Cleanroom design for Cu-CMP processes

With the progress towards more integrated semiconductor devices and narrower wiring pitches, there has been a shift from aluminum wiring to the use of copper wiring due to its lower electrical resistance. However, the high diffusion coefficient of copper has adverse effects on the device characteristics. There is also some concern that the CMP (chemical mechanical polishing) process used to form copper wiring is a source of chemical contamination in cleanrooms. Experiments have confirmed that the copper contained in the waste fluid produced during wafer polishing is scattered around the inside of the CMP unit. Copper leaking outside the units during maintenance is safely removed by a cleanroom HEPA filter since the copper quickly oxidizes to form particles. However, the copper adheres to the shoes and gloves of the operators who maintain the CMP units and causes cross-contamination to other process areas. Because 300 mm wafers are transported automatically using FOUPs (front-opening unified pods), we anticipate that in future, different processes will be combined in cleanrooms that share the same conventional air-flow space. In this context, cross-contamination from the Cu-CMP process backside can be prevented by segregating the cleanroom so as to isolate the copper process wafer carriers.