High-performance RSD poly-Si TFTs with a new ONO gate dielectric

This paper developed a novel polycrystalline silicon (poly-Si) thin-film transistor (TFT) structure with the following special features: 1) a new oxide-nitride-oxynitride (ONO) multilayer gate dielectric to reduce leakage current, improved breakdown characteristics, and enhanced reliability; and 2) raised source/drain (RSD) structure to reduce series resistance. These features were used to fabricate high-performance RSD-TFTs with ONO gate dielectric. The ONO gate dielectric on poly-Si films shows a very high breakdown field of 9.4 MV/cm, a longer time dependent dielectric breakdown, larger Q/sub BD/, and a lower charge-trapping rate than single-layer plasma-enhanced chemical vapor deposition tetraethooxysilane oxide or nitride. The fabricated RSD-TFTs with ONO gate dielectric exhibited excellent transfer characteristics, high field-effect mobility of 320 cm/sup 2//V/spl middot/s, and an on/off current ratio exceeding 10/sup 8/.     

3.4nm超薄SiO2栅介质的特性

用LOCOS工艺制备出栅介质厚度为3.4nm的MOS电容样品,通过对样品进行I-V特性和恒流应力下V-t特性的测试,分析用氮气稀释氧化法制备的栅介质的性能,同时考察了硼扩散对栅介质性能的影响.实验结果表明,制备出的3.4nm SiO₂栅介质的平均击穿场强为16.7MV/cm,在恒流应力下发生软击穿,平均击穿电荷为2.7C/cm².栅介质厚度相同的情况下,P⁺栅样品的击穿场强和软击穿电荷都低于N⁺栅样品.     

Electrical conduction and dielectric breakdown in aluminum oxideinsulators on silicon

Leakage currents and dielectric breakdown were studied in MIS capacitors of metal-aluminum oxide-silicon. The aluminum oxide was produced by thermally oxidizing AlN at 800-1160°C under dry O₂ conditions. The AlN films were deposited by RF magnetron sputtering on p-type Si (100) substrates. Thermal oxidation produced Al ₂O₃ with a thickness and structure that depended on the process time and temperature. The MIS capacitors exhibited the charge regimes of accumulation, depletion, and inversion on the Si semiconductor surface. The best electrical properties were obtained when all of the AlN was fully oxidized to Al₂O₃ with no residual AlN. The MIS flatband voltage was near 0 V, the net oxide trapped charge density, Q_0x, was less than 10¹¹ cm ^-2, and the interface trap density, D_it, was less than 10¹¹ cm^-2 eV^-1, At an oxide electric field of 0.3 MV/cm, the leakage current density was less than 10^-7 A cm^-2, with a resistivity greater than 10 ¹² Ω-cm. The critical field for dielectric breakdown ranged from 4 to 5 MV/cm. The temperature dependence of the current versus electric field indicated that the conduction mechanism was Frenkel-Poole emission, which has the property that higher temperatures reduce the current. This may be important for the reliability of circuits operating under extreme conditions. The dielectric constant ranged from 3 to 9. The excellent electronic quality of aluminum oxide may be attractive for field effect transistor applications     

Time dependent breakdown of ultrathin gate oxide

Time dependent dielectric breakdown (TDDB) of ultrathin gate oxide (<40 Å) was measured for a wide range of oxide fields (3.4<|E_ox|<10.3 MV/cm) at various temperatures (100⩽T⩽342°C). It was found that TDDB of ultrathin oxide follows the E model. It was also found that TDDB t₅₀ starts deviating from the 1/E model for fields below 7.2 MV/cm. Below 4.8 MV/cm, TDDB t₅₀ of intrinsic oxide increased above the value predicted by the E model obtained for fields >4.8 MV/cm. The TDDB activation energy for this type of gate oxide was found to have linear dependence on oxide field. In addition, we found that γ (the field acceleration parameter) decreases with increasing temperature. Furthermore, it was found that testing at high temperatures (up to 342°C) and low electric field values did not introduce new gate oxide failure mechanism. It is also shown that TDDB data obtained at very high temperature (342°C) and low fields can be used to generate TDDB model at lower temperatures and low fields. Our results (an enthalpy of activation of 1.98 eV and dipole moment of 12.3 eÅ) are in complete agreement with previous results by McPherson and Mogul. Additionally, it was found that TDDB is exponentially dependent on the gate voltage     

