Single Crystal Silicon Wafers Research Articles

Contact and contactless porous silicon parameter measurement techniques

In this work we have used contact and contactless techniques to measure the electrical resistivity of single crystal silicon wafers with porous layers of variable thickness synthesized on the surface. The porous layers have been synthesized on the surfaces of single crystal wafers with well pronounced microroughness pattern, either textured or grinded. We have used the classic four-probe method with a linear probe arrangement as the contact measurement technique, and the resonance microwave method based on microwave absorption by free carriers as the contactless measurement technique. Electrical resistivity distribution over the specimen surface has been mapped based on the measurement results. We have demonstrated a general agreement between the electrical resistivity distribution patterns as measured using the contact and contactless measurement techniques. To analyze the electrical resistivity scatter over the specimen surface area we have simulated the field distribution in the electrolyte during porous layer formation in a non-planar anode cell. The regularities of the electrical resistivity spatial distribution in different types of specimens are accounted for by specific porosity formation mechanisms which in turn are controlled by the initial microroughness pattern and the field distribution pattern in the electrolyte for each specific case.

Fabrication, electrical and photovoltaic characteristics of CuInGeSe4/n-Si diode

The CuInGeSe4 thin film was deposited onto n-type single crystal silicon wafers by the electron beam deposition technique. The Au/CuInGeSe4/n-Si/Al heterojunction device has been fabricated. The structure of the CuInGeSe4 thin film was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray analysis (EDX). The dark current–voltage characteristics of the Au/CuInGeSe4/n-Si/Al heterojunction diode have been studied at a temperature range of 303–383 K. Also, the photovoltaic properties were examined at different illumination intensities. The capacitance–voltage characteristics of the CuInGeSe4/n-Si heterojunction were studied at different temperatures in the dark.

Investigation on the Material Removal and Surface Generation of a Single Crystal SiC Wafer by Ultrasonic Chemical Mechanical Polishing Combined with Ultrasonic Lapping.

A new method of ultrasonic chemical mechanical polishing (CMP) combined with ultrasonic lapping is introduced to improve the machining performance of carbide silicon (SiC). To fulfill the method, an ultrasonic assisted machining apparatus is designed and manufactured. Comparative experiments with and without ultrasonic assisted vibration are conducted. According to the experimental results, the material removal rate (MRR) and surface generation are investigated. The results show that both ultrasonic lapping and ultrasonic CMP can decrease the two-body abrasion and reduce the peak-to-valley (PV) value of surface roughness, the effect of ultrasonic in lapping can contribute to the higher MRR and better surface quality for the following CMP. The ultrasonic assisted vibration in CMP can promote the chemical reaction, increase the MRR and improve the surface quality. The combined ultrasonic CMP with ultrasonic lapping achieved the highest MRR of 1.057 μm/h and lowest PV value of 0.474 μm. Therefore this sequent ultrasonic assisted processing method can be used to improve the material removal rate and surface roughness for the single crystal SiC wafer.

Crack plane deflection and shear wave effects in the dynamic fracture of silicon single crystal

Fracture paths in crystalline solid can be significantly altered upon encountering stress perturbations. Here, we investigate the dynamic cleavage deflection in (001) silicon single crystal wafers under three-line bending load. It is found that the crack propagates preferentially along the (110) cleavage plane. However, when the crack front interacts with shear waves induced by the line-contact, it tends to deflect onto the (111) cleavage plane and forms secondary Wallner lines. Yet, the crack deflection is not permanent and a recovery process to the (110) plane is observed, suggesting that the (110) cleavage plane remains energetically prevailing during the high-speed crack propagation. We show that the ratio between the dynamic fracture energy of the (111) plane and that of the (110) plane at the deflection position is invariably larger than the one when the local crack velocity is lower than 40% of the Rayleigh wave speed. This confirms that the crack deflection is triggered by shear waves. Therefore the theory of crystallographic direction dependence of dynamic fracture toughness evolutions proposed in earlier literature needs to be further assessed before generalization.

