Si quantum dot (QD) flash memories have several advantages including high fault toloerence and retentivity. The structure of these devices require arrays of Si QD grown on the dielectric film. SiO₂ has been the dielectric of choice for Si based devices, due to the predictable and high performing nature of Si/SiO₂ interface. However, the low dielectric constant of SiO₂ himders scaling of its thickness. High-k dielectric such as HfO₂ are alternatives enabling high capacitance and hence low thickness of the dielectric layer. However, interface of Si with HfO₂ is not as highly optimized as with SiO₂.

Here we explored the growth of Si QD on HfO₂ by an approach of thermally stressing Si thinfilm. Density functional theory (DFT) based simulations confirmed the feasibility of formation of QD from thinfilm, due to the high thermal stability of Si QD-HfO₂ interface. The thermal stability as obtained by DFT was found to be comparable to Si QD-SiO₂ interface. To study the morphology and optimize the process for growth of Si QD on Hf₂, following proceduere was carried out. HfO₂ thinfilm was sputtered on Si wafer. Following this, amorphous or crystalline Si films were deposited on it by chemical vapour deposition, obtained by varying substrate temperature and vapour flow rate. Finally, the films were subjected to annealing, so as to stress the Si thinfilm into forming nanocrystals. As shown in the AFM image above, the annealing led to the formation of regular shaped nanocrystals from the coherent Si thinfilm. While QD were obtained from both crystalline and amorphous Si thinfilms, crystalline fiilms led to larger sized nanocrystals.

In this way, Si QD were grown on HfO₂, as per the configuration required for scalable flash emmory devices.