Study On Chemical Mechanical Polishing Endpoint Detection Technology Based On Friction Force Online Measurement

Chemical Mechanical Polishing (CMP) is a key technology for forming a multilayer Cu interconnection structure during the integrated circuit (IC) manufacturing process. With the development of IC manufacturing technology, the feature size is narrowing incessantly and the number of interconnection layers is increasing. To reduce RC delay, Cu has replaced Al as the interconnection material beyond the 0.18μm technology node. During forming the multilayer Cu interconnection structure, under-polishing and over-polishing often occur when removing the excessive materials using CMP. The Cu CMP process needs to be reworked if under-polishing occuers. Over-polishing will result in Cu dishing and dielectric erosion. The CMP endpoint detection technology, which can determine accurately when to reach the ideal endpoing of CMP, is a key piece of technology to avoid over-polishing and under-polishing and improve the quality and efficiency of Cu CMP process.The most important processing parameter during the Cu CMP process is the friction force between the wafer and polishing pad, which is the key to realize the material removal. The method that determines when to reach the ideal endpoing of Cu CMP process based on the change of friction force or friction torque caused by the friction force during the Cu CMP process is considered to be the most feasible endpoint detection method. However, at present some theoretical research on the friction torque and friction force during the CMP process is not deep enough, and the usual detecting methods can not meet the structural requirement for the 300 mm wafer CMP system. Therefore, on the base of the reseach on the friction torque and friction force during the CMP process, in this thesis the friction torque and froction force monitoring technology during the CMP process is studied. The main research contents and conclusions are as follows:A model for calcutating the friction torque and friction force during the CMP process is established. The effects of the processing parameters, such as the polishing pressure, the rotational speed of polishing head and polishing platen, on the friction torque and friction force during the CMP process are analyzed. The experimental vertification has been done, and the results of theoretical analysis are well in accordance with that of experiments. The results of theoretical analysis and experiments show the rotational speed of polishing platen and the polishing pressure are the main process parameters affecting the friction force during the CMP process, and that the main parameters influencing the friction torque during the CMP process are the polishing pressure, the rotational speed of polishing head and polishing platen, and the direction of the friction torque does not change under the usual CMP processing parameters.A method for measuring the friction torque, friction force and polishing pressure during CMP process by a strain torque and three-axis force sensor is presented, and a CMP endpoint detection system is developed. The theoretical and experimental results show that the developed system can basically meet the need of endpoint detection for 300 mm wafer Cu CMP process.A signal processing method for determining CMP endpoint is presented. The wavelet denoising is firstly applied to reduce the noise contained in the measured signal, then the signal feature is extracted from the denoised signal, and finally the CMP endpoint is detemined based on the threshold derived using the chebyshev inequality. Applying the signal processing method, the endpoint detection experiment of Cu CMP process is carried out. The experimental results show that the signal processing method can determine when to reach the endpoint during the Cu CMP process.