Single Crystal Silicon Wafers Research Articles

Electrowetting at a liquid metal-semiconductor junction

We report electrowetting at a liquid metal-semiconductor (Schottky) junction using of a mercury droplet resting on silicon. This is demonstrated using n-type and p-type single-crystal silicon wafers of different doping levels. The voltage-dependent wetting contact angle variation of the mercury droplet is observed to depend on both the underlying semiconductor doping density and type. The electrowetting behavior can be explained by the voltage-dependent modulation of the capacitance of a Schottky junction; current-voltage and capacitance-voltage measurements indicate this to be the case. A modified Young-Lippmann electrowetting equation—formulated using a well-established metal-semiconductor junction model—agrees well with the observations.

The Effect of Microstructure, Thickness Variation, and Crack on the Natural Frequency of Solar Silicon Wafers.

Vibration is one of the most common loading modes during handling and transport of solar silicon wafers and has a great influence on the breakage rate. In order to control the breakage rate during handling and facilitate the optimization of the processing steps, it is important to understand the factors which influence the natural frequency of thin silicon wafers. In this study, we applied nonlinear finite element method to investigate the correlation of natural frequency of thin solar silicon wafer with material microstructures (grain size and grain orientation), thickness variation and crack geometry (position and size). It has been found that the natural frequency for anisotropic single crystal silicon wafer is a strong function of material orientation. Less than 10% thickness variation will have a negligible effect on natural frequency. It is also found out that cracks smaller than 20 mm have no dominant effect on the first five natural frequency modes anywhere in the silicon wafer.

An ultra-high Q silicon compound cantilever resonator for Young's modulus measurements

We describe the design of ultra-high Q mechanical cantilever resonators, fabricated from single-crystal silicon wafers. The mechanical resonance mode at f ≈ 8.5 kHz achieves a background damping of Q(-1) </~ 2 × 10(-8) at temperatures below 30 K, which is equal to that of a successful silicon torsional resonator with which the cantilever resonator shares several design elements. The new resonator can be used for accurate measurements of the Young's modulus and internal friction of thin films. It is compatible with both the mounting apparatus and measurement electronics of the torsional resonator, and the two resonators together can be used to provide a complete description of the elastic properties of isotropic thin films.

Analytical Method for Calculating Curvature of Circular Silicon Wafer Caused by Boron Doping

Doping can lead to residual strain and change of elastic properties in silicon. Residual strain makes silicon wafer exhibit curvature, which are used for fabricate MEMS structure. The boron doping profile is not uniform through depth, which makes doped silicon become a inhomogeneous material or Functionally Graded Material. For boron-doped circular single crystal silicon wafer, a analytical method which based on functionally graded plate mechanics theory, is proposed to calculate its curvature. Example was used to verify the analytical method through 3D finite element simulation.

Using Taguchi Method to Optimize Polishing Parameters in Ice Fixed Abrasive Polishing

Ice fixed abrasive polishing (IFAP) was used to polish single crystal silicon wafer. Polishing parameters were polishing pressure, table velocity, eccentricity, and polishing time. Using Taguchi method, the influences of the polishing parameters on material removal rate (MRR) and surface roughness (Sa) were invested. The results show that polishing pressure plays the most significant role on MRR followed by table velocity; as far as Sa is concerned; polishing time is the most important one, followed by table velocity. In order to get high MRR during IFAP of silicon wafer, the optimal processing parameters are: polishing pressure 0.1 MPa, table velocity 400 r/min, eccentricity 30 mm, and polishing time 60 min. The best Sa can be obtained when the optimal processing parameters are: polishing pressure 0.075 MPa, table velocity 300 r/min, eccentricity 20 mm, and polishing time 40 min. The experimental results illustrate that the Taguchi method is a viable way to obtain the optimum conditions for high MRR and best Sa.

Nanoscale friction and wear properties of silicon wafer under different lubrication conditions

The nanoscale friction and wear properties of single crystal silicon wafer under different lubrication conditions are studied in this paper. The experiments were performed with Si3N4 ball sliding on the surface of silicon wafer under four different lubrication conditions: dry friction, water lubrication, hydrogen peroxide lubrication and the static hydrogen peroxide dry friction. The results from the experiments have been analyzed showing the different friction and wear properties of the silicon wafer in different lubrication conditions. It is concluded that the wear rates under the water lubrication and under the hydrogen peroxide lubrication are both small, the chemical reactions are facilitated by the mechanical processes when the load and the sliding speed reach certain levels. This is mainly resulted by the enhanced lubricant performance with the formed silicon hydroxide Si(OH)4 film. Under the water lubrication, the wear is found in a way of material removed in molecule scale. Under the hydrogen peroxide lubrication, the wear is mainly caused by the spalling of micro-cracks. Under the dry friction condition, the wear is found being adhesive wear. And under the static peroxide dry friction, the wear is prevailing adhesive wear. These results are essential and valuable to the development of the efficient and environmental-friendly slurry for the chemical mechanical polishing (CMP) process.

