Single Crystal Silicon Wafers Research Articles

21318 単結晶シリコンウエハにおける破壊挙動と破壊靭性評価(材料強度と構造設(2),OS.5 材料強度と構造設計)

This paper provides an evaluation of fracture behavior and fracture toughness on single crystal silicon wafers. Fracture toughness (K_<IC>) were measured on the major planes of single crystal silicon using both method of indentation fracture (IF) method and controlled surface flaw (CSF) at room temperature. The values of K_<IC> on the surface orientations {100}, {110}, and {111} obtained by IF method were found to be 1.31±0.13, 0.84±0.14 and 1.16±0.13 MPa・m^<0.5> respectively. K_<IC> on the surface orientation {111} obtained by CSF method depends on indenter profiles.

Design of a Hybrid-Type Electrostatically Driven Microgripper Integrated Vacuum Tool

This work is focused on design and fabrication of a hybrid-type electrostatic silicon microgripper integrated vacuum tool. Vacuum tools are integrated in this novel microgripper in order to improve its pick and place capability. Surface and bulk micromachining technology is employed to fabricate the microgripper from single crystal silicon wafer (i.e., no silicon on insulator wafer is used). And the bonding technology is used to form the gas pipes for the vacuum tool. The linear motion of the microactuator is converted into a rotational gripping motion by a system of spring beams. At a driving voltage of 80V, a deflection of 25μm at the arm tip of the gripper is achieved.

Effect of cation on micro/nano-tribological properties of ultra-thin ionic liquid films

Room temperature ionic liquids (RTILs) have some unique characteristics which meet the requirements as high performance lubricants. In this work, three kinds of RTILs films with the same anion but different cations were prepared on single-crystal silicon wafer by dip-coating method. Thermal stability of the RTILs was evaluated using thermal gravity analysis in a nitrogen atmosphere. The morphology, nano-friction and nano-adhesion properties of the RTILs films were experimentally investigated at nano-scale using AFM/FFM. Chemical compositions of the films were characterized with a multi-functional X-ray photoelectron spectrometer. Micro-tribological properties of RTILs films were investigated using AISI-52100 steel ball in ball-on-plate configuration, and compared with perfluoropolyether. The worn surface morphologies were measured with a 3D optical surface profilometer. Results show that 3-butyl-1-methyl-imidazolium tetrafluoroborate exhibited the best anti-wear ability in comparison with the other three lubricants. RTILs films could be used as a kind of novel lubricant for application in M/NEMS. The corresponding friction-reduction and anti-wear mechanisms of the tested ultra-thin RTILs films under tested condition were proposed based on the experimental observation. The investigation revealed that friction-reduction and anti-wear properties of RTILs were strongly dependent on their chemical structures. For the friction at nano-scale, the flexibility and surface energy of the lubricant played significant role, while for the friction at micro-scale, both the rigid cycle structure and flexible chain of the RTILs played crucial role.

Current-voltage characteristics of Si/Si1 − x Ge x heterodiodes fabricated by direct bonding

We have studied the current-voltage (I–U) characteristics of Si/Si1 − xGex (0.02 < x < 0.15) heterodiodes fabricated by direct bonding of (111)-oriented n-type single crystal silicon wafers with p-type Si1 − xGex wafers of the same orientation containing 2–15 at % Ge. An increase in the germanium concentration NGe in Si1 − xGex crystals is accompanied by a growth in the density of crystal lattice defects, which leads to a decrease in the minority carrier lifetime in the base of the heterodiode and an increase in the recombination component of the forward current and in the differential resistance (slope) of the I–U curve. However, for all samples with NGe ≤ 15 at %, the I–U curves of Si/Si1 − xGex heterodiodes are satisfactory in the entire range of current densities (1 mA/cm2–200 A/cm2). This result shows good prospects for using direct bonding technology in the fabrication of Si/Si1 − xGex heterostructures.

