Predictive process simulation of Si nanocluster layer formation by low-energy ion implantation

Memory cells consisting of a metal-oxide-semiconductor field-effect transistor (MOSFET) with a charge-storage floating-gate made of silicon nanocrystals (ncs) are promising candidates for high-storage density low-power memory applications. The information is stored in the floating gate that can be charged and discharged either from the control gate or from the channel of the transistor. Floating gates consisting of Si ncs have been fabricated through the use of different deposition techniques. The multi-dot layer in the very thin gate oxide can be fabricated CMOS-compatibly by ion beam synthesis (IBS) [1]. Here, we present theoretical studies on IBS of multi-dot layers
consisting of Si nanocrystals (NCs) [2]. The NCs are produced by ultra low energy Si ion implantation, which causes a high Si supersaturation in the shallow implantation region. During post-implantation annealing, this supersaturation leads to phase separation of the excess Si from the SiO₂. Kinetic lattice Monte Carlo simulations of Si phase separation have been performed and compared with EFSTEM images [3]. It has been predicted theoretically that the morphology of the multi-dot Si floating gate changes with increasing ion fluence from isolated, spherical NCs to percolated spinodal Si pattern. These patterns agree remarkably with EFSTEM images. However, the predicted fluence for spinodal pattern is lower than the experimental ones. Because oxidants of the ambient atmosphere penetrate into the asimplanted SiO₂, a substantial fraction of the implanted Si is lost due to oxidation.
[1] K.-H. Heinig, T. Müller, B.Schmidt, M. Strobel, W. Möller, Appl. Phys. A 77, 17–25 (2003).
[2] T. Müller, K.H. Heinig, and W. Möller, Appl. Phys. Lett. 81, 2373 (2002).
[3] T. Müller, K.H. Heinig, W. Möller, C. Bonafos, H. Coffin, N. Cherkashin, G. Assayag, S. Schamm, G. Zanchi, A. Claverie, M. Tencé, C. Colliex, Appl. Phys. Lett. 85, 2373 (2004).