| Summary: | 博士 === 國立交通大學 === 電子工程系所 === 94 === The continuous shrinking in the feature dimensions of metal-oxide -semiconductor field-effect transistors (MOSFETs) brings into prominence the single electron effects, among which the most important is the Random Telegraph Signals (RTS). Studies on noise from individual oxide traps in small structures can supply new information of device operation as well as degradation phenomena. Thus, individual traps can be observed in their neutral or charged state and, as a consequence, the current fluctuates between two discrete levels. The low-frequency noise (so-called 1/f noise) can be considered as the superposition of several random telegraph signals (RTS) in frequency domain. The 1/f noise can be used as a potential tool for studying the interface between the semiconductor and insulator.
The main purpose of this dissertation is to deeply investigate the fluctuations and noise in ultrathin oxide devices, high-k devices and process strained devices. Based on the study of different devices, the organization of this dissertation is described below.
First, an introduction to the RTS and noise is described in Chapter 1. The study of the RTS phenomenon in ultrathin oxide devices is demonstrated in Chapter 2 of the dissertation. Coulomb energy is essential to the charging of a nanometer-scale trap in the oxide of a metal-oxide-semiconductor (MOS) system. In this dissertation, we present for the first time experimental evidence from a 1.7-nm oxide: substantial enhancements in Coulomb energy due to the existence of a deeper trap in the oxide. Other corroborating evidence is achieved on a multiphonon theory, which can adequately elucidate the measured capture and emission kinetics. The corresponding configuration coordinate diagrams are established. Then, Chapter 3 presents the study on Coulomb scattering in a two-dimensional electron gas (2DEG) system through the relative amplitude of RTS. Experiments on an individual nanoscale trap in the oxide responsible for random telegraph signals lead to remarkable results. In this work, we demonstrated a study for relationship between the capture time, emission time, and the relative amplitude. Initially, the deeper trap in oxide corresponds to weaker Coulomb scattering in a 2DEG. However, as the 2DEG enters into the strong inversion regime, the amount of Coulomb scattering with an interface trap drops with a faster rate than the deep trap. A stronger screening potential confinement is shown to be the physical origin of this effect. The near-distance effect is expected to remain a challenging issue in the area of nanoscale devices.
Second, the study of the high-k devices is described in Chapter 4. On-off switching behaviors or two-level RTS are measured in the low voltage direct tunneling currents in ultrathin gate stack (10 Å oxide + 10 Å nitride) tunneling diode. The plausible origin is the process-induced defects in terms of localized gate stack thinning (or equivalently the conductive filament). In such extrinsic case, the current trapping-detrapping theories can adequately elucidate the data, particularly the RTS magnitude as large as 18%. The current-voltage (I-V) characteristic associated with a certain defective spot is assessed straightforwardly, showing remarkable compatibility with existing oxide thinning case. The current tunneling through the wire-like weakened spot can be probed by RTS. The role as a sensitive process monitor is demonstrated in terms of the occurrence probability of the defects as well as their locations.
Third, the 1/f noise used to monitor the quality of oxide interface with different tensile stress is presented in Chapter 5. Low-frequency noise measurement in process tensile-strained n-channel metal-oxide-semiconductor field-effect transistors yields the density of the interface states, exhibiting a decreasing trend while decreasing the channel width. This finding corroborates the group of Pb centers caused by the lattice mismatch at (100) Si/SiO2 interface as the origin of the underlying interface states. The present noise experiment therefore points to the enhancement of the tensile strain in the presence of channel narrowing, which in turn reduces the lattice mismatch. Finally, we summarize the conclusion of our works in Chapter 6.
|
|---|
