Marker Layers Research Articles

Arsenic diffusion in Si and strained Si xGe 1−x alloys at 1000 °C

Results of arsenic diffusion under intrinsic diffusion conditions in Si and SiGe (5, 10% Ge) alloys are presented. Epitaxial Si and compressively strained SiGe structures with buried marker layers of arsenic were grown using Molecular Beam Epitaxy. The concentration profiles before and after Rapid Thermal Annealing at 1000 °C have been measured using SIMS. An enhancement of intrinsic arsenic diffusivity in SiGe compared to Si is observed, in agreement with literature. However, for As in Si 0.95Ge 0.05 strain seems to compensate the effect of enhancement due to Ge chemical effect although for Si 0.9Ge 0.1 the chemical effect overcomes the retardation due to strain.

X-ray nanoscale profiling of layer-by-layer assembled metal/organophosphonate films.

The nanoscale structure of multilayer metal/phosphonate thin films prepared via a layer-by-layer assembly process was studied using specular X-ray reflectivity (XRR), X-ray fluorescence (XRF), and long-period X-ray standing wave (XSW) analysis. After the SiO(2) X-ray mirror surfaces were functionalized with a monolayer film terminated with phosphonate groups, the organic multilayer films were assembled by alternating immersions in (a) aqueous solutions containing Zr(4+), Hf(4+), or Y(3+) cations and then (b) organic solvent solutions of PO(3)-R-PO(3), where R was a porphyrin or porphyrin-square spacer molecule. The different heavy metal cations provided X-ray fluorescence marker layers at different heights within the different multilayer assemblies. The XSW measurements used a 22 nm period Si/Mo multilayer mirror. The long-period XSW generated by the zeroth-order (total external reflection) through fourth-order Bragg diffraction conditions made it possible to examine the Fourier transforms of the fluorescent atom distributions over a much larger q(z)() range in reciprocal space than previously achieved.

Reduction of Boron Diffusion in Silicon–Germanium by Fluorine Implantation

This letter investigates the effect of a 185 keV, 2.3 /spl times/ 10/sup 15/ cm/sup -2/ F/sup +/ implant on boron transient enhanced diffusion (TED) and boron thermal diffusion in SiGe by characterizing the diffusion of a boron marker layer in samples with and without a 288 keV, 6 /spl times/ 10/sup 13/ cm/sup -2/ P/sup +/ implant. In samples implanted with F/sup +/ only, the fluorine suppresses boron thermal diffusion by 58%. In samples given both P/sup +/ and F/sup +/ implants, the fluorine completely eliminates boron transient enhanced diffusion caused by the P/sup +/ implant and also significantly reduces boron thermal diffusion. SIMS profiles after anneal show a fluorine concentration in the SiGe layer that is approximately 8 /spl times/ higher than after implant, indicating that fluorine accumulates in the SiGe layer during anneal. A comparison with fluorine profiles in comparable silicon samples also shows that the fluorine concentration after anneal is dramatically higher in SiGe samples than in Si samples. This accumulation of fluorine in the SiGe layer during anneal will have major benefits for boron diffusion suppression in devices like SiGe HBTs, where boron must be kept within the SiGe layer.

Transport numbers of metal and oxygen species in anodic tantala

The transport numbers of metal and oxygen species have been determined in amorphous anodic tantala films, using transmission electron microscopy to locate ion-implanted xenon marker layers within the films. The films were formed on sputtering-deposited tantalum at constant current density, in the range 0.01–10 mA cm −2, in 0.06 wt% H 3PO 4 solution at either 20 or 85 °C. The films grow by migration of metal and oxygen species through the film thickness, with formation of new film material at the film/electrolyte and metal/film interfaces respectively. The cation transport number, t +, increases due to either increase in current density or decrease in temperature: for current densities in the selected range, t + increases from 0.18 to 0.32 at 20 °C, and from 0.14 to 0.29 at 85 °C. Low concentrations of phosphorus species, incorporated into an outer layer of the film, migrate inward during film growth. The migration rates are slower than those of oxygen species, by a factor in the range 0.2–0.3.

