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7331. The influence of oxygen on cobalt silicide formation
Classified abstracts 7326-7333 morphology o f the silicide is strongly affected. In any case, the only crystalline silicide phase that forms is TiSi2 and not TiSi or TisSi3, as confirmed by electron diffraction and high-resolution clectron microscopy. M Heintze et al, J Phys. D : Appl Phys, 23, 1990, 1076 1081. 34 7326. Reaction between Cu and PtSi with Cr, Ti, W, and C barrier layers The Cu/PtSi metallurgy is studied for reaction and thermal stability using several barrier layers, Cr, Ti, W, and a m o r p h o u s C. Using preformed PtSi and Cr, Ti, and W barrier layers, Cu is found to react with PtSi around 350':C. The results are compared with those using similar barriers for the A1/PtSi structure, where an improvement in thermal stability by 50~ 150'C is observed. The low thermal stability of the Cu/PtSi structures is attributed to the high affinity of Cu to Si, with the Cu silicide formation starting around 200:'C for a Cu/Si structure. Using an a m o r p h o u s carbon barrier for the Cu/PtSi structure, a small a m o u n t o f C u silicide is observed at 400+C, but not at 600' C. Migration of Cu into the structure, however, makes uncertain the effectiveness of the carbon barrier. The results are compared with those of A1/C/PtSi, A1/C/Pd/Si, and C/Cu/SiOe to understand the mechanism involved. Chin-An Chang, J Appl Phys, 67, 1990, 6184 6188. 34 7327. Effect of laser-irradiation on structural and electrical properties of CdS thin films CdS films were deposited by a resistivc heating technique onto glass substrates kept at 150'~C. The films were irradiated with laser pulses of various energy densities. A pulsed laser (Nd- doped yttrium aluminum garnet) capable of producing a 20-ns pulse of 0.53 # m wavelength (frequency doubled) with varying energy densities (2 50 mJ cm 2) was employed. X-ray diffraction studies showed that the crystallinity of the films improved with laser irradiation. Direct current conductivity and Hall coefficient measurements were made on the films in the temperature range 77 300 K for both as-grown and laser-irradiated films. It was observed that both the Hall coefficient and mobility increased with an increase of energy density as well as the number of pulses. Typically, the mobility increased from 71 to 121 cm 2 V ~ s t after irradiation with 5(1 laser pulses of energy density 28 mJ cm 2. A L Dawar et al, J Appl Phys, 67, 1990, 6214 6219. 34 7328. Solid phase reaction of molybdenum-nickel ahoy thin films with silicon Solid phase reaction behavior of polycrystalline and a m o r p h o u s alloys of MoNi+ (x = 12, 20, and 88) with silicon in the temperature range 500 7 0 0 C has been studied by glancing angle X-ray diffraction and Auger electron spectroscopy techniques. Two types of reaction mechanisms are observed in these alloy/silicon reactions and both are controlled by the composition of the refractory metal component. In molybdenum-rich polycrystalline alloy (Mos~N ~2) the reaction at 500'C occurs due to outdiffusion of nickel from the alloy, while at 550'C the reaction between the alloy and silicon mainly occurs due to in-diffusion of silicon. On the other hand, in nickel-rich alloy (Mot2Nis8), the reaction at 5 0 0 C is dominated by nickel out-diffusion. The a m o r p h o u s alloy (Mo80Ni20) was found to be stable on silicon up to 500+C and a reaction at 550'C occurs due to crystallization followed by out-diffusion of nickel and large a m o u n t s of silicon in-diffusion. In all these alloy/silicon reactions, a macroscopic phase separation between MoSiz and NiSi or NiSi2 is observed and results in a two-layer structure consisting of [MoSi2+ NiSi(or NiSi2)]/NiSi (or NiSi2)/Si(100). R S Rastogi et al, J Appl Phys, 67, 1990, 6269 6273. 34 7329. Effect of third-element additions on properties of Co-Cr-based films The fundamental effects of adding several elements to the C o Cr system on the properties of Co Cr-based films were extensively investigated. Tantalum, molybdenum, vanadium, and rhenium were chosen as the additives. A large a m o u n t of each element was added to a Co 17-at% Cr film. Ta addition improved the squareness and suppressed the in-plane coercive force without lowering the perpendicular coercive force for the films with perpendicular magnetization, all the additives were effective in suppressing the grain growth. The ternary alloy films were likely to have finer grains than Co Cr films. Ta was found to be the most advantageous in a wide range of content, from the total balance of squareness, coercive force, and grain size. The recording characteristics of Co Cr Ta films 586
