Oriented Silicon Wafers Research Articles

Soft Magnetic Property of [Fe<sub>80</sub>Ni<sub>20</sub>-O/ZnO]<sub><i>n</i></sub> Multilayer Thin Films for High-Frequency Application

A series of [Fe80Ni20-O/ZnO]nmultilayer thin films with different ZnO separate layer thicknesses (t, from 0 to 3 nm) and fixed Fe80Ni20-O layer thickness (about 5 nm) have been fabricated on (100)-oriented silicon wafers and glass substrates by reactive magnetron sputtering. Microstructure analysis and static magnetic measurement results indicate that the magnetic properties of the films can be adjusted by the variation of ZnO monolayers thickness. All films reveal an evident in-plane uniaxial magnetic anisotropy (IPUMA). The values of in-plane uniaxial magnetic anisotropy fields (Hk) and resistivity (ρ) can be changed from 8 to 57 Oe and 62 to 168 μΩ•cm respectively with the t increasing. While the values of hard axis coercivity (Hch) and easy axis coercivity (Hce) reveal minimums of 1.5 and 3 Oe respectively at t = 1 nm.

Optical properties of photo-electrochemical etching of anisotropic silicon (110)

Photo-electrochemical etched Si layers were prepared on n-type (110) oriented silicon wafer. SEM results shows groove structure for etched Si (110). The photoluminescence (PL), Fourier transformed infrared (FTIR) absorption and Raman spectroscopy of etched Si (110) as a function of etching time was studied. All samples showed a PL peak in the visible spectral and the intensity of the PL peak increases with rising of the etching time. It is also found that the Raman peak of the etched Si samples is red shifted and its intensity significantly decreases as the etching time increases.

Fabrication and Morphology of KOH Etching Single Crystalline Silicon Solar Cells

Anisotropic etching process by potassium hydroxide (KOH) and isopropyl alcohol (IPA) mixed solution in the [100] orientation silicon wafer was studied experimentally. The effect parameters of KOH concentration, IPA concentration, reaction time and temperature for wafer surface morphology were analyzed by scanning electron microscope. The results show that: a uniform, high density and good pyramid shaped single crystalline silicon surface can be obtained at 3% KOH solution buffered with 8% IPA at 80°C for 30min. By comparing single crystalline silicon micro-surface with NaOH and IPA mixed solution system of industrial fabrication, the pyramid structure is more regular and uniform by using KOH and IPA mixed solution system, which is expected to obtain better optical properties.

Highly Reliable Radical SiO2 Films on Atomically Flat Silicon Surface Formed by Low Temperature Pure Ar Annealing

The gate oxide films are formed by the microwave exited high density plasma on Si(100) surfaces of various flatness to discuss the reliabilities. By annealing in ultra pure Ar ambient below 900 °C at atmosphere pressure, the whole surface of 200-mm-diameter (100) orientation silicon wafers can be atomically flattened without slip-line defects generation. For the capacitors, the intrinsic life time in charge-to-breakdown (Qbd) characteristics and the breakdown field (Ebd) of radical oxide films are much larger than those of thermal oxide films, and the extrinsic Qbd of radical oxide film is drastically improved by forming on atomically flat silicon surface composed with that on conventional Czochralski (Cz)-wafer surface. Moreover, fabricating radical oxide films on the atomically flat wafers, flattened at 800 or 1100 °C in Ar ambient, the equivalent gate oxide breakdown characteristics are obtained.

Defect Formation in Silicon During Laser Doping

Laser doping in industrial crystalline solar cells creates a selective emitter and thereby enhances the efficiency. Nevertheless, if not done carefully, the irradiation of the semiconductor introduces defects. We have suppressed defect formation by using a laser beam that is focused to a line with a width of only several micrometers. The maximal line width for a defect free recrystallization, however, depends on the surface orientation of the silicon. Using a transmission electron microscope, we find a dislocation-free recrystallized layer on (100)-oriented silicon wafers that are irradiated with a line focus smaller than or equal to 15 μm. For (111)-oriented surfaces, this holds for the use of a 5.2-μm-wide line focus. Wafers that are irradiated with a circular laser focus of diameter D = 36 μm show the formation of microcracks, but no hints of dislocations are found using transmission electron microscopy (TEM).