Preparation of a silicon heterojunction photodetector from colloidal indium oxide nanoparticles

A colloidal indium oxide (In2O3) nanoparticles (NPs) were synthesized by using a Q-switched Nd:YAG laser ablation of indium target in water at room temperature. Optical absorption and x-ray diffraction (XRD) investigation of the prepared samples confirm the formation of In2O3 NPs. A solution-processed silicon heterojunction photodetector, fabricated by drop cast film of colloidal In2O3 NPs onto n-type single crystal silicon wafer, is demonstrated. I–V characteristics of In2O3 NPs/Si heterojunction under dark and illumination conditions confirmed the rectifying behavior and the good photoresponse. The built-in-voltage was determined from the C–V measurements which revealed an abrupt junction.

FABRICATION AND STUDY CHARACTERISTICS OF CDO/SI HETEROJUNCTIONDETECTOR BY CBD TECHNIQUE

In this work CdO/Si heterojunction detector were fabricated by depositing CdO thin film on p-type single crystal silicon wafers by chemical bath deposition technique(CBD) . The effect of cadmium ion concentration on the structural properties of deposited film and optoelectronic characteristics of fabricated detector has been considered in this work . From the x-ray diffraction result, it is shown that the CdO film has a single crystalline in cubic structure with preferential orientation along the (311) crystal plane. The -voltage characteristics under dark result, it is shown that ideality factor of heterojunction has higher value(n˃1).From current-voltage characteristics under illuminations result, it is shown that photocurrent increase with increasing cadmium ion concentration in solution. The capacitance–voltage characteristic shows a typical abrupt heterojunction. The optoelectronic characteristics shows the CdO/Si detector has good spectral responsivity in visible and NIR with higher peak responsivity at 900 nm were found 0.38 A/W.

Characteristics of nanostructured CdO/Si heterojunction photodetector synthesized by CBD

In the present work, CdO/Si heterojunction detectors were fabricated by depositing nanostructured CdO film on single crystal silicon wafer by chemical bath deposition (CBD) technique. Films deposition was carried out at different temperatures. To obtain good film stoichiometry heating of films in static air at temperature of 400°C for 90min was carried out. The structural properties of CdO films was characterized by X-ray diffraction and atomic force microscope (AFM), these investigations showed that the deposited CdO films have cubic structure. The surface morphology investigation revealed that CdO film is almost homogeneous and consisted of the nanowires with diameter less than 100nm at temperature of solution 40°C.The band gap of the films changes from 2.4 to 2.5eV with increasing preparation temperature. The current–voltage characteristics of photodiodes under dark exhibit good rectification behavior and that ideality factor of heterojunction was found to be in the range of 1.56–3.69 depending on solution temperature. The capacitance–voltage characteristic shows a typical abrupt heterojunction and the built-in-potential was determined. CdO/Si detector has good spectral responsivity in visible and NIR and the maximum responsivity was 0.56A/W. Rise time of the photodetectors was strongly dependent on solution temperature and the shortest rise time obtained was 45ns at 2V.

Hybrid photodiodes based on 6,13-bis(triisopropylsilylethynyl) pentacene:poly[2-methoxy-5-(2-ethyl) hexoxy-phenylenevinylene]/p-silicon

6,13-Bis(triisopropylsilylethynyl) pentacene (TIPS) and poly[2-methoxy-5-(2-ethyl) hexoxy-phenylenevinylene] (MEH-PPV) blends with different ratios were deposited onto a p-type silicon (p-Si) single crystal wafer using spin coating technique. The dark current–voltage characteristics of the fabricated diodes were studied at room temperature. This study was carried out to predict the best blend composite to obtain a qualified diode for use in potential application. The obtained results suggest that the diode with 10:4 ratio between TIPS and MEH-PPV has the highest values for both the rectification factor (r=1.7×103) and the ratio between shunt resistance, Rsh, and series resistance, Rs, (Rsh/Rs=1.23×104) among the investigated diodes. Accordingly, the capacitance–voltage–frequency and conductance–voltage–frequency measurements were carried out for this diode in the frequency range between 10kHz and 1MHz at room temperature. Moreover, the I–V characteristics of such a diode were studied under different illumination intensities (P=20:100mW/cm2). The obtained results show a highly optoelectric response; i.e., the diode can be operated as a heterojunction photodiode.

