Xiaobo Jiang

Investigations on Line-Edge Roughness (LER) and Line-Width Roughness (LWR) in Nanoscale CMOS Technology: Part II–Experimental Results and Impacts on Device Variability

In the part I of this paper, the correlation between line-edge roughness (LER) and line-width roughness (LWR) is investigated by theoretical modeling and simulation. In this paper, process-dependence of the correlation between LER and LWR is studied. The experimental results indicate that both Si Fin and nanowire have strongly correlated LER/LWR, and the cross-correlation of two edges depends on the fabrication process. Based on the improved simulation method proposed in the Part I of this paper, the impacts of correlated LER/LWR in the channel of double-gate devices are investigated. The results show that Vth distribution strongly relies on cross-correlation, and can exhibit non-Gaussian distribution and/or multipeak distribution, which enlarges the Vth variation.

Investigations on Line-Edge Roughness (LER) and Line-Width Roughness (LWR) in Nanoscale CMOS Technology: Part I–Modeling and Simulation Method

In this paper, the correlation between line-edge roughness (LER) and line-width roughness (LWR) is investigated. Based on the characterization methodology of auto-correlation functions (ACF), a new theoretical model of LWR is proposed, which indicates that the LWR ACF is composed of two parts: one involves LER information; the other involves the cross-correlation of the two edges. Additional characteristic parameters for LER/LWR are proposed to represent the missing cross-correlation information in conventional approaches of LER/LWR description, other than LER/LWR amplitude and auto-correlation length. An improved simulation method for correlated LERs is also proposed, which can provide helpful guidelines for the characterization, modeling, and the optimization of LER/LWR in nanoscale CMOS technology. The experimental results and device simulation results are discussed in detail in the part II of this paper.

New insights into the design for end-of-life variability of NBTI in scaled high-κ/metal-gate Technology for the nano-reliability era

In this paper, a new methodology for the assessment of end-of-life variability of NBTI is proposed for the first time. By introducing the concept of characteristic failure probability, the uncertainty in the predicted 10-year VDD is addressed. Based on this, variability resulted from NBTI degradation at end of life under specific VDD is extensively studied with a novel characterization technique. With the further circuit level analysis based on this new methodology, the timing margin can be relaxed. The new methodology has also been extended to FinFET in this work. The wide applicability of this methodology is helpful to future reliability/variability-aware circuit design in nano-CMOS technology.

New understanding of state-loss in complex RTN: Statistical experimental study, trap interaction models, and impact on circuits

In this paper, the statistical characteristics of complex RTN (both DC and AC) are experimentally studied for the first time, rather than limited case-by-case studies. It is found that, over 50% of RTN-states predicted by conventional theory are lost in actual complex RTN statistics. Based on the mechanisms of non-negligible trap interactions, new models are proposed, which successfully interpret this state-loss behavior, as well as the different complex RTN characteristics in SiON and high-κ devices. The circuit-level study also indicates that, predicting circuit stability would have large errors if not taking into account the trap interactions and RTN state-loss. The results are helpful for the robust circuit design against RTN.

New observations on complex RTN in scaled high-κ/metal-gate MOSFETs — The role of defect coupling under DC/AC condition

The coupling effect between multi-traps in complex RTN is experimentally studied in scaled high-κ/metal-gate MOSFETs for the first time. By using extended STR method, the narrow “test window” of complex RTN is successfully expanded to full VG swing. Evident defect coupling can be observed in both RTN amplitude and time constants. Interesting nonmonotonic bias-dependence of defect coupling is found, which is due to two competitive mechanisms of Coulomb repulsion and channel percolation conduction. The decreased defect coupling is observed with increasing AC frequency. Based on the new observations on complex RTN, its impacts on the circuit stability are also evaluated, which show an underestimation of the transient performance if not considering defect coupling. The results are helpful for future robust circuit design against RTN.

Experimental study on the oxide trap coupling effect in metal oxide semiconductor field effect transistors with HfO2 gate dielectrics

In this Letter, the coupling effect between multi-traps in HfO2 gate dielectrics is experimentally studied in scaled high-κ/metal-gate metal oxide semiconductor field effect transistors (MOSFETs). Deviated from conventional understanding, mechanism that affects trap coupling is found, which is originated from local carrier density perturbation due to random dopant fluctuation (RDF) in the channel. The competition of conventional Coulomb repulsion effect and RDF induced local carrier density perturbation effect results in the nonmonotonic voltage dependence of trap coupling intensity.

Predictive compact modeling of random variations in FinFET technology for 16/14nm node and beyond

Predictive compact models for two key variability sources in FinFET technology, the gate edge roughness (GER) and Fin edge roughness (FER), are proposed for the first time, and integrated into industry standard BSIM-CMG core model. Excellent accuracy and predictivity is verified through atomistic TCAD simulations. The inherent correlations between the variations of device electrical parameters are well captured. In addition, an abnormal non-monotonous dependence of variations on Fin-width is observed, which can be explained with the newly found correlation between random variations and electrostatic integrity in FinFETs. The impacts of GER and FER on circuits are efficiently predicted for 16/14nm node and beyond, providing helpful guidelines for variation-aware design and technology process development.

Investigation on the amplitude distribution of random telegraph noise (RTN) in nanoscale MOS devices

In this paper, the amplitude (ΔId/Id) distribution of random telegraph noise (RTN) induced by each trap in nanoscale devices is investigated based on the statistical experimental results. The RTN states are extracted through the proposed Gaussian mixture model (GMM). Mont-Carlo simulation is performed to extract the most probable results for mean trap number and each RTN amplitude. The results show that the RTN amplitude distribution is well consistent with the lognormal distribution instead of the exponential distribution for both the DC and AC results, which is helpful for future robust digital circuit design against RTN.

A Device-Level Characterization Approach to Quantify the Impacts of Different Random Variation Sources in FinFET Technology

A simple device-level characterization approach to quantitatively evaluate the impacts of different random variation sources in FinFETs is proposed. The impacts of random dopant fluctuation are negligible for FinFETs with lightly doped channel, leaving metal gate granularity and line-edge roughness as the two major random variation sources. The variations of Vth induced by these two major categories are theoretically decomposed based on the distinction in physical mechanisms and their influences on different electrical characteristics. The effectiveness of the proposed method is confirmed through both TCAD simulations and experimental results. This letter can provide helpful guidelines for variation-aware technology development.

New Insights into the Amplitude of Random Telegraph Noise in Nanoscale MOS Devices

Amplitude distribution of random telegraph noise (RTN) in nanoscale CMOS technology is an open question, with both lognormal and exponential distributions widely reported in literatures. In this paper, we experimentally clarified the underlying reasons for the first time, and revealed that the trap coupling effect is the missing role behind the divergent measured results of RTN amplitude statistics. Based on the proposed new method, “clean” RTN data with and without coupling are successfully characterized. It is found that, with increasing of the coupling strength, the apparent distribution changes from exponential-like to lognormal-like; while the exact form is actually the two-stage lognormal distribution, originating from two categories of traps (located above the channel percolation paths or not). The results are essential for understanding of oxide trap coupling and modeling of RTN and are thus helpful for resilient circuit design against RTN in the future.