Curved Silicon Nanowires with Ribbon-like Cross Sections by Metal-Assisted Chemical Etching

A generic process for the preparation of curved silicon nanowires (SiNWs) with ribbon-like cross sections was developed. The present synthetic approach is based on chemical etching of (100)-oriented silicon wafers in mixture solutions of HF and H(2)O(2) by using patterned thin gold films as catalyst and provides a unique opportunity for the fabrication of extended arrays of zigzag SiNWs, ultrathin straight [111] SiNWs, and curved SiNWs with controlled turning angles. On the basis of our experiments performed under various etching conditions, the factors governing the axial crystal orientation and morphology of SiNWs were systematically analyzed. We proposed a model that explains the formation of the present novel silicon nanostructures during chemical etching of silicon.

Anisotropic Wet Etched Silicon Substrates for Reoriented and Selective Growth of ZnO Nanowires and Enhanced Hydrophobicity

Herein we report the fabrication of ZnO nanowires on anisotropic wet etched silicon substrates by selective hydrothermal growth. <100> oriented silicon wafers were first patterned by anisotropic wet etch with a KOH solution, resulting in V-shaped stripes of different periods. Then, a thin layer of gold was deposited and annealed to promote the hydrothermal growth of ZnO nanowires. It was found that the growth rate of ZnO nanowires on <111> surfaces was much higher than that on <100> surfaces. As a first application of such micro- and nanostructured surfaces, we show enhanced wetting properties by measuring the contact angle of water droplets on the samples obtained under different patterning and growth conditions. Our results also demonstrated the possibility of tuning the contact angle of the sample in the range between 115° and 155°, by changing either the pattern of the silicon template or the hydrothermal growth conditions.

Annealing ambient on the evolution of He-induced voids in silicon

The effects of annealing ambient on the He-induced voids in silicon were investigated using the combination of the Doppler broadening spectroscopy using a variable-energy positron beam and cross-section transmission electron microscopy (XTEM). A 〈1 0 0〉-oriented silicon wafer was implanted with He ions at an energy of 15 keV to a dose of 2 × 10 16 cm −2 at room temperature. Post-implantation, the samples were annealed at a temperature of 1000 °C in the ambient of vacuum, argon, nitrogen, air and oxygen. Positron annihilation spectroscopy (PAS) spectra varied with the annealing ambient. XTEM micrographs demonstrated that the density of He-induced voids could be influenced by the annealing ambient.

Silicon surface microstructures created by 1064 nm Nd∶YAG nanosecond laser

We investigated the evolution of surface microstructures created on single crystal silicon wafers by the cumulative Nd ∶YAG nanosecond laser pulses (wavelength 1064 nm ) in different atmospheres (N2, air and vacuum). Micropore structure and the fracture lines are formed after irradiation of a few laser pulses,compared with ripple structures created by laser pulses of wavelengths of 532 and 355 nm. The fracture line structure is different for (111) and (100) silicon. The fracture lines have 60°and 120° intersections for (111) silicon. For (100)-oriented silicon wafers, two sets of fracture lines intersect at 90° to form a grid that divides the surface into rectangular blocks with side length of from 15 to 20 μm. We think that phase explosions are responsible for the growth of micropore structure. The fracture lines are mainly due to thermal stress. Finally, We studied the formation of microstructures under different atmospheres, and the results show that it is closely related to the etching and growth rate.

Design &amp; Fabrication of a MEMS Piezoresistive Accelerometer with Beam-Film Combined Structure

In this paper, a MEMS (micro-electro-mechanical system) accelerometer has been developed utilizing piezoresistive sensing elements for vibration measurements in large-scale rotating machineries. The accelerometer consists of highly symmetric beam-film combined structure with 4 p-type piezoresistors diffused on beam surface. The beam and two same films, acting as a whole, give the structure a higher mechanical stiffness making the accelerometer’s nature frequency enhanced. During the chip design, classical vibration and elasticity theories are taken advantaged of to determine the dimensions of the sensor chip based on the requirements of industrial practical application. FEM (finite element method) is also used to investigate the performances of the sensor under acceleration load. The device is fabricated by using bulk micromachining technology, and an n-type, (100) oriented silicon wafer is used as the blank of the chip. The packaged sensor is tested and the experimental results show that the sensor has a sufficient linear response (non-linearity≤0.26%FS) up to 50g with a sensitivity of 1.5mV/g/8V. The resonance frequency of the sensor is about2860Hz, and this allows the usage of the sensor in state monitoring with the necessary bandwidth.

