Deposition of uniform Zr-Sn-Ti-O films by on-axis reactivesputtering

We describe the deposition of amorphous Zr-Sn-Ti-O (aZTT) dielectric thin films using conventional on-axis reactive sputtering. Thin films of composition Zr_0.2Sn_0.2Ti_0.6 O₂ have excellent dielectric properties: 40-50-nm thick films with a dielectric constant of 50-70 were obtained, depending on the processing conditions, yielding a specific capacitance of 9-17 fF/μm². Breakdown fields were measured to be 3-5 MV/cm, yielding a figure of merit εε₀E_br=15-30 μC/cm², up to eightfold higher than conventional deposited SiO₂. Leakage currents, measured at 1.0 MV/cm, were in the range 10^-9-10^-7 A/cm². This material appears well-suited for use in Si-IC device technology, for example as storage capacitors in DRAM     

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     

Laser Micromachining of Barium Titanate $({hbox {BaTiO}}_{3})$-Epoxy Nanocomposite-Based Flexible/Rollable Capacitors: New Approach for Making Library of Capacitors

This paper discusses laser micromachining of barium titanate (BaTiO₃)-polymer nanocomposite thin films. In particular, recent developments on high-capacitance, large-area, thin, flexible, embedded capacitors are highlighted. A variety of barium titanate (BaTiO₃)-epoxy polymer nanocomposite-based flexible/rollable thin films ranging from 2 to 25 mum thick were processed on large-area substrates (330 mm times 470 mm, or 495 mm times 607 mm) by liquid coating processes. The electrical performance of composites was characterized by dielectric constant (Dk), capacitance, and dissipation factor (loss) measurements. Nanocomposites provided high capacitance density (10-100 nF/in²) and low loss (0.02-0.04) at 1 MHz. Scanning electron microscopy (SEM) micrographs showed uniform particle distribution in the coatings. Uniform mixing of nanoparticles in the epoxy matrix results in high dielectric (> 3 times 10⁷ V/m) and mechanical strengths (> 3700 PSI). Reliability of the capacitor was ascertained by thermal cycling. Capacitance change was less than 5% after baking at 140degC for 4 h, and 1100 cycles from -55degC to 125degC (deep thermal cycle). A frequency-tripled Nd:YAG laser operating at a wavelength of 355 nm was used for the micromachining study. The micromachining was used to generate arrays of variable-thickness capacitors from the nanocomposites. The resultant thickness of the capacitors depends on the number of laser pulses applied.     

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     

Room-Temperature Deposited Titanium Silicate Thin Films for MIM Capacitor Applications

High-k titanium silicate (i.e., TiSiO₄) thin films of various thicknesses (in the 4.5- to 160-nm range) were successfully deposited by means of a sputter deposition process at room-temperature and integrated into metal-insulator-metal (MIM) capacitors. It is shown that the TiSiO₄-based capacitors can exhibit a capacitance density as high as 30 fF/mum² while maintaining low dielectric dispersion and losses. An excellent voltage linearity was also obtained ( alpha~600 ppm/V² at 8.2 fF/mum²) together with a high dielectric constant of 16.5 and low leakage current of about 10 nA/cm² at 1 MV/cm. Our results thus show that TiSiO₄ films constitute a very promising approach for the achievement of high performance MIM capacitors     

Effects of Al2O3 Dielectric Cap and Nitridation on Device Performance, Scalability, and Reliability for Advanced High- κ/Metal Gate pMOSFET Applications

