Papers by Keyword: Subsurface Damage

Abstract: Mechanical loading and unloading of silicon is a characteristic feature of grinding and diamond turning processes. Such rapid loading and unloading induces damage and phase transformations. While, indentation tests are often used to study such normal loading and unloading via characteristic events in the force-depth plot, such tests involve only normal loading and lack tangential loading. A better alternative is scratch test, both constant and varying depth ones, involving normal and tangential loading on the scratching tool; this better simulates conditions of machining, or grinding. In this research, the mechanical load/unload behavior response of silicon is studied under scratching conditions by comparing increasing and decreasing depth scratch behaviour. In-situ force responses show that after ductile-brittle transition occurs, higher forces, at a given scratch depth, are required to deform the material during increasing depth scratching for a given depth than in decreasing depth scratch. Large surface and sub-surface damages with the presence of radial, median, and lateral cracks are seen to make the material weaker, ahead of the advancing tool, in decreasing depth scratch. Raman intensity ratio of amorphous silicon (a-Si) to nanocrystalline silicon (nc-Si) shows that high amorphization of silicon occurs during increasing depth scratching than decreasing depth. Using such force-depth plots an attempt is made to compare the normal loads while indenting and scratching. This study can help optimize the processing of silicon by grinding and diamond turning.

Abstract: The high strength and good optical performance offered by optical grade silicon could be considered as the reason for its wide usage as optical materials in many industries including electronic, metrology, infrared (IR) optics and solar cells. Due to this, nanoscale manufacturing of these products requires superior quality and enhanced functional performance of the produced materials. Because recent studies have been focusing on correlating both surface and subsurface nature alterations with better functional performance, an MD study of the experiment was carried out in comparison with experiment to match the observed MD model features to the experimental result obtained. The MD study was observed to conform with the R_a result as obtained in the experiment.

Abstract: Quartz glass is a typical hard and brittle material. During the manufacturing process of quartz glass components, ultra-precision grinding is widely used due to its high throughput and good dimensional accuracies. However, grinding will unavoidably induce large surface and subsurface damage. In this study, the surface and subsurface damage characteristics of quartz glass substrates ground by diamond wheels with different grit sizes were investigated in terms of surface roughness, surface topography, subsurface microcrack characteristic, and subsurface damage depth. Discussion was also provided to explore corresponding reasons of surface and subsurface damage induced by diamond grinding wheels with different grit sizes of #1500 and #2000. The experiment results showed that the surface roughness, surface damage, and subsurface damage depth induced by #2000 quartz glass was ground by #1500 diamond grinding wheel, and in ductile mode when ground by #2000 diamond grinding wheel.

Abstract: Three-inch 6H-SiC bulk crystals were grown by the PVT method on the seeds processed by different treatments. The influences of seed surface morphology and subsurface damage on the dislocation density were investigated. The seed surface morphology was characterized by atomic force microscopy (AFM). The extent of the subsurface damage was estimated by electron back-scattered diffraction (EBSD) and Band Contrast (BC) value. The distribution and density of the dislocations were observed by optical microscopy (OM). The results showed that the pit density performed by H₂ 1400°C etching was nearly one order of magnitude lower than that by mechanical polishing (MP) process. So H₂ etching processed at 1400°C for 2h could completely remove the subsurface damage, compared with the MP process with the deep surface damage.

Abstract: Silicon wafers are the most widely used semiconductor substrates. It has been considered that silicon wafers after chemomechanical polishing (CMP) have no subsurface defects. However, in fact, defects such as dislocation and latent microcracks will remain in the wafers if CMP is performed under unsuitable conditions. In this study, we confirmed the existence of subsurface damages at a depth of submicron level in a silicon wafer after CMP, then used a nanosecond pulsed Nd:YAG laser to repair the subsurface damages. It was found that subsurface defects were recovered to a single crystalline structure by laser irradiation without changing the surface topography. The phase transformation of silicon before and after laser irradiation was confirmed by laser Raman spectroscopy and chemical etching using saturated aqueous solution of Ca(OH)₂. The findings from this study contributes to improve the quality of silicon wafers for high-performance semiconductors.

Abstract: Large-aperture lens used for single-lens reflex cameras is generally produced by both ultra-precision grinding and polishing because a mass-produced lens by molding process can hardly achieve the required form accuracy and surface quality. Recently, grinding process of an optical glass should make surface quality as high as possible in order to reduce removal amount in polishing process. Accordingly, evaluation of subsurface damage induced under various grinding conditions has been required because subsurface damage leads to crack initiation or deterioration of the performance. However, evaluation method of subsurface damage on the spherical glass lens after grinding has not yet been established.In this study, the quantitative evaluation method by applying wet-etching of hydrofluoric acid (HF) is proposed, then its validity is verified. From the experimental results, we clarify to evaluate the subsurface damage by examining the surface transition according to etching time.

Abstract: Ultra-precision grinding is widely used in machining of the hard and brittle materials due to its high surface accuracy and machining efficiency. However, grinding inevitably brings about surface and subsurface damage that needs to be removed by the polishing processes. This study investigated the surface and subsurface integrity of glass-ceramics induced by ultra-precision grinding. The characteristics of surface roughness, surface topography and subsurface damage depth of ground glass-ceramics with diamond grinding wheels with different grain sizes were presented and compared. Discussion was also provided to explore corresponding reasons of surface and subsurface integrity induced by diamond grinding wheels with different grain sizes.

Abstract: To effectively machine fibre-reinforced polymer composites using a simple tool, the authors have developed an elliptic vibration-assisted (EVA) cutting technique by applying micro-scale vibrations to a tool tip. This investigation aims to understand the effect of vibration frequency and amplitude on the EVA cutting performance. With the aid of a microstructure-based 3D finite element analysis, this study found that an increased vibration frequency or amplitude can accelerate the fracture of fibres, and reduce cutting forces in both the cutting and normal directions. The fracture mechanism was found to be dominated by the bending of fibres when the vibration frequency or amplitude in the cutting direction was small. With increasing the frequency or amplitude, impact-induced fracture becomes dominant, which reduces subsurface damage. It was found that to promote the performance of EVA cutting, the vibration frequency and amplitude of the cutting tool should be high. However, a too large frequency can bring about severe subsurface damage and bending fracture of fibres beneath the cutting path. A too large amplitude in the cutting direction, however, can accelerate the tool wear, while that in the vertical direction can worsen the fibre-matrix debonding.

Abstract: The machining methods such as waterjet cutting, milling, grinding, lapping, etc. are usually used to manufacture glass fiber reinforced composites (GFRCs) parts. Damages will be produced unavoidably in the machining process, no matter which machining method is employed. Subsurface damage is one of the important parameters to evaluate the surface layer damages. The detection method for the subsurface damages of glass fiber reinforced glass matrix (glass/glass) composite after machining is researched. The characteristics of subsurface damages of glass/glass composite after waterjet cutting, milling, grinding and lapping are investigated mainly, when the fiber direction is either perpendicular or parallel to the cutting surface.

Abstract: Wire saw process is widely used in the machining of hard and brittle materials with low surface damage and high efficiency. Cutting of silicon wafers in integrated circuit (IC), semiconductor and photovoltaic solar industries is also generally using wire saw process. However, the surface layer damage induced by wire saw process will seriously decrease the wafer quality and increase the process time and production costs of the post grinding and polishing. The surface layer qualities of the silicon wafers sawed by the different wire saw processes was investigated in this paper. The characteristics of surface roughness, surface topography and subsurface damage of silicon wafers sliced by the fixed abrasive and the loose abrasive wire sawing respectively were compared and the corresponding reasons were analyzed.