Polished Silicon Research Articles

Comparing single-shot damage thresholds of boron carbide and silicon at the European XFEL.

Xray free-electron lasers (XFELs) enable experiments that would have been impractical or impossible at conventional X-ray laser facilities. Indeed, more XFEL facilities are being built and planned, with their aim to deliver larger pulse energies and higher peak brilliance. While seeking to increase the pulse power, it is quintessential to consider the maximum pulse fluence that a grazing-incidence FEL mirror can withstand. To address this issue, several studies were conducted on grazing-incidence damage by soft X-ray FEL pulses at the European XFEL facility. Boron carbide (B4C) coatings on polished silicon substrate were investigated using 1 keV photon energy, similar to the X-ray mirrors currently installed at the soft X-ray beamlines (SASE3). The purpose of this study is to compare the damage threshold of B4C and Si to determine the advantages, tolerance and limits of using B4C coatings.

Tuning Surface Adhesion Using Grayscale Electron-beam Lithography.

Surface texturing of manufactured products tailors their properties, such as friction, adhesion, biocompatibility, or fluid interactions. However, advancements in this area are largely the result of trial-and-effort testing and generally lack a science-guided framework for determining the surface topography that will optimize performance. The present investigation explores grayscale electron-beam lithography as a means to create multiscale surface patterns to control surface performance. Here, we created and characterized a set of surface textures on a silicon wafer; the textures were superpositions of sine waves of varying wavelengths and amplitudes. First, the multiscale topography of the patterned surface was characterized, using profilometry and atomic force microscopy, to understand its fidelity to the designed-in pattern. The results of this analysis demonstrated how grayscale lithography accurately controlled the lateral size of features but was less precise on the vertical height of the surface, and also introduced inherent roughness below the scale of patterning. Second, a micromechanical tester was used to characterize the adhesion of the surfaces with large-scale polished silicon spheres. The results showed that adhesion could be tailored, with significant contribution from all of the designed-in length scales of topography. The strength of adhesion did not correlate with conventional roughness parameters but could be accurately modeled using simple numerical integration. Taken together, this investigation demonstrates the promise and challenges of grayscale e-beam lithography with multiscale patterns as a method for the tailoring of surface performance.

Controllable Fabrication of Silicon Solar Cells with Inverted or Upright Pyramid Structures by a One-Step Copper Catalysis Method

Silicon has garnered significant attention as the primary material for solar cell preparation. Traditional alkaline etching solutions are limited to creating an upright pyramid structure on monocrystalline silicon surfaces. However, research indicates that an inverted pyramid structure exhibits superior light-trapping properties compared to the upright pyramid structure. In this study, we employed a one-step copper ion metal-assisted chemical etching process to fabricate an inverted pyramid structure on monocrystalline silicon wafers. This method allows for the customization of either inverted or upright pyramid structures by adjusting the concentration of specific solution components. Characterization of the textured silicon wafers reveals that the inverted pyramid structure exhibits lower reflectivity than both the upright pyramid structure and polished silicon. By integrating this texturing technique into the solar cell production line, we successfully produced solar cells with both inverted and upright pyramid structures. Evaluation of various solar cell parameters demonstrates that the inverted pyramid structure outperforms the upright pyramid structure, showcasing lower reflectivity and higher photoelectric conversion efficiency.

Preparation of CeO2 particles via ionothermal synthesis and its application to chemical mechanical polishing

