Monocrystalline Silicon Substrates Research Articles

Measurement for mechanical behavior and fatigue property of Cu films by nanoscale dynamic load method

Mechanical behavior and fatigue properties greatly influence the reliability and life of film materials. Quantitative testing of film fatigue property under dynamic load is realized on the basis of nanometers thick Cu films deposited on monocrystalline silicon substrates by magnetron sputtering system. Microstructure and surface pattern of copper films are characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Film hardness and modulus are measured by quasi-static test and continuous measurements (CMX) systems of nanomechanical testing instrument. Fatigue damage behaviors are investigated by nanoscale dynamic mechanical analysis (nanoDMA) technique. The results indicate that Cu films prepared by magnetron sputtering system present (111) preferred orientation and contain a large number of nanoscale grains with uniform texture and low roughness. As is affected by substrate and small scale effect, CMX method is more suitable than quasi-static method for the measurement of micro-mechanical properties of ultra-thin films. Fatigue dominantly happens in thinner films. Factors, like thickness, inner stress, modulus and hardness, can influence fatigue life of nanoscale Cu films.

Design of Double-Sided Polishing Machine for Functional Crystal Substrate

Responding to the demand on the ultra-precision equipment for machining monocrystalline silicon, sapphire, zirconia ceramics and other large-size functional crystal substrates in the microelectronics and optoelectronics manufacturing, this study analyzes the current state-of-the-art of polishing technologies and the technical challenges to achieving high surface quality substrates. In this study, a planetary double-sided polishing machine is designed to solve the problem between achieving high polishing quality and efficiency. The machine is characterized by process stability, large polishing pressure and high polishing speed, etc. which is verified by polishing zirconia substrates with satisfactory results: material removal rate of 5 μm/h and the surface roughness Ra of 1 nm.

Motion-free all optical inspection system for nanoscale topology control.

We present a novel all optical method for nanoscale pattern inspection. This method uses the chromatic aberration in an imaging optical system and a tunable light source. Such an approach allows stable and precise inspection of nanoscale objects based on an analysis of their defocused diffraction patterns without any external mechanical influence on the sample or optical system. We demonstrate the efficiency of a low cost light source tunable in the range of a light emitting diode bandwidth of ~30 nm (FWHM) for providing the required defocusing. The proposed method is tested using calibrated lines (height 50 nm, length 100 μm, critical dimension (СD) value range 40-150 nm with 10 nm steps) on a monocrystalline silicon substrate with demonstrated measurement accuracy better than 10 nm. A comparison of this all optical method with a mechanical scanning inspection system is discussed.

Anti-friction property of surface patterning nano-hard film on the monocrystalline silicon surface

Purpose – Three types of pattern on the monocrystalline silicon surface were prepared by using laser surface processing equipment. The DLC film and Si-DLC film on the patterning surface were deposited by using PECVD-2D plasma chemical vapor deposition sets. The paper aims to discuss these issues. Design/methodology/approach – The tribological properties of the films were investigated by using the UMT-2 micro friction and wear tester. The surface topography, composition, hardness and elastic modular of the films were determined by Raman spectrum, nano mechanics tester and three-dimensional topography instrument. The worn surface topographies of the surface patterning films were tested by scanning electron microscopy. Findings – The results show that the patterning monocrystalline silicon substrate surface has good anti-friction property under low load. The patterning DLC film and Si-DLC film surface have very good anti-friction property under all the test loads. The reason of these results is that the surface patterning film not only reduces the real contact area of the friction pairs but also has low surface bonding force. Originality/value – This paper prepared three kinds of microscopic patterns on the monocrystalline silicon surface by using laser surface processing equipment. And then deposited DLC film and Si-DLC film on the patterning surface. All kinds of surface patterning monocrystalline silicon had very good anti-friction property under low load. And all kinds of surface patterning nano-hard film had perfect anti-friction property under all test loads.

Effect of the experimental parameters on the shape and formation kinetics of SiNWs formed by electroless chemical etching in aqueous AgNO3/HF/H2O2 solution

AbstractThe discovery at the beginning of 1990 of carbon nano‐tubes awaked the interest for one‐dimensional (1D) nanostructures. Currently, silicon nanowires (SiNWs) formed by electroless chemical etching in aqueous Ag‐NO3/HF/H2O2 solution, arouse great interest due to their physical properties and potential applications. The understanding of physical‐chemical phenomena that occur during the formation of SiNWs, the effect of etching parameters on their morphology, the formation mechanism and formation kinetic raise many questions. In this paper, we investigate the effect of etching parameters; namely AgNO3 concentration, HF concentration, etching time and the volume of H2O2 on the shape of obtained nanostructures. The formation kinetic was investigated by studying the effect of the etching time on the morphology of obtained nanostructures. SiNWs studied in this work were formed on a P type and (100) oriented monocrystalline silicon substrate. Characterization of formed SiNWs was performed using a scanning electron microscope (SEM). (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modification of surface morphology of a textured silicon substrate and its application in heterojunction solar cells

