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7607. The impact of the metallization technology on junction behavior
Classified abstracts 7604-7612 four elements. In addition, a method is suggested to estimate u n k n o w n free energies of formation from observations of thin-film reactions and stability. A S Bhansali et al, J Appl Phys, 68, 1990, 1043-1049. 34 7604. Au/Pt/Ti contacts to p-In0.s3Gao.47As and n-lnP layers formed by a single metallization common step and rapid thermal processing We have demonstrated the viability of depositing a thick A u bonding pad on top of Pt/Ti contacts on both p - I n G a A s and n-lnP within a single evaporation prior to heat treatment. This eliminates the usual post-sinter Au plating process. In particular, A u (500 nm)/Pt (60 nm)/Ti (50 nm) c o m m o n c o n t a c t s t o Z n - d o p e d 5 x 10~Scm 3p-In0.~3Gao.47AsandS-doped 1 x I0 ~8cm -3 n-InP were formed within a single p u m p d o w n electron-gun evaporation and subsequently a single sintering process by means of rapid thermal processing. The lowest resistivity of these ohmic contacts were found to be 0.11 and 0.13 f~ m m (5.5 x 10 -7 and 8 x 10 -6 f~ cm 2) for the p and n contacts, respectively. These values were achieved as a result of heating at 450°C for 30 s. This heat treatment caused a limited reaction at the A ~ P t and PNTi interfaces, which did not lead to any significant intermixing of the Ti and Au. Thus, no significant indiffusion of the Au through the Pt barrier was observed and contact degradation did not occur. The stress of the as-deposited trilayer structure on InP was found to be 3 x l0 s dyn cm 2 tensile and increased to about 2 x 109 dyn cm 2 as a result of the rapid thermal processing at 450°C. A Katz et al, J Appl Phys, 68, 1990, 1123 1128. 34 7605. Growth of native oxide on a silicon surface The control factors controlling the growth of native silicon oxide (Si) surfaces have been identified. The coexistence of oxygen and water or moisture is required for growth of native oxide both in air and in ultrapure water at room temperature. Layer-by-layer growth of native oxide films occurs on Si surfaces exposed to air. Growth of native oxides on n-Si in ultrapure water is described by a parabolic law, while the native oxide film thickness on n+-Si in ultrapure water saturates at 10 A. The native oxide growth on n-Si in ultrapure water is continuously accompanied by a dissolution of Si into the water and degrades the atomic flatness at the oxide-Si interface, producing a rough oxide surface. A dissolution of Si into the water has not been observed for the Si wafer having surface covered by the native oxide grown in air. Native oxides grown in air and in ultrapure de-ionized water have been demonstrated experimentally to exhibit remarkable differences such as contact angles of ultrapure water drops and chemical binding energy. These chemical bond structures for native oxide films grown in air and in ultrapure water are also discussed. M Morita et al, J Appl Phys, 68, 1990, 1272 1281. 34 7606. A study of Ni-Ge interdiffusion on GaAs using rapid thermal annearing with temperature standards A new technique for probing rapid material interactions at low temperatures has been developed. Rapid thermal annealing at 200 and 250°C is exploited as a temperature-time probe to study the fast kinetics of N i - G e and N i ~ G e - A u contact metallizations on GaAs. Temperature standards are employed to establish known reaction temperatures within - 3 to + 13°C & n o m i n a l , while anneal times are limited to 30 s or less. Rutherford backseattering analysis of annealed samples indicates that Ge consumption obeys parabolic kinetics, most likely limited by Ni diffusion, consistent with the growth of a NixGe phase. An activation energy estimate ~ 0 . 7 eV is shown to be consistent with the fast interdiffusion observed, which is attributed to a grain boundary mechanism. The presence of A u plays only a limited role in the reaction for the temperatures and times studied. M B Brooks and T W Sigmon, J Appl Phys, 68, 1990, 1641 1648. 34 7607. The impact of the metallization technology on junction behavior The influence of a t i t a n i u m ~ i t a n i u m nitride (Ti/TiN) barrier metallization on the behavior of junctions has been investigated. Different geometries have been used in order to separate the various contributions to the electrical behavior of junctions. A n increase of the reverse current of junctions is observed in the presence of Ti/TiN/A1 : Si contacts. This fact does not produce an increase of junction defect density, since the reverse current of junctions remains within an acceptable range. The contribution to junction reverse current induced by Ti/TiN/A1 : Si contacts has been characterized ; it has been shown that it is related to contact 686
