Subnanometer-resolution depth profiling of boron atoms and lattice defects in silicon ultrashallow junctions by ion beam techniques

The continued research and development effort on silicon ultrashallow junctions has posed a great challenge to materials characterization, due to the need for depth profiling of dopants and silicon lattice defects with a subnanometer resolution. In this work, we report on a method combining ion beam analysis (Rutherford backscattering, ion channeling, and nuclear reaction analysis) with room-temperature UV-assisted oxidation and chemical wet etching for obtaining high-resolution (∼0.5 nm) depth distributions of total boron atoms, electrically activated boron atoms and silicon lattice defects in silicon ultrashallow junctions. The application of this method was demonstrated by profiling silicon junctions as shallow as 8 nm, created by 200-eV boron ion implantation followed annealing by various techniques. The capability to profile boron at such high resolution has resulted in observation of boron segregation. Additionally, the ability for depth profiling Si lattice defects offered by this method has aided in the understanding of thermal and laser annealing effects on defect formation in Si junctions. Our experimental results are compared with those obtained using other techniques such as secondary ion mass spectroscopy and four-point probe, and differences are discussed in detail.