Imaging the native inversion layer under buried oxide in silicon-on-insulator radio frequency device technology via scanning surface photovoltage microscopy

For radio frequency (RF) wireless integrated circuits and devices fabricated on silicon-on-insulator technologies, there has been indirect evidence of the presence of a parasitic native inversion layer, due to an effective trapped charge, "Q(+)," at the interface of the buried oxide (BOX) and the underlying high resistivity p-type Si substrate in production level wafers. This inversion layer can have adverse implications for the RF performance of active devices fabricated for use in wireless technologies, notably the "RF switch." In this study, the authors characterize the complementary metal-oxide-semiconductor field effect RF transistor used in such a switch. The FET is built on the active epitaxial silicon layer on top of the BOX layer; its purpose is to control input and output RF signals in integrated wireless circuitry. Using scanning surface photovoltage microscopy, the authors present the first data to show quantitatively the extent of this inversion layer into the substrate. They also present device electrical performance data proving the effectiveness of the processes used to suppress the effects of Q(+). Published by the AVS.