Plasma Etch Resistance Switching of oCVD Poly(3,4-Ethylenedioxythiophene) Thin Films via Mild Thermal Anneal and Liquid Water Exposure To Manipulate Antimony Incorporation

Thin, conformal poly(3,4-ethylenedioxythiophene) (PEDOT) films are rapidly deposited on Si and SiO₂ via oxidative chemical vapor deposition (oCVD) using heated monomer and SbCl₅. While this conjugated polymer has previously been reported as a candidate for hybrid optoelectronic device applications, it has also been recently demonstrated as a patterning material during area-selective deposition (ASD) processes to augment lithographic patterning. In this work, we extend the versatility of PEDOT by demonstrating the ability to dramatically change the rate of film etching during plasma exposure. While as-deposited films etch rapidly in O₂ plasma and CHF₃/Ar reactive ion etching (RIE), we find that after a mild 5 min anneal at 350 °C, the etch rate decreases by a factor of 30. Then, after annealing, we surprisingly find that rinsing the films for 10 min in DI H₂O at 80 °C allows them to return to their original rapid-etch condition. The anneal step reduces film thickness, increases density, and leads to an increase in the relative concentration of Sb remaining from the SbCl₅ oxidant used during deposition. High-angle annular dark-field (HAADF) imaging indicates that the Sb remains highly concentrated on the surface after annealing and etching. Under CHF₃/Ar RIE conditions, the etch selectivity for SiO₂ relative to the annealed films exceeds 40:1, which is larger than many other polymeric and dielectric hard masks. These results position PEDOT as a favorable ASD patterning material and plasma hard mask polymer.