Texture on a mono-crystalline silicon substrate can effectively enhance the light trapping, and increase the short-circuit current of silicon hetero-junction solar cell. However, when the amorphous silicon layer deposited on the crystalline silicon substrate, the amorphous and crystalline epitaxial growth of mixed phases is created in the valleys with sharp edges, which leads to reducing the output characteristic parameters of the solar cell. In this paper, we use two methods to modify the microstructure of the textured substrate, and apply them to the silicon heterojunction solar cell. The textured silicon substrate is smoothed through the mixed acid, which makes the pyramid shape become round off and the open circuit voltage of the solar cell change from 564.6 mV to 609.4 mV. In addition, we use tetramethyl ammonium hydroxide (TMAH) instead of alkali solution. It is found that the textured substrate has an effective light trapping, and its micro-morphology is more rounded, the short-circuit current and open circuit voltage of the solar cell have been improved significantly.

In situ high-resolution transmission electron microscopy of material reactions

Abstract

Enhancement of near IR sensitivity of silicon‐silicide based photodetectors

AbstractInvestigation of photo‐emf spectra of heterostructures with embedded chromium and iron disilicide nanoparticles in the monocrystalline silicon substrates was carried out. Formation of the samples was performed using two different methods: ion‐beam synthesis (IBS) and molecular‐beam epitaxy (MBE). The samples contain a precipitates of CrSi2 and β‐FeSi2 obtained after annealing by pulsed ion‐beam treatment of ion‐beam synthesis. In the molecular‐beam deposited samples there were two bilayers of chromium and iron disilicide or eight layers of β‐FeSi2 in the form of nanocrystallites. It was shown, that MBE heterostructure with Cr and Fe shows 3 times higher photoresponse at the energy 0.85 eV compared to reference diode at room temperature. The highest impact at 130 K in the photoresponse signal (about three orders) was achieved in the eight‐period β‐FeSi2MBE sample. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mold Pattern Fabrication by Nanoscratching

MEMS technologies for various nano/micro-devices often requires special facilities and complicated,multistage processes. The fabrication cost is thus extremely high. Consequently, alternative solutions have been sought, and NanoImprint Lithography (NIL) is one of the potential solutions. To date, the nano/micromolds for NIL are mainly fabricated using photolithography or focused ion beams. However, such beam methods generally make use of special instruments and require a long time to draw precise patterns. Thus, this study aims to fabricate nanoscale structures on monocrystalline silicon substrates using nanoscratching, which can potentially be used to fabricate nano/micro-molds for NIL. This paper discusses how various nano/micro-scale structures such as lineand-space, single-layer, and multiple-layer structures were fabricated on a silicon substrate using nanoscratching by an atomic force microscope equipped with a sharp probe made of monocrystalline diamond. Subsequent chemical etching was also conducted on the fabricated groove patterns to enlarge the depth of the fabricated groove patterns. The results confirmed that the groove was deepened several times, with only a slight increase in its width. A nanoimprint experiment was also carried out, and the line-and-space patterns were duplicated successfully on a polycarbonate resin film.

Method for optical inspection of nanoscale objects based upon analysis of their defocused images and features of its practical implementation

A microscopic method to inspect isolated sub 100 nm scale structures made of silicon is presented. This method is based upon an analysis of light intensity distributions at defocused images obtained along the optical axis normal to the sample plane. Experimental measurements of calibrated lines (height 50 nm, length 100 μm, and widths of 40-150 nm in 10 nm steps) on top of a monocrystalline silicon substrate are presented. Library of defocused images of calibrated lines is obtained experimentally and numerically with accordance to experimental setup parameters and measurements conditions. Processing of the measured defocused images and comparison with simulated ones from library allow one to distinguish between objects with a 10 nm change in width. It is shown that influence of optical system aberrations must be taken into account in order to achieve coincidence between simulation and measured results and increase accuracy of line width inspection accuracy. The limits of accuracy for object width measurements using this optical method are discussed.

Effects of indium concentration on the properties of In-doped ZnO films: Applications to silicon wafer solar cells

In the present paper, high-quality In-doped ZnO (ZnO:In) thin films have been prepared by rf-magnetron sputtering on glass and p-type monocrystalline silicon substrates from an aerogel nanopowder target material. The nanoparticles with the [In]/[Zn] ratio varying between 0.01 and 0.05 were synthesized by the sol–gel method and the structural properties have been analyzed. The effect of different dopant concentrations on the electrical, optical, structural and morphological properties of the films has been investigated. The obtained ZnO:In films at room temperature are polycrystalline with a hexagonal structure and a highly preferred orientation with the c-axis perpendicular to the substrate. Scanning electron microscopy and atomic force microscopy have been applied for a morphology characterization of the films' cross-section and surface. The results revealed a typical columnar structure and very smooth surface. Films with good optical transmittance, around 85%, within the visible wavelength region, and low resistivity in the range of 10−3Ω·cm and high mobility of 4cm2/Vs, were produced at low substrate temperature. On the other hand, we have studied the position of the p–n junction involved in an Au/In2O3:SnO2/ZnO:In(n)/c-Si(p)/Al structure by electron beam induced current. Current density–voltage characterizations in the dark and under illumination were also performed. The cell exhibits an efficiency of 6%.

