Performance evaluation of cleaning solutions enhanced with tetraalkylammonium hydroxide substituents for post-CMP cleaning on poly-Si film

The cleaning solutions augmented with tetraalkylammonium hydroxides (TAAHs) with various chain-lengths of hydrocarbon substituents were developed for post-poly-Si chemical mechanical polishing (CMP) cleaning. The cleaning performance with respect to particle, organic, and metal removal as well as surface roughness was evaluated for a series of 3% NH₄OH solutions dosed with 0.26 M of a TAAH and 100 ppm of ethylenediaminetetraacetic acid (EDTA). The experimental results demonstrated that the cleaning solutions enhanced with these surfactants (TAAH) and a chelating agent (EDTA) achieved significantly better removal efficiencies of particle and metal impurities than the control solution containing 3% NH₄OH only. A conceptual model involving surface adsorption and double-layer formation was used to postulate the aqueous-phase surface interactions between the tetraalkylammonium cations and the poly-Si surface, and to explain the removal mechanisms of particle and metal impurities from the surface. The improved electrical properties (current density-electric field and charge-to-breakdown characteristics) of the post-CMP capacitor after cleaning further demonstrated the reliability and feasibility of the proposed cleaning recipes.