Simple cost models of high-process-mix wafer fabs at different capacities

A simple equation-based model of wafer cost as a function of fab capacity is derived by splitting fixed costs into capacity-dependent and capacity-independent components. Simple approximations are presented for these terms. Our model uses Sematech data to show how the following phenomena can be measured: 1) increasing process diversity motivates larger fabs; 2) dedicating tools to eliminate setups motivates larger fabs; 3) slow, cheap, versatile tools are better than fast, expensive, dedicated tools when implementing flexible minifabs.