A simple route to large scale synthesis of crystalline αSi3N4 nanowires

Crystalline Si₃N₄ nanowires were simply prepared by heating a silicon wafer at 1250 °C in a flowing NH₃ and N₂ atmosphere. The obtained nanowires are straight and uniform with diameters of 30–100 nm and of lengths up to tens of microns. The possible reactions in the synthesis process are discussed. The growth mechanism of the nanowires is vapor-solid (VS) process. PACS 81.05.Je; 81.07.Bc; 81.10.Bk; 81.16.Be; 81.20.Ka     

Scanning probe oxidation of Si3N4 masks for nanoscale lithography,micromachining, and selective epitaxial growth on silicon

For studying the physical, chemical, and electronic properties of ultrasmall man-made structures, the major challenge is to fabricate highly uniform structures and control their positions on the nanometer length scale. Local oxidation of metals and semiconductors using a conductive-probe atomic force microscope (AFM) or other scanning probe microscopes in air at room temperature has emerged as a simple and universal method for this purpose. Here the uses of scanning probe oxidation of Si₃N₄ masks for performing nanolithography, nanomachining, and nanoscale epitaxial growth on silicon are reviewed. The three most unique features of this approach are presented: (1) exceptionally fast oxidation kinetics using silicon nitride masks (∼30 μm/s at 10 V for a ∼5-nm-thick film); (2) selective-area anisotropic etching of Si using a Si₃N₄ etch mask; and (3) selective-area chemical vapor deposition of Si using a SiO₂/Si₃N₄ bilayer growth mask.     

Changes in surface stress, morphology and chemical composition of silica and silicon nitride surfaces during the etching by gaseous HF acid

HF acid attack of SiO₂ and Si₃N₄ substrates is analyzed to improve the sensitivity of a sensor based on microcantilever. Ex situ analysis of the etching using XPS, SIMS and AFM show significant changes in the anisotropy and the rate of the etching of the oxides on SiO₂ and Si₃N₄ surface. Those differences influence the kinetic evolution of the plastic bending deflection of the cantilever coated with SiO₂ and Si₃N₄ layer, respectively. The linear dependence between the HF concentration and the Si₃N₄ cantilever bending corresponds to a deep attack of the layer whereas the non-linear behavior observed for SiO₂ layer can be explained by a combination of deep and lateral etching. The cantilever bending is discussed in terms of free surface energy, layer thickness and grain size.     

The comparison of reactive ion etching and plasma etching in a parallel-plate reactor

Reactive ion etching (RIE) and plasma etching (PE) of different materials (GaAs, Si₃N₄ SiO₂ and photoresist Microposit 1350 H) in freon 116 are compared in the present article. The importance of ion bombardment for the etching rate is evident from the experimental results. GaAs is etched only by RIE due to ion milling, the etching rates of Si₃N₄ and SiO₂ are 4 to 5 times higher by RIE than PE.     

Single layer silicon photonic crystal slab

We present here the fabrication and characterization of single layer silicon photonic crystal mirror on a silicon-on-insulator wafer. By a combination of electron beam lithography, fast atom beam etching with deep reactive ion etching, silicon photonic crystal slabs are achieved on 260 nm freestanding silicon membrane and sandwiched with air on the top and bottom. Their high refractive index contrasts enable photonic crystal slabs function as dielectric mirrors for externally incident light. The optical performances of fabricated photonic crystal slabs can be tuned by varying the width of separation grooves or the air-hole size, which represents a significant advantage of offering various approaches for optical response control.     

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 Si₃N₄ 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 Si₃N₄. 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.     

Capturing properties of a threefold coordinated silicon atom in silicon nitride: Positive correlation energy model

The electronic structure and capturing properties of threefold coordinated silicon atoms (≡Si·) and the Si-Si bond in silicon nitride (Si₃N₄) were studied using the ab initio density functional theory. The results show that the previously proposed negative correlation energy (NCE) model is not applicable to Si₃N₄. The NCE model was proposed for interpreting the absence of the ESR signal for threefold coordinated silicon defects and suggested that an electron can transfer between two silicon defects. We proposed that the absence of this ESR signal is due to the creation of neutral diamagnetic Si-Si defects in Si₃N₄. This model offers the most fundamental theory for explaining the hole localization (memory) effect in silicon nitride.     

Pulsed CO2 laser-driven production of ultrafine silicon,silicon carbide,silicon nitride and silicon oxynitride powders

Summary Ultrafine Si, Si₃N₄, SiC and silicon oxynitride powders have been produced by irradiating gas-phase reactants by means of a CO₂ laser. The mechanism of SiH₄ CO₂ laser-induced absorption and dissociation is discussed on the basis of the results of the spectral and time-resolved measurement of fragment chemiluminescence. The role played by the SiH₂ radical in the powder formation is investigated. The quality of Si, Si₃N₄, SiC and silicon oxynitride powders is checked by means of several off-line diagnostics (IR spectroscopy, X-ray diffraction at wide and small angle, BET analysis). The possibility of controlling powder stoichiometry and doping from the gas-phase reactant concentration is discussed.     

