Diffusion of iron in the silicon dioxide layer of silicon-on-insulator structures

The redistribution of iron implanted into the oxide layer of silicon-on-ins ulator structures has been measured using the secondary ion mass spectrosco py technique after annealing at 900-1050 degrees C. Iron diffusion has been found to be much faster in the oxide prepared by the separation-by-implant ation-of-oxygen (SIMOX) procedure compared to the thermally grown oxide in the bonded and etched-back structures. In the latter case, the Fe diffusivi ty exhibits a thermal activation with an energy of 2.8 eV, confirming the L iterature data on silica glass. In the SIMOX oxide, the diffusivity depends only weakly on temperature, indicative of an essentially activation-free d iffusion mechanism. Gettering of Fe at below-the-buried-oxide defects in SI MOX wafers has been observed. No iron segregation has been detected at the SiO2-Si interfaces. (C) 1998 American Institute of Physics. [S0003-6951(98) 02735-1].