Process characterization for tapered contact etch

Abstract

We report the characterization of contact etch processes which give variable sidewall taper angles. Patterning at 248 nm gave contact holes at ∼0.19 μm diameter in photoresist over organic bottom anti reflection coating (BARC). The contact stack and test structures (BARC/oxide/SiN, 5–10 kA total stack thickness) were etched in a medium-density TEL dipole ring magnetron (DRM) system. Bottom hole diameters ranging from 0.17 down to 0.10 μm could be obtained by varying the oxide etch process, which included C4F8 or C5F8, O2, and Ar. A moderate etch selectivity of ∼8:1 (oxide: SiN etch rate ratio) was determined for the main taper process. Etched patterned wafers were characterized using top-down critical dimension scanning electron microscopy (CD-SEM), cross-section SEM, and transmission electron microscopy. Ex situ surface analysis of etched blanket wafers using x-ray photoelectron spectroscopy showed only small dependence of the surface fluorocarbon film thickness and composition on taper etch process cond...