Effect of bottom electrode materials on the electrical andreliability characteristics of (Ba, Sr)TiO3 capacitors

The dielectric constant and the leakage current density of (Ba, Sr)TiO₃ (BST) thin films deposited on various bottom electrode materials (Pt, Ir, IrO₂/Ir, Ru, RuO₂/Ru) before and after annealing in O₂ ambient were investigated. The improvement of crystallinity of BST films deposited on various bottom electrodes was observed after the postannealing process. The dielectric constant and leakage current of the films mere also strongly dependent on the postannealing conditions. BST thin film deposited on Ir bottom electrode at 500°C, after 700°C annealing in O₂ for 20 min, has the dielectric constant of 593, a loss tangent of 0.019 at 100 kHz, a leakage current density of 1.9×10 ^-8 A/cm² at an electric field of 200 kV/cm with a delay time of 30 s, and a charge storage density of 53 fC/μm² at an applied field of 100 kV/cm. The BST films deposited on Ir with post-annealing can obtain better dielectric properties than on other bottom electrodes in our experiments. And Ru electrode is unstable because the interdiffusion of Ru and Ti occurs at the interface between the BST and Ru after postannealing. The ten year lifetime of time-dependent dielectric breakdown (TDDB) studies indicate that BST on Pt, Ir, IrO₂/Ir, Ru, and RuO₂/Ru have long lifetimes over ten gears on operation at the voltage bias of 2 V     

Effect of bottom electrodes on resistance degradation and breakdownof (Ba,Sr)TiO3 thin films

The influence of bottom electrodes (Pt, Ir, Ru) on the degradation of (Ba,Sr)TiO₃ (BST) thin films under dc stress conditions was investigated. The current-time (I-t) and current-voltage (I-V) measurement results indicated that the BST thin films deposited on Ru have faster degradation than those deposited on Pt and Ir. The degradation was considered to be caused by the deterioration of the Schottky-barrier. Under dc stress conditions, the dielectric relaxation current in the BST dielectric films probably enhances the deterioration. The breakdown time was found to be approximated by an exponential function of an electric field [t_B=α exp(-βE)] for dc stress. The value of the exponential factor β for BST deposited on Pt and Ir was about a quarter of that for BST deposited on Ru. The different value of β observed under dc stress indicates that the degradation of BST on Ru would be more serious than on Pt and Ir. The ten years lifetime of time-dependent dielectric breakdown (TDDB) studies indicate that BST on Pt, Ir and Ru have longer lifetime over ten years for operation at the voltage bias of 1 V     

溶胶-凝胶法制备外延Ba1-xSrxTiO3薄膜及其结构与性能研究

应用溶胶-凝胶技术在Pt/MgO(100)衬底上成功地制备了Ba0.65Sr0.35TiO3外延薄膜.XRD和SEM分析结果表明该薄膜在O2气氛中650℃热处理1h后,其(001)面是沿着Pt(100)和MgO(100)面外延取向生长的;薄膜表面均匀致密,厚度为260nm,平均晶粒大小为48.5nm.当测试频率为10kHz时,BST薄膜的介电常数和损耗因子分别为480和0.02.介电常数-温度关系测试结果表明sol-gel工艺制备的Ba0.65Sr0.35TiO3薄膜其居里温度在35℃左右,且在该温度下Ba0.65Sr0.35TiO3薄膜存在扩散铁电相变特征.当外加偏置电压为3V时,BST薄膜的漏电流密度为1.5×10-7A/cm2.该薄膜可作为制备新型非制冷红外焦平面阵列和先进非制冷红外热像仪的优选材料.     

A stacked capacitor technology with ECR plasma MOCVD(Ba,Sr)TiO3 and RuO2/Ru/TiN/TiSixstorage nodes for Gb-scale DRAMs

A Gb-scale DRAM stacked capacitor technology with (Ba,Sr)TiO₃ thin films is described, The four-layer RuO₂/Ru/TiN/TiSi_x, storage node configuration allows 500°C processing and fine-patterning down to the 0.20 μm size by electron beam lithography and reactive ion etching. Good insulating (Ba_0.4Sr_0.6)TiO₃ (BST) films with an SiO₂ equivalent thickness of 0.65 nm on the electrode sidewalls and leakage current of 1×10^{-/6 A}cm² at 1 V are obtained by ECR plasma MOCVD without any post-deposition annealing, A lateral step coverage of 50% for BST is observed on the 0.2 μm size storage node pattern, and the BST thickness on the sidewalls is very uniform, thanks to the ECR downflow plasma. Using this stacked capacitor technology, a sufficient cell capacitance of 25 fF for 1 Gb DRAMs can be achieved in a capacitor area of 0.125 μm² with only the 0.3 μm high-storage electrodes     

