder reflow etched on (001) Si wafer surfaces was the method used to prepare eutectic SnPb solder lines for electromigration.

Phenomena of current reduction with regard to film thickness are studied.

Eutectic SnPb solder interconnect electromigration between a Si chip and a FR4 substrate was examined.

Interfacial reaction morphology in lead-free solder alloys on electroless Ni-P was studied.

Research describing the mechanical properties of modified polyarylether films is presented. In particular various methods are used to measure the coefficient of thermal expansion, hardness and elastic modulus of these dense and porous polymeric films.

Research describing electromigration in thin film solder strips of differing tin-lead composition is presented. The work has implications for microprocessor technology as electromigration may be a serious concern in solder bumps for chip to package interconnects.

Research describing the simulation of current crowding structures is presented. In particular the electromigration phenomena associated with a serpentine structure and a two-phase alloy were investigated.

Interfacial reactions between SnPb and sputtered Cu/Ni(V)/A1 are observed using cross-sectional scanning electron microscopy and transmission electron microscopy.

The heating behavior of doped Si channels was investigated under high current stress.

The wetting behavior of eutectic SnBb on Ni foils and Ni thin films is described.

The evolution of roughness in the Cu6Sn5 intermetallic compound during the soldering reaction of PbSn on Cu and its effects on wettability has been studied. Results indicate that the root mean square roughness and the average distance between asperites have a parabolic dependence on the soldering time. However the ratio of the root mean square roughness with the average distance was observed to increase gradually for the range of soldering periods examined.

Research was conducted to examine the thermoelectric behavior of silicon thin films in silicon-on-insulator wafers. A testing structure was fabricated to measure Seebeck coefficient which is one of the most important thermoelectric parameters. Another testing structure was designed to calculate Peltier cooling effects for the powered Si channels. Results indicate that the thermoelectric power of the Si thin films could be enhanced by appropriate ion implantation and annealing processes.

The use of electrical current instead of thermal annealing to achieve dopant activation in silicon-on-insulator strips is described. Heavily boron- and arsenic-doped silicon-on-insulator strips were activated through the application of a high density electrical current. Hall measurements showed that carrier concentration increased with increased application of current. It was also shown that activation can be accomplished at a temperature lower than that of furnace annealing.

Research was conducted to examine a simple kinetic analysis of interfacial diffusion accompanied by intermetallic compound formation. The kinetics of compound formation were added based on Fisher's grain boundary diffusion model which led to the development of an analytical solution. The solution was compared to experimental data calculated from the penetration of the solder along the electroless Ni interface.

Research was conducted to analyze the solder reaction-assisted crystallization of electroless Ni-P under bump metallization in a multilayer structure. A transmission electron microscopy, energy dispersive x-ray, scanning electron microscopy and electron probe microanalyzer were used. A correlation was found between change in composition of the amorphous matrix and crystallization.

Flip chip solder bonded Si samples were tested under tensile and shear loading as a function of annealing time at 200 deg C. The solder bump was eutectic SnPb and the underbump thin film metallization was Cu/Cr deposited on oxidized Si. Results showed that the failure mode is interfacial fracture and the fracture strength declines fast with annealing time. The fracture was observed by scanning electric microscopy to occur at the Cu-Sn/Cr interface.

A study was conducted to analyze the chain/column evolution and electrorheological effect with glass/oil ER fluid. An experimental chain was assembled by mounting a couple of parallel electrodes of a glass slide. The process of chain and column formation was observed using an optical microscope. Results indicated the existence of three increasing tendencies of interaction among particles associated with processes of sequential transition between states.

The electrical behavior of the p+ and n+ channels and their contacts of these channels under high current densities are examined. The results reveal non-ohmic resistance change in both channels. The resistance of the p+-Si shows a nonlinear increase when current from 1 mA to 80 mA is applied gradually. In comparison, the resistance of the n+-Si increases with current by a smaller amount. It is hypothesized that the high field effect and Joule heating cause the initial nonlinear resistance increase.

A study was conducted to analyze the wetting behaviors of eutectic SnPb solder on copper leadframes plated with Pd/Ni and Au/Pd/Ni thin films. Solder beds of eutectic SnPb were placed in an activated rosin flux to form solder caps on the thin film surface. The solder caps were then studied as a function of varying surface films, reflow time and reflow temperature. Results showed that the solder cap can spread out continuously with reflow time.

Research was conducted on the strong polarity effect on failure at nickel and nickel silicide contacts on both n- and p-type Si under high stress conditions. In a pair of cathode and anode contacts the Ni/n+-si contact pair fails at the anode, while the Ni/p+-Si pair fails at the cathode. Results show that the Ni/Ni2Si/n+-Si and Ni/Ni2Si/p+-Si failed preferentially at the cathode. In situ resistance data indicate that the resistance of the failed contact increases with time while that of the other contact in the pair remains constant.

A study was conducted on the kinetics of Cu3Ge development and reaction with Al using in situ resistivity measurements and other techniques. Results show that Cu3Ge films have low resistivity, as well as excellent oxidation resistance, adhesion on SiO2 and thermal stability on Si. Its applications as adhesion/barrier/passivation layer for Cu ultralarge scale integration metallization were also demonstrated,

A study was conducted on the development of {111} dislocation loops and on the microstructural formation of {113} rodlike effects in silicon using cross-sectional and plan-view transmission electron microscopy. The silicon studied was rapid thermally annealed at 500-1100-degrees celsius temperature range and features a 50 keV 3.6x10(super 14) Si+/cm2 8.0 mA. The growth, nucleation and dissolution of the dislocation loops and rodlike defects were also examined.

