High-resistance Phase Research Articles

Characterization of phase transformation in titanium polycide films

Silicide formation on polysilicon from deposited titanium films and effects of subsequent thermal annealing at different temperatures (C-C) have been investigated by grazing-angle XRD, AFM, ESCA and sheet resistance measurements. The results indicated formation of a high-resistivity isomorphic phase (C49), polymorphic phases (C49 and C54) and low-resistivity isomorphic C54 films at low, medium and high annealing temperatures from C to C. The complete conversion from C49 to isomorphic C54 phase occurs at about C. The influence of phase formations and polymorphic transformation on the surface morphology is studied by estimating the r.m.s. surface roughness using AFM. Samples annealed at C have the highest surface roughness of 15.47 nm owing to agglomeration of C54 grains in films. XPS studies showed the formation of a thin layer of on the surface of .

Low frequency noise analysis as a diagnostic tool to assess the quality of 0.25μm Ti-silicided poly lines

In this paper, do and low frequency noise measurement results on Ti-silicided poly lines are presented and analysed. Besides Raman scattering [1], low frequency noise analysis gives additional information on the presence and the spatial distribution of the high resistive C49 phase in the silicide line. The low frequency noise is strongly dependent on whether or not the distribution of the C49 phase is uniform or spotted-like. The experimental results agree with our model for a uniform C49 phase distribution over the silicided line. A spotted-like distribution of the C49 phase, which causes non-uniform current densities, can not explain the observed noise behaviour.

Spectroscopic ellipsometry investigation of nickel silicide formation by rapid thermal process

Titanium and cobalt silicides are used widely in microelectronics fabrication. There are limitations for both silicides. With TiSi2, a linewidth dependence of sheet resistance for lines narrower than 0.35 μm has become dramatic. The transformation from the high-resistivity C49 phase to the low-resistivity C54 TiSi2 phase is nucleation limited. With CoSi2 there is much less linewidth dependence of the sheet resistance, but more Si is consumed to form the silicide. With the use of NiSi, these problems can be avoided as reported so far in literature. In this article we shall report an investigation of rapid thermal silicidation of nickel on single crystalline silicon wafers in the annealing range of 150–1150 °C. It has been found that there are five zones in the dependence of sheet resistance on silicidation temperatures as follows: below 175, 175–350, 350–650, 650–900, and above 900 °C. In order to extensively study the phase sequence for Ni/Si reactions and the kinetics of nickel silicide formation corresponding to the sheet resistance zones, the spectroscopic ellipsometry (SE) was used to characterize the thin silicide films. The sensitivity and usefulness of SE characterization for studying the intermetallic growth processes and the application of an appropriate algorithm for extracting the information from experimental data is demonstrated. The results obtained by this nondestructive SE technique are compared with measurements done by the well-established but destructive techniques, Rutherford backscattering, scanning electron microscopy, and energy dispersive x-ray spectrometry. A physical picture of nickel silicidation as a function of temperature is also presented.

Materials aspects of Ti and Co silicidation of narrow polysilicon lines

The scalability of Ti and Co self-aligned silicide processes to deep-submicrometer technologies is determined by the fundamental materials aspects controlling phase formation and evolution. The kinetics of the high resistivity phase to low resistivity phase transformation (TiSi 2 C49 to C54 transformation for Ti, and CoSi to CoSi 2 transformation for Co) were studied for films on deep-submicrometer n + gates. For TiSi 2, results of a detailed Johnson-Mehl-Avrami analysis show that activation energies for the transformation increase with decreasing film thickness in the 28–64 nm range and are insensitive to linewidth in the 0.26-0.8 μm range, while transformation times increase as the linewidth or film thickness decreases. For Co, the transformation is diffusion limited, whih the square of CoSi 2 film thickness depending linearly on time. The transformation rate is also observed to be linewidth dependent, while the activation energy is quite insensitive to linewidth. The Co silicide phase tranformation proceeds faster than the Ti silicide phase transformation at low temperatures, resulting in a range of process parameters for which no linewidth dependence is observed for Co silicide and a strong linewidth dependence is observed for Ti silicide owing to incomplete phase transformation of the narrowest lines.

High-resistance phase and low-resistance phase in 1,6-diaminopyrene-p-chloranil (DAP-CHL)

Abstract A combination of DAP and CHL gives two kinds of 1:1 charge transfer complex crystals from the benzene solution. Both of them are electrically insulating at the initial states. The α-form single crystal, however, undergoes an irreversible conductivity change upon mild heating or fracture of the crystal. In both cases, the conductivity change amounts to 10 6 to 10 7 , and the resultant solids are a highly conducting semiconductor. The structural, optical, magnetic, and solid-state NMR studies suggest that the low-resistant phase is mainly composed of the neutral molecules despite its high conductivity.

A high-resistivity phase induced by swift heavy-ion irradiation of Bi: a probe for thermal spike damage?

Pure bismuth samples were irradiated at 20 K with swift heavy ions from 18O to 238U in the GeV range. The rate of the induced damage was deduced from in situ electrical resistance measurements. Above a threshold in the electronic stopping power Se equal to 24 keV nm-1, the damage is due to electronic slowing down. Above 30 keV nm-1, the electronic slowing down is efficient enough to induce latent tracks attributed to the appearance of a high-resistivity phase. The induced latent tracks radii can be up to 21.9 nm for Se=51 keV nm-1 which is the largest value reported so far for non-radiolytic materials. The evolution with Se of the latent tracks radii is calculated on the basis of the thermal spike model, assuming a realistic value for the electron-phonon coupling constant. A rather good agreement is obtained which supports the idea that the thermal spike could be operative in the observed radiation damage.

