Nm Of Si3N4 Research Articles

Benchmarking of HCl-Based Cyclic Deposition / Etch (CDE) and Single Deposition / Etch (DE) Processes for Selective Epitaxial Growth of SiGeC:B Films

In this paper, SiGeC:B growth behaviors at 550 °C, 10 Torr, were studied in a 300 mm industrial Reduced Pressure-Chemical Vapor Deposition reactor using a Si2H6/GeH4/SiH3CH3/B2H6 chemistry. Carbon atoms, for both SiGeC and SiGeC:B layers, were only incorporated into substitutional sites, with concentrations up to ~ 1.4 at%. It appeared that in-situ boron doping at a level of 1x1020 at.cm-3 did not modify the substitutional carbon incorporation. However, carbon and boron atoms were shown to compete for substitutional incorporation sites, as outlined by the increased SiGeC:B films resistivity. Cyclic Deposition / Etch (CDE) and Deposition / Etch (DE) processes were then benchmarked on blanket Si substrates and blanket Si wafers covered with 10 nm of Si3N4, with the aim to achieve selective growth on patterned wafers. The CDE process consisted of 10 cycles with deposition steps at 550 °C, 10 Torr and etch steps at 550 °C, 50 Torr with a very high HCl flow. The simpler DE process consisted in a single deposition step at 550 °C, 10 Torr, followed by a single etch step at 550, 575 or 600 °C, 600 Torr, with a very low HCl flow. CDE and DE processes both resulted in a rather low etch selectivity of 1.8 and produced slightly rough SiGeC:B surfaces. Finally, it was shown that the use of a HCl-based CDE process is not a viable solution to obtain high quality SiGeC:B films on patterned wafers at low growth temperatures. Meanwhile, DE yielded higher quality if slightly rough SiGeC:B layers.

Overcoming the Challenge of High Surface Recombination in Thin‐Film Photovoltaic Cells Based on Subwavelength Arrays for Elevated Light Trapping

Surface arrays of subwavelength photoactive structures have been demonstrated for photovoltaic (PV) applications with elevated omnidirectional and broadband absorption. However, this approach suffers from an increase in surface recombination and loss of photovoltage. Herein, surface decoration with subwavelength dielectric (SiO2) arrays that provide enhanced light trapping without compromising the photovoltage performance is proposed. An increase of ≈ 50% in broadband absorption is shown in an ultrathin film of 200 nm due to the presence of a top surface SiO2 nanopillar array in comparison with the same film decorated with an optimized antireflective coating of 50 nm of Si3N4. Interestingly, the broadband enhancement is not due to lower reflection, but rather the presence of the arrays forces a considerable lower transmission. The distribution of the optical power flux density suggests that the low transmission is due to appreciable refraction, which is induced by the presence of the dielectric arrays. Finally, the photovoltaic performance is examined for various array geometries and absorber acceptor concentrations and an overall increase of >60% in PV efficiency is calculated for a decorated photovoltaic cell in comparison with a PV cell with an antireflection coating of 50 nm Si3N4.

Tailoring the Relative Si3N4 and SiC Contents in Si3N4/SiC Nanopowders through Carbothermic Reduction and Nitridation of Silica Fume

This study demonstrates the synthesis of nanostructured Si3N4/SiC composite powders from silica fume, for the first time. The processing approach to convert the waste silica fume to advanced nanocomposites is based on the integrated mechanical and thermal activation (IMTA) process. The synthesized nanostructured Si3N4/SiC powders have crystallite sizes as small as 17 nm for SiC and 42 nm for Si3N4. It has been shown that the carbothermic reduction and nitridation temperature, as well as the graphite concentration in the starting SiO2 + C mixture are the important parameters to obtain Si3N4 and SiC nanopowders and control their crystal sizes. The synthesis conditions to tailor the relative contents of α‐Si3N4 and α‐SiC (changing from as high as 49 vol.% to as low as 21 vol.% α‐SiC) in the final powder mixture have been investigated, and the mechanisms responsible for the observed relationship between processing conditions and the characteristics of the final powder have been identified.

