CAVITY FORMATION AND IMPURITY GETTERING IN HE-IMPLANTED SI

Cavity microstructures formed in Si after ion implantation of He (30 o r 130 keV) and annealing at 700 degrees C or above are examined with c ross-section transmission electron microscopy. A threshold concentrati on of 1.6 at.% He is identified as required to form cavities that surv ive such anneals. The cavities coarsen with a constant volume correspo nding to similar 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 x 10( 17) He/cm(2). 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 t han to their respective precipitated phases, Co and Fe are more strong ly bound to their silicides; nonetheless, appreciable trapping of Co a nd Fe does occur in equilibrium with the silicides. Cavity trapping ap pears to be an effective gettering mechanism at low impurity levels, a s needed to meet future microelectronics device requirements.