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  • 1
    Electronic Resource
    Electronic Resource
    Chemical sputtering of Al2O3 by fluorine-containing plasmas excited by electron cyclotron resonance (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5329-5336 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reactive ion etching of aluminum oxide has been studied in CHF3 and SF6 plasmas generated by electron cyclotron resonance in conjunction with in situ ellipsometric measurement for thickness variation. Because of the involatility of etch products associated with aluminum, purely chemical reactions cannot desorb etch products at room temperatures, and ion bombardment is essential to etch Al2O3 through chemically enhanced physical sputtering. The higher the oxygen content in a film, the faster the etch rate, resulting from chemical sputtering due to volatile CO molecules in CHF3 plasmas. This dependence on composition is absent in SF6 plasma. The threshold ion energy for physi-chemical sputtering by fluorine-containing species is estimated to be about 20 eV at room temperature, while the threshold for Ar sputtering is 50 eV. In CHF3 plasmas, however, Al2O3 exhibits a larger threshold energy at a lower temperature due to passivating species which inhibit sputtering. These passivating species have a very weak binding energy of roughly 0.1 eV, which has been deduced from a temperature dependence of the threshold energy. A patterned sample always shows vertical profile without undercuts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347027
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of high vacuum and ultra-high-vacuum tantalum diffusion barrier performance against copper penetration (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 300-308 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that depositing Ta diffusion barriers under ultra-high vacuum conditions without in situ oxygen dosing allows for variations both in microstructure and in the concentration of chemical impurities that severely degrade barrier performance. The effects of deposition pressure, in situ oxygen dosing at interfaces, hydrogen and oxygen contamination, and microstructure on diffusion barrier performance to Cu diffusion for electron-beam deposited Ta are presented. 20 nm of Ta diffusion barrier followed by a 150 nm Cu conductor were deposited under ultra-high vacuum (UHV, deposition pressure of 1×10−9 to 5 ×10−8 Torr) and high vacuum (HV, deposition pressure of 1×10−7 to 5×10−6 Torr) conditions onto 〈100〉 Si. In situ resistance furnace measurements, Auger compositional depth profiling, secondary ion mass spectrometry, and forward recoil detection along with scanning and transmission electron microscopy were used to determine the electrical, chemical, and structural changes that occurred in thin-film Ta diffusion barriers upon annealing. Undosed HV deposited Ta barriers failed from 560 to 630 °C, while undosed UHV barriers failed from 310 to 630 °C. For UHV Ta barriers, in situ oxygen dosing during deposition at the Cu/Ta interface increased the failure temperatures by 30–250 °C and decreased the range of failure temperatures to 570–630 °C. Undosed UHV Ta barriers have no systematic relationship between failure temperature and deposition pressure, although correlations between breakdown temperature, oxygen and hydrogen concentrations, and microstructural variations were measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353904
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  • 3
    Electronic Resource
    Electronic Resource
    Tantalum as a diffusion barrier between copper and silicon: Failure mechanism and effect of nitrogen additions (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5433-5444 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of Cu with Si separated by thin (50 nm) layers of tantalum, Ta2N, and a nitrogen alloy of Ta has been investigated to determine the factors that affect the success of these materials as diffusion barriers to copper. Intermixing in these films was followed as a function of annealing temperature by in situ resistance measurements, Rutherford backscattering spectra, scanning electron microscopy, and cross-section transmission electron microscopy. Ta prevents Cu-silicon interaction up to 550 °C for 30 min in flowing purified He. At higher temperatures, copper penetration results in the formation of η‘-Cu3Si precipitates at the Ta-Si interface. Local defect sites appear on the surface of the sample in the early stages of this reaction. The Ta subsequently reacts with the substrate at 650 °C to form a planar hexagonal-TaSi2 layer. Ta silicide formation, which does not occur until 700 °C in a Ta-Si binary reaction couple, is accelerated by the presence of Cu. Nitrogen-alloyed Ta is a very similar diffusion barrier to Ta. It was found that Ta2N is a more effective barrier to copper penetration, preventing Cu reaction with the substrate for temperatures up to at least 650 °C for 30 min. In this case, local Cu-Si reaction occurs along with the formation of a uniform Ta5Si3 layer at the Ta2N-Si interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350566
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  • 4
    Electronic Resource
    Electronic Resource