Submicron-resolved relief formation in poled glasses and glass-metal nanocomposites

The formation of a spatial relief reproducing that of the anode as a result of the thermal poling of glasses and glass-metal nanocomposites in a strong electric field has been studied by atomic force microscopy. The anode surface patterns exhibited either a square grid or a rectangular grating with a depth of 120 nm, a strip width of 0.5 μm, and a period of 1 μm manufactured using electron-beam lithography and ion etching on the surface of an n-type single crystal silicon wafer. The relief depth formed on the surface of poled samples varied within 5–15 nm, depending on the experimental conditions. The mechanism of relief formation in this system is discussed.

Effect of Wettability of Silicon and Poly Silicon on Polishing Performance

Heavily doped poly silicon films have been widely used as gate electrodes and interconnection in MOS circuits. The shrinkage of devices below 100 nm requires more stringent and new CMP processes including poly silicon CMP. Poly silicon can be polished easily with similar pads and slurries as they are used for the planarization of silicon oxide. In this study, single crystal and poly silicon wafers were polished as a function of pH in fumed silica based slurry to understand and compare the polishing mechanism of silicon. The static and dynamic etch rates and polishing temperature were measured as a function of slurry pH (11 ~ 13) with friction forces. The single crystal silicon (bare silicon) showed higher removal rate than poly silicon. However, higher friction force was measured on poly silicon wafer than on bare wafer. The initial wettability of poly silicon with HF and without HF was treatment.

Nano/Microtribological Properties of Ultrathin Functionalized Imidazolium Wear-Resistant Ionic Liquid Films on Single Crystal Silicon

Ionic liquids (ILs) are considered as a new kind of lubricant for micro/nanoelectromechanical system (M/NEMS) due to their excellent thermal and electrical conductivity. However, so far, only few reports have investigated the tribological behavior of molecular thin films of various ILs. Evaluating the nanoscale tribological performance of ILs when applied as a few nanometers-thick film on a substrate is a critical step for their application in MEMS/NEMS devices. To this end, four kinds of ionic liquid carrying methyl, hydroxyl, nitrile, and carboxyl group were synthesized and these molecular thin films were prepared on single crystal silicon wafer by dip-coating method. Film thickness was determined by ellipsometric method. The chemical composition and morphology were characterized by the means of multi-technique X-ray photoelectron spectrometric analysis, and atomic force microscopic (AFM) analysis, respectively. The nano- and microtribological properties of the ionic liquid films were investigated. The morphologies of wear tracks of IL films were examined using a 3D non-contact interferometric microscope. The influence of temperature on friction and adhesion behavior at nanoscale, and the effect of sliding frequency and load on friction coefficient, load bearing capacity, and anti-wear durability at microscale were studied. Corresponding tribological mechanisms of IL films were investigated by AFM and ball-on-plane microtribotester. Friction reduction, adhesion resistance, and durability of IL films were dependent on their cation chemical structures, wettability, and ambient environment.

Effect of anion on micro/nano-tribological properties of ultra-thin imidazolium ionic liquid films on silicon wafer

Four kinds of room temperature ionic liquids (RTILs), as a new kind of lubricant for micro/nano-electromechanical system, with the same imidazolium cation but carrying different anions including hexafluorophosphate, tetrafluoroborate, nitrate and perchlorate were synthesized and these nano-scale films were prepared on single-crystal silicon wafer by dip-coating method. Atomic force microscopy was used to examine the morphologies of the films and evaluate their nano-friction and nano-adhesion properties. Chemical compositions of the films were characterized with a multi-functional X-ray Photoelectron Spectrometer. Micro-tribological properties of RTIL films were evaluated using a ball-on-plate micro-tribometer, and compared to that of perfluoropolyether. Results show that 3-butyl-1-methyl-imidazolium hexafluorophosphate exhibited the best anti-wear ability in comparison with the other four lubricants, so the ionic liquid films could be used as a kind of novel lubricant for application in MEMS/NEMS. Friction-reduction, adhesion resistance and anti-wear properties of RTILs were closely related to their anions. For the friction at nano-scale, the surface energy of the lubricant played a significant role, while the durability and friction-reduction of IL films strongly depend on their anions at micro-scale.

