Simulation of ion-irradiation stimulated Ge nanocluster formation in gate oxides containing GeO2

The control of the MOSFET channel by nanoclusters within the gate oxide, which are charged/decharged due to direct e--tunneling, provides a conceptually very simple non-volatile memory. The development of reliable processes for the production of the required nanocrystals on an industrial scale is a big challenge to current research. The two processes being favored at present are the self-organization of nanocluster-delta-layers after ion implantation [1] and the deposition of Si aerosols [2]. Here, we present an alternative process taking advantage of the well-known self-assembling of Ge quantum dots on (001)Si [3,4] in combination with chemical reduction of GeO2 by Si during thermal treatment [5]. Using process simulations it will be studied, how, in comparison to pure thermal treatment, ion-irradiation induced detachment of Si monomeres from the Si/SiO2 interface accelerates the Ge precipitation due to the GeO2+Si --> SiO2+Ge reaction. For our study it was assumed that self-assembled Ge nanoclusters on Si [3,4] were covered by a Si layer, and, finally, oxidized under special conditions [5] which suppresses Ge segregation. The resulting thin gate oxide with embedded GeO2 clusters is the starting point of our kinetic Monte-Carlo simulations. In an fcc-cell of about 256000 lattice points having periodic boundary conditions in the interface plane, Ising-model-like interactions in the two-component system (Si and Ge) and the reaction GeO2+Si-->SiO2+Ge are taken into account. Additionally, according to ion beam mixing estimated by TRIM calculations, atomic displacements of Si bulk and nanocluster atoms have been considered.
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