Single Crystal Wafers Research Articles

Study of Multichannel QCM Prospects in VOC Detection

Quartz Crystal Microbalance (QCM) is a mass detection sensor capable of measuring mass sensitivity at nanogram levels when based on a thickness shear mode piezoelectric crystal set at high frequencies. These sensors detect with high accuracy while benefiting from simple geometry, low costs, and ease of fabrication. Researchers prefer piezoelectric crystal sensors to the recent methods of gas chromatography/mass chromatography (GC/MC), high pressure liquid chromatography and nuclear magnetic resonance (NMR), which are time-consuming and not cost-effective. Unlike conventional QCM sensors that are limited to a single-electrode structure—which minimizes their scope of detection—the Multichannel QCM (MQCM) incorporates multiple sensors fabricated on a single crystal wafer. Each sensor is selectively coated with a sensing material that promotes the adsorption of target vapours. One of the widely used application of QCM sensors is in Volatile Organic Compounds (VOC) detection. This paper imparts a critical overview of recent publications on the application of MQCMs with various sensing materials.

Influence of Multiple Scattering on Parametric X-Ray Radiation Excited by a Beam of Relativistic Electrons in a Single Crystal

Parametric X-ray radiation generated by a beam of relativistic electrons in a single-crystal wafer is studied in the Bragg geometry under conditions of multiple electron scattering at target atoms. Expressions are obtained that describe the spectral-angular and angular radiation density under conditions of multiple electron scattering. An increase in the influence of multiple scattering on the spectral-angular radiation density is demonstrated both with an increase in the target thickness and a decrease in the energy of relativistic electrons. It is shown that the asymmetry of the electron-field reflection relative to the target surface considerably affects the spectral-angular and angular densities of parametric X-ray radiation under the condition of strong multiple scattering.

The problem of crack formation in thin sublayers of silicon oxide during pulsed heating of interconnects

It is well known that in modern micro- and nanoelectronics thin-film structures are actively used as a gate dielectric, passivating layers, membranes, etc. The research is devoted to the problem of crack formation in thin sublayers of silicon oxide during pulsed heating of interconnects on single-crystal silicon wafers. The purpose of the paper is to study the effect of surface sources of thermal shock on the cracks formation in films and aspects of crack formation in SO2 films have been studied in detail. Experimental verification of the estimates made was carried out on multilayer structures of a silicon substrate-silicon oxide sublayer-aluminum film (Si-SiO2-Al). As substrates, it was used phosphorus-doped silicon single-crystal wafers oriented in the (111) direction, with a resistivity in the range p = 0.1 Ω.сm. The authors studied the temperature fields in silicon wafers (Al-Si system) and silicon oxide wafers (Al-SiO2 system) heated by a surface metallization layer both for the case of a point heat source and for the case of a long rectangular metallization path (provided that the track length significantly exceeds its width). The calculation results showed that the temperature profile of the metallization path (width 75 μm) in the transverse direction is heterogeneous. It was also shown that, in contrast to SiO2 films, the level of appearing mechanical stresses in silicon is insufficient for the formation of cracks near the source of thermal shock. This is due to a higher tensile strength than that of oxide.

Material Removal Model for Lapping Process Based on Spiral Groove Density

The increasing demand for single-crystal wafers combined with the increase in diameter of semiconductor wafers has warranted further improvements in thickness variation and material removal rate during lapping to ensure price competitiveness of wafers; consequently, the lapping process has gained the attention of researchers. However, there is insufficient research on the effect of platen grooves on the lapping process. In this study, the parameters to describe grooves were defined in order to understand their influence on the lapping process, and a material removal model was suggested based on indentation theory and subsequently experimentally validated. The results indicate that changes in groove density affect the lubrication condition at the contact interface as well as the probability of abrasive participation by varying the oil film thickness. When fabricating the groove for a lapping platen, a groove density at the critical groove density (CGD) or higher should be selected. The higher the groove density, the easier it is to avoid the CGD, and the higher is the material removal rate. The results of this study will enable engineers to design lapping platen grooves that are suitable for the production of modern semiconductor wafers.

