Friction and Wear-Mode Comparison in Copper Electrochemical Mechanical Polishing

Abstract

This paper investigates friction and wear mechanisms of copper electrochemical mechanical polishing ͑ECMP͒ in pH and potential parameters as illustrated in the Pourbaix diagram. Three approaches were used in this study. First, a unique experimental setup was designed to investigate the effects of pH and electropotential on planarization. Second, the friction was measured in situ during polishing and used as a monitoring process. Third, the worn areas correlated with the frictional behavior of post-chemical mechanical polishing samples were characterized to study ECMP removal mechanisms. Results showed that friction maps can be generated in conjunction with the equilibrium Pourbaix diagram. This map is helpful in monitoring the removal rate and wear during copper ECMP. These findings can be used as guidance in ECMP process design and optimization.In the last two decades, chemical mechanical polishing ͑CMP͒ has emerged as a standard planarization process in semiconductor industries to fabricate integrated circuits. 1 The low-cost operation has been introduced to silicon, aluminum, tungsten, copper, shallow trench isolation, low-k, and micro/nanoelectromechanical systems. [2][3][4][5] Material removal studies of CMP have been conducted intensively in the past. These studies evaluate the effects of pH, 6,7 slurry chemistry ͑oxidizers, 6-9 complexing agents, 10,11 corrosion inhibitors, 12,13 and abrasives͒ 14-16 on planarization, and vary polishing parameters ͑rotating speed, downforce, 17 and hydrodynamic flow͒ 18,19 to observe the removal rate and generate removal-rate models based on mechanical and chemical approaches. 20-23 Overall, these studies have focused on indirect investigation of CMP, which often present challenging issues to study the removal mechanism due to the complexity of slurry chemistries. These findings also show there is a need to create a simple system in order to monitor and evaluate the removal mechanism of CMP.Planarization in CMP is achieved through rubbing a substrate through a pad in the presence of abrasive slurries. The friction force produced affects the quality of the surface finish. Our prior work has shown that CMP is a polishing technique and operates based on tribochemical principles. 15,24,25 The removal mechanisms involve mechanical abrasion by abrasives and pad, chemical wear, dissolution, and surface passivation due to slurry chemistry. 6,7 Friction plays an important role during polishing. To obtain a better understanding of CMP, we propose to "diagram" the effects of CMP in terms of its frictional behavior. In the present work, we developed a laboratory setup to be able to measure the friction coefficient in situ during polishing. Subsequently, we used an electrochemical approach to conduct copper CMP for pH and potential parameters on the equilibrium Pourbaix diagram. ExperimentalMaterials.-Copper wafers used in this study were electroplated on commercially available 8 in. diameter silicon substrates. The samples were cut into sizes of 3 ϫ 2 cm and were glued to a polishing ...

Development of High-Speed Copper Chemical Mechanical Polishing Slurry for Through Silicon Via Application Based on Friction Analysis Using Atomic Force Microscope

“…If there is high friction on the Cu reaction layer, Cu removal rate would be higher. [9][10][11] Table II shows a summary of slurry characteristics and Table III shows various Cu slurry performances (Slurry A, B, and C) for low, middle, and high-speed Cu removal rates. First of all, the friction for the Cu reaction layers of those slurries is measured using a conventional friction force microscope (FFM), revealing that the friction of high-speed slurry is not the highest of all the slurries.…”

“…8) There is much research on the correlation between the removal rate and friction during polishing, which indicates removal rate increases with increasing friction. [9][10][11] However, since it is considered that friction generates heat, temperature may increase the removal rate. 12,13) On the other hand, chemical components in polishing slurry may change the property of the Cu reaction layer to be removed, suggesting that hydrophobicity of the Cu reaction layer in slurry solution affects the frictional property.…”

Prove of hydrogen formation through direct potential measurements in the rolling slit during cold rolling

“…cold rolling) as proposed by Celis et al [13]. Dedy et al [25] [26] studied the behaviour of surface potentials of different metallic electrodes, scraped inside the solutions with different pH and described the phenomenon of an accelerated hydrogen evolution on freshly cleaved metallic surfaces in aqueous medium; it has been widely reported since then in the literature. For example, Burstein and Kearns [27] did an excellent study on describing an accelerated evolution of hydrogen from freshly generated surfaces of Cr, Fe and their alloys.…”

Transformable Oxidation of Tantalum in Electrochemical Mechanical Polishing (ECMP)

“…It has been reported that the removal mechanisms and surface quality in copper ECMP are affected by the applied potentials and pH values of electrolytes. [6][7][8] We have recently revealed that the mechanism of material removal in Ta ECMP is a synergy between formation and removal of Ta oxide. 9 Furthermore, it was found that there were different types of Ta oxides on the surface after ECMP.…”