THE EFFECT OF THE POLISHING PAD TREATMENTS ON THE CHEMICAL-MECHANICALPOLISHING 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 circui t multi-level interconnects. In this work, we have investigated CMP pe rformances of SiO2 as a function of the time of soaking the pad in wat er, pad conditioning, and pad surface temperature. It has been observe d 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 remo val rate remains practically unchanged. The shear modulus of a polishi ng pad also decreases with the increase of pad temperature. For exampl e, G' of an IC1000 pad drops approximately by a factor of 2 when tempe rature increases from 40 degrees C to 80 degrees C. Correspondingly, i ncreases of both oxide removal rate and planarization efficiency, whic h is the step-height reduction per unit oxide removed on the ''up feat ure'', have been observed when the slurry temperature increases (which raises the pad surface temperature). Pad conditioning is a crucial st ep in CMP. The oxide removal rate decreases with time during a CMP pro cess without pad conditioning until reaching a low steady-state value. On the other hand, the planarization efficiency increases with time d uring a CMP process without pad conditioning. Possible mechanisms whic h may lead to these observations are discussed.