Thermal oxidation of nickel disilicide

The thermal oxidation characteristics of nickel disilicide on Si substrates have been investigated in the temperature range of 700–900 °C in dry oxygen and wet oxygen. A surface layer of SiO2 grows parabolically in time. The growth rate is independent on the crystalline structure (epitaxial or polycrystalline) and thickness of the NiSi2 layer. We surmise that the oxidation mechanism is dominated by oxygen diffusion through the growing SiO2. Activation energies for the dry and wet oxidation are 1.0±0.1 eV and 1.5±0.1 eV, respectively. NiSi2 layers on SiO2 oxidize with the same rate—resulting with progressively Ni-rich NiSi2. Preliminary measurements of the oxide quality yield dielectric strength of 2.1×10^6 V cm^−1, and a pinhole density of about 100 per cm2. A survey of oxidation data for Si and other refractory metal silicides shows that their oxidation does not draw similar kinetics to that of NiSi2

Self-confined metallic interconnects for very large scale integration

A novel method to produce narrow metallic lines is presented. Lines of NiSi2 lithographically formed on SiO2 substrates are oxidized. The formed SiO2 layer consumes most of the Si from the silicide, leaving a metallic Ni line fully confined by SiO2. The associated problems together with the potential utilization are discussed

Electrical characteristics of Al contact to NiSi using thin W layer as a barrier

We show that the thermal instability that is observed in Schottky diodes with an Al film on NiSi contact to can be removed by introducing a very thin (~250 Å) tungsten film between the Al and the NiSi layers. This structure can be formed by sequential evaporation of Ni, W, and Al and subsequent thermal annealing to form NiSi. Schottky barrier measurements show that the contact is thermally stable at 450 °C up to about 1-h annealing with very little change in the electronic barrier height. A model, derived from the electrical measurements, is proposed for the failure mode of the tungsten barrier after excessive annealing

Utilization of NiSi_2 as an interconnect material for VLSI

The applicability of NiSi2as an interconnect material was investigated using narrow (5 µm- × 2600-µm) lines. 2500-Å-thick silicide lines were thermally oxidized to form a passivation layer of SiO_2 for the next metallization level. Isolation of more than 50 V for 2200-Å SiO_2 is achieved. The interconnect resistivity following the oxidation is 1.2-1.4 Ω. The maximum current capability of the lines was found to be > 5 × 106A/cm^2 and their stability under prolonged high current densities was demonstrated. We propose a scheme to increase the local metallization-level density using NiSi_2 as an interconnect

Marker experiments for diffusion in the silicide during oxidation of PdSi, Pd2Si, CoSi2, and NiSi2 films on <Si>

Inert markers (evaporated tungsten and ion implanted Xenon) were used to investigate the mass transport through a silicide layer on a substrate during thermal oxidation at 700–900 °C. The SiO2 growth from PdSi, Pd2Si, CoSi2, and NiSi2 films on is a process limited by the diffusion of the oxidant from the ambient gas to the silicide/oxide interface. Possible diffusion processes through the silicide that supply Si to the growing SiO2 layer, but keep the silicide stoichiometry intact, are discussed. Backscattering spectrometry is used to monitor the marker position in the silicide layer. We find that the diffusing species during oxidation correlate with the moving species during silicide formation