Structured Abrasive CMP: Length Scales, Subpads, and Planarization
Chemical-Mechanical Planarization with structured abrasive uses a subpad to manage the pressure variations due to loading over a range of length scales. The effect of subpad construction on pressure responses related to those scales is illustrated.A minimum length scale for the effect of the subpad is established via contact mechanics. Differences between one- and two-layer subpads are shown. Uniform compression, point loading, and edge exclusion are considered briefly. A model of the subpad as a plate on an elastic foundation is applied to the problem of die doming. The roles of process pressure, die size, and subpad construction are illustrated. Planarization at the intra-die, die, and wafer scales are related to the subpad construction.