Cu post-CMP cleaning and the effect of additives

Abstract

This article investigates the adhesion force of silica particles to copper films, and the role of additives on the adhesion and removal of those particles during post-CMP cleaning. Four different cleaning solutions were designed to understand the effect of adhesion forces on particle adhesion and removal: deionized water, citric acid solution with BTA at pH 2, a mixture of citric acid and BTA adjusted at pH 6 with NH4 OH, and the same mixture with TMAH at pH 6. The results show adhesion force decreases as the citric acid concentration increases because of the larger repulsive electrostatic interaction between surfaces. The addition of benzotriazine (BTA) in the cleaning solution initially decreases adhesion, then increases it at high concentrations due to the change in zeta potentials. The addition of tetramethylammonium hydroxide (TMAH) to citric acid increases the particle adhesion force. However, the addition of NH4 OH results in the lowest adhesion forces.