Effect of electrostatic field on photoresist coating uniformity

As the critical feature size decreases below 0.25 mum in the manufacture of integrated circuits, the control of photoresist coating uniformity becomes more critical to the overall critical dimension control. Normally, the thickness uniformity of photoresist coated by spinning is mainly affected by resist viscosity, solvent evaporation rate, dispense speed, exhaust humidity, wind speed and resist (substrate) temperature. However what we observed on our manufacturing line revealed that electrostatic field induced by piezocrystal also impacted on thickness uniformity of photoresist. Two possible explanations of this phenomenon will be given in this paper. Though there is still not final solution to this problem, we propose track and resist designer to take this issue into consideration to improve the photoresist spin coating uniformity.