Development of Highly stable ceria slurry in acetic acid-ammonium acetate buffer Media for effective chemical mechanical polishing of silicon dioxide

Shallow trench isolation (STI), as a key technology for device isolation, is commonly planarized with ceria slurry in chemical mechanical polishing (CMP). Due to the ceria particles are easily agglomerated, the stability of ceria slurry is still a key issue at present. In order to obtain excellent polishing performance for dielectric, it is necessary to prepare the ceria slurry with stable dispersion. This paper is to propose a new dispersant based on acetic acid that can improve the stability of ceria slurry. By comparing the dispersibility of acetic acid with that of a formulated acetic acid-ammonium acetate buffer solution, the buffer solution was chosen as more effective dispersant. The addition of buffer solution was more beneficial for the stability of the slurry. After 7 days, the zeta potential of ceria decreased from 46.47 mV to 35.01 mV (decreased about 24.6%) with the addition of acetic acid, whereas it decreased from 51.22 mV to 42.19 mV (decreased about 17.6%) with the addition of buffer solution. Furthermore, during the CMP process, the removal rate of TEOS was improved (from 621.59 nm/min to 694.77 nm/min) along with surface roughness (Ra, from 0.37 nm to 0.07 nm). The mechanism was characterized using X-ray photoelectron spectroscopy (XPS), UV–vis spectrometer (UV–Vis), and molecular dynamic simulation. The buffer solution increased the concentration of acetate ions in the slurry, which not only enhanced the adsorption between acetate ions and ceria but also promoted the generation of Ce3+ and oxygen vacancy. Furthermore, the free electrons of Ce3+ facilitated the breaking of the Si–O–Si bonds through electron transfer, increasing the removal rate of silicon dioxide.