Strain effects on polycrystalline germanium thin films

Polycrystalline Ge thin films have attracted increasing attention because their hole mobilities exceed those of single-crystal Si wafers, while the process temperature is low. In this study, we investigate the strain effects on the crystal and electrical properties of polycrystalline Ge layers formed by solid-phase crystallization at 375 °C by modulating the substrate material. The strain of the Ge layers is in the range of approximately 0.5% (tensile) to -0.5% (compressive), which reflects both thermal expansion difference between Ge and substrate and phase transition of Ge from amorphous to crystalline. For both tensile and compressive strains, a large strain provides large crystal grains with sizes of approximately 10 μm owing to growth promotion. The potential barrier height of the grain boundary strongly depends on the strain and its direction. It is increased by tensile strain and decreased by compressive strain. These findings will be useful for the design of Ge-based thin-film devices on various materials for Internet-of-things technologies.

Fabrication of Large-Scale High-Mobility Flexible Transparent Zinc Oxide Single Crystal Wafers.

Single crystal wafers, such as silicon, are the fundamental carriers of advanced electronic devices. However, these wafers exhibit rigidity without mechanical flexibility, limiting their applications in flexible electronics. Here, we propose a new approach to fabricate 1.5 in. flexible functional zinc oxide (ZnO) single crystal wafers with high electron mobility (>100 cm2 V-1 s-1) and optical transparency (>80%) by a combination of thin-film deposition, a chemical solution method, and surficial treatment. The uniformity of the flexible single crystal wafers is examined by an advanced scanning X-ray diffraction technique and photoluminescence spectroscopy. The transport properties of ZnO flexible single crystal wafers retain their pristine states under various bending conditions, including cyclability and endurability. This approach demonstrates a breakthrough in the fabrication of the flexible single crystal wafers for future flexible optoelectronic applications.

Residual stress distribution and flatness of dislocation-free Te-GaSb (100) substrate

Raman spectroscopy has been used to evaluate residual stress distribution across GaSb single crystal wafers with different Te doping concentrations grown by liquid encapsulated Czochralski (LEC) method. Undoped GaSb wafers grown by LEC and vertical temperature gradient freezing method were used as reference wafers for comparison analysis. The residual stress increases but its distribution uniformity improves in LEC-GaSb wafers with the concentration of Te dopant increasing. Moreover, annealing at temperature 650 °C can effectively increase its distribution uniformity and results in an improvement of the flatness. The results also suggest that the flatness of GaSb wafers is better when Te doping concentration is controlled within a certain range.

Virtues of Ir(1 0 0) substrate on diamond epitaxial growth: First-principle calculation and XPS study

The heteroepitaxial growth of single crystal diamond requires substrate of high quality, and Ir(100) is an ideal substrate which can meet the standard perfectly. However, the reason of its outstanding performance still remains unclear. In this paper, the interaction mechanism between carbon atoms and Ir (100) surface at the initial stage of nucleation and its uniqueness caused by distinctive energy changes compared with (100) faces of Cu and Ni are explained by first-principle calculation, which acts as a dominating factor in the transformation from epitaxial films to single crystal wafers. The energy driving force of the dissolution-precipitation process is described, which can completely accord with bias-enhanced nucleation(BEN) method to illustrate the effect of voltage on diamond nucleation. The precipitation of carbon atoms and appearance of primary nuclei with the increase of carbon concentration are discussed, which can effectively explain the special phenomenon of the “domain” formation. A carbon-rich pre-treatment before primary nucleation on Ir (100) surface shows that the initial nucleation process can form supersaturated solid solution of carbon in Ir (100), which can greatly accelerate the subsequent dissolution-precipitation circulation.