Electrical characteristics of metal-dielectric-semiconductor structures with silicon nitride prepared by reactive cathode atomization

The effect of the technology of preparation of silicon nitride in a low temperature gas discharge plasma upon the volt-ampere and volt-farad characteristics of metal-dielectricsemiconductor (MDS) structures (Al-Si₃N₄-Si-Al) is studied. It is shown that by using a heterogeneous Si₃N₄ formation reaction with ionic purification of the silicon surface, it is possible to obtain MDS structures with lower and more stable surface charge in comparison to similar structures in which the Si₃N₄ is grown by other methods (for example, gas transport reaction methods). The conductivity of the Si₃N₄ film is described approximately by the well known Frankel model, and its value is close to that of Si₃N₄ films prepared by other methods.     

Ion irradiation induced spontaneous hypersonic long-range stimulation of silicon nitride synthesis in silicon

We studied the nature of the effect of medium-energy ion implantation on the defect system of a crystal target over distances exceeding by three to four orders of magnitude the average projected range of ions in the target material. Recently, we discovered an especially strong manifestation of this long-range effect in crystal targets: argon ion bombardment stimulated the formation of a Si₃N₄ phase in nitrogen-saturated layers of a silicon wafer, the effect being observed at a distance of up to 600 μm away from the ion stopping zone. An analysis of changes in the electrical and optical properties of the nitrogen-saturated layer depending on the argon ion dose, in comparison to the morphology development on the ion-irradiated silicon surface, suggests that sufficiently effective pulsed sources of hypersonic (in the initial propagation stage) shock waves appear in the Ar⁺ ion stopping zone. These shock waves arise as a result of the jumplike formation and evolution of a network of dislocation loops and argon blisters, accompanied by explosions of the blisters. These processes probably proceed in a self-synchronized or spontaneous manner. Argon in the blisters occurs at T = 773 K in a solid state under a pressure of 4.5×10⁹ Pa, the blister energy reaching up to 5×10⁸ eV. Estimates show that the synchronized explosions of blisters in the region of a nitrogen-saturated layer at the rear side of a 600-μm-thick silicon wafer may produce a peak pressure at the wave front exceeding 10⁸ Pa, which is sufficient to cause the experimentally observed changes.     

Oxidation inhibiting properties of Si3N4-layers produced by ion implantation

The implantation of nitrogen into silicon to produce Si₃N₄ layers was investigated to find an alternative to CVD-Si₃N₄ layers used in ISOPLANAR-and LOCOS-technology. The technological properties of the implanted Si₃N₄ layers in respect to oxidation inhibition and etching are comparable or superior to CVD-Si₃N₄ layers. The implanted layers are more resistent against oxidation for nitrogen doses of 2.4×10¹⁷ cm⁻² at 30keV. The etching behavior is comparable for both types of Si₃N₄-layers. In the implanted layers no pinholes are found and threre is no formation of a bird's beak, as is well known in the case of CVD-nitride.     

SiO2and Si nanoscale patterning with an atomic force microscope

The use of an atomic force microscope (AFM) as a nanolithographic tool is demonstrated. A photoresist layer several nanometre thin isindented by the vibrating AFM tip, where software control switches the tapping force from the imaging to the patterning mode. The resist pattern is transferred into a 10 nm SiO₂layer on Si(100) by wet chemical etching resulting in 20–40 nm wide lines. Subsequent transfer into the Si substrate using anisotropic KOH etching formed 60 nm wide V grooves.     

Reactive ion etching of dielectric and semiconductor layers in CHF3 and C2F6

Anisotropic etching of submicron structures is possible in an apparatus for reactive ion etching. Etch rates of Si, GaAs, SiO₂ and Si₄N₄ have been measured as a function of pressure and rf power in freons 23 and 116. Etch rate of a Microposit 1350 H positive photoresist and selfbias of a cathode have been measured, too. On the basis of obtained results we have considered possibility of the selective etching of different materials used in technology of semiconductor devices.     

Fabrication of silicon webs in the decananometre range

In addition to the high demands on lithography, short-channel effects are problems for miniaturisation of devices. Double-gate MOSFETs are known to improve the short-channel behaviour and are traded in the ITRS roadmap as a part of non-classical CMOS, which can provide a path to scaling MOSFETs below the 65-nm node. For the centre of a special vertical layout a silicon web with 300-nm height and 20-nm width is required. The web lines are made by electron-beam lithography with hydrogen silsesquioxane (HSQ) as negative tone resist. 23-nm wide and 100-nm high lines in HSQ were attained. The transfer of the structures to a substrate by dry etching results in 30-nm-wide and 300-nm-high silicon lines. PACS 81.16.Nd; 81.16.Rf; 85.30.Tv     

