Nickel silicide formation with rapid thermal treatment in the heat balance mode

The formation of nickel silicide layers on (111)-Si substrates during rapid thermal annealing in the heat balance mode was studied by the Rutherford backscattering method, X-ray diffraction, transmission electron microscopy, and electrophysical measurements. Nickel films of about 70 nm thickness were deposited by magnetron sputtering at room temperature. The rapid thermal treatment was carried out in a heat balance mode by irradiating the substrates backside with a non-coherent light flux of quartz halogen lamps in the nitrogen medium for 7 seconds up to the temperature range of 200 to 550 °C. The redistribution of nickel and silicon atoms to monosilicide NiSi composition starts already at a temperature of 300 °С and almost ends at a temperature of 400 °С. In the same temperature range, the orthorhombic NiSi phase with an average grain size of about 0.05–0.1 μm is formed. At a rapid thermal treatment temperature of 300 °C, two phases of silicides (Ni2 Si and NiSi) are formed, while a thin layer of unreacted Ni is retained on the surface. This fact can be explained by the high heating rate at the initial annealing stage, at which the temperature conditions of the NiSi phase formation occur earlier than the entire Ni layer manages to turn into the Ni2 Si phase. The layers with a simultaneous presence of three phases are characterized by a high roughness of the silicide-silicon interface. The dependence of the specific resistivity of nickel silicide layers shows an increase to the values of 26–30 μOhm · cm in the range of rapid thermal treatment temperatures of 200–250 °C and a subsequent decrease to the values of about 15 μOhm · cm at a rapid thermal treatment temperature of 400 °C. This value of specific resistivity is characteristic of the high conductivity of the NiSi phase and correlates well with the results of structure studies.

Ohmic Contact Mechanism for Ni/C-Faced 4H-n-SiC Substrate

In this work, the ohmic contact mechanism of Ni electrodes on C-faced 4H-n-SiC was investigated by evaluating the electrical and microstructural properties in the contact interface as a function of annealing temperatures ranging from 950 to 1100°C. We determined that Ni-silicide, especially the NiSi phase, plays a key role in the formation of ohmic contacts rather than an increase in carbon vacancies in the C-faced SiC substrate. A vertically oriented NiSi phase was observed in the thermally annealed sample at the optimized temperature that behaves as a current path. A further increase in annealing temperature leads to the degradation of ohmic behavior due to the formation of horizontal-type NiSi in the Ni-rich Ni-silicide/NiSi/SiC structure.

Phase Inhomogeneity and Electrical Characteristics of Nickel Silicide Schottky Contacts Formed on 4H-SiC

Nickel silicide Schottky contacts were formed on 4H-SiC by consecutive deposition of a titanium adhesion layer, 4 nm thick, and nickel, 100 nm thick, followed by annealing at temperatures from 600 to 750 °C. It was found that contacts with barrier heights of 1.45 eV, consisting mainly of NiSi phase, formed in the 600-660 °C temperature range, while annealing at around 750 °C led to the formation of Ni2Si phase with barrier heights of 1.1 eV. Annealing at intermediate temperatures resulted in the nucleation of Ni2Si grains embedded in the NiSi film which were directly observed by micro-Raman mapping. It was concluded that the thermodynamically unfavourable NiSi phase appeared in the 600-660 °C temperature range due to the fact that the solid state chemical reaction between Ni and SiC at these temperatures is controlled by nickel diffusion through the titanium barrier.

Thickness Effect on Nickel Silicide Formation and Thermal Stability for Ultra Shallow Junction CMOS

High purity Ni films from 200Å down to 40Å on p-type Si (100) substrates are treated by rapid thermal annealing to form the metastable and stable phases of nickel silicides. The stoichiometric composition of NiSi determined by Rutherford backscattering is independent of the initial Ni thickness under 500°C annealing. Channeling RBS results reveal that the NiSi growth on Si (100) has no preferred orientation. The sheet resistance as well as surface roughness of thinner films starts to increase at a lower temperature, indicating that thinner films are thermally less stable. Agglomeration of NiSi film agrees with the grain boundary grooving model and occurs more easily within thinner films. The transformation from the NiSi phase to the NiSi2 phase is studied by micro-Raman spectroscopy. This phase transition of thinner films begins at a lower temperature than that of thicker ones.

Thermal Stability of Nickel Silicide Films

In view of their potential application in ULSI technology, nickel silicide films were formed on undoped and doped Si(100) substrates. Nickel films of varying thicknesses were sputter-deposited onto the substrates and silicidation was performed ex-situ by rapid thermal annealing in nitrogen ambient. The electrical sheet resistance of the silicides was studied as a function of film thickness and annealing temperature. The process window for forming the NiSi phase and the thermal stability of the NiSi phase were determined as a function of film thickness.