32_28nm Beol Cu CMP Development for Ultra Low k Scheme

Abstract

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.