This paper reports on the formation of FeSi and β-FeSi2by rapid thermal anneal (RTA). Sputtered Fe layers with a thickness of 25 nm and 40 nm on (100) Si wafers were subjected to RTA-treatment at temperatures ranging between 500 and 700 °C. This leads to three different types of growth. Two types of lateral growth and a hillock like growth. All the growth modes were nucleation controlled. The lateral growth rates of β-FeSi2 were measured at temperatures ranging from 625 to 700 °C, this provided a value for the activation energy of this process of about 1.35 eV. Positron annihilation analysis and scanning electron microscopy were used to study the onset of the transformation.
It is suggested that the lateral growth appears when the Fe layer is completely transformed to FeSi before FeSi2 nucleates and that the hillock-like growth emerges when FeSi2 nucleates before the complete transformation of the Fe layer to FeSi.The RTA formed P3-FeSi2 layers have a roughness of the order of the thickness of the layer and a high defect density as observed by cross-section transmission electron microscopy. In order to decrease the surface roughening a-Si and Si3N4 capping layers were deposited with plasma enhanced vapour deposition before RTA.