Scaling analysis of the morphology of nanostructured poly(p-xylylene) films synthesized by vapor deposition polymerization

The surface morphology of poly(p-xylylene) thin films prepared by the vapor deposition polymerization technique in the range of polymerization temperatures from −23°C to +35°C was studied by atomic force microscopy. Silicon (100) single crystal wafers and freshly cleaved mica were used as substrates. To analyze the roughness of polymer films, we studied the height-height correlations for pairs of points on the surface as a function of the distance between them using the scaling approximation. An increase in the substrate temperature results in a decrease in the roughness exponent at temperatures higher than the poly(p-xylylene) glass transition temperature, leading to an increase in the surface irregularity. At polymerization temperatures of +20°C to +35°C and a low rate of polymer film growth on Si substrate of ∼0.5–1 nm/min, the roughness exponent α = 0.73 ± 0.02 can be interpreted as a result of bulk diffusion of the monomer. The effect of the nature of the substrate, growth rate of the polymer film, and temperature of the substrate on scaling coefficients of the synthesized films was discovered. An increase in the growth rate of the polymer film results in an increased roughness exponent.

Effect of Ice Counterparts on the Friction Behavior of Single Crystal Silicon Wafer

The friction behavior of single silicon wafer sliding against different ice counterparts (α-Al2O3, CeO2 and SiO2) at 10±0.5 °C within a velocity of 60 rpm~300 rpm were studied using a home-made friction and wear testing machine. The morphologies and surfaces roughness of the worn silicon wafers were observed and examined on a non-contact surface topography instrument (ADE). It was found that the friction coefficient of the single silicon wafer decreased with the increase of sliding velocity. Single crystal silicon wafer coupled with α-Al2O3 ice counterpart recorded the highest friction coefficient and the biggest surface roughness, while it had the lowest friction coefficient and the smallest surface roughness as with CeO2 ice counterpart. One reason was that a series of tribochemical reactions occurred at the local contact point between the ice counterpart and the silicon wafer during sliding. Under alkaline condition, there would be a soft corrosion layer formed on the surface of the silicon wafer. Another reason was that the hardness of the abrasive particles was different and this caused different cutting depth of them.

XPS analysis of the groove wearing marks on flank face of diamond tool in nanometric cutting of silicon wafer

In nanometric cutting of single-crystal silicon wafers with a diamond tool, minimizing the tool wear is of great significance in order to achieve the satisfied surface quality and dimensional accuracy. For in-depth understanding of the tool wear mechanisms and the associated key factors, an X-ray photoelectron spectroscope (XPS) was employed to detect the chemical compositions of the wafer surface layer generated in the machining. The experimental results reveal that two hard particles, i.e. the silicon carbide (SiC) and diamond-like carbon particles, are generated during cutting, and then those particles scratch and plough on the tool flank face so as to form the groove marks, which lead to the heavy tool wear. The inspections further indicate the carbon diffusion is essential for the formation of SiC and diamond-like carbon particles, and the concentration of diffused carbon left on the machined surface declines along with the increase in cutting distance. Therefore, an efficient solution to suppress the tool wear is much needed, particularly for preventing the diffusion of diamond carbons into silicon wafer. Moreover, the formation of SiC and diamond-like carbon particles has no anisotropy although different crystalline planes of the diamond crystal are used as tool rake and flank faces through orientation arrangements. However, their resistances to the carbon diffusion present visible anisotropy.

Imaging interstitial iron concentrations in boron-doped crystalline silicon using photoluminescence

Imaging the band-to-band photoluminescence of silicon wafers is known to provide rapid and high-resolution images of the carrier lifetime. Here, we show that such photoluminescence images, taken before and after dissociation of iron-boron pairs, allow an accurate image of the interstitial iron concentration across a boron-doped p-type silicon wafer to be generated. Such iron images can be obtained more rapidly than with existing point-by-point iron mapping techniques. However, because the technique is best used at moderate illumination intensities, it is important to adopt a generalized analysis that takes account of different injection levels across a wafer. The technique has been verified via measurement of a deliberately contaminated single-crystal silicon wafer with a range of known iron concentrations. It has also been applied to directionally solidified ingot-grown multicrystalline silicon wafers made for solar cell production, which contain a detectible amount of unwanted iron. The iron images on these wafers reveal internal gettering of iron to grain boundaries and dislocated regions during ingot growth.