Electrical properties of sputtered (Ba, Sr)TiO3 thin films prepared by two-step deposition method

The influence of two-step deposition on the electrical properties of sputtered (Ba,Sr)TiO₃ thin films was investigated. BST thin films with thickness 40 nm were deposited by a simple two-step radio frequency-magnetron sputtering technique, where the BST thin film consisted of a seed layer and a main layer. The dielectric constant was strongly dependent on the thickness of seed layer, but there was no dependence on deposition temperature of the seed layer. For a 2 nm seed layer, the dielectric constants were higher by about 29% than those of single-step BST thin films due to higher crystallinity and the leakage current was nearly the same as that of a single-step sample in bias voltage from −2 to 2.5 V. However, an improvement of the dielectric constant was not observed for samples having above 4 nm thick seed layers. A 40 nm thick BST film with 2 nm thick seed layer deposited by a two-step method exhibited a SiO₂ equivalent thickness of 0.385 nm and a leakage current density of 2.74 × 10⁻⁸A/cm²at+1.5V after post-annealing under an atmosphere of flowing N₂ for 30 min at 750°C.     

Temperature effect on gate leakage currents in gate dielectric films of GaAs MOSFET

The gate dielectrics of Ga₂O₃(As₂O₃) of the GaAs MOSFET were prepared by a low-cost and low-temperature liquid-phase chemically enhanced oxidation method. The temperature and oxide thickness dependence of gate dielectric films on GaAs MOSFET have been investigated. The leakage current and dielectric breakdown field were both studied. Both gate leakage current density and breakdown electrical field were found to depend on the oxide thickness and operating temperature. The increasing trend in gate leakage current and the decreasing trend in breakdown electrical field were observed upon reducing oxide thickness from 30 to 12 nm and increasing operating temperature from −50°C to 200°C.     

高度(100)取向的BST薄膜及其高介电调谐率

用脉冲激光沉积法制备(Ba1-xSrx)TiO3(x=0.35,0.50简称BST35和BST50)介电薄膜。在650℃原位退火10min,获得高度(100)取向柱状生长的晶粒。BST35薄膜的平均晶粒尺寸为50nm,BST50薄膜的晶粒尺寸为150~200nm。在室温和1MHz条件下,BST35的最大εr和调谐率分别达到810和76%,其介电调谐率高于国内外同类文献报道的数据;BST50的εr和调谐率最大分别达到875和63%。薄膜为(100)取向生长,因为薄膜沿平面c轴极化而产生应力,在电场作用下,而获得高介电调谐率。     

钛酸锶钡/铋锌铌多层复合薄膜的制备及性能

采用溶胶一凝胶法在Pt/Ti/SiO2/Si衬底上制备了钛酸锶钡/铋锌铌多层复合薄膜样品.研究了不同退火温度下多层复合薄膜的结构、微观形貌及介电性能.结果表明:在退火温度高于700℃时,所得复合薄膜中会出现立方焦绿石结构的铋锌铌和钙钛矿结构的钛酸锶钡.750℃退火处理得到的多层复合薄膜,表面致密,无裂纹,其相对介电常数...     

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     

Novel ferroelectric epitaxial (Ba,Sr)TiO3 capacitor fordeep sub-micron memory applications

A novel ferroelectric capacitor cell was developed using a (Ba,Sr)TiO₃ (BSTO)/SrRuO₃ (SRO) heteroepitaxial technique on Si and strontium titanate substrates. Distinct ferroelectricity results from the c-axis being elongated due to lattice mismatch between the dielectric and electrode. The epitaxial BSTO capacitor showed distinct ferroelectricity even at 30 nm thickness, which is the thinnest ferroelectric film so far. Its superior ferroelectric properties, reliability, and sub-micron silicon process compatibility were confirmed     

