Investigation of particle agglomeration with in-situ generation of oxygen bubble during the tungsten chemical mechanical polishing (CMP) process

Abstract

This research investigates abrasive particles agglomeration via interaction between O2 bubbles and slurry abrasives during the tungsten chemical mechanical polishing (W CMP) process. The abrasive particles in slurry were highly agglomerated due to higher volumes of O2 bubbles produced in the reaction between the catalyst Fe(NO3)3 and the oxidizer H2O2. Results obtained from a gas pressure sensor confirmed the generation of higher O2 volume via the decomposition of H2O2 at a high catalyst concentration and an increase in reaction temperature. The decomposed O2 volume rate at 80 °C was reported at the maximum value of 2.0 × 10−2 L/s at 120 ppm as compared to the moderate and minimum rates of 3.5 × 10−3 and 3.2 × 10−4 L/s for catalyst concentrations of 60 and 30 ppm, respectively. Images of O2 bubbles, captured using a high-speed camera, exhibited subsequent enhancement in average O2 bubble diameters of 91, 427, and 503 μm at 25, 60, and 80 °C, respectively. Analysis of surface scans confirmed large abrasive particles contamination on the TEOS wafer with an increase in the O2 bubble flow rate and bubbling time. Also, large abrasive particles agglomeration was observed in the presence of O2 bubbles as compared to no bubbles, as measured by dynamic light scattering DLS. It is believed that higher hydrophilicity of abrasive particles with O2 bubbles increased the adhesive force between the abrasive particles and the in-situ generated O2 bubbles. The high drag force generated during the collapse of O2 bubbles is essentially attributed a strong attractive force between the abrasive particles and the TEOS wafer which strongly binds with the abrasive particles and intensifies the defect level as particle agglomeration.