C. H. Ang

National University of Singapore, Tumasik, Singapore

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Publications (45)81.61 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Conventional oxide reliability studies determine oxide lifetime by measuring the time to breakdown or quasi-breakdown (QB). In ultrathin gate oxides with T<sub>ox</sub><14 Å, however, it is hard to observe breakdown or QB under typical stress conditions. Instead, the gate leakage current shows a continuous increase over the entire time period of electrical stress. As the magnitude of the gate current density increase eventually becomes too high to be acceptable for normal device operation, a lifetime criterion based on the increase in gate leakage current is proposed. Our paper also shows that the area-dependence of the gate leakage current density increase in 13.4 Å oxides is different from that in thicker oxide films, indicating a localized and discrete property of the leakage current. It has also been observed that the oxide lifetime based on the new lifetime criterion is shorter when the gate area is smaller, as opposed to the conventional area dependence of time-to-breakdown test. A simple model consisting of multiple degraded spots is proposed and it has been shown that localized gate leakage current can be described by Weibull's statistics for multiple degraded spots.
    IEEE Transactions on Electron Devices 05/2003; 50(4-50):967 - 972. DOI:10.1109/TED.2003.812105 · 2.36 Impact Factor
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    ABSTRACT: The nitrogen-enhanced negative bias temperature instability (NBTI) effect has been studied experimentally and theoretically. It is observed that both the interface state and positive fixed charge generation increase linearly with interfacial nitrogen concentration. The experimental results can be understood in terms of the reaction energies of the hydrogen trapping reactions at the interface, which are obtained from first-principle calculations. These results improve our understanding of the mechanisms responsible for the nitrogen-enhanced NBTI effect. © 2003 American Institute of Physics.
    Applied Physics Letters 03/2003; 82(12):1881-1883. DOI:10.1063/1.1563045 · 3.52 Impact Factor
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    ABSTRACT: By analyzing the change in the Fowler–Nordheim tunneling current as a result of the modulations of both the cathode field and the barrier shape at the tunneling interface caused by electrical stress, the charge trapping modulating the cathode field as well as the barrier change resulting from the charge trapping within the tunneling distance are determined quantitatively. The influence of nitridation on the barrier change and the charge trapping is examined. It is found that nitridation reduces the barrier change and the charge trapping significantly. © 2003 American Institute of Physics.
    Journal of Applied Physics 02/2003; 93(5):3114-3116. DOI:10.1063/1.1542688 · 2.19 Impact Factor
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    ABSTRACT: The influence of nitrogen concentration at a nitrided oxide/silicon interface on the activation energies of both near-interface fixed-charge trapping and interface state generation caused by negative bias temperature instability stress has been studied quantitatively. It is observed that the charge trapping and the interface state generation have about the same activation energy for a given interfacial nitrogen concentration. In addition, their activation energies are found to follow the same dependence on the nitrogen concentration. The results suggest that the charge trapping and the interface state generation have the same origin. A discussion on the mechanism of the nitrogen effect on the charge trapping and interface state generation is presented. © 2003 American Institute of Physics.
    Applied Physics Letters 01/2003; 82(2):269-271. DOI:10.1063/1.1537053 · 3.52 Impact Factor
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    ABSTRACT: We report a new NBTI phenomenon for p-MOSFETs with ultra thin gate oxides. We demonstrate that in a CMOS inverter circuit, the interface traps generated under NBTI stressing in a p-MOSFET (corresponding to the "high" output state of the inverter) are subsequently passivated when the gate to drain voltage switches to positive (corresponding to the "low" output state of the inverter). As a result, it was found that this "Dynamic" NBTI (DNBTI) operating in a CMOS inverter circuit prolongs significantly the device lifetime while the conventional "static" NBTI (SNBTI) underestimates the device lifetime. Furthermore, the DNBTI effect is dependent on temperature and gate oxide thickness, but independent of operation frequency. A physical model is proposed for DNBTI that involves the interaction between hydrogen and silicon dangling bonds. This finding has significant impact on the determination of maximum operation voltage as well as lifetime projection for future scaling of CMOS devices.
