Study On The Contact States Between Polishing Pad And Wafer In CMP

Chemical mechanical polishing(CMP),one of the most important processes in the manufacturing process of chips,is currently the only means to guarantee the submicron integrated circuit chips while maintaining overall and local planarization.With the decrease of the feature size of integrated circuits and the increase of the number of structural layers,the requirements for the global planarization effect of CMP become higher and higher.However,the current understanding of the CMP mechanism is not sufficient,especially the details of the interaction between the wafer,abrasive particles and the polishing pad under different contact states of wafer and the polishing pad in the CMP,the existence condition of each contact state and the material removal differences of them are lack of more in-depth understanding.Therefore,this research is carried out to provide basic theoretical guidance for the mechanism research of CMP.Firstly,the influence of polishing process parameters on the performance of CMP was explored through experiments.The experimental procedures of CMP and the instruments used in the experiment were described in detail.The effects of polishing pressure,polishing speed and polishing time on the surface quality of wafer after polishing and the material removal rate(MRR)during polishing were studied.The results show that there was a large deviation among the MRR's dependence on pressure and velocity in this experiment and the linear relationship proposed by Preston and the proportional relationship proposed by Tseng et al.Secondly,a contact model between the polishing pad and the wafer was established.And the contact area and contact pressure of the asperities in the elasto-plastic deformation phase were obtained.The result shows that both of them changed smoothly and continuously at the critical point.In particular,the contact pressure model established in this dissertation increases monotonically during the elasto-plastic stage,which was more in line with the actual situation.On this basis,considering the full elastic deformation,elasto-plastic deformation and full plastic deformation of the asperities on the surface of the polishing pad,a contact model between the wafer and the polishing pad was established,the real contact area and the average contact pressure of the contact interface were obtained as well.Then,the interaction laws of wafer,abrasive particles and the polishing pad under different contact states between wafer and polishing pad were studied.Based on the contact characteristics,geometric characteristics,mechanical balance of the wafer,abrasive particles and the polishing pad in each contact state,the depth of abrasive particles pressed into the wafer and polishing pad in different deformation states between wafer and polishing pad,the radius of the circle of contact among the abrasive particles and the wafer and the polishing pad,and the force on the individual abrasive particle were calculated out.The area and load distribution of abrasive particles and polishing pad in contact with the wafer at the contact interface were analyzed.The influence of abrasive particles deformation on CMP was also discussed.By calculating the deformation of the abrasive particle,the correction factor was given and the depth of the abrasive particle pressed into the wafer surface was calculated more accurately.Finally,the MRR equation is established under each contact state,and the existence condition of each contact state between the polishing pad and the wafer is studied.Two deformation modes were defined according to the structure of the polishing pad and the material removal rate equations with different contact states under the two modes are established respectively.Different dependences of MRR on pressure under various contact states were obtained and the transition conditions between them were determined.Through comparison with the previous experiments and the existing models,the rationality and completeness of the model were verified.