Adhesion of Alumina Particles to Thin Films

An atomic force microscope was used to study the adhesion of alumina particles to copper, SiO 2 , and tungsten films in aqueous solutions used during integrated circuit manufacture. The solutions included deionized (DI) H 2 O and aqueous solutions containing dilute H 2 O 2 , or NH 4 OH . When different particles with the same nominal diameter and roughness contacted the same surface, variations in the removal force were observed. Although the particles were similar, the precise contact area and roughness distribution at the point of contact varied from particle to particle, and from location to location on the same substrate, and these effects altered the measured force. When the same particle was brought into contact with different substrates in the same aqueous solution, variations in the removal force were seen. This is due to differences in the roughness, surface chemical composition, and mechanical properties of the different substrates. Alumina particles adhere roughly five times more strongly to copper substrates in DI water than in 0.2 wt % H 2 O 2 in DI water. Alumina particles adhere roughly three times more strongly to SiO 2 substrates in 0.2 wt % H 2 O 2 in DI water or 0.2 wt % NH 4 OH in DI water than in DI water alone. Alumina particles adhere roughly two times as strongly to tungsten surfaces in 0.2 wt % H 2 O 2 in DI water than in DI water alone, and they adhere roughly two times as strongly in 0.2 wt % NH 4 OH in DI water than in DI water alone.