Low electric field breakdown of thin SiO2 films understatic and dynamic stress

A comprehensive study of Time-Dependent Dielectric Breakdown (TDDB) of 6.5-, 9-, 15-, and 22-nm SiO₂ films under dc and pulsed bias has been conducted over a wide range of electric fields and temperatures. Very high temperatures were used at the wafer level to accelerate breakdown so tests could be conducted at electric fields as low as 4.5 MV/cm. New observations are reported for TDDB that suggest a consistent electric field and temperature dependence for intrinsic breakdown and a changing breakdown mechanism as a function of electric field. The results show that the logarithm of the median-test-time-to failure, log (t₅₀), is described by a linear electric field dependence with a field acceleration parameter that is not dependent on temperature. It has a value of approximately 1 decade/MV/cm for the range of oxide thicknesses studied and shows a slight decreasing trend with decreasing oxide thickness. The thermal activation E_a ranged between 0.7 and 0.95 eV for electric fields below 9.0 MV/cm for all oxide thicknesses. TDDB tests conducted under pulsed bias indicate that increased dielectric lifetime is observed under unipolar and bipolar pulsed stress conditions, but diminishes as the stress electric field and oxide thickness are reduced. This observation provides new evidence that low electric field aging and breakdown is not dominated by charge generation and trapping     

Gate-oxide breakdown accelerated by large drain current inn-channel MOSFET's

A study of the time-dependent dielectric breakdown (TDDB) of thin gate oxides in small n-channel MOSFETs operated beyond punchthrough is discussed. Catastrophic gate-oxide breakdown is accelerated when holes generated by the large drain current are injected into the gate oxide. More specifically, the gate-oxide breakdown in a MOSFET (gate length=1.0 μm, gate width-15 μm) occurs in ~100 s at an applied gate oxide field of ~5.2 MV/cm during the high drain current stress, while it occurs in ~100 s at an applied gate oxide field of ~10.7 MV/cm during a conventional time-dependent dielectric breakdown (TDDB) test. The results indicate that the gate oxide lifetime is much shorter in MOSFETs when there is hot-hole injection than that expected using the conventional TDDB method     

Low-temperature fabrication of amorphous BaTiO3thin-film bypass capacitors

Amorphous BaTiO₃ thin-film capacitors suitable for integration into a multichip module packaging process were fabricated. The multilayer capacitor structure consisted of an adhesion layer (TiO _xN_y or Ti), a bottom electrode (Cu), a dielectric (amorphous BaTiO₃), and a top electrode (Cu). A 3000-Å amorphous BaTiO₃ film was deposited onto the electrode by the reactive partially ionized beam (RPIB) technique at near room temperature. After a 300°C postdeposition anneal, the capacitors had the following properties: ε_r=17-18 and tanδ<0.01 up to 600 MHz, J_leak=0.06-0.5 μA/cm² at 0.5 MV/cm, and breakdown field E_max=3.3 MV/cm     

Evaluation of thin oxides grown by the atomic oxygen afterglow method

This paper discusses the basic electrical properties of thin, less than 200 Å, films of silicon dioxide grown on silicon by a microwave plasma atomic oxygen afterglow method. This method of remote plasma oxidation of silicon allows gate oxides to be grown at temperatures as low as 400° C, and hence, is possibly attractive in VLSI/ULSI applications. Electrical properties of studied oxides depend strongly upon the composition of the discharge gas. The use of nitrogen as an oxygen diluent has an adverse impact on the fixed oxide charge density and dielectric strength. Superior oxide characteristics were obtained by adding hydrogen to the discharge gas particularly in the area of oxide breakdown statistics. Values of the intrinsic breakdown field in the range from 8 MV/ cm to 14 MV/cm were recorded in this case.     

