WET-ETCH PROCESS IMPROVEMENTS THROUGH SPC

Wet etching is an isotropic process and difficult to control, but prop er application of statistical process control (SPC) can significantly reduce variability. A relatively simple SPC model predicts the tempera ture required to achieve a desired etch rate from the rate at two othe r temperatures, despite the nonlinear dependence upon temperature. Exc ess wet etch scrap can be reduced without the expensive switch to plas ma etching.