Transition from wire formation to island formation in thermal agglomeration of a (111) silicon-on-insulator layer

The effects of Si layer thickness on thermal agglomeration of a (111) bonded silicon-on-insulator (SOI) structure were studied. As starting material, (111) bonded SOI wafers with their top Si layer thinned to 2–9 nm were used. The samples were subjected to thermal treatment at 950 °C in ultrahigh vacuum. Atomic force microscopy revealed that, in the 4–9 nm thickness range, the top Si layer is deformed into wire arrays in the 〈112¯〉 directions. However, at thicknesses below 4 nm, randomly formed Si islands were observed. This structural transition from wires to islands is presumably due to the atomic-scale thickness fluctuation in the initial Si layer.