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 O-2 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 O-2 bubbles produced in the reaction between the catalyst Fe (NO3)8(3) and the oxidizer H2O2. Results obtained from a gas pressure sensor confirmed the generation of higher O-2 volume via the decomposition of H2O2 at a high catalyst concentration and an increase in reaction temperature. The decomposed O-2 volume rate at 80 degrees C was reported at the maximum value of 2.0 x 10(-2) L/s at 120 ppm as compared to the moderate and minimum rates of 3.5 x 10(-3) and 3.2 x 10(-4) L/s for catalyst concentrations of 60 and 30 ppm, respectively. Images of O-2 bubbles, captured using a high-speed camera, exhibited subsequent enhancement in average O-2 bubble diameters of 91, 427, and 503 mu m at 25, 60, and 80 degrees C, respectively. Analysis of surface scans confirmed large abrasive particles contamination on the TEOS wafer with an increase in the O-2 bubble flow rate and bubbling time. Also, large abrasive particles agglomeration was observed in the presence of O-2 bubbles as compared to no bubbles, as measured by dynamic light scattering DLS. It is believed that higher hydrophilicity of abrasive particles with O-2 bubbles increased the adhesive force between the abrasive particles and the in-situ generated O-2 bubbles. The high drag force generated during the collapse of O-2 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.