The retainer ring is installed to prevent separation of wafer adsorbed by the surface tension.
If the amount of polishing is small as in CMP, it is used to actively control the deformation of polishing pad during polishing process.

In general, edge rounding takes place on the wafer's edge due to viscoelastic deformation of polishing pad.
The deformation of polishing pad is small around the edge, which helps enhance process yield.

It has been applied to CMP equipment and has special bond and processing technology that is differentiated from other companies' products, thus showing excellent performance in terms of wafer surface scratch and uniformity.