Cavity formation and impurity gettering in He-implanted Si

Abstract

Cavity microstructures formed in Si after ion implantation of He (30 or 130 keV) and annealing at 700°C or above are examined with cross-section transmission electron microscopy. A threshold concentration of 1.6 at.% He is identified as required to form cavities that survive such anneals. The cavities coarsen with a constant volume corresponding to ∼0.75 lattice sites per implanted He atom and have surface areas 3-7 times that of the wafer area for fluences of 1 × 1017 He/ cm2. Transition metal atoms (Cu, Ni, Co, Fe, Au) are shown to be strongly trapped (1.5–2.2 eV) on the cavity walls by chemisorption. Whereas Cu, Au, and Ni are bound more strongly to the cavity sites than to their respective precipitated phases, Co and Fe are more strongly bound to their silicides; nonetheless, appreciable trapping of Co and Fe does occur in equilibrium with the silicides. Cavity trapping appears to be an effective gettering mechanism at low impurity levels, as needed to meet future microelectronics device requirements.