CeO2 is a widely used abrasive for the chemical mechanical polishing of silicon during chip manufacturing. CeO2 can be synthesized via traditional coprecipitation, hydrothermal, and solvothermal methods; however, these methods have some issues, including high vapor pressure, flammability, toxicity, volatile solvents, and narrow heating temperature range. To overcome these issues, we developed a new ionothermal synthesis approach for high-quality CeO2 particles using 1-ethyl-3-methylimidazolium tetrafluoroborate as an imidazole ionic liquid without a template. Based on the scanning electron microscopy and particle size distribution, CeO2 particles synthesized at a reaction temperature of 210 °C for 16 h displayed sizes ranging between 0.1 and 0.3 μm. Additionally, the spherical shapes exhibited good crystallinity, regular morphology, and uniform dispersion. The results of CMP experiments indicated that the abrasives could reduce the surface roughness from 1.63 to 0.29 nm (scanning area is 5 μm × 5 μm). The obtained synthesized CeO2 particles demonstrated promising performance in Si polishing, achieving removal rates of up to 255.5 nm/min. It found that the removal rate of the abrasive prepared by ionic thermal synthesis in Si polishing was twice as much as other abrasives. Further, a possible mechanism was put forward to explain the formation of CeO2 structures with various morphologies. The proposed method presents a new approach for synthesizing CeO2 particles with uniform morphology and excellent polishing properties.

Surface topography and subsurface structure evolution in laser micro polishing of monocrystalline silicon

Ultra-smooth silicon surfaces, crucial in short-wave optics, can be marred by surface defects and subsurface damage incurred during machining, thereby affecting the imaging quality and transmission efficiency of optical components. Laser micro-polishing emerges as a versatile and efficient technique for ultra-precision polishing. This study aims to scrutinize the surface topography and subsurface structural evolution of monocrystalline silicon wafers during laser micro-polishing experimentally and to formulate an accessible evaluation model that incorporates multiple process parameters for optimal polishing results. As laser fluence escalates, the polishing process can be divided into six regimes: bulge, coalescence, smoothness, groove, ripple, and ablation. Each regime's crystal structure evolution is analyzed using Raman spectroscopy, demonstrating a close relationship with the surface expansion preceding the melting of monocrystalline silicon. Surface roughness diminishes from 6 nm to 0.7 nm, and an optimal crystalline quality devoid of an amorphous layer, residual stress, or significant subsurface damage is achieved. Amorphous silicon, 20 μm thick, is converted into monocrystalline silicon through recrystallization, and subsurface distortions and dislocations are rectified due to silicon atom redistribution. Moreover, a mapping relationship between multiple process parameters and surface polishing effects is established. A dimensionless fluence considering multiple parameters is derived, and a predictive model for process parameter optimization to secure optimal polishing results is proposed.

Impact of varnishing, coating, and polishing on the chemical and mechanical properties of a 3D printed resin and two veneering composite resins

Statement of problemThree-dimensional (3D) printing enables the fast fabrication of definitive fixed dental prostheses (FDPs). However, data on the effects of surface treatments on their chemical and mechanical properties are lacking. PurposeThe purpose of this in vitro study was to examine the influence of different surface treatments on a 3D printed resin in comparison with 2 veneering composite resins. Material and methodsA total of 288 specimens were manufactured from a 3D printed resin (VarseoSmile Crownplus) or veneering composite resins (GRADIA PLUS; VITA VM LC flow). Surfaces underwent varnishing, coating, polishing or remain untreated. Conversion rate (DC), surface roughness (SR), Martens parameter, flexural strength (FS), and 3-body wear (3BW) were determined (n=12). Statistical analysis was performed using Mann-Whitney-U, Kruskal-Wallis, and Spearman correlation tests (α=.05). ResultsAfter polishing, the 3D printed resin showed higher DC, SR, and 3BW but lower Martens parameters compared with veneering composite resins (P<.007). After goat hair brushing, the 3D printed resin showed lower FS than VITA-VCR (P=.043). For the 3D printed resin, goat hair brushing or GC-Varnish reduced SR, while VITA-Varnish showed the lowest 3BW (P<.045). For both veneering composite resins, goat hair brushing led to low SR and 3BW and high EIT and FS (P<.043). Silicone polishing led to low EIT of the 3D printed resin and low EIT and FS of GC-VCR (P<.009). Coating resulted in a lower EIT than the untreated surface and higher 3BW than GC-Varnish (P<.030). ConclusionsThe 3D printed resin showed higher DC, SR, 3BW and lower HM, EIT, and FS values than the veneering composite resins. Polishing with a goat hair brush can be recommended for all tested materials. For the 3D printed resin, varnishing presents a promising alternative with regard to SR and 3BW. Silicone polishing and coating cannot be recommended.

