Sputtering Of Si Research Articles

Obtaining silicide free spacers by optimizing sputter etch for deep submicron CMOS processes

In this paper, we have shown that the sputter etch before cobalt deposition during the silicide processing of a deep submicron CMOS device fabrication needs to be optimized in order to eliminate a detrimental origin of gate (G) to source (S)/drain (D) bridging. It is known that Co cannot reduce even a thin layer of native oxide. Therefore, it is necessary to ensure that Co is deposited on a very clean Si surface. To ensure this, an in-situ sputter etch is commonly conducted before Co deposition. It is observed that this sputter etch process can sputter Si from the S/D area and deposit them on the sidewall spacer (SWS). This sputtered Si in turn will react with deposited Co and form silicide. The worst case leakage currents from poly-Si to composite for long (10 m) and narrow (0.18 micron) poly lines are shown to be on the order of milliampere. Transmission electron microscope (TEM) micrographs included show the existence of cobalt silicide layers (/spl sim/8 nm thick) over sidewall spacer. The silicide thickness on the sidewall spacer is correlated with resistance value calculated from current and voltage (I-V) measurements. The need for optimizing the sputter etch recipe has been validated by TEM and I-V measurements.

Preparation of phosphorous dope beta-irondisilicide thin films and application for devices

Electrical properties of phosphorous-doped n-type poly-crystalline beta-irondisilicide have been studied by preparation of heterojunctions with p-type silicon. The phosphorous-doped poly-crystalline beta-irondisilicide films prepared by sputtering of Si, Fe and Fe 3P show higher conductivity than undoped one and indicate n-type conductivity by thermoelectric power measurement. The heterojunctions show rectifying characteristics at various doping level, although the devices show large backward leak current. These results indicate that the phosphorous doping by co-sputtering of Si, Fe and Fe 3P change the conductivity of the films to n-type.

Influence of nitrogen–argon gas mixtures on reactive magnetron sputtering of hard Si–C–N films

Si–C–N films were deposited on p-type Si(100) substrates by dc magnetron co-sputtering of silicon and carbon using a single sputter target with variable Si/C area ratios in nitrogen–argon mixtures. The film characteristics were primarily controlled by the argon concentration (0–75%) in the gas mixture at a fixed 40% silicon fraction in the magnetron erosion track area. The total pressure and the discharge current on the magnetron target were held constant at P=0.5 Pa and I m=1 A, the substrate temperature was adjusted at T s=600 °C by an ohmic heater and the rf-induced negative substrate bias voltage, U b was −500 V. Mass spectroscopy was used to explain differences between sputtering of carbon and silicon in nitrogen–argon discharges. The films, typically 1.0–1.5 μm thick, were found to be amorphous with a very smooth surface ( R a≤0.8 nm). It was shown that the nitrogen–argon gas mixture composition is an important process parameter in a reproducible production of Si–C–N compounds with controlled properties by dc magnetron co-sputtering using a composed C–Si target with variable Si/C area ratios. With a rising argon concentration in the gas mixture, the Si content in the films rapidly increases (from 19 to 34 at.% for a 40% Si fraction in the erosion target area), while the C content decreases (from 34 to 19 at.%) at an almost constant (39–43 at.%) N concentration. An intensified bombardment of growing films by argon leads to its subplantation into the films (up to 5 at.%) and to a decrease in a volume concentration of hydrogen (from 5 to 1 at.%). As a result, the NSi and SiN bonds dominate over the respective NC and SiO bonds, preferred in a pure nitrogen discharge, and the film hardness increases up to 40 GPa. The effect of the negative substrate bias voltage (from a floating potential of −18 to −500 V) on characteristics of the films prepared in a 50% N 2+50% Ar gas mixture is not too marked at T s=600 °C. A decrease in the T s values to 135–210 °C leads to a higher incorporation of hydrogen into the films (up to 6 at. %) and to a stronger influence of the negative substrate bias voltage.

