32/28nm BEOL Cu CMP process with ultra low k scheme is investigated in the different aspects. Firstly the barrier metal (BM) slurry selection with proper selectivity is the most critical part to reduce topography. The topography can be minimized by precisely control BM slurry’s selectivity. Secondly, the layout design, such as pattern density, line and space width, has significant impact on WID variation. The test results show more topography correction at more dense Cu line for thinner line where BM polishing is the dominate factor. While for fat line, it shows less topography correction at more dense Cu line, since Cu clearance polishing dominates the final topography. Next k value shift evaluation with different barrier metal slurry, cleaning chemicals and post CMP thermal treatment conditions is also studied. The results indicate that although k value shift occurs during polishing, proper chemicals clean and post thermal treatment can restore parts even the whole of k shift. In addition, the removal of moisture and chemical penetrated into ultra low k film is the key of k value shift and reliabilities improvement.
Novel CuCMP slurry was evaluated under different polishing conditions and its impact on topography, thickness and in line test performance was investigated. Generally, topography, such as dishing and erosion, results from over-polishing after Cu polishing step and it can be modified and reduced by fine tuning process parameters. Firstly, different Cu polishing condition has been attempted to produce different topography for barrier polishing to compensate in order to cater for different integration scheme with different oxide material. Secondly, topography can be modified by barrier polishing condition due to high selectivity slurry is used during barrier polishing. Longer polishing time can cause Cu protruded in narrow dense arrays. Electrical data shows Cu polishing overpolishing time has impact on Rs, and longer overpolishing results in higher Rs, as well as high head/platen rotation speed.
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