Improving Total Dose Tolerance of Buried Oxides in SOI Wafers by Multiple-Step ${\hbox {Si}}^ + $ Implantation

A modified hardening technique is proposed to improve the total dose hardness of buried oxides in silicon-on-insulator (SOI) technologies using multiple-step
${\hbox {Si}} + $
ion implantation. Each implanting step introduces a dose of
${5} \times 10^{15}/\hbox{cm}^{2}$
into buried oxides which creates an amorphous/crystalline (a/c) interface within the top Si layer. Inter-implant rapid thermal annealing (RTA) removes implant-induced lattice damages by moving a/c interface towards top silicon surface. The thermal processes between implant steps prevent top silicon layers from total amorphization which is a kind of unrecoverable damage in the single-step method. High Resolution X-Ray Diffraction (HRXRD) technique is exploited to inspect the lattice quality of top silicon in light of a slight crystal orientation mismatch during bonded-wafer fabrication. Pseudo-mos transistor characterization technique confirms the hardening capability of the new method.