Single-crystal Silicon Surface Research Articles

STUDYING THE INFLUENCE OF PROTON IRRADIATION ON THE DISTRIBUTION PROFILE OF Pt AND Cr IN SURFACE LAYERS n-Si˂Pt˃, n-Si˂Сr˃ USING ELLIPSOMETRIC SPECTROSCOPY

In this work, the effect of high-temperature doping and proton irradiation on the depth profile and the creation of layers on the surface of single-crystal silicon was studied. The study used singlecrystal n-type silicon samples doped with phosphorus during growth. These samples were first doped with platinum and chromium and after polishing they were irradiated with protons with an energy of 2 MeV, a dose of 5.1 × 1014 cm–2 at the EG-5 accelerator. Studies of the optical properties of the sample surface were carried out using an ELLIPS-1991 spectroscopic ellipsometer at room temperature

Polarization-Dependent Anisotropy of LIPSSs' Morphology Evolution on a Single-Crystal Silicon Surface.

Utilizing the principle of laser-induced periodic surface structures (LIPSSs), this research delves into the morphological evolution of single-crystal silicon surfaces irradiated by a near-infrared picosecond laser through a scanning mode. With the increase in laser energy density, the nanostructure morphology on single-crystal silicon surfaces induced by incident lasers with different polarization directions sequentially produces high spatial-frequency LIPSSs (HSFLs) with a period of 220 nm ± 10 nm parallel to the laser polarization, low spatial-frequency LIPSSs (LSFLs) with a period of 770 nm ± 85 nm perpendicular to the direction of the polarization, and groove structures. Furthermore, by varying the angle between the laser polarization and the scanning direction, the study examined the combined anisotropic effects of the laser polarization scanning direction angle and the laser polarization crystal orientation angle on the genesis of LIPSSs on single-crystal silicon (100) surfaces. The experiments revealed polarization-related anisotropic characteristics in the morphology of HSFLs. It was found that when the polarization angle approached 45°, the regularity of the LSFLs deteriorated, the modification width decreased, and the periodicity increased. This is critical for the precise control of the LSFLs' morphology.

On the Formation of an Anti-Reflection Layer on the Surface of Single-Crystal Silicon by Ion-Beam Etching

On the Formation of an Anti-Reflection Layer on the Surface of Single-Crystal Silicon by Ion-Beam Etching

Improving machinability of single-crystal silicon by cold plasma jet

Single-crystal silicon has been widely applied in the semiconductor industry due to its excellent properties. However, the material is highly susceptible to surface damage during processing because of its high hardness and brittleness, thus restraining manufacturing quality and practical applications. Although methods like ion implantation have been proposed to reduce hardness and improve machinability, the efficiency is relatively low, and cannot achieve real-time adjustment of material properties during machining. In this paper, we propose a high-efficient and environmentally-friendly method to adjust mechanical properties and improve machinability of the single-crystal silicon by atmospheric-pressure cold plasma. According to nanoindentation and single-point diamond scratching experiments, the cold plasma can effectively reduce microhardness and promote deformation of single-crystal silicon. We then investigate the influence mechanism by surface characterizations using transmission electron microscope, X-ray photoelectron spectrometer, and Raman spectrometer, and discover that the cold plasma forms an amorphous silicon oxides layer on the single-crystal silicon surface. Finally, we perform micro-milling experiments with real-time plasma treatment on the single-crystal silicon surfaces to study the effect of the cold plasma on material machinability. The results demonstrate that the cold plasma can significantly improve surface quality, alleviate chip adhesion and prolong tool life. The proposed real-time cold plasma treatment method may have promising application prospects in precision manufacturing of the single-crystal silicon.

The Spontaneous Escape Behavior of Silver from Graphite-like Carbon Coatings and Its Effect on Corrosion Resistance.

