Key Engineering Materials Vols. 291-292

Abstract: In recent years, there has been a great demand for large-diameter wafers with high flatness of hard and brittle materials that are used as optical and sensor elements. To meet these demands, we have developed an ultra-precision plane honing method as a highly efficient surface finishing technique using a fixed abrasive. This technique offers good finish surface roughness, shallow subsurface damage and high machining efficiency. However, there is a need to improve the surface flatness, which is dependent on the grinding wheel surface flatness and the tilt of the spindles. In this paper, the relationship between grinding wheel surface flatness and the shape of a truer is investigated by calculating the contact length of a point on the grinding wheel with the truer. It was found that there is an optimum shape of the truer to make the grinding wheel surface flat, and the machined 3-inch glass wafer is controlled to a flatness of less than 1µm by using the optimum truer.

Abstract: This paper describes an ultra precision polishing method of aspherical mirrors, and the fundamental research on polishing characteristics. The aspherical mirrors with a diameter of about 30mm made by fused silica glass and CVD-SiC were ELID (electrolytic in-process dressing)-ground to high form accuracy with #4000 cast iron bonded diamond wheel, and then polished with a small polishing tool. As the result, final surface roughness of 1.4nmRa and form accuracy of 1.2 μm was obtained.

Abstract: Recently a technique has been developed to mold aspheric glass lenses by using cemented carbide dies at elevated temperature. The dies are precisely ground by an ultraprecision grinding machine. However the obtained form accuracy is generally around 100nm and is not enough high. In this study, to investigate a possibility of corrective figuring of the dies, a series of experiments of abrasive jet machining of cemented carbide was conducted and fundamental machining characteristics were examined. The used abrasives were fine grains of silicon carbide and aluminum oxide. The silicon carbide abrasives could accomplish a sufficient material removal. Both the material removal rate and the surface roughness increase as the collision angle increases up to 90 degrees. Therefore, in order to obtain a smooth surface finish, it was necessary to take a smaller collision angle and to slow down the material removal rate.

Abstract: A non-contact method of measuring the surface roughness and the thickness of polished silicon wafers using an infrared laser is proposed. The method utilizes the property that the infrared radiation is transmitted through single-crystal silicon. An optical-power meter is used to measure the intensity of an infrared laser beam that is incident to a chamfer on a cornered silicon wafer and which exits from the other side of the chamfer after repeated total reflections inside the wafer. The experimental results show that a significant correlation exists between the intensity of the transmitted infrared radiation and the surface roughness of the silicon wafers, as well as between the intensity and the thickness of the wafers. Therefore, if a calibration curve is pre-set, the surface roughness and the thickness can be estimated from the changes in the intensity of the infrared transmittance.

Abstract: The GaAs wafer is widely applied to semiconductor element related to telecommunication and semiconductor laser. In this research, novel fine polishing technology of GaAs wafer was investigated using TiO2-H2O2-H2O slurry system instead of NaOCl which is conventionally used as polishing slurry. And then the ultraviolet ray was applied in order to investigate the effect of TiO2 photocatalyst. The polishing characteristics were estimated by optical microscope and WYKO optical profiler. It was found that the slurry system was available for GaAs wafer polishing although the polishing rate was lower than NaOCl. Moreover, the effect of the photocatalyst of TiO2 including in slurry was investigated. In this polishing system, the effect of the photocatalyst on GaAs wafer CMP mechanism has not been confirmed yet.

Abstract: The mechanism of the mechanochemical polishing of Si wafers with BaCO3, CaCO3 and ZnO abrasives was investigated by polishing experiments carried out in air, O2 and Ar gas environments on dry condition and static heat treatment experiments of mixed powder of BaCO3 and Si with various mixture ratios for analyzing the reaction mechanism at the interface in polishing operation. Results obtained were (1) Si wafers were smoothly and effectively polished with these all mechanochemical abrasive whether O2 gas existed in the surrounding environment or not, (2) Heat treatment of the mixed powder suggested that oxidation of Si was more actively promoted even when existence of BaCO3 powder was only a little in the mixture and that formation of Ba-Si oxide increased as the mixture ratio of BaCO3 powder to Si powder increased, (3) As the mechanochemical polishing mechanism, two-step reaction process would be the most reasonable, that is, chemical attack of the mechanochemical abrasive for oxidizing the Si surface as the first step and further chemical reaction to form reaction products between the formed SiO2 and the abrasive as the second step.

