Determination of capture cross sections for as-grown electron traps in HfO2/HfSiO stacks

A major challenge for replacing gate SiON with HfO2 is the instability and reliability of HfO2. Unlike the SiON, there can be substantial amount of as-grown electron traps in HfO2. These traps can cause instability in the threshold voltage and contribute to the dielectric breakdown. Despite the early efforts, our understanding of them is incomplete. Agreement on their capture cross sections has not been reached and the reported values spread in a large range of 10(-12)-10(-19) cm(2). The objective of this paper is to determine their capture cross sections unambiguously, which requires knowing the gate current and the electron fluency for filling the trap. A key part of this work is to estimate the trapping-induced transient gate current following the application of a pulse to the gate. This is achieved by numerical simulation. It is found that trapping can reduce the gate current by two orders of magnitude and the gate current can drop substantially within microseconds. The results show the presence of two distinctive capture cross sections in the order of 10(-14) and 10(-16) cm(2), respectively, which most likely originated from two different types of as-grown electron traps in HfO2. These capture cross sections are insensitive to fabrication and processing techniques. (c) 2006 American Institute of Physics.