Double-side Polished Silicon Wafer Research Articles

Photo-Responses of Silicon Photodiodes with Different ARC Thicknesses for Scintillators

We designed and fabricated silicon positive-intrinsic-negative (PIN) photodiodes coupled with a scintillator for radiation detection. The photodiodes were fabricated on an n-type double-sided polished silicon wafer with a diameter of 6-in., a high resistivity ( orientation. To increase the quantum efficiency (QE) of the photodiode, an anti-reflection coating (ARC) was provided on the side where light entered. It is difficult to realize an ARC with an uniform thickness in the sensor fabrication process. The effect of changes in the ARC thickness on the QE of the fabricated sensors was studied in detail. We measured the electrical characteristics and compared their quantum efficiencies as a function of the incident light wavelength for the photodiodes with different ARC thicknesses. In this paper, we present the design of the photodiodes and their measured electrical characteristics and photo-responses for different ARC thicknesses. From measurements of the wavelength-dependent QE, we determined the refractive index of the ARC layer to be 2.25 ± 0.15. The ARC layer improved the QE up to 56% and 63% at the wavelengths of 550 and 475 nm, which correspond to the wavelengths of the scintillation light from CsI(Tl) and CdWO4, respectively.

Study of the effect of local photon annealing on stress in silicon wafers

The effect of photon annealing on deformation in the crystal structure of boron doped Cz-Si wafers has been studied using triple crystal X-ray diffraction. Conventional annealing of the entire surface of double-side polished silicon wafers with halogen lamps (photon annealing mode) and rapid thermal annealing produce compression deformation. Annealing with special phototemplate providing for local annealing of multiple separated wafer areas (local photon annealing mode) at relatively low wafer temperatures (less than 55 °C) produces tensile deformation. This effect however is not observed if the reverse side of the annealed wafer contains a mechanical gettering layer. A mechanism explaining the experimental results has been suggested and can be used for the synthesis of charge pumps in photoelectric converter structures.

A Novel, Hybrid-Integrated, High-Precision, Vacuum Microelectronic Accelerometer with Nano-Field Emission Tips.

In this paper, a novel, hybrid-integrated, high-precision, vacuum microelectronic accelerometer is put forward, based on the theory of field emission; the accelerometer consists of a sensitive structure and an ASIC interface (application-specific integrated circuit). The sensitive structure has a cathode cone tip array, a folded beam, an emitter electrode, and a feedback electrode. The sensor is fabricated on a double-sided polished (1 0 0) N-type silicon wafer; the tip array of the cathode is shaped by wet etching with HNA (HNO3, HF, and CH3COOH) and metalized by TiW/Au thin film. The structure of the sensor is finally released by the ICP (inductively coupled plasma) process. The ASIC interface was designed and fabricated based on the P-JFET (Positive-Junction Field Effect Transistor) high-voltage bipolar process. The accelerometer was tested through a static field rollover test, and the test results show that the hybrid-integrated vacuum microelectronic accelerometer has good performance, with a sensitivity of 3.081 V/g, the non-linearity is 0.84% in the measuring range of −1 g~1 g, the average noise spectrum density value is 36.7 μV/ in the frequency range of 0–200 Hz, the resolution of the vacuum microelectronic accelerometer can reach 1.1 × 10−5 g, and the zero stability reaches 0.18 mg in 24 h.

Integrated magnetic-sensitive differential circuit based on heterojunction silicon magnetic-sensitive transistor

This paper presents an integrated magnetic-sensitive differential circuit, consisting of two heterojunction silicon magnetic-sensitive transistors (HSMSTs) with opposite magnetic-sensitive directions and two collector load resistors. The two HSMSTs have a common emitter (E), two bases (B1, B2), two collectors (C1, C2) and two output terminals of the collector voltage. Through using the micro-electro-mechanical system (MEMS) technology and the chemical vapour deposition (CVD) method, chips were designed and fabricated on a p-type 〈100〉 double-side polished silicon wafer with a high resistivity. When VDD=10.0V and IB=6.0mA, the magnetic sensitivity (Sv) of the proposed differential circuit was 275mV/T at room temperature and its temperature coefficient (αST) was −1.668%/°C. The experimental results show that the magnetic sensitivity and temperature characteristics of proposed magnetic field sensors can be improved by using integrated differential circuits based on HSMSTs.

