Effect of the End Effector

An end effector, also called a pad dressor or a pad conditioner, is used to condition the polish pad to retrieve polish rate. If this is not done, the surface of a pad can become glazed and the pad austerity lost (see Fig. 9). The austerity of a pad is required in CMP otherwise, hydroplaning will occur, which means that contact between a pad and a wafer surface no longer exists. 

An end effector consists of diamond grit or similar silicon carbide materials. These extremely hard materials can scrape off the topmost layer of a pad during conditioning if properly deployed, an end effector can help flatten a polish pad and improve polish uniformity. If not, the surface can be roughened and the nonuniformity worsened. 

If back pressure is used in CMP, the wafer can be polished more at its center. The resultant pad profile is flat. In this case, the end effector conditioning profile would also be set flat. Otherwise, a mismatch between the polishing profile and the end effector conditioning profile would cause more problems. 

Another issue with the end effector is its down force during conditioning. This down force must be as low as possible, as long as the polish rate remains stable. If the down force is set too high, the resultant high wear rate shortens the pad life. Once the grooves on the pad are worn out, the pad can no longer deliver slurry. 

Deposit Less, Polish Less vs Deposit More, Polish More (Uniformity vs Planarity) 

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