Improvement in the Mechanical Properties of Silicon Nitride Ceramic in High-Temperature Deformation Processes

Studies have been made on the changes in structure and properties of sintered materials: Si3N4 - 5 mass% Y2O3 - 2 mass% Al2O3, Si3N4 - 5 mass% Y2O3 - 5 mass% Al2O3, and Si3N4 - 40 mass% TiN on deformation in a high-pressure chamber of toroid type (pressure 4–5 GPa, temperature 1000–1600 °C), and also by direct extrusion with degrees of reduction of 55 and 72% (temperature 1750–1850 °C, pressure on the plunger 20–30 MPa). After pressure-chamber treatment, the materials have elevated mechanical characteristics: HV10 ≈ 16.7 GPa, KIc up to 8.4 MPa · m1/2 for the system Si3N4 - Y2O3 - Al2O3; and HV10 ≈ 16.9 GPa, KIc up to 9.4 MPa · m1/2 for Si3N4 - TiN. A structure feature is the small size of the coherent-scattering regions: 51 nm for Si3N4 and 65 nm for TiN in the system Si3N4 - TiN, and 33 nm for specimens in the system Si3N4 - Y2O3 - Al2O3. High-temperature extrusion results in a structure with β-Si3N4 grains elongated along the deformation direction. The anisotropic structure has KIc values in directions perpendicular to and parallel to the direction of extrusion of 11.5–12.0 MPa · m1/2 and 7.5–7.8 MPa · m1/2, respectively. The hardness after extrusion becomes 16.0 GPa.

Carboxylic acid terminated monolayer formation on crystalline silicon and silicon nitride surfaces. A surface coverage determination with a fluorescent probe in solutionElectronic Supplementary Information (ESI) available: analytical data of the new compounds and general information on the instruments used for their characterization. See http://www.rsc.org/suppdata/jm/b3/b312273e/

Carboxylic acid terminated (–COOH) monolayers (ML) have been covalently anchored on the surface (S) of crystalline silicon (Si) and silicon nitride (Si3N4) by using wet-chemistry methods. Their concentration has been determined adopting a stepwise procedure with a fluorescent probe in solution. First, 7-amino-4-methylcoumarin (H2N–C10H7O2, AMC) is covalently bonded to the monolayer on the surface through an amidation reaction forming an amide-terminated surface monolayer, S–(CH2)n–CO–NH–C10H7O2, then the surface is intensely washed in order to remove any physisorbed species, finally AMC is detached from the surface via hydrolysis of the –CO–NH– bond and quantified by a fluorescence analysis in water solution. The yields of both the amidation and hydrolysis reactions have been evaluated. By this method, submonolayers ≤0.1 ± 0.03 ML can be determined. It has been possible to evaluate the different extent of surface functionalization changing the substrate between Si and Si3N4 and for Si changing the monolayer formation reaction: heat- (Δ) or light- (hν) promoted or via cathodic electrografting (CEG). It came out that submonolayers are formed in any case, Si3N4 is functionalized to a larger extent than Si on heating (0.52 vs. 0.15 ML) and Si is best functionalized via cathodic electrografting: Δ, 0.15; hν 0.20; CEG, 0.44 ML. Surface topography of some monolayers on Si and Si3N4 substrates was investigated by Atomic Force Microscopy (AFM). On clean Si, AFM showed topographical variations of 0.3–0.4 nm while for the clean Si3N4 the corrugation was around 3–4 nm. After functionalization the two surfaces were uniformly covered and the corrugation increased in both samples with a corrugation in topography of 1–2 nm for Si and 5–6 nm for Si3N4.

AFM and SNOM characterization of carboxylic acid terminated silicon and silicon nitride surfaces

Silicon and silicon nitride surfaces have been successfully terminated with carboxylic acid monolayers and investigated by atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM). On clean Si surface, AFM showed topographical variations of 0.3–0.4 nm while for the clean Si 3N 4 surface the corrugation was around 3–4 nm. After material deposition, the corrugation increased in both samples with a value in topography of 1–2 nm for Si and 5–6 nm for Si 3N 4. The space distribution of specific chemical species was obtained by taking SNOM reflectivity at several infrared wavelengths corresponding to stretch absorption bands of the material. The SNOM images showed a constant contribution in the local reflectance, suggesting that the two surfaces were uniformly covered.

Structural and luminescence properties of nanostructured ZnS:Mn

We have studied structural and luminescence properties of nanostructured (NS-) ZnS:Mn which has potential applications in thin-film electroluminescence (TFEL) devices. As a NS-ZnS:Mn system, a ZnS:Mn/Si3N4 multilayer having thicknesses of 2.5 nm for ZnS and 0.6 nm for Si3N4 was prepared by a conventional rf-magnetron sputtering method. Grazing incidence x-ray reflectometry and x-ray diffractometry show that ZnS:Mn nanocrystals were formed between the amorphous Si3N4 layers. Photoluminescence intensity associated with the Mn2+ transitions per total thickness of the ZnS:Mn layers is increased in NS-ZnS:Mn in comparison with that of the ZnS:Mn thin film, indicating the effects due to quantum confinement. The TFEL device with NS-ZnS:Mn as an emission layer exhibits a reddish-orange broad band emission with the maximum luminance of 2.8 cd/m2 under the 1-kHz sinusoidal wave operation at a voltage of 20.5 V0−p.

