Abstract
Ni silicide is an attractive candidate to replace Ti silicide due to its low resistivity and the absence of fine line effect. The appropriate improvement on thermal stability of NiSi thin films is a very important issue for using NiSi in the fabrication of deep-submicron devices.Capping layer process has been developed for metal salicide process to reduce the surface diffusion of Si leading to a better process window and to prevent ambient contamination. Reactive Ti capping layer is compared favorably with relatively inert TiN capping layer due to its ability to reduce the interface oxide and capture the contamination during annealing. Ti capping layer suppresses the oxidation at the interface between the silicide layer and the silicon substrate, which was believed to induce interface roughness.High-resistivity NixTiySiz phase was found to form at the top layer in the samples of Ti capping thickness thicker than 10nm even at the temperature below to the transient temperature of low-resistivity NiSi phase to high-resistivity NiSi2 phase. The low-resistivity phase can be stabilized by the presence of the Ti capping layer. The result is attributed to the formation of NixTiySiz layer at the top of the sample by capturing the Si atoms from the nickel silicide layer. As a result, the phase transformation of NiSi to NiSi2 was retarded.The roughness of interface in Ti capped samples after annealing at 700℃ are smoother than that in blank-Si samples. The spiking of epitaxial NiSi2 into Si substrate can be alleviated by using a thin Ti capping layer.