Effect of the Ge preamorphization dose on boron diffusion and defect evolution in silicon

Abstract

In this paper, we study the effect of the Ge + preamorphization dose on boron diffusion and on the thermal evolution of end of range (EOR) defects during annealing. Amorphizations were carried out by implanting Ge + at 150 keV to doses ranging from 1×10 15 to 8×10 15 ions/cm 2 . Boron was subsequently implanted at 3 keV with a dose of 1×10 14 ions/cm 2 . Rapid thermal annealing (RTA) was performed for various time/temperature combinations in nitrogen ambient. Secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) were used to study boron diffusion and defect evolution, respectively. We have found that after a given annealing, both the defect size and boron diffusivity are independent on the Ge ion dose. Increasing this dose only results in an increase of the defect density. These results are discussed and definitely show that EOR defects are involved in a quasi-conservative Ostwald ripening process during annealing. The diffusive behavior of boron suggests that the coupling of boron atoms with the “mean field” of Si interstitial atoms in dynamical equilibrium with the defects is responsible for transient enhanced diffusion (TED).