The effect of the polishing pad treatments on the chemical-mechanical polishing of SiO2 films

Polishing pads play an important role in chemical-mechanical polishing (CMP) which has recently been recognized as the most effective method to achieve global planarization in very large scale integrated circuit multi-level interconnects. In this work, we have investigated CMP performances of SiO2 as a function of the time of soaking the pad in water, pad conditioning, and pad surface temperature. It has been observed that the dynamic shear modulus G' of an IC1000 pad decreases to two thirds of its dry value during 5 h water soaking, while its oxide removal rate remains practically unchanged. The shear modulus of a polishing pad also decreases with the increase of pad temperature. For example, G' of an IC1000 pad drops approximately by a factor of 2 when temperature increases from 40 degrees C to 80 degrees C. Correspondingly, increases of both oxide removal rate and planarization efficiency, which is the step-height reduction per unit oxide removed on the ''up feature'', have been observed when the slurry temperature increases (which raises the pad surface temperature). Pad conditioning is a crucial step in CMP. The oxide removal rate decreases with time during a CMP process without pad conditioning until reaching a low steady-state value. On the other hand, the planarization efficiency increases with time during a CMP process without pad conditioning. Possible mechanisms which may lead to these observations are discussed.