A pFET threshold-voltage (Vt) reduction of about 200 mV is demonstrated by inserting a thin Al₂O₃ layer between the high-k dielectric and the TiN gate without noticeable degradation of other electrical properties. HfSiO_propcapped with 9 Aring of thin Al₂O₃obtains a low long-channel Vt of -0.37 V (the lowest among those with TiN gate), a high mobility of 59 cm² /V ldr s at 0.8 MV/cm (92% of universal value), a negligible equivalent- oxide-thickness (EOT) increase of 0.1 Aring (compared to the uncapped reference), and a low Vt instability of 4.8 mV at 7 MV/cm. It also passes the ten-year negative-bias-temperature-instability (NBTI) lifetime specification with a gate overdrive of -0.7 V. This indicates that thin Al₂O₃obtains caps are beneficial to the pFET applications. In contrast, nitrogen incorporation in the Al₂O₃-capped HfSiO_prop is not favorable because it increases the Vt by 50-140 mV, degrades the mobility by 10%-22%, increases the EOT by 0.5-0.8 Aring and the Vt instability by 5-13 mV, and reduces the NBTI lifetime by four to five orders of magnitude. Compared to postcap nitridation, high-k nitridation results in more severe degradation of these properties by incorporating nitrogen closer to the Si/SiO₂ interface.     

Investigation of inductively coupled plasma gate oxide on lowtemperature polycrystalline-silicon TFTs

By optimizing the inductively coupled plasma (ICP) oxidation condition, a thin oxide of 10 nm has been grown at 350°C to achieve excellent gate oxide integrity of low leakage current<5×10^-8 A/cm² (at 8 MV/cm), high breakdown field of 9.3 MV/cm and low interface trap density of 1.5×10¹¹ /eV cm². The superior performance poly-Si TFTs using such a thin ICP oxide were attained to achieve a high ON current of 110 μA/μm at V_D=1 V and V_G=5 V and the high electron field effect mobility of 231 cm²/V·S     

Studies of yttrium oxide films prepared by RF magnetron sputtering

Films of yttrium oxide (Y₂O₃) were deposited on Si substrates from a Y₂O₃ target by RF magnetron sputtering. MIS capacitors in the form of Al and Y₂O₃ (400 Å)-Si were then fabricated. The leakage current density was about 10^-6 A/cm² at 1.3×10⁶ V/cm, and the breakdown field of the films was about 2.75×10⁶ V/cm. The dielectric constant of the sputtered Y₂O₃ was found to be about 12-12.7     

Understanding the effects of wave function penetration on theinversion layer capacitance of NMOSFETs

A comprehensive analysis of the effects of wave function penetration on the capacitance of NMOS capacitors has been performed for the first time, using a self-consistent Schrodinger-Poisson solver. The study reveals that accounting for wave function penetration into the gate dielectric causes carrier profile to be shifted closer to the gate dielectric reducing the electrical oxide thickness. This shift increases with increasing gate voltage. For example, in one simulation, the peak is shifted by about 0.2 nm at a surface field of 1.96 MV/cm and 0.33 nm at a surface field of 3.7 MV/cm. This shifting results in all increased capacitance. The increase in capacitance observed in the inversion region is relatively insignificant when a poly gate electrode with a doping of less than 1×10²⁰ cm^-3 is used due to the poly-depletion effect. A physical picture of the effect of physical thickness on the tunneling current is also presented     

Voltage tunable capacitors using high temperature superconductorsand ferroelectrics

In this paper we report the construction of both slot capacitors on bulk substrate and thin film interdigital capacitors using YBa₂ Cu₃O_7-δ (YBCO) and Ba_xSr _1-xTiO₃. Slot capacitors made on bulk Ba_x Sr_1-xTiO₃ (BST) yielded variations in capacitance of more than 6 to 1 at 86 K with a peak electric field strength of 25 kV/cm. With a metal organic deposition (MOD) grown Ba_xSr_1-xTiO₃ 300-nm overcoat on a YBCO thin film, an interdigital capacitor on LaAlO₃ substrate yielded an approximate tuning range of 10% for peak field of 66 kV/cm over temperatures ranging from 50 K to 120 K     

