Modeling the Etching Rate and Uniformity of Plasma-Aided Manufacturing Using Statistical Experimental Design

Abstract

The response characteristics of an O₂/CF₄-based plasma process used to desmear and etch back multi-layer rigid-flex printed circuit board were examined using a two-level fractional factorial experimental design. The effects of variation in RF power, temperature, gas proportion and gas flow (CF₄ and O₂) on several output variables, including etch rate, process uniformity and selectivity were investigated. The screening factorial experiment was designed to isolate the most significant input parameters. In the experiments conducted, increases in the etching rate generally corresponded to decreases in uniformity. Etch uniformity was strongly dependent on temperature and gas proportion. The relative significance of polymer deposition and ion bombardment was separated. Using this information as a platform from which to proceed, the subsequent phase of the experiment developed empirical models of etch behavior using response surface 3-D plots. The models were subsequently used to optimize the etching process.

Keywords:

• Design of experiments
• Etch rate
• Plasma
• Uniformity

ACKNOWLEDGMENTS

The financial support for this research work from the Hong Kong Innovation and Technology Commission grant (ITS/034/05) and its industrial members is gratefully acknowledged.