Study of low-frequency charge pumping on thin stacked dielectrics

The application of low-frequency charge pumping to obtain near-interface, or bulk trap densities, on thin stacked gate dielectrics is studied. A review of the theory governing the low-frequency charge pumping technique, developed to extract bulk trap densities from metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated with thick SiO/sub 2/ dielectrics, is given. In this study, the technique is applied to a series of n-channel MOSFETs fabricated with stacked gate dielectrics. The dielectric stacks were comprised of rapid thermal oxide (RTO) interface layers and rapid thermal chemical vapor deposited (RTCVD) oxynitride layers, which incorporated varying concentrations of nitrogen. The effect of DC tunneling currents on the technique is studied, and a procedure to remove these components from the measured substrate current is outlined. Distortions in the experimentally measured charge pumping current plotted as a function of gate bias is modeled and found to be due to the contribution of bulk traps. Finally, the limitations of applying a model that was originally developed for thick SiO/sub 2/ dielectrics to thin stacked gate dielectrics are discussed.

I. Introduction

As the scaling of metal-oxide-semiconductor field-effect transistor (MOSFET) devices continues toward sub-0.1- gate lengths, thickness values of 1.5 nm and below are required. It has been well documented that will be difficult, if not impossible, to use in this thickness regime because of a number of issues including high leakage currents and inadequate reliability [1], [2]. While the thickness at which fails is debatable, it is clear that to continue on the projected scaling timeline a suitable replacement for must be found. Much attention is being paid to materials that have higher dielectric constants, such as: , , , , , , , and Barium Strontium Titanate (BST) [3]–[17]. It is still unclear, however, which high-k dielectric will ultimately replace .