Crystal Silicon Research Articles

Cutting depth-oriented ductile machining of infrared micro-lens arrays by elliptical vibration cutting.

Infrared micro-lens arrays (MLAs) are widely used in advanced optical systems due to their advantages such as low focusing depth and high sensitivity. Elliptical vibration cutting (EVC) is a promising approach for the fabrication of MLAs on infrared brittle materials. However, the mechanism of ductile machining of MLAs prepared by EVC has not been fully elucidated so far. In this paper, based on the vibration intermittent cutting characteristics and the transient material removal state, a ductile machining model of MLAs on brittle material by EVC was established. This model effectively calculates the subsurface damage of the machined surface and realizes the prediction of the critical depth for ductile machining of MLAs. Furthermore, the concave micro-lenses were prepared on single crystal silicon by EVC and ordinary cutting (OC) to verify this model. The results demonstrated that EVC could significantly enhance the critical depth by approximately 4.3 times compared to OC. Microstructural surface damage predominantly occurs at the exit side of the tool cutting. This proposed model accurately predicts the actual critical depth, with an average error of about 7.5%. Additionally, elevating the amplitude in the depth of cut direction could increase the critical depth, but a larger amplitude would inhibit the increase of the critical depth. This study contributes to a better understanding of ductile machining of microstructure on brittle materials and facilitates the process optimization of MLAs fabrication using EVC.

Pulsed Rapid Thermal Annealing as a Low Thermal Budget Semiconductor Fabrication Process

Thermal annealing is required in the fabrication of many semiconductor devices. A proper annealing condition, e.g., temperature, atmosphere, and time, can improve the device performance, e.g., by reducing defect densities in bulk films and at interfaces. In addition, the annealing step can generate new structures in previously deposited thin films for various new functions. However, when the annealing condition is improper, e.g., the temperature is too high or the annealing time is too long, the device performance can deteriorate or dysfunction due to damage to the composing material, structure, or even the substrate. The thermal budget is critical in the thermal annealing step.Pulsed rapid thermal annealing (PRTA), which exposes the sample to repeated cycles of short-period heating and cooling, is a low thermal budget process. In this presentation, the principle of PRTA is presented. Examples of using PRTA in the crystallization of amorphous silicon on the glass substrate to polycrystalline thin films for thin film transistors (TFTs) and solar cells, improving high-k gate dielectric properties for MOS capacitors and solid state incandescent light emitting devices (SSI-LEDs), and preparation of nanocrystals embedded high-k structure for nonvolatile memories will be shown (1-4). Limitations of PRTA and possible improvements will be discussed. Kuo and P. M. Kozlowski, Appl. Phys. Lett., 69(8), 1092-1094 (1996).Kuo, C.-H. Lin, and M. Zhu, IEEE Photovoltaic Specialist Conf. PVSC 35, 3698-3701 (2010).Y. Kuo and C. H. Lin, ECS 237th Meeting # 130648, May 10-15, 2020.Y. Kuo, ECS 227th Meeting # 47306 (1333), May 24-28, 2015.

Photonic crystal fiber-based silicon polyamide-coated fiber Bragg gratings

Photonic Crystal Fiber (PCF) constructions, controlled light propagation for measuring amplitude, phase, polarization and wavelength of the spectrum, and PCF-incorporated interferometry techniques are the foundations upon which sensors operate. But the existing PCF techniques have very large stretching that tends to be difficult to align due to the cross-polarization mode of the optical fiber structure. Hence, the novel Polymer graphene-based Hexagonal cladding is designed by using a hexagonal hollowed core and a cladding material of Polymethyl methacrylate reinforced with gyroidal graphene which increases confinement strength. Once the crystal structure is designed, normally the presence of substrate the Q-factors is degraded. On substrates, Q-factors are enhanced by fine-tuning the position of the neighboring holes. Hence, the novel Bilayer Grating Stratum solves the degrading issues in Q-factors, which utilizes a Silicon polyamide-coated FBG in the crystal that is incorporated using the Femto-laser technique thereby increasing the wavelength tenability. To identify the electric field pattern, the designed structure is simulated in COMSOL software. Thus, the proposed system has a high sensitivity of 22 with a low material loss of 0.1% and a low response time of 0.2[Formula: see text]s.

