Piezo CMP improvements
Due to the high stiffness of the piezo elements the profile of the carrier and thus the pressure distribution for chemical mechanical polishing (CMP) can be adjusted over the entire wafer surface with high accuracy. The company is seeking prospective partners to do industrial testing and application in specified processes.
The University of Dresden has characterised removal behaviour on a laboratory CMP machine using the system. The pressure distribution of the controlled carrier measured before polishing with Tekscan flexible pressure sensor arrays between the polishing pad and wafer is identical to the achieved removal profile.
Only three piezo actuators are needed on each ring to give an even, rotationally symmetric distribution of pressure. The wafer-in-wafer non-uniformity (WIWNU) can be improved by 50% through control of the rings in one correction step. The aim of further development is the local as opposed to rotationally symmetric influence of the removal profile as well as integration of process control sensor technology. TTI believes that retrofits of the new technology are possible.
Previous industry attempts to achieve adequate planarisation uniformity have involved special retaining rings, back pressure as well as global convex or concave deformation of the carrier to obtain an even removal profile.
