Advanced Materials Research Vol. 1136

Abstract: Lithium tantalate (LiTaO₃) has piezoelectric, electro-optical and nonlinear optical characteristics, and a wide transparency range going from ultraviolet to infrared. It is desirable that LiTaO₃ wafer was a smooth surface in order to function with good quality. Chemical mechanical polishing (CMP) has been used to planarize integrated circuits (ICs) or obtain a high surface quality of the substrates. This paper investigates the effect of citric acid as an additive in the slurry for LiTaO₃ CMP. The roughness of the wafers was measured by an atomic force microscopy (AFM, XE-100) after polishing. The slurry, which contains citric acid as an additive, has a higher material removal rate and friction force than a slurry without an additive. After polishing, the surface roughness of the LiTaO₃ wafer can be reduced down to 1.7Å of R_a.

Abstract: Finishing process of sapphire wafer is meeting huge challenge to fulfill the strict requirement of high surface quality in semiconductor industry. Fixed abrasive process, although can guarantee the profile accuracy, leaves damaged layer on the surface or subsurface of sapphire wafer. Chemical mechanical polishing (CMP) is famous for providing great surface roughness, however, sacrifices surface geometrical accuracy. Therefore, a new chromium oxide (Cr₂O₃) sapphire grinding wheel based on chemical mechanical grinding (CMG) principle has been developed and its performance has also been put into examination. The experiment result has demonstrated that Cr₂O₃ possesses an outstanding potential in terms of a high material removal rate of sapphire wafer, meanwhile, largely reduces surface roughness from about 150nm to below 10nm in 1 hour. In addition, the design of experiment (DOE) has also been carried out to study the effect of influencing factors towards ultimate surface roughness of sapphire wafer. It reveals that the revolution speed of sapphire wafer bears twice greater influence towards surface roughness than the revolution speed of grinding wheel.

Abstract: A sapphire substrate is essential for epitaxial growth of GaN, which is used for high brightness light-emitting diodes (LEDs), high-power and high-frequency devices. However, the material removal rate (MRR) of sapphire in conventional polishing is very low because of its high hardness and chemical inertness. We proposed application of plasma assisted polishing using a resin-bonded silica grinding stone for finishing of sapphire surface and investigated basic removal properties. The results of a ball-on-disc type test results showed that irradiation of water vapor containing atmospheric pressure Ar gas plasma promoted the MRR of sapphire by a factor of 7.4. Strong emission from hydroxyl radical was observed by an optical emission spectroscopy measurement of the plasma. XPS measurements revealed that the surface of both sapphire and silica were hydroxylated after the plasma irradiation. From these experimental and measurement results, we proposed the removal model in plasma assisted polishing of sapphire as follows. Firstly, irradiation of water vapor plasma hydroxylates the surfaces of sapphire and silica. Then, Al-O-Si bonding is formed by dehydration reaction between sapphire and silica surfaces. Finally, surface atom of sapphire is removed by the motion of silica abrasive. In this paper, we describe the preliminary experimental results and measurement results which support the proposed removal model in plasma assisted polishing of sapphire.

Abstract: A fundamental study on finishing aided by an ultraviolet ray (generally mashining:referred to as U-RAM^R) was conducted to evaluate its applicability to the polishing of aluminum alloy. Qualitative analysis with X-ray photoelectron spectroscopy (XPS) was used to estimate the chemical reaction induced on Al surfaces that were immersed in some solutions. Inductively coupled plasma spectroscopy (ICPS) was employed to quantitatively analyze the amount of oxidized/dissolved Al, Mg and Fe. The following conclusions were obtained by investigation of the aluminum alloy polishing process. Aluminum does not dissolve in TiO₂-solution, whereas a small amount of Al dissolves into cathilon dye solution. Although only a small amount of Al dissolves in TiO₂-cathilon dye solution in the absence of UV irradiation, the amount of Al dissolved increases slightly under UV irradiation with the formation of oxide, nitrogen oxide and nitride on the Al surface. In addition, a small amount of an aluminum chloride dissolves into TiO₂-cathilon dye solution. An Al alloy (A5052) surface was made flat by polishing with TiO₂-cathilon dye slurry under UV irradiation.