低漏电、高击穿电容的HDPCVD工艺研究

介绍了一种低漏电、高击穿电容的HDPCVD(ICPCVD)工艺,并对制备的电容进行了电性能分析和失效分析。通过优化确定了工艺的最佳反应条件,研制出的电容其击穿场强达到8.7MV/cm,在电压加到200V时其电容漏电小于0.5μA。通过与传统的PECVD工艺进行对比,充分体现了HDPCVD(ICPCVD)工艺生长介质的低温生长、低漏电、较高击穿场强、无H工艺等优点。随后的失效分析表明,电容上下电极金属对电容成品率有着很大影响。     

Conduction mechanisms in barium tantalates films and modificationof interfacial barrier height

The leakage current-voltage characteristics of rf-magnetron sputtered BaTa₂O₆ film in a capacitor with the top aluminum and the bottom indium-tin-oxide electrodes have been investigated as a function of applied field and temperature. In order to study the effect of the surface treatment on the electrical characteristics of as-deposited film we performed an oxygen plasma treatment on BaTa₂O₆ surface. The dc current-voltage, bipolar pulse charge-voltage, dc current-time, and small ac signal capacitance-frequency characteristics were measured to study the electrical and the dielectric properties of BaTa₂O ₆ thin film. All of the BaTa₂O₆ films in this study exhibited a low leakage current, a high breakdown field strength (3-4.5 MV/cm), and a high dielectric constant (20-30). From the temperature dependence of the leakage current, we could conclude that the dominant conduction mechanism under high electrical fields (>1 MV/cm) is ascribed to the Schottky emission while the ohmic conduction is dominant at low electrical fields (<1 MV/cm). Furthermore, the oxygen plasma treatment on the surface of as-deposited BaTa₂O ₆ resulted in a lowering of the interface barrier height and thus, a reduction of the leakage current at Al under a negative bias. This can be explained by the formation of Ba-rich metallic layer by surface etching effect and by filling the oxygen vacancies in the bulk     

Lifetime of thin oxide and oxide-nitride-oxide dielectrics withintrench capacitors for DRAMs

An investigation of the field acceleration of the time-dependent dielectric breakdown behavior of a thermal oxide and an oxide-nitride-oxide (ONO) dielectric on planar- and trench-cell MIS capacitors under a constant field stress of 5-9 MV/cm at 150°C is discussed. Defect-related and intrinsic failures are distinguished by a statistical analysis of the breakdown distributions. Planar- and trench-cell capacitors with an ONO dielectric exhibit reduced early failures and a more favorable field-acceleration behavior than capacitors with a thermal-oxide layer. A method which determines the number of intrinsic failures by extrapolation of the accelerated constant field stress data to the device area and down to the operational electric field strength is proposed. The extrapolation predicts, for trench-capacitor arrays with a 5-mm² active device area and a 13.5-nm oxide dielectric operating at 3 MV/cm and 150°C, a mean intrinsic failure rate slightly below 100 Fit in the first year, whereas trench structures with an ONO-dielectric reach the same number of cumulative failures after 1 million years     

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     

The effect of electrode material on the electrical conduction of metal-Pb(Zr0.53Ti0.47)O3-metal thin film capacitors

The electrical conduction of metal–PZT–metal thin-film capacitors depends on the electrode material due to the different magnitudes of the work functions. In this work, Au/PZT/Pt and Pt/PZT/Pt capacitors were fabricated and their electrical properties compared. At the low temperature range of 300–375 K, the electrical conduction of Au/PZT/Pt capacitor is space-charge-limited current (SCLC), whereas Pt/PZT/Pt capacitor shows ohmic conduction at low field (<0.55 MV/cm) and Frenkel–Poole emission at higher fields (0.55 MV/cm). The current level of Au/PZT/Pt is much lower than that of Pt/PZT/Pt at low field (<0.4 MV/cm) due to the larger barrier height for holes of Au/PZT. At high temperatures (375–450 K), the conduction mechanism of Au/PZT/Pt capacitor changes to Schottky emission, whereas that of Pt/PZT/Pt capacitor remains the same as in low temperatures of 300–375 K. The energy band diagrams of the Au/PZT/Pt and Pt/PZT/Pt systems are constructed to explain the different current–voltage characteristics.     

