Post-deposition Annealing Conditions Research Articles

Deposition process effect on crystalline structure of (Pb, La) TiO3thin films by multi – ion – beam reactive cosputtering technique

Abstract Multi—ion—beam reactive cosputtering (MIBRECS) technique is a promising technique for preparing multi—component oxide thin films. However, the deposition processes are critically important for preparing thin films with prospected stoichiometry and good quality. In this paper, the effect of deposition processes, such as substrate temperature, ion beam energy and current, and the postdeposition annealing conditions on the composition and crystalline structure of (Pb, La) TiO3 ferroelectric thin films prepared by MIBRECS technique are reported.

Thin Oxynitride Films Prepared by Low Pressure Rapid Thermal Chemical Vapor Deposition

ABSTRACTThin silicon oxynitride (Si-O-N) films have been deposited using low pressure rapid thermal chemical vapor deposition (RTCVD) with silane (SiH4), nitrous oxide (N2O), and ammonia (NH3) as the reactive gases. Structural analysis coupled with a study of deposition conditions indicate that an increase in NH3/N2O flow rate ratios leads to an increased N/O atomic ratio and a decreased Si-O-N deposition rate. Thin film (55-75A) polySi/Si-N-O/Si capacitors and transistors were fabricated for NH3/N2O flow rate ratios from 20% to 100%. Some of the films were subjected to a post deposition anneal at 950°C for 15 seconds in both argon and oxygen. Capacitance voltage measurements indicate a mid-gap interface trap density of ≤ 6 × 1010 eV−1cm−2 for all the films independent of both nitrogen content and post deposition annealing conditions. The transconductance was studied as a function of NH3/N2O flow rate ratio and decreasing peak gm values but improved high field degradation was observed for increased nitrogen content. This is consistent with previous work on nitrided oxides and suggests that the films are under tensile stress. Hot carrier stress at maximum substrate current was performed with the Si-O-N films displaying larger threshold voltage shifts when compared to furnace SiO2 indicating the possible existence of hydrogen related traps.

Aerosol assisted chemical vapor deposition of superconducting YBa 2Cu 3O 7−χ

A hybrid process, aerosol-assisted chemical vapor deposotion (AACVD), is described for reproducible preparation of superconducting thin films of YBa 2Cu 3O 7−χ. The process consists of atomizing a toluene solution of the Y, Ba, and Cu tetramethylheptanedionato complexes using an aerosol generator. The aerosol is transported into a CVD reactor where solvent and precursor evaporation and deposition occur at atmospheric pressure on heated substrates. The process provides stable evaporation rates for all three precursors, yielding constant film stoichiometry throughout the deposition period and from film to film. Superconducting films may be deposited in-situ at substrate heater temperatures above 825°C, or may be formed at lower temperatures by deposition followed by post-deposition annealing at higher temperatures. The microstructure and quality of films are highly dependent on the conditions employed in deposition and in the case of films deposited below 825°C, the post-deposition annealing conditions. Superconducting films prepared by the AACVD/post-annealing process have a metallic normal state resistivity signature with a zero resistance temperature typically above 88K, and are highly c-axis oriented. Transport critical current densities measured at 75 K on polycrystalline films prepared by the AACVD process are 220 000 A/cm 2 and 84 000 A/cm 2 at self-field and 0.1 T, respectively.

Highly Reliable WGe Ohmic Contact to GaAs-AlGaAs HBTs

ABSTRACTWe report a highly reliable, sputtered WGe emitter contact for npn heterojunction bipolartransistors. A specific contact resistance of 7.5 × 10−7 Ω-cm2 and a transfer resistance of 4.0 × 10−2 Ωmm were obtained after 380°C, 1 min alloy. The contact was patterned by SF6 dry etching at low bias using a Au mask. This novel contact has comparable resistance to conventional AuGe-based metallization while having superior thermal stability. We have studied the dependence of contact properties on the post-deposition annealing conditions by transfer length method of electrical characterization and Auger analysis, and will also report long-term reliability results in comparison to AuGe-based metallization.