On-chip superconductivity via gallium overdoping of silicon

We report on superconducting properties of gallium-enriched silicon layers in commercial (100) oriented silicon wafers. Ion implantation and subsequent rapid thermal annealing have been applied for realizing gallium precipitation beneath a silicon-dioxide cover layer. Depending on the preparation parameters, we observe a sharp drop to zero resistance at 7 K. The critical-field anisotropy proofs the thin-film character of superconductivity. In addition, out-of-plane critical fields of above 9 T and critical current densities exceeding 2 kA/cm2 promote these structures to be possible playgrounds for future microelectronic technology.

Smoothing of microfabricated silicon features by thermal annealing in reducing or inert atmospheres

In this work, high-temperature annealing of reactive ion etched silicon microstructures in H2 and Ar gases is studied. Three types of structural features were etched with four different masks into ⟨100⟩-oriented silicon wafers. Scanning electron microscope and atomic force microscope (AFM) results show that when smoothing due to surface diffusion and desorption of silicon is taking place in both the argon and hydrogen gas environments, the three types of features respond differently to the treatments. The surface diffusion was observed to be strongly dependent on temperature in argon, whereas the transport was more linear and controllable in the hydrogen gas environment. For hydrogen, AFM studies were performed to observe the details of the smoothing process. Finally, some potential applications of these transport phenomena are discussed.

Diffractive microlens with a cascade focal plane fabricated by single mask UV-photolithography and common KOH:H2O etching

A diffractive microlens with a cascade focal plane along the main optical axis of the device is fabricated using a low-cost technique mainly including single mask ultraviolet (UV) photolithography and dual-step KOH:H2O etching. Based on the evolutionary behavior of converse pyramid-shaped microholes (CPSMs) preshaped over a {1 0 0}-oriented silicon wafer in KOH etchant, the first-step KOH etching is performed to transfer initial square micro-openings in a SiO2 film grown by plasma enhanced chemical vapor deposition (PECVD) and patterned by single mask UV-photolithography, into CPSMs with needed dimension. After completely removing a thinned SiO2 mask, basic annular phase steps with a relatively steep sidewall and scheduled height can be shaped in the overlapped etching region between the neighboring silicon concave-arc microstructures evolved from CPSMs through the second-step KOH etching. Morphological measurements demonstrate a desirable surface of the silicon microlens with a roughness in nanometer scale and the feature height of the phase steps formed in the submicrometer range. Conventional optics measurements of the plastic diffractive microlens obtained by further hot embossing the fine microrelief phase map over the nickel mask made through a common electrochemical method indicate a highly efficient cascaded focusing performance.

Study of Deposition of Aluminum Nitride Thin Films by Hollow Cathode Electron Beam Vapor Deposition Method

Aluminum nitride (AlN) thin films were deposited on (100) oriented silicon wafers substrates by Hollow Cathode Electron Beam Vapor Deposition system (HCEBVD) under various Ar/N2 mass flow ratio. The films were characterized by Atomic Force Microscopy (AFM), Glancing Incident X-ray Diffraction (GIXRD) techniques and Ultraviolet/Visible Spectrophotometer (UV/VIS). It was found that the thin films are polycrystalline and have a hexagonal wurtzite structure with (002) preferred orientation, as revealed by GIXRD. AFM analysis indicates that the surface of the thin films is smooth, with average RMS (Root Mean Square) roughness Ra of 0.7nm, which is suitable for application in surface acoustic wave devices. The film thickness and optical refractory properties of the AlN thin films were investigated.

Atomically Flattening Technology at 850ºC for Si(100) Surface

We demonstrate a low temperature flattening method for the 200-mm-diameter (100) orientation silicon wafers. By annealing in ultra pure argon ambient at 850ºC or above, atomically flat surfaces composed of atomic terraces and steps appear uniformly in the whole 200mm wafer. The width of atomic terrace changes with the off angle of wafer surface. It is found that with the off angle of 0.50º or below, only mono-atomic steps appear on the atomically flat surface, and the terrace widths are almost equal to the calculation values. Moreover, we have found using the vertical furnace the whole 200mm wafer surface can be atomically flattened in shorter time by increasing the argon gas flow rate or the annealing temperature. Furthermore, after annealing at 900ºC or below, there is no slip-line defect in the whole wafer. This low temperature flattening method is very suitable to be applied in the LSI manufacturing.