High Density and Low Leakage Current in $ hbox{TiO}_{2}$ MIM Capacitors Processed at 300 $^{circ} hbox{C}$

We report Ir/TiO₂/TaN metal-insulator-metal capacitors processed at only 300degC, which show a capacitance density of 28 fF/mum² and a leakage current of 3 times 10^-8 (25degC) or 6 times 10^-7 (125degC) A/cm² at -1 V. This performance is due to the combined effects of 300degC nanocrystallized high-kappa TiO₂, a high conduction band offset, and high work-function upper electrode. These devices show potential for integration in future very-large-scale-integration technologies.     

An 1800 V triple implanted vertical 6H-SiC MOSFET

6H silicon carbide vertical power MOSFETs with a blocking voltage of 1800 V have been fabricated. Applying a novel processing scheme, n ⁺ source regions, p-base regions and p-wells have been fabricated by three different ion implantation steps. Our SiC triple ion implanted MOSFETs have a lateral channel and a planar polysilicon gate electrode. The 1800 V blocking voltage of the devices is due to the avalanche breakdown of the reverse diode. The reverse current density is well below 200 μA/cm² for drain source voltages up to 90% of the breakdown voltage. The MOSFETs are normally off showing a threshold voltage of 2.7 V. The active area of 0.48 mm² delivers a forward drain current of 0.3 A at Y_GS=10 V and V _DS=8 V. The specific on resistance was determined to 82 mΩdcm² at 50 mV drain source voltage and at V_GS =10 V which corresponds to an uppermost acceptable oxide field strength of about 2.7 MV/cm. This specific on resistance is an order of magnitude lower than silicon DMOSFET's of the same blocking capability could offer     

Electrical properties of low-temperature pyrolytic SiO2on InP

The first application of a new technique (SiH₄+O₂ at 83-330°C and 2-12 torr) for deposition of SiO₂ on InP is reported. SiO₂ deposited at 150-330°C has breakdown strength of 8-10 MV/cm, resistivity >10¹⁵ Ωcm, and refractive index of 1.45-1.46 comparable to thermal SiO ₂ grown at 1100°C. C/V measurements on Al/SiO₂/InP MIS structures suggest that very low temperature oxides (90-100°C) have the best interfacial properties     

Simulation of the variability in microelectronic capacitors havingpolycrystalline dielectrics

The scaling down of on-chip microelectronic capacitors presents a considerable challenge for future microelectronic devices. High-permittivity polycrystalline dielectrics such as Ta₂O ₅, SrTiO₃ (STO), or (Ba, Sr)TiO₃ (BSTO), have been considered as a potential replacement for conventional amorphous SiO₂ and SiN_x. The polycrystalline microstructure of these materials may lead to capacitor-to-capacitor variations in charge storage capacity and charge retention. In this letter, a Monte Carlo simulation is used to assess these variations. Results show that as the average crystalline grain size becomes greater than 1% of the capacitor size, variations of 10% in capacitance and between 3-150% in leakage should be expected     

Oxidized Ta2O5/Si3N4dielectric films on poly-crystalline Si for dRAMs

A dielectric film technology characterized by a novel multilayer structure formed by oxidation of Ta₂O₅/Si₃ N₄ films on polysilicon has been developed to realize high-density dRAMs. The dry oxidation of the Ta₂O₅/Si₃N₄ layers was performed at temperatures higher than 900°C. This film has a capacitance per unit area from 5.5 to 6.0 fF/ μm², which is equivalent to that of a 6.0- to 6.5-nm-thick SiO₂. The leakage current at an effective electric field of 5 MV/cm is less than 10^-9 A/cm². Under such an electric field, the extrapolated time to failure for 50% cumulative failure can be as high as 1000 years