Optimal low‐energy SIMS conditions for characterizing ZrO2/Si interfaces

AbstractDevelopment of high‐K gate dielectric materials has placed a stringent demand for inspection tools with ultrahigh depth resolving power and detection sensitivity. Low‐energy SIMS is potentially the technique of choice provided that the analytical related artifacts are well understood and efficiently suppressed. In this work we profiled superficial and buried metal–organic chemical vapour deposited ZrO2 films and investigated the artifacts involved in SIMS profiling at various beam conditions. It was demonstrated that O2+ beams at near‐normal incidence yielded extremely broad Zr down‐slopes in Si, an artifact likely due to a pronounced preferential sputtering of Si when the instantaneous surface reached the ZrO2/Si interfaces. Suppression of this artifact can be realized by probing O2+ beams at oblique incidence, favorably at 60° for a 1 keV O2+. Nevertheless, the normal‐incidence O2+ beam remained optimal for characterizing the up‐slope of Zr at the polycrystalline Si (polySi)/ZrO2 interface, owing to the minimized matrix effects and suppressed surface roughness. For profiling a gate stack (polySi/ZrO2/Si) at oblique incidences, the high depth resolution of low‐energy SIMS was hindered by the pronounced roughness in poly‐Si. This can be remedied by ion beam smoothing of the poly‐Si prior to SIMS profiling. Using the optimal SIMS conditions, we profiled poly‐Si/ZrO2/Si wafers with and without dopant activation anneal. The SIMS data revealed significant reactions between ZrO2 and Si upon thermal anneal at 1025°C for 10 s. Copyright © 2002 John Wiley & Sons, Ltd.

The role of nucleation and heteroepitaxial processes in nanostructuring of Si

Self-assembly represents a large prospective class of nanoscale fabrication techniques for future electronics. Understanding the mechanisms underlying the processes of nanostructure formation is crucial for establishing the control over their dimensions, spatial distribution, and uniformity. In this work, nanostructuring of Si was studied by silicon heteroepitaxy on NiSi2 nucleated at the Ni/Si interface during low-temperature Si sputtering on a thin Ni prelayer. The formation of spatially separated Si wires is discussed in terms of nucleation phenomenon, strain relaxation in the lattice-matched systems, and Si deposition kinetics.

Self-assembly of spatially separated silicon structures by Si heteroepitaxy on Ni disilicide

A nonlithographic approach to produce self-assembled spatially separated Si structures for nanoelectronic applications was developed, employing the metal-induced silicon growth. Densely packed Si whiskers, 500–800 nm thick and up to 2500 nm long, were obtained by magnetron sputtering of Si on a 25 nm thick Ni prelayer at 575 °C. The nucleation of the NiSi2 compound at the Ni–Si interface followed by the Si heteroepitaxy on the lattice-matched NiSi2 is suggested to be the driving force for the whisker formation.

Chemistry in grain aggregates: a source of complex molecules?

ABSTRA C T The aggregation of grains in dense protostellar clouds brings together materials such as silicates, carbons, polycyclic aromatic hydrocarbons and ices to form porous structures with high internal volume. Some physical and chemical properties of these aggregate grains are discussed in the context of the role that they may play in the formation of complex organic and organometallic compounds. One characteristic of such grains that is unique outside planetary systems is the availability of all elements and a number of their common compounds in a composite solid. In dark clouds, the chemistry inside aggregate grains will be driven by cosmic ray heating and sputtering. This occurs in an environment where the products of such reactions can be retained within the dust particle. Hot atom chemistry and secondary reactions are facilitated by the re-entrant nature of such aggregated structures, leading to the possible formation of complex organic compounds. In particular, the sputtering of Si, Mg and Fe from silicate dust is discussed, and it is shown that a variety of organometallic compounds could be expected in ices within aggregate grains. The optical depth for ultraviolet light within aggregates is large, so that materials inside such grains will be effectively shielded from ambient radiation. However, the incorporation of luminifors such as those grain components responsible for the extended red emission converts ultraviolet to visible and near-infrared radiation, and might moderate photochemistry within aggregates. It is suggested that the chemical environment within aggregates may be conducive to the formation and retention of complex molecules such as amino acids, peptides and a variety of organometallic compounds.