Epitaxial growth on gas cluster ion-beam processed GaSb substrates using molecular-beam epitaxy

Chemical mechanical polished (CMP) (100) GaSb substrates were processed using gas cluster ion beams (GCIB) to improve surface smoothness, reduce subsurface damage, and produce a thermally desorbable oxide layer for molecular-beam epitaxy (MBE) overgrowth. In this article, we report the growth of GaSb/AlGaSb epilayers on GCIB processed GaSb substrates. The substrates were processed using either O2 or CF4/O2 as the gas cluster in a dual-energy recipe that included a moderate energy (10 keV) etch step followed by a low-energy (3 keV) smoothing step, with a relatively low total dose of 4×1015 ions/cm2. Half of each wafer was masked such that the epitaxial layers were grown on both CMP and GCIB polished surfaces. Atomic force microscopy showed the elimination of CMP surface scratches on the GCIB processed surfaces. X-ray photoelectron spectroscopy results indicate that the surface oxide composition and thickness can be engineered through the GCIB process recipes. AlGaSb marker layers were used to chart the evolution of the overgrown layers. Cross-sectional transmission electron microscope images of the substrate/epi-interface show that the CMP finished regions contained defects that propagated into the epilayers as compared to the GCIB finished region that showed no penetrating defects, indicating an improved substrate/epi-interface. This work demonstrated that GCIB processing of semiconductor materials has the potential to produce “epiready” surfaces.

Observation and simulation of plasma mix after reshock in a convergent geometry

Experiments to study the effect of a second, counterpropagating shock on the growth of hydrodynamic instabilities in a convergent, compressible system have been performed on the Omega Laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] at the University of Rochester. Direct laser illumination of a cylindrical target launches a strong shock across hydrodynamically unstable interfaces formed between an epoxy ablator material on the outside, a buried aluminum marker layer and low-density CH foam on the inside. The Richtmyer–Meshkov instability mixes the marker into the two adjacent materials. Of particular interest is what happens when the mixing region is reshocked by using a second, coaxial central cylinder to reflect the incident shock back into the mixing region. These experiments have been extensively modeled, in two dimensions, using the hydrocodes NYM [P. D. Roberts et al., J. Phys. D 13, 1957 (1980)], PETRA [D. L. Youngs, Physica D 12, 32 (1984)], and RAGE [R. M. Baltrusaitis et al., Phys. Fluids 8, 2471 (1996)]. Good agreement is shown between the simulations and experimental data.

Production and Metrology of Cylindrical Inertial Confinement Fusion Targets with Sinusoidal Perturbations

Shock waves generated during inertial confinement fusion implosions propagate toward the center of the capsule encountering interfaces between materials with different densities, such as between the ablator and the DT fuel. These interactions are hydrodynamically unstable and the resulting instability causes mixing of the materials at the interface, which is predicted to have detrimental effects on fusion burn. In this experiment, the growth of a single-mode perturbation machined into a radiographically opaque marker layer, driven by a strong shock, is measured during a cylindrically symmetric implosion. These measurements are used to validate simulations and theories of the complex hydrodynamics. Since any perturbation on the marker layer surface will lead to instability growth, precise knowledge of the initial conditions is critical. The targets used in this experiment have up to a 3.0-μm-amplitude, mode 28 (θ = 98 μm) sinusoidal perturbation machined into a 438-μm-outerradius aluminum band with a nominal thickness of 8 μm. The perturbations were machined using a fast-tool servo [B. JARED and T. A. DOW, Precision Engineering Center Annual Report, North Carolina State University, Raleigh NC, p. 123 (1996)] and were metrologized using a linear variable differential transformer [FRANK J. OLIVER, Practical Instrumentation Tranducers, p. 42-45, Hayden Book Company (1971)]. In this paper, the importance of metrology is discussed and is shown to be critical to the interpretation of experimental results.