Design of a multi-physics coupling MEMS pressure sensor

The pressure measurement of explosion shock wave puts forward high requirements on the temperature resistance and response speed of the sensor. In this paper, a multi-physics coupling pressure sensor is designed to meet requirements. The sensor mainly consists of a Fabry-Perot cavity optical fiber sensing unit, a piezoelectric pressure sensing unit and a thermometric resistance temperature measurement module. Firstly, the structure of the sensor is designed. The top and bottom surfaces of the Fabry-Perot cavity are composed of a silicon diaphragm and a quartz glass. The piezoelectric pressure sensing unit is an AlN film including its electrodes. Pt thermometric resistance is developed to realize real-time temperature monitoring. Secondly, the fabrication process of the sensor is discussed, especially three key technologies. An Al film is sputtered to increase the reflectivity of the quartz glass. The SU-8 photoresist is applied to accurately control the thickness of Fabry-Perot cavity. Etching is adopted to work out the graphics of the AlN piezoelectric film. At last, a complete fabrication process of the sensor is described. The fabrication of multilayer films begins with a double-sided polishing silicon wafer, while Fabry-Perot cavity was from a double-sided polishing quartz glass. Then two parts of the sensor are combined to ensure the multi-physics coupling sensor to achieve complete function.

Comparative study on the effects of different polishing methods on tooth surface microstructure and roughness following initial periodontal treatment.

To investigate the effects of different polishing methods on the surface microstructure and roughness of teeth following initial periodontal treatment. Teeth were divided into three groups (silica onegloss, polishing disc, and polishing strip) in vitro. Tooth surface microstructure was characterized via scanning electron microscopy. Roughness was measured by profilometry and laser scanning confocal microscopy (LSCM). According to the in vitro results, one group was chosen for further clinical trials. Effects of the chosen polishing method on patient plaque control and satisfaction were assessed via plaque staining and visual analog scale (VAS). Electron microscopy results revealed that the polishing disc group had smoother roots and crowns than did the other two groups. Roughness analysis revealed that the crown roughness with the polishing disc and silica onegloss was lower, and the root roughness with the polishing disc was the lowest (p < .05) The LSCM results showed that the pigment deposition depth with the polishing disc and silicon onegloss in the crowns and roots were significantly lower than those with the other two methods (p = .000). The polishing effect of the polishing disc was best among the three groups. Clinical trials were performed to verify the polishing disc effects. Plaque staining results showed that the decrease in plaque in the polishing disc group was greater than that ofthe rubber cup group (p = .020), which was similar to the results of LSCM. The VAS results showed that the polishing disc made teeth feel smoother, similar to the results of the roughness detection, and the procedure was more comfortable (p < .05). However, there was no significant difference between the two groups regarding foreign body sensation during pronunciation (p = .178). Combining in vitro and in vivo evaluations, the use of a polishing disc following periodontal treatment yielded superior polishing effects on teeth and was better accepted by patients.

A novel heat transfer characterization method for a thermal management scheme of 3D-IC chips

A novel surface-modified silicon-based thermal management technology has been proposed for 3D IC architecture in this study. 2 × 2 cm2 double sides polished silicon chips’ surface with micro-fin (MF) and micro-pin fin (MPF) structures have been achieved by applying silicon microfabrication technology of deep reactive ion etching, which is applicable to the interlayer of 3D IC packaging technology. By integrating a mini wind tunnel with Raman spectrometer, the transient thermal property measurement system is originally designed to evaluate the cooling capability of the surface-modified silicon interlayer. Finite Element Analysis was involved to confirm this view by taking fluid dynamics and heat transfer into account. The sample with 100 × 100 µm2 MPF structure expresses the appropriate exponential decay time constant τ (with unit of 1), which is 4.71 and 8.53 under cooling and heating measurement conditions, respectively. This also proved that the combination of Raman thermometry with forced gas flow could be a relevant measurement tool for transient thermal property.