A Hybrid MEMS–Fiber Optic Tunable Fabry–Perot Filter

This paper describes a bulk-micromachined electrostatically tunable Fabry-Perot interferometric filter. The device is a hybrid optical filter combining fiber optics and microelectromechanical systems (MEMS) technologies. The static mirror is a Bragg grating mirror built on the end face of an optical fiber that is integrated with a MEMS device, which includes the tunable gold-coated mirror. The MEMS device is fabricated in ¿100¿-oriented silicon wafers using modified and optimized batch MEMS processes. A two-stage approach was used to achieve high finesse (F) and broad tunability simultaneously. In the first stage, actuator issues and mirror structural defects were corrected for by optimizing the fabrication-process parameters. In this stage, near-theoretical performance has been achieved with a pure Si MEMS tunable etalon. In stage two, optical fibers with dielectric stack mirrors from Micron Optics, Inc. have been integrated with the MEMS devices to form tunable cavities. The device insertion loss was below 15 dB and was mostly attributed to absorption losses in the gold coating. We measured a pass bandwidth of around 0.54 nm and a tuning range of nearly 120 nm resulting in an F of over 220.

Wafer-Scale Synthesis of Single-Crystal Zigzag Silicon Nanowire Arrays with Controlled Turning Angles

Silicon nanowires (SiNWs) having curved structures may have unique advantages in device fabrication. However, no methods are available to prepare curved SiNWs controllably. In this work, we report the preparation of three types of single-crystal SiNWs with various turning angles via metal-assisted chemical etching using (111)-oriented silicon wafers near room temperature. The zigzag SiNWs are single crystals and can be p- or n-doped using corresponding Si wafer as substrate. The controlled growth direction is attributed to the preferred movement of Ag nanoparticles along 001 and other directions in Si wafer. Our results demonstrate that metal-assisted chemical etching may be a viable approach to fabricate SiNWs with desired turning angles by utilizing the various crystalline directions in a Si wafer.

Low-temperature transition to a superconducting phase in boron-doped silicon films grown on (001)-oriented silicon wafers

We report on a detailed analysis of the superconducting properties of boron-doped silicon films grown along the 001 direction by Gas Immersion Laser Doping. The doping concentration cB has been varied up to approx. 10 at.% by increasing the number of laser shots to 500. No superconductivity could be observed down to 40mK for doping level below 2.5 at.%. The critical temperature Tc then increased steeply to reach 0.6K for cB = 8 at%. No hysteresis was found for the transitions in magnetic field, which is characteristic of a type II superconductor. The corresponding upper critical field Hc2(0) was on the order of 1000 G, much smaller than the value previously reported by Bustarret et al. in Nature (London) 444, 465 (2006).

Modelling of the hole mobility in p-channel MOS transistors fabricated on (1 1 0) oriented silicon wafers

The paper deals with the investigation of the hole mobility in p-channel MOS transistors fabricated on (110) oriented silicon wafers. At first, we showed that the conventional methods used to extract the conduction parameters such as the low field mobility or the mobility attenuation factor could not be applied for this orientation. This is the consequence of a change in the origin of the scattering mechanisms limiting the effective mobility. While in the case of the (100) p-MOS transistors the phonon scattering is the unique mechanism defining the effective mobility, this one is characterized by an arrangement of the Coulomb scattering, phonon scattering as well as surface roughness scattering in the case of the (110) p-MOS transistors. A consequence is that the modelling of the mobility must include all three mechanisms in order to simulate accurately the static characteristics of Si(110) p-MOS transistors, making then a necessity for us to develop a more adapted model. Finally, it has been seen that the effective mobility in the p-MOS transistors on Si(110) is not only higher than the one in the p-MOS transistors on Si(100) but appears to be almost electric independent over the usual range of polarisations making it more stable and then pleading even more in this new orientation’s favour.

Properties of silicon homojunctions with pulse-magnetron sputtered crystalline n+-emitter layers

Highly phosphorus doped crystalline silicon films were grown by pulse-magnetron sputter deposition on (100) and (111) oriented silicon wafer substrates at low temperatures of 450–550 °C. Rapid thermal annealing (RTA) and plasma hydrogenation (PH) were applied as postgrowth treatments. To explore the nature of the junction transport processes the I-V characteristics were studied in different device geometries as a function of temperature. The analysis suggests that depending on the substrate orientation (hkl) both postgrowth treatments influence the bulk-related current component J0b(hkl) of the saturation current density in different manners and introduce additional conduction paths at the perimeter of the measured diode structures. For diodes grown on Si(100) postgrowth treatment by RTA results in a decrease in J0b(100) to respectable 4×10−11 A cm−2, whereas no major influence of RTA for the Si(111) based junctions could be obtained. They prove to be sensitive to PH post-treatment, which resulted in a reduction in J0b(111) to 8×10−11 A cm−2. The perimeter induced excess current is most strongly pronounced for the hydrogenated diodes on Si(111) and much less relevant for the RTA treated Si(100) structures.