Papers by Keyword: Subsurface Damage

Abstract: Double-substrate angle polishing is presented for detecting depth of sub-surface damage layer during sapphire substrate grind process. Bimorph overlap bond is used in the double-substrate angle polishing, and when measuring the beveled corrosion crack, measurement errors caused by the traditional angle polish which results in fussy boundaries between polished bevel and the edge of the original wafer plane is avoided. Also digital length measurement is used to measure specimens polished bevel machining contours, then calculate accurate slant angles, eliminate errors of inaccurate angle values and improve measurement accuracy. This experiment has tested the length of mono-crystal polished bevel crack is 175um, the angle of slant is 4.85°. According to theoretical calculation, the double-sided grinding substrate subsurface damage layer is 15um, and the depth of double-sided crystal surface is about 30um. Grinding parameters: 320# boron carbide aqueous solution, lapping pressure 110g/cm², grinding speed 30r/min.

Abstract: Experiments were carried out to study the effect of ultrasonic vibration on the surface roughness and subsurface damage (SSD) in rotary ultrasonic machining (RUM) of glass BK7. As a comparison, some conventional grinding (CG) experiments were also performed under the same process parameters with there of the RUM ones. The surface roughness of the RUM/CG samples was measured with a surface profilometer. The SSD of these specimens was assessed and characterized by a measuring microscope with the help of the taper polishing method. Also, the influence of process parameters (cutting depth, feed speed, and spindle speed) on the surface/subsurface quality was discussed. As a result, both the surface roughness and the SSD depth of the RUM/CG specimens were reduced with the increased spindle speed, while increased with the increasing of feed speed and cutting depth of the diamond tool. Compared with the CG process, the introduction of ultrasonic vibration resulted in the higher surface roughness and SSD depth, due to the fact that the max cutting depth of the abrasive in the RUM process increased by an amplitude compared with that in the CG process.

Abstract: The paper is mainly to research the subsurface damage depth and morphology on grinding and polishing substrates on optical materials, and analyze different subsurface damage morphologies caused by different processing technologies. The best etching solution is selected by experiments, grinding and polishing substrates are etched for proper time by divided stages. Use 120×optical microscope and scanning electronic microscope to observe subsurface damage morphology and Taylor Hobson PGI1240 to measure the etching depth to obtain the subsurface damage depth.

Abstract: Single crystal SiC is one of the most attractive semiconductor materials for next generation power device applications. However, it is very difficult to be precisely machined due to its high hardness and chemical inertness. We evaluated the machining characteristics of 4H-SiC using different processes including diamond abrasives lapping, chemical mechanical polishing (CMP) and plasma assisted polishing (PAP). Scratches were introduced through diamond abrasives lapping due to the high hardness of diamond, which resulted in the worsening of surface roughness. A damage layer was observed in the cross-sectional transmission electron microscopy (XTEM) images. A scratch-free surface was obtained through CMP, but it’s not atomically flat since step/terrace structure couldn’t be clearly observed. PAP was newly proposed for the finishing of difficult to machine materials. In PAP, water vapor plasma oxidation and soft abrasive polishing were repeatedly conducted. Ceria which is much softer than SiC was used as the abrasive material. PAP was proved very effective to achieve surfaces out of scratches. Also, due to the low hardness of ceria, no damage layers were introduced. The roughness of PAP processed surface was decreased to about 0.1 nm rms. The surface was also observed by XTEM, which proved an atomically flat surface without crystallographical damage was obtained.