Wettability and reactivity of molten silicon with various substrates

Contact angles of molten silicon on various substrates have been determined using the sessile drop method and reactivity has been investigated by examining cross sections between silicon and substrates with an electron-probe microanalyzer (EPMA). The contact angles between molten silicon and oxide substrates, such as SiO₂(s), Al₂O₃(s) and MgO(s), are in the range 85° to 88°. The reaction zone is composed of forsterite (2MgO·SiO₂) and clinoenstatite (2MgO·2SiO₂) on the MgO(s)-side of the interface between the Si and MgO. The contact angle between molten silicon and Si₃N₄ is about 90°. Molten silicon spreads over the SiC plate and the contact angle is estimated to be 8°. Large contact-angle values (around 145°) have been observed on BN substrates. At the interface between Si(l) and the BN substrate, a discontinuous Si₃N₄ layer is believed to form and might retard the dissolution of BN into molten silicon. The BN substrate is regarded as being the most suitable substrate for supporting a molten silicon drop during surface tension measurements, due to the large contact angle and low contamination. PACS 68.08.Bc; 06.30.Bp; 73.40.Ns; 61.72.Tt     

AlN/Si3N4纳米多层膜的外延生长与力学性能

采用射频磁控溅射方法制备单层AlN, Si₃N₄薄膜和不同调制周期的AlN/Si₃N₄纳米多层膜.采用X射线衍射仪、高分辨透射电子显微镜和纳米压痕仪对薄膜进行表征.结果发现,多层膜中Si₃N₄层的晶体结构和多层膜的硬度依赖于Si₃N₄层的厚度.当AlN层厚度为4.0nm、 Si₃N₄层厚度 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 应力场 超硬效应     

Optical and electrical properties of nanostructured implanted silicon n+-p junction passivated by atomic layer deposited Al2O3

This paper investigates the optical and electrical properties of nanostructured implanted silicon junctions passivated by Al₂O₃ layers. A two-step ion implantation method has been developed to fabricate the nanostructured n⁺-p junctions with theoretical support of two dimensional Monte Carlo simulations to predict and optimize the junction profile. Dense and uniform arrays of silicon nanopillars and nanocones were formed by combining nanosphere lithography and dry etching, exhibiting a low reflectance in a broad spectrum from 300 to 800 nm. A conformal Al₂O₃ layer was deposited on the array by using thermal atomic layer deposition (ALD) to achieve chemical passivation effect. External quantum efficiency and power conversion efficiency of the junctions were measured versus nanostructuration and Al₂O₃ passivation. The results showed that significant enhancement of efficiency can be achieved on the passivated nanopillar-based junctions.     

Fabrication of freestanding nanoscale gratings on silicon-on-insulator wafer

We report a bottom-up process for the fabrication of freestanding nanoscale gratings on silicon-on-insulator (SOI) wafer. Freestanding membrane devices suffer deflection due to the residual stress of the buried oxide layer of SOI wafer. The deflection will affect the device shape and result in the fracture problem for devices fabricated on thin silicon membrane. The bottom-up process is developed to overcome the fabrication issue for thin silicon membrane gratings. The silicon handle layer is removed through back wafer etching of silicon, where the buried oxide layer acts as an etch stop layer. The grating structures are then defined on thin silicon device layer by electron beam lithography and generated by fast atom beam etching. The grating structures are finally released in vapor HF to form the freestanding nanoscale gratings. The freestanding linear/circular gratings, 1,500-nm period grating with the grating width of 200- and 850-nm period grating with the grating width of 100 nm, are successfully achieved on 260-nm silicon device layer.     

High-resolution analytical electron microscopy of catalytically etched silicon nanowires

We report on the characterization of hexagonally ordered, vertically aligned silicon nanowires (SiNW) by means of analytical transmission electron microscopy. Combining colloidal lithography, plasma etching, and catalytic wet etching arrays of SiNW of a sub-50 nm diameter with an aspect ratio of up to 10 could be fabricated. Scanning transmission electron microscopy has been applied in order to investigate the morphology, the internal structure, and the composition of the catalytically etched SiNW. The analysis yielded a single-crystalline porous structure composed of crystalline silicon, amorphous silicon, and SiO _x with x≤2.     

Crystallization of amorphous Si3N4 and superhardness effect in HfC/Si3N4 nanomultilayers

HfC/Si₃N₄ nanomultilayers with various thicknesses of Si₃N₄ layer have been prepared by reactive magnetron sputtering. Microstructure and mechanical properties of the multilayers have been investigated. The results show that amorphous Si₃N₄ is forced to crystallize and grow coherently with HfC when the Si₃N₄ layer thickness is less than 0.95 nm, correspondingly the multilayers exhibit strong columnar structure and achieve a significantly enhanced hardness with the maximum of 38.2 GPa. Further increasing Si₃N₄ layer thickness leads to the formation of amorphous Si₃N₄, which blocks the coherent growth of multilayer, and thus the hardness of multilayer decreases quickly.