Papers by Keyword: Etching

Abstract: An etch pit shape of off-angled 4H-SiC Si-face formed by different halogen gases such as chlorine trifluoride (ClF3) and a mixed gas (O2+Cl2) of oxygen and chlorine in nitrogen (N2) ambience has been studied. One kind of etch pit with the crooked hexagon was formed at etching temperature under 500oC. The angle of etch pit measured by the cross-sectional atomic force microscope image was about 10o from the [11-20] view. A dislocation type of the etch pit was discussed in comparison with the etch pit shape and an X-ray topography image.

Abstract: In the early days of the microelectronics industry, it became clear that even trace contaminants could have detrimental impact on the electronic properties of fabricated devices. This realization led to the development of the so-called RCA clean for silicon surfaces [], which uses sequential baths in basic and acidic hydrogen peroxide solutions, now known as SCA-1 and SCA-2, to oxidize organic materials, remove particulates, and bind metallic impurities. The detailed characterization of this process as well as its simplicity and economic viability soon led to its widespread industrial adoption. Although the RCA clean includes an optional etch in dilute HF between the two cleaning solutions to remove the native oxide layer, the overall process results in an extremely clean but electronically defective oxide-terminated and thus extremely hydrophilic silicon surface, which we now know is quite rough on an atomic scale [].

Abstract: Since Tetramethylammonium Hydroxide (TMAH) became widely used as a silicon etchant, e.g. the dummy gate removal for gate-last approach (RMG) [1, or Si fin formation on FinFET [, some careful preparations and optimizations have required implementation. These adaptations have involved not only chemical-related issues, but also hardware-related in order to satisfy the necessary process performance.

Abstract: In this article, the polystyrene (PS) microspheres monolayer film was manufactured on silicon substrate by spin-coating, and the effect of PS microspheres concentration on preparation of monolayer film was discussed in detail. With a view to the application of graphic substrate technology, the etching effect with different technological parameter (etching time and power) was researched, and a set of appropriate process parameter were obtained, which met the requirements of preparation of the extension graphics silicon substrate.

Abstract: Focusing neutron beam with wide wavelength range is an indispensable technique used to compensate for weak signals from tiny samples in various experiments using pulsed neutron beam generated from high intensity proton accelerator facilities, such as J-PARC. Aspherical supermirror device is one of the most effective optical devices for focusing neutron beam with wide wavelength range since it has no chromatic aberration. Stack of aspherical supermirror enables us to focus neutron beams with wide divergence. Thin mirrors with a millimeter thickness are required to minimize the absorption loss of incident neutron beams since the thickness of a mirror shadows the reflective area of the other mirrors. Previously, we developed a fabrication process of a precise millimeter-thick elliptical supermirror. This process consists of noncontact figuring by the numerically controlled local wet etching technique, the finishing of surface without degrading mirror shape by low-pressure polishing, and the ion beam sputter deposition of NiC/Ti multilayers on both sides of the mirror substrate to compensate for film stress. In this paper, we report fabrication of elliptical supermirror with a thickness of 1 mm and development of multiply-arranged neutron focusing mirror device using stacked 4 fabricated elliptical supermirror with a thickness of 1mm.

Abstract: We have developed a chemical process for atomic planarization of gallium nitride (GaN) using a platinum catalyst and ultraviolet (UV) light irradiation. The process is mediated by a hydrolysis reaction catalyzed by platinum as a solid catalyst. Because the reaction occurs selectively from the step edges, a flat surface composed of a straight step-and-terrace structure is obtained. In the absence of UV light, owing to the low step edge density, the removal rate is quite slow, approximately 1 nm/h. In contrast, under UV light, etch pits are formed on the terraces by photo-electrochemical etching causing an increase in the step edge density. We achieved surface planarization with a removal rate of 9.6 nm/h assisted by irradiation with UV light.

Abstract: Aspherical supermirrors are some of the most useful neutron-focusing optics. We aim to develop multiple aspherical supermirror devices using high-precision figured aspherical focusing supermirrors to focus neutron beams with high intensities, because multiple mirrors collect a very large beam divergence. Thin mirrors with millimetre thickness are required to minimize the absorption loss of incident neutron beams since the thickness of a mirror shadows the reflective area of other mirrors. However, it is difficult to fabricate thin mirror substrates with a form accuracy at the sub-micrometre level by conventional machining. Conventional machining deforms a substrate by machining force and spring back after machining causes figure error. Furthermore the deposition of supermirrors deforms the mirror substrate by film stress. Thus, we developed a new process of fabricating a precise millimetre-thick elliptical supermirror. This process consists of non-contact figuring by the numerically controlled local wet etching technique, the minimization of surface roughness without degrading form accuracy by low-pressure polishing with a polishing pressure less than about 7 kPa (1psi), and the ion beam sputter deposition of NiC/Ti multilayers on both sides of the mirror substrate to compensate for film stress. In this paper, we report on the fabrication results of aplano-elliptical mirror substrate with a thickness of 1 mm.

Abstract: Step-terrace structures were observed at on-axis/4o off 4H-SiC {0001} surfaces after Si-vapor etching which we have been supposed as an original technique to planarize and etch the SiC surfaces by utilizing a TaC crucible in temperature ranged from 1600 to 2200 oC. The structures obtained after the Si-vapor etching obviously indicated temperature dependence. There were two types of step-terrace structures in terms of the step height and the shape of the step edges at on-axis surfaces. Step bunched surfaces consisting of full unit cell height (= 1.0 nm) steps with {1-10n} facets at the step edges were observed at 4H-SiC (0001) in lower temperatures below 2000 oC, while smooth isotropic surfaces with half unit cell height (= 0.5 nm) steps and without any stable facets at the step edges were observed at 4H-SiC (0001) in higher temperatures above 2000 oC and in all temperature conditions (1600 - 2200 oC) at 4H-SiC (000-1). Similar tendency was also confirmed at 4o off 4H-SiC {0001} surfaces. From the comparison with 6H-SiC, macro step bunching (~10 nm height) was revealed to be a unique phenomenon at 4H-SiC (0001) surface in the etching.

Abstract: Relationship between the chemical reactivity and the orientation of SiC substrates was investigated. Thermal etching of 4H-SiC in the mixed gas of oxygen and chlorine was carried out as the chemical reaction. The etching rate did not change monotonously with the increase of the off angle in 4H-SiC (000-1) C substrate. By the use of such tendency in the thermal etching, the three dimensional structure with the specific pyramidal plane was able to be obtained.

Abstract: Cup wheel grinding and etching pretreatment are widely used in complex coated cemented carbide cutting tools machining process. The two processes determine different surface properties due to various mechanical and thermal loads in grinding and complex chemical reaction in etching pretreatment. In this paper, the effect of the grinding wheel speed, the grinding feed rate and the etching time with the Murakami and acid solution on the residual stress and surface topography of coated cemented carbide cutting tools are investigated. After each process, the samples are characterized by scanning electron microscopy and X-ray diffraction. It is found that the grinding wheel speed has a significant influence on residual stress measured in the WC phase. Etching by Murakami generated smooth surface, which partly removed the near-surface residual stress quickly but cannot eliminate.