Polyimide-Damage-Free, CMOS-Compatible Removal of Polymer Residues from Deep Reactive Ion Etching Passivation

Abstract

A method for removal of passivation polymer residues from deep reactive ion-etching (DRIE) has been systematically investigated in this study. The method combines dry oxygen plasma ashing and conventional photoresist wet stripping. Samples were carefully examined by x-ray photoelectron spectroscopy (XPS), energy-dispersive x-ray spectroscopy (EDX), and study of surface morphology. XPS and EDX analysis showed that the polymer residues consisted mainly of C-O, CF x (x = 1, 2, 3), and C-CF bonds. Optimized oxygen plasma ashing effectively removes most of the fluorocarbon content, except some nano-residues. Subsequent conventional wet stripping in organic solvents could eliminate these stubborn nanoparticles while dissolving the underlying photoresist. Excellent removal is apparent from scanning electron microscopy images. The fluorine content determined by EDX analysis showed that the residues were completely removed. The metal layers, oxide insulator layers, and the polyimide insulators function well after this critical surface treatment. The excellent results show this is an outstanding method for removal of DRIE passivation polymer residues for MEMS fabrication.