Gamma-ray induced photo emission from GaN single crystal wafer

Gamma-ray-induced photoemissions from GaN are investigated for as-grown and gamma-ray-irradiated single crystal wafers at room temperature. The GaN crystals are irradiated with gamma rays of 1.17 and 1.33 MeV from a cobalt-60 source. The gamma-ray-induced photoemission is analyzed by a spectroscope using the optical fiber cable placed in front of GaN. In the gamma-ray-induced photoemission from as-grown GaN wafers, the yellow luminescence (YL) is observed with a peak at around 600 nm in the spectrum around 440 nm–900 nm. The main YL peak is attributed to the Ga vacancy. The emission intensity increases almost in proportion to the wafer thickness when the thickness of the single crystal wafer increases from 0.25 mm to 0.75 mm due to the strong penetration of gamma rays in the crystal. In He–Cd laser excitation, the emission intensity does not depend on the thickness of the sample because the penetration of He–Cd laser light is near the surface. On the other hand, a gamma-ray-induced photoemission from GaN irradiated with a total gamma-ray dose of 990 kGy is observed with a peak at around 700 nm in the spectrum around 450 nm to 850 nm. The energy of the emission peak is close to the transition energy (1.83 eV) from the +1 state to the +2 state of the Ga interstitial. The gamma-ray-induced photoemission from GaN at room temperature suggests the possibility of GaN single crystal wafers to be used as a gamma-ray detector.

Anisotropic Structures for Concentrating Thermal-Neutron Fluxes

An experiment has been prepared and performed to prove the feasibility of creating anisotropic structures in which surfaces of thermal-neutron sinks are formed with the subsequent concentration in selected areas. A device capable of selecting neutrons by the direction in space is based on the effect of neutron reflection from the surface of materials. Experimental confirmation has been obtained for the operability of a neutron concentrator design in devices that form and use directed high-intensity thermal-neutron beams with elliptical-profile channels. The neutron concentrator is made of blocks of profiled-graphite and aluminum plates. The operability of a slowing-down and focusing structure (SFS) based on a package of elliptical neutron mirrors has been experimentally verified. The SFS is able to form oriented thermal-neutron beams from the outgoing flow of reactor neutrons. Silicon single-crystal wafers are used, with which it is possible to obtain distributions of integral neutron fluxes in a reactor to detect the effect of selective thermal-neutron separation. The experiments have been carried out in the GEK-4 channel at the IRT-T reactor of the National Research Tomsk Polytechnic University with an integral neutron flux of (2.30−3.02) × 1017 cm−2. The neutron flux is determined from the change in the electrical resistivity of single-crystal silicon wafers. The effect of the thermal-neutron concentration has been detected both on a block of graphite neutron mirrors and on a block of thin-walled aluminum elliptical mirrors.

Precision laser slicing technology for single crystal SiC wafers

Precision laser slicing technology for single crystal SiC wafers

Effect of mechanical treatment type on the strength of undoped single crystal indium antimonide wafers

Thin (100) wafers of single crystal undoped InSb have been strength tested by plane transverse bending. The strength of the wafers (≤ 800 mm in thickness) has been shown to depend on their mechanical treatment type. If the full mechanical treatment cycle is used (grinding + chemical polishing) the strength of the InSb wafers increases twofold (from 3.0 to 6.4 kg/mm2). We show that the strength dependence on mechanical treatment type for (100) wafers is similar to that for (111) wafers, the strength of (111) wafers being 2 times higher. The roughness of the thin wafers after the full mechanical treatment cycle has been measured using contact profilometry. After the full mechanical treatment cycle the roughness of the InSb wafers Ra decreases from 0.6 to 0.04 mm leading to general surface smoothening. We have compared the strength and roughness between (100) InSb and GaAs wafers. The roughness of InSb and GaAs wafers after the full mechanical treatment cycle decreases significantly: by 10 times for InSb due to the general surface smoothening and by 3 times for GaAs (Rz from 2.4 to 0.8 mm) due to a reduction of the peak roughness component. The full mechanical treatment cycle increases the strength of InSb wafers by removing damaged layers through the sequence of operations and reducing the risk of mechanical damage development.