    Temperature and substrate dependence of Ar sputtering of CoSi2 thin films (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4527-4532 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature dependence of 300 eV argon ion sputtering of CoSi2 thin films has been investigated in the range 50–600 °C. Compared with the low-temperature values, the high-temperature etch rate of CoSi2 on Si decreases by a factor of 3, while the sputtering yield ratio of Si to Co increases by a factor of 3.5. This leads to effective motion of the silicide layer into the Si substrate at temperatures above 400 °C. During sputtering of CoSi2 on SiO2, the thickness of the silicide layer decreases almost linearly with bombardment time until all the silicide is removed. Similar behavior is observed in low-temperature sputtering of CoSi2 on Si. However, at elevated temperatures (400 °C〈T≤600 °C), the etch rate of the silicide decreases significantly after an initial fast sputtering period. For CoSi2 on Si, experimental results show that while Si atoms are sputtered from the surface, Co atoms are released and diffuse to the silicide/Si interface where they react with the underlying Si substrate to form new CoSi2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351385
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  • 5
    Electronic Resource
    Electronic Resource
    Kinetic analysis of C49-TiSi2 and C54-TiSi2 formation at rapid thermal annealing rates (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4978-4980 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used in situ resistance versus temperature measurements to demonstrate that a 60 nm titanium thin film on polycrystalline silicon heated at rates up to 3000 °C/min always forms high-resistivity base-centered orthorhombic C49-TiSi2 before the low-resistivity face-centered orthorhombic C54-TiSi2 phase. Kinetic analysis of the shift in transformation temperatures with heating rate indicates that the activation energies for the formation of C49-TiSi2 and C54-TiSi2 are 2.1±0.2 and 3.8±0.5 eV, respectively, when formed during the same annealing cycle. The higher activation energy of formation of C54-TiSi2 as compared to C49-TiSi2 suggests that under very high heating rates and annealing temperatures, the formation of C49-TiSi2 before C54-TiSi2 might be completely or partially bypassed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352018
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  • 6
    Electronic Resource
    Electronic Resource
    The relationship between deposition conditions, the beta to alpha phase transformation, and stress relaxation in tantalum thin films (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4918-4924 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes a large decrease in the resistance of thin films and a complete stress relaxation in films that were intrinsically compressively stressed. 100 nm beta tantalum thin films with intrinsic stresses of 2.0×1010 dynes/cm2 (tensile) to −2.3×1010 dynes/cm2 (compressive) were deposited onto thermally oxidized (100) silicon wafers by evaporation or dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured at 10 °C/min up to 850 °C in purified helium. Upon heating, the main stress mechanisms were elastic deformation at low temperature, plastic deformation at moderate temperatures and stress relief because of the beta-to-alpha phase transition at high temperatures. The temperature ranges over which the elastic and plastic deformation and the beta-to-alpha phase transition occurred varied with deposition pressure and substrate biasing. Incomplete compressive stress relaxation at high temperatures was observed if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800 °C due to substrate biasing during the deposition. We conclude that the main stress relief mechanism for tantalum films with intrinsic compressive stresses to completely relax their stress is the beta-to-alpha phase transition, while for intrinsically tensile films, this transformation has a much smaller effect on the stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352059
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  • 7
    Electronic Resource
    Electronic Resource
    Stability of C49 and C54 phases of TiSi2 under ion bombardment (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2660-2666 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transformation of C49 phase TiSi2 to the low resistivity C54 phase is necessary for many microelectronic applications. Here, we report on attempts to decrease this transformation temperature by low-energy ion bombardment at elevated temperature. Ion irradiation was performed using a broad beam Kaufman ion source operated in N2 or Ar gas between 0.1 and 2 keV beam energy, with ion doses ranging from 2.0×1016 to 1.9×1018 ions/cm2, and sample temperatures from 480 °C to 735 °C. For comparison, room-temperature Ar+ implantation at higher energy (105–210 keV) was performed with a dose of 1016 ions/cm2 with projected ranges within and beyond the TiSi2 layer thickness. Resistivity measurements as a function of temperature, x-ray diffraction, and Rutherford backscattering spectrometry were used to determine the composition and phases. Results show that low-energy ion bombardment does not promote the C49-C54 transformation at the temperatures studied, while ion implantation actually raises the temperature for the transformation. In addition, bombardment of C54 TiSi2 does not cause it to revert to the C49 phase, indicating that both phases appear to be surprisingly stable under ion bombardment. Simulations of defect production using the trim code indicate the formation of a higher number of displaced atoms than are usually required to initiate a transformation. We conclude that the defects introduced into C49 TiSi2 by ion bombardment at energies up to 2 keV are either not sufficient to nucleate the C54 phase or they are annealed out too quickly at the temperature needed for C54 phase growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349380