Synthesis and Characterization of Silicon–Carbon Powder and Its Resistance to Electron Irradiation

The issue of crystallization of silicon oxide at low temperatures is a topical issue for the electronics of the future. Organosilicon oligomers and polymers are “ideal” sources for obtaining ultrapure silicon ceramics and silicon nanoparticles. This paper presents the results of the synthesis of highly dispersed silicon-carbon powder from an organohydrosiloxane oligomer and the method for increasing its crystallinity at low temperatures. The diffraction pattern of the resulting powder corresponds to the amorphous–crystalline state of the components in this material, as evidenced by two intense and broadened amorphous halos in the region of Bragg angles 2θ = 7–11° and 18–25°. The resulting silicon–carbon powder was subjected to electron irradiation (E = 10 MeV; D = 106–107 Gy). This paper presents the data on the changes in powder properties via IR-Fourier spectroscopy, X-ray phase analysis, and scanning electron microscopy. Irradiation with fast electrons with an absorbed dose of 106 Gy leads to a slight crystallization of the amorphous SiO2 phase. An increase in the absorbed dose of fast electrons from D = 106 to D = 107 Gy leads to the opposite effect. An amorphization of silica is observed. This study showed the possibility of the crystallization of a silicon–carbon powder without a significant increase in temperature, acting only with electron irradiation. It is necessary to continue further research on expanding the boundaries of the optimal doses of absorbed radiation from fast electrons in order to achieve the maximum effect of the crystallization of silicon–carbon powder.

Analysis of the formation of interweaved strips in cast quasi-single crystal silicon ingots

Unlike the impurity behavior of conventional polycrystalline silicon ingots, we have found that impurities are generated at the solid–liquid interface during the growth of quasi-single crystal silicon ingots. Due to the absence of large-angle grain boundaries in quasi-single crystal silicon ingots, impurities become enriched at the solid–liquid interface of the silicon ingot and exhibit a specific directional tilt during crystal growth. The accumulated impurities areas often exhibit a dark interweaved strip morphology detected by an infrared detector of quasi-single crystal silicon ingots. In this study, the dark interweaved strip is identified as an “interweaved shadow”. Additionally, the use of chemical corrosion technology and microscope observations revealed that interweaved shadows were present within the silicon ingot and could be extracted as white filament impurities. Subsequently, the interweaved shadows and dislocations of various morphologies in the silicon brick were analyzed. The interweaved shadows contained a mixture of carbon, oxygen, and nitrogen impurities. The degree of dislocation depended on the size of the filament impurities in the interweaved shadow. Specifically, the concentrations of carbon and nitrogen exceeded the solid solubility and the filament impurities with a diameter greater than 2.1 μm resulted in more severe dislocation defects.

Tool wear prediction method based on bidirectional long short-term memory neural network of single crystal silicon micro-grinding

Tool wear prediction method based on bidirectional long short-term memory neural network of single crystal silicon micro-grinding

Cutting force modeling and control of single crystal silicon using wire saw velocity reciprocation

Single crystal silicon wafers are often used as substrate material for integrated circuits. Often the wafer is cut by a wire with fixed abrasive diamond owning to a narrow kerf and a low cutting force. The cutting force changes during the process as the direction of wire movement continuously reverses (i.e., reciprocates), which may cause the wire saw to break, the wafer to collapse, and the wafer surface roughness to decrease even if the wire saw tension and the contact length between the wire and the wafer are fixed. In this work, a cutting force model including both normal and tangential forces was established to determine the relationship between the normal and tangential forces and the commanded wire speed. Separate controllers were developed to regulate both the normal force and the tangential force by adjusting the wire velocity. Experimental studies were conducted for wire saw processing of single crystal silicon wafers. Compared with a process using constant wire velocity, regulating the normal force can significantly reduce the processing time and the wafer surface roughness. The average improvements in processing time and wafer surface roughness are approximately 11% and 56%, respectively, when using normal force control, and approximately 29% and 30%, respectively, when using tangential force control. The results show that the normal and tangential forces can be well regulated during the machining process. In addition, the wafer surface roughness and machining time were lower in both experiments where the forces were regulated than in the experiment where a constant wire velocity was used. This paper demonstrates that the novel concept of regulating process forces in wire saw machining by adjusting the wire velocity can be used to optimize the cutting process of single crystal silicon, making the process more productive while decreasing the part roughness.

