Investigation of planarization characteristics and novel defects in metal CMP affected by physical, chemical and mechanical factors

Chemical Mechanical Planarization (CMP) has emerged as a widely used technology in the present day fabrication of Integrated Circuit (IC) chips in microelectronics. With the device size shrinking every year, the need for smaller and faster chips is also increasing. The use of novel materials and methods of fabrication are becoming inevitable. The replacement of aluminum with copper, low-k dielectrics in place of SiO2 in the Back End Of the Line processing (BEOL), multi-level metallization are some of the recent developments which the industry has witnessed. The patterning of features with smaller critical dimensions requires the Depth Of Focus (DOF) to be as low as possible. The requirement on the DOF hence increases with the reduction in the critical dimensions hence increasing the planarity requirements. Three different factors that impact the planarity in metal CMP have been investigated in detail in the thesis. The first topic of the thesis deals with a novel defect in Cu patterned wafer polishing where the feature experiences extra erosion at the edge of the feature in comparison to the center. Various first-step Cu slurries with different passivation chemistries were employed in the study supported by CFD modeling of slurry flow over patterned features. The relative roles of slurry passivation and fluid flow on the inception of the defect were investigated. The second topic deals with the impact of process temperature in CMP. Different factors such as process variables, slurry components and its effect on process temperature were investigated. The effect of process temperature on slurry physical properties in turn affecting the slurry performance was investigated in detail with different first-step Cu slurries. The final topic of the thesis deals with some important factors that determine the planarization efficiency in metal CMP. The impact of slurry physical properties, pad and wafer specifications and slurry abrasive content were studied in detail.