As outlined in the International Technology Roadmap for Semiconductors (ITRS), the stringent requirements for Cu interconnects has become more aggressive as the device size shrinks, wafers increase in diameter from 200mm to 300mm and the underlying dielectric's k value gets lower, not to mention the increasingly complex integration schemes employing various barrier, dielectric and cap/stop layers. Additionally, CMP defects that could be ignored in the past are becoming critical as the industry is forced to change its manufacturing practices to attain maximum yield with multilevel copper interconnects. Copper CMP processes are more complex and involve more than one polish step using different pads and slurries. For copper/TEOS wafer processes, and the next-generation Cu/low-k CMP processes, the slurry and its chemistry play a major role in controlling defects and various wafer metric parameters such as dishing, erosion, selectivity, non-uniformity, etc. Robust slurries must have the ability to repeatedly produce wafers with minimal defects and stable wafer metrics. This presentation focuses on minimizing various types of CMP defects on copper wafers through the proper selection of slurry chemistry, process optimization and slurry handling. A variety of wafers with different metal layers and test patterns were polished on an AMAT Mirra~R tool with Rodel~R EPL2361 for first step copper polish and Rodel~R CUS1351 for the barrier polish. It is evident that for a slurry/pad combination, process tuning of various equipment parameters helped minimize the CMP-related defects. Slurry handling, such as proper filtration methodology, slurry flow rate, pad rinse, and pad cleaning, along with properly tuned equipment parameters, resulted in further reduction of the amount and severity of the CMP-related defects. Since most of the CMP defects are preferentially positioned on the copper surface, the first-step copper process plays a significant role in the final defectivity of the wafer. It is very difficult to minimize defect levels if the first-step process introduces significant damage to copper lines or large surface areas such as bond pads. Since the second-step barrier polish process is typically designed to remove minimal copper and maintain the total metal thickness in the damascene structures, an optimized first-step copper removal process that dramatically lowers overall defect density definitely improves final defect levels after second-step barrier CMP.
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