A nanoscale silver paste containing 30-nm silver particles that can be sintered at 280degC was made for interconnecting semiconductor devices. Sintering of the paste produced a microstructure containing micrometer-size porosity and a relative density of around 80%. Electrical and thermal conductivities of around 2.6times10⁵ (Omegamiddotcm)^-1 and 2.4W/K-cm, respectively, were obtained, which are much higher than those of the solder alloys that are currently used for die attachment and/or flip-chip interconnection of power semiconductor devices. The sintered porous silver had an apparent elastic modulus of about 9GPa, which is substantially lower than that of bulk silver, as well as most solder materials. The lower elastic modulus of the porous silver may be beneficial in achieving a more reliable joint between the device and substrate because of increased compliance that can better accommodate stress arising from thermal expansion mismatch

Pressure-assisted low-temperature sintering of silver paste is shown to be a viable alternative to solder reflow as a die-attachment solution. A quasihydrostatic pressure is used to lower the sintering temperature. The effect of parameters such as temperature and pressure are investigated. Characterization of the silver-attached samples shows a significant improvement in electrical conductivity, thermal conductivity and mechanical strength of the joint. Given that silver deforms with little accumulation of inelastic strains, and given the absence of large voids in the attachment layer, it is also expected that the joint to be more resistant to fatigue failure than a solder attached junction. Due to the high melting temperature of silver, this alternative process is also suitable for high temperature packages.

In this paper, we present the realization of high-temperature operation of SiC power semiconductor devices by low-temperature sintering of nanoscale silver paste as a novel die-attachment solution. The silver paste was prepared by mixing nanoscale silver particles with carefully selected organic components which can burn out within the low-temperature firing range. SiC Schottky diodes were placed onto stencil-printed layers of the nanoscale silver paste on Au or Ag metallized direct bonded copper (DBC) substrates for the die-attachment. After heating up to 300degC and dwell for 40 min in air to burn out the organic components in the paste and to sinter the nanoscale silver, the paste consolidated into a strong and uniform die-attach bonding layer with purity >99% and density >80%. Then the die-attached SiC devices were cooled down to room temperature and their top terminals were wire-bonded to achieve the high-temperature power packages. Then the power packages were heated up from room temperature to 300degC for high-temperature operation and characterization. Results of the measurement demonstrate the low-temperature silver sintering as an effective die-attach method for high-temperature electronic packaging. An advanced packaging structure for future SiC transistors with several potential advantages was also proposed based on the low-temperature sintering technology.

The effects of hydrostatic pressure on the solid‐phase epitaxial growth (SPEG) rate v of intrinsic Ge(100) and undoped and doped Si(100) into their respective self‐implanted amorphous phases are reported. Samples were annealed in a high‐temperature, high‐pressure diamond anvil cell. Cryogenically loaded fluid Ar, used as the pressure transmission medium, ensured a clean and hydrostatic environment. v was determined by in situ time‐resolved visible (for Si) or infrared (for Ge) interferometry. v increased exponentially with pressure, characterized by a negative activation volume of −0.46Ω in Ge, where Ω is the atomic volume, and −0.28Ω in Si. The activation volume in Si is independent of both dopant concentration and dopant type. Structural relaxation of the amorphous phases has no significant effect on v. These and other results are inconsistent with all bulk point‐defect mechanisms, but consistent with all interface point‐defect mechanisms, proposed to date. A kinetic analysis of the Spaepen–Turnbull interfacial dangling bond mechanism is presented, assuming thermal generation of dangling bonds at ledges along the interface, independent migration of the dangling bonds along the ledges to reconstruct the network from the amorphous to the crystalline structure, and unimolecular annihilation kinetics at dangling bond ‘‘traps.’’ The model yields v = 2 sin(θ)v_snr exp[(ΔS_f + ΔS_m)/k] exp− [(ΔH_f + ΔH_m)/kT], where ΔS_f and ΔH_f are the standard entropy and enthalpy of formation of a pair of dangling bonds, ΔS_m and ΔH_m are the entropy and enthalpy of motion of a dangling bond at the interface, v_s is the speed of sound, θ is the misorientation from {111}, and n_r is the net number of hops made by a dangling bond before it is annihilated. It accounts semiquantitatively for the measured prefactor, orientation dependence, activation energy, and activation volume of v, and the pressure of a ‘‘free‐energy catastrophe’’ beyond which the exponential pressure enhancement of SPEG cannot continue uninterrupted due to a vanishing barrier to dangling bond migration. The enhancement of v by doping can be accounted for by an increased number of charged dangling bonds, with no change in the number of neutrals, at the interface. Quantitative models for the doping dependence of v are critically reviewed. At low concentrations the data can be accounted for by either the fractional ionization or the generalized Fermi‐level‐shifting models; methods to further test these models are enumerated. Ion irradiation may affect v by altering the populatio