Papers by Author: Ren Ke Kang

Abstract: In CNC machining, the constant following error was caused by the uniform motion of feed drive, which could induced contour error in the multi-axis movement, and the contour error would affect machining accuracy. In this paper, the produce principle of following error is analyzed, as well as the influences of following error on contour of linear and circular interpolation. The following error was compensated by velocity feedforward controller, and a new method for identifying coefficient of velocity feedforward controller is presented, based on the actual observed values of following error. The following error was eliminated after compensating with the proposed method.

Abstract: Invar 36 alloy is widely used in the field of precision manufacturing owing to its minimal thermal expansion coefficient. Grinding is very important in Invar surface processing, and the thermal characteristics is a key factor to affect the residual stress and deformation of grinding. In this paper, the thermal characteristics of Invar 36 alloy during plane grinding was tested. The thermal characteristics of Invar 36 alloy was found to be between carbon steel and nickel-based superalloy. The lower grinding temperature and better ground surface with lower residual stress can be obtained by using the reasonable grinding parameters.

Abstract: With the development of IC manufacturing technology, the machining precision and surface quality of silicon wafer are proposed much higher, but now the planarization techniques of silicon wafer using free abrasive and bonded abrasive have the disadvantage of poor profile accuracy, environmental pollution, deep damage layer, etc. A soft abrasive wheel combining chemical and medical effect was developed in this paper, it could get super smooth, low damage wafer surface by utilizing mechanical friction of abrasives and chemical reaction among abrasives, additives, silicon. A comparison experiment between #3000 soft abrasive wheel and #3000 diamond abrasive wheel was given to study on the grinding performance of soft abrasive wheel. The results showed that: wafer surface roughness ground by soft abrasive wheel was sub-nanometer and its sub-surface damage was only 0.01µm amorphous layer, which were much better than silicon wafer ground by diamond abrasive wheel, but material removal rate and grinding ratio of soft abrasive wheel were lower than diamond wheel. The wafer surface ground by soft abrasive wheel included Ce4+, Ce3+, Si4+, Ca2+ and Si, which indicated that the chemical reaction really occurred during grinding process.

Abstract: In order to better understand the grinding mechanism, the rough, semi-fine and fine ground silicon wafer subsurface damage models are experimentally investigated with the aid of advanced measurement methods. The results show that the rough ground wafer subsurface damage model is composed of large quantity of microcracks with complicated configurations, high density dislocations, stalk faults and elastic deformation layer. Among them microcracks, dislocations and stalk faults are dominant. Apart from the above damage, the amorphous layer and polycrystalline layer (Si-I, Si-III, Si-IV and Si-XII) exist in the semi-fine ground and fine ground wafer subsurface damage models. The amorphous layer depth firstly increases from rough grinding to semi-fine grinding and then decreases from semi-fine grinding to fine grinding. The damage model can be divided in severe damage part and elastic deformation part with high stress. When the material is removed by ductile mode two parts are all small and the ratio of second part is relatively great.

Abstract: The demand for extremely-thin Si wafers is expanding. Current manufacturing technologies are meeting great challenges with the continuous decrease in Si wafer thickness. In this study, a novel single step thinning process for extremely thin Si wafers was put forward by use of an integrated cup grinding wheel (ICGW) in which diamond segments and chemo-mechanical grinding (CMG) segments are alternately allocated along the wheel periphery. The basic machining principle and key technologies were introduced in detail. Grinding experiments were performed on 8-in. Si wafers with a developed ICGW to explore the minimal wafer thickness and grinding performance. The experimental results indicate that the proposed grinding process with the ICGW is an available thinning approach for extremely thin Si wafer down to 15μm

Abstract: Nanoindentation tests with the aid of acoustic emission monitoring were performed on single crystal MgO (001) plane to investigate the deformation of MgO under high indentation pressures. The results indicated that the deformation of MgO under nanoindentation with a sharp indenter could be classified into three stages: elastic deformation, elastoplastic deformation, and fragmentation. The elastic energy release and fracture occurred could be identified using acoustic emission signals.

Abstract: The calculating model of surface non-uniformity of polishing pad and the kinematical model between polishing pad and conditioner are initially established. Then the effects of several conditioning parameters were investigated by using the two models. The results of simulation and calculation show that the width ratio of diamond band of conditoner and the rotation speed at the same speed ratio between pad and conditioner have little effect on the surface non-uniformity of polishing pad, while at high non-integer rotation speed ratio, the surface non-uniformity of polishing pad is better than that at low integer speed ratio. The research results are available to select appropriate conditioning parameters especially for the stringent requirement of within-wafer non-uniformity in next generation IC.

Abstract: In the process of CMP SiO2 ILD, the nano-particle with high surface energy in slurry has an essential impact on the efficiency and quality of CMP. In this paper the mode of nano-particle on the surface of SiO2 ILD is analysed and adhesion removal model corresponding to that is established. Through cycle polishing experiments, the change of nano-particle size and the state of particle surface before and after polishing is observed with TEM and Zeta potential analyzer, based on which the adhesion removal model is verified.

Abstract: An innovative fixed abrasive grinding process of chemo-mechanical grinding (CMG) by using soft abrasive grinding wheel (SAGW) has been recently proposed to achieve a damage-free ground workpiece surface. The basic principle, ideas and characteristics of CMG with SAGW are briefly introduced in this paper. The CMG experiments using newly developed SAGW for Si wafer are conducted at the condition of dry grinding. The grinding performances are evaluated and analyzed in terms of surface roughness, surface topography and surface/subsurface damage of ground wafer by use of Zygo interferometer, Scan Introduction ning Electron Microscope (SEM) and Cross-section Transmission Electron Microscope (Cross-section TEM). The component of product of ground Si surface is studied by X-ray Photoelectron Spectroscopy (XPS) to verify chemical reaction between the abrasive / additives of grinding wheel and Si wafer. The CMG process model by using SAGW is developed to understand the material removal mechanism and generation principle of damage-free surface. The study results show that the material removal mechanism of CMG by using SAGW can be explained as a hybrid process of chemical and mechanical action.

Abstract: This paper investigates two kinds of grinding wheels prepared by the combination of mechanical alloy and hot-press sintering (MA-HPS). Scanning electro microscopy, Optical microscope, Talysurf surface profiler, X-Ray diffraction and Raman spectroscopy were used to characterize two kinds of grinding wheels and identify the removal mechanism. It was found that FeNiCr matrix-TiC (FMT) grinding wheel yielded higher removal rate than TiAl abrasiveless carbophile (TAC) grinding wheel, which conversely owned good polishing quality; diamond was removed by transformation diamond to non-diamond carbons and then removed by mechanically or diffusion to grinding wheel during polishing process with FMT grinding wheel. While TAC grinding wheel polishing CVD diamond film mainly depended on the reaction between diamond carbon and titanium.