Kelvin-Probe Force Microscopy Defect Study of Ion Implanted Thermal Oxide Thin Films on Silicon

We have studied changes to the surface potential of thermally grown oxides on silicon implanted with 15 keV P or Si using Kelvin-probe force microscopy (KFM). Oxides of 15 nm thickness were implanted through photoresist masks to create disk like islands of 3 μm diameter in the underlying silicon substrate with fluences up to 1×10¹⁴ cm^-2. Atomic force microscopy shows no change to the topology of the sample except for the case of samples implanted at high fluence (1×10¹⁴ P/cm²) and flux (4.7×10¹⁰ cm^-2s^-1), which lead to observable depressions in the oxide. Results from KFM measurements show that there is a change in the surface potential of implanted areas for all samples however. Phosphorus implanted samples show a larger change in potential compared with preliminary results from silicon implanted samples. This increased change may be due to a flux dependence on defect generation but chemical effects associated with phosphorus or the effect of ionised phosphorus cannot be ruled out. Results from samples that have the implanted P activated by rapid thermally annealing at 1000°C for 5 seconds show the surface potential of implanted areas to be reduced but not eliminated. The residual difference may be due to the change in the substrate workfunction due to activated P donors. The measured change in surface potential has also been found to depend on the imaging height