Decoration of swift heavy ion tracks in nickel-oxide with gold atoms

We have investigated the swift heavy ion beam induced relocation of Au marker layers in NiO. It was found that, above a certain threshold value, the electronic energy deposition results in gettering of the nearby Au atoms into the latest excited ion track. In that way a continuous Au redistribution from a recent track into a new one occurs. For Kr-ions only short and partly segmented Au-containing cylinders of about 5 nm in diameter are found, which are symmetrically located around the initial marker plane. In beam direction the laterally averaged Au distribution shows a slight broadening, which saturates at relatively low fluences. In case of Xe- and Au-ions coherent cylindrical Au-decorated zones are formed which reach up to the surface, and which obviously allow for transversal Au transport towards the surface and for segregation of the Au in spherical nano-particles on top of the surface. The transversal transport mechanism is not of diffusion-like nature, but most probably by pressure induced viscous flow in the molten ion track.

Magnetization profile at the Fe/GaAs(0 0 1)-4×6 interface

The magnetization of a thin Fe film epitaxially grown on GaAs(0 0 1)-4×6 was studied at different depths from the metal/semiconductor interface using a single layer of Fe 0.5Co 0.5 as a marker layer through a double-wedge Fe film. By measuring the X-ray magnetic circular dichroism spectroscopy at the L 2,3 of Co, the magnetic response of the film could be sensed at different distances from the interface. Data show a reduction of the magnetization at the interface though the existence of a magnetically “dead” layer is completely ruled out. Moreover, the magnetization was found to be reduced at the Fe film surface.

Boron Diffusion and Silicon Self-Interstitial Recycling between SiGeC layers

ABSTRACTSubstitutional carbon is known to locally reduce silicon self-interstitial concentrations and act as a barrier to self-interstitial migration through the carbon rich regions. A silicon spacer between two carbon rich SiGe layers is fabricated in this work to examine self-interstitial generation in a region that is isolated from self-interstitial formation at the surface or in the silicon bulk. Boron marker layers above, below and in between two SiGeC layers are used to monitor the self-interstitial concentration between the substitutional carbon. No evidence of self- interstitial depletion in the silicon spacer is observed, despite annealing in conditions believed sufficient to allow the self-interstitials to reach and react with surrounding substitutional carbon. Simulations of the self-interstitial and carbon indicate that the silicon self interstitial concentration in the spacer layer can be sustained in part due to a silicon self-interstitial recycling process through a reverse “kick-out” reaction.

Effect of 3,4,3',4'-tetrachlorobiphenyl on the reworking behavior of Lumbriculus variegatus exposed to contaminated sediment.

The reworking response (bioturbation) of the oligochaete Lumbriculus variegatus was measured by following the burial rate and spread of a 137Cs marker layer translating worm activity into a biological burial rate (Wb) and a biological diffusion rate constant (Db) for surficial sediment mixing. Reworking was measured at 10 and 22 degrees C in two sediments: a reference site sediment dosed with 3,4,3',4'-tetrachlorobiphenyl (TCBP) and a field-collected sediment from a polychlorinated biphenyl (PCB)-contaminated site in Dicks Creek (DCC, Middletown, OH, USA). The body residue associated with response to TCBP also was determined. Reduction in the temperature from 22 to 10 degrees C reduced both Wb and Db by a factor of approximately two. The internal TCBP concentration to reduce the Wb by 50% was 96 nmol/g (95% CI 45-225 nmol/g) and 124 nmol/g (40-547 nmol/g) (28 and 36 microg/g) wet weight at 22 and 10 degrees C, respectively, and was independent of temperature. The Wb for the DCC sediment was lower than observed for the highest TCBP treatment. The internal body residue for total PCB for worms exposed to DCC sediment was 20-fold lower than TCBP in worms exposed to the lowest TCBP treatment on a molar basis. Comparing body residues of total PCB to TCBP assumes that the PCB congeners act additively on a molar basis. The DCC site contained a higher proportion of coarse material and a lower organic carbon concentration. The difference in sediment characteristics was assumed to be responsible for differences in the Wb.

