V. D. Maheta

A critical re-evaluation of the usefulness of R-D framework in predicting NBTI stress and recovery

Reaction-Diffusion (R-D) framework for interface trap generation along with hole trapping in pre-existing and generated bulk oxide traps are used to model Negative Bias Temperature Instability (NBTI) in differently processed SiON p-MOSFETs. Time, temperature and bias dependent degradation and recovery transients are predicted. Long-time power law exponent of DC degradation and uniquely renormalized duty cycle and frequency dependent AC degradation data from a wide range of sources are shown to have universal features and a broad consensus across industry/academia. These universal features can also be predicted using the classical R-D framework.

Isolation of NBTI Stress Generated Interface Trap and Hole-Trapping Components in PNO p-MOSFETs

In this paper, a simple phenomenological technique is used to isolate the hole-trapping and interface trap generation components during negative bias temperature instability (NBTI) stress in plasma nitrided oxide (PNO) p-MOSFETs. This isolation methodology reconciles the apparent differences between experimentally measured NBTI power-law time exponents obtained by ultrafast on-the-fly IDLIN method, which are the ones obtained using slightly delayed but very long-time measurements, and the corresponding exponents predicted by the reaction-diffusion model. A systematic validation of the isolation technique is provided through degradation data taken over a broad range of operating conditions and a wide variety of PNO processes, to establish the robustness and uniqueness of the separation procedure.

Material Dependence of NBTI Physical Mechanism in Silicon Oxynitride (SiON) p-MOSFETs: A Comprehensive Study by Ultra-Fast On-The-Fly (UF-OTF) I DLIN Technique

An ultra-fast on-the-fly (UF-OTF) IDLIN technique having 1 mus resolution is developed and used to study gate insulator process dependence of NBTI in silicon oxynitride (SiON) p- MOSFETs. The nitrogen density at the Si-SiON interface and the thickness of SiON layer are shown to impact temperature, time, and field dependencies of NBTI. The plausible material dependence of NBTI physical mechanism is explored.

Mobility degradation due to interface traps in plasma oxynitride PMOS devices

Mobility degradation due to generation of interface traps (Deltamueff(NIT)) is a well-known phenomenon that has been theoretically interpreted by several mobility models. Based on these analysis, there is a general perception that Deltamueff(NIT) is relatively insignificant (compared to Deltamueff due to ionized impurity) and as such can be safely ignored for performance and reliability analysis. Here, we investigate the importance of considering Deltamueff(NIT) for reliability analysis by analyzing a wide variety of plasma oxynitride PMOS devices using both parametric and physical mobility models. We find that contrary to popular belief this correction is fundamentally important for robust and uncorrupted estimates of the key reliability parameters like threshold-voltage shift, lifetime projection, voltage acceleration factor, etc. Therefore, in this paper, we develop a generalized algorithm for estimating Deltamueff(NIT) for plasma oxynitride PMOS devices and systematically explore its implications for NBTI-specific reliability analysis.

The Impact of Nitrogen Engineering in Silicon Oxynitride Gate Dielectric on Negative-Bias Temperature Instability of p-MOSFETs: A Study by Ultrafast On-The-Fly

Degradation of p-MOSFET parameters during negative-bias temperature instability (NBTI) stress is studied for different nitridation conditions of the silicon oxynitride (SiON) gate dielectric, using a recently developed ultrafast on-the-fly IDLIN technique having 1-mus resolution. It is shown that the degradation magnitude, as well as its time, temperature, and field dependence, is governed by nitrogen (N) density at the Si/SiON interface. The relative contribution of interface trap generation and hole trapping to overall degradation as varying interfacial N density is qualitatively discussed. Plasma oxynitride films having low interfacial N density show interface trap dominated degradation, whereas relative hole trapping contribution increases for thermal oxynitride films having high N density at the Si/SiON interface.