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  • 8
    Electronic Resource
    Electronic Resource
    Formation of C54 TiSi2: Effects of niobium additions on the apparent activation energy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6409-6415 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of C54 TiSi2 using Ti–Nb alloys deposited on polycrystalline Si substrates was studied by means of in situ x-ray diffraction and resistance measurements during temperature ramping. Alloys with Nb contents ranging from 0 to 13.6 at. % were used. The formation temperature of C54 TiSi2 was reduced in the presence of Nb. However, the addition of Nb in Ti did not cause fundamental changes in the evolution of resistance versus temperature. This latter observation suggests that the mechanism for the formation of C54 TiSi2 remained the same in spite of the enhancement effect. For alloys with up to 8 at. % of Nb, the C49 TiSi2 phase formed first, as with pure Ti. When annealing the alloy with 13.6 at. % Nb, neither C49 TiSi2 nor C54 were found in the usual temperature ranges, instead, C40 (Nb,Ti)Si2 was observed. This phase transformed to C54 (Nb,Ti)Si2 above 950 °C. The apparent activation energy associated with the formation of C54 TiSi2 was obtained by annealing the samples at four different ramp rates from 3 to 27 K/s; it decreased continuously from 3.8 to 2.5 eV with increasing Nb content from 0 to 8 at. %. The apparent activation energy for the formation of C40 (Nb,Ti)Si2 was found to be 2.6 eV. The possible physical meaning, or lack thereof, of the high activation energies derived from experimental measurements is extensively discussed. A qualitative model is proposed whereby nucleation would be rate controlling in pure TiSi2, and interface motion in samples with 8 at. % Nb. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413952
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  • 9
    Electronic Resource
    Electronic Resource
    Mechanisms for microstructure evolution in electroplated copper thin films near room temperature (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2516-2525 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a model which accounts for the dramatic evolution in the microstructure of electroplated copper thin films near room temperature. Microstructure evolution occurs during a transient period of hours following deposition, and includes an increase in grain size, changes in preferred crystallographic texture, and decreases in resistivity, hardness, and compressive stress. The model is based on grain boundary energy in the fine-grained as-deposited films providing the underlying energy density which drives abnormal grain growth. As the grain size increases from the as-deposited value of 0.05–0.1 μm up to several microns, the model predicts a decreasing grain boundary contribution to electron scattering which allows the resistivity to decrease by tens of a percent to near-bulk values, as is observed. Concurrently, as the volume of the dilute grain boundary regions decreases, the stress is shown to change in the tensile direction by tens of a mega pascal, consistent with the measured values. The small as-deposited grain size is shown to be consistent with grain boundary pinning by a fine dispersion of particles or other pinning sites. In addition, room temperature diffusion of the pinning species along copper grain boundaries is shown to be adequate to allow the onset of abnormal grain growth after an initial incubation time, with a transient time inversely proportional to film thickness. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371086
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  • 10
    Electronic Resource
    Electronic Resource
    ADULT ectodermal dysplasia syndrome resulting from the missense mutation R298Q in the p63 gene (2004)
    Oxford, UK : Blackwell Science Ltd
    Clinical and experimental dermatology 29 (2004), S. 0 
    Details
    ISSN: 1365-2230
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Several ectodermal dysplasia syndromes have been shown to result from mutations in the gene that encodes the transcription factor p63. We describe an 11-year-old boy, with clinically normal parents, who had a developmental disorder that resembled EEC (ectrodactyly ectodermal dysplasia-clefting) syndrome (OMIM 604292). He had ectrodactyly and missing middle fingers bilaterally, onychodysplasia, hypodontia with missing teeth, hypohidrosis and lacrimal duct obstruction. DNA sequencing disclosed a heterozygous G→A substitution at nucleotide 893, that converts an arginine residue (CGA) to glutamine (CAA), the mutation being designated R298Q. This mutation occurs within the DNA-binding domain of p63, and is close to many of the published EEC syndrome mutations. However, R298Q has been described once previously in a large German pedigree, not with EEC syndrome, but another ectodermal dysplasia disorder, ADULT (acro-dermato-ungual-lacrimal-tooth) syndrome (OMIM 103285). Further clinical assessment in our patient revealed that, apart from not having cleft lip and/or palate, he had an exfoliative dermatitis of his hands and feet, and some freckling on his face and shoulders. Collectively, these features support a diagnosis of ADULT syndrome. This study has identified a specific genotype–phenotype correlation in a rare ectodermal dysplasia syndrome and the findings are useful in improving genetic counselling in this family.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2230.2004.01643.x
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