Submicron particle adhesion and removal in chemical mechanical polishing and wafer cleaning processes

As feature sizes in semiconductor devices keep shrinking, cleaning techniques for silicon wafers and post-CMP device wafers becomes critically important. Although numerous studies have been conducted in cleaning process development, the effect of adhesion-induced deformation on particle removal has not been understood. In this thesis, the effects of particle adhesion on wafer cleaning and post-CMP cleaning are studied. The removal models of hydrodynamic, ultrasonic and megasonic cleaning techniques are evaluated. The particle removal mechanism of pad and brush asperities are also proposed for post-CMP cleaning.; The conventional CMP removal rate model considered surface deformation by abrasive particles as an elastic Hertzian process and did not included the effects of particle adhesion. In this thesis, a nonlinear removal model is proposed to implement Preston Equation with the consideration of the particle adhesion forces. For the first time, a new removal rate model incorporating the important contribution of particle adhesion forces is established to monitor the polishing process and the model's prediction is in good agreement with experimental removal rate data. The effects of the adhesion forces on the removal rate, surface roughness, surface scratch and post-CMP cleaning are also addressed.