The effects of process conditions and chamber geometry on the uniformity of Al etched by Cl-2 were measured in a Lam TCP(TM) 9600 SE etch reactor. A computer simulation accurately predicted etch uniformity and aided in the explanation of uniformity trends. Parameters used in the experimental matrix included pressures between 6 and 24 mT, flow between 25 and 100 sccm, power supplied to the plasma between 0 and 350 W, and chamber heights ranging from 6 to 12 cm. The distinctive features of this study include the large number of input parameters studied in a commercial reactor and the accurate predictions obtained from a self-consistent simulation without free parameters. Reducing residence time in the experiments by adjusting chamber height or flow rate produces a more center-fast etch, as expected. The flow simulations were useful in corroborating intuitive arguments and in explaining anomalous results such as the effect of pressure on etch uniformity. More specifically, comparison of simulations and measurements demonstrated the quantitative connection between the Peclet number, the residence time, and the edge uniformity over a large range of process conditions. In addition to explaining general trends with residence time, Peclet number considerations also clarify the differing effects of pressure, flowrate, and chamber height change on uniformity. No attempt was made to impose plasma effects in the flow simulation because measurements of the neutral temperature and dissociation fraction were not available. Plasma power was observed experimentally to slightly improve uniformity without changing the average etch rate.