Abstract: A novel polishing technique combined with the irradiation of atmospheric pressure plasma known as plasma assisted polishing (PAP) is proposed for the finishing of difficult-to-machine materials. In this paper, we mainly focus on the case of 4H-SiC substrate. We used helium-based water vapour plasma to modify the mechanical and chemical properties of the SiC surface. The results of X-ray photoelectron spectroscopy (XPS) measurements indicate that the surface was efficiently oxidized after plasma irradiation, and the main product was silicon oxide. A small amount of silicon oxycarbide was also observed which was identified as the interface oxide. The result of a nanoindentation test revealed that the hardness of oxidized SiC surface decreased by one order of magnitude compared with the unprocessed surface. The decrease of hardness of modified surface enables us to flatten the surface without forming any scratches and subsurface damage by using soft abrasive compared with the base material. We used CeO₂ as the abrasive material in PAP, the hardness of which was near to that of the oxidized surface. The microscopic interferometer images of the PAP processed surface showed us that scratches disappeared and surface roughnesses also decreased from 4.410 nm p-v, 0.621 nm rms to 1.889 nm p-v, 0.280 nm rms. From the atomic force microscopy (AFM) images, a step and terrace structure was observed on the surface after PAP, which means that an atomically flat surface was obtained. We conducted reflection high-energy electron diffraction (RHEED) measurement to evaluate the residual strain of the PAP processed surface. The results indicate that the lattice constants approached the ideal value, which meansthat the PAP technique did not introduce crystallographical subsurface damage.

Abstract: Reported in this paper is an investigation of the process parameter effects on surface roughness and subsurface damage (SSD) in CMP of single crystalline Silicon. For the given experiments, the appropriate method to examine the SSD can be obtained. The surface roughness and figure accuracy were measured with an atomic force microscope (AFM) and Taylor-Hobson profilometer. The experiments results indicate proper process parameter for the best surface roughness, which can be divided into two stages. It should use longer time in the finish polishing stage, while shorter time and reduce the ratio of polishing pads and head in the ultra-finish polishing stage. Generally speaking, the isotropic etching of single crystalline Silicon, anisotropic etching of single crystalline Silicon and hand burnishing are mostly used to find the SSD and it is found that the last method is the best one to see the SSD by SEM.

Abstract: This paper aims to develop a laser assisted grinding process capable of manufacturing micro features in high strength materials. A diode laser with wavelength 808 nm was set on a precision grinding machine. Micro grooves were fabricated on high strength materials including silicon nitride and aluminium oxide by using the laser assisted grinding process, i.e. laser pre-heat workpiece flowed by micro grinding. The experimental results showed that the laser assisted grinding process resulted in deeper grooves due to thermal expansion of workpiece materials caused by laser heating. However, the machined surface roughness was more consistently better than that obtained using solo grinding process and applying coolant. No subsurface damage was observed in the SEM images of cross sections of the machined workpieces when laser assisted grinding process was used.

Abstract: This paper presents a method of measuring subsurface damage by roughness variation along the bevel surface, which is prepared by MRF taper polishing. Experiments for the ground K9 glass samples show that roughness varies obviously at the position where the subsurface damages go to disappear. Discussions indicate that the method is quantitative and simple for measuring subsurface damage.

Abstract: Fixed-abrasive lapping (FAL) is a new machining technology and is adopted to manufacture hard brittle materials to obtain the high surface quality. In the same machining condition, K9 glasses are lapped by abrasives and fixed-abrasive, respectively. Two grain sizes of diamond abrasives are adopted in every lapping means. Differential chemical etch method (DCEM) is employed to measure the depth of subsurface damage (SSD) of different lapping means. Surface damages are compared by Microscope. The results show that the depth of SSD is 53 and 15.2μm after abrasives lapping (AL) by 40 and 28μm diamond abrasives. FAL with 40 and 28μm diamond abrasive leads to 4.5 and 3.4μm subsurface damage depth, respectively. FAL can get smaller surface damage and shallower depth of SSD than AL. And FAL can obtain the higher surface quality than AL.

Abstract: Differential chemical etch method (DCEM) was employed to study the effect on the surface/subsurface damage depth of K9 glass lapped by different particle sizes of fixed diamond abrasives. The advantage of DCEM is that both the lapped and substrate samples are placed in the chemical etch at the same time to decrease or eliminate the effect of etching condition variation. K9 glasses are firstly fixed-abrasive lapped with 40, 28, 14 and 10μm diamond abrasives, respectively. Surface damages of K9 glass after FAL are measured by Microscopy. The results show that the corresponding subsurface damage (SSD) depths of K9 glass are 4.5, 3.4, 2.8 and 1.6μm when the fixed diamond abrasive particle size are 40, 28, 14 and 10μm.With the decreasing of diamond particle size, the SSD depth decreases obviously and surface quality of K9 glass is improved significantly.