Effect of fluorine on boron diffusion under interstitial injection from the surface

In this paper, a point defect injection study is performed to investigate the effect of fluorine on boron diffusion when interstitials are injected from the surface. 185keV, 2.3x1015 cm-2 fluorine is implanted into silicon with a boron marker layer located at about Rp/2 of the fluorine implant. This is followed by rapid thermal annealing at 1000oC for times 15 ~120s in an oxygen ambient. The wafers are covered with different layers prior to anneal to introduce different point defect injection effects. When interstitials are injected from the surface, fluorine strongly suppresses boron diffusion for anneal times of 15 and 30s. For longer anneal times, fluorine becomes progressively less effective and the boron diffusion coefficient approaches the value obtained in samples without fluorine. This effect of fluorine on boron diffusion suppression correlates with the presence of a shallow SIMS fluorine peak at ~Rp/2. These results support earlier work showing that vacancy-fluorine clusters at ~Rp/2 are responsible for the suppression of boron diffusion and that these clusters anneal out during long anneal times. Under inert anneal, fluorine has little effect on boron diffusion. An issue of boron cross contamination during the fluorine implant is also identified.