================================================================= TITLE: Chemical Mechanical Polishing Designers should be aware of the layout requirements imposed by Chemical Mechanical Polishing or CMP. The move to deep sub-micron processes has placed conflicting requirements on the photolithographic systems employed by wafer vendors. The feature size of the process is directly proportional to the numerical aperture of the lenses used for printing while the depth-of- field of the lenses is inversely proportional. Hence, this situation has forced wafer manufacturers to implement severe planarity requirements on their deep sub-micron processes which can only be achieved by using CMP. CMP removes material from uneven topography on a wafer surface until a flat (planarized) surface is created, allowing subsequent photolithography to take place with greater accuracy and enabling film layers to be built up with minimal height variations. CMP combines the chemical removal effect of an acidic or basic fluid solution with the "mechanical" effect provided by polishing with an abrasive material. The CMP system usually has a polishing "head" that presses the rotating wafer against a flexible pad. A wet chemical slurry containing a micro-abrasive is placed between the wafer and pad. It is the designer's responsibility to achieve a minimum density on various layers to provide the necessary structural support for this process. If the design does not intrinsically contain sufficient density, then additional "fill" material should be used. However, the designer must be careful not to use this material in such a way that the primary circuit is affected. CMP is performed primarily in the interconnect structure of the chip, where it is used multiple times. CMP is especially critical for the fabrication of copper wiring structures. This advanced planarization capability enables chipmakers to continue shrinking circuits and extends the performance of lithographic tools. For additional information, access: CMP =================================================================