Titanium Dioxide (TiO2) Single Crystal Holder with a Cold Trap and a Heating Mechanism Mounted on a Conflat Flange with an Outer Diameter of 70 mm

We introduce a titanium dioxide (TiO2) single crystal holder with a cold trap and a heating mechanism mounted on a conflat flange with an outer diameter of 70 mm. The basic design of the TiO2 holder is the same with the holder for the silicon (Si) single crystal wafer [E. Kobayashi, A. Nambu, T. Kakiuchi, and K. Mase: Shinku, 50 (2007) 57]. A TiO2 single crystal wafer is fixed on a Si wafer, and the TiO2 is heated by the direct-current heating of the Si wafer. Using this holder we prepared clean TiO2(110)-1×1.

Growth of niobium oxide films on single-crystal silicon

200-nm-thick niobium films grown on single-crystal silicon wafers by magnetron sputtering have been oxidized by annealing in flowing oxygen. X-ray diffraction examination revealed the metal-like phase Nb6O in the as-deposited films. Annealing in flowing oxygen for 1 h led to the formation of tetragonal NbO2 at 570 K and hexagonal Nb2O5 at temperatures above 770 K. The grain size and surface roughness of the films were evaluated using atomic force microscopy.

Coherent Spin Transport through a 350 Micron Thick Silicon Wafer

We use all-electrical methods to inject, transport, and detect spin-polarized electrons vertically through a 350-micron-thick undoped single-crystal silicon wafer. Spin precession measurements in a perpendicular magnetic field at different accelerating electric fields reveal high spin coherence with at least 13pi precession angles. The magnetic-field spacing of precession extrema are used to determine the injector-to-detector electron transit time. These transit time values are associated with output magnetocurrent changes (from in-plane spin-valve measurements), which are proportional to final spin polarization. Fitting the results to a simple exponential spin-decay model yields a conduction electron spin lifetime (T1) lower bound in silicon of over 500 ns at 60 K.

Research on Nano-Mechanical and Micro-Tribological Behaviors of C&lt;sup&gt;+&lt;/sup&gt;- Implanted Silicon

The knowledge of tribological properties of silicon is important due to its potential application for micromechanical devices. Single crystal silicon wafers were implanted by carbon ion with an energy of 80 keV and different implantation doses of 2×1015 ions/cm2 and 2×1016 ions/cm2, respectively. The nanohardness and elastic modulus of silicon wafers before and after C+ implantation were studied on the nano-mechanical testing system. The micro sliding tests on silicon wafers before and after C+ implantation were performed on the UMT-2 Micro-tribometer to investigate the coefficient of friction and wear volume. The results demonstrate that the nanohardness and elastic modulus of silicon wafer at the implantation dose of 2×1015 ions/cm2 decrease and those of 2×1016 ions/cm2 have little change. C+ implantation improves friction-reducing effect of silicon wafers and the coefficient of friction decreases to a great extent. But when the load reaches a certain value, the coefficient of friction increases sharply and the worn trace occurs on the silicon surface. Adhesive and abrasive wear are the main mechanisms at light loads and micro fatigue is the main mechanism at heavy loads.

A Raman scattering study of [formula omitted] trapped near O in Si

Single-crystal silicon wafers exposed to a hydrogen plasma are studied by Raman scattering. Three Raman signals at 3727(1), 3733(1), and 3740 ( 1 ) cm - 1 ( T → 0 K ) are assigned to ro-vibrational modes of H 2 bound to interstitial oxygen ( O – H 2 ) . By monitoring the trapping kinetics of interstitial H 2 at oxygen it is found that ortho- and para- H 2 have similar diffusivities. At 77 K, an ortho-to- para conversion of H 2 within the O – H 2 complex is observed. This conversion occurs with similar kinetics as has been previously observed for isolated interstitial H 2 in Si, and is suggested to be caused by interaction of H 2 with the nuclear magnetic moment of 29Si.

