S. Gujrathi

Characterization of reactively evaporated TiN layers for diffusion barrier applications

Thin TiN layers have been successfully produced on Si and SiO2 by reactive evaporation combined with rapid thermal annealing. Results of composition, resistivity, and stress measurements on these layers are reported. The TiN layers have a resistivity around 40 μΩ cm and a high stress of between 1 and 6 GPa. The composition ratio of nitrogen to titanium, measured by elastic recoil detection (ERD), combined with time‐of‐flight, was found to vary between 0.8 and 1.0 depending on the deposition conditions. In addition to the stoichiometry determination, ERD also clearly shows the presence of a TiSi2 layer between the TiN and the Si substrate. It is also shown that good TiN layers can be produced by reactive evaporation for nitrogen partial pressures between 1.0 and 2.0×10−5 mbar and for titanium evaporation rates between 0.3 and 0.5 nm/s.

XPS and FTIR analysis of nitrogen incorporation in CNx thin films

Abstract CNX thin films have been deposited on Si(100) substrates using a new hybrid deposition system. This system combines excimer laser ablation of a graphite target and an atomic nitrogen source from a remote surface wave plasma. The films were characterized using X-ray photoelectron spectroscopy (XPS), elastic recoil detection (ERD) and Fourier transform infrared spectroscopy (FTIR). We found that the atomic nitrogen source enhances the incorporation of N in the CN x layers, for example, from N/C = 0.04 (plasma off) to 0.18 (plasma on). In addition, as nitrogen pressure in the deposition chamber is increased from 2mTorr to 1 Torr, the N/C ratio increases from 0.18 to 0.56. The XPS and FTIR spectra indicate that at deposition pressures above 100 mTorr, nitrogen incorporation is enhanced through the formation of hydrogenated carbon nitride groups, while at lower pressures, only simple and double CN bonds are detected.

Heavy-ion energy resolution of SSB detectors

Abstract The energy resolution of the silicon surface barrier detectors currently used for ERD (elastic recoil detection) and HIRBS (heavy-ion Rutherford backscattering spectroscopy) limits both the mass and depth resolution achieveable. Although the timing properties and pulse height defect of SSBDs have been well documented, only limited studies of their heavy-ion energy resolution in the energy range 5–20 MeV were available. Data on the energy resolution and line shape of two Ortec BA-017-100-100 detectors are presented and compared with a survey of SSB detector resolution data available in the literature.

Pulse height defects for 16O, 35Cl and 81Br ions in silicon surface barrier detectors

Abstract The total pulse height defects (PHDs) of a silicon surface barrier detector (SSBD) for 16 O, 35 Cl and 81 Br ions in the energy range 2–40 MeV have been measured. To evaluate the contribution E w of the dead layer, its thickness was measured using α-particles. The nuclear defect E n was calculated in first-order approximation, using Zieglers values [J.F. Ziegler, J.P. Biersack and U. Littmark, The Stopping and Ranges of Ions in Matter, vol. 1 (Pergamon Press, New York, 1985)] for both the nuclear and the electronic stopping powers, and the results are compared with other calculations of E n . The observed total defects could be essentially accounted for by E w + E n , suggesting that E r , the contribution due to residual defects, is small, in agreement with estimates based on the plasma recombination model [E.C. Finch et al., Nucl. Instr. and Meth. 163 (1979) 467].

Depth profiling of hydrogen using the high efficiency ERD-TOF technique

Abstract The hydrogen detection efficiency using the ERD-TOF technique, based on the use of 10 μg/cm2 carbon foil as a start detector, was measured with respect to the second conventional ERD detector with an absorber placed at nearly comparable geometry in the same experiment. The probing beams were 30 MeV 35Cl and 4 MeV 4He, with a detection angle of 30 ° with equal entrance and exit angles with respect to the target surface. From the studies of films of Mylar, Kapton and deuterated polyethylene as well as PECVD a-Si:H, Si3N4, and a-C:H targets, the ERD-TOF hydrogen efficiency was found to be ∼ 40% at 2.43 MeV hydrogen recoils, which increased gradually at lower energies. The hydrogen detection efficiency was also studied as a function of the MCP detector bias by scattering 1 and 3 MeV protons from a thin (100 A) Au film. The energy variation in the efficiency using nearly saturated MCP detector bias was found to be proportional to the energy loss ( d E d x ) of protons in the carbon. A considerable improvement in the efficiency was noted by coating the carbon foil with a thin low density MgO layer. The hydrogen depth profiles using the ERD-TOF technique show better depth resolution and an increased accessible depth than the ERD using absorber. The improved depth resolution, along with the intrinsic ability of the ERD-TOF technique to completely resolve the light element recoils, can be applied in many fields such as the study of hydrogen diffusion in double layer LPCVD Si3N4 structures and polymer diffusions with lower diffusion coefficients.

