The current status of (Ba,Sr)TiO3 [BST] capacitor technology using a liquid source chemical vapor deposition (CVD) method is reviewed, focusing on the CVD techniques and the physical, electrical and process-integration-related properties of Ru/BST/Ru capacitors. The use of a new titanium metalorganic (MO) source, titanium bis(tert-butoxy) bis(dipivaloylmethanato) [Ti(tertBuO)2 (DPM)2] dissolved in tetrahydrofuran (THF) turned out to enable highly conformal deposition of BST films with a coverage ratio of ∼ 70 % for a trench with an aspect ratio of ∼ 5. Electrical properties of a 24-nm-thick BST film, deposited on a Pt substrate at a low substrate temperature of 480 °C, were also confirmed to be equivalent SiO2 thickness (teq) of ∼ 0.5 nm and leakage current of ∼ 1 ×10-7 A/cm2 at 1 V. As for the Ru/BST/Ru capacitors, no deteriorations of Ru electrode and BST/Ru interface were observed after 750 °C post-annealing experiment, showing good thermal stability of Ru as a practical electrode material. Although current leak through Ru/BST/Ru capacitors slightly increased after the H2 annealing, such degradation in the leakage properties was restored by post-annealing in N2 ambience. Integrated Ru/BST/Ru capacitors with a 30-nm-thick CVD-BST film were fabricated by 0.5 μm ULSI technology, and low leakage current was confirmed for the stacked capacitors. Regarding the reproducibility of BST deposition by the liquid source CVD method, the deviation ratio of ∼ ± 2.3 % in film thickness was obtained for ∼ 100 successive depositions, thickness uniformity across the wafers was ∼ ± 1.1 %. The above results imply the potential applicability of BST capacitor technology using a liquid source CVD method for Gbit-scale DRAMs.

Long recognized as the best potential solution to the continued scaling of the onetransistor/one-capacitor standalone dynamic random access memory (DRAM) beyond a gigabit, barium strontium titanate (BST) and other high permittivity dielectrics are fast becoming enablers to embedding large amounts of memory into a high performance logic process. System requirements such as granularity, bandwidth, fill frequency, and power pose major challenges to the use of high density standalone DRAM, leading to the current push for embedded solutions where very wide buses are possible. As a result, projected embedded memory sizes are rapidly approaching that of the standalone products, and with the high wafer cost of the combined logic plus memory process, bit cell scaling is critical. The BST memory cell, with its low thermal budget processing, very high charge storage density, and high conductivity metal electrodes has the potential to be efficiently embedded with traditional logic flows if the materials and integration challenges of the required three dimensional (3D) bit cell capacitors can be solved. BST materials properties such as dielectric relaxation, interface capacitance, and resistance degradation and their impact on capacitor scaling will be reviewed along with the electrode materials issues associated with certain 3D capacitor designs. The scaling limits of BST bit cells in the deep sub-micron regime will be discussed.

We have investigated the dielectric relaxation currents of Mn doped polycrystalline Ba0.7Sr0.3TiO3 (BSTO) thin films as a function of applied electric field and temperature (4.2 - 473 K). The dielectric relaxation currents followed a power law time dependence, J(t) = Jot-n, over the entire temperature range. Plots of log(Jo) vs. reciprocal temperature were not linear and showed slopes approaching values of 0.35 eV at high temperatures which rapidly decreased to 0.25 meV at lower temperatures. The relaxation currents were found to be nonlinear with applied field. The observed nonlinearity of the field dependence of the relaxation currents can be understood in terms of the nonlinear relaxation component of the total capacitance. An equivalent circuit model for a paraelectric BSTO thin film capacitor is presented and possible polarization mechanisms are briefly discussed.

Metalorganic chemical vapor deposition (MOCVD) has been used to grow (Ba,Sr)TiO3 thin films on Ir/SiO2/Si substrates. β-diketonates of Ba, Sr, and Ti were used as the precursors, and delivered to the reactor via direct-liquid injection. Growth rate and film thickness were monitored by in-situ spectroscopic ellipsometry, and determined after growth. Film growth was studied as a function of film thickness, composition, substrate temperature, and mixture of O2 and N2O with and without microwave plasma enhancement. Dense, mirror-like films were obtained under all conditions except when pure oxygen plasma enhancement was used. Surface roughness of the films appears strongly dependent on film thickness and composition. Film composition and growth temperature determine growth texture of the films. This paper describes these results as well as the correlation between these results and dielectric properties.

