Contact Pressure Distribution in the Chemical Mechanical Planarization of 450mm Wafers
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1249-E05-05
Contact Pressure Distribution in the Chemical Mechanical Planarization of 450mm Wafers Pádraig Timoney1, Eamonn Ahearne1 and Gerald Byrne1 1 Advanced Manufacturing Science (AMS) Research Centre, Mechanical Engineering, University College Dublin, Belfield, Dublin 4, Ireland. ABSTRACT Optimization of spatial uniformity of material removal in chemical mechanical planarization requires an understanding of the mechanics of the wafer carrier system. Finite element analyses have been carried out by researchers identifying relationships between von Mises stress distribution and material removal rate. However, in many of these wafer scale models, the derivation of the material properties of the polishing pad and sub pad is unclear and consequently a large variation in values used is observed. Models are generally validated with a procedure different to that simulated in the model and with different output variables. Few models have incorporated the industry standard method of pressurizing the backside of the wafer independently to the wafer carrier loading using a pressurized air chamber located directly behind the backside of the wafer. The anticipated introduction of 450mm diameter wafers has surprisingly not been accompanied by wafer scale models investigating the issues that will arise from the diameter and thickness scaling ratio of the wafer. This paper presents a unique approach to finite element modeling of CMP incorporating realistic boundary conditions for the wafer carrier and platen assemblies. Model predictions of interfacial contact pressure for a 200mm wafer loaded by a lip seal type carrier head were validated by unique measurements of the contact pressure between the wafer and the pad using Fujifilm Prescale TM pressure measurement film and accompanying analysis software. The results demonstrated a close correlation between the model’s prediction and the measured values. Results are presented for the upscaling of this validated model to 450mm wafer dimensions. The results indicate a doubling of the contact pressure maximum values compared to the 200mm wafer model. These results illustrate the extent of the challenge facing CMP tool vendors in increasing the level of control of the mechanical force distributed by the wafer carrier on 450mm wafers. The model can be used as a design tool to optimize machine and process parameters. INTRODUCTION The challenges facing the chemical mechanical planarization process in semiconductor manufacturing continue to be augmented by wafer diameter increases, feature size decreases, device density increases and the demands for increasing device efficiency. Optimization of the von Mises stresses in CMP requires optimization of the wafer carrier and the pressure distribution it delivers to the backside of the wafer [1]. The resulting pad wafer static von Mises stress distribution is reported to be proportional to the polishing uniformity [2]. Recent finite element modeling work by Chen et al. [3] studied the effect of polishing pad elasticity and geometry, the mecha
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