Formation of silicides in the Ti, Ti(Ox)/Si(111), and Ti/SiO2/Si(111) systems

Abstract

Reactions at Ti/Si and Ti/SiO2/Si interfaces under the conditions of steady-state thermal annealing and cw Ar+ laser annealing have been studied using a variety of techniques including Auger electron spectroscopy (AES), x-ray photoemission spectroscopy (XPS), Rutherford backscattering, and x-ray diffraction. Ti thin films on silicon have been transformed to Ti5Si3, TiSi, and TiSi2 after steady-state annealing at 500–600 °C, and only TiSi2 can be observed after annealing above 650 °C. In the case of the Ti/SiO2/Si system a Ti5Si3 thin film with a TiO overlayer has been formed in the temperature range 750–1000 °C. The growth of the Ti–Si2 layer on silicon and the Ti5Si3 layer on SiO2 shows a diffusion-limited behavior, i.e., x∝t1/2. Continuous-wave Ar+ laser scanned annealing can induce the solid-phase reaction of Ti/Si at a power density less than 2.7 kW/cm2, but a liquid-phase reaction at a power density of about 3.8 kW/cm2. A mixture of TiSi2 and pure Si was observed after the liquid-phase reaction. Ti(Ox) on atomically clean Si(111) and on Si(111) with native oxide has been studied using ultraviolet photoemission spectroscopy, XPS, and AES. The sequential deposition of Ti(Ox) at room temperature on clean Si(111) showed that the interface is unreacted. However, with moderate annealing (300 °C), the intermixing of Ti and Si atoms has been observed. Ti(Ox) on a clean Si(111) surface produces oxygen chemisorption of the Si(111) surface, but Ti(Ox) on Si(111) with native oxide produces the Ti oxides—TiO and TiO2.