BIC Formation and Boron Diffusion in Relaxed Si0.8Ge0.2

ABSTRACTThe relationships between Boron Interstitial Cluster (BIC) evolution and boron diffusion in relaxed Si0.8Ge0.2 have been investigated. Structures were grown by Molecular Beam Epitaxy (MBE) with surface boron wells of variant composition extending 0.25 [.proportional]m into the substrate, as well as boron marker layers positioned 0.50 [.proportional]m below the surface. The boron well concentrations are as follows: 0, 7.5×1018, 1.5×1019, and 5.0×1019 atoms/cm3. The boron marker layers are approximately 3 nm wide and have a peak concentration of 5×1018 atoms/cm3. Samples were ion implanted with 60 keV Si+ at a dose of 1×1014 atoms/cm2 and subsequently annealed at 675°C and 750°C for various times. Plan-view Transmission Electron Microscopy (PTEM) was used to monitor the agglomeration of injected silicon interstitials and the evolution of extended defects in the near surface region. Secondary Ion Mass Spectroscopy (SIMS) concentration profiles facilitated the characterization of boron diffusion behaviors during annealing. Interstitial supersaturation conditions and the resultant defect structures of ion implanted relaxed Si0.8Ge0.2 in both the presence and absence of boron have been characterized.

The Effect of Fluorine Implantation on Boron Diffusion in Metastable Si0.86 Ge0.14

ABSTRACTThis paper investigates the effect of varying F+ implantation energy on boron thermal diffusion and boron transient enhanced diffusion (TED) in metastable Si0.86Ge0.14 by characterising the diffusion of a boron marker layer in samples with and without P+ and F+ implants. The effect of two F+ implantation energies (185keV and 42keV) was studied at two anneal temperatures 950°C and 1025°C. In samples implanted with P+ & 185keV F+, the fluorine suppresses boron transient enhanced diffusion completely at 950°C and suppresses thermal diffusion by 25% at 1025°C. In samples implanted with P+ & 42keV F+, the fluorine does not reduce boron transient enhanced diffusion at 950°C. This result is explained by the location of the boron marker layer in the vacancy-rich region of the fluorine damage profile for the 185keV implant but in the interstitial-rich region for the 42keV implant. Isolated dislocation loops are seen in the SiGe layer for the 185keV implant. We postulate that these loops are due to the partial relaxation of the metastable Si0.86Ge0.14 layer.

Direct evidence of the recombination of silicon interstitial atoms at the silicon surface

In this experiment, a Si wafer containing four lightly doped B marker layers epitaxially grown by CVD has been implanted with 100 keV Si + ions to a dose of 2 × 10 14 ions/cm 2 and annealed at 850 °C for several times in an RTA system in flowing N 2. TEM and SIMS analysis, in conjunction with a transient enhanced diffusion (TED) evaluation method based on the kick-out diffusion mechanism, have allowed us to accurately study the boron TED evolution in presence of extended defects. We show that the silicon surface plays a key role in the recombination of Si interstitial atoms by providing the first experimental evidence of the resulting Si ints supersaturation gradient between the defect region and the surface. Our results indicate an upper limit of about 200 nm for the surface recombination length of Si interstitials at 850 °C in a N 2 ambient.

Coupling of atom-by-atom calculations of extended defects with B kick-out equations: application to the simulation of boron ted

We present simulations of B TED based on a complete calculation of the extended defect growth/shrinkage during annealing. The Si self-interstitial supersaturation calculated at the extended defect depth is coupled to the set of equations for the B kick-out diffusion through a generation/recombination term in the diffusion equation of the Si self-interstitials. The simulations are compared to the measurements performed on a Si wafer containing several B marker layers, where the amount of TED varies from one peak to the other. The good agreement obtained on this experiment is very promising for the application of these calculations to the case of ultra-shallow B + implants.