Reliability of ultra thin ZrO2 films on strained-Si

Ultra thin high-k zirconium oxide (equivalent oxide thickness 1.57 nm) films have been deposited on strained-Si/relaxed-Si_0.8Ge_0.2 heterolayers using zirconium tetra-tert-butoxide (ZTB) as an organometallic source at low temperature (<200 °C) by plasma enhanced chemical vapour deposition (PECVD) technique in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of 66.67 Pa. The trapping/detrapping behavior of charge carriers in ultra thin ZrO₂ gate dielectric during constant current (CCS) and voltage stressing (CVS) has been investigated. Stress induced leakage current (SILC) through ZrO₂ is modeled by taking into account the inelastic trap-assisted tunneling (ITAT) mechanism via traps located below the conduction band of ZrO₂ layer. Trap generation rate and trap cross-section are extracted. A capture cross-section in the range of 10⁻¹⁹ cm² as compared to 10⁻¹⁶ cm² in SiO₂ has been observed. The trapping charge density, Q_ot and charge centroid, X_t are also empirically modeled. The time dependence of defect density variation is calculated within the dispersive transport model, assuming that these defects are produced during random hopping transport of positively charge species in the insulating layer. Dielectric breakdown and reliability of the dielectric films have been studied using constant voltage stressing. A high time-dependent dielectric breakdown (TDDB, t_bd > 1500 s) is observed under high constant voltage stress.     

Dielectric Characteristics of Ba0.65Sr0.35TiO3 Thin Films by Sol-Gel Method

Ferroelectric Ba0.65Sr0.35TiO3 (BST) thin films on the Pt/Ti/SiO2/Si substrate have been successfully prepared by sol-gel. Such films have approximately 300 nm thicknesses with a remnant polarization of about 2.95 C/cm2 and a coercive field of about 21.5 kV/cm. The investigations of X-ray diffraction and atomic force microscopy show that the BST films annealed at 650 ℃ exhibit a tetragonal structure and that the films dominantly consist of large column or grains of about 89 nm in diameter. The curves of the temperature dependence of dielectric coefficient in different frequencies display the curie transition at the temperature around 23 ℃. The dielectric loss tangent of BST thin films at 100 kHz is less than 0.04. As a result, the BST thin films are more applicable for fabrication of infrared detector compared with the BST thin films reported previously.     

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     

Electrical characteristics of high quality La2O3 gate dielectric with equivalent oxide thickness of 5 Å

Electrical and reliability properties of ultrathin La₂O ₃ gate dielectric have been investigated. The measured capacitance of 33 Å La₂O₃ gate dielectric is 7.2 μF/cm² that gives an effective K value of 27 and an equivalent oxide thickness of 4.8 Å. Good dielectric integrity is evidenced from the low leakage current density of 0.06 A/cm² at -1 V, high effective breakdown field of 13.5 MV/cm, low interface-trap density of 3×10¹⁰ eV^-1/cm², and excellent reliability with more than 10 years lifetime even at 2 V bias. In addition to high K, these dielectric properties are very close to conventional thermal SiO₂      

Bi_(1.5)Zn_(1.0)Nb_(1.5)O_7/Ba_(0.5)Sr_(0.5)TiO_3复合薄膜介电性能的频率特性研究

采用射频磁控溅射法在蓝宝石基片上制备了Bi1.5Zn1.0Nb1.5O7(BZN)/Ba0.5Sr0.5TiO3(BST)双层复合薄膜,并研究了该薄膜在100 kHz~6 GHz频率范围内的介电性能。研究结果表明,BZN/BST复合薄膜的介电性能具有良好的频率稳定性。该复合薄膜的介电常数在研究的频率范围内基本与频率无关;其介电损耗在频率低于1 GHz时与频率无关,在频率高于1 GHz时随频率的上升而略微增大;薄膜在研究的频率范围内具有稳定的介电调谐率。     

Structural and Electrical Characters of Ba0.6Sro.4TiO3/La0.5Sr0.5CoO3 Thin Films by Plus Laser Deposition

Epitaxial Ba0.6Sr0.4TiO3 (BST) thin films were deposited on LaAlO3 (LAO) substrates with the conductive metallic oxide La0.5Sr0.5CoO3 (LSCO) film as a bottom electrode by pulsed laser deposition (PLD). Xray relationship of BST/LSCO/LAO was [001] BST//[001]LSCO//[001] LAO. The atomic force microscope (AFM)revealed a smooth and crackfree surface of BST films on LSCOcoated LAO substrate with the average grain size of 120 nm and the RMS of 1.564 nm for BST films.Pt/BST/LSCO capacitor was fabricated to perform CapacitanceVoltage measurement indicating good insulating characteristics. For epitaxial BST film, the dielectric constant and dielectric loss were determined as 471 and 0.03, respectively. The tunabilty was 79.59% and the leakage current was 2.63×107 A/crm2 under an applied filed of 200 kV/cm. Furthermore, it was found that epitaxial BST (60/40) films demonstrate wellbehaved ferroelectric properties with the remnate polarization of 6.085 μC/cm2 and the coercive field of 72 kV/cm. The different electric properties from bulk BST (60/40)materials with intrinsic paraelectric characteristic are attributed to the interface effects.     