    Reliability Physics Symposium Proceedings, 2003. 41st Annual. 2003 IEEE International; 01/2003
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    ABSTRACT: For the first time, a dynamic negative bias temperature instability (DNBTI) effect in p-MOSFETs with ultrathin gate oxide (1.3 nm) has been studied. The interface traps generated under NBTI stressing corresponding to p-MOSFET operating condition of the "high" output state in a CMOS inverter, are subsequently passivated when the gate to drain voltage switches to positive corresponding to the p-MOSFET operating condition of the "low" output state in the CMOS inverter. Consequently, this DNBTI effect significantly prolongs the lifetime of p-MOSFETs operating in a digital circuit, and the conventional static NBTI (SNBTI) measurement underestimates the p-MOSFET lifetime. A physical model is presented to explain the DNBTI. This finding has significant impact on future scaling of CMOS devices.
    IEEE Electron Device Letters 01/2003; DOI:10.1109/LED.2002.805750 · 3.02 Impact Factor
  • Shyue Seng Tan, Tu Pei Chen, Chew Hoe Ang
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    ABSTRACT: In this work, influences of nitridation on barrier height change caused by electrical stress with Fowler-Nordheim (FN) injection have been studied: We have employed a novel approach to analyze the small change in the FN tunneling current through the nitrided oxide after electrical stress to quantitatively examine the changes of both effective gate/oxide barrier height and charge trapping density. For both the pure oxide and the nitrided oxides the FN injection. leads to positive charge trapping in the oxides and an increase in the barrier height, however, the nitridation can reduce the barrier height change and the charge trapping significantly.
    Japanese Journal of Applied Physics 12/2002; 41(12B). DOI:10.1143/JJAP.41.L1425 · 1.06 Impact Factor
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    ABSTRACT: The kinetics of the interfacial layer (IL) growth between Hf aluminates and the Si substrate during high-temperature rapid thermal annealing (RTA) in either N2 ( ∼ 10 Torr) or high vacuum ( ∼ 2×10−5 Torr) is studied by high-resolution x-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy. The significant difference of the IL growth observed between high vacuum and relatively oxygen-rich N2 annealing (both at 1000 °C) is shown to be caused by the oxygen species from the annealing ambient. Our results also show that Hf aluminates exhibit much stronger resistance to oxygen diffusion than pure HfO2 during RTA in N2 ambient, and the resistance becomes stronger with more Al incorporated into HfO2. This observation is explained by the combined effects of (i) smaller oxygen diffusion coefficient of Al2O3 than HfO2, and (ii) higher crystallization temperature of the Hf aluminates. © 2002 American Institute of Physics.
    Applied Physics Letters 11/2002; 81(19):3618-3620. DOI:10.1063/1.1519733 · 3.52 Impact Factor
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    J Huang, T.P Chen, M.S Tse, C.H Ang
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    ABSTRACT: The gate-controlled-diode (GCD) characteristic of a deep submicron MOSFET is changed dramatically following a Fowler–Nordheim (FN) injection. The changes can be explained by the trap generation on the Si surface close to the channel/drain edge and the interface trap generation in the channel region. By examining the change in the reverse drain current under accumulation and inversion in the GCD measurements, the information of trap generation in the surface region close to the channel/drain edge is obtained (note that the trap generation in this region could be different from that in other interface regions); and by measuring the reverse drain current under depletion, the interface trap generation in the channel region is obtained.