Formation of PbS microstructured films by CBD method and study of structural properties

Microcrystalline lead sulfide (PbS) films were synthesized using the chemical deposition method. The films were deposited on pre-cleaned glass substrates and polished silicon wafers. Chemicals of high purity were utilized in the process. The morphology, composition, and structure of the films were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The films exhibited a galena phase with a face-centered cubic structure belonging to the Fm-3m space group. The average grain size was determined using the WilliamsonHall method, revealing a homogenous structure. Raman spectroscopy further confirmed the structural integrity of the films. The obtained results contribute to the understanding of the synthesis and properties of microcrystalline PbS films.

Effect of oxygen flow on electrical and optical properties of ITO films synthesized by magnetron sputtering method

The tin-doped indium oxide thin films were synthesized by DC magnetron sputtering on the surface of polished silicon samples and glass slides in a mixed argon-oxygen atmosphere. The other deposition parameters: operating pressure, magnetron power and substrate rotation speed were kept constant. Thickness and density of thin films were measured by X-ray Reflectometry. The effects of oxygen flow rate and substrate temperature on the optical and electrical properties were investigated. The electrical properties (resistivity, Hall mobility and charge concentration) of the thin films were measured by the Van der Pauw method using the Hall effect. The minimum value of resistivity 0.52 × 10-3 Ohm·cm, and maximum charge mobility 28 cm2V-1s-1 was achieved at an oxygen proportional gas mixture of 2.6% (0.71 sccm). The transmission spectra of the films were measured in the wavelength range from 300 to 1100 nm. The transmittance of all films exceeds 75% in the visible and near-infrared spectral ranges. It was found that increasing the oxygen flow rate and heating of the substrate up to optimal value 150°C led to an increase in the crystallinity of the films and, consequently, to an increase in the Hall mobility and the transmittance.

Mechanism of surface modification on monocrystalline silicon during diamond polishing at nanometric scale

The demand for polished silicon wafers has increased significantly in recent years to cater to the development of the semiconductor industry. For example, polished silicon wafer has direct applications in integrated circuits, radio frequency amplifiers, micro-processors, micro-electromechanical systems, etc. To carry out mechanical polishing, lapping, grinding, or single-point diamond turning of silicon, diamond abrasives were extensively used before the implementation of chemo-mechanical polishing. During the diamond-based polishing, a few problems have already been identified, such as the formation of an amorphous phase, heat-affected zones, low material removal, etc. Some research work has also reported that nano-structured abrasives lead to a thin layer of the amorphous phase and a better material removal rate. In the same direction, a molecular dynamics simulation is carried out in this paper to investigate the mechanism of material removal from monocrystalline silicon during the diamond-abrasive-based polishing process. The present work is mainly focused on the dynamics of material removal phenomena near the abrasive particles at the nanometric scale by considering stress, lattice, cohesive energy, etc. This reveals that a higher value of indentation force results in surface buckling, which creates a zone of both compressive and tensile stresses, which increases the coordination number and forms β-silicon just ahead of the abrasive particle. This mechanism happens by developing a β-silicon phase on the surface with a thickness beyond a certain value of indentation force on the zone of compression. Buckling on this phase happens due to stress localisation in compression, as the flow stress of this phase is less than that of diamond cubic lattices. To avoid the mechanism of surface buckling and process silicon material on the surface, the indentation force needs to be maintained below a critical value. In the present case, it was found that the indentation force of less than or equal to 190 nN for the abrasive size of ϕ8 nm does the material removal by surface processing only without surface buckling. It was also found that surface processing helps to reduce the depth of the amorphous layer significantly without compromising the material removal rate or the generation of a wavy surface. Thus, the present mechanism will help in the polishing of silicon with minimum defects and reduce processing time for the final stage of polishing towards manufacturing ultra-smooth and planer surfaces.

