Low-temperature bonding of Si wafers has been studied utilizing reactive ion etching-mode plasma activation. The hydrophilic Si and thermally oxidized Si wafers were exposed to N 2 , Ar, or O 2 plasma prior to bonding in air or vacuum. After plasma treatment the wafers were cleaned in RCA-1 solution and/or deionized water. Strong bonding was achieved at 200°C with all the investigated plasma gases, if proper bonding and cleaning procedures were used. Extended RCA-1 cleaning deteriorated the bond strength, but a short cleaning improved bonding. We found that the activation of the thermal oxide has a larger influence on the bond strength than the activation of the native oxide surface in Si/oxide wafer pairs. We suggest that the plasma treatment induces a highly disordered surface structure, which enhances the diffusion of the water from the bonded interface. As a result of the plasma exposure the number of the surface OH groups is greatly increased enabling strong bonding at a low temperature.

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The reaction mechanisms in the Si/Ta/Cu metallization system and their relation to the microstructure of thin films are discussed on the basis of experimental results and the assessment of the ternary Si-Ta-Cu phase diagram at 700°C. With the help of sheet resistance measurements, Rutherford backscattering spectroscopy, x-ray diffraction, a scanning electron microscope, and a transmission electron microscope, the Ta barrier layer was observed to fail at temperatures above 650°C due to the formation of TaSi 2 , the diffusion of Cu through the silicide layer, and the resulting formation of Cu 3 Si precipitates. However, in order for the TaSi 2 phase to form first, the Ta diffusion barrier layer must be thick enough ͑e.g., 50-100 nm͒ to prevent Cu diffusion into the Si substrate up to the temperature of TaSi 2 formation ͑ϳ650°C͒. Independent of the Ta layer thickness, Cu 3 Si was present as large nodules, whereas the TaSi 2 existed as a uniform layer. The resulting reaction structure was found to be in local equilibrium on the basis of the assessed Si-Ta-Cu phase diagram at 700°C, and therefore no further reactions were expected. The role of oxygen was also found to be important in the reactions and it seems to have a strong effect on the thermal stability of the barrier layer.

The epitaxial regrowth of ion-implanted amorphous layers on 〈100〉 Si with partly compensated doping profiles of 11B, 75As, and 31P was studied. Single implants of these impurities are found to increase the regrowth rate at 475 and 500 °C. The compensated layers with equal concentrations of 11B and 31P or 11B and 75As show a strong decrease of the regrowth whereas for the layers with overlapping 75As and 31P profiles no compensation has been found.