Thin film ceramic Au/BaxSr(1−x)TiO3/YBCO/MgO planar capacitors with x ranging from 1 to 0.4 were fabricated using pulsed laser deposition (PLD). Structural and chemical characterisation showed the ferroelectric layers to be of perovskite crystallography, with cation stoichiometry close to that of the target. Auger depth profiling showed the interface between ferroelectric and lower electrode to be reasonably chemically sharp.

Capacitance versus temperature measurements performed in air showed a pronounced difference in behaviour between bulk and thin film devices. Bulk samples exhibited the expected capacitance anomaly at the Curie temperature. In contrast, thin film capacitors showed a prominent peak in capacitance at temperatures between 7 and 25°C on heating, irrespective of composition and did not show any evidence of expected Curie anomalies.

Further characterisation under vacuum and with deliberate additions of water vapour to the vacuum chamber indicated that the peaks observed in thin film devices described above could be attributed to the presence of atmospheric water vapour. This demonstrates that water vapour in the air can have a significant effect on the dielectric response of thin film capacitors around room temperature.

Studies on higher quality films showed a reduced response to water vapour.

LaNiO3 (LNO) films were used as conductive bottom and top electrodes for the fabrication of (Ba0.5Sr0.5) TiO3 (BST) capacitors on silicon substrates. LNO as well as BST films were grown in-situ using a pulsed laser deposition technique with no subsequent heating or oxygenation treatments. Capacitance and leakage current measurements of BST films were carried out using LNO/BST/LNO/Si structures. Using these measurements, the dielectric constant and leakage current of BST films were found to be ∼250 and ∼10−8 A/cm2, respectively. The results obtained in the present study suggest that LNO is a good contact electrode material for BST films in the fabrication of BST capacitors with good structural and electrical properties.

Barium zirconate-titanate (Ba(ZrxTi1−x)O3, BZT) films with thickness around 60 nm were deposited on Ir substrates using RF magnetron sputtering. The effect of zirconium atomic fraction (x = 0.14 to 0.7), substrate temperature (380 °C to 550 °C) and oxygen partial pressure (0 to 5 mTorr with total pressure 30 mTorr) on leakage current, dielectric constant and dielectric dispersion (capacitance reduction with increasing frequency) was studied. We found that the Zr/Ti ratio played a crucial role in determining the dielectric constant and dispersion. The dielectric constant varies from 26 to 168 while dispersion ranges from 0.80 to 2.58 % loss in capacitance (dielectric constant) per decade of frequency. Low leakage currents (< 1× 10−7 A/cm2) were observed.

((Ba0.5Sr 0.5)TiO3 thin films of two different thicknesses (∼ 250 Å and ∼ 1330 Å) epitaxially prepared on MgO(100) using pulsed laser deposition were studied by synchrotron x-ray scattering measurements. The film initially grew on MgO(100) with a cube-on-cube relationship, maintaining it during further growth. As the film grew, the surface of the film became rougher significantly, but the interface between the film and the substrate did not change so much. In the early stage, the film was highly strained in a tetragonal structure with the longer axis parallel to the surface normal direction. As the growth proceeded further, it was mostly relaxed to a cubic structure with the lattice parameter of the bulk value and the mosaic distribution improved significantly in both the in-plane and the out-of-plane directions. The thinner film showed only one domain limited mainly by the film thickness, but the thicker film exhibited three domains along the surface normal direction.

A high stability electrode technology with TaSiN as a barrier metal was used to fabricate a stacked SBT capacitor array on polySi plugs, and hysteresis characteristics and contact properties of the stacked capacitor were studied.

A new electrode barrier structure based on noble metals Pt and Ir alloys and their oxides was proposed for the integration of PZT capacitors into high density nonvolatile memories. The proposed PtIrOx/PtIr/PtIrOx structure with Pt rich compositions (∼90%) is an excellent conducting electrode for the ferroelectric capacitor and a very good diffusion barrier for species like oxygen and Si. These structures are thermally stable up to the PZT processing temperatures of 650°C. PZT deposited on these electrodes crystallized predominantly in pervoskite phase. The test capacitors showed well saturated hysteresis loops with Pr and Ec of 21.3 µC/cm2 and 43 kV/cm, respectively. An extremely low polarization fatigue of 3% after 1× 1011 repetitions and leakage currents close to those on Pt were observed.