Silver-doped graphite-like carbon (Ag-GLC) coatings were prepared on the surface of aluminum alloy and single-crystal silicon by magnetron sputtering under different deposition parameters. The effects of silver target current and deposition temperature, as well as of the addition of CH4 gas flow, on the spontaneous escape behavior of silver from the GLC coatings were investigated. Furthermore, the corrosion resistance of the Ag-GLC coatings were evaluated. The results showed that the spontaneous escape phenomenon of silver could take place at the GLC coating, regardless of preparation condition. These three preparation factors all had an influence on the size, number and distribution of the escaped silver particles. However, in contrast with the silver target current and the addition of CH4 gas flow, only the change in deposition temperature had a significant positive effect on the corrosion resistance of the Ag-GLC coatings. The Ag-GLC coating showed the best corrosion resistance when the deposition temperature was 500 °C, which was due to the fact that increasing the deposition temperature effectively reduced the number of silver particles escaping from the Ag-GLC coating.

Ионно-лучевое формирование серебросодержащей поверхности пористого кремния

The results of a study of the formation of a silver-containing porous layer on the surface of single-crystal silicon KEF-4,5 by ion-beam alloying are presented. A computer simulation of the process of ion doping of silicon with KEF-4,5, high-energy helium and silver ions was carried out using the TRIM/SRIM software package in order to determine the dose and energy neighborhoods of helium and silver ions necessary and sufficient in the experiment. The relief of the porous surface, the density of quasi-pores on the surface of implanted silicon, the elemental composition of the obtained porous composite silver-containing layers, taking into account the effect of intermediate heat treatment on it, are studied. The ion-beam formation of a silver-containing coating ensures the creation of a developed surface relief at the nanoscale with high reproducibility and controllability inherent in the ion doping method, which contributes to an increase in the yield of usable solar cell products. The technological modes of high reproducibility and controllability inherent in the ion doping method are determined based on the experimental data obtained for studying the relief of a porous surface and the density of quasi-pores on the surface of implanted silicon from the energy and dose of helium ions. Based on the study of the elemental composition of the quasi-porous composite silver-containing layer obtained by implantation of silver ions, the recommended parameters of implantation of silver ions have been established.

In English

We report the synthesis of β-SiC/por-Si/mono-Si heterostructure by a hybrid method, consisting of the electrochemical etching of the single-crystal silicon surface with a subsequent carbidization by a thermal annealing in a methane atmosphere. This method has a number of advantages over the known ones, because it is cheap enough and allows one to form the silicon carbide layers of high- quality. The formed structure was studied by means of SEM, EDX and XRD methods. As a result, the dense β-SiC layer, consisting of an array of the spherical islands with diameters of 2–6 μm, coated with the small pores, was formed on the por-Si/mono-Si surface. The geometric dimensions of the islands were studied by calibrating the sample image in the ImageJ software package. The maximum value of the linear size (diameter) of the island dmax = 5.95 μm and the minimum value dmin = 2.11 μm were found in the studied area. In general, the average diameter of the islands is d = 3.72 μm. The distribution has the left-sided asymmetry, that is, the smaller islets predominate. Roundness (the ratio of the area to the square of the larger axis) R = 0.86. According to the results of EDX analysis, it was found that the synthesized structure surface consists exclusively of the carbon and silicon atoms, indicating the high quality of the formed structures. It was found that the SiC film crystallizes in the cubic phase. The formation of the islands is explained by means of the layer-plus-island growth model according to Stranski-Krastanow mechanism, which is characterized by the formation of the dense wetting layer with the massive island complex on the surface. It should be also noted that the porous SiC layers of island type can, in turn, show the perspective as the buffers with the heteroepitaxy of the silicon substrate materials.

Molecular dynamics simulation on crystal defects of single-crystal silicon during elliptical vibration cutting

In recent years, elliptical vibration cutting (EVC) has become a promising technique to fabricate high quality surface of single-crystal silicon. However, our understanding for its cutting mechanism, especially the evolution of the crystal defects in subsurface workpiece is insufficient. In this paper, molecular dynamics simulation was carried out to explore the formation mechanism of crystal defects in single-crystal silicon during EVC. A three-dimensional MD model was adopted to demonstrate the interaction between subsurface damage and tool movement in one vibration cycle. The results indicate that the formation mechanism of surface morphology including elastic recovery and side flow is greatly determined by the cutting stage in EVC. Meanwhile, the preferred slip motion during subsurface damage formation is distinct in the extrusion and shear stage. Furthermore, the influence of cutting temperature and speed on the formation of crystal defects was investigated. It is found that at elevated temperature, the proportion of the Shockley partial dislocations are apparently increased, and recrystallization process is apparently promoted on the interface of the distorted/crystal region. As the speed ratio increases, the generation and propagation of the crystal defects are suppressed, which is advantageous for suppressing the subsurface damage. These findings provide a comprehensive theoretical basis for improving the understanding in the formation mechanism of crystal defects of single-crystal silicon in EVC.

