Scanning electron microscopy study of seeded recrystallization of silicon-on-insulator layers with either polycrystalline or epitaxially deposited silicon in the seed windows

Silicon-on-insulator layers have been produced under conditions which are compatible with three-dimensional device integration. The layers were formed by zone melting recrystallization of two types of seeded silicon films in a dual electron beam system. High-resolution scanning electron microscopy was used to observe the starting materials and the stages of recrystallization from unseeded regrowth through seeded regrowth to under oxide melting. With the standard structure, which has an overall layer of polycrystalline silicon, good seeding requires melting into the bulk. However, when the silicon is deposited under conditions which give epitaxial growth in the seed windows, seeded recrystallization does not require melting in the substrate or even across the complete width of the window. A study of the silicon mass flow for the various stages is presented and the processing conditions for the minimum thickness variation of the silicon film are reported.