Confirmation of n‐Hexane as an Inert Co‐Solvent in the Production of Functionalized Silicon Nanoparticles from Reactive High‐Energy Ball Milling

AbstractAlkanes such as n‐hexane have been used as co‐solvents in the production of functionalized semiconductor nanoparticles from alkenes and alkynes using Reactive High Energy Ball Milling (RHEBM) under the assumption that they are non‐reactive under typical milling conditions. In this paper, a comparative study with two hydrocarbon solvents of comparable chain length, 1‐hexyne, and n‐hexane, and their milling products using three different commercially available silicon precursors, namely single crystal silicon wafers and polycrystalline particles having a nominal size of 4 µm and 1 mm, is reported. It is found that nanoparticle formation and surface functionalization in all the three silicon systems occurs only with 1‐hexyne; n‐hexane is non‐reactive and does not lead to appreciable functionalized nanoparticle formation under the conditions studied. Nanoparticles (where formed) and microparticle byproducts of appropriate samples are characterized by Transmission electronic microscope (TEM), Fourier transform infrared (FTIR), Photoluminiscence spectroscopy (PL), Nuclear magnetic resonance 1H/13C NMR, and thermogravimetry TGA to separately confirm nanoparticle formation and surface functionalization.

Use of 3D-printing cerebral aneurysm model assisting microcatheter shaping in neurovascular intervention technique training

BackgroundMicrocatheter shaping plays a vital role in coil embolization of cerebral aneurysms, while the complicated method and insufficient training opportunities make it difficult for junior neurovascular clinicians to master this technique. In this program, we constructed a novel training method and assessment system for microcatheter shaping in coil embolization of cerebral aneurysms with 3D technique, and evaluated its efficacy for microcatheter shaping training in junior neurovascular clinicians. MethodsPatient-specific models for cerebral aneurysms in different locations and with different morphologies were selected by experienced senior neurovascular clinicians. The solid polylactic acid model and the soft hollow crystal silicone model of intracranial aneurysms were then made separately for shaping reference and assessment in the training course. Twelve residents without prior experience of microcatheter shaping and 25 neurovascular clinicians who have in vivo experience of microcatheter shaping on 3–5 occasions were selected for this training program and randomly divided into the traditional training group and the experimental training group. Four senior neurovascular clinicians assisted and guided the trainees in two groups and evaluated the time and accuracy of microcatheter shaping. ResultsEighteen trainees were assigned to the traditional training group, among which 4 had prior experience in microcatheter shaping. The other 19 were assigned to the experimental training group, including 8 with prior experience. No statistical difference in the distribution of experienced students between the two groups was noted(P = 0.295). After the training session, the shaping time was found shorter in the experimental training group than that in the traditional training group (40.3.5 ± 16.2 s vs. 54.2 ± 16.4 s, P = 0.014), while the shaping score was found higher in the experimental training group than that in the traditional training group (4.4 ± 0.5 vs. 2.6 ± 1.2, P < 0.001). Specifically, for the trainees without prior experience, the experimental training group also showed less time consumption and higher score (Time: 52.7 ± 7.7 vs. 61.5 ± 9.5, P = 0.02; Score 4.1 ± 0.5 vs. 2.3 ± 1.1, P < 0.01). Meanwhile, for the trainees with prior experience, the advantage was noted in shaping score (4.7 ± 0.3 vs. 3.9 ± 0.6, P < 0.01) but not in time consumption (23.3 ± 4.4 vs. 28.5 ± 3.9, P = 0.07). ConclusionThis training program is quite effective at teaching junior neurovascular physicians the essential surgical abilities required for coiling cerebral aneurysms.