I_{\rm DLIN}

Flicker noise is studied in SiON p-MOSFETs before and after NBTI stress. Pre-stress noise magnitude and slope are correlated and used to verify N density distribution in gate dielectric. Post-stress noise magnitude and slope are used to explore distribution of trap generation during NBTI stress, and independently verified by using MFCP measurements. Consequence of N distribution (in SiON) on NBTI stress and recovery results is shown.

Technique

An ultrafast on-the-fly technique is developed to study linear drain current (I DLIN) degradation in plasma and thermal oxynitride p-MOSFETs during negative-bias temperature instability (NBTI) stress. The technique enhances the measurement resolution (ldquotime-zerordquo delay) down to 1 mus and helps to identify several key differences in NBTI behavior between plasma and thermal films. The impact of the time-zero delay on time, temperature, and bias dependence of NBTI is studied, and its influence on extrapolated safe-operating overdrive condition is analyzed. It is shown that plasma-nitrided films, in spite of having higher N density, are less susceptible to NBTI than their thermal counterparts.

A comprehensive study of flicker noise in plasma nitrided SiON p-MOSFETs: process dependence of pre-existing and NBTI stress generated trap distribution profiles

Reaction-Diffusion (R-D) theory, well-known to successfully explain most features of NBTI stress, is perceived to fail in explaining NBTI recovery. Several efforts have been made to understand differences between NBTI relaxation measured using ultra-fast methods and that predicted by R-D theory. Many alternative theories have also been proposed to explain ultra-fast NBTI relaxation, although their ability in predicting features of NBTI stress remains questionable. In this work, a hole-trap/interface-trap (NHT/NIT) separation framework (Fig. 1a) is used to demonstrate that NIT relaxes slower compared to overall NBTI and this NIT relaxation is consistent with R-D theory. The framework also explains, perhaps for the first time, the observed impacts of nitrogen, stress-time, temperature, frequency, duty cycle, etc. on NBTI degradation. In sum, together with NHT, the R-D model governing NIT is shown to explain NBTI stress and recovery features in nitrided gate oxide p-MOSFETs.

Development of an Ultrafast On-the-Fly

The time, temperature, and oxide-field dependence of negative-bias temperature instability is studied in HfO2/TiN, HfSiOx/TiN, and SiON/poly-Si p-MOSFETs using ultrafast on-the-flyI DLIN technique capable of providing measured degradation from very short (approximately microseconds) to long stress time. Similar to rapid thermal nitrided oxide (RTNO) SiON, HfO2 devices show very high temperature-independent degradation at short (submilliseconds) stress time, not observed for plasma nitrided oxide (PNO) SiON and HfSiOx devices. HfSiOx shows lower overall degradation, higher long-time power-law exponent, field acceleration, and temperature activation as compared to HfO2, which are similar to the differences between PNO and RTNO SiON devices, respectively. The difference between HfSiOx and HfO2 can be attributed to differences in N density in the SiO2 IL of these devices.

I_{\rm DLIN}

Generation and recovery of degradation during and after negative bias temperature instability (NBTI) stress are studied in a wide variety of plasma-nitrided (PN) silicon oxynitride (SiON) p-MOSFETs. An ultrafast on-the-fly linear drain current (I_DLIN) technique, which is capable of measuring the shift in threshold voltage from very short (approximately in microseconds) to long (approximately in hours) stress/recovery time, is used. The mechanics of NBTI generation and recovery are shown to be strongly correlated and can be consistently explained using the framework of an uncorrelated sum of a fast and weakly temperature (<i>T</i>)-dependent trapped-hole (¿<i>V</i> _h) component and a relatively slow and strongly <i>T</i>-activated interface trap (¿<i>V</i> _IT) component. The SiON process dependences are attributed to the difference in the relative contributions of ¿<i>V</i> _h and ¿<i>V</i> _IT to the overall degradation (¿<i>V</i> _T), as dictated by the nitrogen (N) content and thickness of the gate insulator.