Fast ultra-deep silicon cavities: Toward isotropically etched spherical silicon molds using an ICP-DRIE

Etienne Herth (1) , Maciej Baranski (1) , Djaffar Berlharet , Samson Edmond (2) , David Bouville (3) , Laurie E Calvet (2) , Christophe Gorecki (1)

1 FEMTO-ST - Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174)
2 C2N (UMR_9001) - Centre de Nanosciences et Nanotechnologies
3 C2N - Centre de Nanosciences et de Nanotechnologies [Orsay]

The paper investigates the parameter optimization of isotropic bulk silicon micro-scale etching using an Inductive Coupled Plasma-Deep Reactive Ion Etching (ICP-DRIE) system. Etch profile characteristics, depending on process and feature size, have been studied. We report detailed observations of the resulting for various etching parameters, covering: pressure from 30 to 70 mTorr, SF 6 flow rate from 100 to 500 sccm, platen power from 20 to 150 W and ICP power from 2000 to 2500 W. This goal here is to present how anisotropic and isotropic etch processes for a wide range of applications in microfluidics, micro-electro-mechanical-systems (MEMS) and Micro Optoelectronic Mechanical System (MOEMS) fabrication. A deep anisotropic etch through a 1.4 mm thick silicon wafer with smoothly etched surfaces has been achieved. Isotropic plasma etching is obtained, including a relation between the etching depth, the undercut and the normalized radius of curvature (ROC) of the profile. We have demonstrated an isotropic plasma potential that is much higher than those that can be produced by isotropic wet etching of silicon for the generation of more complex forms such as the manufacturing microlens molds. In particular, we have presented the possibility of creating aspheric shapes with a desirable negative conic constant (k<0) and a potential high NA numerical aperture. The choice of using photoresist masks provides a better flexibility and economical processing. The presented results can be valuable for a wide range of applications, thus allowing a massive production using only a single commercial ICP DRIE tool, low cost and compatible with an industrial perspective.

Domaines: Micro et nanotechnologies/Microélectronique

Etienne Herth, Maciej Baranski, Djaffar Berlharet, Samson Edmond, David Bouville, et al.. Fast ultra-deep silicon cavities: Toward isotropically etched spherical silicon molds using an ICP-DRIE. Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics, 2019, 37 (2), pp.021206. ⟨10.1116/1.5081503⟩. ⟨hal-02389090⟩