Dec 12, 2018

Fabrication of 1 Inch Mosaic Crystal Diamond Wafers


We fabricated so-called mosaic single-crystal-diamond (SCD) wafers that consist of SCD sub-crystals with identical characteristics. These sub-crystal clones were obtained from a SCD seed crystal by repeating the lift-off process using ion implantation. We found that the junctions between the cloned sub-crystals were smoothly covered and no abnormal crystal growth occurred along the junctions. Therefore, the lift-off process can be applied to the production of freestanding SCD wafers with the same size. Based on these findings, we have succeeded in synthesizing 1 in. mosaic diamond wafers.


Source:IOPscience

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Nov 26, 2018

X-ray Radiographs Taken with Silicon Single Crystal Wafers by Divergent X-ray Method

By our own Divergent X-ray Method, X-ray radiographs consisted of broad Laue-spots with X-ray spectral lines were simply and easily taken with the wafers of silicon single crystals of various kinds. On each of the Laue-spots, many X-ray spectral lines of various shapes and ground figures consisted of somewhat broadened lines, straightened or curved, were revealed. It is considered that these X-ray spectral lines and the ground figures of the Laue-spots are mostly produced by the dislocations and other imperfections in the crystal wafer, and that from the appearances of these X-ray spectral lines and ground figures the bodily distribution of the dislocations and other imperfections can be presumed.


Source:IOPscience

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Nov 12, 2018

Deformation of Single Crystal Wafers of Silicon Caused by Lapping


Two types of deformation of single crystal wafers of silicon introduced by lapping one face of a wafer are observed. There exists a critical thickness, Tc, above which the deformation is symmetric with respect to the center of wafers (spherical deformation), and below which the deformation is symmetric with respect to a certain diameter (cylindrical deformation). The plots of the deflection for the spherical deformation at any cross section and for the cylindrical deformation at cross section perpendicular to axis of symmetry coincide with parabolic lines. In the case of {100} wafers, there are two stable modes for the cylindrical deformation and the axes of symmetry coincide with <100> on {100}. Whereas {111} wafers have a single stable mode: some axes of symmetry coincide with <211> and/or <110> but the rest does not coincide with any direction having low indices. It is likely that both types of deformation originate from the plastically deformed layer on the lapped face and that large portion of a wafer is deformed elastically except for the layer.




Source:IOPscience

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Aug 17, 2018

Laser optoacoustic method for quantitative nondestructive evaluation of the subsurface damage depth in ground silicon wafers

This paper is a report on the novel laser optoacoustic method for nondestructive evaluation of the depth of the subsurface damage in ground single-crystal silicon wafers. It is based on different mechanisms of laser excitation of ultrasound by absorption of Q-switched Nd:YAG laser pulses at the fundamental wavelength: the concentration-deformation mechanism in the undamaged single-crystal silicon and the thermoelastic one in the subsurface damaged layer. Due to the uniform heating of the whole damaged layer during the laser pulse action the amplitude of the compression phase of the laser-induced ultrasonic signal is proportional to the damaged depth. The rarefaction phase of this signal arises by absorption of the remaining laser energy in the single-crystal silicon beneath the damaged layer. The empirical relation between the depth of the subsurface damage and the ratio of the amplitudes of compression and rarefaction phases of the laser-induced ultrasonic signal can be fitted by a linear function within the depth variation and the corresponding spread of the signal amplitudes. The proposed method attracts some interest for in situ control of the solid surface condition that is important in different tasks of linear and nonlinear optics.


