Integration of Single Ion Implantation Method in Focused Ion Beam System for Nanofabrication

A method of single ion implantation based on the online detection of individual ion impacts on a pure silicon substrate has been implemented in a focused ion beam (FIB) system. The optimized silicon detector integrated with a state-of-art low noise electronic system and operated at a low temperature makes it possible to achieve single ion detection with a minimum energy detection limit about 1 to 3.5 keV in a FIB chamber. The method of single ion implantation is compatible with a nanofabrication process. The lateral positioning of the implantation sites are controlled to nanometer accuracy (~5 nm) using nanofabricated PMMA masks. The implantation depth is controlled by tuning the single ion energy to a certain energy level (5-30 keV). The system has been successfully tested in the detection of 30 keV Si+ single ions. The counting of single ion implantation in each site is achieved by the detection of e-h pairs (an outcome of ionization energy) produced by the ion-solid interaction; each 30 keV Si+ ion implanting through a 5 nm SiO₂ surface layer and stopping at a pure silicon substrate produces an average ionization energy about 7.0 keV. A further development for improving a detection limit down to less than 1 keV in FIB for low energy phosphorus implantation and detection is outlined. Fabrication of nanometer-scaled phosphorus arrays for the application of qubits construction is discussed.