Role of fluorine in low temperature dopant activation of boron

Summary form only given. MOS device scaling requires a decrease in lateral dimensions and in junction depths. Current projections call for junction depths in the 300 Å range in order to reduce short-channel effects of 0.07 μm gate-length technologies. The key limiting factors in boron doped junctions are transient enhanced diffusion (TED) and the more recent concept of boron enhanced diffusion (BED). Typically, in the creation of shallow junctions, a high temperature spike anneal is used. The annealing process has the side effect of TED. (311) crystalline defects provide interstitials which cause enhanced dopant diffusion. The result is a short period of highly increased diffusivity that can be several thousand times higher than standard boron diffusion with no crystal damage present. Other studies show that TED is not the only limiting factor in the creation of ultra-shallow junctions. High B concentration in the absence of damage also enhances B diffusivity, termed BED, and is present during spike anneals of 1050°C. This study investigates these factors and the role of fluorine in the formation of ultra-shallow junctions using low energy boron and BF₂ ion implantation as they relate to low temperature boron activation. Boron implantation has been performed on n-type <100> Si wafers using B (2.2 keV), BF₂ (10 keV) and B and F ions separately at equivalent energies. The wafers were annealed using spike anneals and lower temperature furnace anneals in the temperature range 600-800°C. The resulting diffusion profiles were studied using SIMS, spreading resistance analysis and four point probe resistivity measurements