Si Flux Research Articles

Plasma diagnostic study of silicon nitride film growth in a remote Ar–H2–N2–SiH4 plasma: Role of N and SiHn radicals

A remote expanding thermal plasma operated on an Ar–H2–N2–SiH4 mixture has been studied by several plasma diagnostics to obtain insight into the plasma processes and the hydrogenated amorphous silicon nitride (a-SiNx:H) growth mechanism from the N2–SiH4 reactant mixture. From Langmuir probe measurements, ion mass spectrometry, and threshold ionization mass spectrometry, it is revealed that the Ar–H2–N2 operated plasma source leads mainly to N and H radicals in the downstream region. The H radicals react with the SiH4 admixed downstream creating a high SiH3 density as revealed by cavity ringdown spectroscopy. By cavity ringdown measurements, it is also shown that Si and SiH have a much lower density in the downstream plasma and that these radicals are of minor importance for the a-SiNx:H growth process. The ground-state N radicals from the plasma source do not react with the SiH4 injected downstream leading to a high N density under the a-SiNx:H deposition conditions as revealed by threshold ionization mass spectrometry. From these results, it is concluded that N and SiH3 radicals dominate the a-SiNx:H growth process and the earlier proposed growth mechanism of a-SiNx:H from the N2–SiH4 mixture [D. L. Smith et al., J. Vac. Sci. Technol. B 8, 551 (1990)] can be refined: During deposition, an a-Si:H-like surface layer is created by the SiH3 radicals and at the same time this a-Si:H-like surface layer is nitridated by the N radicals leading to a-SiNx:H formation. This growth mechanism is further supported by the correlation between the SiH3 and N plasma density and the incorporation flux of Si and N atoms into the a-SiNx:H films as deposited under various conditions.

Erratum: Morphological and Compositional Evolution of theGe/Si(001)Surface During Exposure to a Si Flux [Phys. Rev. Lett.90, 216104 (2003)

Erratum: Morphological and Compositional Evolution of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">G</mml:mi><mml:mi mathvariant="normal">e</mml:mi><mml:mo>/</mml:mo><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>001</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>Surface During Exposure to a Si Flux [Phys. Rev. Lett.<b>90</b>, 216104 (2003)

Morphological and compositional evolution of the ge/si(001) surface during exposure to a si flux.

By using scanning tunneling microscopy we found that the surface reconstruction of Ge/Si(001) epilayers evolves from (M x N) to (2 x N), and eventually to (2 x 1), during exposure to a Si flux. This sequence appears to be just the inverse of that observed during the growth of Ge or SiGe alloys on Si(001). However, molecular dynamics simulations supported by ab initio calculations allow us to interpret this morphological evolution in terms of Si migration through the epilayer and complex Si-Ge intermixing below the top Ge layer.

Effect of Cl/H input ratio on the growth rate of MoSi 2 coatings formed by chemical vapor deposition of Si on Mo substrates from SiCl 4–H 2 precursor gases

Under chemical vapor deposition (CVD) conditions of Si on Mo substrate limited by mass transport of reactant gas species through a gas boundary layer, the effect of the Cl/H input ratio on the growth rate of MoSi 2 coating at 1200 °C was investigated using a horizontal hot-wall reactor and SiCl 4–H 2 gas mixtures. The growth kinetic of the MoSi 2 coating obeyed a parabolic rate law irrespective of Cl/H input ratios. The growth rate of MoSi 2 coating initially increased with increasing Cl/H input ratio until the maximum growth rate was reached, and then decreased inversely proportional to the Cl/H input ratio at higher Cl/H input ratio. This suggests that there is a limit to the increase in growth rate for MoSi 2 coating due to the etching effect of Si with respect to the input ratio of Cl/H. The etching effect of the Cl/H input ratio on the growth rate of the MoSi 2 coating was explained by thermodynamic calculations based on the variation of silicon activity on the surface of the MoSi 2 coating. The mass balance between the Si flux supplied by the mass transport step and that consumed by solid-state diffusion to form MoSi 2 coating was considered to be responsible for the activity of silicon.