Transport Considerations in the Plasma-Assisted Oxidation of Copper Films

The oxidation of copper films in a helical resonator oxygen discharge was performed over the temperature range of 150 to 300°C. Significant increases in the oxidation rate relative to thermal oxidation are observed. Oxidation rates followed a parabolic rate expression, with a rate constant of at 250°C, and an effective activation energy over the temperature range studied of 0.58 eV. Marker experiments using either gold or molybdenum as the marker layer indicated that both oxygen and copper species transported during oxidation. The location of the copper/copper-oxide interface relative to the marker position demonstrated that copper is the primary transporting species responsible for oxidation, analogous to results reported for the thermal oxidation of copper at higher temperatures. © 2003 The Electrochemical Society. All rights reserved.

Reduction of boron thermal diffusion in silicon by high energy fluorine implantation

This letter investigates the effect of a deep F+ implant on the diffusion of boron in silicon. The effects on boron thermal diffusion and transient enhanced diffusion are separately studied by characterizing the diffusion of a buried boron marker layer in wafers with and without a 185 keV, 2.3 ×1015 cm−2 F+ implant, and with and without a 288 keV, 6 ×1013 cm−2 P+ implant. In samples given both P+ and F+ implants, the fluorine completely eliminates the transient, enhanced boron diffusion caused by the P+ implant, and in samples implanted with F+ only, the fluorine suppresses the boron thermal diffusion by 65%. These results are explained by the effect of the fluorine on the vacancy concentration in the vicinity of the boron profile.

Influence of current density on transport numbers in anodic oxide films on an anodized Al–5.7at.%W alloy

The ionic transport numbers in barrier anodic films, formed on an Al–5.7at.%W alloy in 0.1 M sodium tungstate electrolyte at 293 K, have been measured for current densities from 0.1 to 1000 mA cm −2. For this purpose, a xenon marker was ion implanted with a fluence of 1.5 × 10 15 ions cm −2 into a film formed to 10 V on the alloy, which was then further anodized to 150 V. The position of the marker layer in the final film was determined by transmission electron microscopy and Rutherford backscattering spectroscopy. The cation transport number was ∼0.38, with no dependence upon current density to an accuracy of ∼10%.

Interface structure of Fe/Ag multilayers prepared by pulsed laser deposition

Fe/Ag multilayers with single layer thicknesses in the nanometer range have been deposited on Si(100) using pulsed laser deposition. Conversion electron M\"ossbauer spectroscopy in conjunction with Rutherford backscattering spectrometry and x-ray reflectivity have been used for the evaluation of the interface structure of these multilayers. In the Fe-Ag system, with a large positive heat of mixing, a solid solution of bcc Fe(Ag) has been found by placing an enriched ${}^{57}\mathrm{Fe}$ marker layer at different distances to the multilayer interfaces. The interface structure mainly depends on dynamic effects during the deposition processes. From the analyses, we have obtained an asymmetric intermixing at lower and upper interfaces of the individual Fe layers: the intermixing of Fe into Ag is lower than that of Ag into Fe. The studies of the interface structure were performed by varying parameters such as the thickness of the elemental layers and the target-to-substrate distance during the deposition process.

Determination of spin distributions in ion-beam magnetic textured iron films by magnetic orientation Mössbauer spectroscopy

A promising approach by which to gain information about the spin distributions in different sample layers using depth-sensitive angle-dependent conversion electron Mössbauer spectroscopy is presented in combination with magneto-optical Kerr effect, Rutherford backscattering spectrometry and x-ray diffraction investigations. Three 77 nm thick Fe films containing a 15 nm Fe57 marker layer at different depths were deposited on Si(100) substrates and irradiated under well defined mechanical stress with 200 keV Xe ions. The distribution of the spins in the sample plane was analyzed by Mössbauer spectroscopy and by tilting the sample toward the incident γ beam and observing the variation in angle-dependent relative intensity of the sextet lines. For the sample with the sensitive marker layer in the middle of the ferromagnetic film, all spins were found to be oriented exactly along the mechanical stress axis. This agrees with the angular properties of the macroscopic hysteresis curves measured by the magneto-optic Kerr effect.