High speed anisotropic etching of Pyrex^® for microsystems applications

We report high speed etching of glass (Pyrex^® 7740) substrates using an inductively coupled plasma (ICP) reactive ion etching (RIE) process employing sulfur hexafluoride/argon (SF₆/Ar) based chemistry. Electroplated Ni over a patterned Cr/Au seed layer was used as the hard mask for etching. Detailed process characterization was performed by varying the process parameters which include substrate temperature, ICP power, substrate power, operating pressure, distance of substrate holder from ICP source and composition and flow rates of the etching gases. An rms surface roughness of 1.97 nm at a high etch rate of 0.536 μm/min was achieved by process optimization. We used least square fit to find the direction of maximum variance in the process parametric space and to reduce the dimensionality of the process parametric space. The etch rate was then linearly related to a new variable termed as the etch rate number.