Measurement of the diffusion rate of Li in silicon by the use of bipolar cells

Due to the lack of diffusion data of Li in solid silicon at room temperature, we decided to determine the diffusion coefficient of Li in solid silicon by the use of a bipolar cell system where a sheet of silicon sample is sandwiched as the bipolar electrode between two facing bipolar cell compartments. In both of the cell compartments counter and reference electrodes were mounted. In one of the cell compartments (Cell A), an electrolyte containing Li + was filled, while the facing compartments (Cell B) was filled with an electrolyte containing Na + instead of Li +, and a needle-like W/WO x electrode, which can sense the Li + concentration, was mounted near the surface of the bipolar electrode. At first the potential of the bipolar electrode in Cell A was set at the natural potential, and the potential in Cell B was polarized at a sufficiently positive potential, then the potential in Cell A was set at a definite cathodic potential and the signal–time curve of the W/WO x electrode in Cell B was recorded. During the cathodic polarization in Cell A Li + was incorporated in the bipolar electrode, migrating from the Cell A side to the Cell B side, and transferred to the electrolyte in Cell B compartment. As a result, the signal of the Li + sensing electrode began to increase after a time delay which corresponds to the time for Li to migrate in the bipolar electrode from the Cell A side to the Cell B side. From the value of time delay we could calculate the diffusion coefficient by the use of a diffusion equation where a parameter of the thickness of the bipolar electrode is involved. The obtained value of the diffusion coefficient of the vacuum-deposited film was 10 −9 cm 2 s −1 independent of the polarization potential. In contrast, the silicon single crystal sample obtained by thinning the silicon single crystal wafer gave about 2 × 10 −11 cm 2 s −1. The larger value obtained with the vacuum-deposited film is attributed to the loose structure of the deposited film.

Electrical characterization of amorphous silicon carbide thin films deposited via polymeric source chemical vapor deposition

Polymeric source chemical vapor deposition (PS-CVD) was used to synthesize amorphous silicon carbide (a-SiC) thin films. The PS-CVD process was conducted at temperatures between 750 and 1000 °C. The substrates used were silicon single crystal wafers of p-type and n-type, and thermally grown silicon dioxide substrates. The chemical and electrical properties of the films were studied by various techniques, including Fourier transform infrared spectroscopy, elastic recoil detection (ERD), and capacitance–voltage technique. A correlation was observed between the average concentration of oxygen in the films and the deposition temperature, linking a low oxygen concentration to a high deposition temperature. However, the concentration of oxygen in the films deposited at the same temperature is independent of the substrate. The thin films deposited at low temperature showed insulating behaviour, while the semiconducting behaviour is obtained at high deposition temperatures. Ohmic contacts were obtained on the deposited semiconductor thin film by evaporating nickel contacts, followed by annealing of the sample at 800 °C for 2 min.

Characteristics of a commercially available silicon-on-insulator MEMS material

Design of microelectromechanical systems (MEMS) requires an understanding of the material characteristics inherent to the specific processing technologies. In this study, several design-critical characteristics of a silicon-on-insulator (SOI) MEMS fabrication technology (SOIMUMPs) have been examined and compared to a surface micromachined MEMS fabrication technology (polyMUMPs), both produced by MEMSCAP, Inc. Diagnostic structures were utilized to evaluate material characteristics including: minimum achievable feature size, deviation of feature size from nominal design dimensions, through-thickness residual strain gradient, in-plane residual strain, resistivity, surface roughness, and fracture strength. In general, most of the measured characteristics were similar for SOIMUMPs and polyMUMPs, in spite of their very different fundamental process constraints. For example, the characteristic fracture strength was 1.97 and 1.43 GPa, with associated Weibull moduli of 8.9 and 14.0, respectively. These values are similar given the very different sources of silicon: mechanically thinned single crystal silicon wafers versus low-pressure chemical vapor deposition for polycrystalline films. Fractography suggests that fracture strength for the both technologies is controlled by surface topography features: individual sidewall etching defects drive SOIMUMPs failures whereas top-surface grain boundary crevices drive polyMUMPs failures. Discussion focuses on the ramifications of the process-controlled material characteristics in SOIMUMPS and polyMUMPs to the design of MEMS components.