Correlation between high-density trap states and local stress near SOI/BOX interface in SIMOX wafers

Separation by implanted oxygen (SIMOX) wafers and bonded wafers are commercially available silicon-on-insulator (SOI) wafers. In particular, SIMOX process technologies have become important in system-on-a-chip (SoC) fabricated on SOI/Bulk hybrid substrates composed of SOI region for the logic circuits and bulk region for the dynamic random access memories (DRAMs) in recent years. However, we found that low-dose SIMOX wafers have energetically localized acceptor-like and donor-like trap states with the density of 10¹¹ cm^-2 at the SOI/buried oxide (BOX) interface by back-gate characteristics. In addition, we estimated that the high-density trap states are distributed within about 30 nm from the SOI/BOX interface in SOI layer by front-gate characteristics in MOSFETs with SOI layers of different thicknesses. Furthermore, we speculated that the distribution of the trap states in the SOI layer is attributed to nano-scale roughness at the SOI/BOX interface, which is peculiar to the SIMOX process. In this paper, we discuss the origins of the high-density trap states in SOI layer of SIMOX wafers considering the roughness at the SOI/BOX interface.