Multi-Scale Model of the RF Diode Sputter Deposition of GMR Thin Films

A reactor-scale model incorporating the principal physical processes involved in RF diode sputtering has been developed and then integrated into a detailed steady-state input-output model of the growth of copper films. The model links critical aspects of the process (plasma power and pressure), the geometry of the chamber, and the materials (working gas, target materials) to the surface morphology of thin metal films. Experiments revealed a strong dependence of the surface morphology upon power and pressure. The reactor scale model successfully predicted the functional form of these trends and therefore establishes a causal linkage between the method and conditions of processing and the morphology of the resulting thin film. The model has been coarse grained and used to investigate the sensitivity of the process outcome to the conditions of processing. Very small changes in process set point are found to significantly reduce control of film thickness. This observation is especially critical for efforts to grow GMR film where small variations in copper layer thickness lead to large variations in magnetoresistive properties. Finally, the use of a curved target, guided by simulations of the integrated model, led to substantial improvements in the within-wafer uniformity of sheet resistance and saturation field in qualification tests.