Self-Supported Bragg Stacked Microcavities for DNA Sensing

Porous silicon (PSi) layers are prepared on the single-crystal silicon surface by electrochemical etching, and PSi membranes (PSiMs) are fabricated by separating the PSi layers from the single-crystal silicon substrate using high-current pulses. PSiMs have better adsorption and response time than nonseparated PSi layers, making them more suitable for sensing applications. PSi microcavity (PSM) structures are widely used for the detection of biomolecules in biosensors because of their high transmission resonance peaks with narrow full-width at half-maximum (FWHM) in the reflection spectra. However, when compared to PSiMs, the permeability of the PSM on the silicon substrate is low, resulting in a significant reduction in its detection sensitivity. In this study, an efficient self-supported Bragg stacked microcavity (SBSM) structure was prepared for the detection of DNA biomolecules by combining the advantages of PSM and PSiMs. The redshift of the reflectance spectra obtained in the concentration range of 0.1– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5 ~\mu \text{M}$ </tex-math></inline-formula> shows a good linear relationship, with a detection limit of 2.2 nM. The detection sensitivity is improved by more than a factor of ten when compared to the PSM structure on the silicon substrate. The novel device allows DNA biomolecules to enter the porous layers more easily, especially the defective layer, thus improving its detection sensitivity.

Vacuum as a continuum medium forming energy inhomogeneities with high energy density in the liquid phase

A method for the formation of metal nanoparticles in a localized volume with a high energy density due to the flow of a pulsed electric discharge and the effect of cavitation has been studied. The mechanism of formation of energy inhomogeneities, which provides the generation of nanoparticles with high specific energy intensity, is considered. The formation of dynamic heterogeneity is carried out in three stages. There is a breakdown of the interelectrode space and the formation of a vacuum volume, which is filled with a vapor-gas medium. As a result of an increase in pressure in the bubble, a pulsed gas discharge is ignited, which leads to the generation of metal nanoparticles. As a result, there is a localized volume in which the energy in the discharge reaches a value of up to 106 K. The growth of energy in the bubble leads to its collapse and metal nanoparticles pass from a medium with high energy (106) into water at room temperature, which leads to their hardening. Particularly pure nanoparticles of various metals with a size of 5–15 nm are obtained, which can be grown on a single-crystal silicon surface at room temperature and positioned on the surface of porous materials and products of complex configuration.

Tuning the Plasma Etching Mode for the Atomic-Scale Smoothing of Single-Crystal Silicon

Atomic-scale smooth surfaces of single-crystal silicon (Si) are indispensable for cutting-edge applications, such as semiconductor chips, quantum devices, and X-ray optics. Here, we vary the CF4/O2 reactant gas ratio to tune the etching mode from isotropic and orientation-selective etching to atom-selective etching in an atmospheric inductively coupled plasma (ICP). At low CF4/O2 ratios, the diffusion of the etching species dominates, resulting in isotropic etching. By contrast, the kinetics of ICP etching becomes dominant upon increasing the CF4/O2 ratio to between 1:1 and 2:1, inducing orientation-selective etching. Notably, CF4/O2 ratios above 2:1 result in atom-selective etching, whereby atoms around rough surface sites can be selectively removed. The atom-selective etching mode was used to achieve an atomically smooth surface with a Sa roughness of 0.14 nm. The results of this study demonstrate that atom-selective etching is an efficient and effective approach for manufacturing Si atomic surfaces.