Design and fabrication of micromachined pyroelectric infrared detector array using lead titanate zirconate (PZT) thin film

Abstract Pyroelectric infrared detector array using lead zirconate titanate (PbZr 0.3 Ti 0.7 O 3 , PZT) thin film as a sensing layer was fabricated on Si 3 N 4 /SiO 2 /Si substrate by a microelectromechanical system (MEMS) technique. Si 3 N 4 /SiO 2 layers, used as the etching mask and supporting layer, were grown on both sides of 4-in. double-side polished silicon wafer(100, p-type). The silicon-window was etched by a series of processes for photoetching, dry-etching and wet-etching. Pt/TiO 2 bottom electrode was deposited and patterned by using photoetching and RF magnetron sputtering. 800 nm-thick PZT thin film was deposited at 600 °C by RF magnetron sputtering. Au top electrode and the infrared absorption layer of black-gold were deposited and patterned by photoetching and DC sputtering. The dielectric constant and loss tangent of PZT film are 440 and 0.021 at 1 kHz, respectively. The remnant polarization ( P r ) and the coercive field ( E c ) are 25 μC/cm 2 and 40 kV/cm, respectively. The pyroelectric coefficient of the film was measured by a quasi-static method and is 300 μC m −2 K −1 . The pyroelectric infrared detector array has potential applications on safety monitoring and smart appliances.

A Silicon-Based Porous Thin Membrane as a Cancer Cell Transmigration Assay

This paper presents a novel microfabricated Boyden chamber in silicon with well-defined pore sizes and controlled membrane thickness for cell migration analysis. The chip-based chamber is fabricated employing lithography and deep reactive ion etching techniques on a double-sided polished silicon wafer. The device contains micro-pores with a silicon oxide layer at the top and a deep microfluidic channel at the bottom, which is anodically-bonded to a glass wafer for sealing and facilitating the imaging and chemoattractant feeding. The applicability of the chip has been demonstrated through the distinct migratory behaviors of highly metastatic breast cancer cells, MDA-MB-231, through pores with 8 $\mu \text{m}$ in diameter, 50 $\mu \text{m}$ in spacing, and 30 $\mu \text{m}$ in thickness. Employing the above technique, the membrane thickness variation among different chips was below 10%. Utilizing this micro-Boyden chamber device, we have shown that MDA-MB-231 cells migrated distinctively in higher rate than the cells which had gone through sphingosine kinase inhibitor drug treatment or no chemoattractant feeding over a course of 12 hours. Furthermore, we validated the performance of the micro-Boyden chamber by quantifying the migration rate of the cancer cells under different chemoattractant gradient profiles. [2016-0103]

Fabrication Technology and Characteristics of a Magnetic Sensitive Transistor with nc-Si:H/c-Si Heterojunction.

This paper presents a magnetically sensitive transistor using a nc-Si:H/c-Si heterojunction as an emitter junction. By adopting micro electro-mechanical systems (MEMS) technology and chemical vapor deposition (CVD) method, the nc-Si:H/c-Si heterojunction silicon magnetically sensitive transistor (HSMST) chips were designed and fabricated on a p-type <100> orientation double-side polished silicon wafer with high resistivity. In addition, a collector load resistor () was integrated on the chip, and the resistor converted the collector current () to a collector output voltage (). When = 8.0 mA, = 10.0 V, and = 4.1 kΩ, the magnetic sensitivity () at room temperature and temperature coefficient () of the collector current for HSMST were 181 mV/T and −0.11%/°C, respectively. The experimental results show that the magnetic sensitivity and temperature characteristics of the proposed transistor can be obviously improved by the use of a nc-Si:H/c-Si heterojunction as an emitter junction.

Silicon Wafer: a Direct Output Coupler in Tm:YLF Laser**Supported by the Science and Technology Project of Shenzhen under Grant Nos JCYJ20140509172609175 and JSGG20140519104809878, and the Science and Technology Project of Guangdong Province under Grant No 2014B010131006.

We present a high power diode-pumped continuous-wave Tm:YLF (Tm3+-doped lithium yttrium fluoride) laser with apiece of silicon wafer as the output coupler (Si-OC laser) directly. Under the pump power of 40 W at 793 nm, a maximum output power of 12.1 W is obtained with a beam quality of M2 ≤ 1.55 at 1887 nm, corresponding to an optical-to-optical efficiency of 30.25% and a slope efficiency of 33.21%. To the best of our knowledge, this is the first report on directly utilizing silicon as an output coupler (Si-OC) in the solid Tm:YLF laser system. Due to the intriguing characteristics of silicon, such as negligible absorption in the wavelength region around 2 μm, high damage threshold, low cost and long-pass filter properties, double-side polished monocrystalline silicon wafer is considered as an outstanding candidate output coupler in the high-power laser system 2 μm spectral region, which may dramatically reduce the total manufacturing costs of the 2 μm laser system.

