Effect of Catalyst Induced Bubble on Particle Agglomeration during W CMP Process

Abstract

As the design rule of semiconductor devices have decreased, W RMG (Replacement Metal Gate) CMP in FEOL (Front End of Line) and W contact CMP in MOL (Middle of Line) have been introduced as essential processes in semiconductor device manufacturing processes of 14 nm or less. Abrasive particles contained in the W CMP slurry are agglomerated into a large particle during the CMP process. The large particle size over 0.5 μm is one of the major causes of metal and dielectric defects due to scratches or contaminants formed on the wafer surface during the CMP process. Because it will affect the yield of semiconductor device manufacturing, it is necessary to investigate and control the cause of the particles agglomeration and its defects. In this study, the oxygen (O2) bubble generated and its effect on abrasive particles agglomeration induced by the catalytic reaction during W CMP slurry was studied. In this experiment, TEOS (Tetraethyl orthosilicate) wafer with 8-inch diameter was used and 3 wt% of 140 nm colloidal silica was used as abrasive particles. As additives, Fe-based catalysts, FeSi and Fe(NO3)3, and 1.5 wt% H2O2 were used to generate bubbles at various catalyst concentrations and temperature conditions. The oxidizer H2O2 is decomposed by the catalysts to generate ∙OH radicals, which form a stable passivation layer of WO3 component. O2 bubbles were generated during the decomposition of H2O2, and the effect on the actual particle agglomeration was evaluated. First, the amount of bubble generated was evaluated using a gas pressure sensor, and the shape and behavior of the bubbles were confirmed using a high speed camera. As a result, it was confirmed that as the catalyst concentration and temperature increased, the amount of bubble generation increased, and the size and density of the bubble also increased. Accordingly, it was predicted that the particle agglomerated rate would be increased under the conditions where a lot of bubbles were generated. In the case of confirming the agglomeration of the particles, the size distribution of the particles after the catalytic reaction was measured using DLS and Accusizer. With increase in catalyst concentration and reaction temperature, enhancement in large particles was observed. In addition, the O2 bubble was injected directly into the solution with the different bubble exposed rate and time to compare the contamination level. The solution was contaminated on the wafer with spin coater, and the surface of the wafer was analyzed using a surface scanner and an optical microscope. It was confirmed that the high contamination level of particles appeared under high bubble flow rate. Therefore, it was found that the presence of bubbles is one of the causes of the particle agglomeration. Thus, careful consideration is necessary to control the bubble through additives such as H2O2 stabilizers.