Study on silica slurry with surface active agent for improving planarization performance in tungsten chemical mechanical polishing (CMP)

With shrinkage of the minimum feature size to sub-14 nm, grain topography and protrusion/dishing issues in chemical mechanical planarization (CMP) processes have become increasingly important to address. In this study, we propose an advanced slurry formulation with a surface active agent to improving planarization performance in tungsten chemical mechanical polishing (CMP). We first studied slurries to remove nano topography caused by tungsten (W) grains. W topography creates a large error in the patterning process, which causes device performance problems. Therefore, the smaller the size of the device, the more important is the removal of the W topography. This research suggests ways to reduce nano topography that can become a problem in increasingly sophisticated semiconductor processes. When a surfactant is added, the polishing of W shows non-Prestonian behavior. This allows removal of the topography without loss of W when polished in a relatively high pressure region. To demonstrate this, we observed the CTAB concentration and non-Prestonian behavior in W CMP and observed the roughness change of the surface through AFM (Atomic Force Microscopy). Second, we studied nano-sized protrusions around the gate after Bulk CMP due to differences in material properties between W and silicon oxide (SiO2). In the presence of surface active agent, blanket removal rates on both W and SiO2 films showed non-Prestonian behavior at a low threshold pressure, which is explained by adsorption characteristics of the surface active agent on the films. To study the effect of the surface active agent on W protrusion, W-patterned wafers were polished at the threshold pressure. As the concentration of the surface active agent increased from 0 to 12 mM, W protrusion from patterns with line/space widths of 0.5 ??m/0.5 ??m decreased significantly from 186 to 30 ???. The mechanism on the significant decrease in W protrusion behavior in the presence of the surface active agent is discussed.Maste