Design and micro-machining fabrication of piezoelectric diaphragm chambers for biomaterial detection

Mass sensitive piezoelectric biosensors based on micro-electro-mechanical system (MEMS) fabrication techniques were developed for biomaterial detection. In this work, both 4-inch double-sided polished silicon wafer was used as support layers. The SiO2/Si3N4 layers were firstly grown on both sides of the wafer to serve as the etching mask and the potassium hydroxide solution (KOH) wet etching stop layer. The diaphragm chambers were then wet etched in KOH solution until the remaining thickness of silicon was about 50μm. The residual thin silicon layer could reduce the stress and maintain a good mechanical strength for the following fabrication processes. After that, the bottom electrode/piezoelectric layer/polyimide layer/top electrode was fabricated and patterned on the other side of the wafer successively. Then the residual thin silicon layer in the chambers was etched away and a Au layer with 50nm thickness was sputtered on the bottom of the chambers as the immobilization surface for biomaterial specific adsorption. The square sensors with different length of sides were designed to investigate the size effect on the resonance performance. The resonant frequency shifts could be measured and the corresponding mass of the attached biomaterial could be calculated. The piezoelectric diaphragms sensors have a potential application for biomaterial detection.

Simulation, Design, Fabrication, and Testing of a MEMS Resettable Circuit Breaker

We describe a novel concept for a microelectromechanical systems (MEMS) resettable circuit breaker. The concept involves fabricating the circuit breaker and the reset switch using a single microcantilever. The MEMS resettable circuit breaker consists of a microcantilever that is pulled toward the bottom electrode by electrostatic actuation. The MEMS cantilever also has a thermal heater, and when a current passes through the heater, it overcomes the electrostatic actuation force thereby disconnecting the circuit. A detailed finite element analysis using thermal-electric-structural multiphysics phenomena was studied. Electrostatic-structural coupled-field analysis shows the circuit breaker switch has a pull-in voltage of about 31 V for a singlecrystal Si cantilever with a thickness of 2 μm, a length of 1000 μm, and a width of 500 μm. Thermal-electric coupledfield analysis shows the switch maximum temperature is 80.5 °C at a 50-mA current flow. Thermal-electric-structural sequential analysis shows the cantilever tip has a maximum upward displacement of 0.3 μm, which is just enough to open the switch. The impact of the initial film stress in the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> insulation layer was also simulated, and the results show that the film stress has a significant impact on the initial cantilever position after release. Fabrication of the chips was done using two wafers, a silicon-on-insulator (SOI) wafer, and a double-side polished silicon wafer. The SOI wafer device silicon layer was selected as cantilever material. Platinum was selected as heater material and chrome-gold was selected for bonding, trace, and electrostatic electrodes. Electrical testing results confirmed the proposed and simulated operation principle of the MEMS resettable circuit breaker. The results showed that the switch achieved good contact at an electrostatic switch-ON voltage of about 55 V. The measured circuit breaker current threshold is in the range of 45-55 mA.

Fizeau-type interferometric probe to measure geometrical thickness of silicon wafers.

We developed an optical interferometric probe for measuring the geometrical thickness and refractive index of silicon wafers based on a Fizeau-type spectral-domain interferometer, as realized by adopting the optical fiber components of a circulator and a sheet-type beam splitter. The proposed method enables us to achieve a much simpler optical composition and higher immunity to air fluctuations owing to the use of fiber components and a common-path configuration as compared to a bulk-type optical configuration. A femtosecond pulse laser having a spectral bandwidth of 80 nm at a center wavelength of 1.55 µm and an optical spectrum analyzer having a wavelength uncertainty of 0.02 nm were used to acquire multiple interference signals in the frequency domain without a mechanical phase-shifting process. Among the many peaks in the Fourier-transformed signals of the measured interferograms, only three interference signals representing three different optical path differences were selected to extract both the geometrical thickness and group refractive index of a silicon wafer simultaneously. A single point on a double-sided polished silicon wafer was measured 90 times repetitively every two seconds. The geometrical thickness and group refractive index were found to be 476.89 µm and 3.6084, respectively. The measured thickness is in good agreement with that of a contact type method within the expanded uncertainty of contact-type instruments. Through an uncertainty evaluation of the proposed method, the expanded uncertainty of the geometrical thickness was estimated to be 0.12 µm (k = 2).

