IMPURITY GETTERING EFFECTS IN SEPARATION-BY-IMPLANTED-OXYGEN (SIMOX) WAFERS - WHAT GETTERS WHAT, WHERE AND HOW

Two technologically attractive concepts are currently being evaluated for front-side gettering in the vicinity of the active device region ( proximity gettering). The first one employs high-energy carbon implant ation and annealing to form a carbon-rich layer. The second approach i nvolves the implantation of helium followed by annealing to create a c avity-containing layer. In this study we are concerned with the getter ing behaviour of two typical transition-metal impurities, namely Cu an d Fe, in as-received SIMOX material and in SIMOX wafers incorporating such proximity gettering layers. The structures are characterised by s econdary-ion-mass spectrometry, Rutherford backscattering/channelling spectrometry, transmission electron microscopy and elastic recoil dete ction. It is shown that the final impurity distributions are sensitive to the depth location of the proximity-gettering layers. Both C and H e implants are found to capture efficiently Cu atoms whereas cavity mi crostructures act as gettering centres for Cu, but provide no detectab le trapping of Fe. Appreciable depletion of Fe is only achieved in the presence of C-rich gettering layers. From this viewpoint, implanted C layers may be preferable to cavity-containing zones formed by He impl antation.