TEM study of Ge-nanoclusters in thin SiO2 layers

Semiconductor nanoclusters embedded in a dielectric matrix are of great interest for future optical and electrical applications in microelectronic circuits. The contribution is focused on the study of Ge-nanoclu-sters generated by ion beam synthesis (IBS) in thermally grown thin SiO2 layers (20-50 nm). TEM and RBS analysis show, that the cluster formation and the elemental Ge distribution is strongly influenced by the annealing condi-tions, which is described in detail for furnace and rapid thermal processing (800°C-1100°C). TEM investigation revealed that in dependence on specific implantation and annealing conditions a broad nanocluster band in the centre of SiO2-layer or a d-like one in the distance of 5-7 nm from the SiO2/Si interface can be generated. HRTEM characterisation of samples emerge that the Ge clusters in the thin SiO2 films are amorphous opposite to earlier results were crystalline Ge nano-cluster were created in 500 nm SiO2 layers [1]. Long-term stability of grown clusters is an important feature for their further use in microelectronics. We identified the preparation conditions where the Ge nanocluster have a high stability and do not change with time and where the cluster are unstable and disappear completely after 2 month storage without any thermal treatment. Experiments with strong electron irradiation performed in a TEM with a FEG show the possibility of in-situ crystallisation of existing cluster as well as crystalline cluster formation in the samples where clusters before irradiation were not observed.
[1] J. v. Borany, R. Grötzschel, K.H. Heinig, A. Markwitz, W. Matz, B. Schmidt and W. Skorupa "Multimodal impurity redistribution and nanocluster formation in Ge implanted silicon dioxide films", Appl. Phys. Lett. 71 (22) 3215 (1997)