Optical interferometric approach for measuring the geometrical dimension and refractive index profiles of a double-sided polished undoped Si wafer

In this investigation, we propose a technique to obtain not only the dimensional profile of an undoped double-side polished silicon (Si) wafer but also its refractive index profile simultaneously. This technique is based on low coherence scanning interferometry using a near-infrared light around 1 µm wavelength, for which transmission is non-zero for undoped silicon and also detectable by the typical visible CCD camera. As the experimental results show, the profiles of optical thicknesses, geometrical thicknesses, group refractive indices and phase refractive indices were successfully obtained by the proposed technique, and the mean values were 1869.6 µm, 490.45 µm, 3.8121 and 3.516, respectively. Compared to the reference values of the group refractive index and the phase refractive index of the Si wafer given by the previous researches, the deviations were 0.055 and 0.04, respectively. The deviations were attributed to the position error of the scanning stage. In addition, the combined technique with spectrally-resolved interferometry was also discussed to improve the measurement accuracy of the system.

Hardware Design Optimization and Process Control for a Low Friction Coefficient Substrate and Film: A Case Study in the Semiconductor Industry

For semiconductor devices, the use of amorphous carbon films as a sacrificial hard mask material is commonplace in the integration for patterning of 90 nm and below technology node devices. These films have an intrinsically low friction coefficient. At the same time, for planarity reasons, double‐side polished (DSP) wafers have been progressively introduced. The combination of double side polished silicon wafers, together with their covering with amorphous carbon film, dramatically decreases the friction coefficient and incommodes their robotic handling. This issue may be faced by developing a tool designed for that specific purpose, and by optimizing the deposition conditions so as to obtain a reliable industrial high‐yield process.

Measuring brain activity with magnetoresistive sensors integrated in micromachined probe needles

An alternative neuroscience tool for magnetic field detection is described in this work, providing both micrometer-scale spatial resolution and high sensitivity to detect the extremely small magnetic fields (nT range) induced by the ionic currents flowing within electrically active neurons. The system combines an array of magnetoresistive sensors incorporated on micro-machined Si probes capable of being inserted within the brain current sources. The Si-etch based micromachining process for neural probes is demonstrated in the manufacture of a probe with 15 magnetoresistive sensors in the tip of each shaft. The probe shafts are formed by double-sided deep reactive ion etching on a double-side polished silicon wafer. The shafts typically have the dimensions 1.2 mm × 40 μm × 300 μm and end in chisel-shaped tips with an incorporated magnetoresistive sensor with dimensions of 30 μm × 2 μm. An accompanying interconnect flexible cable is glued and wirebonded enabling precise and flexible positioning of the probes in the neural tissue. Our analyses showed sharply defined probes and probe tips. The electrical and magnetic behavior of the sensors was verified, and a preliminary test with brain slices were performed.

Slam-Freezing as a Cryopreservation Tool for X-Ray Scattering Study on Membrane Samples

Reducing radiation damage is critical in X-ray scattering experiments for biological systems. A common technique involves rapidly freezing the sample and preserving it at cryogenic temperatures. However, this approach is only applicable to small samples, whose sizes are usually less than several tens of microns. To study 2D structures on a large, flat surface, we adopted the slam-freezing technique by using a modified cryostat and a computer-controlled linear motor. A special sample cell with an 80 µm-thick, double side polished silicon wafer was designed, with the aqueous solution having a contact area with silicon substrate of about 1 cm2. The influence of Polyethylene glycol (PEG) as a cryoprotectant was investigated. The aqueous solution could reach vitreous state at a PEG concentration of about 50% (v/v), verified by both in-situ grazing small angle X-ray scattering (GISAXS) and wide angle X-ray diffraction (WAXD) experiments. 2D assembly of tobacco mosaic virus (TMV) on lipid mono-layer grown on Octadecyltrichlorosilane-coated (OTS-coated) silicon surface was tested under both native state (in solution) and vitreous state using slam-freezing technique. It was shown that current protocol could significantly increase the dose tolerance of the sample in X-ray scattering experiments.

Slip band distribution in rapid thermally annealed silicon wafers

X-ray diffraction imaging of 200 mm diameter (100) oriented double-side polished silicon wafers has revealed that the slip band distribution, following rapid thermal annealing (RTA), has a lower symmetry than predicted from the material crystallography. Finite element (FE) modelling of the thermal processes has been undertaken and it is found that, in order to predict the measured temperature distribution during the annealing sequence in a commercial RTA furnace, an anisotropic heat flux distribution in the furnace must be included. When such an anisotropic heat flux is used to predict the wafer temperature, it is found that the temperature gradients are not equivalent in the radial direction. Calculation of the resolved shear stresses on the five independent slip systems associated with these gradients predicts asymmetry between the stress on slip bands that project into the [011] and [01¯1] directions. The anisotropy of the resolved shear stress distribution predicts accurately the asymmetry of the experimentally observed slip band length and density. Rotation of the wafer with respect to the furnace axes results in characteristic and systematic changes in the symmetry of the distribution, which is in good agreement with the finite element predictions.

