Completely Planarized W Plugs using MnO2 CMP

In tungsten (W) polishing, MnO2 has been used as an abrasive to form plugs without etching holes in seams during CMP. We found that MnO2 polishes 1.5 times faster than the standard A12O3 abrasive, and can be completely removed during the cleaning process. Introduction Chemical Mechanical Polishing (CMP) is used to form tungsten plugs [1, 2]. In CMP, only the tungsten surface is oxidized by the oxidizer in slurry. This oxidized film is removed by an abrasive which is followed by a rapid reformation of oxidized film. Continuous cycles of formation, removal, and reformation of oxidized film continue until he plug is formed [3]. Currently, the standard commercial abrasive used is Al2O3, and an oxidizer is mixed into the slurry to oxidize the tungsten surface [4]. This added oxidizer may make holes in seams, or abrasive may remain after cleaning because there is no cleaning solution which dissolves the A12O3. We searched for an abrasive which is in itself an oxidizer and readily dissolves in a cleaning solution. We found that MnO2 satisfies these conditions. Figure 1 is a diagram of the polishing model using the MnO2, The MnO2 polishes the tungsten surface, which was oxidized by the MnO2 oxidizer. This means that we do not need to add additional liquid oxidizer and can therefore avoid seam etching. The MnO2 is also readily soluble in an appropriate cleaning liquid, so that no abrasive remains on the surface after cleaning. Experiment First we examined the dependence of the polishing rate on the MnO2 concentration. Table 1 lists the polishing conditions used for our experiments. We then examined the effects of the MnO2 abrasive to determine if there were any seam etching effects. We deposited a tungsten layer on our SiO2 test piece and then used our MnO2 abrasive for CMP. We then used Scanning Electron Microscopy (SEM) to determine the extent of