Control of Silicon Quantum Dots nucleation and growth by CVD

摘要

To be successfully integrated in nano-electronics devices, silicon quantum dots (Si-QDs) density, density uniformity, size and size dispersion must be controlled with a great precision. Nanometric size Si-QDs can be deposited on insulators by SiH_4 CVD. Their formation includes two steps : nucleation and growth. We study the experimental parameters which influence each step in order to improve the control of the Si-QDs morphology. We show that the nucleation step is governed by the reactivity of the substrate with the Si precursors. On SiO_2, OH groups are identified as nucleation sites. By controlling the OH density on the SiO_2 surface, we can monitor the Si-QDs density on more than one decade for the same process conditions. Moreover, Si-QDs density as high as 1.5 10~(12)/cm~2 can be obtained. On the contrary, the growth step depends on process conditions. By modifying the gas phase composition, i.e by using SiH_2Cl_2 as Si precursor, we can grow the nuclei already formed during the nucleation step without formation of new Si-QDs. We discuss the advantages of this process to improve the control of the Si-QDs size and limit the size dispersion.