Ion Irradiation Assisted Fabrication of Si Quantum Dots for Ultra-Low Power Electronics

The use of single electron transistors in large-scale integrated circuits promises a further boost for higher integration density and lower power consumption. However, in order to achieve single electron operation at room temperature, quantum dots (QDs) with a few nanometers in diameter and defined tunnel junctions have to be fabricated. A technological route to achieve such requirements is the fabrication of Si QDs embedded in SiO2 by phase separation of metastable SiOx (x<2).
In a CMOS-compatible manner, a Si rich oxide layer is produced by ion beam irradiation through a Si/SiO2/Si stack [1]. Choosing the right thickness of the oxide layer of ~7 nm leads to the formation of QDs in the middle of the layer [2]. The position of the Si QDs formed by the subsequent phase separation can be further controlled by applying geometrical constrains to the self-assembly process. This can be achieved in two ways. Firstly, the Si concentration in the SiO2 is strongly enhanced locally by focused ion beam induced mixing. Secondly, under broad beam irradiation of pillars consisting of Si/SiO2/Si stacks, the local mixing is defined by the pillar diameter. It is predicted by 3D kinetic Monte-Carlo (kMC) simulations that a single Si QD of few nm in diameter is formed in the middle of the SiO2 layer of the pillar structure. The optimal geometries and irradiation condition for fabricating reproducible QDs are explored by means of 3DkMC using input data from dynamic 3D ion collision simulations (TRI3DYN).
We will discuss the underlying principles and the mechanism of Si QD formation by ion induced directed self-assembly and present first results of focused Ne+ ion irradiations of a Si/SiO2/Si layer stack as well as Si+ broad beam irradiations of pillars.
This work is part of the project IONS4SET (Horizon 2020 research and innovation program, Grant Agreement No 688072).
[1] K.-H. Heinig et al., Appl. Phys. A77, 17 (2003).
[2] L. Röntzsch et al., phys. stat. sol.(a) 202, R170(2005).