C. H. Ang

Nanyang Technological University, Singapore, Singapore

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Publications (40)68.55 Total impact

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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; · 2.79 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. · 3.79 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; · 3.79 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. · 1.92 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. · 2.79 Impact Factor
  • Electrochemical and Solid State Letters - ELECTROCHEM SOLID STATE LETT. 01/2002; 5(4).
  • Japanese Journal of Applied Physics 01/2002; 41. · 1.07 Impact Factor
  • Source
    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 01/2002; · 0.91 Impact Factor
  • Electrochemical and Solid State Letters - ELECTROCHEM SOLID STATE LETT. 01/2002; 5(4).
  • Shyue Seng Tan, Tu Pei Chen, Chew Hoe Ang
    Japanese Journal of Applied Physics 01/2002; 41. · 1.07 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 01/2001; 40. · 1.07 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. · 1.92 Impact Factor
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    ABSTRACT: We have observed that stress-induced leakage currents (SILC) in thin gate oxides (4.5 nm) could be reduced by applying a low gate bias to the oxides after stress, regardless of the polarity of the applied gate bias. The reduction of SILC increased with the applied gate bias and began to saturate after 105 s. In addition, the reduction of SILC was significantly enhanced in a hydrogen ambient, suggesting a strong link between the reduction of SILC and trapped-hole annealing. © 2000 American Institute of Physics.
    Journal of Applied Physics 08/2000; 88(5):3087-3089. · 2.21 Impact Factor
  • C.H. Ling, C.H. Ang, D.S. Ang
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    ABSTRACT: Two components of the low-field current have been identified in thin oxides, following 10 KeV X-ray irradiation. The first component, observed in the direct tunneling region, can be removed by a 100°C anneal, and is also greatly suppressed if the irradiation is done in vacuum or in a nitrogen ambient, or if the oxide is preannealed before irradiation. The origin of this current is speculated to be related to adsorbed water molecules on the gate surface. The second component is observed to begin in the pre-Fowler-Nordheim tunneling (FNT) region and extends into the FNT region, only in oxides less than ~8 nm thick, and persists even after several days of anneal at 300°C. This current exhibits a power law dependence on radiation dose. The origin of this second component is believed to be due to the trap-assisted tunneling via neutral electron traps, similar to the leakage current observed in the oxide after high-voltage stress
    IEEE Transactions on Electron Devices 04/2000; · 2.06 Impact Factor
  • Journal of The Electrochemical Society - J ELECTROCHEM SOC. 01/2000; 147(12).
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    ABSTRACT: This paper presents the results of investigation on integrity of X-ray/E-beam irradiated thin gate oxides. A large increase of gate oxide leakage current is observed after irradiation on thin gate oxide under X-ray/E-beam lithography conditions. This radiation-induced leakage current (RILL) can be removed by a thermal annealing at 400°C and above, without adverse effect to the oxide integrity. In addition, it is found that ionizing exposures do not significantly affect the breakdown and quasi-breakdown characteristics in ultra-thin oxide.
    Microelectronics Reliability 01/2000; 40(8):1609-1613. · 1.14 Impact Factor
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    ABSTRACT: The carrier-separation characteristics of a p-channel metal-oxide-semiconductor field-effect transistor with 29 Å gate oxide has been measured at various temperatures from 90 to 375 K. It is found that the gate and source/drain currents at low gate voltage regime (below 0.5 V) were correlated and strongly dependent on temperature above 250 K. The earlier observation has been attributed to the existence of a temperature-sensitive hole direct-tunneling current due to the strong temperature sensitivity of surface hole's concentration at low voltage regime.
    Journal of Applied Physics 01/2000; 88:2872-2876. · 2.21 Impact Factor

Publication Stats

535 Citations
68.55 Total Impact Points

Institutions

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