Quantum information approach to the implementation of a neutron cavity

Using the quantum information model of dynamical diffraction we consider a neutron cavity composed of two perfect crystal silicon blades capable of containing the neutron wavefunction. We show that the internal confinement of the neutrons through Bragg diffraction can be modelled by a quantum random walk. Furthermore, we introduce a toolbox for modelling crystal imperfections such as surface roughness and defects. Good agreement is found between the simulation and the experimental implementation, where leakage beams are present, modelling of which is impractical with the conventional theory of dynamical diffraction. Analysis of the standing neutron waves is presented in regards to the crystal geometry and parameters; and the conditions required for well-defined bounces are derived. The presented results enable new approaches to studying the setups utilizing neutron confinement, such as the experiments to measure neutron magnetic and electric dipole moments.

Analytical modeling of subsurface damage and material removal energy in elliptical vibration cutting of micro-structures on brittle materials

Elliptical vibration cutting (EVC) is a promising technique for the fabrication of micro-structures on brittle materials. In this work, the surface quality and material removal energy in ultra-precision machining of micro-structures on brittle materials by EVC were investigated. Theoretical models were first established for predicting subsurface damage and specific cutting energy (SCE) based on the intermittent material removal characteristics of EVC. The models correlated cutting parameters with the tool vibration trajectory parameters, target surface geometry parameters, and material removal modes. Furthermore, the material removal behaviors in the nominal cutting direction and the feeding direction were comprehensively considered. To verify the model, the experiments of EVC and ordinary cutting (OC) were performed on single crystal silicon, and the surface morphology and cutting force were characterized. The results indicated that, compared with OC, the maximum subsurface damage depth is reduced by 61.82% and the SCE stability value is reduced to 45.87% by applying EVC to fabricate micro-structures. EVC could significantly improve the machining quality and reduce energy consumption. In addition, increasing the vibration amplitude in the depth of cut direction could further save energy, but a larger amplitude would increase subsurface damage. This work not only promotes the recognition of the material removal mechanism of EVC, but also presents effective guidance for achieving high-quality and sustainable machining of micro-structured surfaces.

Influence of crystallographic effect on tool wear, cutting stress, cutting temperature, cutting force and subsurface damage in nano cutting of single crystal silicon carbide

Single crystal 3C-SiC as a typical hard and brittle material. Due to its extremely high hardness and brittleness, diamond tools can have drastic wear problems in a short period of time when performing nano-machining processes. Single-crystal 3C-SiC has good anisotropy. In order to gain insight into the effect of crystal orientation on the tool wear behavior during nano-cutting, this paper investigated the tool wear for six cutting crystals downward using molecular dynamics simulation. The tool wear process was analyzed in terms of tool wear, cutting stress, cutting temperature, cutting force and subsurface damage. The results showed that the tool is subjected to large hydrostatic stress concentrations, radial forces and tool temperature concentrations during machining. Under these effects, abrasive wear, graphitic wear and amorphous phase change were produced. In addition, the clearance face of the tool is more severely worn than the rake face. By reasonably selecting the cutting crystal orientation, well control and improvement of tool wear and machined surface quality can be achieved.

Influence of current density on constant current electric field enhanced aluminum induced crystallization of amorphous silicon thin films

In this study, electric field-enhanced aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) thin films was investigated considering various current densities. Constant electric currents of 4, 5, and 6 A were applied to assess the Joule heating characteristics during specific durations (40, 15.5, and 9 s). The samples were prepared by depositing a 200-nm thick a-Si layer on a glass substrate and sputtering a 300-nm thick aluminum (Al) layer onto the a-Si layer. During the AIC process, layer exchange occured via the diffusion of silicon (Si) into the Al layer. This phenomenon was verified by the in-situ reflectivity, which was in excellent agreement with thin-film optics calculations. During the annealing, processing temperatures were lower than 470 °C, which is less than the Al-Si eutectic temperature of 577 °C. The Raman peak observed near a wavenumber of 519 cm−1 revealed the formation of polycrystalline silicon films through Joule heating processes. Field-effect scanning electron microscopy images were captured and analyzed to investigate the surface morphology of the samples, specifically focusing on grain growth.

