The Effect of an Ag Nanofilm on Low-Temperature Cu/Ag-Ag/Cu Chip Bonding in Air

Low-temperature Cu-Cu bonding technology plays a key role in high-density and high-performance 3D interconnects. Despite the advantages of good electrical and thermal conductivity and the potential for fine pitch patterns, Cu bonding is vulnerable to oxidation and the high temperature of the bonding process. In this study, chip-level Cu bonding using an Ag nanofilm at 150 °C and 180 °C was studied in air, and the effect of the Ag nanofilm was investigated. A 15-nm Ag nanofilm prevented Cu oxidation prior to the Cu bonding process in air. In the bonding process, Cu diffused rapidly to the bonding interface and pure Cu-Cu bonding occurred. However, some Ag was observed at the bonding interface due to the short bonding time of 30 min in the absence of annealing. The shear strength of the Cu/Ag-Ag/Cu bonding interface was measured to be about 23.27 MPa, with some Ag remaining at the interface. This study demonstrated the good bonding quality of Cu bonding using an Ag nanofilm at 150 °C.

UNDERSTANDING INSIGHT OF METHANOL ADSORPTION ON 2 ATOMIC COPPER DEPOSITED OVER ZNO(10¯1 0) SURFACE: A DFT STUDY

In this study, depositing with two copper atoms (2Cu) on ZnOsurface, obtaining 2Cu/ZnO surface model, and its applications then for adsorbed CH3OH were investigated using the density functional theory (DFT). In performances, 2Cu was adsorbed on ZnOsurface to form the model of 2Cu deposited over ZnO (2Cu/ZnO). Further, on 2Cu/ZnO surface model, the resulted analysis as density of state (DOS) and electron density difference (EDD) contour plot pointed out that two atomic Cu were formed by the transferred electrons from Cu to ZnO, leading Cu oxidation to become Cu+ ion, while was modeled 2Cu/ZnOsurface. To investigate CH3OH adsorption, many configurations of adsorbed CH3OH on the surface found, in which the most stable configurations were also identified. This result presented that methanol adsorption on 2Cu/ZnO is more favorable than that on ZnO in our previous works.

Maturation experiments reveal bias in the chemistry of fossil melanosomes

Fossil melanosomes are a major focus of paleobiological research because they can inform on the original coloration, phylogenetic affinities, and internal anatomy of ancient animals. Recent studies of vertebrate melanosomes revealed tissue-specific trends in melanosome-metal associations that can persist in fossils. In some fossil vertebrates, however, melanosomes from all body regions are enriched only in Cu, suggesting diagenetic overprinting of original chemistry. We tested this hypothesis using laboratory experiments on melanosomes from skin and liver of the African clawed frog Xenopus laevis. After maturation in Cu-rich media, the metal chemistry of melanosomes from these tissues converged toward a common composition, and original differences in Cu oxidation state were lost. Elevated Cu concentrations and a pervasive Cu(II) signal are likely indicators of diagenetically altered melanosomes. These results provide a robust experimental basis for interpretating the chemistry of fossil melanosomes.

X-ray absorption spectroscopy of small copper-oxide cluster ions for analyses of Cu oxidation state and Ar complexation: CuOAr+ and Cu2O2+

Small copper-oxide cluster cations, namely, CuOAr+ and Cu2O2+, are studied by mass spectrometry and X-ray absorption spectroscopy (XAS) to investigate the oxidation state of copper atoms. The XAS in Cu L3-region revealed that the oxidation number of Cu is almost +2.1 and +2.3 for CuOAr+ and Cu2O2+, respectively, which are consistent with the natural charges obtained by quantum chemical calculation. It was also revealed that the binding energy of Ar to CuO+ is unexpectedly high to form CuOAr+ dominantly as a result of a significant amount of charge transfer to the Ar atom.