Source:IOPscience

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Aug 5, 2018

Wafer-scale synthesis of monolayer and few-layer MoS2 via thermal vapor sulfurization

Monolayer molybdenum disulfide (MoS2) is an atomically thin, direct bandgap semiconductor crystal potentially capable of miniaturizing optoelectronic devices to an atomic scale. However, the development of 2D MoS2-based optoelectronic devices depends upon the existence of a high optical quality and large-area monolayer MoS2 synthesis technique. To address this need, we present a thermal vapor sulfurization (TVS) technique that uses powder MoS2 as a sulfur vapor source. The technique reduces and stabilizes the flow of sulfur vapor, enabling monolayer wafer-scale MoS2growth. MoS2 thickness is also controlled with great precision; we demonstrate the ability to synthesize MoS2 sheets between 1 and 4 layers thick, while also showing the ability to create films with average thickness intermediate between integer layer numbers. The films exhibit wafer-scale coverage and uniformity, with electrical quality varying depending on the final thickness of the grown MoS2. The direct bandgap of grown monolayer MoS2 is analyzed using internal and external photoluminescence quantum efficiency. The photoluminescence quantum efficiency is shown to be competitive with untreated exfoliated MoS2 monolayer crystals. The ability to consistently grow wafer-scale monolayer MoS2 with high optical quality makes this technique a valuable tool for the development of 2D optoelectronic devices such as photovoltaics, detectors, and light emitters.

Source:IOPscience

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Jul 23, 2018

Continuous Wave and Q-Switched Mode-Locking of a Nd:YVO4 Laser with a Single Crystal GaAs Wafer

We realized both continuous wave (CW) and Q-switched mode-locking in a diode-pumped Nd:YVO4 laser by using a single crystal GaAs wafer as the saturable absorber as well as an output coupler. The GaAs wafer was coated to have a continuously variable reflectivity and the laser intensity within the GaAs saturable absorber can be changed by simply translating the GaAs wafer. CW mode-locked pulses of 1.5 W average power and 31 ps duration were generated at 154 MHz repetition rate. For Q-switched mode-locking, the repetition rate and pulse duration of the Q-switched pulses were 133–300 kHz and 100–350 ns, respectively.


Source:IOPscience

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Jul 1, 2018

Crystal-Originated Singularities on Si Wafer Surface after SC1 Cleaning

It is clarified that a new type of singularity is formed on Si wafer surface by the Standard Cleaning 1 (SC1) of the RCA cleaning process. Such singularities are perceived by laser particle counters as small particles on wafers. It is shown that the singularities correspond to small shallow pits caused by the etching effect of the SC1 cleaning solution. The origin of the pits is presumed to be some kind of defect in the melt-grown crystals.


Source:IOPscience

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Jun 25, 2018

A new accurate technique for determination of crystallographic orientation of surfaces of single crystal wafers

A technique based on high resolution X-ray diffractometry employing multicrystal X-ray diffractometers is described. The wafer is mounted against the flat surface of a device and is aligned for diffraction of X-rays from lattice planes that are nearly parallel to its surface. The device is rotated azimuthally around an axis perpendicular to the wafer surface in a stepwise manner. The specimen has to be reoriented after each step to be on the peak of the diffraction curve due to finite angle alpha between the visible surface and the lattice planes. A plot of the reorientation angle as a function of the azimuthal position gives a sinusoidal curve. From three such plots at different known azimuthal orientations of the wafer with respect to the device, the value of angle alpha can be determined. The spatial orientation of the normal to the lattice planes is obtained. A general mathematical formulation has been given for the first time. The finite angle between the axis of rotation of the device and its flat surface against which the specimen is held, is determined. Once a device has been characterised only two azimuthal positions of the wafer are sufficient to determine its crystallographic orientation. Illustrative results of characterisation of a device and determination of orientation of a (111) silicon wafer are described. An overall uncertainty of +or-6 arc sec in the determination of alpha is achieved.

Source:IOPscience

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Jun 5, 2018

Room-temperature wafer bonding of Si to LiNbO3, LiTaO3 and Gd3Ga5O12 by Ar-beam surface activation

A room-temperature wafer bonding method using surface activation by Ar-beam sputter etching were applied to the bonding between dissimilar materials. LiNbO3, LiTaO3 and Gd3Ga5O12 wafers were successfully bonded to Si wafers without any heat treatment. This method is free from the various problems caused by the large thermal expansion mismatch between these materials during heat treatment in the conventional wafer bonding processes. The bond prepared by the Ar-beam treatment is so strong that fracture from inside the bulk materials is observed after the tensile test. The results of the bonding of Si wafers to both 128° Y-cut and Z-cut LiNbO3 wafers indicate that the influence of the crystal orientation on the bonding strength is negligible in this method. This method provides a very low damage bonding process for various material combinations regardless of any thermal expansion mismatch or crystal lattice mismatch.