Fabrication and mechanical properties of silicon carbide–silicon nitride nanocomposites

A powder mixture of ultrafine β –SiC–35 wt% α –Si3N4 containing 6 wt% Al2O3 and 4 wt% Y2O3 as sintering additives were liquid–phase sintered at 1800°C for 30 min by hot–pressing. The hot–pressed composites were subsequently annealed at 1920°C under nitrogen–gas–pressure to enhance grain growth. The average grain–size of the sintered bodies were ranged from 96 to 251 nm for SiC and from 202 to 407 nm for Si3N4, which were much finer than those of ordinary sintered SiC–Si3N4 composites. Both strength and fracture toughness of fine–grained SiC–Si3N4 composites increased with increasing grain size. Such results suggested that a small amount of grain growth in the fine–grained region (≤250 nm for SiC and ≤400 nm for Si3N4) was beneficial for mechanical properties of the composites. The room–temperature flexural strength and fracture toughness of the 8–h annealed composites were 698 MPa and 4.7 MPa · m1/2, respectively.

Suppression of boron transport out of p+ polycrystalline silicon at polycrystalline silicon dielectric interfaces

The transport of B atoms out of p+ polycrystalline silicon (poly-Si) gate electrodes through SiO2 gate oxides to the Si–SiO2 interface during dopant activation anneals degrades performance and reliability of hole-conducting (p-channel) field effect transistors. This article studies the suppression of B atom transport by using remote plasma processing to form ultrathin Si3N4 and silicon oxynitride diffusion barrier layers between p+ poly-Si gate electrodes and SiO2 gate dielectrics. Suppression of B atom transport has been monitored through electrical measurements, demonstrating that ∼0.8 nm of Si3N4, equivalent to a N areal density of ∼4.5×1015 atoms cm−2, is sufficient to effectively suppress B out diffusion during aggressive anneals of ∼1 min at 1000 °C. The suppression and transport mechanisms in nitrides, oxides, and oxynitrides have been studied by varying the N atom areal density by alloying. Quantum chemistry calculations suggest that B transport occurs through the formation of donor-acceptor pair bonds between B+ ions and nonbonding electron pairs on oxygen atoms with the transport process requiring a connected O atom percolation pathway. Donor-acceptor pair bonds with B+ ions are also formed with N atoms in nitrides and oxynitride alloys, but with a binding energy more than 1.5 eV higher than B+ ion O-atom bonds so that nitrides and oxynitride alloys effectively block B diffusion through the formation of a deep trapping site.

Nanopatterning of Thin Cobaltdisilicide Layers by Local Oxidation

ABSTRACTLocal oxidation of thin cobaltdisilicide layers (10–30 nm) allows patterning with distances between silicide pads as small as 70 nm. The epitaxial silicide layers were grown by molecular beam allotaxy (MBA) on Si(100) substrates. They were characterized by TEM, RBS and sheet resistance measurements showing good crystal quality and excellent thermal stability up to 1200°C. Similar to the well established technology for local oxidation of silicon (LOCOS), the silicide layer was caped by 20 nm SiO2 followed by 300 nm of Si3N4. The nitride was patterned by optical lithography and dry etching. During dry oxidation at temperatures ranging from 900°C to 1000°C SiO2 is formed on the unprotected areas of the silicide. The Co atoms diffuse from the SiO2/CoSi2 interface to the CoSi2/Si interface to form CoSi2. Near the edges of the nitride mask the silicide layer thins and finally separates. Two metallic pads electrically separated by Si and SiO2 with a gap of 70 nm were produced this way. Monte Carlo simulations of the process revealed that the reason for the separation is stress dependent diffusion due to the stress induced by the nitride mask. The stress dependence of the separation process was experimentally verified using different nitride thicknesses. SEM and TEM studies showed perfect lateral patterning. This patterning process could be used in the fabrication of MOSFET's with ultrashort gatelengths.

Electrical breakdown induced by silicon nitride roughness in thin oxide–nitride–oxide films

The time-dependent dielectric breakdown (TDDB) characteristics of thin oxide–nitride–oxide (ONO) films containing 4 nm of Si3N4 were found to be exclusively determined by statistical thickness fluctuations of the Si3N4 layer. A two-parameter statistical model describes this roughness and explains experimental TDDB data. A simple growth model combined with the statistical model reduces the number of parameters to one. It is consistent with TDDB data and is in quantitative agreement with transmission electron microscopy and x-ray photoelectron spectroscopy data and is able to explain the origin of the roughness. On an ONO with a 4 nm Si3N4 layer and an area of 8 cm2—corresponding to the total storage area of a 256 Mbit dynamic random access memory—the thinnest point in the Si3N4 can be expected to be below 10 Å. So eliminating the Si3N4 roughness would bring a drastic improvement in reliability.