Structural and Electrical Characters of Ba0.6Sr0.4TiO3/La0.5Sr0.5CoO3 Thin Films by Plus Laser Deposition

Epitaxial Ba0.6Sr0.4TiO3 (BST) thin films were deposited on LaAlO3 (LAO) substrates with the conductive metallic oxide La0.5Sr0.5CoO3 (LSCO) film as a bottom electrode by pulsed laser deposition (PLD). X-ray diffraction ~2 and Ф scan showed that the epitaxial relationship of BST/LSCO/LAO was [001] BST//[001] LSCO//[001] LAO. The atomic force microscope (AFM) revealed a smooth and crack-free surface of BST films on LSCO-coated LAO substrate with the average grain size of 120 nm and the RMS of 1.564 nm for BST films. Pt/BST/LSCO capacitor was fabricated to perform CapacitanceVoltage measurement indicating good insulating characteristics. For epitaxial BST film, the dielectric constant and dielectric loss were determined as 471 and 0.03, respectively. The tunabilty was 79.59% and the leakage current was 2.6310-7 A/cm2 under an applied filed of 200 kV/cm. Furthermore, it was found that epitaxial BST (60/40) films demonstrate well-behaved ferroelectric properties with the remnate polarization of 6.085 C/cm2 and the coercive field of 72 kV/cm. The different electric properties from bulk BST (60/40) materials with intrinsic paraelectric characteristic are attributed to the interface effects.     

Zn掺杂对BST薄膜介电调谐性能的影响

用sol-gel法在Pt/SiO2/Si基片上制备了未掺杂和掺杂Zn的钛酸锶钡(BST)薄膜。用XRD对BST薄膜进行了物相分析,研究了Zn掺杂对薄膜的表面形貌和介电调谐性能的影响。结果表明:室温下,随着Zn加入量的增加,BST薄膜的介电常数减小,介质损耗降低,介电调谐量增加。x(Zn)为0.025的BST薄膜具有最大的优越因子(FOM),其值为29.28。     

Highly reliable SiO2/Si3N4 stackeddielectric on rapid-thermal-nitrided rugged polysilicon for high-densityDRAM's

Experimental results are presented demonstrating that by using rapid thermal nitridation (RTN) of rugged poly-Si surface prior to Si ₃N₄ deposition, the quality and reliability of reoxidized Si₃N₄ dielectric (ON dielectric with an effective oxide thickness of about 35 Å) can be significantly improved over ON films on rugged poly-Si without RTN treatment. These improvements include significantly reduced defect-related dielectric breakdown, 10³ × increase in TDDB lifetime, lower leakage current, and suppressed electron-hole trapping and capacitance loss during stress     

Integration of high dielectric Ba0.5Sr0.5TiO3 films into amorphous TaSiN barrier layer structures

The high-k dielectric material (Ba,Sr)TiO₃ has been intensively investigated for possible applications in dynamic random access memory circuits. During the BST deposition process in O₂ ambient, typically at 650°C, the diffusion of oxygen through the bottom electrode into the poly Si plug must be prevented. Amorphous TaSiN films are excellent candidates as oxygen barrier layers. Ba_0.5Sr_0.5TiO₃ (BST) films with thickness of 100 nm were deposited on the electrode structure SiO₂/TaSiN/Pt. The sol–gel method was used to grow the BST films. The barrier effect for oxygen diffusion is studied in TaSiN layers with thickness of 50 nm, which were deposited by a reactive sputter process. X-ray photoemission spectroscopy results confirm that this amorphous material is a suitable barrier against oxygen diffusion at 650°C. The BST films, deposited at 650°C and post-annealed at 650°C show a dielectric constant of 100 at 100 kHz and a dissipation factor of less than 5%.