Abstract: The friction force of wafer surface plays an important role in removing material of wafer surface and the friction force distribution on wafer surface has a direct influence on nonuniformity of material removal in wafer CMP process. In this paper, models of friction force distribution and friction force on wafer surface were built according to the CMP process. Then the relationships between friction force and CMP process variables, such as the motion variables and pressure, are obtained. Measuring data of friction force on wafer surface are accord with analytical results. The research of this paper is helpful to further understanding the material removal mechanism in wafer CMP.

Abstract: The slurry of Copper chemical mechanical planarization for ultra large-scale integrate circuit (ULSI) usually contains oxidizer, etchant, complexing reagent and corrosive inhibitor. In planarization process, the corrosive inhibitor has an important effect on the planarization. Only if the concave surface of the wafer is properly protected from corrosion by the inhibitor, the process can obtain perfect surface planarity. In this paper, with Fe(NO3)3 as an oxidant and several corrosive inhibitors selected, the corrosive efficiency of slurries are investigated. The static etching rate and the polishing material removal rate of wafer are obtained. The electrochemical behavior of the slurry is investigated by the potentiodynamic polarization studies. And the inhibitive efficiency of the related corrosive inhibitors is calculated from the polarization data. X-ray diffraction is applied to analyze the composition modification of the copper surface. Atom force microscopy is applied to measure the surface topography of corrosive copper wafer and the value of surface roughness is measured by ZYGO surface analysis system. The result shows that the benzotriazole (BTA) is a perfect corrosive inhibitor. With addition of 0.1wt% BTA into 1.5wt% Fe(NO3)3 solution, the inhibitive efficiency can reach 99.1%. The polishing test shows that if only 1.5wt% Fe(NO3)3 is added as an oxidizer without any other additive, the surface roughness of the polished wafer is 26.9Å, while with 0.1wt%BTA added in the meantime, 5.2 Å of surface roughness can be obtained.

Abstract: Nanometer-scale protuberance and groove processing was performed on a silicon (Si) surface by diamond tip sliding using atomic force microscopy (AFM). The protuberances of 0-5 nm height were obtained the silicon surface by using the diamond tip of approximately 200 nm radius and the grooves of 0-2 nm depth were processed by the tip of about 50 nm radius. It was observed that both protuberance and groove were produced using the tip of about 100 nm radius. Indentation measurements show the hardness of processed parts was greater than that of unprocessed parts. Potassium hydroxide (KOH) solution etching was performed on the mechanochemically processed sample. The processed areas were prevented from etching due to the formation of a dense oxide layer. This may be because the processed parts were oxidized by tip sliding due to the effect of mechanochemical oxidation.

Abstract: To realize ultrahigh density recording in high precision using polycarbonate as a recording media, the nanometer-scale mechanical processing properties of polycarbonate and fluorocarbon plasma-treated polycarbonate were investigated using atomic force microscopy (AFM). The surface free energy of the polycarbonate specimen can be reduced by fluorocarbon plasma-treatment, resulting in processing force being reduced. Thus, nanometer-scale precise processing of polycarbonate can be realized. Lines and spaces with intervals minimized to 60 nm were performed on the fluorocarbon plasma-treated polycarbonate. Viscoelastic properties of the fluorinated polycarbonate were evaluated using AFM in force modulation mode. Fluorocarbon plasma treatment can reduce friction force of a polycarbonate sample and improve its wear resistance. Therefore, the friction durability corresponding to the reliability of data reproduction was markedly improved.