    Microelectronics Journal 08/2002; DOI:10.1016/S0026-2692(02)00034-4 · 0.92 Impact Factor
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    ABSTRACT: High-resolution x-ray photoelectron spectroscopy (XPS) was applied to characterize the electronic structures for a series of high-k materials ( HfO <sub>2</sub>)<sub>x</sub>( Al <sub>2</sub> O <sub>3</sub>)<sub>1-x</sub> grown on (100) Si substrate with different HfO <sub>2</sub> mole fraction x. Al 2p, Hf 4f, O 1s core levels spectra, valence band spectra, and O 1s energy loss all show continuous changes with x in ( HfO <sub>2</sub>)<sub>x</sub>( Al <sub>2</sub> O <sub>3</sub>)<sub>1-x</sub>. These data are used to estimate the energy gap (E<sub>g</sub>) for ( HfO <sub>2</sub>)<sub>x</sub>( Al <sub>2</sub> O <sub>3</sub>)<sub>1-x</sub>, the valence band offset (ΔE<sub>ν</sub>) and the conduction band offset (ΔE<sub>c</sub>) between ( HfO <sub>2</sub>)<sub>x</sub>( Al <sub>2</sub> O <sub>3</sub>)<sub>1-x</sub> and the (100) Si substrate. Our XPS results demonstrate that the values of E<sub>g</sub>, ΔE<sub>ν</sub>, and ΔE<sub>c</sub> for ( HfO <sub>2</sub>)<sub>x</sub>( Al <sub>2</sub> O <sub>3</sub>)<sub>1-x</sub> change linearly with x. © 2002 American Institute of Physics.
    Applied Physics Letters 08/2002; 81(2-81):376 - 378. DOI:10.1063/1.1492024 · 3.52 Impact Factor
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    ABSTRACT: The effect of high nitrogen concentration incorporation using decoupled plasma nitridation (DPN) of ultra-thin gate oxide (≈15–17 Å) on p-channel MOSFET performance has been investigated and compared with the conventional thermal nitridation process. Boron penetration is successfully suppressed in the ultra-thin gate dielectric prepared by the DPN process. This is confirmed by the measurements of gate leakage current, flat-band voltage shift and interface trap densities. The success in blocking boron penetration by DPN is attributed to its capability in incorporating a high level of nitrogen to near the top interface of the gate oxide. However, as a result of high level nitridation by DPN, a degradation in transconductance (Gm) is observed and interface trap density is also increased, compared to the conventional thermal nitridation process.
    Semiconductor Science and Technology 05/2002; 17(6):L25. DOI:10.1088/0268-1242/17/6/101 · 2.21 Impact Factor
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    ABSTRACT: The degradation of 0.13μm NMOS and PMOS transistors caused by microtrenching (μT) under hot-carrier and edge FN stress is studied. DAHC stress was found to be a sensitive technique for characterizing the NMOS transistors while edge FN stress was more suitable for the PMOS transistors. Interface state generation was also identified as the dominant degradation mechanism.
    Plasma- and Process-Induced Damage, 2002 7th International Symposium on; 02/2002
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    ABSTRACT: The impact of nitrogen plasma nitridation on the interfacial quality of ultrathin oxide (1.8 nm and 2.6 nm) and negative bias temperature instability (NBTI) have been investigated. It is found that the plasma-nitridation can more effectively suppress nitrogen-induced and boron-induced hole mobility degradation than that of thermal nitridation. Therefore, a higher amount of nitrogen can be incorporated into the plasma-nitrided oxide to suppress boron penetration without compromising the oxide interfacial quality. Furthermore, plasma-nitrided oxides have higher resistance to NBTI and longer NBTI-lifetime than that of thermal-nitrided oxides.