Porous SiO2 films analyzed by transmission electron microscopy

Porous SiO2 films derived from a novel organic-inorganic composite sol-gel process were studied for possible applications in the microelectronics industry. The films were capped with plasma-enhanced chemical-vapor-deposited silicon nitride and characterized using ellipsometry, IR spectroscopy and cross-sectional transmission electron microscopy (TEM). TEM cross-sections were prepared using a focused ion beam (FIB) system, because traditional TEM preparation by polishing was too harsh for the fragile samples. The TEM analysis determined the film thickness to be 155 nm for SiO2 and 83 nm for Si3N4, and showed high porosity in the SiO2 film and vertical pores in the Si3N4 film.

Local structure of β′-sialons: an EXAFS study study

The local environments of aluminium and silicon in β′-sialons, Si6−zAlzN8−zOz, have been studied by extended X-ray absorption fine structure spectroscopy. The silicon and aluminium atoms are always in tetrahedral coordination and the refined average bond length between two atomic positions becomes a measure of the distribution of nitrogen and oxygen over the nearest neighbour positions to the absorbing atom. Two β′-sialons samples with different composition, z=1 and z=2.7, were used in the study with α-Si3N4, SiO2 (cristobalite, albite and a xerogel), zeolite NaA, anorthite and AIN as reference substances. The calculated distances to the first coordination sphere for silicon were 0.169 nm for z=1 and 0.168 nm for z=2.7, compared to 0.171 nm for Si3N4 under the same conditions. In the aluminium environment, the calculated distances were 0.177 nm for z=1 and 0.176 nm for z=2.7. The results indicate that the β′-sialons are built up by aluminium- and silicon-containing tetrahedra with mixed oxygen and nitrogen environments, although there seems to be a stronger tendency for the formation of Si-N and Al-O bonds, compared to Si-O and Al-N bonds. The results are not precise enough to allow calculation of the contribution from different bond types to the observed average bond lengths; in particular this is due to the short (< 200 eV) AlK edge available for structural studies of the β′-sialons.

Laser‐Chemical Vapor Precipitation of Submierometer Silicon and Silicon Nitride Powders from Chlorinated Silanes

The laser‐chemical vapor precipitation (L‐CVP) of Si3N4 powders from miktures of SiH2Cl2 and NH3 or SiC1,4 and NH3, was studied. The reactant gases were mixed in the laser beam, thus preventing low‐temperature reactions. In a high‐temperature electrostatic precipitator (ESP), Si3N, was collected and separated from the waste product NH4Cl. In the ESP, Si was collected at a lower temperature. A major problem in utilizing chlorinated silanes was their poor absorption of the 10.6‐μm radiation. SF6 was explored for use as an inert sensitizer. Si was prepared from SiH2Cl2. Particle diameters were typically 20 to 40 nm for Si3N4 and 50 nm for Si.

Device fabrication by nanolithography and electroplating for magnetic flux quantization measurements

100-keV e-beam lithography and electroplating of gold have been used to fabricate a device for the measurement of quantum changes in magnetic flux. The structure is defined in a 200-nm-thick layer of a copolymer of methyl methacrylate and methacrylic acid (PMMA/MAA) on top of a Si wafer covered by 150 nm of Si3N4. The device is a square frame of 2×2 μm2 and 100-nm linewidth. Gold was electroplated to a thickness of 100 nm. This technique allows the fabrication of high resolution, high aspect ratio gold structures.

Effects of various encapsulating films on laser recrystallization of silicon on SiO2

Single-crystal silicon-on-oxide was produced by laser recrystallization of a 0.6-μm polysilicon film deposited on 1 μm of thermal SiO2. Oriented growth commenced where the polysilicon film was in contact with the silicon substrate, and proceeded laterally over the fully recessed SiO2. Typical dimensions of the single-crystal silicon-on-oxide film are 25 μm by 7 mm. The laser annealing was done with several different encapsulating films above the polysilicon, including 11.0, 16.4, and 32.9 nm of Si3N4, 25 nm of SiO2, 25 nm SiO2 +32.9 nm Si3N4, and uncapped samples. In addition, samples were laser annealed with and without an 1100 °C N2 preanneal of the structure. The 1100 °C anneal reduced the nucleation of misoriented grains in all samples, and extended the range of useable powers for the Si3N4 capped samples. The 32.9-nm Si3N4 cap produced the smoothest film and the most efficient coupling of the laser light into the silicon. The maximum distance of single-crystal growth was the same for all nitrogen-annealed samples, and showed a weak dependence on the melt width induced by the beam used for recrystallization. TEM micrographs of the recrystallized silicon show that the defects lie predominantly in the 110 direction. Their density increases away from the seed region, and they coalesce to form the grain boundaries at the transition to polysilicon growth.