CMP related/CMP revealed short- and long-range integration interactions in copper dual damascene technology
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CMP related/CMP revealed short- and long-range integration interactions in copper dual damascene technology Yehiel Gotkis and Rodney Kistler Lam Research Corporation, Fremont, CA, USA CMP/Clean Technology Division More than 4 years have passed since IBM made the official announcement approving copper dual damascene (Cu2D) technology, which drew the rest of the semiconductor world into the Cu2D race. And the technology appeared to be a hard nut to crack. Nowadays, after more than three years of extensive R&D work, the EOL yields are still low, and a lot of process integration work has to be done to make it mass production ready. CMP is one of the most, if not the most, critical and important operations in Cu2D technology because, in the first place, yields are extremely sensitive to CMP performance. Secondly, as it goes through all metal deposits (barrier, Cu seed, and Cu bulk) and touches the dielectric, CMP represents a kind of reversed processing sequence. In this sense, it can be considered not only as a manufacturing operation, but also as a quality control procedure, revealing problems appearing at the previous process steps. After most of the inherent process issues are solved and particular technology operations passed into a reasonably mature state, the next level of so-called process integration, or operation interaction problems has to be resolved. At this phase the key to success is to link the problem to its true root cause, which frequently is located at a remote operation step, and it takes more efforts to discover the link than to fix the problem. CMP related factors affecting yield. In addition to the well-known metal and oxide loss and formal particulate defectivity, which are in most cases directly related to CMP performance, some other yield affecting issues appear at the post-CMP wafer surface: 1) scratching; 2) micro-cracking; 3) corrosion; 4) by-products re-deposition; 5) remaining residuals; 6) voids; 7) barrier integrity damage; and 8) oxide depressions/discoloration. Scratching issues. Cu is a very soft and easily scratched material. The following objects can be listed as potential Cu and dielectric scratchers: slurry abrasives (agglomerates), tool debris/delaminated diamonds, pad roughness features (groove edges, conditioning created features, etc.), and solid process byproducts accumulated over the pad surface, causing shallow “chemical” scratching (CuO + Cu →2Cu2O). Methods for scratch prevention in Cu CMP: 1) Avoid usage of silica-based slurries for Cu removal without a well-justified reason, because Cu2+ ions stimulate silica agglomeration. 2) Minimize accumulation of process by-products over the pad surface by proper pad conditioning and cleaning. 3) Avoid excessive pad grooving and pad over-conditioning. 4) Prevent flake formation during barrier removal phase by use of pseudo-mechanical rather than barrier aggressive slurries for barrier removal. Removing material during CMP results in accumulation of by-products and debris in pad pores and groves, absorption of chemicals by pad mater
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