X-ray photoelectron spectroscopy surface charge buildup used to study residue in deep features on integrated circuits

Abstract

A major problem is encountered in characterizing the surfaces at the bottom of submicrometer holes formed by plasma etching operations in the fabrication of submicrometer circuitry. Using monochromated x rays to excite photoemission spectra, surface charge buildup can occur on insulating surfaces causing the spectra to shift relative to the spectra of electrically conductive surfaces. In the case of silicon dioxide on Si, the oxide surface can charge up to a significant voltage relative to the silicon substrate making the two regions spectroscopically resolvable. When an electron flood gun is used in conjunction with monochromatic x rays, the insulated regions can be made to shift in kinetic energy relative to the substrate thereby allowing precise identification of various electrically different regions. In this initial study, residues at the bottoms of 0.75-μm-wide paths etched in 0.9-μm-thick silicon dioxide were identified. Patterns were etched in silicon dioxide using Freon-based plasma etching and various final cleaning procedures. The residue layers observed are similar to those observed on CHF3 etched silicon.