Source:IOPscience

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May 15, 2018

Resonance ultrasonic vibration diagnostics of elastic stress in full-size silicon wafers

A resonance vibration approach is developed to measure residual stress non-destructively in full-size multicrystalline silicon wafers used in solar cell manufacturing. This method is based on excitation of longitudinal resonance ultrasonic vibrations in the material using an external piezoelectric transducer combined with high-sensitive ultrasonic probe and data acquisition of the frequency response to make the method suitable for in-line diagnostics during wafer and cell manufacturing. Theoretical and experimental analysis of the vibration mode in single-crystal and multicrystalline silicon wafers is used to provide a benchmark reference analysis and validation of the approach.


Source:IOPscience

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May 8, 2018

Fabrication of microdomains at the +Z surface of near-stoichiometric lithium tantalate crystals

Scanning force microscopy is used to investigate microscale ferroelectric domains at the +Z surface of near-stoichiometric lithium tantalate (SLT) single crystals. Both line and lattice patterns of microdomains are fabricated at the +Z surface of SLT wafers, which are switched by scanning these wafers with the external field exceeding the coercive field. The +Z polar surface in these patterns is etched by a mixture of acid aqueous solution (HF : HNO3 = 1 : 1), which reveals the precise microdomain structure. The analysis of the experimental data indicates that the rearrangement of the ferroelectric domain structure occurs during the chemical etching process; the effect of both defect and crystal structure on the microdomain growth process is also discussed. The present results are helpful for us to realize the fabrication of the expected microdomain morphology.


Source:IOPscience

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Apr 24, 2018

Etching Characterization of {001} Semi-Insulating GaAs Wafers

The characteristics of {001} semi-insulating GaAs wafers have been investigated by the etching/optical microscopy. New etch features such as groove have been revealed in only LEC crystals together with ridge features by an AB etch, but not in boat-grown crystals. The groove features are specifically revealed on gathering and twisting dislocations such as cell or lineage structures, and coincide with each dislocation lying near the surface. Small pits along the ridge features have been revealed in undoped LEC crystal, but not in undoped boat grown crystals. The distribution of the ridge features with the small pits correlates with that of 0.80 eV photoluminescence intensity in the wafer.

Source:IOPscience

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Apr 4, 2018

Effect of Crystal Pulling Rate on Formation of Crystal-Originated "Particles" on Si Wafers

It was recently revealed that singularities (crystal-originated "particles") formed on Si wafers after SC1 cleaning originate from some defects in crystals and were perceived by laser particle counters. In this paper, the size distribution of crystal-originated "particles" is examined in detail by means of repeated SC1 cleanings. It is shown that, as the crystal pulling rate becomes faster, the size distribution of crystal-originated "particles" shifts toward smaller size, and the total number of origins of crystal-originated "particles" increases.

Source:IOPscience

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Mar 14, 2018

Influence of aluminum nitride crystal orientation on MEMS energy harvesting device performance

Aluminum nitride (AlN) is a widely researched piezoelectric material due to its CMOS compatibility. One of the most common applications for AlN is in the area of vibrational energy harvesting. The piezoelectric quality of AlN is related to the crystal orientation of the film and optimal conditions are obtained when AlN is c-axis aligned with a (0 0 2) orientation. AlN can be a challenging material to integrate into a fabrication process due to orientation dependency of the fabrication process. This paper reports on the effects of non-(0 0 2) oriented AlN peaks on an energy harvesting MEMS cantilever structure. Results show that FWHM values of the AlN films from different wafers were approximately the same 8.5°, 8.7°, and 9°, however wafer 1 had additional peaks at (1 0 2) and (1 0 3), which significantly affected the piezoelectric constants and the amount of power generated. The measured d31 value for the wafers were 2.04, 1.97, and 0.84 pm V−1, and the power generated was 0.67, 0.64, and 0.24 µW respectively. These values show that non-peaks of AlN can cause a significant decrease in the piezoelectric constant, which causes significant decrease in the ability to generate power from an AlN film.