Low frequency dielectric loss and nonlinearity in pulsed laser deposited SrTiO3 thin films were studied. A low loss tangent in the order of 10−4, close to the level found in SrTiO3 single crystals, was observed. Combined with a large tunability, this resulted in a figure of merit for frequency and phase agile materials that can rival that observed in single crystals. The SrTiO3 thin films with thickness ranging from 25 nm to 2.5μ1 were grown on SrRuO3 electrode layers. The loss depends strongly on the thickness, but differently above and below T ∼ 80 K. Our result suggests that, in the high temperature regime, the interfacial dead layer effect dominates while, in the low temperature regime, the losses related to the structural phase transition and quantum fluctuations are important. The effect of interfacial potential was studied by using different electrode materials that result in different Schottky barriers.

Ferroelectric properties of a Pb(Zr,Ti)O3 (PZT) thin film capacitor with a conventional Al/TiN/Ti interconnect are seriously degraded by annealing at around 400°C. The degradation of the PZT capacitor is reduced as the interconnects are narrowed while the total area of the interconnects on the capacitor is fixed. This result cannot be understood by supposing that Ti diffusion into PZT degrades the ferroelectric properties. A possible cause for the degradation is stress placed on the PZT film during the 400°C annealing.

The preparation of ferroelectric and high-dielectric perovskite materials, which is performed at high temperatures in oxidizing environments, imposes strong limitations on the choice of suitable electrode materials which can be used for integration of these materials with semiconductor devices. Because of the complex compositions of the perovskites and of some of the electrode materials the two can interact and result in the deterioration of the structures. The electrode materials have, therefore, to be used often in combination with suitable barriers which block diffusion of the elements of the perovskite and of the Si device and prevent interactions between the components. These requirements can result in complex, multilayered electrode/barrier structures that can affect the crystallization of the perovskite material and its electrical properties as well as the perovskite properties during subsequent processing steps (e.g. in forming gas anneals). The present paper will review the different electrode/barrier structures that have been proposed for integration of ferroelectric thin films with semiconductor devices and discuss their effects on the properties of ferroelectric and high-dielectric materials.

Iridium acetylacetonate, dicarbonylacetylacetonato iridium, and tetrakisiridium dodecacarbonyl (iridium carbonyl) have been evaluated for metallorganic chemical vapor deposition (CVD) of pure iridium films. Temperature programmed mass spectroscopy reveals that iridium tris-acetylacetonate and dicarbonylacetylactonato iridium have high thermal stability and sublime at 200 and 100 °C in vacuum, respectively. Iridium carbonyl decomposes upon sublimation at temperatures above 120 °C. Pure CVD Ir films were obtained using iridium carbonyl; however, carbon is incorporated into the iridium films with the iridium trisacetylacetonate and dicarbonylacetylactonato iridium precursors unless a reactive gas, such as oxygen is co-dosed. Co-dosed oxygen also increases the film deposition rate and significantly decreases the film growth temperatures. Particles were found on the films grown with iridium carbonyl between 280 to 400 °C, indicating that gas phase nucleation occurred during deposition.

RF magnetron sputter deposited PZT films were prepared on various bottom electrode systems such as Pt/Ti/SiO2/Si, IrO2/SiO2/Si, Pt/IrO2/SiO2/Si and Ir/IrO2/SiO2/Si substrates using the ceramic PZT target with Pb1.1(Zr0.52Ti0.48)O3 composition. In order to obtain single perovskite phase, PZT films were sputter-deposited at room temperature under Ar only plasma condition followed by high temperature annealing under oxygen ambient. Regardless of the bottom electrode system, reasonable ferroelectric properties such as 2Pp, Vc could be obtained by 650°C post annealing. Their values were over 20μ C/cm2 and below ± 1.OV when drive voltage was ± 3V, respectively. Hybrid electrode system, namely, thick Pt or Ir and thin IrO2 shows good leakage current characteristics, of ∼ 10−8A/cm2. Fatigue properties of PZT capacitor depend on the test condition. However, retention after 3×104sec showed a degradation of 15% when writing voltage was −5V irrespective of bottom electrode system. Imprint characteristics also showed good results within ± 1 as a figure of merit (FOM).