Characterization of Al/p-Si/n-AgGaSe2/Au thin films heterojunction device

Crystalline Al/p-Si/n-AgGaSe2/Au heterojunction device was fabricated by depositing AgGaSe2 thin films at temperature 473 K, onto p-type single crystal silicon wafers with surface orientation (111) and glass substrates. The crystalline nature and the chemical composition of the deposited AgGaSe2 films have been confirmed using both X-ray diffraction (XRD) and energy dispersive X-ray spectrometer (EDX) techniques. The dark current–voltage characteristics of the heterojunction diode have been investigated at various temperatures to elucidate the electrical conduction mechanisms. It was found that at forward bias voltages ≤100 mV, the current is controlled by the thermionic emission mechanism, whereas, at bias voltages higher than 100 mV, the current is controlled by the space charge limited current mechanism. The reverse current mechanism of the diode is controlled by the carrier generation–recombination process in the depletion region. The photovoltaic parameters were determined from the current–voltage characteristics under illumination. The built-in potential, effective carrier concentration and barrier height were also evaluated from the C–V measurement.

結晶粒径の異なる銅薄膜のヒロック形成温度と初期残留応力の関係

We deposited copper films which have a different grain size on the silicon single crystal wafer with dc magnetron sputtering. The crystal grain size of the copper films was varied by changing the substrate temperature Ts, which is one of the sputtering deposition conditions, between 64°C and 200°C. The obtained copper films were set on an optical microscope equipped with a vacuum heating device. The films surface were observed with the microscope throughout the thermal cycling between room temperature to 800°C. Next, we examined the temperature which hillocks begin to form. As a result, we confirmed the clear relationship between the temperature which the hillocks begin to form and the initial grain size of the copper film. In the case of low substrate temperature of Ts = 64°C, the initial grain size of copper film was very small, and many hillocks were formed at low heating temperature of 300°C. On the other hand, in the case of high substrate temperature of Ts = 200°C, the initial grain size of copper film was large, and hillocks were not formed below heating temperature of 800°C.

A high-performance multi-beam microaccelerometer for vibration monitoring in intelligent manufacturing equipment

A piezoresistive microaccelerometer with multi-beam structure is developed for vibration monitoring in intelligent manufacturing equipment. The proposed accelerometer provides a promising solution to the trade-off between the cost-effective development and demands on high-performance sensors. By incorporating tiny sensing beams, the multi-beam accelerometer obtains a higher resonant frequency and favorable measurement sensitivity compared with the quad-beam one. Theoretical analysis and finite element method (FEM) simulation demonstrate satisfactory results of an improved resonant frequency increased by a factor of 1.81 at the expense of slight sensitivity loss. Fabricated on an n-type single crystal silicon wafer, the sensor chips with multi-beam structure and quad-beam structure are wire-bonded to printed circuit boards (PCBs) and simply packaged for experiments. The static and dynamic characteristics of the two types of sensors are tested and compared. The temperature coefficient of offset output is also measured. The results show that the developed accelerometer has favorable features that allow its usage in the demanding application.

Experimental Study on the Nanoindentation of Thin Copper Films from Deep Submicron to Nano-Scale

AbstractThis study uses the nanoindentation technique to evaluate the mechanical properties of thin copper films at indentation depths measured in the order of nanometers. Copper films with various thicknesses are deposited on a single crystal silicon wafer with a (100) orientation and on a polymethylmethacrylate (PMMA) substrate, respectively. The experimental results show that for soft thin films on a hard substrate, the substrate effect is negligible when the indentation depth is less than 20% of the film thickness. However, the results suggest that hard films on a soft substrate should be treated as a composite system in indentation because the substrate effect is significant. Finally, the results reveal that a significant indentation size effect exists for thin films with a thickness of less than 100nm. A number of possible reasons for the depth dependence of the hardness properties at ultra-shallow indentation depths are proposed and discussed.

Study of the morphological growth features and optical characteristics of multilayer porous silicon samples grown on n-type substrates with an epitaxially deposited p +-layer

This study is concerned with the growth features of multilayer porous silicon with layers of different porosity, obtained by electrochemical etching on an n-type single-crystal silicon (111) wafer with a p+-layer epitaxially deposited onto the surface. The possibility of obtaining a multilayer system of ordered pores of various sizes within a single technological cycle is demonstrated. The differences in the optical characteristics of separate layers of the grown structure are shown.

