Deep dry etching of borosilicate glass using SF6 and SF6/Ar inductively coupled plasmas

Deep reactive ion etching (DRIE) of borosilicate glass was carried out using SF6 and SF6/Ar plasmas in an inductively coupled plasma (ICP) reactor. Electroplated Ni on Cu (≅50 nm)/Cr (≅100 nm)/glass structure using patterned SU-8 photoresist mask with a line spacing of 12-15 μm was used as a hard-mask for plasma etching. Plasma etching of borosilicate glass was performed by varying the various process parameters such as the gas chemistry, the gas flow ratio, the top electrode power, and the dc self-bias voltage (Vdc). In the case of using SF6 gas only, the profiles of the etched channel showed the undercut below the Ni hard-mask due to a chemical etching and the microtrenching at the bottom of the etched channel. An optimized process using the SF6 plasmas showed the glass etch rate of ≅750 nm/min. The addition of the Ar gas to the SF6 gas removed the undercut and microtrenching but decreased the etch rate to ≅540 nm/min. The increasing and decreasing time-dependent etch rates with the etch depth in the SF6 (200 sccm) and SF6(60%)/Ar(40%) plasmas, respectively, were ascribed to the different ion-to-neutral flux ratios leading to the different etch process regime.