Structure and properties of Si incorporated tetrahedral amorphous carbon films prepared by hybrid filtered vacuum arc process

The mechanical properties and atomic bond structure of Si incorporated into tetrahedral amorphous carbon (ta-C) films were investigated. The films were deposited by a filtered vacuum arc of graphite with simultaneous sputtering of Si. The Si concentration in the film could be controlled by changing the flow rate of the Ar sputtering gas. It was observed that the incorporated Si preferentially substituted sp 3 bonded carbon when the Si concentration was less than 2.5 at.%. Since the SiC bond generated by the substitution was weaker than CC bond, the Si incorporation could cause the relaxation of nearby distorted CC bonds by inducing large strain in the SiC bond. This structural change resulted in a significant decrease in the residual compressive stress in this Si concentration range. In contrast, the incorporated Si which has only sp 3 hybridization, generated the weaker SiC bonds without breaking the three-dimensional interlinks of the atomic bond structure. Hence, the hardness and the plane strain modulus gradually decreased with Si incorporation. The saturated mechanical properties observed when the Si concentration was higher than approximately 10 at.% are due to the formation of a large amount of SiC phase in the deposited film.

Sputtering of Si with decaborane cluster ions

Decaborane cluster ions (B10Hx+) may play an important role in the manufacturing of future semiconductor devices, as they facilitate a very shallow implantation of B with a relatively high beam energy, due to its partition among the constituent atoms. While the formation of B-doped shallow junctions in Si has been demonstrated, little is known about other effects of these complex ions on a solid. We have measured the sputtering yield of Si with decaborane cluster ions at 12 keV and demonstrated that their impacts smooth rather than roughen the surface, similarly to much larger Ar cluster ions. The results have implications for the understanding of low-energy atomic impacts in terms of collective motion of many surface atoms and of the behavior of solids far from equilibrium.

Layer-by-layer etching of Cl-adsorbed silicon surfaces by low energy Ar+ ion irradiation

Layer-by-layer etching of Si(100) has been investigated by alternating chlorine adsorption and Ar+ ion irradiation. As the Ar+ ion source, a helicon plasma has been used to invoke the surface reaction of Si with the adsorbed chlorine. At a chlorine partial pressure of 10mPa, the Si surface was found to be fully saturated with adsorbed chlorine in 20s. In order to achieve the layer-by-layer etching of Si, the Ar+ ion acceleration energy should be above 20eV at the time of chlorine adsorption. At energies above 40eV, however, sputtering of Si was found to occur. The self-limited etch rate was measured to be half monolayer per cycle, which was 0.68Å per cycle. The roughness of Si surface was found to increase during the etching by about 22% after 900 cycles.

Nonadditive sputtering of silicon by keV energy molecular projectiles of heavy and light elements

In the present work a positive secondary ion emission from a silicon produced by Au m − projectiles (m = 1–3) with energies of E 0 = 9 and 18 keV and by Al m − projectiles (m = 1,2) with energies of E 0 = 6, 9, 12, and 18 keV have been studied. Anomalous high nonadditivity of sputtering as large cluster Si n + ions (n > 4) under molecular Au m − ion bombardment has been found. As compared with heavy (Au m −) projectiles, the light (Al m −) projectiles are not effective for sputtering of large cluster ions. For molecular Al m − ion bombardment nonadditivity of sputtering of small cluster Si n + ions (n ≤ 4) increases with decreasing of the energy E 0 from 9 to 6 keV/atom. This effect shows that the efficiency of nonadditive sputtering strongly depends on the penetration depth of molecular projectile and, hence, on the energy density deposited by molecular projectile into subsurface layers of the target from which the cluster ion emission occurs.

Phenomenological model of reactive r.f.-magnetron sputtering of Si in Ar/O 2 atmosphere for the prediction of SiO x thin film stoichiometry from process parameters

The process of reactive sputtering from a silicon target in an Ar/O 2 gas mixture is investigated. An optical plasma regulating circuit using the intensity of the 251.9 nm-Si I line as setpoint is employed to stabilize the sputtering process. A phenomenological model of the process is derived that, in contrast to previous models, it allows to calculate the composition of the growing SiO x film exclusively from measurable process parameters and accounts for the non-uniform deposition at the substrate. Film compositions x, predicted this way for different setpoints were verified by Rutherford backscattering spectroscopy. As an example, a SiO 2/SiO 1.5/SiO 2 layer stack was prepared and via anneal transformed into a thin layer of nanocrystalline silicon embedded in an oxide matrix, a structure with potential for application in memory devices and Si-based light emitters.