Formation process and microstructural evolution of Ni-silicide layers grown by chemical vapor deposition of Si on Ni substrates

The formation process and microstructural evolution of Ni-silicide layers formed by chemical vapour deposition (CVD) of Si on Ni substrate at deposition temperatures between 900 and 1050 °C using horizontal hot-wall reactor and SiCl 4–H 2 gas mixtures was investigated. The Ni-silicide layers grew sequentially in a series of γ-Ni 5Si 2, δ-Ni 2Si and θ-Ni 2Si layers with increasing deposition time. After an incubation time necessary for nucleation of each Ni-silicide phase, the growth kinetics of each layer obeyed a parabolic rate law and was controlled by solid-state diffusion of Ni leading to void formation at the interface of the Ni-silicide layers and the Ni substrate. The growth rates of γ-Ni 5Si 2 and δ-Ni 2Si layers were faster at the early deposition stage than those at the later deposition stage. The formation process and microstructures of each Ni-silicide layer was influenced by the effect of deposition parameters especially on the difference between the Si flux supplied by CVD process and the Ni flux diffusing through each Ni-silicide layer.

6H- AND 4H-SiC(0001) Si SURFACE RICHNESS DOSING BY HYDROGEN ETCHING: A WAY TO REDUCE THE FORMATION TEMPERATURE OF RECONSTRUCTIONS

In 6H- or 4H-SiC(0001) surface technology, a Si-rich 3 × 3 reconstruction is usually first prepared by heating at 800°C under Si flux, and two other most stable [Formula: see text] or [Formula: see text] reconstructions are obtained by further extensive annealing at higher temperatures ranging between 900 and 1250°C. The 3 × 3 Si excess is thus progressively depleted up to a graphitized C-rich surface. By crystallographic (LEED) and chemical surface characterizations (XPS and UPS), we show that all these reconstructions can be obtained at a unique, low formation temperature of 800°C if the Si richness is controlled before annealing. This control is achieved by exposing the 3 × 3 surface to atomic hydrogen at room temperature. This procedure allows one to etch or partially deplete the (3 × 3)-associated Si excess, and make it more comparable to the final Si coverages, required to form the less Si-rich [Formula: see text] or [Formula: see text] reconstructions. After annealing at 800°C, the latter reconstructions are no longer determined by the heating time or temperature but only by the initial Si coverage set by the H doses inducing the low temperature etching. The high temperature treatment, required to remove by sublimation a significant Si amount associated with the Si-rich 3 × 3 reconstruction, is thus avoided. Such a methodology could be applied to other binary systems in the formation of reconstructions that depends on surface richness.

Inputs, Outputs, and Internal Cycling of Silica in a Large, Tropical Lake

A silica budget was constructed for Lake Malawi by measuring major cycling processes, including river input/output, atmospheric deposition, sinking, burial, and vertical flux within the water column. A large proportion (> 80%) of the annual input to the lake occurred in the December to March rainy season. During this period, biogenic Si (BSi) made up 61% of Si input from rivers. Microscopic examination indicated that a large fraction of BSi was phytoliths, which likely originated from cultivated maize and terrestrial grasses. Over an annual cycle, river input made up approximately 25% of total Si input to the epilimnion, while 75% resulted from vertical exchange with Si-rich deep water. Due to its long hydraulic residence time, Lake Malawi retains nearly all of the Si that enters it. Despite high temperatures, a relatively high proportion (7 to 11%) of diatom production is permanently buried. A Si flux model is used to demonstrate that river discharge and vertical mixing can have similar effects on BSi burial rate over short time scales (one to two decades), but very different effects over longer time periods. This temporally dependent response must be taken into account when interpreting sediment records.

Direct effect of ice sheets on terrestrial bicarbonate, sulphate and base cation fluxes during the last glacial cycle: minimal impact on atmospheric CO 2 concentrations

Chemical erosion in glacial environments is normally a consequence of chemical weathering reactions dominated by sulphide oxidation linked to carbonate dissolution and the carbonation of carbonates and silicates. Solute fluxes from small valley glaciers are usually a linear function of discharge. Representative glacial solute concentrations can be derived from the linear association of solute flux with discharge. These representative glacial concentrations of the major ions are ∼25% of those in global river water. A 3-D thermomechanically coupled model of the growth and decay of the Northern Hemisphere ice sheets was used to simulate glacial runoff at 100-year time steps during the last glacial cycle (130 ka to the present). The glacially derived fluxes of major cations, anions and Si over the glaciation were estimated from the product of the glacial runoff and the representative glacial concentration. A second estimate was obtained from the product of the glacial runoff and a realistic upper limit for glacial solute concentrations derived from theoretical considerations. The fluxes over the last glacial cycle are usually less than a few percent of current riverine solute fluxes to the oceans. The glacial fluxes were used to provide input to an oceanic carbon cycling model that also calculates changes in atmospheric CO 2. The potential change in atmospheric CO 2 concentrations over the last glacial cycle that arise from perturbations in glacial solute fluxes are insignificant, being <1 ppm.

