Direct Observation of Radiation Induced Precipitation in High Voltage Electron Microscope

Long needle-shaped radiation induced precipitates oriented along <110> directions were first reported by Nes and Washburn from observation using hot stage high voltage electron microscopy. Similar long rod-like defects have also been observed in boron ion implanted silicon. Our recent results show that most long rod-like defects formed during postimplantation annealing of boron ion implanted silicon are boron precipitates. The cause for the formation of these long rod-like defects is assumed to be replacement of substitutional boron by silicon selfinterstitials. To substantiate this mechanism two samples were irradiated in the high voltage electron microscope. Sample A was a boron doped <111> oriented silicon of resistivity 0.75 Ω-cm (2.5x10l6 B/cm3) and sample B was phosphorous doped, of resistivity 2 Ω-cm (2.7x10l5 p/cm3). Figure 1 shows the sequential development of long rod-like defects in sample A held at 620°C during irradiation with 650 keV electrons.