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 SiH4 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 SiO2, OH groups are identified as nucleation sites. By controlling the OH density on the SiO2 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 1012 /cm2 can be obtained. On the contrary, the growth step depends on process conditions. By modifying the gas phase composition, i.e by using SiH2Cl2 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.