Sidewall profile control of thick benzocyclobutene reactively ion etched in CF₄/O₂ plasmas

The feasibility of controlling the sidewall angle of thick benzocyclobutene (BCB) etched in a CF₄/O₂ plasma using thick photoresist as an etch mask has been investigated. Sidewall angle, BCB etch rate, and BCB to photoresist selectivity as functions of chamber pressure and CF₄ to O₂ ratios are reported. Through the use of postdeveloped reflown photoresist, an optimum sidewall angle of less than 60° was achieved at 33 mT chamber pressure and a 19% CF₄/O₂ ratio. The method presented here achieves deep, residue-free etching of thick BCB with a sidewall profile suitable for e-beam evaporated and lifted metal for use in vertical interconnects.