The use of high-dielectric-constant (high-κ) materials for embedded capacitors is becoming increasingly important. Tantalum oxide (Ta2O5) is a prominent candidate as a high-κ material for embedded capacitor use. Metal drift in Ta2O5 (κ∼25) was investigated by bias temperature stress and triangular voltage sweep testing techniques on metal/Ta2O5∕SiO2∕Si structures. At a temperature of 300°C and 0.75MV∕cm bias conditions, Al, Ta, and Ti do not diffuse in Ta2O5, but Cu clearly showed a drift. The Cu drift is attributed to the lack of a stable Cu oxide which can limit Cu ion generation and penetration.

The effects of substrate heating on the stoichiometry and the electrical properties of pulsed dc reactively sputtered tantalum oxide films over a range of film thickness (0.14to5.4μm) are discussed. The film stoichiometry, and hence the electrical properties, of tantalum oxide films; e.g., breakdown field, leakage current density, dielectric constant, and dielectric loss are compared for two different cases: (a) when no intentional substrate/film cooling is provided, and (b) when the substrate is water cooled during deposition. All other operating conditions are the same, and the film thickness is directly related to deposition time. The tantalum oxide films deposited on the water-cooled substrates are stoichiometric, and exhibit excellent electrical properties over the entire range of film thickness. “Noncooled” tantalum oxide films are stoichiometric up to ∼1μm film thickness, beyond that the deposited oxide is increasingly nonstoichiometric. The presence of partially oxidized Ta in thicker (>∼1μm) noncooled tantalum oxide films causes a lower breakdown field, higher leakage current density, higher apparent dielectric constant, and dielectric loss. The growth of nonstoichiometric tantalum oxide in thicker noncooled films is attributed to decreased surface oxygen concentration due to oxygen recombination and desorption at higher film temperatures (>∼100°C). The quantitative results presented reflect experience with a specific piece of equipment; however, the procedures presented can be used to characterize deposition processes in which film stoichiometry can change.

A novel flip-chip flex-circuit packaging platform is described that enables integration of multiple power dies and control circuitry with an advantageous form factor. A key attribute of this packaging platform is to extend the well-established flex-circuit and flip-chip soldering technologies in signal electronics to power electronics applications. The planar interconnection and flip-chip method facilitate multilayer packaging structure with reduced packaging dimensions and reduced packaging parasitics. A half-bridge test vehicle designed and fabricated for dc/ac inverter applications (42 V, 16 A) with an overall flex-circuit module footprint less than 30% that of a discrete device printed circuit board implementation has been modeled and demonstrated experimentally. Electrical results, confirmed with circuit simulation incorporating parasitic inductance electromagnetic modeling, have shown a turn-off voltage overshoot reduction of over 40% and a switching energy loss reduction of 24% with the flip-chip flex-circuit implementation. The power flex platform has a strong potential for integrated multichip power module applications that require minimized packaging size and parasitic inductance for high switching frequency and efficiency.

An experimentally verified analytical model for pulsed dc reactive sputtering of tantalum oxide films is described. The influences of important process variables, like oxygen flow rate and sputtering ion current, on the oxygen partial pressure in the chamber, deposition rate, as well as film breakdown and leakage characteristics, are predicted using this model. The experimentally established existence of multiple oxygen partial pressures at a given oxygen flow rate (hysteresis loop) is theoretically explained using steady state analysis. The partial pressure of oxygen during deposition can be used to correlate and predict the critical oxygen flow rate required to achieve insulating dielectric films (with no metallic tantalum) for a specified sputtering ion current. The experimental results suggest that in order to ensure the electrical reliability of tantalum oxide films, deposition should be done at oxygen flow rates more than that required to go beyond the hysteresis region in partial pressure versus flow rate curve. In addition, the observed hystereses in breakdown field and leakage current density of tantalum oxide films closely follow the hystereses in the oxygen partial pressure curve with oxygen flow rate. The stabilities of different steady state operating points with respect to fluctuations in flow rate are discussed.

The large physical size of capacitors and/or excessive values of associated lead inductance are two major limitations in the development of novel packaging modules, with high packaging density, high performance and reliability along with low system cost. Embedded capacitor technology in thin film form offers a promising solution to these limitations. A design space with capacitance density and breakdown voltage as performance properties, with material dielectric constant and film thickness as parameters has been explored, focusing on tantalum pentoxide (Ta/sub 2/O/sub 5/) as the dielectric material. An inherent tradeoff is established between breakdown voltage and capacitance density for thin film capacitors. The validity of the proposed design space is illustrated with thin films of Ta/sub 2/O/sub 5/, showing deviation from the "best can achieve" breakdown voltage for films thinner than 0.4 /spl mu/m and films thicker than 1 /spl mu/m.

This paper presents a novel flex-circuit power packaging platform that enables integration of power dies and control components with an advantageous form factor. The flex-circuit offers the benefits of planar interconnection and multilayer layout design flexibility with reduced parasitic inductance compared to conventional wire bonds. A half-bridge test vehicle that implements the flex-circuit packaging platform has been designed and fabricated for automotive applications (42 V, 16 A). The power flex module presents a compact configuration with electrical results indicating improved package parasitics.

Amorphous tantalum oxide films were deposited using a pulsed de reactive magnetron sputtering technique at low temperature (less than or equal to 200 degreesC). A test vehicle (metal- insulator-metal structure) was designed and fabricated for the high frequency characterization of the dielectric thin film. The dielectric constant and loss tangent of the amorphous tantalum oxide thin film were measured using dc, time domain reflectometry (TDR), and network analyzer up to 10 GHz. The measured dielectric constant and loss tangent was 22 and 0.007, respectively from 1 KHz to 10 GHz. The high frequency properties of the amorphous tantalum oxide thin film show little dispersion up to 10 GHz. However, the resonance oscillation due to the parasitics is evident between 10 GHz and 40 GHz and depends on the capacitor area. Modeling of the equivalent circuits would allow us to identify the parasitic components and their effects on the measured scattering parameters.

The development of high-density packaging for power electronics applications has been driven by the requirement for system functionality enhancement and cost reduction. In this paper we explore a novel power packaging concept, the flip-chip flex-circuit package, that eliminates bond wires and exhibits potential for high-level component integration with an established flex-circuit technology. A baseline power electronic module involving a half-bridge circuit has been fabricated and evaluated electrically.

Dramatic dependence of dielectric properties on the pulsing frequency was found for titanium oxide films deposited using the pulsed dc magnetron sputtering technique at room temperature. The frequency range studied was between 50 and 250 kHz by varying the oxygen pressure. A minimum leakage current density of 0.22 μA/cm2 at 0.5 MV/cm electric-field strength for a film with dielectric constant of 26 was achieved for relative oxygen pressure P=60% [P(%)=PO2/(PO2+PAr] and frequency f=200 kHz.

Understanding that integral passives can offer significant performance and cost leverages, the General Electric Research and Development Center, Schenectady, NY, has teamed with Rensselaer Polytechnic Institute (RPI), Arizona State University (ASU), Sheldahl, and the Mayo Foundation on the development of thin film deposition processes for the fabrication of passive elements on polyimide films. This program was targeted at developing manufacturing processes for the fabrication of integral resistors, capacitors and inductors to be used in digital and mixed mode (combined analog/digital) applications operating in the GHz regime. To demonstrate the developed technology, multichip modules were fabricated that included a microwave frequency down converter circuit (shifting the input signal from 5 GHz to 500 MHz), a biphase demodulator, a 500 MHz filter, a 5 GHz filter, and a splitter. The design and fabrication methodology implemented a novel double sided flex approach positioning the thin film capacitors on one side and the resistors and inductors on the reverse side. The capacitor material set consisted of tantalum oxide (Ta2O5) and diamond like carbon (DLC). Spiral geometric patterns of electroplated Cu formed the inductors, while the resistors used reactively sputtered tantalum nitride (Ta2N). The high yield (> 95%) of integral passive components on the fully functional multichip modules demonstrate the feasibility of incorporating thin film passive components with the manufacture of polyimide flex circuitry.

Room temperature deposition of tantalum oxide films on metallized silicon substrates was investigated by reactive pulsed magnetron sputtering of Ta in an Ar/O2 ambient. The dielectric constant of the tantalum oxide ranged from 19 to 31 depending on the oxygen percentage [P(%)=PO2/(PO2+PAr)] used during sputtering. The leakage current density was less than 10 nA/cm2 at 0.5 MV/cm electric field and the dielectric breakdown field was greater than 3.8 MV/cm for P=60%. A charge storage as high as 3.3 μF/cm2 was achieved for 70-Å-thick film. Pulse frequency variation (from 20 to 200 kHz) did not give a significant effect in the electrical properties (dielectric constant or leakage current density) of the Ta2O5 films.

Utilizing THE Combustion Chemical Vapor Deposition (CCVD) process, submicron dielectric films were deposited on copper foils and platinum-coated silicon wafers for embedded capacitors to be incorporated in muitichip modules (MCM) and printed circuit boards (PCB) for higher packaging density and better electronic performance. Critical CCVD processing parameters influencing microstructure and phase formation were studied. Electronic, chemical and physical properties were characterized. For CCVD) dielectrics-coated silicon wafers, less than 2% variation in thickness and, correspondingly, capacitance was observed. Capacitance density ranged from 23 to 331 nF/cm(2), leakage current density as low as 1 nA/cm(2), measured at 0.5 MV/cm, and breakdownfieid of 2.11-5.44 MV/cm were achieved for multichip modules. Far PCB applications, the yield of silica capacitors on copper foils was improved from 83-90% to 97% by reducing copper foil surface roughness. The capacitance density was in the range of 37-109 nF/cm(2) breakdown voltage was similar to 2.5 MV/cm while leakage current density was similar to 10(7) A/cm(2) at 10V. The as-deposited specimens on copper exhibited peel strength up to 3.7 lb/in, while shear stress rests of the as deposited SiO2 specimens showed a shear strength over 373 lb/in(2). These results and related corrosion resistance studies showed very promising potential of the CCVD thin films for embedded capacitors.

Integration of discrete passive components into either integrated circuit (IC) chips or into electronic packaging structures extends the technology applications beyond those feasible with just the stand-alone passive components. For example, use of the miniscule capacitors in each storage cell of a dynamic random access memory (DRAM). Integration also has potential for competitive leverages over their unintegrated counterparts (resistors, capacitors and inductors) in terms of cost and/or performance achieved by reduced physical size and simplified structures.This paper focuses on thin dielectric films for integrated capacitors. It highlights interdependencies between the materials properties, such as dielectric constant and breakdown field strength, which define the intrinsic boundaries of the design space. It addresses some effects of the structural environment (such as microroughness of the metal interconnection layers) which restrict the intrinsic design space. It indicates challenges/restrictions which result from the need for compatible manufacturing processes (such as deposition temperature) and materials. Topics deemed desirable for further studies conclude the paper. It is augmented by the companion paper [1].

The reactive pulsed de magnetron sputtering technique was used to deposit high quality high dielectric oxides onto both metallized Si and polyimide substrates. This low temperature deposition method proved effective in reducing target poisoning associated with reactive sputtering. Tantalum oxide, TaOx, films deposited onto Si exhibited exceptional properties: a low leakage current density of less than or equal to 4.0.10(-9) A/cm(2) measured at 0.5 MV/cm and a high breakdown held strength of approximately 5 MV/cm. Tantalum oxide capacitors were also made on polymer substrates, and an increase in the leakage current density and lowering of the breakdown field strength were attributed to the surface microstructure of the novel substrates. The high frequency properties of the tantalum oxide showed little to no dispersion up to several GHz. Multilayer and composite films consisting of tantalum oxide and titanium oxides were deposited to increase the dielectric constant achievable with just tantalum oxide. The dielectric constant was indeed found to increase from 22 to 38 for the composite and 44 for the multilayer. Both films displayed an increase in the leakage current density (1.10(-6) A/cm(2) for the composite and 3.4.10(-8) A/cm(2) for the multilayer) and a decrease in the breakdown field strength (2.3 MV/cm for both films). Overall, the electrical properties of both the tantalum oxide and tantalum oxide/titanium oxide multilayer and composite dielectrics dictate that the reactive pulsed de magnetron sputtering technique used is well suited for producing high quality high dielectric thin films.

The crystallization of thin amorphous TaOx films formed by d.c. reactive sputtering was investigated at temperatures from 500–700 °C. The films remained amorphous for times up to 100 h at 500 °C. The formation of discrete, single crystallites of the orthorhombic β-Ta2O5 phase was observed after annealing at 600 °C for times from 8–108 h. The crystallites were 0.35 μm×0.35 μm after 8 h and grew to approximately 2.5 μm×2.0 μm after 108 h. A (2 0 0) fibre texture with a 6° spread was observed. More rapid in-plane growth in the [0 1 0] direction resulted in a near-rectangular shape and is attributed to a ledge growth mechanism. Higher temperature anneals at 650 and 700 °C produced less-textured polycrystalline films with remnant amorphous regions. © 1998 Kluwer Academic Publishers

A novel low temperature deposition process using reactive pulsed de magnetron sputtering has been developed to deposit thin dielectric films composed of either a composite or alternating layers of tantalum oxide and titanium oxide. Capacitors fabricated from these dielectric materials have been found to exhibit exceptional electrical properties. For the composite material, one him containing 22% TiOy had a high dielectric constant of 38, a leakage current density of 10(-6) A/cm(2) at 0.5 MV/cm, and a relatively high breakdown field strength of 2.3 MV/cm. By a slight modification of the deposition conditions, alternating layers of tantalum oxide and titanium oxide were deposited to form a high dielectric constant material, The electrical properties of these films were also exceptional: a dielectric constant of 44, a leakage current density of 3.4 +/- 10(-8) A/cm(2) at 0.5 MV/cm, and a breakdown field strength of 2.3 MV/cm. These films have potential applications in memory and advanced electronics packaging.

The dc magnetron reactive sputtering deposition of tantalum pentoxide (Ta2O5) thin films was investigated. By combining Schiller's criterion and Reith’s “target preoxidation” procedure, high quality Ta2O5 thin films were prepared at a high deposition rate of about lOOÅ;/min. The deposited films were amorphous, with a refractive index around 2.07 and a dielectric constant of 20. An optical transmit-tance of 98.6% was obtained for a 4500Â thick film. The leakage current density is 5 × 10−9 A/cm2 at an electric field strength of 1 MV/cm and its breakdown field strength is above 2 MV/cm. The temperature coefficient of capacitance for capacitors fabricated using the deposited films is approximately +230 ppm/°C. X-ray photoelectron spectroscopy shows that the films are stoichiometric tantalum pentoxide, Ta2O5, and exhibit good stability.

Amorphous tantalum pentoxide (Ta2O5) thin films on n-type Si substrates were prepared by d.c. magnetron reactive sputtering deposition technique. It was observed that the leakage current decreased with time when a voltage bias was first applied. The cause of this behavior was investigated using bias-temperature-stress test technique combined with the capacitance-voltage measurement with structures of Al/Ta2O5/Si metal-oxide-semiconductor (MOS) capacitors, and was identified to be owing to electron trapping in the Ta2O5 film and at the Ta2O5/Si interfaces. The current injection technique was further used to correlate the amount of charge trapped in the Ta2O5 with the leakage current passed through the Ta2O5 film, and it was found that most of the trapped electrons were located at the Ta2O5/Si interface. This electron trapping effect on the conduction mechanisms of the Ta2O5 films and the related reliability issues in dynamic random access memories applications are discussed.

Buried interfaces of thin Al/Ta2O5 and Ta2O5/Al films were studied using the x-ray photoelectron spectroscopy technique. The peak decomposition technique was employed to identify the composition and chemical states at the interface region. It was observed that there is an “intermixing layer” at the Al/Ta2O5 interface, where Ta2O5 has been reduced to lower binding energy states due to the reaction of Al with Ta2O5 during deposition. On the other hand, the Ta2O5/Al interface is relatively stable, consisting of Ta2O5 and Al2O3 interfacial layers. Based on a uniform multilayer structure model, the thickness of the interfacial layers was estimated by using the relative photoelectron intensities.