Journal of Electronic Materials

The effects of Ni doping on microstructural variations and interfacial reactions in Cu/Sn-3.0Ag-0.5Cu-xNi/Au/Ni sandwich structures were investigated. The sandwich structures, i.e., Cu/Sn-3.0Ag-0.5Cu/Au/Ni and Cu/Sn-3.0Ag-0.5Cu-0.1Ni/Au/Ni (wt.%), were reflowed and isothermally aged at 150°C for 500 h. The behavior of Ni and Cu migration in the solders before and after aging was investigated using field-emission electron probe microanalysis (FE-EPMA), and the microstructure evolution of the solders with Ni doping was investigated. It was observed that Ni migrated to the board Cu-side, while Cu tended to migrate toward the Ni/Au package side, and two different types of (Cu,Ni)6Sn5 intermetallic compounds (IMCs), one with 19.8 at.% to 23.4 at.% Ni and the other with 1.3 at.% to 6.4 at.% Ni content, were found. Regarding interfacial reactions, it was identified that the local Ni and Cu concentrations affected the formation of (Cu,Ni)6Sn5. Redistribution of Ni and Cu was correlated with the formation mechanism of interfacial (Cu,Ni)6Sn5.

Barrier layers are integral parts of many metal interconnect systems. In this paper we review the current status of barrier layers for copper metallization for ultra-large-scale-integration (ULSI) technology for integrated circuits (ICs) manufacturing. The role of barrier layers is reviewed and the criteria that determine the process window, i.e. the optimum barrier thickness and the deposition processes, for their manufacturing are discussed. Various deposition methods are presented: physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical deposition (ECD), electroless deposition (ELD), and atomic layer CVD (ALCVD) for barrier layers implementation. The barrier integration methods and the interaction between the barrier and the copper metallization are presented and discussed. Finally, the common inspection and metrology for barrier layer are critically reviewed.

Ni-doped tetrahedrites Cu12−xNixSb4S13 (x = 0.1–0.4) were prepared by mechanical alloying (MA) and sintered by hot pressing (HP). The tetrahedrite phase could be synthesized by MA without post-annealing, and was stable after HP without phase transition. As the Ni content increased, the lattice constant decreased from 1.0312 nm to 1.0246 nm, confirming that the Ni was successfully substituted for Cu sites. As the Ni content increased, the Seebeck coefficient increased but the electrical conductivity decreased because the carrier (hole) concentration decreased owing to the substitution of Ni2+ at the Cu+ site. The power factor of 1.0 mW m−1 K−2 was obtained at 723 K for the Ni-doped specimen with x = 0.1, and decreased with increasing Ni content. In addition, as the Ni content increased, the electronic thermal conductivity decreased, but the total thermal conductivity of the specimen with Ni content x = 0.2 showed the lowest value of 0.65–0.79 W m−1 K−1 at 323–723 K owing to the lowest lattice thermal conductivity of 0.38 W m−1 K−1 at 723 K. As a result, the dimensionless figure of merit ZT = 0.92 was obtained at 723 K for Cu11.8Ni0.2Sb4S13.

The bonding chemistry and the role of the additional HCl-based prebonding treatment when combined with ozone and oxygen plasma treatments on the GaAs/GaAs direct bonding were investigated using multiple internal transmission Fourier transform infrared spectroscopy (MIT-FTIR) and atomic force microscopy (AFM). The results showed that the additional HCl-based pretreatment led to an increased bonding strength and a qualitative reduction in the void density. The removal of the initial native oxide facilitates the diffusion of water to the GaAs wafer surface where it can react to form primarily Ga-based oxides, leading to a substantially increased bond strength compared to those without the removal of interfacial native oxide.

In astrophysics, in the infrared domain, the most widely used detectors are based on HgCdTe technology, where the light-sensitive HgCdTe layer is grown on a CdZnTe substrate. When located on space-based instruments, these detectors are submitted to ionizing particle irradiation. It has been shown in the literature that, when the CdZnTe substrate is not fully removed, an increase in the detector background is observed. This increase was suspected to be linked to CdZnTe substrate luminescence: carriers excited by the passage of the ionizing particle lose their energy by emitting photons, which are in turn detected by the HgCdTe detection layer. We validate this assumption with a model and an irradiation campaign performed on real detectors, and demonstrate that the pollution mainly comes from low-energy photons emitted within the substrate. The application of the model relies on CdZnTe material properties. In particular, luminescence characteristics are of prime importance. No data were available in the literature at 100 K (detector operating temperature) with 4% zinc concentration. Thus, we performed optical measurements on CdZnTe substrates identical to those used in IR detector fabrication. Measurement results are presented within this paper. Three samples were submitted to different sets of measurements: one CdTe sample used as a reference and two CdZnTe samples. We present photoluminescence measurements from 4 to 50 K and cathodoluminescence spectra acquired at 80 K, 100 K, and 300 K. We show that excitonic recombination dominates up to 100 K in the CdTe and CdZnTe material. We have also performed ellipsometry measurements at 80 K, 100 K, and 300 K. Each measurement has been carefully analyzed and compared to published data. These measurements helped us to understand the luminescence properties of the CdZnTe material, and then were directly used in the application of the model to infer the response of infrared detectors under irradiation.

Thermal oxidation in water vapor of AlInAs layers lattice-matched to InP is reported. Vertical oxidation rate, analyzed vs temperature and duration, is compared to lateral oxidation. The activation energies for both lateral and vertical oxidation on the one hand and kinetics of vertical oxidation on the other hand have been investigated. The doping dependence on vertical oxidation rate is also examined. The resistivity and breakdown field of these oxide films have been found to be high enough for device applications, while the refractive index has been determined through ellipsometry. Some information about the microstructure of the native oxide are also reported.

Selective-area growth and regrowth using conventional atmospheric pressure metalorganic chemical vapor deposition is investigated for wavelength tuning in strained layer InxGa1-xAsGaAs-Aly Ga1-yAs quantum well lasers. Growth inhibition from a silicon dioxide mask is the mechanism used for the selective-area growth rate enhancement. By varying the width of the oxide stripe opening, differences in the growth rate yield different quantum well thicknesses, and hence different lasing wavelengths for devices on the same wafer. Both two-and three-step growth processes are utilized for selective-area epitaxy of strained layer InxGa1-xAs-GaAs quantum well active regions, with lasers successfully fabricated from the three-step growth. Scanning electron microscopy and transmission electron microscopy indicate that the absence of an oxide mask during AlyGa1-yAs growth is essential for successful device operation. A wide wavelength tuning range of over 630Å is achieved for lasers grown on the same substrate.

Ni bottom contacts and Al top gate organic field effect transistors of Poly 3-hexylthiophene and cross-linked Poly Vinyl Alcohol with different channel lengths (5 μm, 10 μm, 20 μm and 40 μm) were made on glass substrates, using standard photolithography and oxygen plasma etching. The transistors presented good charge mobility, high ION/IOFF and excellent environmental and temporal stability. The Shockley model and the Transmission Line Method (TLM) were applied to characterize the transistors. Mobility was extracted by both methods, and the differences were discussed. The shorter the channel length and the higher the conductivity of the semiconductor, the greater the impact of the contact resistance. In such cases, the use of TLM for parameter extraction becomes essential.