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

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 NH 4 OH 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 NH 4 OH. 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.