Tutor: Len Borucki, Motorola
Chemical/mechanical polishing utilizes a liquid slurry containing very fine particles to planarize the surface of a wafer. The slurry coats the top of the wafer and is pressed between the wafer and a flexible circular rotating pad. The surface of the pad in contact with the slurry is not smooth, but contains grooves and is "conditioned" so that the entire surface contains small scratches. The conditioning process greatly affects the polishing performance. So does the pressure applied to the pad.
The liquid in the slurry is formulated to have a slight etching effect. As the slurry flows over the wafer surface, the suspended particles abrade the surface and the liquid in the slurry etches the abraded area. The process is somewhat like using a rotary buffer to polish the finish on a car. The overall objective is to understand how the achievable flatness is related to the many variables that might be controlled in the process, for example the pressure on the pad, the rotation speed, the sizes of the particles in the slurry, the pad conditioning, the chemistry of the liquid used in the slurry, etc.