Surface Morphology and Magnetic Properties of CoFe<sub>2</sub>O<sub>4</sub> Thin Films Prepared via Sol–Gel Method

The thin films of CoFe2O4 spinel ferrite were prepared on the substrates of monocrystalline silicon(100) at low temperature by means of a developed citrate processing.Structural properties and surface morphology of deposited films were examined using an X-ray diffractometer (XRD) and a field emission scanning electron microscope (FESEM). XRD patterns of all deposited films consisted of a single phase of cobalt ferrite and they did not have any preferred orientation. FESEM micrographs of CoFe2O4 films showed that the film calcined at 400°C had a surface morphology different from the ones at 700°C and 800°C. The surface morphology of the samples was very different with various alcined temperatures. Magnetic properties measured at room temperature showed that the films did not have any magnetically preferred orientation. The maximum values of the coercivities measured at perpendicular and in-plane directions were 3.873 and 2.70 kOe, respectively.

Annealing effect on the magnetic properties of evaporated CoCr thin films

Series of Co x Cr 1− x thin films have been evaporated under vacuum onto monocrystalline silicon substrate, x being atomic percent of cobalt. The thickness ranges from 17 to 220 nm, values measured by Rutherford backscattering spectrometry. The samples have been annealed under vacuum for one hour at 700 °C. The as deposited films show a hexagonal close packed (hcp) structure while the annealed films show both hexagonal close packed and face centered cubic (fcc) structures. While the as deposited films are under a compressive stress, the annealed films, on the contrary, are under a tensile stress. The hysteresis loops present the same features for the as deposited and annealed films concerning the in-plane and out-of-plane anisotropies. Nevertheless, the coercive field is strongly improved for the annealed films . Moreover, these latter films present very high values of the squareness. A squareness value up to 0.96 has been measured. All these results and others are analyzed and discussed.

Exfoliated ∼25μm Si Foil for Solar Cells with Improved Light-Trapping

ABSTRACTInvestigation of optical absorption in ∼25μm thick, monocrystalline silicon (Si) substrates obtained from a novel exfoliation technique is done by fabricating solar cells with single heterojunction architecture (without using intrinsic amorphous silicon layer) with diffused back junction and local back contact. The ease of process flow and the rugged and flexible nature of the substrates due to thick metal backing enables use of various light-trapping and optical absorption enhancement schemes traditionally practiced in the industry for thicker (>120μm) substrates. Optical measurement of solar cells using antireflective coating, texturing on both surfaces, and back surface dielectric/metal stack as mirror to reflect the long wavelength light from the back surface show a very low front surface reflectance of 4.6% in the broadband spectrum (300nm-1200nm). The illuminated current voltage (IV) and external quantum efficiency (EQE) measurement of such solar cell shows a high integrated current density of 34.4mA/cm2, which implies significant internal photon reflection. Our best cell with intrinsic amorphous silicon (i-a-Si) layer with only rear surface textured shows an efficiency of 14.9%. EQE data shows improved blue response and current density due to better front surface passivation. Simulations suggest that with optimized light trapping and surface passivation, such thin c-Si cells can reach efficiencies >20%.

Photoluminescences and structrue performances of Si-rich silicon nitride thin films containing Si quantum dots

Silicon-rich silicon nitride (SiNx) thin films are deposited at 220 ℃ on n-type monocrystalline silicon substrates by plasma enhanced chemical vapor deposition using NH3 and SiH4 as the reaction gases. The samples are annealed at temperature in a range of 500-1100 ℃ in N2 atmosphere. We analyze the crystalline states of silicon quantum dots (Si-QDs) and calculate the crystalline ratios of samples under different annealing conditions according to the Raman spectra. The crystalline ratio is less than 18% when the annealing temperature is lower than 950 ℃, when the temperature reaches 1100 ℃, the crystalline ratio is increased to 53%, which indicates that most of the Si-QDs have been converted into crystallines. Fourier transform infrared spectra are measured at room temperature to investigate the evolutions of the bonding structures within the SiN_x matrix. We find that the wavelengths of Si-N and Si-H bond shift toward higher wavelength, which manifests the formation of near stoichiometric silicon nitride. Photoluminescence generated from all samples is investigated in detail. We find five luminescence peaks, whose origins are analyzed. We conclude that the obvious green luminescence (centred at 500-550 nm) oringinates from Si-QDs and the others come from different defects in the films. The effects of sizes and distribution of Si-QDs on the shift of the luminescence peak are discussed. We acquire that the sizes of Si-QDs are in a rang from 1.6 nm to 3 nm, which have an obvious confinement effect. These results are useful for fabricating contronllable Si-QDs and achievement of luminescent devices based on Si-QDs.