    Physical and Failure Analysis of Integrated Circuits, 2002. IPFA 2002. Proceedings of the 9th International Symposium on the; 02/2002
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    ABSTRACT: The effects of postdeposition anneal of chemical vapor deposited silicon nitride are studied. The Si/sub 3/N/sub 4/ films were in situ annealed in either H/sub 2/(2%)/O/sub 2/ at 950/spl deg/C or N/sub 2/O at 950/spl deg/C in a rapid thermal oxidation system. It is found that an interfacial oxide was grown at the Si/sub 3/N/sub 4//Si interface by both postdeposition anneal conditions. This was confirmed by thickness measurement and X-ray photoelectronic spectroscopy (XPS) analysis. The devices with H/sub 2/(2%)/O/sub 2/ anneal exhibit a lower gate leakage current and improved reliability compared to that of N/sub 2/O anneal. This improvement is attributed to a greater efficiency of generating atomic oxygen in the presence of a small amount of hydrogen, leading to the elimination of structural defects in the as-deposited Si/sub 3/N/sub 4/ film by the atomic oxygen. Good drivability is also demonstrated on a 0.12 /spl mu/m n-MOSFET device.
    IEEE Electron Device Letters 01/2002; 23:124-126. DOI:10.1109/55.988812 · 3.02 Impact Factor
  • Electrochemical and Solid-State Letters 01/2002; 5(4). DOI:10.1149/1.1455824 · 2.15 Impact Factor
  • Electrochemical and Solid-State Letters 01/2002; 5(4). DOI:10.1149/1.1459682 · 2.15 Impact Factor
  • Japanese Journal of Applied Physics 01/2002; 41. DOI:10.1143/JJAP.41.L1031 · 1.06 Impact Factor
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    ABSTRACT: The effect of X-ray lithography (XRL) process on the reliability of thin gate oxide has been investigated. A large increase in the low-field excess leakage current was observed on irradiated oxides, which was very similar to the electrical stress-induced leakage currents. However, it has been found that the long-term reliability of ultra-thin gate oxide is not affected by XRL process. The excess leakage current could be eliminated by thermal annealing at 400°C and above and no residual damages in the oxide were observed after the annealing.
    Japanese Journal of Applied Physics 04/2001; 40. DOI:10.1143/JJAP.40.2819 · 1.06 Impact Factor
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    ABSTRACT: The mechanism and characteristics of bias annealing of Fowler-Nordheim stress-induced leakage currents [SILC) in thin silicon dioxide films (4.5 nm) at room temperature have been investigated. It is shown that the degree of SILC reduction increases with the anneal gate bias, irrespective of the polarity of the anneal bias. Furthermore, the bias annealing of SILC is found to be greatly enhanced in a hydrogen ambient, thus providing a strong physical evidence that trapped holes are contributing significantly to SILC. The result also suggests that the mechanism uf bias annealing is: like ly related to the annealing of trapped holes. In addition, unbiased thermal annealing of SILC has been studied and compared to the bias annealing. A portion of the SILC apparently annealed out by bias annealing can be reactivated, while thermal annealing causes a permanent annihilation of SILC.
    Journal of The Electrochemical Society 12/2000; 147(12). DOI:10.1149/1.1394122 · 2.86 Impact Factor
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    ABSTRACT: Low-field leakage currents in thin gate oxides can be induced by 10 keV x-ray irradiation and electrical stress. The characteristics of radiation-induced leakage current (RILC) and stress-induced leakage current (SILC) in thin oxides have been studied and compared. The characteristics of RILC are found to be very similar to SILC, indicating that both RILC and SILC have essentially the same conduction mechanism, and are contributed by common defects generated in the gate oxides during irradiation or electrical stress. In particular, it has been demonstrated that oxide-trapped holes contribute significantly to both RILC and SILC.
    Semiconductor Science and Technology 09/2000; 15(10):961. DOI:10.1088/0268-1242/15/10/305 · 2.21 Impact Factor

Publication Stats

791 Citations
81.61 Total Impact Points

Institutions

  • 2005
    • National University of Singapore
      • Department of Chemistry
      Tumasik, Singapore
  • 2002–2004
    • Nanyang Technological University
      • School of Electrical and Electronic Engineering
      Singapore, Singapore
    • Nanyang Normal University
      Nan-yang-shih, Henan Sheng, China