Device fabrication in {100} silicon-on-oxide produced by a scanning CW-laser-induced lateral seeding technique

By using a CW-laser-beam-induced lateral seeding technique, which is a zone-melting crystal-growth process, single-crystal silicon-on-oxide with
{100}
orientation has been obtained. To adopt this process for silicon-on-insulator (SOI) MOS transistor fabrication, a masking level has been added to an exisiting n-MOSFET mask set so that a fully recessed oxide layer may be grown in selected regions of a silicon wafer; the exposed silicon region becomes the seed region. After depositing a 0.5-µm-thick layer of undoped low-pressure CVD polysilicon on the wafer, a laser process is performed to induce epitaxial growth in the polysilicon-on-silicon region, which in turn seeds the zone growth of the polysilicon-on-oxide region as the beam is traversed across the surface of the wafer. N-channel MOS transistors have been fabricated in the silicon-on-oxide material using projection printing lithography. Both complete-island-etch (CIE) and LOCOS techniques have been used for device-to-device and device-to-substrate isolation. Surface electron mobilities as high as 740 cm
²
/V . s, comparable to that obtainable in bulk-type devices, have been measured in 5-µm channel-length devices. It is shown that the back interface between the recrystallized silicon and the oxide layer is the dominant contributor to the subthreshold leakage current due to a combined effect of a high fixed oxide charge density and drain-induced barrier lowering. A high dose (
\sim 10^{12}
cm
^-2
) deep boron implantation centered at the back interface and a back-gate bias have been shown to be effective in suppressing the leakage current to as low as 1-pA/µm channel width at V
DS
= 2 V, comparable to the best results obtained in silicon-on-sapphire (SOS).