磨料对铜化学机械抛光过程的影响研究

Study on Abrasive Effect in Copper Chemical-Mechanical Polishing

利用CP-4型抛光试验机对直径为50.8 mm、表面沉积厚530 nm的铜硅片(表面粗糙度Ra为1.42 nm)进行化学机械抛光(CM P)试验,评价了CM P过程中不同磨料作用下的摩擦系数和材料去除率;利用ZYGO表面形貌分析系统测试含不同磨料抛光液抛光后的硅片表面粗糙度;采用扫描电子显微镜分析CM P后的铜硅片表面损伤形貌.结果表明,磨料的浓度和粒径直接影响CM P过程的摩擦系数:采用5%粒径25 nm硅溶胶为抛光液时的摩擦系数低于超纯水抛光时的摩擦系数;当磨料的添加量和粒度增加时摩擦系数增大.在相同试验条件下,采用10%粒径25 nm硅溶胶抛光材料的去除率为50.7 nm/m in;粒径为1μm白刚玉磨料的抛光材料去除率为246.3 nm/m in;单纯磨料使铜硅片表面变得粗糙,即用10%粒径25 nm硅溶胶抛光后的表面粗糙度仍大于原始表面(Ra值达3.43 nm);在单纯磨料或超纯水为抛光液抛光下铜硅片表面出现划伤.

In order to test friction coefficient and material removal rate of different abrasive, copper Chemical-Mechanical polishing （CMP） experiment was performed using CETR polisher with wafers in 50.8mm and deposited 530 nm copper. Surface roughness of wafer polished by different abrasive was measured by ZYGO surface analysis system. Surface of wafer was also analyzed by means of SEM to explore wear scar of abrasive. During polishing test, polishing carrier rotated at 150-250 r/min,applied pressure was 26.7-53. 4N, and slurry flow rate was 100 mL/min. It was found that concentration and particle size have directly effect on friction coefficient of copper CMP process. Friction coefficient using slurry with 5% 25 nm colloidal silica is lower than that using ultrapure water. Friction coefficient increased with abrasive size and concentration increased. Size of abrasive directly influencs material removal rate of copper CMP. Under the same condition, material removal rate of copper polished with10% 25 nm colloidal silica is 50. 7 nm/min,but for1μm sized Al2O3 abrasive, material removal rate of copper is 246.3 nm/min. Abrasive made surface rough during process of CMP. Surface roughness of wafer polished with 10wt%25 nm colloidal silica is 34. 3 А, which is also large than that of original surface. Ultrapure water and pure abrasive as slurry without addition of any additive can produce nano meter scale scratch on surface.