Source:IOPscience

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Mar 6, 2018

Growth of bulk GaN crystals by the Na-flux point seed technique

In this paper, progress in the Na-flux point seed technique (SPST) will be reviewed. Bulk GaN crystals with a diameter of 2.1 cm, a height of 1.2 cm, and large dislocation-free areas were successfully produced by SPST. Panchromatic cathodoluminescence images of a wafer sliced parallel to the c-face from the crystal showed the lack of dark spots due to dislocations over a large area of the wafer. Structural properties were evaluated using synchrotron X-ray diffraction analysis at SPring-8. The full width at half maximum of the 006 rocking curve was found to be 2.1 arcsec, close to the calculated value of 2.0 arcsec for a perfect GaN crystal, indicating that crystals grown by SPST have an almost perfect structure. In addition, we have extended the use of SPST to the coalescence growth of GaN crystals to increase the wafer diameter and obtained a 2 in. GaN wafer with a low dislocation density and a low curvature by this technique.

Source:IOPscience

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Feb 8, 2018

A facility for plastic deformation of germanium single-crystal wafers

Abstract

A facility for plastic deformation of single-crystal germanium wafers is described. It consists of a commercial tube furnace which radiates heat to evacuated quartz-glass tubes housing the tools for bending and flattening of the wafers. The facility is semi-automatic and requires minimal attention. All movements and temperature changes are done by a robot via a PLC-control system. Two nine-crystal focusing monochromators (54 × 116 and 70 × 116 mm2) made from 100 wafers with average mosaicity ∼13′ have been constructed. Summaries of the test results are presented.
Source:ScienceDirect

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Jan 31, 2018

Hard-to-stretch silicon becomes superelastic

stretchable silicon

Illustration of the growth of stretchable silicon nanowires. Credit: Xue et al. ©2017 American Chemical Society


As a hard and brittle material, silicon has practically no natural elasticity. But in a new study, researchers have demonstrated that amorphous silicon can be grown into superelastic horseshoe-shaped nanowires that can undergo stretching of more than twice their original length, and still maintain their excellent electric properties.


The results are exciting news for the area of stretchable electronics, as they suggest that silicon nanowire springs could serve as a stretchable semiconducting material for future flexible, bendable electronic devices. So far, almost all of the stretchable electronics that have been demonstrated have been made of polymer and organic semiconductors, whose semiconducting properties are inferior to those of silicon.
The researchers, who are from Nanjing University, Peking University, and CNRS-Ecole Polytechnique, have published a paper on their new method for growing stretchable silicon springs in a recent issue of Nano Letters.
In previous efforts to fabricate stretchable silicon, some of the best results have come from using electron beam lithography. In this technique, ultra-thin crystalline silicon is etched into various patterns, such as serpentine shapes and fractal patterns, that endow the resulting silicon device with stretchability. However, electron beam lithography is expensive and impractical for fabricating large-area electronics.
As the researchers explain in the new paper, one ideal and relatively inexpensive method for making stretchable silicon naqnowires would be similar to the crystal pulling methods used to grow silicon crystal ingots from molten silicon. In these methods, which are widely used in the silicon industry, a seed crystal is dipped in molten silicon and slowly pulled upward, drawing with it a long crystalline silicon ingot.
As the researchers explain, the new method is somewhat like a nanoscale, in-plane version of crystal pulling. The process, called line-shape engineering, involves guiding molten indium droplets to move along a pre-patterned track that is coated with amorphous silicon. As the droplet moves along the track, it takes in amorphpus silicon and precipitates crystalline silicon nanowires.
In their demonstrations, the researchers grew crystalline silicon nanowires more than a millimeter long into patterns such as horseshoe shapes and a Peano curve, which has previously been shown to be one of the best fractal patterns for achieving large stretchability. In previous work, the researchers had demonstrated the guided growth of silicon nanowires in straight lines, but the ability to grow them in tightly curved patterns like these is essential for achieving stretchability. Tests revealed that the springs can be pulled to more than twice their original length—almost into a straight line—while maintaining their electric properties and quickly recovering their original shape when released.
In the future, the researchers plan to investigate techniques for transferring the silicon nanosprings from the growth substrate onto a softer surface that is more practical for applications. Overall, they expect that the growth method demonstrated here represents an important step toward developing high-performance, stretchable silicon electronics.
"In view of future industrial applications, the fabrication can be extremely low-cost and scalable, so that the size of a 1D spring array can be several meters wide and rollable in production," coauthor Linwei Yu, at Nanjing University and Peking University, told Phys.org. "Our vision is to define a new wafer technology, catering to the needs of large-area electronics, that offers batch-manufacturable, robust, and stretchable crystalline silicon channels to instill good performance into the emerging soft electronics. Our latest progress has demonstrated a complete free-standing network of such silicon springs. An immediate application will be deploying them upon skin for sensors, as well as mechanical devices, field-effect devices, and NEMS. Hopefully, these new results will come out soon."
Source:PHYS