Evaluation of the dielectric breakdown of reoxidized nitrided oxide (ONO) in flash memory devices using constant current-stressing technique

The dielectric breakdown time of reoxidized nitrided oxide (ONO) in flash memory devices has been evaluated using the constant current-stressing technique. The dielectric performance of ONO was severely impaired by the stressing effects of a current. A positive constant current of 5 μA stressing on a 280 Åthick ONO layer (via two polysilicon electrodes), covering an area of 50,000 μm² took only a mere 20 s to breakdown. The situation worsened when a negative current of 5 μA was stressed on it—the ONO layer almost instantaneously broke down. The electrical tolerance of the ONO interpoly dielectric is still mediocre upon stressing with a smaller current. With a 1 μA positive constant current-stressing test, the average breakdown time of the dielectric layer was about 50 s, but it broke down instantaneously again upon a 1 μA negative constant current-stressing test. The probable causes for the rapid degradation of ONO dielectric properties are the rough surface of bottom polysilicon layer, the trapped fluoride ions in the device, and the changes in the occupancy of the interfacial states. There can be the occurrence of current surging through the devices during their fabrication e.g. stack-etching. Hence, with the future scaling of memory devices, situations of higher current density surging through the devices will be realized. It will be beneficial to investigate how the ONO layer conducts upon current-stressing. The constant current-stressing technique is a simple and most straightforward method to address and simulate the current-stressing conditions.     

Characteristics of Al/sub 2/O/sub 3//TiO/sub 2/ nanolaminates and AlTiO thin films on Si

This letter reports a metal-insulator-semiconductor structure based on Al/sub 2/O/sub 3//TiO/sub 2/ nanolaminates and AlTiO films evaporated on an unheated p-Si substrate. The structure exhibits a low hysteresis in the capacitance-voltage characteristics, a larger dielectric constant leading to a quantum mechanically corrected effective oxide thickness of 1.35-2.1 nm, good stability of the electrical characteristics to thermal processes, a large breakdown electric field of 7.5 MV/cm, and a leakage current density below 5/spl times/10/sup -7/ A/cm/sup 2/ at an electric field of 2 MV/cm.     

Kinetics of copper drift in PECVD dielectrics

We quantified the drift of Cu ions into various PECVD dielectrics by measuring shifts in capacitance-voltage behavior after subjecting Cu-gate MOS capacitors to bias-temperature stress. At a field of 1.0 MV/cm and temperature of 100°C, Cu ions drift readily into PECVD oxide with a projected accumulation of 2.7×10¹³ ions/cm ² after 10 years. However, in PECVD oxynitride, the projected accumulation under the same conditions is only 2.3×10¹⁰ ions/cm². These findings demonstrate the necessity of integrating drift barriers, such as PECVD oxynitride layers, in Cu interconnection systems to ensure threshold stability of parasitic field n-MOS devices     

Transients during pre-breakdown and hard breakdown of thin gate oxides in metal–SiO2–Si capacitors

Time–resolved electrical measurements show transient phenomena occurring during degradation and intrinsic dielectric breakdown of gate oxide layers under constant voltage Fowler–Nordheim stress. We have studied such transients in metal/oxide/semiconductor (MOS) capacitors with an n⁺ poly-crystalline Si/SiO₂/n-type Si stack and with oxide thickness between 35 and 5.6 nm. The data adds new information concerning the intrinsic breakdown mechanism and these are shown and discussed together with the adopted measurement techniques.     

Electrical characteristics of highly reliable ultrathin hafniumoxide gate dielectric

Electrical and reliability properties of ultrathin HfO₂ have been investigated. Pt electroded MOS capacitors with HfO₂ gate dielectric (physical thickness ~45-135 Å and equivalent oxide thickness ~13.5-25 Å) were fabricated. HfO₂ was deposited using reactive sputtering of a Hf target with O₂ modulation technique. The leakage current of the 45 Å HfO₂ sample was about 1×10^-4 A/cm ² at +1.0 V with a breakdown field ~8.5 MV/cm. Hysteresis was <100 mV after 500°C annealing in N₂ ambient and there was no significant frequency dispersion of capacitance (<1%/dec.). It was also found that HfO₂ exhibits negligible charge trapping and excellent TDDB characteristics with more than ten years lifetime even at V_DD=2.0 V     

The effect of 1300-1380°C anneal temperatures and materialcontamination on the characteristics of CMOS/SIMOX devices

The characteristics of CMOS transistors fabrication on silicon implanted with oxygen (SIMOX) materials were measured as a function of the silicon superficial layer contamination levels. In addition, postimplant anneal temperatures of 1300°C, 1350°C, and 1380°C were examined. It is found that the transistor leakage currents as well as the integrity of the gate oxide and implanted SIMOX oxide are functions of the carbon content in the starting material. Leakage currents below 1.0×10^-12 A/μm of channel width have been measured when the carbon concentration is reduced to 2×10¹⁸/cm². In addition, the integrity of the transistor gate dielectric, SIMOX implanted oxide, and oxygen precipitate density are seen to be a function of the postimplant anneal temperature. A gate dielectric breakdown field of 10 MV/cm has been achieved when the postimplant temperature is increased to 1380°C     