The Development of a New Piezoresistive Pressure Sensor for Low Pressures

This paper presents the design methodology and fabrication process of a novel piezoresistive pressure sensor with a combined cross-beam membrane and peninsula (CBMP) diaphragm structure for micropressure measurements. The sensor is then analyzed through various experiments. The sensor is primarily designed based on the optimized sensitivity, and a finite-element method is used to predict the stresses that are induced in the piezoresistors and the deflection of the membrane under different pressures. Compared to other traditional diaphragm types, a significant increase in sensitivity can be achieved by the proposed sensor, and the membrane deflection and nonlinearity error considerably decrease. The sensor fabrication process is performed on an n-type single-crystal silicon wafer, and photolithography is used with five masks to fabricate the sensing elements. Additionally, piezoresistors are formed by boron implantation. The experimental results indicate that the fabricated sensor with the CBMP membrane yields a high sensitivity of 25.7 mV/kPa and a low nonlinearity of −0.28% full-scale span for a pressure range of 0–5 kPa at room temperature.

Understanding near infrared absorption in tin doped indium oxide thin films

Tin doped indium oxide (In2O3:Sn (ITO)) thin films RF sputtered under similar conditions on soda lime glass and single crystal silicon wafers (c-Si) are used to study near infrared optical absorption variations during film growth. The presence of strong free carrier absorption and phonon absorption in the low photon energy spectral range provides an opportunity to disentangle tailing effects extending in the near infrared to visible spectral range. Toward that end, a model describing ITO film optical properties in the form of the complex dielectric function (ε = ε1 + iε2) from ex situ ellipsometry collected over 0.4 to 4.1 meV, 0.035 to 0.4 eV, and 0.75 to 5.89 eV spectral range is developed to describe these features along with other higher energy electronic transitions. In situ real time spectroscopic ellipsometry (RTSE) from 0.75 to 5.89 eV is used to track changes film structure and optical response during thin film growth. Optical emission spectroscopy indicates the plasma is very stable during deposition implying that film property changes with thickness are not correlated with changes in plasma chemistry. Film resistivity (ρ), mobility (µ), scattering time (τ), and carrier concentration (n) are determined from the free carrier absorption component of ε. Increased near infrared absorption manifested in ε obtained from RTSE data analysis is hypothesized to originate from enhancement of OH-group phonon absorption due to the presence of water molecules in the chamber at the beginning of growth.

Investigation of the Characteristics of Heterojunction Solar Cells Based on Thin Single-Crystal Silicon Wafers

The operating characteristics of heterojunction solar cells based on single-crystal silicon wafers with a reduced thickness are investigated experimentally. It is found that a decrease in the wafer thickness by 40% as compared to the standard values leads to degradation of the photoelectric-conversion efficiency to 5%. The obtained results could be used for estimating the commercial feasibility of the production of solar cells with a reduced wafer thickness.

Unimorph mirror for adaptive optics in space telescopes.

This paper presents a unimorph deformable mirror intended to be used as secondary corrector in space telescopes. The deformable mirror consists of a single-crystal silicon wafer (76.2mm diameter, 500μm thickness) covered with an optical coating on the front side and an array of 25 independent piezoelectric transducer (PZT) actuators acting in d31 mode on the back side. The mirror is mounted on an isostatic support with three position linear actuators controlling the rigid-body motion. The first part of the paper presents the experimental results obtained with the manufactured prototype. The mirror was tested in terms of root mean square (RMS) wavefront error, open-loop long-term stability, voltage budget for active control, rigid-body actuation, reflectivity, and dynamic response. The prototype is fully compliant with the requirements set by the European Space Agency (ESA). The second part of the paper, purely based on numerical simulations, presents a robust way to face thermal distortion, inherent to unimorph architecture.