Modelled glacial and non-glacial HCO 3−, Si and Ge fluxes since the LGM: little potential for impact on atmospheric CO 2 concentrations and a potential proxy of continental chemical erosion, the marine Ge/Si ratio

The runoff and riverine fluxes of HCO 3 −, Si and Ge that arise from chemical erosion in non-glaciated terrain, are modelled at six time steps from the Last Glacial Maximum (LGM) to the present day. The fluxes that arise from the Great Ice Sheets are also modelled. Terrestrial HCO 3 − fluxes decrease during deglaciation, largely because of the reduction in the area of the continental shelves as sea level rises. The HCO 3 − fluxes, and the inferred consumption of atmospheric CO 2 are used as inputs to a carbon cycle model that estimates their impact on atmospheric CO 2 concentrations ( atmsCO 2). A maximum perturbation of atmsCO 2 by ∼5.5 ppm is calculated. The impact of solutes from glaciated terrain is small in comparison to those from non-glaciated terrain. Little variation in terrestrial Si and Ge fluxes is calculated (<10%). However, the global average riverine Ge/Si ratio may be significantly perturbed if the glacial Ge/Si ratio is high. At present, variations in terrestrial chemical erosion appear to have only a reduced impact on atmsCO 2, and only little influence on the global Si and Ge cycle and marine Ge/Si ratios during deglaciation.

A Review of the Role of Excess si in SIO2 at the Growing Oxide Interface.

AbstractThis paper discusses the issues that arise when ab excess of Si or SiO flux is used to adjust the Deal -Grove model to match the observed growth in the early stages of oxidation. The author uses the insight gained from the modeling of the oxidation of Si-Ge alloys as a background to the discussion. A recent simulation of the thin oxide problem by M. Uematsu et.al. invokes the role of “excess Si” near the interface to adjust the D&amp;G reaction coefficient and also add additional flux to the growing oxide.This paper assesses some of the points in this model as well as the relation with sub bonded Si and/or the reaction barrier layer to oxidationmechanism. A recent proposal by Pasquarello et.al opens new insight into the way the interface may adjust to the growing oxide which challenges our previous mechanistic notions.

Preparation of amorphous Si 1− xC x (0≤ x≤1) films by alternate deposition of Si and C thin layers using a dual magnetron sputtering source

Amorphous Si 1− x C x (0≤ x≤1) films have been prepared by alternately depositing thin Si and C layers on aluminosilicate glass substrates by magnetron sputtering. The apparatus used in the experiment was a dual-cathode sputtering machine with a carrousel type substrate holder. When a substrate passes in front of the cathode by rotating the substrate holder at a rotation rate of 60 rev./min, a thin Si layer of 0.057 nm (d.c. current: 0.2 A) and a thin C layer of 0.028 nm (d.c. current: 0.4 A) were alternately deposited on the substrate, resulting in the preparation of SiC film. The C/Si compositional ratio of films deposited was controlled by changing the discharge power (the flux) of Si and C. The structural, optical and mechanical properties of the deposited films were examined as a function of C concentration ( x). Results of X-ray photoelectron spectroscopy showed that the film composition changed from x=0 to x=1 with increasing C flux ratio. The peak positions of Si 2p and C 1s shifted also, showing the formation of SiC bond in the films. The X-ray diffraction measurements showed that films deposited were amorphous for all the composition. The maximum hardness of approximately 30 GPa was obtained for a film deposited at x≈0.5 by a nanoindentation. This value was almost equal to that of a SiC film deposited by conventional r.f. sputtering of SiC. Internal stresses of films ranged from −0.5 to −1.0 GPa (compressive) and were 1/2–1/4 compared to that of the SiC film deposited from a by a conventional sputtering of SiC without rotating substrate.

Reversible shape evolution of Ge islands on Si(001).

The evolution of strained Ge/Si(001) islands during exposure to a Si flux was investigated by scanning tunneling microscopy. Dome islands display appreciable shape changes at Si coverages as low as 0.5 monolayer. With increasing coverage, they transform into [105]-faceted pyramids, and eventually into stepped mounds with steps parallel to the <110> directions. These morphological changes are induced by alloying and represent a complete reversal of those previously observed during Ge island growth. The results are interpreted with a simple model in which the equilibrium shape of an island mainly depends on its volume and composition.