Atomic Force Microscopy Exploration and Optical Characteristics Analysis of Nanosecond Fiber Laser Micro-textured Single-Crystal Silicon Surfaces

Atomic Force Microscopy Exploration and Optical Characteristics Analysis of Nanosecond Fiber Laser Micro-textured Single-Crystal Silicon Surfaces

Vacuum as a continuum medium forming energy inhomogeneities with a high energy density in the liquid phase

A method for the formation of metal nanoparticles in a localized volume with a high energy density due to the flow of a pulsed electric discharge and the cavitation effect was studied. The mechanism of the formation of energy inhomogeneities providing for the generation of nanoparticles with a high specific energy intensity was considered. Dynamic heterogeneity forms in three stages. There is a breakdown of the inter-electrode gap and the formation of a vacuum volume filled with a vapor-gas medium. When the pressure inside the bubble increases, a pulsed gas discharge is ignited, thus generating metal nanoparticles. This leads to the formation of a localized volume in which the discharge energy reaches values of up to 106 K. The increase in energy in the bubble leads to its collapse, after which the metal nanoparticles pass from the high-energy (106) medium into water at room temperature, resulting in their hardening. Highly pure nanoparticles of various metals 5–15 nm in size are obtained; these can be grown on a single-crystal silicon surface at room temperature and positioned on the surface of porous materials and products of complex configuration.

Optical second harmonic generation: role of symmetry and local resonances (review)

We report some results of studying optical second-harmonic generation (SHG) on surfaces and at interfaces of centrosymmetric media, in resonant nano- and microstructures, and in ferroelectric materials. The research was carried out at the Department of Quantum Electronics of the Lomonosov Moscow State University under the supervision of Professor O.A. Aktsipetrov, and subsequently developed by his disciples. As examples that clearly demonstrate the possibilities of the SHG method for examining nonstandard objects of nonlinear optics, we discuss the behaviour of the nonlinear optical response of single-crystal silicon and germanium surfaces and their interfaces with oxides, as well as nonlinear electroreflection. Optical interferometry and its possibilities are briefly described using the example of these systems. Unique sensitivity of SHG to the symmetry and resonance properties of nanostructures, including magnetic ones, is shown, which determines the efficiency of this method for investigating such systems. Finally, we demonstrate that the SHG effect is a unique remote and sensitive method for studying ferroelectric structures.

Influence of ion-beam etching by Ar ions with an energy of 200-1000 eV on the roughness and sputtering yield of a single-crystal silicon surface.

The behavior of sputtering yield and the surface roughness of monocrystalline silicon of orientations ⟨100⟩, ⟨110⟩, and ⟨111⟩ under the ion-beam bombardment by neutralized Ar ions with energies of 200-1000 eV is studied. The significant dependence (modulation) of sputtering yield on incidence angle due to crystalline structure is observed. It is shown that a sharp increase in the sputtering yield and a decrease in the effective surface roughness at energies above 400 eV occurs. At energies of more than 400 eV for orientations ⟨100⟩, ⟨110⟩, and ⟨111⟩ at normal ion incidence, smoothing of the effective roughness in the range of spatial frequencies ν∈[4.9⋅10-2-6.3⋅101µm-1] up to a value of 0.17 nm is observed. This makes it possible to use the ion-beam etching technique for finishing polishing, aspherization, and correction of local shape errors of single-crystal silicon substrates, which are of the greatest interest for synchrotrons of the 3rd+ and 4th generation and x-ray free electron lasers.

The generation mechanism and suppression method of the "comet tail" defect on the single-crystal silicon surface polishing with magnetorheological

Single-crystal silicon is an important material in the high precision reflector, and its processing quality directly affects the overall performance index of the reflector. Aiming at the problem of “comet tail” defect produced by the magnetorheological machining process, the process parameters are controlled by the combination of experiments and simulations, and the surface roughness changes after different scanning speeds under the same removal depth are compared and analyzed. The results show that under the same process parameters, the probability of “comet tail” defects are related to density and surface quality. The main factors affecting the occurrence probability and density of “comet tail” defects are process parameters. In actual processing, it is necessary to establish a threshold of process parameters, so that the “Comet tail” defect is less within the threshold and can be quickly removed. The final threshold range is: buffing wheel speed< 220rpm, flow rate< 80L/min, depth coefficient< 0.25, magnetic field strength< 7A. By discussing the “Comet tail” defect suppression method and key technology, it provides technical support for the realization of high precision control manufacturing of single-crystal silicon.