Geomorphometry and microelectronic metrology: Converged realms

AbstractThis article discusses the application of geomorphometric methods in microelectronic metrology. Six typical microelectronic items were geomorphometrically analyzed using their digital elevation models with nano‐ and micrometer‐range resolution and elevation difference: (1) a silicon–quartz structure; (2) a mechanically polished silicon wafer; (3) a photovoltaic blend sample; (4) an X‐ray optical element (a fused quartz spherical concave substrate); (5) a Bosch process‐formed, 20 aluminum layered membrane; and (6) a silicon–glass assembly with a volumetric defect. Geomorphometric modeling increases significantly the visibility and informativeness of data presentation, allowing to identify effectively the spatial distribution of nano‐ and microforms of the surface of microelectronic items. Geomorphometric methods provide an opportunity to study the size, location, and characteristic features of nano‐ and microtopographic inhomogeneities of microelectronic items using maps of minimum, maximum, mean, and unsphericity curvatures as well as other morphometric variables.

Material removal rate prediction and surface quality study for ultrasonic vibration polishing of monocrystalline silicon

Material removal rate prediction and surface quality study for ultrasonic vibration polishing of monocrystalline silicon

Surface study of RF magnetron sputtered silicon nitride thin films

Silicon nitride thin films were deposited on the one-sided P-type polished boron-doped silicon wafer substrate via RF magnetron sputtering using stochimetric silicon nitride target at various target-to-substrate distances. Target to substrate spacing, a nonconventional parameter, was varied to optimize the surface roughness and grain size. This optimization provided a normal distribution of homogenous, densely packed silicon nitride thin film free of surface cracks.. Atomic Force Microscopy was employed to explore the accurate surface roughness parameters of Silicon nitride thin films. The surface roughness and grain analysis for all samples exhibited a direct relation to each other and have an inverse correlation with the target to substrate spacing. The surface morphology of Si3N4 was analyzed by the following parameters; average roughness, root-mean square roughness, maximum peak to valley height, ten-point average roughness, skewness, and kurtosis of the line. The surface roughness of silicon nitride films has notable significance in the manufacturing of bio-sensor based on silicon nitride waveguides.

Chemically-induced active micro-nano bubbles assisting chemical mechanical polishing: Modeling and experiments

The material loss caused by bubble collapse during the micro-nano bubbles auxiliary chemical mechanical polishing (CMP) process cannot be ignored. In this study, the material removal mechanism of cavitation in the polishing process was investigated in detail. Based on the mixed lubrication or thin film lubrication, bubble-wafer plastic deformation, spherical indentation theory, Johnson-Cook (J-C) constitutive model, and the assumption of periodic distribution of pad asperities, a new model suitable for micro-nano bubble auxiliary material removal in CMP was developed. The model integrates many parameters, including the reactant concentration, wafer hardness, polishing pad roughness, strain hardening, strain rate, micro-jet radius, and bubble radius. The model reflects the influence of active bubbles on material removal. A new and simple chemical reaction method was used to form a controllable number of micro-nano bubbles during the polishing process to assist in polishing silicon oxide wafers. The experimental results show that micro-nano bubbles can greatly increase the material removal rate (MRR) by about 400% and result in a lower surface roughness of 0.17 nm. The experimental results are consistent with the established model. In the process of verifying the model, a better understanding of the material removal mechanism involved in micro-nano bubbles in CMP was obtained.

High efficiency chemical mechanical polishing for silicon wafers using a developed slurry