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Jan 24, 2018

Compositional, strain contour and property mapping of CdZnTe boules and wafers

The authors have developed detailed non-destructive mapping and spatial imaging techniques for comparing boule and wafer properties with analytical predictions from high-fidelity process models for seeded vertical Bridgman-Stockbarger growth of CdZnTe crystals. They have emphasized the prediction of the magnitude and distribution of residual stress and strain, as well as longitudinal and radial segregation within the boules and across wafers cut from the boules. Boule and wafer compositional distributions were mapped using photoreflectance, precision lattice parameter measurements and FTIR spectroscopy. Defect and strain distributions within the boules and wafers were imaged using synchrotron topography, synchrotron strain contour mapping, and double-crystal rocking-curve mapping. Thermomechanical and thermosolutal models specifically addressing the seeded vertical Bridgman-Stockbarger growth of CdZnTe crystals were developed and empiricized. These models addressed solute redistribution and stress generation as a result of the interface shape, aspect ratio and growth parameters during the seeding, initial transient (including the shoulder), steady-state and terminal transient regions of the boule. Finally, the stress and strain distributions on specific wafers 'cut' from the processed (modelled) boules were predicted and X-ray synchrotron strain contour, double-crystal rocking-curve, FTIR, and photoreflectance maps were generated on the real wafers for comparison. Implications of these results with respect to substrate quality, screening, performance and producibility, will be discussed.

soource:Iopscience




Crystallographic cracking behavior in silicon single crystal wafer

Abstract

Crystallographic cracking behavior was studied on three-point-bending specimens of silicon single-crystal wafer having (11̄0) [112̄]-oriented precrack. Crystallographic cracking occurred on alternating {111} planes after traversing about 500 μm from crack front at the brittle–ductile-transition temperature, and the main crack was almost parallel to the loading axis. The preferentially activated slip systems ahead of the crack tip resulted in the characteristic fracture in the specimens. The experimental results could be well explained by calculating the shear stress on all possible tetrahedral slip planes around the crack tip.

Keywords

Brittle–ductile-transition,
Three-point bending,
Silicon
Crack,
Cross-slip zone

Source:ScienceDirect

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Jan 17, 2018

The Relationship between the Bending Stress in Silicon Wafers and the Mechanical Strength of Silicon Crystals

Silicon wafers horizontally stacked in a vertical furnace bend downward due to their weight. Using a linear elastic theory, we calculated the shear stress caused by the wafer bending and investigated the mechanical strength by comparing the shear stress with the upper yield stress of silicon crystals. We concluded that the maximum shear stress increased with the increase in the wafer diameter, 0.20, 0.30, and 0.55 MPa for 6, 8, and 12 inch wafers. In bending the 12 inch wafers, oxygen precipitates, lowering the upper yield stress, caused serious wafer warping because the shear stress exceeded the lowered yield stress.

soource:iopscience