were also examined in comparison with those of Co Cr films. The recording density and the signal-to-noise ratio of Co Cr Ta films were appreciably higher than those of Co Cr films. M Sagoi and T lnoue, J Appl Phvs, 67, 1990, 6394 6398. 34 7330. Formation and structure of epitaxial ruthenium sificides on (11 l)Si Epitaxial ruthenium silicides have been successfully grown on silicon for the first time. Chemical electroless plating of a Ru thin film on silicon with subsequent annealing is a new approach and also the first demonstration of epitaxial growth of these silicides. Transmission electron microscopy was applied to characterize phases of silicides, microstructure, and orientation relationships. Three different epitaxial phases were found and identified to be Ru2Si> RuSi, and Ru:Si. RuSi and Ru2Si are two new phases discovered in comparison with those previously reported in thin film reactions. Furthermore, Ru2Si, was found to be a stable phase at elevated temperatures since it can be transformed t¥om Ru2Si and RuSi by sufficiently long annealing. Various diffraction patterns were analyzed and orientation relationships were determined. Moire's fringes of RuSi and interracial dislocations of Ru2Si~ and Ru2Si were found. The average spacings were measured to be t¥om 1000 to 4000 /~ for Ru2Si~/Si. The composition of the silicides was measured by scanning Auger electron spectroscopy and 2% phosphorus was found. Y S Chang and M L Chou, J Appl Phvs, 68, 1990, 2411 2414. 34 733 i. The influence of oxygen on cobalt silicide formation By evaporating cobalt onto Si(100) substrates in an oxygen ambient, oxygen concentrations of 2, 6 and 16 at% could be gettered in three cobalt films. Auger depth profiles and Rutherford backscattering spectra were obtained from samples annealed for 20 min at 440, 500, 600 and 700"C. At 440"C silicide formation is slowed down in cobalt films with a higher oxygen content. Silicide formation during 20 rain at annealing temperatures higher than about 600'C is not significantly affected by oxygen contents of 2 and 6 at%. No silicide formation occurred at these annealing temperatures for cobalt films with an oxygen content of t6 at%. The influence of oxygen on the rate of silicide formation is explained in terms of oxygen segregation according to the Langmuir relation for equilibrium interface concentration. H C Swart et al, Thin Solid Films, 189, 1990, 321 327. 34 7332. Phase formation sequence for the reaction of multUayer thin films of Nb/AI We have investigated the phasc tbrmation sequence for the reaction of Nb and A1 in multilayer films using cross-sectional transmission electron microscopy and X-ray diffraction. NbAI3 is the first intermetallic phase to form. Contrary to previous reports, we lind evidence from crosssectional transmission electron microscopy that the sigma phase, Nb:AI, is not bypassed in the reaction sequence. Instead, its formation is concurrent with the formation of the super conducting A 15 phase, Nb3AI. However, depending on the periodicity and the composition of the film, the Nb2A1 phase can be consumed by thc Nb3AI phase for long annealing times. The significance of this phase formation sequence to powder metallurgically processed magnet wire is discussed. K Barmak, J Appl Phys, 67, 1990, 7313 7322. 34 7333. Isotopic study of oxygen diffusion in silicon dioxide thin films Diffusion of oxygen in thin films of silicon dioxide has been studied using oxygen isotopically enriched in oxygen of atomic mass 18 (~O). This subject is of interest because thin films of dielectrics such as SiO2 arc proposed for usc as protective coatings for solar mirrors in low earth orbit, which is a strongly oxidizing enviromnent. Films of this material were prepared with a dc magnetron using reactive sputtering techniques. To produce t ~O-enriched SiO> a standard silicon wafer 3.5 in. in diameter was reactively sputtered using ~80-enriched (95%) molecular oxygen as the plasma feed gas. The films were characterized using Rutherford backscattering spectrometry and secondary-ion mass spectroscopy (SIMS) to establish stoichiometry and purity. Subsequently, the films were exposcd to an air-derived oxygen plasma in a standard laboratory plasma reactor for durations of up to 10 h. The concentration of ~60 as a function of depth was determined using SIMS profiling and compared with a baseline non-plasma-exposed sample. A value for the diffusivity of oxygen near the surface of these films was obtained and found to be about 10 +~cm-'s ~ a t 5 0 ' C . G A Gnfino el al, Thin Solid Films, 188, 1990, 237 246.
