Analysis of hot-carrier-induced degradation in deep submicron Unibond and SIMOX N-MOSFETs using charge pumping and noise techniques

Abstract

Hot-carrier-induced degradation in SOI devices is more complex than that in bulk devices because of the SOI structure (two interfaces, floating body, etc.). At low V/sub g/, the parasitic bipolar transistor (PBT) action induced by floating body effects can reinforce the impact ionization rate as well as the device degradation. This effect can be reduced with a grounded body. However, for fully depleted (FD) SOI devices, the back interface degradation can also influence the front channel operation due to the interface-coupling effect. In this respect, the poor electrical properties of the buried oxide (BOX) of SIMOX devices could be a problem for SOI device operation in the deep sub-/spl mu/m range. A new SOI material technology, Smart-Cut was recently developed for the fabrication of Unibond wafers (Bruel et al. 1995). Good Si layer uniformity without defects and a very sharp bonded interface have been obtained from this technology. The aim of this paper is thus to present a thorough investigation of hot-carrier-induced device aging by monitoring the degradation of maximal transconductance (G/sub mmax/) and the threshold voltage (V/sub t/) shift, the charge pumping current and the noise magnitude, for deep submicron Unibond and SIMOX N-MOSFETs. The 0.2 /spl mu/m N-channel Unibond and SIMOX MOSFETs used in this study are FD (t/sub Si/=40 nm) devices, with 4.5 nm gate oxide and 380 nm buried oxide thicknesses. A body terminal is available in these devices. Stress experiments were performed at V/sub g/=V/sub t/ and V/sub g/=V/sub d/ over 10000 sec and the body terminal was grounded or floating during the stress. All measurements were performed with a front-gate control.