Annealing-induced void formation in SiO2 layers on Si substrates: Influence of surface orientation and hydrocarbon exposure

Abstract

• Void formation by thermal decomposition of SiO 2 layers on Si substrates. • Void shape depends on surface orientation of a Si substrate. • Ring structures inside voids are induced by Si layer adhering to the void sidewall. • Surface carbonization strongly affects formation of ring structures. This study investigated void formation induced by annealing and subsequent cooling in SiO 2 layers grown on Si substrates using scanning electron microscopy and atomic force microscopy. The results show that distinct Si layers form along the entire sidewall of each void and that the shape of the void depends on the surface orientation of the Si substrate, despite the amorphous nature of the SiO 2 layer. These findings suggest that reaction in areas peripheral to the void is the rate-limiting step in void growth for all oxide thicknesses. The orientation dependence of the void shape reflects the anisotropic migration of Si monomers that form the Si layer on the void sidewall. Surface carbonization was also found to suppress the migration of the Si monomers, which leads the Si layer remnants to form ring structures inside the voids. The observed ring structures indicate that voids only begin to form immediately after the onset of annealing; therefore, a likely trigger of initial void formation is the differential thermal expansion between the oxide layer and the silicon substrate.