Abstract: The ultra-thin 304 stainless steel sheet will be used in flexible displays for substrate material. In chemical mechanical polishing of ultra-thin stainless steel, the pH value of polishing slurry has an important influence on the material removal rate (MRR). In this paper, the influences of pH regulator in slurry on MRR had been studied in CMP of ultra-thin 304 stainless steel based on alumina (Al₂O₃) abrasive in acidic polishing slurry. The research results show that, in the same conditions, different pH value had a different chemical action mechanism and a different MRR. And also, different oxidant with pH regulator had a different chemical action mechanism and a different MRR. The research results can provide the reference for studying the slurry in CMP of ultra-thin stainless steel.

Abstract: This work examined improvements in cutting efficiency obtained during the slicing of sapphire workpieces when adding CeO₂ to the cutting fluid. Various machining parameters, including the cutting temperature, machining surface tolerance, surface quality and tool wear, were assessed. It was confirmed that both the cutting temperature and the machining surface tolerance are reduced by the presence of CeO₂ in the cutting fluid. Observations of the machined surfaces and the cutting tool also demonstrated that both brittle fracturing of the surface and loss of abrasive grains were suppressed following the addition of CeO₂. These results suggest that the cutting temperature likely affects the accuracy of the cutting process and that CeO₂ appears to improve cutting efficiency by reducing the workpiece temperature and by stabilizing the cutting process.

Abstract: Retaining ring which keeps the wafer in place is an essential component in chemical mechanical polishing. Meanwhile, it helps to reduce the edge exclusion region where the material removal rate deviates significantly from that of the central region of the wafer. However, it may increase the slurry flow resistance and hence decrease the slurry flow rate. For properly designing a retaining ring of reasonable structure, the effects of retaining ring on slurry flow and contact pressure distribution in CMP process are analyzed by the mixed elastohydrodynamic lubrication model. It is found that the slurry flow is sensitive to the protrusion height of retaining ring used in the first generation carrier. The same as the first generation carrier, the slurry flow is obviously reduced with increasing pressure acting on the retaining ring in the second generation carrier. In addition, the floating retaining ring used in the second generation CMP carrier has better performance and is more controllable than the fixed retaining ring used in the first generation CMP carrier.

Abstract: Rocking motion wire saw with the additional rocking motion of either the wire or the workpiece is a new machining method compared with the traditional wire saw. The length of contact between the wire and the workpiece changes in this new saw process. In this paper, the wire motion and the contact length were theoretically researched. Wire motion path equation with the rocking motion was established. The theoretical equation of the contact length in half a swing period was derived out. The results indicated that the wire motion was a single pendulum movement with a length line segment, which the swing pivot was moved with a feed rate. The contact length had significant changes in half a swing period in the rocking motion wire saw. The contact length varied periodically with the same amplitude in the square ingot sawing, which varied periodically with the variation amplitude in the circle ingot sawing. The contact length with the rocking motion was obviously shorter than the case without the rocking motion for either the square ingot or the circle ingot.

Abstract: Precision slicing tests were performed for single-crystal silicon by using a newly developed dicing wire saw system and diamond wires. The developed dicing wire saw enables slicing thick workpiece of hard and brittle materials which could not be sliced by conventional dicing machines. To achieve high precision and efficiency, the dicing wire saw system adopted tension control and high speed control technologies which provides a maximum wire feeding speed of 2000m/min. In this study, the diamond wire was driven in a single direction at a speed of 750-1750m/min and the slicing force, wire wear and workpiece surface roughness after slicing were investigated experimentally. The results showed that as a new slicing system, the developed dicing wire saw was useable for high-precision slicing of thick workpiece.

Abstract: Aiming at the difficulty of 65% volume fraction SiCp/Al composites micro-hole machining and the problem of exit defects, the ultrasonic vibration-assisted grinding (UVAG) method for micro-hole machining was experimental studied taking Φ2-3mm hole for example. Results indicated that the thrust force was reduced by 79.8% through UVAG with lower fluctuation and the tool wear was much less than conventional drilling (CD). Lower thrust force and better exit quality were obtained with the increasing of the ultrasonic amplitude.