Polishing Slurries with Aluminate-modified Colloidal Silica Abrasive
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Polishing Slurries with Aluminate-modified Colloidal Silica Abrasive Irina Belov *, Joo-Yun Kim, Paula Watkins, Martin Perry and Keith Pierce Praxair Electronics, Indianapolis, Indiana ABSTRACT This study has developed a route for increasing stability of colloidal silica particles in acidic polishing slurries. Drastic improvement in colloid stability has been achieved by using SiO2 particles with increased negative surface charge through doping /modification with metallate ions Me(OH)4¯, particularly with aluminate ions. Novel Copper CMP slurries employing aluminate-doped colloidal silica provide high removal rates, good planarization and dishing performance, demonstrate required stability and long shelf life while preserving all the morphological advantages of colloidal abrasive particles. The developed route is also useful for production of acidic polishing slurries for other applications, such as Tungsten and STI CMP, as well as in polishing hard drive disks, fiber optic connectors, etc. INTRODUCTION CMP has been established as a key processing step to remove copper overburden during formation of multilevel interconnects of advanced generation IC devices and to meet stringent planarization requirements imposed by smaller device dimensions, increasing packaging density and multiple metal interconnect levels. Successful CMP slurry for the removal of copper overburden must provide high polishing rate, high planarization efficiency, uniformity of copper line thickness across the wafer, low copper dishing and a wide processing window for clearing of copper residue. Also, the post-CMP wafer surface must be free of defects such as microscratches, pits and particles (1). These performance requirements have resulted in the current trend of developing Copper CMP processes with reduced contribution of mechanical removal, through either reduction of polishing downforce or employing softer abrasive particles and low abrasive content (2- 4). Slurries containing colloidal silica - amorphous, nonagglomerated particles with spherical morphology and lower hardness than fumed silica and alumina abrasives - tend to give smooth post-CMP surfaces with fewer defects. However, the reduced mechanical action of abrasive particles results in the decreased removal rates – a well-known drawback of colloidal SiO2-based slurries. Acceleration of copper removal can be achieved by using more aggressive slurry chemistries, i.e. lower pH, higher concentration of removal accelerators. However, pH decrease as well as increase in ionic strength of slurry associated with increasing content of removal accelerating compounds leads to reduced surface charge, hence destabilization of colloidal SiO2 particles (5) and irreversible deterioration of slurry performance and shelf life. This work has been aimed at the development of stable acidic low-abrasive colloidal silica slurries that meet the polishing / planarization requirements for copper overburden CMP. EXPERIMENTAL Aqueous low-abrasive (LA) slurries of the present study contained unmodified as
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