Ion Beam synthesis of Nano-crystals for Electronics and Photonics

One of the main goals of materials research using ion beams is to synthesize nanostructures, for example semiconducting or metallic nanocrystals (NCs) in insulating films. A great effort is currently devoted to NC fabrication for micro- and optoelectronics by ion beam synthesis (IBS), because this method is compatible with modern CMOS technology. The present contribution addresses the Si NC formation by conventional ion implantation into the gate oxide and by a non-conventional IBS approach of ion beam mixing of SiO2/Si interfaces in thin gate oxides, with special emphasis on well-controlled size and position tailoring. The two approaches will be compared and related technological challenges discussed. Compared to conventional Si NC synthesis by Si+ ion implantation into the gate oxide, we take advantage of the self-alignment ion beam mixing process, i.e., the Si NCs are formed in SiO2 at a well-controlled small distance of ca. 2 nm from the Si/SiO2 interfaces. The technical applications in non-volatile nanocrystal memories and in light emitting field-effect transistors (LEFET) are demonstrated.
The Si NC MOSFETs were fabricated as nMOSFET devices in a standard 0.6 µm CMOS process line. Their electrical characteristics have been evaluated in terms of write/erase voltage, duration of the programming time, endurance and retention for different ion irradiation and annealing conditions. For the investigation of the light-emitting characteristics of the same nMOSFETs, an AC voltage was applied to the gate in order to inject charges of both polarities into the NCs. AC voltage and frequency dependent electroluminescence spectra in the wavelength region of 400-1000 nm were recorded for different annealing conditions. The performance of the Si NC memories and LEFETs with further possibilities of optimization of efficient charge storage and light emission properties will be discussed.