Size and Location Control of Si Nanocrystals at Ion Beam Synthesis in Thin SiO2 Films

TL;DR

This study combines collision and Monte Carlo simulations to control the size and placement of silicon nanocrystals in SiO2 films, optimizing them for nonvolatile memory applications.

Contribution

It introduces a simulation approach to precisely control nanocrystal size and location during ion implantation and annealing processes.

Findings

Nanocrystals form above a thin oxide layer at the Si/SiO2 interface.

Nucleation regime maintains constant tunneling oxide width and nanocrystal size.

Simulations suggest optimal conditions for nonvolatile memory device fabrication.

Abstract

Binary collision simulations of high-fluence 1 keV Si ion implantation into 8 nm thick SiO2 films on (001)Si were combined with kinetic Monte Carlo simulations of Si nanocrystal (NC) formation by phase separation during annealing. For nonvolatile memory applications, these simulations help to control size and location of NCs. For low concentrations of implanted Si, NCs form via nucleation, growth and Ostwald ripening, whereas for high concentrations Si separates by spinodal decomposition. In both regimes, NCs form above a thin NC free oxide layer at the SiO2/Si interface. This, self-adjusted layer has just a thickness appropriate for NC charging by direct electron tunneling. Only in the nucleation regime the width of the tunneling oxide and the mean NC diameter remain constant during a long annealing period. This behavior originates from the competition of Ostwald ripening and Si loss to the Si/SiO2 interface. The process simulations predict that, for nonvolatile memories, the technological demands on NC synthesis are fulfilled best in the nucleation regime.