L. R. Zheng

Lateral diffusion of Ni and Si through Ni2Si in Ni/Si couples

Lateral diffusion couples of Ni on Si layers and Si on Ni layers were used in conjunction with scanning electron microprobe measurements to investigate the growth of Ni silicides in the temperature range 400–700 °C. The phase Ni2Si grows proportional to (time)1/2 until a length of 25–30 μm (at 600 °C) where the phase sequence Ni5Si2, Ni2Si, Ni3Si2, and NiSi is observed. Both Ni and Si diffuse through Ni2Si with an effective diffusion coefficient D≃0.02 cm2/s ×exp[−(1.4±0.1) eV/kT]. The diffusion of Si was also observed by the growth of Ni2Si in Ni films at the periphery of contact openings in SiO2 layers on Si.

Morphological degradation of TiSi2 on 〈100〉 silicon

Evidence of instability of TiSi2 layers during high‐temperature high vacuum annealing has been observed. Rutherford backscattering and scanning electron microscopy measurements showed that at high vacuum annealing conditions, the laterally homogeneous silicide layer breaks up into islands. In between these TiSi2 islands, growth of an epitaxial silicon layer was observed.

Redistribution of dopant arsenic during silicide formation

A systematic study of arsenic redistribution in Ni, Cr, Ta silicide forming systems has been performed by implanting arsenic into metal layers or into single‐crystal silicon substrates. During silicide formation arsenic accumulates near the interface region, incorporates in the silicide, or diffuses out of the silicide into the surrounding ambient. Differences in the dopant redistribution are related to the arsenic initial location relative to the moving species in silicide formation and the diffusivity of dopant atoms at the metal‐silicon reaction temperature.

Transmission electron microscopy studies on the lateral growth of nickel silicides

Transmission electron microscopy (TEM) has been utilized to study the nickel‐silicide growth in self‐supported lateral‐diffusion, thin‐film couples by overlapping deposited layers of Ni and Si between two silicon oxide deposited films. Energy‐dispersive x‐ray spectroscopy, microdiffraction, and selected area diffraction were used to identify the Ni‐silicide phases and their crystal structures. Long‐grain growth of Ni2Si, as a result of phase‐boundary migration induced by diffusion, was observed during in situ annealing between 500 and 750 °C in TEM. No preferred orientation or particular crystallographic relationship was found among the long grains.Transmission electron microscopy (TEM) has been utilized to study the nickel‐silicide growth in self‐supported lateral‐diffusion, thin‐film couples by overlapping deposited layers of Ni and Si between two silicon oxide deposited films. Energy‐dispersive x‐ray spectroscopy, microdiffraction, and selected area diffraction were used to identify the Ni‐silicide phases and their crystal structures. Long‐grain growth of Ni2Si, as a result of phase‐boundary migration induced by diffusion, was observed during in situ annealing between 500 and 750 °C in TEM. No preferred orientation or particular crystallographic relationship was found among the long grains.

Interaction of TiSi2 layers with polycrystalline Si

Interactions of silicide films with undoped polycrystalline layers of Si grown by chemical vapor deposition at 630 °C were investigated by MeV He ion backscattering spectrometry, scanning electron microscopy, and transmission electron microscopy. For TiSi2, heat treatment in vacuum at temperatures above 850 °C results in erosion of the polycrystalline Si layer and growth of Si crystallites in the silicide film. The same phenomenon is observed for NiSi, Pd2Si, and CrSi2 at temperatures above one‐half of melting point of the corresponding silicide.

Lateral-diffusion couples studied by transmission electron microscopy

Abstract A method is described for making self-supporting lateral-silicide diffusion couples for transmission electron microscopy (TEM) investigations. The lateral growth of Ni and Pd silicides is compared. Also, a comparison is made between two different methods of preparing the NiSi couples. These diffusion couples are annealed in situ in a TEM heating holder and studied using conventional TEM, high-resolution electron microscopy (HREM), energy-dispersive X-ray spectroscopy (EDS), and microdiffraction.

Influence of Au as an impurity in Ni‐silicide growth

The growth of Ni silicides in Ni films on Si and in lateral diffusion couples with Ni films on Si patterns on Al2O3 is strongly influenced by the presence of 1–2 at. % Au in Ni. During silicide formation, Au accumulates at the silicide/ Ni and silicide/Si interface and retards phase formation at temperatures below the Au/Si eutectic. At temperatures of 400–500 °C (above the eutectic), the growth rate is enhanced by over two orders of magnitude. We believe the increase is due to the segregation of Au at the Ni‐silicide grain boundaries and the transport of Si in the Au‐Si liquid. The growth rate is independent of temperature from 600–800 °C and is limited by the diffusion of Si in the Au‐Si liquid at a value of 10−5 cm2/sec.

Effects of arsenic ion irradiation on Ti silicide formation

Abstract Effects of arsenic irradiation on lateral silicide formation have been studied with scanning electron microscopy and the electron microprobe in device geometry structures formed by deposition of Ti films on patterned Si substrates. The extent of lateral diffusion was greatly reduced and exhibited a dose dependence. By varying the energy of incident beams, we found that implanting arsenic into the Ti films is more effective in retardation of lateral diffusion than implantation through the Ti films. When the samples were irradiated with Si ions, lateral diffusion was not affected in comparison with the unimplanted samples. These observations suggest that the suppression of lateral diffusion is primarily due to interactions of impurities with the matrix. Similar observations have been obtained in planar structures where the presence of arsenic in Ti/Si thin films slows down the silicide formation.

Lateral Silicide Growth

Silicide formation and growth kinetics have been investigated with lateral diffusion couples formed by deposition of Ni and Cr layers on patterned Si substrates and by deposition of Ni patterns on Si films. For annealing temperatures between 520 and 650°C the growth of CrSi 2 follows a (time) ½ dependence with an activation energy of 1.4± 0.1 eV. In Ni-silicide formation at temperatures below 600°C, Ni was the predominant moving species. As the temperature increased, the motion of Si became significant. The apparent activation energy for silicide formation varied from E a ≅ 1.4 eV for Ni motion at relatively low temperatures to E a ≅ 2.3 eV for Si motion that occurs at high temperatures. Lateral diffusion in device geometry structures resulted in degradation of contact planarity due to the penetration of metal silicides in Ni-Si structures or the erosion of silicon in Cr-Si structures.

Lateral diffusion of platinum through Pt2Si in Pt/Si couples☆

Abstract Lateral diffusion couples formed by depositing platinum islands on silicon layers on Al 2 O 3 were used in conjunction with scanning electron microprobe measurements to investigate the growth of platinum silicides in the temperature range 400–700 °C. The phase Pt 2 Si grows over a length of 4–30 μm with a rate proportional to the square root of time and an activation energy of approximately 1.3 eV. With samples containing 7 at.% Rh in the platinum, the growth rate of Pt 2 Si is reduced and the activation energy is increased to about 2.0 eV. In these Pt-7at.% Rh samples, electron-induced X-ray measurements indicate that rhodium remains in the original deposited region while both platinum and silicon diffuse in the formed Pt 2 Si region.