Study on Chemical Mechanical Planarization Performance Characteristics of Cobalt CMP Slurry according to Corrosion and Passivation Behavior

Abstract

As the integration of semiconductor increases, laminated structure is becoming more complicated. With this trend, Chemical Mechanical Planarization(CMP) became a key process in semiconductor process. Copper, Aluminum, and Tungsten have been used in metal wiring process. However, with smaller dimensions of structure and resistance is getting more worse, Cobalt(Co) has emerged as a leading candidate for the conductive layer replacement. In the CMP of Co, there are many conditions to be satisfied. Among them, removal rate and surface characteristics are key performance parameter. In general, however, there is a trade-off in their relationship. In acidic condition, I can get high removal rate. However, there are corrosion pits on the surface. At pH 10, There are no corrosion pits. However, it does not guarantee a high removal rate. This thesis examined slurry performance in acidic and alkaline conditions. At first, I used 5-amino-1H-tetrazole as a corrosion inhibitor in acidic condition and an X-Ray Photoelectron Spectroscopy analysis and potentiodynamic polarization analysis were conducted on how this chemistry inhibits corrosion. Second, potassium persulfate was used as an oxidizer that must be added in metal CMP to improve Co film removal rate in alkaline condition. Lastly, performance comparison of each condition was carried out. Acidic slurry using corrosion inhibitor showed a high selectivity of 240:1, while alkaline slurry using K2S2O8 obtained 30:1. However, it has better performance in alkaline condition in terms of surface roughness. The surface roughness Rq in acidic slurry was about 1.6 and 1.4 in alkaline slurry slightly lower than 1.6. There are many other characteristics to compare, however in this paper, the most representative characteristics were compared. Based on these characteristics, I expect more detailed studies to be conducted.