End-of-range (EOR) dislocation loops in silicon implanted with 50 keV 10(super 16) Si/sq.cm. were examined by transmission electron microscopy. Furnace anneals at 850 degrees C and rapid thermal anneals at 1000 degrees C were conducted. The two kinds of EOR dislocation loops were found to ripen. They were faulted Frank dislocation loops and perfect prismatic dislocation loops. Their distribution profiles were found to be different from that of conventional Ostwald ripening for precipitates. The size distribution profile of faulted Frank dislocation loops can be fitted by a normal Gaussian probability function.

The wetting characteristics of eutectic SnPb solder caps on pure Au foils at 200 degrees C were examined. Intermetallic compound (AuSn4) was found on the surface of the solder cap as early as 2 sec. of reflow at 200 degrees C. The wetting angle decreased with reflow time but remained constant after 180 sec. of reflow. However, the side-band width and the diameter of the solder cap continuously increase with the reflow time to 5 min. when the entire eutectic SnPb solder cap is fully used up by intermetallic compound formation.

Resistivity, carrier mobility and density of charge carriers of epsilon1-Cu3Ge thin films indicate that they are metals with an electric resistivity of 6 micro-ohmcentimeters at room temperature. The Block-Gruneisen relation and a Debye temperature of 240 Kelvin influence the temperature dependence of the resistivity. The temperature and film thickness have no influence on the hole density.

Electromigration-induced stress evolution in narrow confined metal interconnects was investigated. The results showed that electromigration flux was resisted by the evolution of mechanical stresses in the interconnects. When dislocations and internal parameters were present, large vacancy supersaturations could not arise. Stress at the blocking boundary increased in proportion to the square root of time. In addition, the stresses located next to voids were generally small.

The effect of stress on the microstructural characteristics and grain growth and void formation in submicrometer aluminum thin films were investigated. The results showed that grains grew during Al deposition. However, voids were only observed in the confined samples. In the confined samples, stepwise annealing at 400 degrees celsius caused retarded grain growth. As for unconfined samples, abnormal grain growth was observed at only 200 degrees celsius.

The whisker growth caused by the ntermetallic compound formation in Sn-0.7Cu flip chip solder joints under electromigration is analyzed. The amount of the intermetallic compound is shown to be main determinant factor of the difference of mass extrusion.

Polychromatic microfocused synchrotron x-ray beam is used for measuring the bending and residual stress of flip chips caused by the mismatch of thermal expansion between the chip and the substrate. The studies have shown that thermal stress on the circuits and the solder joints in a flip chip has depended on temperature and the distance from the center of the chip, which has shown that interconnects at the corner and edge of a flip chip are of reliability concerns.

In situ synchrotron x-ray white beam microdiffraction is used for studying the electromigration-induced hydrostatic elastic stress in Pb-free SnCu solder joints. The compressive stress gradient between the cathode and the anode is much larger than that is required for initiating Sn whisker growth and the effective charge number of [beta]-Sn derived from the electromigration data has agreed well with the calculated value.

In situ stress measurements were performed during high frequency pulse electrodeposition of nanotwinned Cu thin films to understand the periodic stress changes during pulse-on and pulse-off periods. The stress profile showed an abrupt increase in tensile stress to about 400 MPa during the pulse-on period and a stress relaxation during the pulse-off period.

The thermal stability of {111}/ nanotwins is studied by in situ transmission electron microscopy (TEM) characterization. The studies have shown that inverse migration of (112) twin boundary driven by a high strain is possible if sufficient stress is applied to the copper.

An in-depth synchrotron radiation based white beam x-ray microdiffraction study of plasticity in individual grains of an Al (Cu) interconnect during the early stage of electromigration (EM) is described. The analysis has shown a rearrangement of the geometrically necessary dislocations (GNDs) in bamboo typed grains during that stage.

Composite SnPb flip chip solder joints are used to study the combined effect of electromigration and thermomigration. The result has shown that at the last stage of void propagation, due to large Joule heating and bad heat dissipation, the composite solder joint partially melted before an electrical opening occurred.

The composite solder joints of 97Pb-3Sn and 37Pb-63Sn are examined at room temperature under high current densities to investigate the effect of current density and Joule heating on electromigration-induced failure. Simulation is used to show the effect of voids formed during electromigration tests by emphasizing the effect of current crowding and Joule heating on electromigration-induced failure.

The role of 0.5 wt % Cu in the base Sn-3.5%Ag solder is highlighted to reduce the dissolution of the Cu bond pad in ball grid array applications. It was found that after 0.5 wt% Cu addition, the rate of dissolution of Cu in the molten Sn-3.5%Ag solder slowed down significantly.

Mechanical strengths of the solder joints for Sn-Ag eutectic alloy with the Au/electroless Ni(P)/Cu bond pad were measured for three different Ni (P) layers. Results reveal that the formation of crystalline phosphorous-rich Ni layer at the solder interface of Au/electroless Ni (P)/Cu bond pad with Sn-Ag eutectic alloy deteriorates the mechanical strength of the joints severely.

The electromigration damage in flip chip solder bumps of eutectic SnPb and SnAg(sub 3.8)Cu(sub 0.7) was studied after current stressing at 120 degrees C. with 1.5 A. For eutectic SnPb, the effective charge number, Z*, is about 36-100 after 39.5 h of electromigration, but for SnAg(sub 3.8)Cu(sub 0.7) the marker movement was too small to measure Z* even after 200 h of current stressing.

In multilevel interconnects, current crowding occurs whenever the current changes direction, such as when passing through a via. We propose that in current crowding, the current-density gradient can exert a driving force strong enough to cause excess vacancies (point defects) to migrate from high to low current-density regions. This leads to void formation in the latter. This is a key feature of electromigration-induced damage in very large scale integrated interconnects. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]