perimeter, it is independent o f m a n y relevant process steps, and it is reduced by thermal treatments after metal deposition. By assuming that this contribution is due to a generation-recombination center induced by Ti/TiN contacts, the analysis of current voltage characteristics versus temperature gives an activation energy for this contribution. However, at present the available data do not allow us to identify its cause. M L Porignano and N Circelli, JAppl Phys, 68, 1990, 1869-1877. 34 7608. Thermal diffusivity of amorphous semiconductor superlattice films The thermal diffusivity of a series of a m o r p h o u s semiconductor superlattice films (a-Si:H/a-SiNx:H, where a - S i : H is hydrogenated amorphous silicon and a-SiNx : H is hydrogenated a m o r p h o u s SiNx) has been investigated both experimentally and theoretically. The mirage effect detection technique has been used to determine the difference between two phase measurements of photothermal signals, where the heating beam illuminates the front and the rear surface of the sample successively. Using a one-dimensional model and an appropriate theoretical calculation, we have been able to determine the thermal diffusivity of the superlattices by the experimental measurement of the phase lag. These results are in good quantitative agreement with a model based on the effective medium approximation. Z C Zhang et al, Thin Solid Films, 186, 1990, 361 366. 34 7609. Annealing-induced structural changes in tellurium dioxide thin films Tellurium dioxide (TeO2) thin films grown in a m o r p h o u s phase up to a substrate temperature o f 200°C undergo phase transformation in the polycrystalline state, when annealed, from a mixed phase of orthorhombic and tetragonal structure to pure tetragonal structure as a function of annealing temperature. X-ray diffraction and transmission electron microscopy have been used for elucidation of structural details and scanning electron microscopy has been employed to study surface topography of the films. Shiv Kumar and Abhai Mansingh, J Phys D: Appl Phys, 23, 1990, 1252 1255. 34 7610. Role of recoil implanted oxygen in determining boron diffusion in silicon Annealing of silicon implanted with boron through a surface oxide results in an enhanced diffusion of boron. This enhanced diffusion is suppressed during an initial incubation period. An activation energy o f 2 eV is associated with the enhanced diffusion, indicating excess silicon interstitials m a y be involved. On the other hand, the process leading to the onset of enhanced diffusion possesses an apparent activation energy of 3.7 eV. Two-step annealing reduces the latter value to 2.6 eV, the activation energy for interstitial oxygen diffusion. The different activation energies evaluated for the saturation process will be discussed. Transmission electron microscopy shows that the coalescence of dislocations, as well as the growth of faulted loops, proceeds rapidly after the incubation period for enhanced diffusion. Precipitates along small dislocation loops are also observed after the incubation period. It is proposed that oxygen precipitation, with emission of silicon interstitials, predominates for annealing beyond the incubation period and is therefore responsible for the enhanced diffusion o f boron. The enhanced diffusion sequence is initially incubated by trapping oxygen at dislocations. The real onset of the enhanced diffusion occurs when the dislocations are saturated and the oxide precipitation at the dislocations commences. D Fan and R J Jaccodine, J Appl Phys, 67, 1990, 6135~140. 34 7611. SiO diffusion during thermal decomposition of SiO2 Chemically prepared thin oxide films were decomposed in an ultrahigh vacuum at temperatures of between 760 and 850°C. By measuring the remaining oxide thickness as a function of time we could extract the diffusion coefficient o f SiO in SiO2. This was determined to be D(cm 2 s - I ) = 1.48×10 3 exp ( 3.2 eV kT ~). The results arc discussed in respect to an appropriate heat cleaning of wafers in a Si-molecular-beam epitaxial system. H-E Sasse and U K6nig, J Appl Phys, 67, 1990, 619445196. 34 7612. Formation and high-temperature stability of CoSi. films on a n S i O 2 substrate A thin ~-Co layer with an a m o r p h o u s Si underlayer has been sputter
