Deep Isotropic Chemical Etching (DICE) process for fabricating highly symmetric hemispherical silicon molds

This paper introduces the deep isotropic chemical etching (DICE) process developed for wafer-scale manufacturing of highly symmetric hemispherical silicon molds. The DICE process uses silicon nitride concentric rings as a masking layer during hydrofluoric, nitric, acetic etching of ⟨111⟩ silicon substrate. These concentric rings pop up and widen the etch aperture as etch depth increases, thereby allowing control of vertical and lateral etch rates until reaching the desired mold dimensions. Our comparative experiments demonstrate that the pop-up rings are remarkable at creating molds with enhanced symmetry compared to the conventional pinhole masks. We have demonstrated the effectiveness of our approach compared to single pinholes by producing a super-symmetric 0.1 mm hemispherical mold (R_Z/R_X = 1) using two concentric rings surrounding a pinhole. We have then shown how the DICE process can be used to fabricate larger silicon molds and presented the results of a single concentric ring that achieves fabrication of a 0.25 mm-deep mold with an aspect ratio of R_Z/R_X ≈ 0.75.