Structural analysis of 6H–SiC([formula omitted]) surface by RHEED rocking curves

Surface structures of 6H–SiC(0001)3×3R30° and 3×3 reconstructions have been studied by rocking curves of reflection high energy electron diffraction (RHEED) intensities in one-beam condition. The 3×3R30° reconstruction is observed by annealing the Si pre-deposited specimen in the Si flux at 1030°C for 5 min. The 3×3 reconstructions is observed by annealing the Si pre-deposited specimen in the Si flux at 1000°C for 5 min and by successive annealing of the 3×3 surface in the Si flux at 940°C for 5 min. Normal components of atomic positions and layer densities are determined by analysis with RHEED dynamical calculations for the 3×3. For the 3×3 surfaces, we determined surface normal components of atomic positions for three possible structure models.

The [formula omitted] reconstruction on hexagonal 6H–SiC([formula omitted]) surface with and without a Si flux

The (3×3)R30° reconstruction on hexagonal 6H–SiC(0001) surface and its properties were studied by using reflection high-energy electron diffraction (RHEED) and RHEED multislice dynamical calculations. A Si coverage of 1/3 monolayer occupying the threefold-symmetric T4 or H3 sites develops upon a lower Si flux and/or at a higher annealing temperature and/or upon a longer time annealing. However, Si trimers centered on the T4 positions with 1 monolayer coverage may be another appropriate candidate for the (3×3)R30° reconstruction obtained under a very Si-rich condition and/or at a lower annealing temperature and/or upon a shorter time annealing.

A time series study of silica production and flux in an eastern boundary region: Santa Barbara Basin, California

A high‐resolution data set describing the annual silica cycle between January 1994 and August 1999 in the Santa Barbara Basin (SBB) captures processes and events occurring in both surface and deep basin waters. Increases in biogenic silica (bSi) concentrations in the surface waters indicated strong bloom events in the early spring of each year and sporadic blooms during the summer and fall. Lithogenic silica (lSi) was present at elevated concentrations in surface waters in the winter and spring. At times, the siliceous biomass in the SBB is comparable to that in major global upwelling regions. However, anomalously low annual depth‐integrated bSi concentrations were observed during the E1 Niño conditions of 1997–1998. A 1.5‐year time series of biogenic silica production rate measurements was used to calculate the highest resolution estimate of annual silica production to date, an estimated 5.5 mol Si m −2 yr−1. This silica production rate approaches that estimated for the major global upwelling zones (8.3 mol Si m−2 yr−1). Eastem boundary regions outside of the major coastal upwelling zones would account for 30–40% of global silica production if the Santa Barbara Basin is representative of these coastal regions. Since the sediments of the SBB contain a high‐resolution climate record, an understanding of the coupling between surface processes and deep basin sedimentation events is of value. Fluxes of bSi and lSi to 470 m were not strongly coupled to the seasonal cycle of particulate concentrations or production rates in surface waters. Continuous sediment trap collections of sedimenting particles indicate that both lSi and bSi tend to be exported at the highest rates during the spring and summer. As particles sink, lSi becomes enriched relative to bSi and consistently dominates the mass flux of silica at 470 m. Brief increases in the percent contribution of bSi to Si flux may create microlaminae within larger‐scale laminations which are thought to be annual varves. A comparison of annual bSi sedimentation rates with annual silica production estimates reveal that ∼30% of the annual silica production is exported to a depth of 470 m. This export rate is the highest observed to date and suggests the potential for large quantities of silica burial in coastal sediments.

Identification of Growth Precursors In Hot Wire CVD of Amorphous Silicon Films

ABSTRACTA soft ionization laser-based technique using 10.5 eV photon energy has been used to probe radical growth precursors in the hot wire chemical vapor deposition (HW-CVD) of a-Si:H. Using a Re filament, it is shown that Si, SiH3, and Si2H6are the major silicon-containing species formed from the hot wire dissociation of silane, and SiH2is at most a very minor product. However, chamber history is found to influence the radical species produced; i.e. SiH3 and Si2H6are largely related to the chamber wall and filament conditions. The gas species produced by W and Re filaments at wire temperatures between 1000oC and 2000oC have been studied and compared. Heating the filament to higher temperatures increases the flux of Si, SiH3 and Si2H6 in a similar fashion for both filament materials. Above 1800oC, the Si intensity saturates, while SiH3 and Si2H6show monotonic increase without saturation up to 2000oC.

