Chemical mechanical planarization of germanium shallow trench isolation structures using silica-based dispersions

Germanium (Ge) shallow trench isolation (STI) structures were polished with two different slurries: (A) 12 wt.% fumed silica particles +0.5 wt.% H2O2 at pH 2 and (B) 3 wt.% colloidal silica particles +1 wt.% H2O2 + 0.2 M KNO3 + 0.1 mM cetyl trimethyl ammonium bromide at pH 8, as both were reported earlier to be good candidates to achieve planarization. Two dimensional before and after polish profiles of 160 nm wide Ge STI structures were used to characterize planarization performance. A two step CMP process, where the Ge overburden was first polished with slurry A followed by polishing with fumed silica particles at pH 11, resulted in the desired slightly recessed oxide but also a high root mean square roughness (RMS) surface roughness value (∼0.7 nm) and some oxide loss. Planarization with a dishing value of ∼15 nm and an RMS value of ∼0.3 nm was achieved when polished with slurry A in a single step for 37 s, which also showed self-limiting planarization behavior. The dishing may be reduced with tight end point control. Slurry B produced higher dishing values.

(A) 2D profile of 160 nm trenches of Ge STI structures before and after polishing with fumed silica slurry + 0.5 wt.% H2O2 at pH 2 and 2 psi polishing pressure. Cross sectional SEM images of Ge STI structures after polishing with this slurry for (B) 15 s, (C) 30 s and (D) 90 s.Figure optionsDownload as PowerPoint slideHighlights
► Germanium STI structures were polished using two different SiO2 based slurries.
► A two step process yields a slightly recessed oxide that is desirable but 0.7 nm RMS surface roughness.
► A single step polishing yields ∼15 nm dishing even after polishing for 90 s and an RMS roughness of only 0.3 nm.
► The dishing may be reduced with tight end point control.