Study On Nonlinear Compression Behavior Of Polishing Pad

In recent years,higher requirements on the integration of chips,performance and production costs are putting forward with the development of integrated circuit industry.In order to improve the integration of IC chips and reduce the production costs,the feature size is shrinking while the wafer size is expanding continuously.Due to this trend,the planarization process,which is a key technology of semiconductor manufacturing,is facing great challenges.Chemical mechanical planarization(CMP)has been an enabling technology in the planarization with excellent reproducibility and acceptable product yields through mechanical removal with the help of chemical reactions.The contact behavior of pad have a great influence on both chemical reaction and mechanical action in CMP process.The polishing pad is a main consumable in the chemical mechanical polishing(CMP)system.The properties of the surface layer have a significant impact on planarization performance in CMP.In recent studies,it has been assumed that pad can be decomposed into asperity and the bulk layer.The stiffness of the asperity layer mainly dominates the slurry retention on plate and the material removal rate,while the pad bulk stiffness is hypothesized to most strongly impact initial film thickness,within die uniformity and layout pattern density effects.However,the relationship between pad’s physical and structural parameters and compression stiffness is not explicit,and the existing methods are difficult to obtain local deformation of the multi-layered and multi-level structured pad Besides,due to the viscoelastic properties of the pad asperity,the real contact area is changing with time.The prediction of the real contact area determines the prediction of the material removal rate.In this paper,the experimental and theoretical models are used to study the contact behavior of the polishing pad,the mechanical properties and deformation of the polishing pad.In this study,the basis for the quantitative analysis and method for prediction of the CMP process are established,which can be utilized to guide the optimization of the process parameters and help the design of pad of next-generation.The main contents of this paper are as follows:(1)Based on the experimental analysis of the compression stiffness of the polishing pad with multi-stage structure,an effective spring model considering the deformation of the asperity layer of the polishing pad was established.In the proposed model,the relationship between the pad stiffness and the geometrical parameters is depicted explicitly,which is convenient for designing the groove structure to achieve a desirable polishing performance.(2)The actual environment of the polishing pad was simulated to observe the microscopic contact behavior under varied loading history,and the loading history on the microscopic contact behavior of the polishing pad was analyzed.Additionally,the viscoelastic properties of the pad asperity were studied.The viscoelastic constitutive model is used to predict the change of the real contact area caused by the deformation accumulation of the polishing process.(3)The local deformation of the Politex pad and the IC1000/SUBA IV pad were measured by means of Digital Image Correlation method(DIC),Through this method,the deformation characteristics of the polishing pads were discovered,which is helpful in the quantitative analysis of CMP process.