High yield uniformity in pseudo-vertical diamond Schottky barrier diodes fabricated on half-inch single-crystal wafers

We fabricated diamond pseudo-vertical Schottky barrier diodes using a half-inch semi-insulative diamond (100) wafer. Most diodes exhibited a large rectifying ratio (>1010) with undetectable leakage current at a reverse bias of 5 V (0.6 MV cm−1), with only 2% of diodes exhibiting an Ohmic-like leakage current. Surface defects were observed under the Schottky barrier diode, and their impacts on electrical properties were analyzed using a Murphy model and correlation factor analysis. We found that most crystalline defects (surface hillocks) were electrically non-active and that non-epitaxial crystallites and process-related field-plate cracks were the main defects that induced a large leakage current. Schottky barrier diodes without such killer defects showed a high electric field strength of ∼5 MV cm−1.

Fabrication and optical properties of transferable three-dimensional GaP nanopore array film by electrochemical exfoliated method

Abstract The fabrication of transferable three-dimensional GaP nanopore array film (3D GaP NPs film) has been first proposed and realized on the n-GaP (111) wafer substrate by electrochemical exfoliated method in a mixed solution. One GaP single crystal wafer can be repeated stripping dozens of times using this strategy, which gives a higher utilization ratio of GaP wafer compared to other methods. 3D GaP NPs films were systematically characterized by different techniques, and the etching mechanism was explored. The average size of the nanopores can be adjusted by changing etching conditions. The GaP NPs film shows much higher Raman intensity due to the coupling of the incident and the scattered fields with the low-order-structure resonances in nanopores. Besides, its photoluminescence is enhanced because more photogenerated carrier recombination arises from surface state defects. The transferable 3D GaP NPs film provides possibilities for establishing different X/GaP/Y sandwich structure heterojunctions, which could be used in functional devices.

2-Dimensional Ga2O3 Based Field Effect Transistor for Hydrogen Sensing Application

β-phase gallium oxide (β-Ga2O3) has attracted a lot of interest for the applications of high-power electronics, gas sensors, and solar-blind photodetectors. β-Ga2O3 is an alternative semiconducting material for high-power and high-temperature devices due to a large bandgap energy of 4.9 eV and high critical breakdown field (> 8 MV/cm). The Baliga’s figure of merit is 3400, which is 4-10 times higher than those of GaN and SiC. Ga2O3 based devices is expected to be more efficient with reduced size and high level of integration because the theoretical on-state resistance is almost one order magnitude lower than those of GaN and SiC devices at the same breakdown voltage. When compared to GaN and SiC, single crystal Ga2O3 wafers are available at low cost with floating zone and the edge-defined film-fed growth methods. The monoclinic β-Ga2O3 is the most stable form among five different crystal phases of Ga2O3. The large lattice constant of 12.23 Å of β-Ga2O3 along [100] direction enables to achieve the facile cleavage of β-Ga2O3 crystal into 2-dimensional flake though β-Ga2O3 is not a Van der Waals material. The thin channel of Ga2O3 flake is beneficial to the FET (field effect transistor) type gas sensor. In this study, the fabrication of 2-dimensional β-Ga2O3 flake based field effect transistor and its hydrogen sensing characteristics for hydrogen sensor application will be presented.

Water-assisted femtosecond laser drilling of 4H-SiC to eliminate cracks and surface material shedding

This study adopted femtosecond laser with a wavelength of 515 nm to drill high-aspect-ratio micro through holes on a 500-μm thickness single-crystal SI-type 4H-SiC wafer. Firstly, through holes with a high aspect ratio of 20 were fabricated in air. However, the heat affect zone (HAZ), cracks, and surface material shedding around entrances and exits of the holes are inevitable in air even after chemical corrosion post-processing. In order to remove these defects, the water-assisted femtosecond laser drilling of 4H-SiC was investigated. The high-quality through holes free of cracks, surface material shedding, and HAZ were obtained under the action of internal scour and heat diffusion of water. Besides, the water layer thickness and the laser repetition frequency have a great influence on the processing quality and efficiency of the micro-holes. Finally, high-quality high-ratio-rate through micro-hole arrays on 4H-SiC were fabricated with the optimal process parameters, which is significant for the development of SiC electronic devices and the high-quality micro-fabrication of other hard and brittle materials.

