PHENOMENOLOGICAL VIEW OF NUCLEATION AND GROWTH OF SiON THE Si(111)-(7×7) SUPERLATTICE

The influence of surface structure on epitaxial growth, which has not been considered before in the crystal growth theory, is discussed for the case of epitaxial growth of Si on Si(111)-(7×7) substrate. Since the rearrangement of surface structure is essential for progressing the epitaxial growth, the activation energy for the rearrangement is considered into the free energy change in the nucleation and growth processes. From a phenomenological consideration, some features of island shape and size distribution, which had been observed, are clearly explained. The size distribution is discontinuous according to the size of the unit cell of the superlattice and the shape will be almost triangular. These features are caused by prevention of the lateral growth at the faulted half in the 7×7 structure. After the evaporation has been stopped, the detachment of atoms from corners of the triangular island starts and the island shows a rounded shape. The detachment after the deposition is also explained by the difference in the free energy changes between during and after deposition. It is suggested that the activation energy for the rearrangement process of the 7×7 structure with island growth is much higher than that for the formation process with thermal decay of the Si island.