A.M. Narsale

Stoichiometry in Ti-N barrier layers studied by X-ray emission spectroscopy☆

Titanium nitride is an interesting material for use in microelectronic devices, particularly for use as a barrier layer. Considerable work has been done on these films and the relationdhip between the resistivity and film composition is now fairly well known, with the minimum resistivity occuring at the stoichiometric concentration. However, it is rather difficult to evaluate quantitatively the deviation of the film composition from the stoichiometry. We have produced Ti-N films with d.c. reactive sputtering at different nitrogen concentrations. These films were characterized with Auger electron spectroscopy and wavelength dispersive spectroscopy (WDS) and with X-ray diffraction. The experimental results of resistivity vs. WDS Kα line shifts indicate a possible relationship between these two quantities. It could then be feasible to use the WDS Kα line shifts for determining the resistivity of films near the stoichiometric composition.

Structural investigation of Al2O3 formed by ion implantation at various doses

Abstract X-ray diffraction using Seeman-Bohlin geometry and scanning electron microscopy measurements have been carried out on 30 keV O+2-implanted Al at various doses. At doses less than 5 × 1017 O atoms cm−2, γ-Al2O3 is prominently seen. α-Al2O3 is also formed. At higher doses, the XRD spectrum is similar to that of an amorphous surface with a few sharp lines due to α, gg and Al phases. The SEM micrographs show bubbles at low doses, with a maximum concentration at a dose of 5 × 1017 O atoms cm−2. The specimen implanted at a dose of 1 × 1018 O atoms cm−2 reveals no structure in SEM micrographs, as expected for a flat amorphous surface, correlating well with the XRD results. The bubbles give evidence of bombardment induced O loss as predicted recently using the surface binding energy effects. The proposals that the crystal structure of γ-Al2O3 is stable and α-Al2O3 becomes amorphous under ion bombardment, fit well with the present observations.

Study of aluminium oxide films formed by plasma anodization

Abstract Anodic oxidation plays an important role in microelectronics as well as in thin film devices. Oxide films obtained on metals such as aluminium and tantalum by anodization using a gaseous electrolyte are found to be superior to those formed by using aqueous solution. Earlier researchers have shown that anodization can be carried out more efficiently at an optimum pressure of 6.7 Pa (50 mTorr) and an optimum bias voltage of 5 V. It is also reported that the optimum pressure depends on the system geometry. This work was carried out to determine the effect of cylindrical geometry. It is observed that the optimum pressure for the cylindrical geometry is 26.8 Pa (200 m Torr) while the optimum bias voltage is found to be 5 V. Formation of Al 2 O 3 is confirmed by using electron spectroscopy for chemical analysis. Small-angle X-ray diffraction results indicate the formation of the γAl 2 O 3 phase at low bias voltageswhereas the βAl 2 O 3 phase is more dominant at higher bias voltages.

Sample curvature and dislocation density studies on ion-implanted GaAs by x-ray diffraction

We have studied semi-insulating (001) GaAs wafers implanted with 70 MeV 120Sn ions to various doses ranging from 5 × 1012 to 5 × 1014 ions cm−2 following the procedures in our earlier work, Nair et al (2001 Nucl. Instrum. Methods B 184 515–22). The sample curvature is studied at various doses and compared with the theoretically expected values. Also, a survey of some reported implantations with similar experimental data has been carried out for comparison. The bending of the sample, related to defects and linear dislocation density due to implantation, is modelled and compared with the estimates for the same by x-ray diffraction. The samples have been annealed using a rapid thermal annealing system and the variation in curvature and dislocation density with annealing temperature has been studied.

Superconductor ferromagnet bilayers; experimental investigation of spin polarized transport across the interface

Deposition of high temperature superconducting thin films by pulsed laser deposition (PLD) started a flurry of activities in the area of rare earth class of oxide manganites. Studies have been carried out by injection of the polarized spins from a ferromagnetic metal, into the superconductor via a thin insulating barrier. However because of the presence of an insulating layer possible role of joule heating in limiting the spin polarized transport across the interface cannot be ruled out. We would like to present some of the results of our work carried out on LaAlO3/La0.7Ca0.3MnO3/YBa2Cu3O7-δ (LAO/LCMO/YBCO) LCMO on top and LaAlO3//YBa2Cu3O7-δ La0.7 Ca0.3 MnO3 (LAO/YBCO/LCMO) YBCO on top heterostructures deposited on LAO substrates without any insulating layer separating the two. PLD technique was used to deposit a 500 micron wide line of LCMO followed by deposition of YBCO layer which was subsequently patterned into a 500 micron line directly on top of the LCMO line. Here we report the suppression in the critical current Ic of the superconductor due to pair-breaking phenomenon when polarized spins are injected into YBCO in case of LAO/LCMO/YBCO (LCMO on top) sample. Surface and interface characterization of these bilayers was performed by SQUID, AFM, SIMS and four probe techniques.

Electrical characteristics of high-energy 120Sn implantation in n+GaAs

Abstract Single crystal n + GaAs substrates of 〈1 0 0〉 orientation have been implanted at room temperature with 120 Sn ions at 70 MeV energy to varying doses of 1×10 14 , 1×10 13 and 1×10 12 ions / cm 2 . The room temperature I – V characteristics of as-implanted samples were recorded from which their effective resistance was obtained. The samples implanted to the dose of 1×10 13 ions / cm 2 were annealed to various temperatures between 100°C and 1000°C and their room temperature resistance was measured. Low-temperature resistance measurements of samples implanted to the dose of 1×10 13 ions / cm 2 indicate that for samples annealed up to 350°C, the conduction mechanism is dominated by variable range hopping. The electrical conduction for the sample annealed at 450°C is dominated by carriers in the extended states at room temperature and above.

Evaluation of electrical properties of vanadium suicide-silicon Schottky diodes formed by ion implantation

Vanadium suicide Schottky diodes are fabricated using high-dose ion implantation on p-type single-crystal silicon substrates. Their electrical properties are evaluated using the resistivity, current-voltage (IV), and capacitance-voltage (CV) techniques. The resistivity of these layers decreases on annealing, and a metallic behaviour of the suicide surface layer is observed. The temperature coefficient of resistance (a) is found to be 6.8 × 10−3/K. The barrier height φb measured using the IV technique is 0.75 eV. This high value of φb is the result of formation of inversion layer at the suicide-silicon interface. On annealing the diode at 750°C for 30 min, the ideality factor n improves to 1.01 indicating that the current transport is mainly by the thermionic emission process across the junction. The φb value measured using the Cz.sbnd;V method differs from that obtained by IV measurements. This discrepancy is attributed to the presence of multiphase suicide contact and the implant damage.