On the S/W stoichiometry and triboperformance of WSxC(H) coatings deposited by magnetron sputtering

WSxC(H) coatings were deposited on single crystal silicon(100) wafers by magnetron co-sputtering and reactive sputtering at various target-substrate distances. Upon increasing the distance, the stoichiometric S/W ratio increases from 0.51 to 1.89. Also, the porosity of coatings gradually augments and a columnar microstructure tends to form. Preferential sulfur resputtering rather than contaminations primarily accounts for the low S/W ratio. TEM reveals randomly oriented WS2(002) platelets in the WSxC coatings when deposited at a large distance, which is supported by XRD. The composite coatings exhibit a decreasing hardness and elastic modulus with increasing target-substrate distance. The triboperformance is strongly affected by the coating composition, the target-substrate distance and the testing environment. Cross-sectional TEM of formed tribofilms reveals an obvious reorientation of WS2(002) basal planes parallel to the plane of sliding, leading to an ultralow friction.

Characterization of recrystallized depth and dopant distribution in laser recovery of grinding damage in single-crystal silicon

A nanosecond pulsed Nd:YAG laser was irradiated on a boron-doped single-crystal silicon wafer with a diamond grinding finish to recover the grinding-induced subsurface damage. In order to visualize and measure the depth of the laser melted/recrystallized layer, small-angle beveled polishing was performed in pure water followed by KOH etching. It enabled the direct observation of the recrystallized region using a differential interference microscope and the measurement of its depth using a white light interferometer. Crystallinity analysis of the recrystallized region was carried out by using laser micro-Raman spectroscopy, and the dopant concentration profile was characterized by using radio frequency glow discharge optical emission spectrometry (rf-GD-OES). The results showed that the crystallinity and boron distribution in the recrystallized region changed after laser recovery. The dopant concentration becomes higher at the boundary of the recrystallized region and the bulk. This study demonstrates the possibility of boron concentration control by using suitable laser parameters.

Field induced decrystallization of silicon: Evidence of a microwave non-thermal effect

It is rather strange and not fully understood that some materials decrystallize when exposed to microwave radiation, and it is still debatable if such a transformation is a thermal or non-thermal effect. We hereby report experimental evidences that weight the latter effect. First, a single crystal silicon wafer exposed to microwaves showed strong decrystallization at high temperature. Second, when some areas of the wafer were masked with metal coating, only the exposed areas underwent decrystallization. Transmission electron microscopy analysis, x-ray diffraction data, and thermal conductivity measurements all indicated strong decrystallization, which occurred in the bulk of the material and was not a surface effect. These observations favor the existence of a non-thermal microwave effect.

Structure and properties of lanthanum doped AlCrN coatings

AlCr(La)N coatings were grown through mid-frequency reactive magnetron sputtering on cemented carbide (YG8) and single-crystal silicon (111) wafer. The composition, microstructure and mechanical properties of the coatings deposited under different La target currents were evaluated. The concentration of La changed from 0 at.% to 7.73 at.% displaying a low rate of back-scattering compared to Al and Cr. La partly acted as a partial solid solution in the AlCrN lattice, whereas an increased amount of La was likely to be intergranular gathered, resulting in segregation at the grain boundaries and a grain size decrease. During this phenomenon, nc-AlCrLaN crystalline grains combined with a-La2O3/a-LaN were formed. The multilayer morphology appeared as the La target current increased. The friction coefficient of the AlCrLaN coating decreased due to the solid lubrication of La2O3. The AlCrLaN coating under the La target current of 1 A (La concentration 1.39 at.%) obtained the highest H/E ratio, H3/E⁎2 ratio, abrasive resistance and adhesion strength.

Исследование характеристик гетеропереходных солнечных элементов на основе тонких пластин монокристаллического кремния

AbstractThe operating characteristics of heterojunction solar cells based on single-crystal silicon wafers with a reduced thickness are investigated experimentally. It is found that a decrease in the wafer thickness by 40% as compared to the standard values leads to degradation of the photoelectric-conversion efficiency to 5%. The obtained results could be used for estimating the commercial feasibility of the production of solar cells with a reduced wafer thickness.