Feasibility study of single-crystal silicon ductile-regime turning via fast tool servo

Due to the material properties of single-crystal silicon, it is difficult to achieve high-efficiency processing in conventional turning. Fast tool servo (FTS) turning has emerged as a favorable technology for processing brittle materials. This paper investigates the tool radius, feed speed, and cutting depth effects on the maximum undeformed chip thickness (MUCT). A high-frequency low-coupling FTS system is designed for processing experiments. Effects of the tool rake angle, tool radius, cutting speed, and vibration frequency on the critical undeformed chip thickness (CUCT) are explored in this paper. Experimental results indicate FTS technology can increase the CUCT from 80 nm to 580 nm. Surface and subsurface morphology tests of conventional and FTS single-crystal silicon cutting verify that FTS technology can obtain an optical surface roughness of 5 nm and lower subsurface damage. Moreover, FTS turning can reduce tool wear. Lastly, through Raman spectroscopy analysis, the amorphous phase remaining on the machined surface is lower when FTS turning is employed.

Characterization of randomly rough surfaces using angle-resolved scattering of light and atomic force microscopy

The roughness of four samples of silicon single-crystal surfaces roughened by anodic oxidation is studied using atomic force microscopy (AFM) and angle-resolved scattering of light. The power spectral density functions (PSDFs) are determined on the basis of the measured values of the intensity of the scattered light. This is done on the basis of three models, which establish relation between the intensity of the light scattered in the given direction and the values of the PSDF at a certain spatial frequency. Two of the models are based on the scalar diffraction theory (SDT), while the third is based on the Rayleigh–Rice perturbation theory. The formulae corresponding to the SDT are derived in the theoretical part of the paper. The condition for the Fraunhofer diffraction is not satisfied if the values of the wavelength, distance to the detector and the dimensions of the illuminated spot on the sample used in the experiment are considered. However, it is shown that if the calculation of the intensity of the scattered light is performed in a certain way, then the validity of the expansion only up to the linear terms in the phase terms, i.e. in the same way as in the Fraunhofer diffraction, is not limited by the dimensions of the light spot but by the autocorrelation length of the randomly rough surface. The results obtained by the optical methods are compared with those obtained by AFM. It is shown that there is a good agreement between these results.

Nanoindentation Characterization of Single-Crystal Silicon with Oxide Film

In order to obtain ultra-smooth surfaces of single-crystal silicon in ultra-precision machining, an intensive study of the deformation mechanism, mechanical properties, and the effect of oxide film under load is required. The mechanical properties of single-crystal silicon and the phase transition after nanoindentation experiments are investigated by nanoindentation and Raman spectroscopy, respectively. The results show that the pop-in event occurring in the theoretical elastic region of single-crystal silicon is caused by the stress concentration at the interface between the oxide film and the substrate. This causes the single-crystal silicon to be converted from the elastic deformation zone to the plastic deformation zone. And at this time, the elastic domain area is almost negligible, which seriously affects the machinability of single-crystal silicon for ultra-precision processing. In addition, the experimental data of single-crystal silicon under ultra-low load deviates greatly relative to the real value and fluctuates widely. However, when the nanoindentation experiment enters the fully plastic deformation zone of single-crystal silicon, the test results of its mechanical properties will be more accurate.

Experimental Research on Discharge Forming Cutting-Electrochemical Machining of Single-Crystal Silicon

During the wire electrical discharge machining (WEDM) process, a large number of discharge pits and a recast layer are easily generated on the workpiece surface, resulting in high surface roughness. A discharge forming cutting-electrochemical machining method for fabricating single-crystal silicon is proposed in this study to solve this problem. On the same processing equipment, single-crystal silicon is first cut using the discharge forming cutting method. Second, electrochemical anodic reaction technology is used to dissolve the discharge pits and recast layer on the single-crystal silicon surface. The machining mechanism of this process, the surface elements of the processed single-crystal silicon and a comparison of the kerf width are analyzed through experiments. On this basis, the influence of the movement speed of the copper foil electrode during electrochemical anodic dissolution on the final surface roughness is qualitatively analyzed. The experimental results show that discharge forming cutting-electrochemical machining can effectively eliminate the electrical discharge pits and recast layer, which are caused by electric discharge cutting, on the surface of single-crystal silicon, thereby reducing the surface roughness of the workpiece.