Behaviour of silicon-doped CFC limiter under high heat load in TEXTOR-94

In order to study the impurity production, recycling and power deposition a Si doped CFC test limiter (NS31) was used in TEXTOR-94. The release of impurities (C, Si, O, Cr, CD radicals) was measured spectroscopically. A reduced methane production was found in the Si doped graphite when compared to a pure graphite limiter. A smaller decrease of the carbon fluxes could also be observed. The limiter contained about 1%–1.5% of Si, but a relative Si flux (Si/D) from the Si doped CFC surface between 0.12% and 0.4% has been measured. A chemical erosion of Si due to formation of SiDx has not been observed. Silicon evaporated from the surface at temperatures above 1500 °C. This led to an increase of Si concentration and total radiation losses from the plasma. Surface analysis shows the formation of microcracks and holes on the plasma exposed limiter surface. The released Si was deposited in the vicinity of the tangency point of the limiter. Whereas a Si depletion was observed in the area of highest power loading with values reaching in and in-between fibres values of 0.03% and 0.02% respectively.

Upper ocean export of particulate organic carbon and biogenic silica in the Southern Ocean along 170°W

Abstract Upper-ocean fluxes of particulate organic carbon (POC) and biogenic silica (bSi) are calculated from four US JGOFS cruises along 170°W using a thorium-234 based approach. Both POC and bSi fluxes exhibit large variability vs. latitude during the seasonal progression of diatom dominated blooms. POC fluxes at 100 m of up to 50 mmol C m −2 d −1 are found late in the bloom, and farthest south near the Ross Sea Gyre. Biogenic Si fluxes also peak late in the bloom as high as 15 mmol Si m −2 d −1 , but this flux peak occurs at a different latitude, just south of the Antarctic Polar Front (APF), which is centered around 60°S along this cruise track. The ratios of both POC and bSi export relative to their production rates are large, suggesting an efficient biological pump at these latitudes. The highest relative bSi/POC flux ratios at 100 m are found just south of the APF, coincident with a bSi/POC flux peak seen in 1000 m traps during this same program by Deep-Sea Research II (Honjo et al., Deep-Sea Research II 47, 3521–3548). These data suggest that efficient export at these latitudes can support the high accumulation rates of bSi found in the sediments under and south of the APF, despite the generally low biomass and productivity levels in this region.

Carbon segregation in silicon

Carbon doping strongly suppresses the diffusion of boron. This is very important for later high temperature processing steps, e.g. for the fabrication of a high doped SiGe-base in a heterojunction bipolar transistor. We investigated (with a novel method) the segregation of C in Si (100) at growth temperatures between 500 and 700°C. A C-doped Si layer was grown by MBE under constant C and Si fluxes. The growth temperature was switched between 300°C and the investigated growth temperature. As the temperature was switched, the surface-accumulated C concentration was perturbed, causing a spike or depression in the SIMS depth profile. The surface segregation at a given temperature was measured by the amount of adlayer density in the spike. Clear evidence of the surface segregation of carbon in Si is found by these experiments.

A Single-Crystal XRD and TEM Study of “ScB17C0.25”

In auxiliary metal fluxes (Si, Sn) at temperatures around 1650°C the crystal growth of “ScB17C0.25” was successfully performed. While in the Si flux agglomerates of whisker-like crystals are formed, the change to Sn significantly improved the quality of the columnar crystals with respect to size and surface smoothness. Based on single-crystal X-ray data collected on a four-circle diffractometer using MoKα radiation and high-resolution transmission electron microscopy (HRTEM) the structure was solved by direct methods and refined to an reliability value R1 of 0.055 for 661 Fo>4σ and 64 variables. The novel crystal structure belongs to the hexagonal system (space group P6/mmm), with lattice constants a, b=14.5501(15) Å and c=8.4543(16) Å and is formed by a framework based on B12 icosahedra which are radially connected to unusual “tubular” boron-based structural units. The Sc atoms reside on interstitial sites. In addition to the boron based clusters interstitial B atoms are found in the structure. The main structural features, which are governed by the arrangement of the boron clusters and the Sc atoms in the unit cell, could be unambiguously resolved by HRTEM, and simulated images match observed ones perfectly.