Ion Implantation To The Interaction Between The Impurities And Defects

As technology generations advance and devices become smaller, it is necessary to create sharp, ultrashallow profiles with high concentrations of electrically active dopants. Ion implantation is the most widely used technique for forming shallow junctions. The recent trends in integrated circuit processing point towards the use of low temperature anneals to limit the redistribution of dopants. This method decreases the percentage of impurities activation.Boron is the commonly used dopant in Si processing for the formation of p-type doped regions. Anomalous diffusion of ion-implanted boron during thermal anneal is the main problem in shallow junction formation. Besides TED (transient enhanced diffusion), a striking feature of anomalous diffusion is that the peak portion of boron profile is not electrically activated and has remained immobile during annealing. For this study, (100) Czochralski Si wafers with a boron concentration of 3×1017cm-3 were implanted with Si ions at 50 keV using a Veeco-2100MP ion implanter. Implants were carried out at room temperature with doses ranging from 5×1013cm-2 to 2×1015cm-2. Uniformly boron-doped wafers were used to investigate the impact of ion implant damages on the redistribution of boron atoms. Si ions instead of dopants such as B, P and As atoms were implanted into the Si wafers to avoid data analysis difficulties. The boron segregation to three types of dislocation loops, EOR dislocation loops, clamshell defects and Rp defects, was investigated with SIMS and XTEM. The evolution of boron segregation peaks is closely related to the evolution of dislocation loops.At present, simulation tools designed to predict dopant diffusion during device processing are not capable of dealing with this phenomenon in a satisfactory manner. From this perspective, it is crucial to improve our understanding of the physical mechanisms of B diffusion. In this article, a simple model for boron segregation to Rp defects has been developed to explain the boron anomalous diffusion which is not adequately considered by the most widely used process simulation codes. The inactive boron peak below the equilibrium solubility during annealing is explained with this model. Rp defect decay time constant and the boron segregation energy have been found to fit the data to a reasonable extent. The experimental boron profiles for different annealing times can be well reproduced with this model. Implementation of this model into process simulators allows one accurately forecast of the boron and carrier distributions after annealing.