Molecular dynamics simulations of ion self-sputtering of Ni and Al surfaces

We present results of molecular dynamics simulations of Ni+ impacting Ni(111) and Al+ impacting Al (111) and amorphous Al surfaces. Sputter yields and sticking probabilities were calculated as a function of ion fluence, impact angle (0–90°) and energy (25–150 eV). We find that the simulated sputter yields are in reasonable agreement with experiments and a commonly used empirical formula. For Al+ impacting at normal incidence, sputter yields were approximately the same for both Al(111) and amorphous Al. The initial penetration depth exhibited a linear dependence with velocity, and was approximately the same for both Al+/Al(111) and Ni+/Ni(111) if the distances were scaled by the lattice constants. The average calculated time between ion impact and atom ejection was less than 25 fs for 100 eV Ni+/Si(111) sputter events.

Mechanism of the chemical erosion of SiC under hydrogen irradiation

Abstract The erosion yield of SiC due to D bombardment has been determined by the weight-loss method as a function of temperature and energy in the range of 20–300 eV up to 1100 K. A temperature dependence exists clearly below 100 eV. For 20 eV D, the yield is 0.5% at 300 K and 1.5% in the maximum at 500 K. Contrary to Si erosion, no formation of silane was observed with mass spectrometry. Hydrocarbons, predominantly CD 4 molecules, are only found at 20 eV. From the erosion of a thin SiC layer investigated using MeV ion beam analysis, segregation and preferential erosion of carbon are ruled out, because the layer thickness decreases while the composition stays constant. As no volatile silane production is detected, it is assumed that sputtering of Si or silane precursors with low binding energy occurs at low ion energies. The mechanism of the chemical erosion of Si in presence of C and absence of C is different.

Two-band photoluminescence spectra from nanometre Si particle-embedded Si oxide films

Nanometre Si particle (NSP)-embedded Si oxide films were deposited on p-type Si substrates by the r.f. magnetron sputtering technique using Si and SiO2 composite sputtering targets. All samples were annealed in a nitrogen ambient at 600° for 30 min. X-ray photoelectron spectroscopy and optical absorption measurements were performed on the samples. The sizes of the NSPs were increased by increasing the relative area of the Si wafer in the co-sputtering target. The photoluminescence spectra of all the samples exhibited two bands with their peaks located at 370 nm (3.4 eV) in the ultraviolet spectral range and 650–665 nm (1.9 eV) in the orange–red spectral range. The experimental results indicate that there are two types of photoexcitation processes in the NSP-embedded Si oxide films: one for the orange–red band occurring in the NSPs and the other for the ultraviolet band occurring in the SiO2 layers. Copyright © 2001 John Wiley & Sons, Ltd.

Palladium and Aluminum Gate Metals/Aluminum Nitride/Silicon Balanced Capacitors for Selective Hydrogen Sensing

AbstractAn alternate array of Pd/AlN/Si and Al/AlN/Si metal-insulator-semiconductor (MIS) devices has been developed using plasma source molecular beam epitaxy (PSMBE) method for deposition of AlN on Si and magnetron sputtering for deposition of Pd and Al electrodes (via mask) on AlN. Both devices show essentially identical capacitance (C) versus voltage (V) characteristics of the typical MIS capacitor. However, the C-V characteristic of a Pd-device shows a clear shift in the presence hydrogen, while that of an Al-device shows no shift. These sensors were characterized using C(V) and C(time) measurements under varying hydrogen concentration. The effects of oxygen and hydrocarbon gases on the sensors were also studied. The Pd-device responds selectively to hydrogen. These results suggest the possibility of fabricating a balanced sensor structure, which might have significant practical importance, as it would cancel all thermal and material sources of drift in the electrical component of the sensor response.

