Insights into Tungsten Chemical Mechanical Planarization: Part II. Effect of Pad Surface Micro-Texture on Frictional, Thermal and Kinetic Aspects of the Process

Abstract

The effect of different types of conditioners used during tungsten chemical mechanical planarization (CMP) on frictional, thermal, and kinetic aspects of the process was investigated. Based on previous work, regarding the effect of conditioner type and downforce on the evolution of pad surface micro-texture during break-in, two significantly different discs were employed (i.e. conventional vs. CVD-coated). First, mini-marathon style tungsten CMP runs were conducted for each disc. These were followed by tungsten polishing at various pressures and velocities. Pad samples were extracted before and after the mini-marathon polishing runs for confocal microscopy (CM) analysis of their surface micro-texture. Compared to the CVD-coated disc, the more aggressive conventional disc produced summits that were 60 percent taller and 50 percent sharper. It also caused for contact density to be more than four times higher likely due to the many more pad fragments that it generated. Consequentially, the surface micro-texture generated by the conventional disc produced a 50 percent higher directivity and a 60 percent higher removal rate. For both discs, we found that mechanical effects were rate-limiting for tungsten removal. The conventional disc resulted in a Preston's constant that was 24 percent higher than its CVD counterpart owing to its more aggressive nature and pad surface micro-texture that it generated.