Efficient and reliable detection of rhodamine B using SERS from silver-decorated photonic crystal silicon nanoscale pores

Porous silicon photonic crystal (PSi PhC) decorated with silver nanoparticles (AgNPs) is shown to provide a new substrate for the improvement of SERS. AgNPs are obtained through immersion of PSi PhC samples in AgNO3 solutions and successive thermal annealing. The nanocomposite material generated by adding AgNPs inside the silicon nanoscale pores, integrates the ability of metal surfaces to amplify Raman scattering signals and an enlarged surface area. Besides, PhC structure formed by multilayer PSi increases interaction time of light and matter of the multilayer structure. The experimental results show that the AgNPs-decorated PSi PhC has the largest Raman intensity in comparison with other SERS substrates based on Si. The enhancement of Raman signals also reduces the threshold of the detection down to below 10-10 M. The analytical enhancement factor of AgNPs/PSi PhC SERS substrate for the detection of Rhodamine B (RhB) reaches 1010. This proposed AgNPs/PSi PhC SERS substrate could serve as a potential candidate for detecting RhB in foodstuffs at very low concentrations.

A novel method to optimize the growth of crystal silicon – Current assisted directional solidification

Large grain size and less impurity enrichment in polysilicon is always the key and difficult point for crystal quality improvement. In this work, polysilicon ingots were prepared by direct current (DC) assisted directional solidification. The Joule heat effect of DC was used to introduce a microscopic heat source which was directly acting on the solid–liquid interface front. The application of current regulates the thermal field distribution at the front of the solid–liquid interface, reduces the supercooling in the melt, and promotes lateral grain growth. The average grain size reached 297.62 μm at 55% solidification ratio, which got a 40.55% improvement compared to the ingots without current. In addition, the Joule heating effect can regulate the composition supercooling at the grooves and reduce the impurities in polysilicon ingots. In this paper, the mechanism of the effect of DC on crystal growth was investigated and the improvement of crystal size and the effect of impurity removal were achieved simultaneously.

FTIR Analysis and Characterizations of (SnO2:Ga2O3, CeO2 /Cu2S/c-pSi) Heterojunctions Solar Cells

Compounds from tin oxide doped with gallium oxide and cerium oxide were synthesized. Thin films from (SnO2:Ga2O3,CeO2) with different doping ratios were prepared on glass and single crystal silicon as substrates with the use of the pulsed laser deposition technique. The results of FTIR spectrums analysis was presented. Varies heterojunctions were fabricated from (SnO2:Ga2O3,CeO2 /Cu2S/c-pSi) heterojunctions solar cell which are formed from two layers: the first was Cu2S and the second was layer from tin oxide doped with two oxides named gallium oxide and cerium oxide with different doping ratios (0, 0.03, 0.05, and 0.07). The heterojuntion (SnO2:5%Ga2O3 /Cu2S/c-pSi photovoltaic structure exhibits open circuit voltage (Voc) of 150mV, short circuit current (Isc) of 15mA, fill factor of 0.622and efficiency of conversion of 2.8% under an intensity of illumination of 100mW/cm2.

Connection of ssDNA to Silicon Substrate Based on a Mechano-Chemical Method.

A novel fabrication process to connect single-stranded DNA (ssDNA)to a silicon substrate based on a mechano-chemical method is proposed. In this method, the single crystal silicon substrate was mechanically scribed in a diazonium solution of benzoic acid using a diamond tip which formed silicon free radicals. These combined covalently with organic molecules of diazonium benzoic acid contained in the solution to form self-assembled films (SAMs). The SAMs were characterized and analyzed by AFM, X-ray photoelectron spectroscopy and infrared spectroscopy. The results showed that the self-assembled films were covalently connected to the silicon substrate by Si-C. In this way, a nano-level benzoic acid coupling layer was self-assembled on the scribed area of the silicon substrate. The ssDNA was further covalently connected to the silicon surface by the coupling layer. Fluorescence microscopy showed that ssDNA had been connected, and the influence of ssDNA concentration on the fixation effect was studied. The fluorescence brightness gradually increased with the gradual increase in ssDNA concentration from 5 μmol/L to 15 μmol/L, indicating that the fixed amount of ssDNA increased. However, when the concentration of ssDNA increased from 15 μmol/L to 20 μmol/L, the detected fluorescence brightness decreased, indicating that the hybridization amount decreased. The reason may be related to the spatial arrangement of DNA and the electrostatic repulsion between DNA molecules. It was also found that ssDNA junctions on the silicon surface were not very uniform, which was related to many factors, such as the inhomogeneity of the self-assembled coupling layer, the multi-step experimental operation and the pH value of the fixation solution.