Stress damage process of silicon wafer under millisecond laser irradiation

The stress damage process of a single crystal silicon wafer under millisecond laser irradiation is studied by experiments and numerical simulations. The formation process of low-quality surface is monitored in real-time. Stress damage can be observed both in laser-on and -off periods. Plastic deformation is responsible for the first stress damage in the laser-on period. The second stress damage in the laser-off period is a combination of plastic deformation and fracture, where the fundamental cause lies in the residual molten silicon in the ablation hole.

An improved structural design for accelerometers based on slotted eight-beam structure

PurposeThe purpose of this paper is proposed a new structure design for high performance accelerometer.Design/methodology/approachAn improved sensitivity structure considering sensitivity, natural frequency and cross-axis sensitivity is established and realized. The proposed structure was designed to improve the trade-off between the sensitivity and the natural frequency of piezoresistive accelerometer and eliminate the lateral sensitivity effect by the specific configuration, which is made possible by incorporating slots into the eight-beam structure. The mechanical model and its mathematical solution are established for calculating the sensitivity and natural frequency behavior of the designed structure. The developed sensor is fabricated on the n-type single-crystal silicon wafer and packaged for experiment. The accelerometer prototype was tested in the centrifugal machine and dynamic calibration system.FindingsThe experimental results show that the sensitivity of the designed sensor is 0.213 mV/(Vg) and the natural frequency of the sensor is 14.22 kHz. Compared with some piezoresistive accelerometers in literatures, the designed sensor possesses a suitable characteristic in sensitivity, natural frequency and transverse effect, which allows its usage in measuring high frequency vibration signals.Originality/valueThe accelerometer with slotted eight-beam structure shows a good performance in the static and dynamic experiments and can be used in measuring high frequency vibration signals.

Fabrication of Hexagonal Microlens Arrays on Single-Crystal Silicon Using the Tool-Servo Driven Segment Turning Method.

Single-crystal silicon microlens arrays are increasingly required in advanced infrared optics. In this study, the authors attempted to fabricate hexagonal microlens arrays, which offer high optical efficiency, on a single-crystal silicon wafer using diamond turning. A tool-servo driven segment turning method was proposed to reduce the dynamic error of the machine tool induced by lenslet edges during lens array cutting. From the results of both cutting experiments and theoretical analysis of the machine tool dynamic error, it was demonstrated that the segment turning method reduced significantly the dynamic errors and led to high form accuracy. As a result, sharp edges among the lenslets were generated precisely and microlens arrays with a form error of ~300 nm peak-to-valley and surface roughness of ~5 nmSa, which meets the requirements of infrared optical systems, were successfully fabricated. The subsurface damage, such as the amorphization of silicon, caused by machining was also reduced.

Resistivity Characterization of Solid Electrolyte Interphase on Lithium Ion Battery Silicon Anodes

Lithium-ion battery (LIB) technology plays a critical role the clean energy sector, with applications in electronic devices, electric and hybrid vehicles, and stationary energy storage. In order to improve battery efficiency and performance, novel materials must be developed and studied. Battery anode materials are of particular interest, and silicon has been selected for materials research due to its high theoretical storage capacity as well as the extensive existing knowledge regarding silicon material processing and fabrication. The initial cycling of a LIB, regardless of anode material, results in the formation of a solid electrolyte interphase (SEI) layer between the electrolyte and the anode. This passivating layer, consisting of decomposition products from the electrolyte solution, is critical to the reliability and performance of the battery. The SEI must be both electronically insulating and ionically conductive: permeable to lithium ions yet resistant to electron flow. The resistance can be inhomogeneous along the anode plane or perpendicular to it. To our knowledge, no characterization technique has been capable of measuring spatial variation in SEI resistivity. In order to measure SEI resistivity with nanometer-scale resolution, our group has utilized scanning spreading resistance microscopy (SSRM) with a specialized atomic force microscopy (AFM) system installed in an argon glove box to minimize sample exposure to oxygen and water. The setup employs a doped diamond coated silicon probe that exhibits high wear resistance and low electronic resistance. Through application of a sample-probe bias voltage while utilizing variable forces on the probe in AFM contact mode, the technique allows for the measurement of SEI resistivity laterally and vertically. The vertical depth of measurement is controllable by the applied probe force (as well as raster scan line density) and is thus capable of milling away SEI material to measure resistivity at defined depths. Subsequent AFM height measurement allows for measured resistance to be associated with the depth of measurement. The electronic system attached to the system measures current through the probe-sample with a logarithm-scale amplifier, which can be directly converted to resistance or resistivity. Our measurements of resistance vs. depth for SEIs formed on single-crystal silicon wafers [001] after a single cycle of lithiation/delithiation demonstrate strong trends for decrease in resistance as the probe penetrates deeper levels of the SEI. Such plots provide an interesting basis for the study of SEIs formed under different cycling conditions with distinct electrolyte solutions. Figure: (a) Schematic diagram of electronic setup of the described system, (b) resistance map at a depth of 43 nm on a SEI formed on a single-crystal silicon wafer [001], with a single cycle of lithiation (0.01 V for 5 hours) and delithiation (1.0 V for 5 hours) in a battery cell containing ethylene carbonate (EC) and diethyl carbonate(DEC) electrolytes, (c) topography map displaying the SEI depth of resistance mapping. Figure 1