Effect of the nitrous oxide plasma treatment on the MIM capacitor

We report the demonstration of near zero voltage coefficient of capacitance (VCC) by exposing the silicon nitride dielectric of the metal-insulator-metal capacitor (MIM) to nitrous oxide (N₂O) plasma. Oxidization in the N₂O plasma enhanced the hard breakdown field, whereby an excess of 9 MV/cm was achieved. In addition, low-temperature coefficient of capacitance (TCC) of < 20 ppm/K and high dielectric constant ⩾ 6.5 were preserved     

Field and temperature dependence of TDDB of ultrathin gate oxide

The results of an investigation of time-dependent breakdown (TDDB) of intrinsic ultrathin gate oxide are presented for a wide range of oxide fields 4.6ox<10.4 MV/cm at elevated temperatures. It was found that TDDB of ultrathin oxide follows the E model down to 4.6 MV/cm. The data show that TDDB t₅₀ starts deviating from the 1/E model for fields below 7.2 MV/cm. The data also show that the TDDB activation energy for this type of gate oxide is linearly dependent on oxide field. In addition, we show that the field acceleration parameter γ decreases as temperature increases     

薄栅介质层可靠性与陷阱统计分析

本文以高电场(＞11.8MV/cm)恒电流TDDB为手段研究了厚度为7.6、10.3、12.5、14.5nm薄氧化层的击穿统计特性.实验分析表明在加速失效实验中测量击穿电量Q_bd的同时,还可以测量击穿时的栅电压增量ΔV_bd.因为ΔV_bd的统计分布反映了栅介质层中带电陷阱的数量及其位置分布,可以表征栅介质层的质量和均匀性.此外由Q_bd和ΔV_bd能够较合理地计算临界陷阱密度N_bd.实验结果表明本征击穿时N_bd与测试条件无关而随工艺和介质层厚度变化.同样厚度时N_bd反映不同工艺生成的介质质量.陷阱生成的随机性使N_bd随栅介质厚度减小而下降.氧化层厚度约10nm时N_bd达到氧化层分子密度的1%发生击穿(10²⁰cm^-3).N_bd的物理意义清楚,不象Q_bd随测试应力条件变化,是薄栅介质层可靠性的较好的定量指标.     

Entirely gate-surrounded MOS capacitor to study the intrinsic oxidequality

The intrinsic dielectric strength of gate oxides is investigated by MOS capacitors which are designed so that the gate poly does not cross the field oxide edge. Using the charge to breakdown in the high-injection regime as a sensitive indicator, it is shown that poly-surrounded capacitors are required to measure the intrinsic oxide quality, whereas conventional devices may be sensitive to process variations in the MOS isolation sequence and oxide thinning at the field oxide edge     

Study of MOS gate dielectric breakdown due to drain avalanche breakdown

This work reports the effects of drain impact ionization injection on the gate dielectric breakdown. Results show that due to the high energy hot carrier injection, the gate oxide can break down twice at a low oxide electric field (<1.2 MV/cm). The first breakdown occurs simultaneously with the drain avalanche breakdown whereas the second breakdown occurs beyond the drain breakdown. It is further identified that the first gate oxide breakdown is governed by the thermionic emission of hot electrons at low oxide fields (<1.0 MV/cm) and by the scattering processes at higher oxide fields. The second breakdown is attributed to the Fowler–Nordheim (F–N) tunneling.     

Time-Dependent Dielectric Breakdown of 4H-SiC MOS Capacitors and DMOSFETs

Time-dependent dielectric breakdown measurements were performed at 200 $^{ circ}hbox{C}$ on 4H-SiC MOS capacitors and vertical DMOSFETs with 50-nm-thick nitrided oxides in order to better understand the physical mechanisms of failure and to predict the component reliability. Oxide breakdown locations are shown to have no correlation to defects in the SiC epitaxial layer. Characterization of the electric-field acceleration of failures indicates that failure modes differ at low and high electric fields. Specifically, extrapolations from measurements at electric fields greater than 8.5 MV/cm predict anomalously high reliability at normal operating fields. Thus, we have shown that SiC MOS reliability characterization must ensure that electric field stresses be performed at low electric fields in order to accurately predict failure times.