We have investigated interface formation and degradation at the junction of preimidized po1yimide and Cu by means of scanning Auger and secondary electron microscopies, and x-ray photoelectron spectroscopy. Our approach has been to spin on ultrathin (tens of A.) polyimide overlayers onto Cu substrates, cure the polyimide while in contact with the Cu in an inert atmosphere, and then expose the interface to different environments. We found that only a very small amount of oxidation occurs during the curing process itself. This result is expected on the basis of the preimidization step prior to contact with Cu. The limited amount of oxidation appears to be due to the formation of a Cu-amine complex at the interface. Storage in vacuum leaves the interface abrupt and no further oxidation occurs. However, exposure to room-temperature air or high humidity at 85°C causes more extensive Cu oxidation to occur. In the case of exposure to high humidity at 85°C, metal oxidation is accompanied by Cu outdiffusion and polyimide decomposition. The interface degradation process after curing appears to be driven by absorption of water, and the primary degradation reaction product is CuO.

We describe a structural determination of pseudomorphic Si on Ge(OOl) by means of x-ray-photoelectron diffraction. By comparing the measured angular coordinates of the forward-scattering-induced [001] peak with those calculated by means of single-scattering theory, we find that the lattice constant perpendicular to the interface is 5.34 ±0.04 A. This value exceeds that predicted by elastic theory by 0.08 A.The effects of strain on the band offset at a semiconductor heterojunction are significant, yet they are not completely understood and are often ignored. l Experimental determination of tetragonal distortion in strained semiconductor overlayers has proven to be an exceedingly difficult task, largely because the layer of interest is often only a few atomic spacings in thickness. Thus, theoretical rather than experimental means have often been used to determine the strain. Both classical elastic theory and full quantum-mechanical calculations have been employed. However, there are very few experimental values of the lattice constant normal to the interface, a±, with which to compare theoretical results.In this Letter, we describe the use of x-ray photoelectron diffraction (XPD) in conjunction with low-energy electron diffraction (LEED) and high-energy-resolution x-ray photoelectron spectroscopy (XPS) to characterize a lattice-mismatched heterojunction, Si/Ge(001), prepared with different amounts of strain and intermixing. We have determined a± by comparison of experimental XPD angular distributions with those calculated via single-scattering theory 2 for various amounts of strain, and have assessed the effects of strain and intermixing on core-level binding energies.All experiments were performed in a system of three interconnecting ultrahigh vacuum chambers equipped for sample preparation, molecular-beam epitaxial (MBE) growth, and interface characterization by means of XPS, XPD, and LEED. 3 Scanned-angle XPD measurements were carried out with a full angle of acceptance of 5°, and with a precision and accuracy of ±0.2°. Highenergy-resolution XPS measurements were made using a monochromatic Al Ka x-ray source, yielding a total energy resolution of 0.74 eV, as judged by the full width at half maximum of the Au 4/7/2 peak from a clean Au surface. The binding energy of the Au 4/7/2 peak was monitored frequently during the course of the investigation to insure that the spectrometer electronics were sufficiently stable to insure highly accurate core-level binding energies. These measurements yielded a constant value of 84.00 ±0.01 eV. Ge(001) surfaces were prepared by growing 150-200 A of epitaxial Ge at a temperature of 350 °C on clean, semi-insulating GaAs substrates cut to within ±0.5° of (001). Thin epilayers of Si were then grown at temperatures of 335 °C, which is near the minimum temperature required for good epitaxy and laminar growth of up to four monolayers (ML) of Ge on Si(OOl), 4 and 450 °C, which is ~50°C above the onset temperature for intermixing. 5 Thicknesses were determined by means of calibrated qua...

A highly accurate prediction of hermeticity lifetime is made for eutectic 63Sn37Pb and 80Au20Sn alloy solder sealed optical fiber-Kovar™ nosetube feedthroughs subjected to repetitive thermal cycling. Thermal fatigue fracture of the Sn-Pb solder/Kovar™ interface develops when cracks, initially generated from creep deformation of the solder, propagate gradually through the junction in the axial direction. A nonlinear axisymmetric finite element analysis of the 63Sn37Pb fiber feedthrough seal is performed using a thermo-elastic creep constitutive equation, and solder joint fatigue based on accumulated strain energy associated with solder creep imposed by temperature cycling is analyzed. Additionally, thermal effective stress and plastic strain is studied for alternative 80Au20Sn solder by the finite element method with results indicating significant increase in useful life as compared to 63Sn37Pb. SEM/EDX metallurgical analysis of the solder/Ni-Au plated Kovar™ nosetube interface indicates that AuSn 4 intermetallic formed during soldering with 63Sn37Pb also contributes to joint weakening, whereas no brittle intermetallic is observed for 80Au20Sn. Hermetic carbon coated optical fibers metallized with Ni,P-Ni underplate and electrolytic Au overplating exhibit correspondingly similar metallurgy at the solder/fiber interface. Combined hermeticity testing and metallurgical analysis carried out on 63Sn37Pb and 80Au20Sn alloy solder sealed optical fiber feedthroughs after repetitive temperature cycling between 65 and +150 C, and 40 and +125 C validated the analytical approach.Index Terms-80Au20Sn, FEM, fiber-optic, helium leak, hermetic feedthrough, intermetallic, Kovar™, SEM/EDX, 63Sn37Pb, solder.

Due to an error in production, the top of Fig. 5 was inadvertently published upside-down. Figure 5 should have appeared as follows: