Eugene J. Rymaszewski

Frequency-dependent pulsed direct current magnetron sputtering of titanium oxide films

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.

Reactive sputtering deposition of low temperature tantalum suboxide thin films

A relatively simple direct current sputtering deposition scheme has been employed to deposit 1000 A tantalum oxide thin films at low temperature. At ≂190 °C substrate temperature, without further annealing, tantalum oxide films with a dielectric constant of 21–22 and a leakage current density as low as 10 nA/cm2 at 0.5 MV/cm electrical field strength (∼5 V of applied voltage) are obtained. These properties are achieved over a wide range of O2/Ar ratios when the total flow rate is kept constant. XPS measurements reveal that these films are nonstoichiometric with a composition of TaOx where x≂1.5. These low temperature, high dielectric constant thin films have potential applications as decoupling capacitors in very high speed electronic circuits and packaging.

X-ray photoelectron spectroscopy study of Al/Ta2O5 and Ta2O5/Al buried interfaces

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.

Electrical characteristics of thin Ta2O5 films deposited by reactive pulsed direct-current magnetron sputtering

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-A-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.

Dielectric constant dependence of Poole-Frenkel potential in tantalum oxide thin films

Abstract A change of more than five orders of magnitude of leakage current density has been observed in tantalum oxide films with a dielectric constant ranging from 20 to 45. The films were deposited by a simple DC reactive sputtering technique. The measured leakage current density dependence on the films dielectric constant can be explained by the Poole-Frenkel potential barrier model in which the barrier height is inversely proportional to the dielectric constant of the material. This intrinsic dielectric constant dependence of the trap barrier may give a limit on the lowest leakage current density that one can obtain in a high dielectric constant film.

Composite and multilayered TaO/sub x/-TiO/sub y/ high dielectric constant thin films

A novel low temperature deposition process using reactive pulsed dc 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 film containing 22% TiO/sub y/ had a high dielectric constant of 38, a leakage current density of 10/sup -6/ A/cm/sup 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 electric at properties of these films were also exceptional: a dielectric constant of 44, a leakage current density of 3.4/spl middot/10/sup -8/ A/cm/sup 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.

Effects of substrate temperature on properties of pulsed dc reactively sputtered tantalum oxide films

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) nonc...

High‐frequency response of capacitors fabricated from fine grain BaTiO3 thin films

Fine grain BaTiO3 thin films with a grain size ranging between 100 and 1000 A were deposited using the reactive partially ionized beam deposition technique at 550–600 °C. A metal/insulator/metal structure of these materials was fabricated and the dielectric response was measured up to 40 GHz using a network analyzer. It is shown that these films are not ferroelectric. However, these films show a dielectric relaxation in the frequency interval between several MHz and 1 GHz. We propose that this indicates a relaxation mechanism not related to the ferroelectric domain walls.

High frequency response of amorphous tantalum oxide thin films

Amorphous tantalum oxide films were deposited using a pulsed dc reactive magnetron sputtering technique at low temperature (/spl les/200/spl deg/C). 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.

Study of electron trapping in the amorphous tantalum oxide thin films prepared by d.c. magnetron reactive sputtering

Abstract 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.