Post Tungsten CMP Cleaning: Optimization for Cleaning Efficiency and Corrosion Reduction

Abstract

Tungsten chemical-mechanical planarization (W CMP) is among the first applications of the CMP process implemented in high volume semiconductor manufacturing. Alkaline chemicals such as diluted NH4OH have been the predominant choice of post W CMP clean due to charge repulsion between W and dielectric/abrasive surface in high pH. However, W dissolution occurs spontaneously above pH ∼ 4.0. Consequently, W corrosion can happen during post-CMP cleaning. From that perspective, acidic chemistry (e.g., pH < 4.0) seems a more benign choice to protect W, although at such low pH, isoelectric potential curves suggest coulombic attraction between W and oxide/silica surfaces, making it unfavorable for particle removal. The above pH dilemma for post-CMP cleaning and W protection can be managed by adding corrosion inhibitor to an alkaline chemical. Results from blanket and patterned wafers suggest reduction in surface defects and W dissolution can be accomplished simultaneously by an alkaline clean chemical with corrosion inhibitor (pH ∼ 9.78), which shows high cleaning efficiency and reduced W loss than citric acid-based chemical (pH ∼ 2.66), DIW, and diluted NH4OH. In addition, we show that DIW alone can induce severe W dissolution in features of fine geometry. Possible counter measures against such DIW-induced W corrosion are discussed.