were also examined in comparison with those of Co Cr films. The recording density and the signal-to-noise ratio of Co Cr Ta films were appreciably higher than those of Co Cr films. M Sagoi and T lnoue, J Appl Phvs, 67, 1990, 6394 6398. 34 7330. Formation and structure of epitaxial ruthenium sificides on (11 l)Si Epitaxial ruthenium silicides have been successfully grown on silicon for the first time. Chemical electroless plating of a Ru thin film on silicon with subsequent annealing is a new approach and also the first demonstration of epitaxial growth of these silicides. Transmission electron microscopy was applied to characterize phases of silicides, microstructure, and orientation relationships. Three different epitaxial phases were found and identified to be Ru2Si> RuSi, and Ru:Si. RuSi and Ru2Si are two new phases discovered in comparison with those previously reported in thin film reactions. Furthermore, Ru2Si, was found to be a stable phase at elevated temperatures since it can be transformed t¥om Ru2Si and RuSi by sufficiently long annealing. Various diffraction patterns were analyzed and orientation relationships were determined. Moire's fringes of RuSi and interracial dislocations of Ru2Si~ and Ru2Si were found. The average spacings were measured to be t¥om 1000 to 4000 /~ for Ru2Si~/Si. The composition of the silicides was measured by scanning Auger electron spectroscopy and 2% phosphorus was found. Y S Chang and M L Chou, J Appl Phvs, 68, 1990, 2411 2414. 34 733 i. The influence of oxygen on cobalt silicide formation By evaporating cobalt onto Si(100) substrates in an oxygen ambient, oxygen concentrations of 2, 6 and 16 at% could be gettered in three cobalt films. Auger depth profiles and Rutherford backscattering spectra were obtained from samples annealed for 20 min at 440, 500, 600 and 700"C. At 440"C silicide formation is slowed down in cobalt films with a higher oxygen content. Silicide formation during 20 rain at annealing temperatures higher than about 600'C is not significantly affected by oxygen contents of 2 and 6 at%. No silicide formation occurred at these annealing temperatures for cobalt films with an oxygen content of t6 at%. The influence of oxygen on the rate of silicide formation is explained in terms of oxygen segregation according to the Langmuir relation for equilibrium interface concentration. H C Swart et al, Thin Solid Films, 189, 1990, 321 327. 34 7332. Phase formation sequence for the reaction of multUayer thin films of Nb/AI We have investigated the phasc tbrmation sequence for the reaction of Nb and A1 in multilayer films using cross-sectional transmission electron microscopy and X-ray diffraction. NbAI3 is the first intermetallic phase to form. Contrary to previous reports, we lind evidence from crosssectional transmission electron microscopy that the sigma phase, Nb:AI, is not bypassed in the reaction sequence. Instead, its formation is concurrent with the formation of the super conducting A 15 phase, Nb3AI. However, depending on the periodicity and the composition of the film, the Nb2A1 phase can be consumed by thc Nb3AI phase for long annealing times. The significance of this phase formation sequence to powder metallurgically processed magnet wire is discussed. K Barmak, J Appl Phys, 67, 1990, 7313 7322. 34 7333. Isotopic study of oxygen diffusion in silicon dioxide thin films Diffusion of oxygen in thin films of silicon dioxide has been studied using oxygen isotopically enriched in oxygen of atomic mass 18 (~O). This subject is of interest because thin films of dielectrics such as SiO2 arc proposed for usc as protective coatings for solar mirrors in low earth orbit, which is a strongly oxidizing enviromnent. Films of this material were prepared with a dc magnetron using reactive sputtering techniques. To produce t ~O-enriched SiO> a standard silicon wafer 3.5 in. in diameter was reactively sputtered using ~80-enriched (95%) molecular oxygen as the plasma feed gas. The films were characterized using Rutherford backscattering spectrometry and secondary-ion mass spectroscopy (SIMS) to establish stoichiometry and purity. Subsequently, the films were exposcd to an air-derived oxygen plasma in a standard laboratory plasma reactor for durations of up to 10 h. The concentration of ~60 as a function of depth was determined using SIMS profiling and compared with a baseline non-plasma-exposed sample. A value for the diffusivity of oxygen near the surface of these films was obtained and found to be about 10 +~cm-'s ~ a t 5 0 ' C . G A Gnfino el al, Thin Solid Films, 188, 1990, 237 246.