Dry etching of silicon is an important process in the manufacturing of integrated circuits and micromachined devices. Traditionally, the etch rate limiting step for an isotropic silicon etching process is considered to be the arrival of fluorine atoms directly from the gas phase onto the silicon surface, and the mechanism to promote anisotropy is the prevention of lateral etching by the formation of an inhibiting layer on the vertical walls. Furthermore, isotropic dry etching is considered to etch features in the same way as isotropic wet etching. Conventional mechanisms cannot explain, however, the perfect anisotropic etching of silicon with pure SF6, when no polymer is formed. Neither can it be understood how a deep (>50 μm), isotropic, dry etching process applied to silicon can result in structures with a pinched neck and sharp ridges, in contrast with a wet etching process, where the corners are rounded and no pinching of the neck is observed. It is proposed that long-range diffusion of fluorine atoms can precede the eventual binding to a silicon atom. The rate of binding increases if the silicon is bombarded with high energy ions. Tests were performed to corroborate this model which is also consistent with the findings of others.
Ni-Cr based composites with and without the addition of solid lubricants (MoS2, Ag and CaF2) were prepared by powder metallurgy method. The samples were sintered at 1200°C in flowing argon atmosphere for 1 h. The physical properties such as sintered density, relative density and porosity were studied. The microstructures and phase studies of the Ni-Cr based composites were conducted using SEM analysis while the hardness of the composites were measured by Vickers Micro Hardness Tester. The friction tests were conducted with ball on disc configuration following ASTM G-99-95a standard. The MoS2 solid lubricant provides best lubrication at room temperature which is demonstrated by a low friction coefficient compared to pure Ni-Cr composites (0.176 compared to 0.394). The SEM pictures of worn out showed into evidence plastic deformation, solid debris distribution, and filling of pores with solid lubricant phases. The time taken for stabilization of friction coefficient also varies with the type of solid lubricant. Dual and multiple addition of solid lubricants are also able to reduce the friction of coefficient compared to pure Ni-Cr composite. SEM analysis shows the spreading of solid lubricant/s during the sliding test to provide lubrication to both contacting metals.
Optical imaging is performed with temporal and spatial resolution in a capacitively coupled plasma. The region imaged is in front of an RF biased planar probe embedded in the center of the ground electrode of a standard Gaseous Electronics Conference (GEC) reference cell. Two main periods of interest stand out. The local sheath induced by the biasing and the main plasma bulk are affected. The first interesting period is at the onset of the RF burst on the planar probe. The voltage applied to the surface can locally reverse the sheath in front of this surface. A second interesting period is after the build up of self bias and before the extinction of the RF burst. During the steady self-bias phase, the local perturbation of optical emission amounts to less than 10%, whereas in the sheath reversal phase it reaches 70%.
This article describes how to extract accurate information about a plasma from a capacitively coupled planar probe that is biased using pulsed radio-frequency excitation. The conditions necessary to observe correct saturation of the probe current are investigated, particularly the use of correct geometry and biasing for the guard ring. With these precautions the probe is an effective diagnostic for electron tail temperature at energies beyond those probed by conventional cylindrical probes. The dynamic response of the probe is investigated using conventional sweep voltages and shows the onset of displacement current and inertial effects associated with ions and electrons. In addition the effect of insulating films on the probe surface is examined, showing how the probe continues to operate even when it is coated. Characteristic changes caused by the presence of an insulating film give information about its electrical properties and its thickness.
Hexamethyldisiloxane (HMDSO) is an organosilicon compound with a modifiable bandgap, depending on the deposition conditions. This material has many unique properties due to its stability, low toxicity, and strong adhesion, making it useful as a protective barrier against corrosion, moisture, and oxidation. In this work, HMDSO films were deposited on glass substrates by the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique at different deposition times. The optical properties of HMDSO films, such as dielectric permittivity, refractive index, extinction and absorption coefficients, and band gap energy, are inferred from transmission and reflection spectra. As the deposition time increased, the real part of the dielectric constant, the refractive index, and the bandgap energy showed a decrease, dropping from 4.24 to 3.40, from 2.06 to 1.84, and from 2.85 eV to 2.03 eV, respectively. The latter result is determined using classical models such as the O’Leary-Johnson-Lim (‘OJL’) interband transition and the harmonic oscillator model. HMDSO and Silver are used in this study for the fabrication of optical filters using two types of structures, a multiple cavity metal–dielectric (MCMD) and the Fabry–Perot structure. The silver layers are deposited by a sputtering process. The MCMD optical filter shows a higher transmittance of about 30%, but a wide range of wavelengths is transmitted. In contrast, the Fabry–Perot filter showed high contrast but a lower transmittance of about 20%.
