Poly silicon is the preferred gate material in terms of fabrication process in the fab, and gate height control is one of the factors determining transistor performance. If we can have a better uniformity control of poly CMP, it will be beneficial not only to CMP but also to the downstream etch process. Thus, we evaluated two poly slurries (Slurry A, B), analyzed each characteristic and performance on the device area and applied to 7nm CMP process furthermore.

We found that slurry A, ceria-based poly slurry, has excellent WiD uniformity, less than 2nm, and good end-point (motor torque) detection point which is good in terms of manufacturing perspective. However, shelf life is a big challenge that we loss the selectivity of nitride and oxide after 15 days and also found visible white precipitate in the slurry loop. We did the shelf life test for both the additive only and the slurry. Data shows that the removal rate, pH and particle size of the additive only did not change a lot; however, the slurry became more unstable after 11 days with the increasing of the nitride loss, ten times the baseline. Chemical reaction happened between the abrasive and the additive. We can avoid the slurry deterioration by using the in-line mixing instead of pre-mixing. Table 2 shows the center die uniformity of slurry A is 1.9nm, much less than our target, 5nm. We also measured the CMP house pad topography for the slurry marginality test. Slurry A also has the better capability to stop on nitride, however, slurry B, the silica based slurry, has no removal rate at donut and center area. It can be caused by the slurry distribution on the pad or the high additive concentration. We will have a completed analysis of the ratio of slurry B and additive analysis and also dig more deeply about how slurry react with additive and what factor would be the major driving force of poly process in the full paper.