Thermoanalytical Characterization Of Thermoset Polymers For Chemical Mechanical Polishing

摘要

Chemical Mechanical Polishing (CMP) has emerged as the premier technique forrnachieving both local and global planarization in sub 0.5 micron silicon integrated circuitrnmanufacturing. In a CMP process, a rotating polymer-based pad is pressed against thernmetal/oxide surface layers of a wafer. Normally, CMP occurs in the presence ofrnchemically active slurry. The removal of a polished layer and surface planarization isrnachieved due to combination of various factors, such as consumable parameters, CMPrntool design, etc., which jointly affect polishing performance. CMP process depends onrnprocess conditions, chemical interaction between slurry, pads, and polished metal layers,rneffects of heat due to mechanical friction, etc. influence. Thus, optimization of CMPrnprocess depends on optimization of the properties of CMP consumables. In turn,rnprediction and optimization of the CMP consumable properties depends on their accuraterncharacterization.rnIn this paper, several advanced analytical methods are used to analyze the thermomechanicalrnproperties of polyurethane thermoset pad under conditions similar to thosernfound during CMP processing. Two classes of CMP pads ("Soft" and "Hard” pads) werernstudied. The retention of the pad properties after exposure to deionized water and slurryrnwas monitored using Thermal Mechanical Analysis (TMA), Dynamical MechanicalrnAnalysis (DMA), Modulated Differential Scanning Calorimetry (MDSC), ThermalrnGravimetric Analysis (TGA). In addition, effects of heat treatment were investigated. Thernpads were exposed at room temperature to DI water and slurries for different timerndurations. Additionally, to simulate the effect of slurry pH on the slurry absorption andrnpad properties, some pad samples were exposed to various pH buffer solutions.rnThermal and mechanical propertie s of the pads were affected by soak in slurryrnand water. The most interesting findings are listed below:rn1. TMA results for soft pads indicated considerable shrinkage of the pads after soakrnfor four weeks in slurry and water.rn2. DMA results for soft pads showed 40% decrease of glassy modulus and 25%rndecrease of macromolecular mobility after pad soak in slurry for four weeks.rn3. MDSC results for hard pads revealed irreversible endothermic reaction in thernrange of 20℃ to 130℃. Heat of this reaction was not affected by soak in waterrnfor as long as one month; however, it increased significantly after soak in slurryrnfor two weeks.rnCorrelations between the experimental observations, pad molecular structure, and padrnperformance in CMP processes will be discussed.