Effect of conditioner type and downforce, and pad break-in time, on pad surface micro-texture in chemical mechanical planarization

The impact of conditioner types and downforces during pad break-in, and the resulting effects on the evolution of pad surface micro-texture was investigated. Two different conditioning discs were used with 3 possible downforces to break-in pads. Pad samples were extracted throughout the break-in process and confocal microscopy was used to analyze the samples for their surface micro-topography and pad-wafer contact. Results showed that all experimental cases resulted in similar trends of mean summit height. More importantly, each case resulted in a different evolution of summit height distribution. Comparing the two discs used, one disc was observed to be more sensitive to changes in downforce compared to the other. The differences in the behavior of the two discs is explained by the differences in cutting mechanics, which is due to the different characteristics of the two discs. Both discs generated large amounts of pad fragments, which were shown to cause pore obscuration on the pad surface. In 4 out of 5 cases, the pad surface micro-texture stabilized within 30 minutes of break-in and all cases stabilized within 60 minutes. This work demonstrated the importance of understanding how different conditioner types react to changes in downforce when breaking-in a pad.