Mechanics prediction of the fracture pattern on scratching wafers of single crystal silicon

The effect of anisotropy on the response and fracture pattern on scratching {100} and {111} single crystal silicon wafers in two characteristic directions, i.e. 〈100〉 and 〈110〉 in a {100} wafer, and 〈110〉 and 〈112〉 in a {111} wafer, respectively, was studied. Predictions of the locations of the onset of fracture, as well as the fracture patterns on the wafer surfaces, were obtained applying a “minimum crack length” criterion assisted by numerical determination of the stress states using the finite element method. It was found that the first crack appears on the {111} or {110} cleavage plane. The 〈112〉 scratching direction on the {111} wafer is the weakest among the four directions studied, since it provides the highest resolved tensile stress and the shortest initial defect for crack propagation. The 〈100〉 scratching direction in the {100} wafer appears to be strongest. Experiments validated the approach and also showed a higher reliability in the {100}〈100〉 and {111}〈110〉 directions. The methodology used in this manuscript can be applied to the determination of fracture patterns in other single crystal materials, under scratching or other mechanical loading conditions.

Tribological Properties of MACs-APS Films

Multiply-alkylated cyclopentanes (MACs) with different molecular structure were deposited on single crystal silicon wafers coated with a thin aminopropyltrimethoxylsilane (APS) film as an adhesive layer to form MACs-APS films. The thickness, wetting behavior and nano-scale morphologies of the films were characterized by means of ellipsometry, contact angle measurement, and atomic force microscopy (AFM). The friction and wear behaviors of the thin films sliding against a Si3N4 ball were examined on a UMT-2MT tribometer in a ball-on-disk contact mode. The worn surfaces of the MACs-APS films and the counterpart Si3N4 balls were investigated with a scanning electron microscope (SEM). It was found that the water contact angles on the MACs-APS film increased with the MACs alkyl chain-length. The MACs-APS film exhibited higher load-carrying capacity and better friction reduction and anti-wear behavior as compared with the APS film. This is suggested to occur because the APS acts as a strongly bonded lubricant phase and MACs as a mobile lubricant phase in the MACs-APS film. The increase of the chain-length of the alkyl substituent in the MACs compounds resulted in improved tribological properties of MACs-APS film. It is suggested that the longer alkyl chains are much more flexible and can dissipate the mechanical energy during the shearing process more easily than the short chain compounds. MACs with the longer chains have stronger chain-chain interactions and the larger MAC molecules have stronger intermolecular interactions, resulting in the good tribological properties of MACs-APS film.

A miniaturized bulk micromachined triaxial accelerometer fabricated using deep reactive etching through a multilevel thickness membrane

We present the design, fabrication and characterization of an application specific triaxial accelerometer for post-surgery heart monitoring. The accelerometer chip is designed as a 2 × 4 × 1.2 mm3 chip with nominal acceleration range of ±4 g and frequencies below 50 Hz. It has been fabricated using a multiproject wafer service with an additional deep reactive ion etching process to obtain controlled etch-through of membranes of 3, 23 and 400 μm thicknesses simultaneously. The novelty of the work presented here is the bulk micromachining technique using both deep reactive dry etching and alkali-based anisotropic wet etching of single crystal (100) silicon wafers used to obtain a space efficient design. Proof of concept is demonstrated with preliminary testing, with an acceleration sensitivity of ~0.04 mv/V/g for out of plane (z axis) acceleration.

Melting and solidification behavior of laser-crystallized silicon thin-films studied by transient conductance measurements

In this paper we report on transient conductance measurements during melting and solidification of thin silicon films on foreign substrates, which were irradiated with an excimer laser. The silicon films were deposited on borosilicate float glass or single crystal silicon wafers that were coated with different intermediate layers. Our results show that the laser fluence required to melt the entire Si layer is mainly determined by the silicon–substrate interfacial thermal resistance and not by the heat conductivity of the bulk substrate. The solidification velocity, on the other hand, is strongly influenced by the heat conductivity of the bulk substrate and reaches a maximum value of 0.95m/s for c-Si compared to 2.19m/s for borosilicate float glass.

Manipulation of Microobjects Based on Dynamic Adhesion Control

Due to scale effects, microoperation, especially the releasing of microobjects, has been a long-standing challenge in micromanipulation applications. In this paper a micromanipulation method is presented based on dynamic adhesion control with compound vibration. This adhesion control technique employs inertia force to overcome adhesion force achieving 100% repeatability with releasing accuracy of 4± 0.5μm, which was experimentally quantified through the manipulation of 20–100μm polystyrene spheres under an optical microscope. The micromanipulation system consists of a microgripper and a piezoelectric ceramics module. The compound vibration comes from the electrostatic actuator and the piezoelectrically driven actuator. Surface and bulk micromachining technology is employed to fabricate the microgripper used in the system from a single crystal silicon wafer. Experimental results confirmed that this adhesion control technique is independent of substrate. Theoretical analyses were conducted to understand the picking up and releasing mechanism. Based on this preliminary study, the micromanipulation system proved to be an effective solution for active picking up and releasing of micromanipulation.