Delineation of MEMS microstructures in silicon using CF 4 /O 2 gas mixtures in reactive ion etching

Experiments performed in a reactive ion etching (RIE) system are discussed with the purpose of studying the influence of the addition of O₂ in different ratios in the main CF₄ gas flow for silicon etching. Conventional planer reactive ion etching system has been utilized for etching of SiO₂ and silicon in fluorine chemistry. The patterns were delineated in SiO₂ using photo-resist as the mask material using CHF₃ gas in combination with argon. Sidewall passivation technique has been employed to achieve microstructure profile control in silicon. The quantity of O₂ gas was varied from 2 to 10% in the total CF₄ gas flow (10 sccm) at self dc-bias of -250 volts and process pressure 30 mTorr to achieve a balance between fluorine and oxygen radicals. Anisotropic etched profiles with smooth bottom surfaces were obtained at 2% O₂ flow in CF₄. The usefulness of this technique has been demonstrated for the delineation of MEMS microstructures in silicon.