Electroluminescent study of the efficiency of silicon heterostructural solar cells

A strong (by more than an order of magnitude) change in the electroluminescence intensity is observed for the first time in high-quality heterojunction solar cells that are based on a single-crystal silicon and have an efficiency of 18 to 20.5%. This effect occurs due to the sharp change in the concentration of the recombination centers on the surface of single-crystal silicon wafers in the course of their pyramidal texturing and also due to the rise in the series resistance. The effect can be used for a quantitative highly sensitive characterization of the texturing, which is a fundamentally important stage in fabricating highly efficient silicon solar cells.

Influence of deposition temperature during LPCVD on surface properties of ultrathin polysilicon films

The selection of the proper materials for the fabrication of the micro electro mechanical systems (MEMS) is a very important issue in the MEMS research. The materials should be adequate for the fabrication process as well as they have to demonstrate in particular good adhesive (to avoid stiction between contacting/sliding components) and frictional/tribological properties. We fabricated ultrathin (50 nm thick) polysilicon films on single crystal silicon wafers at various deposition process conditions and observed the effect of the process parameters on surface topography and adhesive as well as frictional properties of the produced films. The atomic force microscope was used in these studies equipped with special cantilevers. We identified interesting correlations between the process parameters and adhesive/frictional properties of the studied films which enable to optimize the process to decrease adhesion (stiction) and friction between sliding components of MEMS devices and compared them to previous research done at samples with thicker layer. Topography of both samples and cantilevers has been studied in depth to allow later simulation of the interface. Additional measurements of friction in various humidites should be done next in order to assess the influence of its impact on friction coefficient. Further comparison of adhesion to friction in particular environmental properties might also increase our understanding of MEMS surface interactions.

Electrical Investigation of Nanostructured Fe2O3/p-Si Heterojunction Diode Fabricated Using the Sol–Gel Technique

Iron oxide (α-Fe2O3) nanocrystals have been synthesized via the sol–gel technique. The structural and morphological features of these nanocrystals were studied using x-ray diffraction, Fourier transform-infrared spectroscopy and transmission electron microscopy. Colloidal solution of synthesized α-Fe2O3 (hematite) was spin-coated onto a single-crystal p-type silicon (p-Si) wafer to fabricate a heterojunction diode with Mansourconfiguration Ag/Fe2O3/p-Si/Al. This diode was electrically characterized at room temperature using current–voltage (I–V) characteristics in the voltage range from −9 V to +9 V. The fabricated diode showed a good rectification behavior with a rectification factor 1.115 × 102 at 6 V. The junction parameters such as ideality factor, barrier height, series resistance and shunt resistance are determined using conventional I–V characteristics. For low forward voltage, the conduction mechanism is dominated by the defect-assisted tunneling process with conventional electron–hole recombination. However, at higher voltage, I–V ohmic and space charge-limited current conduction was became less effective with the contribution of the trapped-charge-limited current at the highest voltage range.