The effects of pad design on chemical mechanical planarization (CMP) performance.

摘要

As the critical dimension (CD) has decreased and novel materials are increasingly used, CMP has emerged as a key enabling technology in semiconductor fabrication. However, the complicated removal mechanism is not yet fully understood. Specially, the effects of pads are not well understood and few rules for the pad design have been developed.; In this dissertation, the effects of pad design on CMP performance were investigated. To understand the micro topographies on a pad surface, a conventional pad was measured and characterized with a white light interferometer. Pores and wall structures were characterized over the horizon surface of the pad. Vertically, pad micro features were categorized according to their function with respect to the slurry (e.g. reaction region, transition region and reservoir region). The correlation between material removal rate (MRR) and pad degradation was also analyzed. As the pad surface degrades during polishing, the real contact area between pad and wafer increases, resulting in the decrease of the real contact pressure. And the pad degradation reduces the space for fresh slurry at the pad/wafer interface. Due to these phenomena in pad degradation, MRR dropped over 50% after only 4 minutes. By measuring surface height, bearing ratio, and histogram, the pad degradation with respect to MRR was quantitatively.; Based on this characterization of pad features, novel design rules were suggested for guiding pad development. The design rules have specific impacts at the macro, micro and nano scales. Three types of pads based on these design rules were prototyped using micro molding fabrication technology. Each pad has micro features for slurry flow control (type A: an array of cubes (40mum), type B: wing and V shape (40-200mum), type C: honeycomb (40-250mum)). The slurry efficiency of the type A and B pads was simulated with a commercial fluid simulation program, FLUENT and the type B pad showed 8 times higher slurry flow efficiency than the type A pad.; In an oxide CMP test, as the simulation results predicted, the type B pad showed 2 times higher MRR than the type A pad. The type C pad showed higher MRR than a conventional pad with the reduced overpolishing as expected. In copper CMP, the type C pad showed 5 times higher MRR than a conventional pad, and improved the dishing and erosion performance.; The polishing results showed that MRR is dependent on the designs of micro feature distribution, which control the slurry efficiency. And, overpolishing, dishing and erosion are dominantly affected by the size of contact area.; As CMP becomes more sophisticated in parallel with the advances in IC design, the consumables used should be "engineered" to provide optimum performance. The result of this dissertation can contribute to the development of new efficient CMP consumables.