Fracture of Cr2O3 single crystals on the microscale

Studying cleavage properties of protective oxide scales is imperative to understand their fracture behaviour, since transgranular fracture is observed in many cases. The small thickness and polycrystalline structure of such scales makes it difficult to identify active cleavage planes directly from mechanical testing. To resolve this issue for Cr2O3, we present an approach to experimentally identify cleavage planes through micro-cantilever bending. Single crystal wafers are used to prepare micro-cantilevers of pentagonal cross-section in different orientations, targeting possible cleavage planes. Fracture surface imaging showed rhombohedral and pyramidal fracture, though surface energy studies predict rhombohedral as the dominant plane. There does exist a preference for rhombohedral fracture over pyramidal, which is also revealed from the experiments.

Experimental confirmation of a new method for selective neutron separation

The article presents an experimental confirmation of the operability of neutron concentrators in devices that form and use directed high-intensity thermal neutron beams with elliptical channels made as blocks of profiled graphite and aluminum plates. The effect of neutron reflection from the surface of materials is the basis of a device capable of selecting neutrons by their directions in space. The study experimentally confirmed the efficiency of a moderating-focusing structure (MFS) based on a pack of elliptical neutron mirrors, which makes it possible to form oriented thermal neutron beams from the outgoing neutron flux. To record the effects of selective thermal neutron separation, silicon single-crystal wafers were used, due to which it was possible to obtain portraits of integral neutron fluxes in the reactor. The experiments were carried out in a horizontal experimental channel (HEC-4) at the IRT-T reactor of the National Research Tomsk Polytechnic University. The integral neutron flux was (2.3–3.02)·1017 cm–2. The neutron flux was detected by the change in the specific electrical resistivity of the single-crystal silicon wafers. The effect of concentration of thermal neutrons was recorded both on the block of graphite neutron mirrors and on the block of aluminum thin-walled elliptical mirrors. In the near future, on this basis, it will be possible to solve such problems as extending the reactor life by reducing the hydrogen uptake in the inner walls. In addition, the experiments have proved the possibility of creating anisotropic structures that lie outside the formalism of Liouville’s theorem, in which the surfaces of thermal neutron sinks are formed with subsequent concentration in the areas separated by aluminum or graphite plates.

Microwave Volt–Impedance Spectroscopy of Semiconductors

The previously proposed technique of microwave volt–impedance spectroscopy of semiconductors has been experimentally verified. The technique allows one to determine the local values of electrical parameters of a semiconductor. The investigations have been carried out on a homogeneous single-crystal GaAs wafer with a system of concentric antennas formed on the top of it. The resolution is determined by the antenna central disk diameter, which has been 12, 27, and 57 μm. A dc bias voltage of 0 V ≤ U ≤ 5 V has been applied between antenna contact pads. The complex Z(f, U) impedance spectrum of each antenna has been measured on a Cascade Microtech probe station in the frequency range of f = 0.1–10 GHz. The electrical characteristics of the semiconductor have been determined from the Z(f, U) spectra by solving the inverse problem. The n-type of the semiconductor has been established, and the contact potential difference at the interface with a metal has been determined. The local values of electron density, mobility and electrical conductivity have been found have been found. The four-point probe Hall effect measurements of the surface-averaged values of the same parameters have shown good agreement of the results for the investigated homogeneous wafer.

Four-step heating process for solid-phase crystallization of Ge leading to high carrier mobility

Solid-phase crystallization is rapidly developing as a method for obtaining high-quality polycrystalline Ge layers. We propose a four-step heating process, focusing on post-deposition annealing (PDA), which is performed between the film deposition and crystallization. PDA at an appropriate temperature (500 °C) reduces the grain size while improving the crystallinity of Ge (150 nm thickness), which leads to the reduction of the grain boundary barrier height (5 meV). The resulting hole mobility (530 cm2 V−1 s−1) is higher than that of any other semiconductor thin films (<300 nm) and even single-crystal Si wafers. These findings will further improve Ge thin-film transistors for advanced devices.