Growth And Characterization Of Low-Barrier ErSi_2-x And YSi_2-x Films

As the feature size of modern complementary metal-oxide-semiconductor devices is continuously scaling, the urgent demand for low contact resistivity with Si as well as the emerging of new source/drain structures requires the Schottky barriers of silicide contacts on Si to be very low. Rare earth (RE) silicides such as ErSi_2-x and YSi_2-x have aroused much research interest in recent years for their very low Schottky barriers on n-type Si. However, RE silicides suffer from oxidation problems and surface morphological defects. In this dissertation, a study has been carried out on ErSi_2-x and YSi_2-x prepared by evaporation, sputtering and rapid thermal annealing (RTA). Various characterization methods were employed to investigate the phase, morphology and electrical properties of the formed silicide layers on Si(100). The dissertation obtained the following results.1. Growth and properties of YSi_2-x on Si(100)By evaporation of Y on Si(100) substrate followed by RTA, YSi_2-x film can be formed at 500℃annealing and keep stable up to 950℃annealing. However, oxidation problems could not be avoided. As the silicide formed, pinholes were also observed to form in the silicide layers. The pinhole has a shape of either a square or a rectangle. The contact barrier of YSi_2-x on p-Si(100) was found to be between 0.633 eV and 0.686 eV which does not vary significantly with different annealing temperatures. The I-V-T characteristics of YSi_2-x/n-Si(100) Schottky diodes show that microscopic inhomogeneity of Schottky barrier height (SBH) exists in this contact system, which can be described by a Gaussian distribution model. The mean SBH of the YSi_2-x/n-Si(100) diode was shown to be 0.460, 0.376, 0.324 eV for annealing temperatures of 500, 600, 900℃, respectively, and possibly even lower for 700 and 800℃annealing temperatures. The diodes annealed at 700 and 800℃showed ohmic-like behaviour even when cooled down to temperature as low as 90 K.2. Growth and properties of ESi_2-x on Si(100)By sputter deposition of Er on Si(100) followed by RTA, ErSi_2-x film can be formed at 500℃annealing and keep stable up to 1000℃annealing. The solid phase reaction of the Er film on the Si substrate can be considered as a competition between the silicidation at the Er/Si interface and the oxidation at the film surface. Pinholes or pyramidal defects were observed to form in the formed ErSi_2-x film depending on the initial Er thickness. When the silicide layer is thick, the SBH of the ErSi_2-x/p-Si(100) contact was found to vary between 0.783 and 0.805 eV for annealing temperature ranging from 500 to 900℃. As the thickness of the ErSi_2-x layer is reduced, the contact properties of the ErSi_2-x/p-Si(100) diode are degraded due to severe oxidation problems. The SBH inhomogeneity also exists in ErSi_2-x/n-Si(100) contacts, which can also be well described by the Gaussian distribution model. The mean SBHs of the ErSi_2-x/n-Si(100) contacts were extracted to be 0.343-0.427 eV for different annealing temperatures. And the SBH inhomogeneity for the diodes annealed at 700, 800 and 900℃was found to be larger than for those annealed at 500 and 600℃, which explains well the ohmic-like behaviour at low temperatures for the diodes annealed at 700, 800 and 900℃.3. Formation of ErSi_2-x film with W capping layerA W capping technique was investigated to fabricate self-aligned ErSi_2-x/p-Si(100) diodes. With the W capping, the formed ErSi_2-x film was observed to be quite smooth without any pinhole or pyramidal defect. This technique also helps to suppress oxidation and to improve the contact properties of the ErSi_2-x on p-type Si.4. Effect of erbium interlayer on nickel silicide formation on Si(100)In the study of Ni/Er/Si(100) ternary system, the NiSi formation temperature was found to increase depending on the Er interlayer thickness (0.5-3.0 nm). With Er(2 nm) interlayer, the formed NiSi₂ after annealing at 700℃or above was observed to be highly textured with (100) preferred orientation. During the NiSi formation, Er segregates to the surface with little remaining at the NiSi/Si(100) interface. Therefore, no appreciable SBH modulation was observed in the NiSi/n-Si(100) contact by Er addition.5. Effect of Pt addition on the stress of NiSi film formed on Si(100)Systematic in-situ stress measurement on Ni_1-xPt_xSi formed on Si(100) showed that the residual thermal stress at room temperature is 775 MPa and 1.31 GPa for NiSi and PtSi films grown on Si(100) substrates, respectively. For the Ni_1-xPt_xSi alloy film, the residual stress was observed to increase steadily with Pt composition. The stress relaxation temperature, which also increases with the Pt composition, was found to be reason for such a law.