Phosphonate-Anchored Monolayers for Antibody Binding to Magnetic Nanoparticles

Targeted delivery of magnetic iron oxide nanoparticles (IONPs) to a specific tissue can be achieved by conjugation with particular biological ligands on an appropriately functionalized IONP surface. To take best advantage of the unique magnetic properties of IONPs and to maximize their blood half-life, thin, strongly bonded, functionalized coatings are required. The work reported herein demonstrates the successful application of phosphonate-anchored self-assembled monolayers (SAMs) as ultrathin coatings for such particles. It also describes a new chemical approach to the anchoring of antibodies on the surface of SAM-coated IONPs (using nucleophilic aromatic substitution). This anchoring strategy results in stable, nonhydrolyzable, covalent attachment and allows the reactivity of the particles toward antibody binding to be activated in situ, such that prior to the activation the modified surface is stable for long-term storage. While the SAMs do not have the well-packed crystallinity of other such monolayers, their structure was studied using smooth model substrates based on an iron oxide layer on a double-side polished silicon wafer. In this way, atomic force microscopy, ellipsometry, and contact angle goniometry (tools that could not be applied to the nanoparticles' surfaces) could contribute to the determination of their monomolecular thickness and uniformity. Finally, the successful conjugation of IgG antibodies to the SAM-coated IONPs such that the antibodies retain their biological activity is verified by their complexation to a secondary fluorescent antibody.

Residual stress in piezoelectric poly(vinylidene-fluoride-co-trifluoroethylene) thin films deposited on silicon substrates

The residual stress and its evolution with time in poly(vinylidene-fluoride-co-trifluoroethylene) (P(VDF-TrFE) (72/28)) piezoelectric polymer thin films deposited on silicon wafers were investigated using the wafer curvature method. Double-side polished silicon wafers with minimized initial wafer warpage were used to replace single-side polished silicon wafers to obtain significantly improved reliability for the measurement of the low residual stress in the P(VDF-TrFE) polymer thin films. Our measurement results showed that all the P(VDF-TrFE) films possessed a tensile residual stress, and the residual stress slowly decreased with time. Our analysis further indicates that the tensile stress could arise from the thermal mismatch between the P(VDF-TrFE) film and the silicon substrate. Besides possible viscoelastic creep mechanism in thermoplastic P(VDF-TrFE) films, microcracks with widths in the range of tens of nanometers appeared to release the tensile residual stress.

Fabrication of AC-coupled double-sided silicon strip sensor

The AC-coupled double-sided silicon microstrip sensors are designed and 14 masks are used to produce prototype strip sensors. The biasing resistors are made of p-doped polysilicons and the coupling capacitors are built by separating implanted strips and readout strips by a thin oxide layer. The p-stops in the atoll patterns are introduced to disrupt an electron accumulation layer at the Si–SiO2 interface on the ohmic side. The junction side has a double metal structure using two metal layers separated from each other by a thick insulator layer. The strip sensors are fabricated on a 5-in., high resistivity, 〈100〉-orientation, and 380μm thick n-type double-sided polished silicon wafer. The prototype sensor with an area of 2.8×2.8cm2 consists of 256(512) readout channels with a strip pitch of 100(50)μm. The leakage currents and the bulk capacitances as a function of the reverse bias voltage are measured to understand the fabrication process of the prototype sensors. The signal to noise ratios are measured by using a 90Sr radioactive source in order to evaluate performance of the sensors. The design of the AC-coupled double-sided silicon strip sensor and its various components are described, and measurements of the electric characteristics and the signal to noise ratio are presented.

Piezoeletric Micropump for Drug Delivery System Fabricated Using Two Optical Masks

. In this study, a Piezoelectric Actuated Valveless Micropump (PAVM) has been designed and successfully fabricated using MEMS fabrication processes. A PZT: Pb (ZrTi) Ox (lead titanate zirconate) disc is used to actuate a silicon membrane by applying an alternating electrical field across the actuator. The resultant reciprocating movement of the pump membrane is then converted into pumping effect. Preliminary analysis of the fluidic characteristics of this micropump was performed using CoventorWare Simulator with MEMs-FSI (Fluid Structure Interaction) module to understand the working behaviour of the pump system. The pump is fabricated in a simple micromachining process with two optical masks using a double side polished silicon wafer. The tests carried out on the micropump have produced promising results to be used in the drug delivery system.