Inhomogeneous nanostructured honeycomb optical media for enhanced cathodo- and under-x-ray luminescence

Photo-, radio-, and pulse cathodoluminescence spectra from sol-gel derived titania, doped with strontium and terbium, deposited on porous anodic alumina (PAA) films are reported. The morphology and qualitative elemental depth distributions have been examined by transmission electron microscopy, scanning electron microscopy, and radio-frequency glow discharge optical emission spectroscopy. PAA films with pore and cell sizes ranging from 170 to 190 and 240 to 270 nm, respectively, have been generated on aluminum and monocrystalline silicon substrates followed by spin-on sol-gel derived coating with the subsequent thermal treatment. The resultant PAA surface is not coated with a continuous xerogel film; the xerogel is mainly distributed near the pore bases, leaving much of the pore volume unfilled. The xerogel/PAA structures reveal terbium-related luminescence under x-ray excitation and cathodoluminescence. The same xerogels generated on monocrystalline silicon revealed no cathode- or under-x-ray luminescence. Thus, PAA enhances strongly the cathode- and under x-ray luminescence from terbium and strontium-doped titania xerogels confined in the porous matrix. The fabricated structures are considered as a type of low-cost, thin-film convertor of x-rays, and cathode ray irradiation into visible light, with an average cell size of the convertor of about 250 nm.

Electronic interface properties of silicon substrates after ozone based wet-chemical oxidation studied by SPV measurements

The preparation of ultra-thin oxide layers on mono-crystalline silicon substrate surfaces with ozone dissolved in ultra pure water at ambient temperature was investigated as a low cost alternative to current wet-chemical cleaning and passivation processes in solar cell manufacturing. Surface photovoltage technique was applied as fast, nondestructive, and surface sensitive method, to provide detailed information about the influence of oxidation rate and substrate surface morphology on electronic properties of the oxidised silicon interfaces and subsequently prepared hydrogen terminated surfaces. Sequences of wet-chemical oxidation in ozone containing ultra pure water and subsequent oxide removal in diluted hydrofluoric acid solution could be utilised to prepare hydrophobic substrates, which are predominantly required as starting point for layer deposition and contact formation. On so prepared hydrogen-terminated substrates values of interface state densities Dit,min≈5×1011eV−1cm−2 could be achieved, comparable to values obtained on the same substrates by the standard RCA process followed by HF dip.

Optimization of Post-Texturization Cleans for Heterojunction Solar Cells

Solar cells employing heterojunction emitters of amorphous silicon (a-Si) on a monocrystalline silicon (c-Si) substrate have demonstrated high efficiencies without requiring high-temperature processing [. An example of such a cell structure is shown in Figure 1. It has been found that the cell efficiency can be boosted by inserting a thin undoped (intrinsic) a-Si layer between the a-Si emitter and the c-Si substrate. The thin intrinsic layer provides very good passivation of interface defects, thus reducing the surface recombination velocity.

Influence of Technical Parameters on the Residual Stress in the Diamond Coating

The diamond coatings were prepared by hot filament chemical vapor deposition(HFCVD) on the mono-crystalline silicon substrates. The influence of the technical parameters such as methane volume ratio, substrate temperature and reaction pressure on the residual stress in the diamond coating was studied. The results showed that the residual stress in the coating was compressive stress in the range of parameters studied, and too high or too low substrate temperature, chamber pressure and methane volume ratio would all increase the residual compressive stress. This relationship can be explained by the influence of amorphous carbon content, vacancy density and grain size on the residual stress.

The influence of deuteration and helium-implantation on the surface morphology and phase structure of scandium thick film

The effects of deuteration and helium-implantation on the surface morphology and phase structure of scandium (Sc) thick film are investigated by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) methods. The preferred orientation of (002) crystal plane is observed for both films deposited on substrates of monocrystalline-silicon and polished-molybdenum. A great number of holes appear on surface after deuteration and the grain size of ScD2 is bigger than that of Sc, whereas a few ScD0.33/Sc grains with relatively small grain size retain inside crystal. The surface morphologies of scandium and scandium deuteride films are slightly affected by helium-implantation. The formation of helium bubbles with a preferred orientation in the crystal lattice of scandium and scandium deuteride, generated by the aggregation of ion-implanted helium, causes the corresponding diffraction peaks of scandium and scandium deuteride phase to shift towards smaller angles.