Transport of ionic species in skin: contribution of pores to the overall skin conductance.

Two methods are reported that allow visualization of high conductance paths in skin at current densities typically used during clinical iontophoretic drug delivery (10-200 microA/cm2). In the first method, the counter-directional iontophoretic transport of Fe(CN)6(4-) and Fe3+ across skin results in the precipitation of colloidal prussian blue, Fe4[Fe(CN)6]3, at sites of high iontophoretic flux. The appearance of localized deposits of Fe4[Fe(CN)6]3 is recorded by video microscopy and used to document the activation of low-resistance paths. In the second method, the ionic flux of Fe(CN)6(4-) through pores is directly imaged by scanning electrochemical microscopy (SECM). Both methods demonstrate that the iontophoretic flux across skin is highly localized. Activation of low-resistance pores in hairless mouse skin is shown to occur during iontophoresis. The spatial density of current carrying pores increases from 0 to 100-600 pores/cm2 during the first 30-60 min of iontophoresis. At longer times, the active pore density approaches a quasi-steady-state value that is proportional to the applied current density. The total conductance of the skin is proportional to the number of pores, consistent with a model of conduction in skin that is comprised of low-resistivity pores in parallel with a high-resistivity bulk phase. The contribution of pores to the total skin conductance during iontophoresis increases from an initial value of 0-5% to a quasi-steady-state value of 50-95%.

Comparison of transformation to low-resistivity phase and agglomeration of TiSi/sub 2/ and CoSi/sub 2/

The phase transformation and stability of TiSi/sub 2/ on n/sup +/ diffusions are investigated. Narrower n/sup +/ diffusions require higher anneal temperatures, or longer anneal times, than wider diffusions for complete transitions from the high-resistivity C49 phase to the low-resistivity C54 phase. A model is presented which explains this in terms of the probability of forming C54 nuclei on narrow diffusions and the influence of diffusion width on C54 grain size. The results are that more C49 and C54 nucleation events are required to completely transform narrow lines. For thin TiSi/sub 2/ (40 nm), there is a narrow process window for achieving complete transformation without causing agglomeration of the TiSi/sub 2/. The process window decreases with decreasing silicide thickness. A significantly larger process window is achieved with short-time rapid annealing. Similar studies are performed for CoSi/sub 2/ on n/sup +/ and p/sup +/ diffusions. No linewidth dependence is observed for the transformation from CoSi/sub x/ to CoSi/sub 2/. There is a broad process window from 575 degrees C to 850 degrees C using furnace annealing, for which the low-resistivity phase is obtained without causing agglomeration.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Shear-induced orientation effects and resistivity transition in high- T c superconductor Bi 0.95Al 0.05SrCaCu 2O x

Superconducting Bi 0.95Al 0.05SrCaCu 2O x ( T c = 83 K) is found to undergo a transition to a high-resistance phase on subjecting the sintered pellet to shear stresses by grinding. The transformed material is semiconducting and has a high negative thermoelectric power. X-ray diffraction patterns reveal that grinding results in randomization of orientation which was present in the superconducting sample. Repelletization of the powder restores the orientation, which is further enhanced on increasing the compaction pressure, but the material remains in the high-resistance phase. The highly compacted pellet, when reheated and annealed at 1123 K reverts to the superconducting phase with an improved T c of 87 K.

Magnetic and electrical properties of Fe-B-N amorphous films (invited)

A new type of ferromagnetic amorphous alloy with a two-phase structure was found in cosputtered Fe-B-N films. The microstructure was identified to be composed of two amorphous phases with about 50 Å or less in size; one is a ferromagnetic amorphous phase of Fe-B-N alloy and the other is a nonmagnetic and high resistive amorphous phase of boron nitride. The homogeneous mixture of these two phases in the films resulted in unique features for magnetic and electrical properties. In comparison to sputtered Fe-B films, the Fe-B-N films exhibit higher saturation magnetizations and the electrical resistivity is about 3–103 times higher. The compositional dependence of Curie and crystallization temperatures also differs from those of the sputtered amorphous Fe-B films. Furthermore, the corrosion resistance of the films is improved in the presence of nitrogen.

GaAs f.e.t.s with silicon-implanted channels

Field-effect transistors with channel doping profiles fabricated by the implantation of silicon ions into high-resistivity vapour phase epitaxial GaAs have given noise figures of 2.9 dB with an associated gain of approximately 5 dB at 10 GHz. Similar measurements on F.E.T.S fabricated in an identical manner, except for the channel fabrication, where silicon ions were implanted directly into a Cr-doped semi-insulating GaAs substrate, have resulted in nose figures typically 1 dB higher.

On the physical nature of the long-period conductivity relaxations in GaSb

Long-period conductivity relaxations in n-GaSb (S) are reported. These can be stimulated by sample cooling, by pressure or by light illumination of 0.2 eV ≲ ħω ≲ 2 eV spectral interval. In the latter case the 'memory effect' is observed. The model accounting for these phenomena suggests the inclusions of a high-resistive phase in a semiconductor. The relaxation processes are related to a slow overcoming of the potential barrier on phases boundary.