Lead-Zirconate-Titanate (PZT) films were etched with CF4/Ar mixed gases in high-density plasmas. Etch characteristics of the PZT film were investigated by using in-situ plasma diagnostic tools in conjunction with the surface analysis after etching. Densities of ionic species such as F+ and CFx+(x=1∼3) and their ion energy distributions within the plasma were measured by a mass spectrometer. Characteristics of the CF4/Ar plasma were obtained by using Langmuir probe measurements. Etch rate of the PZT film was sharply increased up to a peak at 30 % CF4 as the gas ratio of CF4/(Ar+CF4) increased, and then was gradually decreased. After etching, the surface of PZT film was covered with fluorine that was bonded chemically with underlying PZT film. Ion assisted etching mechanism for the PZT was proposed and its validity was confirmed by using the results of the plasma diagnostics.

This paper examines factors affecting the oxidation behavior of Ir thin film electrodes and the stability of bilayer Ir/Ir-Ir-O-Si electrodes on silicon substrates. We first examine the morphology and texture of faceted IrO2 extrusions formed on the Ir films during thermal oxidation, and show that an Ir grain-growth anneal in N2 at 650°C for 5 min prior to the oxidation treatment increases both the areal density of IrO2 extrusions and the IrO2<110> x-ray diffraction intensity while decreasing apparent film roughness. We then examine the stability of bilayer lr(100 nm)/Ir(20 nm) films on polycrystalline silicon and show how fairly mild oxygen anneals of the Ir(20 nm)/Si structures can provide an in-situ formed Ir-O-Si barrier that protects the subsequently deposited Ir(100 nm) layer from silicidation reactions during annealing in N2 ambients at 750°C. Transmission electron microscopy indicates that this in-situ formed barrier at the Ir/Si interface has a two layer structure comprising an IrSix underlayer in contact with the silicon substrate and an SiO2 overlayer directly below the remaining Ir.

Chemical vapor deposition (CVD) of noble metal thin-films is increasingly important for future memory storage applications. Integration of ferroelectric perovskites and/or high permittivity oxides requires specialized metal interconnect technologies. Platinum and iridium are two preferred metal electrode materials being explored since they are highly resistant to corrosion and exhibit excellent stability at high temperatures. Further, the formation of stable oxides (IrO2) provides a mechanism for decreased inter-diffusion of oxygen and elemental film constituents, and provides improved reliability in silicon-based devices. CVD provides conformal electrode films that are required to achieve high-densities; high purity films of both platinum and iridium were deposited in this research, using (β-diketonate)Ir(I)L and (MeCp)Me3Pt(IV) as the precursors.

Concurrently, chemical etching of these metals is highly desirable for creating patterns of the electrical contacts and for CVD reactor cleaning. To date, etching of noble metal electrodes has relied upon physical sputtering or chemically assisted etching. In this paper, we also report the first chemical etching of iridium films under ambient conditions, such as room temperature.

Ruthenium dioxide films have been prepared by rf reactive magnetron sputtering at different oxygen partial pressures and total sputtering pressures. The films have been characterized by scanning electron microscopy, X-ray diffraction and electrical conductivity. The films prepared at low oxygen partial pressure and total pressure show a strong preferred orientation along the [110] direction. As both pressures increased, the peak intensity decreases. All the films are subject to a compressive stress. As the total pressure is decreased and the oxygen partial pressure is increased, the stress increases. When the total pressure is lower than 6 × 10−3 mbar and the oxygen partial pressure is higher than 1 × 103 mbar, the films peeled off automatically from the substrate because of the high stress. The films prepared at high oxygen partial pressure and high total pressure have a rough surface and those prepared at low pressure show smooth surface. In this paper, these phenomena have been discussed. In addition, the electrical properties of the films are also discussed.

Conductive RuO2 thin films have been grown epitaxially on (100) MgO and (100) LaAlO3 substrates by metal-organic chemical vapor deposition(MOCVD) at different temperatures. The microstructural properties of the RuO2 films have been studied using x-ray diffraction and scanning electron microscopy. Different growth and microstructure properties were observed for the films deposited on the two substrates. The films on MgO are epitaxial at deposition temperatures as low as 350°C, and consist of two variants with an orientation relationship given by (110) RuO2 /(100) MgO and [001] RuO2//[011]MgO. The films on LaAlO3, on the other hand, are epitaxial only at deposition temperatures of 600°C and above, and contain four variants with an orientation relationship given by (200)RuO2//(100)LaAlO3 and [011] RuO2//[011] LaAlO3. The observed microstructures of epitaxially grown films can be explained based on geometric considerations for the films and substrates.