perimeter, it is independent o f m a n y relevant process steps, and it is reduced by thermal treatments after metal deposition. By assuming that this contribution is due to a generation-recombination center induced by Ti/TiN contacts, the analysis of current voltage characteristics versus temperature gives an activation energy for this contribution. However, at present the available data do not allow us to identify its cause. M L Porignano and N Circelli, JAppl Phys, 68, 1990, 1869-1877. 34 7608. Thermal diffusivity of amorphous semiconductor superlattice films The thermal diffusivity of a series of a m o r p h o u s semiconductor superlattice films (a-Si:H/a-SiNx:H, where a - S i : H is hydrogenated amorphous silicon and a-SiNx : H is hydrogenated a m o r p h o u s SiNx) has been investigated both experimentally and theoretically. The mirage effect detection technique has been used to determine the difference between two phase measurements of photothermal signals, where the heating beam illuminates the front and the rear surface of the sample successively. Using a one-dimensional model and an appropriate theoretical calculation, we have been able to determine the thermal diffusivity of the superlattices by the experimental measurement of the phase lag. These results are in good quantitative agreement with a model based on the effective medium approximation. Z C Zhang et al, Thin Solid Films, 186, 1990, 361 366. 34 7609. Annealing-induced structural changes in tellurium dioxide thin films Tellurium dioxide (TeO2) thin films grown in a m o r p h o u s phase up to a substrate temperature o f 200°C undergo phase transformation in the polycrystalline state, when annealed, from a mixed phase of orthorhombic and tetragonal structure to pure tetragonal structure as a function of annealing temperature. X-ray diffraction and transmission electron microscopy have been used for elucidation of structural details and scanning electron microscopy has been employed to study surface topography of the films. Shiv Kumar and Abhai Mansingh, J Phys D: Appl Phys, 23, 1990, 1252 1255. 34 7610. Role of recoil implanted oxygen in determining boron diffusion in silicon Annealing of silicon implanted with boron through a surface oxide results in an enhanced diffusion of boron. This enhanced diffusion is suppressed during an initial incubation period. An activation energy o f 2 eV is associated with the enhanced diffusion, indicating excess silicon interstitials m a y be involved. On the other hand, the process leading to the onset of enhanced diffusion possesses an apparent activation energy of 3.7 eV. Two-step annealing reduces the latter value to 2.6 eV, the activation energy for interstitial oxygen diffusion. The different activation energies evaluated for the saturation process will be discussed. Transmission electron microscopy shows that the coalescence of dislocations, as well as the growth of faulted loops, proceeds rapidly after the incubation period for enhanced diffusion. Precipitates along small dislocation loops are also observed after the incubation period. It is proposed that oxygen precipitation, with emission of silicon interstitials, predominates for annealing beyond the incubation period and is therefore responsible for the enhanced diffusion o f boron. The enhanced diffusion sequence is initially incubated by trapping oxygen at dislocations. The real onset of the enhanced diffusion occurs when the dislocations are saturated and the oxide precipitation at the dislocations commences. D Fan and R J Jaccodine, J Appl Phys, 67, 1990, 6135~140. 34 7611. SiO diffusion during thermal decomposition of SiO2 Chemically prepared thin oxide films were decomposed in an ultrahigh vacuum at temperatures of between 760 and 850°C. By measuring the remaining oxide thickness as a function of time we could extract the diffusion coefficient o f SiO in SiO2. This was determined to be D(cm 2 s - I ) = 1.48×10 3 exp ( 3.2 eV kT ~). The results arc discussed in respect to an appropriate heat cleaning of wafers in a Si-molecular-beam epitaxial system. H-E Sasse and U K6nig, J Appl Phys, 67, 1990, 619445196. 34 7612. Formation and high-temperature stability of CoSi. films on a n S i O 2 substrate A thin ~-Co layer with an a m o r p h o u s Si underlayer has been sputter