Improving the material removal rate (MRR) of silicon wafers is a challenge in chemical mechanical polishing (CMP), to meet the demands of the development of integrated circuits. In this study, four environmentally friendly additives, including sorbitol, gluconic acid, citric acid, and ammonium citrate, were incorporated into polishing slurries to promote the MRR of silicon wafers. The polishing results reveal that the highest MRR was obtained by ammonium citrate as an additive. When the concentration of ammonium citrate was 0.05 mol/L, the MRR increased by 71.6% to 1979.88 Å/min, and the surface roughness Sa was decreased from 1.131 nm to 0.563 nm. Meanwhile, the polishing slurry containing colloidal silica as abrasives maintained good dispersibility. Polishing mechanism was interpreted using electrochemical analysis, X-ray photoelectron spectroscopy, and coefficient of friction tests. It is indicated that NH4+ions, generated by hydrolysis of ammonium citrate, could modify the electrical characteristics of the silicate layer and catalyze the chemical reactions between Si atoms and H2O on the surface of silicon wafers. This work emphasizes the interfacial action between the polishing slurry and silicon wafers and provides a new idea for high efficiency CMP of silicon wafers in the manufacture of integrated circuits and photovoltaic industry.

Surface hydroxylation process of YAG crystal in aqueous solution.

Surface hydroxylation is the basis for material removal in chemical mechanical polishing (CMP) of monocrystalline silicon, diamond, and YAG crystals. Existing studies use experimental observations to investigate surface hydroxylation, but lack in-depth understanding of the hydroxylation process. In this paper, for the first time to the best of our knowledge, we analyze the surface hydroxylation process of YAG crystals in an aqueous solution using first-principle calculations. The presence of surface hydroxylation was verified by X-ray photoelectron spectroscopy (XPS) and thermogravimetric mass spectrometry (TGA-MS) detections. This study complements the existing research on the material removal mechanism of the CMP process of YAG crystals and provides theoretical support for the future improvement of the CMP technology.

Nanogap-Rich Surface-Enhanced Raman Spectroscopy-Active Substrate Based on Double-Step Deposition and Annealing of the Au Film over the Back Side of Polished Si.

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive and rapid detection technique that is used for detection of various analytes in trace quantities. We present a sensitive, large-area, and nanogap-rich SERS-active substrate by altering a thin gold (Au) film on the unpolished side of a single-side polished silicon wafer by repeated thermal deposition and annealing in an argon environment. The repeated thermal deposition and annealing process was compared on both sides of a one-side-polished silicon wafer; however, the rear side (etched/unpolished side) demonstrated a more enhanced Raman signal owing to the larger effective area. The proposed substrate can be fabricated easily, having a high density of hotspots distributed uniformly all over the substrate. This ensures easy, rapid, and sensitive detection of analytes with a high degree of reproducibility, repeatability, and acceptable uniformity. The optimized substrate shows a high degree of stability with time when exposed to the ambient environment for a longer duration of 148 days. The reported substrate can detect up to 10-11 M concentrations of 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT), with limits of detection (LODs) of 1.22 and 1.26 ng/L, respectively. This work not only presents the efficient and sensitive SERS-active substrate but also shows the advantages of using the rear side of a one-side-polished silicon substrate as a SERS-active chip.

Non-noble Si NWs@ZnO core–shell heterojunction anode enables a photo-assisted mirco direct methanol fuel cell

Micro-direct methanol fuel cells (μ-DMFCs) show the promising feasibility in the various portable practical scenes, although the anode still remains the high cost and low anti-toxic ability of noble metal (viz. Pt). Using photo-responsive anodes to boost the performance of fuel cell activity and stability with the aid of light illumination has been as the new strategy and herein we construct core–shell structure of Si nanowires (NWs)@ZnO anode to investigate the performance of μ-DMFCs under light illumination. The short circuit current and open circuit voltage of Si NWs@ZnO heterojunction are 100.5 μA cm−2 and 0.7 V, respectively, which are 3.5 and 1.3 times higher than Si NWs under light illumination. The Si NWs@ZnO photoanode also kept 97.3 % of current density for the second reused. A record-high discharge voltage of 0.7 V and more than 12 h of discharge time were achieved in photo-assisted μ-DMFCs. Carefully designed core–shell structure and the matched energy levels between Si NWs and ZnO contribute to the significant improved performances, where they can attenuate the light reflexes of the polished silicon, strengthen photos absorption and boost the charge transfer kinetics. This study opens an appealing research direction based on photo-assisted non-noble semiconductor anode toward the high-performance μ-DMFCs.