Process Control of the Chlorobenzene Single-Step Liftoff Process with a Diazo-Type Resist

Introduction of the single-step chlorobenzene liftoff process using a diazo-type resist to manufacturing lines produced problems not encountered during development and pilot-line work. Variances in the structure of the photoresist liftoff image are the result of complex interactions among exposure, chlorobenzene soaking, development, and post-application baking conditions. Effects produced by these variables can be controlled by monitoring the linewidth, overhang, and height of the liftoff resist structure using a scanning electron microscope (SEM). Loss of resist thickness during the chlorobenzene soak is used instead of penetration, as measured on SEM photographs, to monitor the soaking process. Data are presented on the creation and stability of the overhang structure, the process controls required to achieve that stability, and the interactions among the process variables. The process, as practiced in a manufacturing mode, was found to have greatest reproducibility at low exposure, with a combination of long soaking times and high post-application baking temperatures.