The pH Effect On Chemical Mechanical Planarization Of Copper
- PDF / 118,395 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 237 Views
F6.6.1
The pH Effect On Chemical Mechanical Planarization Of Copper Tianbao Du and Vimal Desai Advanced Materials Processing and Analysis Center University of Central Florida Orlando, FL 32816, U. S. A. ABSTRACT This study explores the effect of pH on the chemical mechanical polishing (CMP) characteristics of copper in H2O2 and KIO3 based slurries under various dynamic and static conditions. High purity copper disc was used to study the dissolution and oxidation kinetics at various pH (2 to 10) with 5% H2O2 or 0.1M KIO3. Electrochemical techniques were used to investigate the dissolution/passivation behavior of Cu. The affected surface layers of the statically etched Cu-disc were investigated using X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). In 5% H2O2, the Cu removal rate decreases with an increase in pH and reaches minimum at pH 6, and then increases under alkaline conditions. XPS results indicate that the surface oxide formed at various pH values was responsible for this CMP trend. However, with 0.1M KIO3, the CMP removal rates were found to be lower at pH 2. The maximum was observed at pH 4, then the removal rate decreased with the increase of pH. The lower value of removal rate at pH2 was due to the fast interaction between Cu and KIO3 and the precipitation of CuI on the pad, which makes the pad glassy, resulting in lowered removal rates. This was confirmed by XPS measurements. The decreased CMP removal rates when the pH is higher than 4 might be due to the weaker oxidation power of KIO3 with the increase of pH. INTRODUCTION Copper is replacing aluminum as the interconnect metal in integrated circuits due to its higher electrical conductivity and superior electromigration resistance [1]. Integration of copper into an IC manufacturing process is implemented by using dual damascence technique [2,3], in which chemical-mechanical polishing (CMP) technique has been applied to remove the overburden material and to planarize the wafer surface. Compared to CMP for silicon dioxide, the copper CMP process needs more understanding, mainly due to the electrochemical interactions between slurry and copper film during polishing, and the coupled effect of these on the mechanical properties of the surface. Early studies on copper CMP by Carpio and coworkers [4] showed successful slurries containing oxidizer and complexing agents. H2O2 and KIO3 are the most common oxidizers used in commercial slurries [5]. CMP of copper can be conducted in either acidic or neutral or alkaline media [6-8]. The pH of the slurry plays a very important role in copper CMP removal. Usually, in alkaline condition, complexing agents such as ammonia need to be added in order to increase the solubility of copper by forming soluble copper-amine complexes. However, the neutral pH regime is more attractive, because the copper polish rate selectivity with respect to SiO2 is unfavorable under alkaline conditions, with associated ILD erosion. Future optimization of CMP for copper will require a deeper understanding of the m
Data Loading...