Secondary defects of as-grown oxygen precipitates in nitrogen doped Czochralski single crystal silicon

In this work, as-grown defects and their secondary defects in 300 mm nitrogen-doped Czochralski-grown single-crystal silicon (NCZ-Si) are investigated. Secondary defects are revealed by homogeneous epitaxial layer growth, and as-grown defects are decorated via gaseous hydrogen chloride (HCl) etching. Localized light scattering (LLS) technique is utilized to inspect defect distribution and provide the latex sphere equivalent (LSE) size to differentiate defect types. With the locations of LLS, the morphology of defect is observed by scanning electron microscopy (SEM). According to the results, it indicated that secondary defects are extrinsic dislocation loops and stacking fault (SF) loops, which are induced by as-grown oxygen precipitates during the growth and cooling process. Furthermore, the correlation between the counts of secondary defects and nitrogen concentration is obtained. It contributes to the optimization of nitrogen doping to avoid the generation of detrimental defects for device operation.

Structure and optical band gap of porous nano-Cu-SiC composite films prepared via magnetron sputtering

Porous nano-Cu-SiC composite films were prepared using double-target co-sputtering technology combined with annealing process by using high-purity copper and SiC as target materials, methane and nitrogen as the reaction gas, and argon as the working gas. The surface morphology, crystal structure, and optical transmission properties of the composite films were characterized and analyzed using modern testing and analytical techniques. The results show that the prepared composite film has a uniform and porous microstructure. Further analysis shows that SiC was dispersed in the copper matrix and well combined with the copper matrix. Annealing was conducive to carrier transmission. After annealing, the composite films recrystallized and grew again, thus increasing the stability of the structure. Raman spectra show that annealing can lead to the separation and crystallization of silicon and carbon phases in composite films. With the increase of energy density, the crystallization degree of porous SiC increases continuously, and the crystallization quality of the composite film and the light transmittance are improved. The prepared porous nano-Cu-SiC composite films have semiconductor properties, and the optical band gap is 0.17 eV. The porous nano-Cu-SiC composite films prepared using this method have good application prospects in high-performance composite film materials, such as heat conduction and wave absorption.

A realistic assessment of the prospect of silicon be replaced by other materials for IC applications

Silicon is the most common material used in semi-conductor. It can be used to make single crystal silicon wafer. Though it has the widest usage, silicon has high calorific value. Also, the performance loss is high compared to silicon carbide and the operating temperature is relatively low compared to gallium oxide. Luckily, there are several materials that could possibly replace silicon. The first one is 2D semiconductor. The prospective evaluation of 2D semiconductors is high. But now the biggest problem is the low-resistance connections with them. The second one is gallium nitride. It has high hardness, melting point and stability. This makes it a good material for high temperature, high frequency and high power devices. However, excellent property brings high cost. This disadvantage prevents gallium nitride to be widely used. The last one is graphene. It has strong electrical conductivity, ultra-high strength, excellent electrical properties, and strong electron interaction. It has a higher carrier mobility than silicon. While every coin has two sides, producing graphene on a large scale is difficult and expensive. Besides, graphene is highly reactive with oxygen and heat. What’s more, zero band gap nearly makes it impossible to become a semi-conductor material. Even though there are many methods of opening the bandgap, these methods still bring inevitable drawbacks. All in all, there are still many problems to be solved when new materials replace silicon in integrated circuit applications.