Properties of amorphous ternary alloy films a-Si xC yGe z:H prepared by magnetron co-sputtering

Amorphous Si x C y Ge z :H ( x+ y+ z=1; z∼0.1) have been deposited by reactive sputtering of Si–Ge composite target in argon–methane gas mixtures. The effects of the addition of Ge and the methane partial pressure P on the film properties were investigated. At high P, the addition of Ge could improve the reduction of the photoconductivity with increasing P observed in a-Si x C y :H ( z=0).

High rate deposition of poly-Si thin films at low temperature using a new designed magnetron sputtering source

We have deposited poly-Si thin films on Si(100) and glass substrates at growth temperature of below 400°C using a newly developed high rate magnetron sputtering method. To improve the sputtering yield and the growth rate, a high power (10–30 W/cm 2) magnetron sputtering system was designed and constructed. Based on the results of computer simulation, we built up the magnetron sputter source with unbalanced magnetron and Si ion extraction grid. The maximum deposition rate reached was 0.35 μm/min due to a high ion bombardment. This is five times higher than that of conventional sputtering methods, and the sputtering yield was also increased up to 80%. The best film was obtained on Si(100) surface using Si ion extraction grid under 9.0×10 −3 torr of working pressure and 11 W/cm 2 of the target power density. The electron mobility of the poly-Si film grown on Si(100) at 400°C with ion extraction grid was 96 cm 2/Vs. In this study, however, we found that the target power density is a more important factor than working pressure to influence the growth rate, mobility, and the film quality. During sputtering, moreover, the characteristics of Si sputter source were also analyzed with an in situ Langmuir probe method and optical emission spectroscopy.

Heteroepitaxial growth of SiGe films and heavy B doping by ion-beam sputtering

Epitaxial growth of Si and SiGe films on Si(100) substrates was examined using ion-beam sputtering technique. The critical epitaxial film thickness on Si homo-epitaxial growth was found to be thicker than that of the MBE grown films. This may be due to the bombardment effects by sputtered particles. Layer by layer growth was carried out by Si and Ge alternate sputtering. Although up to 600°C, periodic structure was observed to be formed by XRD analysis, it disappeared at 700°C because of interdiffusion. In situ B-doping of SiGe films was examined using a GeB target. Epitaxial growth was observed in spite of the fact that B was doped as heavy as 2.7×1021 cm−3. For the B-doped film a Hall mobility of 400 cm2/V s was obtained at a hole concentration of 4×1017 cm−3.

AlSi xN y as an embedded layer for attenuated phase-shifting mask in 193 nm and the utilization of a chemically amplified negative resist NEB-22 for maskmaking

AlSi xN y (x∼0.31, y∼0.45) thin film as a new embedded material for AttPSM in 193 nm lithography was presented. With the good controlling of plasma sputtering of Al (100∼130 W) and Si (20∼50 W) under Ar (75 sccm), and nitrogen (2.5∼5 sccm), AlSi xN y has enough deposition latitude to meet the requirements as an embedded layer. For required phase shift 180 degree, the calculated thickness d 180 of AlSi xN y films is in the range of 87∼100 nm. The T% in 365 and 488 nm for optical inspection and alignment is below 40%. Its sheet resistance R s, is less than 0.8 kΩ/square. Helicon wave plasma etcher and Taguchi design of experiment have been applied to the study of the etching selectivity of AlSi xN y over substrate fused silica and negative resist NEB-22. Under chamber pressure 3 mtorr, BCl 3 45 sccm, Cl 2 7 sccm, plasma source power 1400 W and substrate bias RF power 30 W for the selectivity of AlSi xN y over NEB-22 was found to be 4.8:1. The selectivity of AlSi xN y over fused silica was 12.3:1 under chamber pressure 9 mtorr, BCl 3 13 sccm, Cl 2 45 sccm, O 2 8 sccm, plasma source power 1400 W and substrate bias RF power 30 W. A 0.3 μm line/space etched pattern using AlSi xN y as embedded layer was successfully fabricated.