In situ pulsed laser deposition of Nd1.85Ce0.15CuO4−y

Thin films of the electron-charge-carrying high-temperature superconductor, Nd1.85Ce0.15CuO4−y have been deposited by pulsed laser deposition on to 〈100〉 MgO and SrTiO3 substrates. Film composition, structure, and transport properties were measured as a function of deposition conditions (substrate temperature, oxygen deposition pressure, and postdeposition annealing conditions). C-axis oriented, single-phase films were formed at high substrate temperatures (900 °C) in high background pressures of oxygen (200 mTorr), but were semiconducting when quenched to room temperature in either oxygen or nitrogen. A reduced oxygen background pressure during deposition at 900 °C resulted in films that were transparent and insulating due to the loss of copper. Films which were deposited at 900 °C (Poxygen≥200 mTorr) and then slowly cooled in a vacuum were superconducting with a maximum Tc (onset) of 15 K and Tc(R = 0) of 11 K.

Interface state densities for metal-nitride-oxide-silicon devices

The interface state density of metal-nitride-oxide-silicon (MNOS) devices was investigated as a function of silicon nitride (Si3N4) deposition temperature and postdeposition annealing conditions. The interface state density around the midgap of the oxide-silicon interface of the MNOS structures as a function of deposition temperature between 650 to 850 °C increased from 1.1 to 8.2×1011 cm−2 eV−1, for as-deposited silicon nitride films,; but decreased from 5.0 to 3.5×1011 cm−2 eV−1, for films annealed in nitrogen at 900 °C for 60 min; and further decreased and remained constant at 1.5×1011 cm−2 eV−1, for films which were further annealed in hydrogen at 900 °C for an additional 60 min. The interface state density increase is due to an increase in the loss of hydrogen at the interfacial region and also due to an increase in the thermal stress caused by differences in thermal expansion coefficients of silicon nitride and silicon dioxide films at higher deposition temperatures. The interface state density is subject to two opposing influences; an increase by thermal stress, and a reduction by hydrogen compensation of these states. Thus either low-temperature processing or subsequent hydrogen annealing after high processing temperatures is warranted.

Superconducting thin films of Bi-Sr-Ca-Cu-O obtained by laser ablation processing

Thin films of Bi-Sr-Ca-Cu-O, deposited on (100) cubic zirconia by laser ablation from a bulk superconducting target of nominal composition BiSrCaCu2 Ox , have been investigated by dc resistance and magnetically modulated microwave absorption measurements. The latter technique reveals important features regarding the phase purity of superconducting samples that are masked in the dc resistance measurements. The superconducting behavior of the films, as a function of the substrate temperature during deposition and the post-deposition annealing conditions, is discussed.

Preparation of high-Tc Y-BA-CU-O superconducting films by plasma spraying and suspension methods

Superconducting thick films of Y-Ba-Cu-O materials of abaut 20 μm were deposited on different ceramic and metallic substrates by methods like plasma spraying, screen printing, electrophoretic deposition and painting. Electrical resistivity, critical current density, and microstructure of the films were studied for the different deposition and for the different post-deposition annealing conditions. The films exhibited superconductivity at 87 K. Critical current densities of 100 – 270 A/cm 2 were achieved on plasma-sprayed films.

Growth of YBa 2Cu 3O 7− x thin films by ion beam sputtering

Polycrystalline, superconducting YBa 2Cu 3O 7− x films have been grown by ion beam sputtering (IBS) of bulk stoichiometric ceramic target. We found that the superconducting properties of the films are very sensitive to the choice of the substrates and post-deposition annealing conditions. Films deposited on SrTiO 3 substrates were found to be the best with a critical onset transition temperature, T c to be as high as 95 K with a maximum current carrying capacity in superconducting state of 1.5 × 10 5 A/cm 2 which is close to the best reported value for single-crystal YBa 2Cu 3O 7− x films.

Defect structures in tetrahedral amorphous thin film materials

The dependence of the optical and transport properties of tetrahedral amorphous thin film materials on deposition and post-deposition annealing conditions is known to relate to the reactivity of defect structures (voids and dangling bonds) that are incorporated into the films during the growth process. Plasma deposition techniques such as the glow discharge decomposition of silane (SiH 4) or sputtering in reactive (ArH 2) gas mixtures are effective in passivating (or hydrogenating) silicon dangling bonds and thereby producing films with low numbers of recombination centers. However, results indicate that it is equally important to eliminate the microstructure as well in order to achieve material that shows no post-deposition oxidation and is suitable for opto-electronic applications, e.g. solar cells, photoreceptors, thin film transistors etc. In this paper details of the reactive deposition process are reviewed, particularly the role of bombardment by charged particles in obtaining structurally and compositionally homogeneous hydrogenated amorphous silicon and SiO 2.