An ERD/RBS/PIXE apparatus for surface analysis and channeling

Abstract A system for surface analysis, lattice localisation of impurities, defect studies in crystalline solids and routine ERD (elastic recoil detection) is described. The apparatus features a high vacuum chamber, a computer controlled precision goniometer and an energy plus time-of-flight mass discrimination system. First results of channeling/ERD experiments using 15–30 MeV 35Cl beams on silicon crystals implanted with B+ and BF2+ are presented, as well as data on the effect of beam induced damage on the boron distribution.

An iterative computer analysis package for elastic recoil detection (ERD) experiments

Abstract A computer program for routinely calculating the depth profiles of elements in the surface layers of solids from experimental elastic recoil detection (ERD) spectra is described. The program, which is capable of handling a large number of multielement layers, rapidly converges to yield accurate atomic concentration ratios without any a priori assumptions about the composition of an unknown target. The analysis package contains a menu-driven database which facilitates the manipulation and storage of data. It meets the analysis needs of thin-film material sciences, such as microelectronics, where consistent, accurate and fast turnaround of data from a large number of samples is demanded. The output contains a summary of the average concentrations, the widths (in μg/cm2) of each layer, the mass and energy spectra, the individual element depth profile plots as well as a composite depth profile plot of all the elements under consideration.

The detection of heavy ions with PIN diodes

Abstract The pulse height defect (PHD) and the resolution (ΔE) of a low-cost PIN photodiode (Hamamatsu Model S 1223-01) have been studied for 11B (0.2–16.2 MeV), 35Cl (1.0–8.2 MeV) and 81Br (0.5–8.0 MeV) ions, and found comparable to those of ORTEC silicon surface barrier detectors. The major contribution to the difference in performance of the PIN diode may come from the surface dead-layer which was measured to be 90 ± 11 nm. The dependence of diode properties on the bias voltage shows that even at 0 V the relative pulse height is ≥95% of the value of saturation which is attained within 5 V. The relative resolution (ΔE/E) is nearly constant for all bias values up to 30 V (maximum reverse bias). Some preliminary results on the effect of radiation dose on the leakage current are also presented. These results demonstrate that the low-cost PIN diode can be successfully used as a charged-particle detector in applications such as ion beam analysis (RBS, HIRBS, ERD) and space technology.

Lifetime of 19 Ne * (4.03 MeV)

The Doppler-shift attenuation method was applied to measure the lifetime of the 4.03 MeV state in {sup 19}Ne. By utilizing a {sup 3}He-implanted Au foil as a target, the state was populated using the {sup 20}Ne({sup 3}He, {alpha}){sup 19}Ne reaction in inverse kinematics at a {sup 20}Ne beam energy of 34 MeV. De-excitation {gamma} rays were detected in coincidence with {alpha} particles. At the 1{sigma} level, the lifetime was determined to be 11{sub -3}{sup +4} fs and at the 95.45% confidence level the lifetime is 11{sub -7}{sup +8} fs.

Effect of the oxidation of TiN on the stability of the Al/TiN interface

The stability of TiN barriers deposited between Si or SiO2 substrates and AlSiCu metallic alloy contacts was investigated as a function of the sintering temperature and of the application of an oxidation step to the barrier. It was found that Al penetrates the barrier during the sintering at 450 °C for 1 h, which also results in the diffusion of Ti inside the Al alloy. This mutual interdiffusion increases with temperature but when oxygen is present at the barrier surface, the intensity of diffusion processes decreases considerably. It is also established that the barrier remains more stable on SiO2 than on the Si substrate. It is suggested that the better reaction resistance of oxidized TiN compared with oxygen‐free nitride may be due to the blocking of fast‐diffusion paths of Al diffusion by oxygen and subsequently the formation of Al2O3, AlN, and TiAl3 phases during sintering.